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Vysoká škola báňská – Technical University of Ostrava
Materials Forming and Casting
Practice
(lecture notes)
doc. Ing. Radim Kocich, Ph.D.
doc. Ing. Petr Lichý, Ph.D.
Ostrava 2015
1. Formed products
Time to study: 1 hour
Aim: After study of this chapter you will know
Basic fabrication processes
Initial intermediate products and the range of final products
Individual forming technologies
Lecture
Forming technologies can be separated into two main groups according to the original
intermediate products, which can either be bulk or flat. Forming starting with bulk
intermediate products are technologies like forming, rolling, drawing and extrusion. Forming
starting with flat intermediate products are e.g. stamping and bending. In the following text,
purely bulk intermediate products forming methods (metallurgical forming methods) will be
dealt with.
All the technologies can be used to produce semi-products from various types of steels, as
well as from non-ferrous metals and their alloys. Cast materials are typically used as initial
intermediate products for production of final formed products. They can be separated into
three main groups. The first group is continuously cast slabs, which are used e.g. to produce
thick sheets and strips. A typical feature of slabs is their shape with a rectangle cross-section,
i.e. ratio of sides higher than 1:1.4 with height of 80-200 mm and width up to 1 600 mm. The
second group consists of blocks used to produce beams, rails etc. They have a characteristic
geometry with the ratio of sides 1:1 to 1:1.4 and dimensions 140x140 mm to 320x320 mm.
The last group is billets used to produce profiles, wires, tubes etc. The geometric shape of
billets is defined with the ratio of sides 1:1 to 1:2 and dimensions 40x40 mm to 130x130 mm.
However, billets can also have circular cross-sections with diameters 90-120 mm. In the past,
intermediate products with thicknesses of 6 to 36 mm and widths mostly 300 mm (sheet
billets) were also used. Nevertheless, they are not common at present. Among continuously
cast intermediate products, ingots are also sometimes used. This is mostly for small-lot
productions or for formed products from specific materials. In special cases, initial materials
prepared using powder metallurgy can also be used.
Forged products
There are two basic types of forging – open die forging and die forging. Die-forged products
are forged using special forms – dies. Die-forged products are e.g. cogwheels, piston rods,
automobile components, stirrups, locks, pegs etc. Open die-forged products are usually large
products, such as crankshafts, ships components, rolls for rolling mills, pistons, flanges etc.
Special forged products are circles, sleeves and rail wheels.
Rolled products
Rolled products can be separated into flat and long products. Flat products are sheets or strips
rolled under hot or cold conditions. Sheets are divided into thin and thick ones separated by
the limit of 3 mm. Long products are rods, wires, tubes, thin-wall profiles, products of
complex shapes (profiles, sheet piles, rails…). Special products are welded tubes welded from
rolled strips or sheets.
Drawn products
Drawn products are usually wires, rods and tubes. Wires are drawn if a diameter smaller than
the limit down to which they can be rolled (5.5 mm) is required, or if a high-quality surface or
specific properties are needed. Drawn products have generally higher dimensional accuracy
than the rolled ones.
Extruded products
Extruded products can be solid or hollow. The mostly fabricated extruded products are
profiles used for fabrication of e.g. windows, doors and window-sills.
-
2. Theory of plastic deformation
Time to study: 10 hours
Aim: After study of this chapter you will know
Possible mechanisms of plastic deformation
Definitions of forming under hot and cold conditions
How to define and influence formability
Differences between individual recovery mechanisms
Mathematic expressions of plastic deformation
Lecture
Conditions for plastic deformation to occur
The aim of forming is to apply plastic deformation to impart required shape and dimensions
to a work-piece. At the same time, material failure/rupture has to be prevented. For plastic
deformation to occur, a certain limit stress within the formed material – deformation
resistance – has to be overcome. Deformation resistance of a material is a reaction to the
effect of external forces during forming. Determination of deformation resistance is difficult,
since it is influenced by several factors, such as thermo-mechanic parameters (temperature,
strain, strain rate), geometry, friction etc. By forming, structure of the final material
(especially grain size) and therefore mechanical properties can be influenced and optimized.
Nevertheless, other factors (chemical composition, heat treatment etc.) are important as well.
Mechanisms of plastic deformation
Slip deformation mechanism, progressing by movement of line defects (dislocations), prevails
during most of the forming processes in metal materials. Deformation then progresses by a
continuous slip of individual crystal layers along slip systems – crystallographic layers and
directions – depending on the type of the particular lattice. The slip distance is a multiple of
the smallest interatomic distance (Burgers vector). The slip direction (layer) is usually
identical to the direction (layer) with the highest atomic density. Each lattice type has a
different number of basic slip systems. It is 48 for cubic body centered (α-Fe, Cr, W…), 12
for cubic face centered (γ-Fe, Cu, Al…) and 3 for hexagonal close packed (Mg, Ti…) lattice.
The more active slip systems within the lattice, the better formability of the individual metal.
Mathematic expressions of deformation
There are several types of mathematic relations expressing shape changes during plastic
deformation. These are summarized in Table 1.
Table 1. Mathematic expressions of deformation
type of deformation symbol unit elongation widening ramming
Absolute Δ [mm] Δl = l1-l0 Δb = b1-b0 Δh = h0-h1
Relative ε [%]
logarithmic e [-]
deformation coefficient λ β γ [-]
Basic laws of plastic deformation
Law of constant volume
When the original dimensions of a body are denoted as 0 and the deformed dimensions are
denoted as 1, the following equation can be written:
h0∙b0∙l0 = V0 = h1∙b1∙l1 = V1 [-] (1)
where: h … height [m]
b … width [m]
l … length [m]
The following can be derived from Equation (1):
[-] (2)
By a logarithmic calculation of Equation (2), the above mentioned law can be expressed using
logarithmic deformations.
→ [-] (3)
This law has exceptions, such as extensibility of metals by the influence of heat or lattice
defects. In these cases, material density changes while weight remains constant. Therefore
small changes in volume can occur.
Law of material movement by the path of least resistance
Material always flows plastically in the direction which has the least resistance. This direction
is perpendicular to the free surface of a work-piece. This law explains the phenomena of
barreling during forging (Figure 1) and widening during rolling.
Figure 1: Barreling during forging
Law of additional stresses and non-uniformity of deformation
Deformation within a material is almost never uniform. This is a result of a non-homogeneous
penetration of force into the volume of a formed work-piece, which causes its non-uniform
deformation (barreling). Due to the non-uniform deformation, additional stresses occur within
a formed material, by the influence of which the stress state becomes non-uniform as well.
This is not favorable, since it can result in a (local) failure of the formed metal.
Stresses and stress states
A unit cube is given in a right-angle coordinate system. Stress effecting perpendicularly on a
plane in a certain point is denoted as normal stress – σ. Stress effecting parallel on a plane in a
certain point is denoted as tangential (shear) stress – τ. A general stress state in a grid system
defined by axes x, y and z consists of three normal and six tangential stress components.
These components are depicted in Figure 2.
Figure 2: General stress state in a unit cube.
In a system of main axes 1, 2 and 3, the tangential components are equal to zero and for the
normal components the following is valid: σ1 ≥ σ2 ≥ σ3. Pressure components are denoted as
negative (-) and tension components are denoted as positive (+). Generally, there can be 9
different stress states: 4 three-dimensional states (+++, ++-, +--, ---), 3 planar states (++,+-,--),
2 uniaxial states (+, -). These states are schematically depicted in Figure 3.
Figure 3: Stress states.
A stress state can be mathematically expressed using the coefficient of stress state, defining
prevalence of either tension or pressure components. Tension stresses increase the probability
of material failure, while pressure stresses increase formability. Therefore formability can
significantly be influenced using a favorably selected forming process. The stress state
coefficient can graphically be expressed using the Kolmogorov diagram.
[-] (4)
Friction
Friction can be described using a friction coefficient, which can have wide range of values
depending on the contacting surfaces, friction forces and possible lubrication and can be
determined using various methods. Friction is usually a negative factor and it should be
minimized. However, friction during forming is also positive. Without friction, capture of a
material into rolls and the entire rolling process would not be realizable.
Friction can be separated into several basic types according to its origin. Generally, it is
higher for cold forming than for hot forming. Therefore, lubrication is used for these
processes. On the other hand, lubrication can also be used during hot forming.
Plastic deformation under hot and cold conditions
Materials are formed under hot conditions if the deformation is performed at temperatures
higher than 40% of the melting temperature – Tm. More precisely, the value should be
between 30 and 80% of Tm, the value depends on the type of material (alloy). Materials can
always be hot formed within a certain interval of forming temperatures. With an increasing
temperature, deformation resistance generally decreases and formability increases, since
dislocation mobility and diffusion speed increase. However, if the temperature is too high and
crosses the upper limit of a forming temperatures interval, overheating or burning of the
material occurs and formability decreases rapidly. Overheating features abnormal coarsening
of grains, the material can still be restored by a proper heat treatment. Burning occurs at very
high temperatures, material can be restored only by remelting since it disintegrates during any
further forming due to a significant grain boundaries weakening.
Cold forming is performed at temperatures lower than 40% of Tm of a material – under
recrystallization temperature. Such forming features strengthening of materials and therefore
high deformation resistances. With progressing deformation, plasticity of a material decreases
and its strength increases. Cold formed materials deform by slip mechanism but also by
twinning, which is a competing process.
During forming, grains significantly flatten and elongate in the direction of main deformation.
Aligning of structural phases (e.g. inclusions) in that direction also occurs and texture,
causing anisotropy of properties, develops continuously. Anisotropy can be planar
(differences between different directions within a material plane), or normal (differences
between two perpendicular planes within a material). Texture can be defined as a regular
geometric and crystallographic structure and substructure alignment within a poly-crystal
metal. Deformation texture can be divided to structural texture (originating from
inhomogeneity of chemical composition and presence of inclusions) and crystalline
(originating from alignment of grains in a certain preferred orientation characteristic for each
lattice type). Recrystallization texture develops after recrystallization.
Softening processes
During forming grains change their shapes while their volumes remain constant. To be able to
refine grains, some of the structure-forming recovery processes have to be activated in the
material. The type of the process depends on the type of forming process – forming under hot
or cold conditions. To start such a process, a certain limit of accumulated energy has to be
exceeded. This energy is imposed into a material by forming processes, due to which defects
and dislocation densities increase.
Softening processes can be separated, from the point of view of time, to dynamic and post-
dynamic. Dynamic processes occur during deformation. Post-dynamic occur after forming is
finished, which can be after finishing of the entire forming cycle, during cooling, or also
between individual passes (e.g. during continuous rolling).
After hot forming, material usually experiences recrystallization during which new grains
nucleate and further grow at energetically favorable locations (grain boundaries). To start
recrystallization, it is necessary to reach a certain critical strain together with meeting other
conditions, such as sufficient temperature etc.
During cold forming, recovery can occur. This is a method of non-perfect softening of a
material, during which dislocation density decreases by their annihilation and rearrangement
and sub-grains generation (polygonization). To evoke recrystallization, i.e. perfect softening
of a structure, additional energy has to be supplied, e.g. by recrystallization heat treatment.
Dynamic recovery of materials is described by the Zener-Hollomon parameter (5). A higher Z
value means shifting of the curve towards higher stresses and strains.
[-] (5)
where: γ … strain rate [s-1
]
Q … activation energy [kJ∙mol-1
]
T … temperature [K]
R … molar gas constant [J∙K-1
∙mol-1
]
3. Fabrication technologies
Time to study: 15 hours
Aim: After study of this chapter you will know
Basic fabrication processes
Concrete application of forming technologies for fabrication of individual
products
Characterization of individual forming processes
Influences of individual forming processes on properties of formed
products
Lecture
Forging
Open die forging
Open die forging is performed on forging machines – hammers and presses – without any
specialized dies. Initial intermediate products are usually forging ingots. The first purpose of
forging is to derange the original cast ingot structure and increase its formability. During the
first forging steps, characteristic fiber structure replaces the dendritic cast structure and
casting defects continuously diminish. High forging temperatures support diffusion, which
also contributes to homogenization of cast structure. The influence of forging on mechanical
properties of a given semi-product is evaluated using a contract unit – forging degree. This
can generally be expressed by Equation (4). For casual ingots, the forging degree should be
PK > 3.
[-] (4)
where: A … ramming equivalent (A = 0,7 – 0,9) [-]
P … degree of ingot ramming ( ) [-]
Sp … surface area of transverse cross-section of rammed ingot [m2]
Si … surface area of the mean ingot transverse cross-section [m2]
Sv … surface area of the largest final forged-piece transverse cross-section [m2]
K … degree of ingot elongation ( ) [-]
n … number of ramming steps [-]
For open die forging includes several basic forging operations.
Elongation
Approximately ¾ of all forging fabrication steps comprise elongation. By elongation, the
transverse cross-section of a semi-product is decreased, while its length is increased. The
entire volume of a formed work-piece is forged continuously by compressions of its parts.
The forged-piece is continuously moved forward and rotated during forging. The strain
imposed during these steps contributes to derangement of the cast dendritic structure, which
results in an increase in plasticity and formability of a material. Elongation can be applied as a
preparation but also finishing forging operation for forged-pieces such as rods, shafts etc.
A correct determination of the relative capture length is essential (Equation (5)). This quantity
influences penetration of the deformation to a specific depth into the forged material and
therefore the stress state and (in)homogeneity of deformation within the entire forged-piece.
The most favorable forming conditions for forming also the axial part of the forged-piece is
achieved when the value of this factor ranges between 0.5 and 0.7. A slight overlap of the
captures (forged areas) in subsequent elongation steps (offset of deformation zones)
contributes to homogenization of deformation.
[-] (5)
where: lz … length of forging area [m]
h0 … thickness of elongated body [m]
The width of the open forging dies should be selected, considering the particular forged semi-
product, according to the following equation (6).
[m] (6)
where: B … width of forging open dies [m]
bk … final width of forged-piece [m]
The basic tools for elongation are flat and shaped open dies. Flat open dies are favorable for
elongation of semi-products with square cross-sections, since they create a favorable
deformation zone reaching to the axis of a forged-piece. Shaped open dies are more favorable
for elongation of semi-products with circular cross-sections, since an unfavorable shape of the
deformation zone develops during elongation of such semi-products by flat open dies and the
deformation influences only peripheral areas of a work-piece. Shaped open dies have a higher
contact surface with circular forged-pieces, reduce widening and favorably influence the
stress state.
During elongation of large ingots, intentional cooling of their surface is sometimes performed.
This results in a generation of large temperature gradients (250 – 350°C) throughout their
cross-sections and additional pressure stresses in their axial parts. This results in a more
intense closing of axial cavities and casting defects during forming.
Elongation of hollow work-pieced is performed using a mandrel. Width of the open dies and
length of the capture are half the sizes comparing to elongation process applied to solid
forged-pieces. Rings are flattened on a mandrel.
Ramming
During ramming, the height of a forged-piece decreases and its cross-section increases. It is
energetically more demanding, since the open dies influence the entire volume of the forged-
piece at once. Deformation is inhomogeneous, since the open dies are in contact with the
upper and lower surfaces of the forged-piece where material cannot flow freely due to the
influence of friction. This results in a generation of additional tension stresses and subsequent
barreling, as mentioned above. This effect is more evident with larger cross-sections and
smaller heights. Deformation inhomogeneity can decrease by using semi-products with lower
slenderness or by forging with larger reductions. Flat open ramming dies are used to forge
smaller semi-products and disks, shaped open ramming dies are used for ingots which are
intended to further be elongated. Forging in simple preparative dies can be used for ramming
of shouldered forge-pieces and flanged disks. Ramming effectively increases the forging
degree.
Narrowing
Such forging steps are in principle elongation of given parts of a forged-piece. More
specifically, this operation is denoted as narrowing if a middle part of a forged-piece is
elongated and shouldering if the end part of a forged-piece is elongated.
Offsetting
Offsetting is a forging step, during which a certain material volume of a forged-piece is
transversely shifted, while the axis of the offset material remains parallel to the axis of the
original forged-piece. Before offsetting, the diameter of the forged-piece has to be increased
to enable offset of a material without fracturing the original forged-piece.
Die forging
Die forging can again be performed using hammers and presses. However, this time a special
form – die – is used to impart a required shape to a material. Die forging is performed under
hot conditions and is characterized by very short working times. Material flow is limited by
die walls. Nevertheless, heat transfer and consequent material cooling occurs during contact
of material with die and it is thus favorable to minimize the contact time periods.
Die forging can be either precise, or the forging dies can be slightly overfilled with material.
For the latter one, the redundant metal is pressed into a flash groove in the dividing plane and
generates a flash, which has to be cut after forging is finished. The flash can contain up to
30% of the entire metal volume and is therefore the largest material loss during the entire
forging process. However, it also has several advantages. Due to its large surface area, the
flash increases the resistance against material outflow from a die and supports the pressure
stress state, which contributes to a perfect filling of the die cavity. It also effects as a shock-
absorber during closing of the dies and helps to balance volume differences between the semi-
product and die cavity. For precise forging, the die is perfectly filled with a metal with no
flash. On the other hand, a precise calculation of the volumes of the die cavity and metal and
their correlation is needed. The die has to also have a suitable construction. Such dies can be
used only for axisymmetric forgings. In precise dies, defects caused by non-perfect fillings of
some parts of the die cavity can occur. Nevertheless, a significant advantage of precise
forging is a favorable flow of material fibers, since they are not disrupted by additional
machining of the forged-piece.
The original intermediate products for die forging are usually rolled bars (for precise forging
they can also be drawn due to their higher dimensional accuracy). The rods are then cut to
required pieces and heated in furnaces. Heating is followed by a preliminary forging in
preparatory dies and eventually forged in final dies. After possible flash cutting, finishing
operations, such as heat treatment, calibration and straightening can be performed.
Rolling
Rolling is a continuous process, during which height reduction is performed on a material via
its forming between rotating work rolls (material thickness decreases). Rolling can be
characterized as longitudinal, transverse and rotary rolling according to the positions of axes
of the rolls towards the axis of a formed material. The most widespread is longitudinal rolling.
Most of the flat and long products, such as sheets, strips, rods and wires are produced by
longitudinal rolling. The work rolls can be either straight or shaped, the latter of which is used
to produce e.g. profiles and rails. Rotary rolling is typically used to roll tubes. Transverse
rolling is a special case applied e.g. to roll grinding balls. The intermediate products for rolled
products are usually slabs, billets and blocks, which can be rolled from ingots or continuously
cast.
Theory of longitudinal rolling
During longitudinal rolling, the metal is captured into the rolling gap using two rotating work
rolls. The rolled semi-product is deformed between the work rolls in the deformation zone,
which is depicted in Figure 4. The length of the deformation zone can be mathematically
derived and described using the following equations (7-10).
; [m] (7,8)
[m] (9)
[m] (10)
where: ld … length of deformation zone [m]
O, A, C … significant points on a roll in Figure 4
R … roll diameter [m]
Δh … height reduction [m]
It is also possible to calculate the width of the deformation zone according to Equation 11.
[m] (11)
where: bd … width of deformation zone [m]
b1 … width of material before entering rolling gap [m]
b0 … width of material after entering rolling gap [m]
The deformation zone consists of several zones according to the way in which the rolls
influence the rolled material.
Figure 4: Deformation zone.
Longitudinal rolling on shaped rolls
Besides straight rolls, shaped rolls can also be used for longitudinal rolling. Along the
perimeter of each roll, there is a groove of a certain shape. Usually, a groove forming only a
half (or a part) of the final shape is made on one roll, while the other half (part) is made on the
opposite roll. When the rolls are positioned in a stand, the whole shape is formed. However,
there is always a gap between the individual rolls (they are not in contact). Only one shape
can be made on one pair of rolls. However, one pair of rolls usually contains more shapes. A
set of individual shapes following each other is called a shaped-rolling line and the order of
shapes is given by the individual technological process.
Transverse rolling
For this type of rolling the axis of the rolled semi-product is parallel to the axes of the rolls.
Both the rolls rotate in the same direction, while the semi-product rotates in the opposite
direction as a result of friction forces. Transverse rolling is used to produce shafts or grinding
balls for cement mills.
Rotary rolling
Rotary rolling is a special case of transverse rolling. The plastic deformation mechanism is
similar, but the axes of work rolls are skewed, which ensures not only rotation of the semi-
product, but also its forward movement. Rotary rolling is used to produce seamless tubes. It is
one of the most widespread processes for production of hollow semi-products.
Drawing
The principle of drawing lies in passing of a wire through a conical opening (drawing die).
The wire elongates in the direction of the main acting stress and its diameter decreases.
Drawing is processed under cold conditions, which results in an intensive strengthening and
decreases in plasticity and formability of the drawn wires. The stress state in the drawing die
is three-dimensional with pressure transversal stress providing sufficient deformation.
Nevertheless, the main longitudinal stress invoked by the drawing force is tensile stress and
thus the tensile stress state prevails. This decreases the maximum amount of strain which can
be imposed during one pass. Formability can furthermore be decreased by a presence of
inclusions, inner defects, impurities, surface cracks and others. A scheme of drawing is
depicted in Figure 5.
The initial intermediate product is a rolled wire. For drawing, special drawing machines are
used. They can include single or multiple drawing stands and can operate at dry or wet
working conditions. Heat treatment or metal coating can be applied as a final, or semi-final,
operation.
Figure 5: Schematics of drawing.
Extrusion
Extrusion can be performed under hot and cold conditions. The 3D stress state is very
advantageous – a complete pressure. This enables application of extrusion also for forming of
brittle and low-plasticity materials. This technology can be applied to produce semi-products
(pipes, rods, profiles etc.) and also final products (tubes, cartridges etc.).
The initial material is inserted into a closed supply container and then extruded through a die
with an opening of a required shape using a punch. Extrusion can be either forward, or
backward. During forward extrusion, the material is extruded through a stationary die and the
direction of its movement is conformable with the direction of movement of the punch.
During backward extrusion, the extruded material moves in a direction opposite to the
direction of the punch. This type is used to produce hollow products with possible fins, when
the thickness of the walls is very small comparing to the diameter, or contrariwise.
The quality and initial state of the material have a significant influence on the extrusion
process and technology. Materials, for an extrusion of which a significantly high pressure has
to be applied (more than 2,500 MPa), or which cannot be deformed with more than 25% one-
step reduction due to their chemical composition (high strengthening), are unfavorable.
Materials with low strength can be extruded in one step (aluminum and its alloys). Steels and
other metals are extruded in multiple steps. Deformation for formable steels is up to 60% (e.g.
with carbon content to 0.1%). Extrusion is followed by a surface treatment and possible heat
treatment.
4. Production facilities
Time to study: 5 hours
Aim: After study of this chapter you will know
Basic production facilities
Differences between individual machines and their specification
Principles of individual devices
Lecture
Description of all the individual production facilities reaches way beyond the range of this
text. Therefore, only the basic equipment for the most wide-spread production facilities
(rolling mills) is described in this section. Details on other forming technologies can be found
is specialized literature referenced at the end of the lecture.
Rolling mills
The basic equipment of rolling mills is rolling stands. These can be characterized according to
several factors, one of which is number of rolls, another one direction of their rotation (single-
direction, reversible). Construction of a rolling stand is selected according to the number of
work and backup rolls. The position of the rolls can be horizontal, vertical, or sideways.
Two-rolls stand – duo
The rolling stands with two horizontally positioned rolls are the most widespread. The engine
drives either both the rolls (upper and lower), or only one roll (usually the lower one, the
upper one rotates as a result of friction with the rolled work-piece). The stands can be one-
directional, or reversible. For one-directional duo stand, both the rolls rotate in the same
direction. The work-piece enters only from one direction and has to return to the original
position before a subsequent pass. For reversible stands, the direction of rotation of the rolls
changes after every pass. This type is widely used to roll intermediate products from ingots,
heavy profiles and thick sheets.
Three-rolls stand – trio
Such rolling stands have three horizontally positioned rolls rotating always in the same
direction. They are widespread for production of long work-pieces, since they can be
equipped with more shapes than duo stands. The work-piece is rolled between the lower and
middle rolls in one pass and in another pass it returns between the middle and upper rolls. The
stationary middle roll is driven, while the lower and upper rolls are usually movable and
driven by a transmission.
Four-rolls stand – quarto
The rolling stand has four rolls positioned horizontally in one vertical plane – two inner work
rolls and two outer backup rolls. The backup rolls enable to use higher rolling forces and
decrease bending of work rolls. Small diameters of work rolls enable greater elongation of the
rolled-piece and also achievement of more favorable thickness accuracy. Work rolls are
driven. Quarto stands are used to roll steel sheets and strips under hot and cold conditions and
can be used as one-directional and reversible.
Multi-rolls stand
Such stands can have six, seven, twelve and twenty horizontally positioned rolls. For all the
types, two rolls are always work rolls (usually driven), others are backup rolls (trailing).They
are used to roll very thin sheets, strips and foils.
Universal and special stands
Such stands have vertically positioned rolls supplementing the horizontal rolls. These are
driven by a transmission of conical cogwheels. Vertical rolls ram the work-piece from sides
and therefore form side walls, precise angles and sharp edges. They are usually located on the
front side of a stand, less commonly on the rear side, but also on both sides. Universal stands
are used to roll slabs and wide steel profiles. For rolling of wide-legged beans, the vertical
rolls are positioned in the same plane as the axes of the horizontal rolls. Only horizontal rolls
are driven.
5. Final processing of formed products
Time to study: 10 hours
Aim: After study of this chapter you will know
Basic possibilities of final processing of formed material
Types of heat treatments
The mostly used surface processing of formed products
Lecture
Final processing of formed products includes surface treatment and heat treatment applied to
modify inner structure.
Heat treatment – structure modification
Heat treatment can be used as a semi-final or final operation for all the basic forming
methods. A material is heated to a desired temperature selected according to the required type
of structural changes. The heating is followed by a time dwell and subsequent cooling (free or
controlled).The mostly applied heat treatment is annealing. This can be either with or without
phase transformation and can be separated into several basic groups. Annealing can be
supplemented with quenching and/or tempering. To correctly understand the entire heat
treatment system, it is advised to be familiar with the Fe-Fe3C diagram and IRA and ARA
diagrams.
Annealing without phase transformation
Recrystallization annealing
The aim is to restore plastic properties (eliminate strengthening) after cold forming by a
generation of new ferrite grains. A material is heated to its recrystallization temperature
(usually 550 – 700°C for steels), followed by a short dwell and cooling. Recrystallization
start is influenced by various factors, especially the deformation degree. Therefore the heating
temperature depends on the deformation degree. However, it must not exceed Ac1
temperature to prevent phase transformation.
Spheroidization annealing
The aims are conversion of lamellar pearlite to globular, spheroidization of carbides, possibly
achievement of homogenization of structure suitable for subsequent annealing. Steels with the
content of carbon above 0.4%, eutectoid and above-eutectoid steels experience decrease in
hardness and therefore improvement of cold machinability. The annealing consists in heating
to a temperature slightly under or at phase transformation temperature (approximately 750°C
for steels, depending on chemical composition), dwell or slight oscillation around the
temperature and controlled cooling, usually in a furnace.
Annealing to decrease internal stress
Residual tension inside a material can generate as a result of non-uniform cooling, welding,
local heating or similar processes. The process consists in a slow heating (100 – 200°C/h.)
followed by a dwell on the temperature to uniformly heat the entire material (usually 1 to 2
hours) and slow cooling (30 – 50°C/h.). The temperatures between 450 and 650°C are
especially sensitive.
Annealing with phase transformation
Homogenizing annealing
The aim is to homogenize chemical composition within a material via diffusion. This type of
annealing is applied especially for ingots, in which a lot of casting defects and
inhomogeneities are present. Zone heterogeneity (liquation) depends on the type of the cast or
formed semi-product and includes especially inhomogeneities and gases. Inter-dendritic
heterogeneity (segregation) depends on the morphology of dendrites influencing distribution
of alloying and admixture elements. Homogenizing annealing consists of heating to a
temperature significantly higher than Ac3 or Acm (1000 - 1200°C for steels), long time dwell
(6 – 15 h.) and slow cooling depending on the shape of the particular casting.
Normalizing annealing
It is usually applied to achieve fine equiaxed structure consisting of a mixture of ferrite and
pearlite. Normalizing annealing includes a rapid heating to a temperature 30 – 50°C above
Ac3 or Acm, a short temperature homogenization throughout the cross-section of the work-
piece and further cooling on air (100 – 200°C/h). It is mostly used for castings, forged-pieces
and cold-pressed products. The final structure of steel after normalizing heat treatment
depends on the particular chemical composition and size of the work-piece.
Quenching
The principle of quenching is in a rapid cooling of a work-piece from a high temperature after
forming or annealing. This procedure imparts hard martensitic or bainitic structures. It is
usually performed using cooling media with higher cooling capacities than air, such as water
of various temperatures, oil or salt melts.
Tempering
Tempering is a heat treatment following quenching and is used primarily for steels. The aim is
to achieve a state close to the equilibrium state. It consists of a heating to a temperature lower
than A1, dwell on the temperature and subsequent controlled cooling. Since inner stresses can
cause development of cracks and fracture after quenching, tempering should follow
immediately after quenching. It can be divided to high-temperature and low-temperature
tempering. An increase in tempering temperature usually leads to decreases in strength and
hardness and increases in plasticity and ductility.
Temper embrittlement
Tempering at temperatures between 250 and 400°C leads to low-temperature embrittlement.
This is caused by processes occurring on the boundaries of the original austenite grains
(precipitation of cementite, possibly nitrides) leading to their embrittlement. This
embrittlement type is irreversible.
For alloyed steels (typically with Cr, Ni, Mn), high-temperature embrittlement occurs during
tempering around 550°C. This is caused by diffusion of atoms of impurities and trace
elements (P, S, Sn, Sb, Bi) to boundaries of the original austenite grains. This embrittlement
type develops isothermally or anisothermally during a slow cooling from high tempering
temperatures (~ 650°C). It can be eliminated by a reheating to a temperature above 650°C and
a rapid cooling into water or oil. A tendency of steel to embrittle is reduced by additions of
molybdenum or tungsten. Contrary to the low-temperature embrittlement, this embrittlement
is reversible.
Surface treatment
Surface treatment procedures are performed to increase surface quality of a work-piece, but
also as a protection against corrosion of the basic material. The surface of a work-piece can be
coated with a protective organic or inorganic layer or with a metal. Metal coating can be
performed via hot-dip galvanization or electrolytically using zinc, aluminum, tin or copper.
The mostly used industrial process is hot-dip zinc galvanization. Zinc-coating by dipping is
the most effective and economic way of protection of steels and cast irons against corrosion.
It is usually performed between 450 and 470°C (low-temperature zinc-coating) or at
temperatures around 520°C (high-temperature zinc-coating). Between 470 and 520°C
dissolubility of iron increases. Therefore, there is a danger of rapid wear of steel galvanizing
tanks used to store the melted metal. At temperatures above 520°C, iron dissolubility
decreases again. Zinc-coating can also be performed electrolytically.
Copper-coating is applied primarily to wires – as an intermediate step during drawing, since
copper coating decreases friction between the wire and drawing die. The final layer is usually
thicker. It is used typically for mattress springs and welding wires. Coper-coating is
performed electrolytically.
Aluminum-coating is performed by hot-dip galvanization. Aluminum coating is more
corrosion resistant than zinc coating in aggressive atmospheres (2-3x). In practice, alloys of
aluminum and zinc are mostly used for coatings.
Tin has very good protective properties since it passivates by an oxide layer. It is not toxic
and therefore is used especially in food-processing industry and due to its good solderability
also in electotechnics. Tin-coating can be performed either by hot-dip galvanization at
temperatures to 310°C, or electrolytically.
Chromium coating is a favorite decorative final treatment. The coatings are highly resistant to
corrosion and to mechanical wear at elevated temperatures.
Literature for further study
[1] HUMPHREYS, F.J., HARTLEY, M. Recrystallization and related annealing
phenomena. 2nd ed. Oxford: Pergamon; 1996, 617 p. ISBN 978-0080441641.
[2] VERLINDEN, B., DRIVER, J., SAMAJDAR, I., DOHERTY, D.R. Thermo-Mechanical
Processing of Metallic Materials, Pergamon Materials Series- series ed. R.W. Cahn,
Elsevier, Amsterdam, 2007, 332 p. ISBN 978-0-08-044497-0.
[3] LENARD, J.G. Primer on Flat Rolling, 1st ed. Linacre House, Jordan Hill, Elsevier,
London 2007, 342 p. ISBN: 978-0-08-045319-4.
[4] ŽÍDEK, M., KUŘE, F. Válcování, VŠB Ostrava, 1986, 379 s.
[5] PŘEPIORA, Z. Tváření neželezných kovů, VŠB Ostrava, 1991, 200 s.
[6] SOMMER, B. Technolgie kování, VŠB Ostrava, 1978, 200 s.
6. Production of castings into single-use and permanent molds
Time to study: 2 hours
Aim: After study of this chapter you will know
Basic casting terms
Technological steps for castings production
Basic types of used molds
Lecture
Foundry is an industrial field enabling to fabricate a product from an original material in the
shortest way – by casting. Casting enables production of work-pieces of such shapes, which
could not be manufactured by any other process. During casting, a melted metal (or another
material) is poured into a mold, the cavity in which has the shape and size of the desired final
product. The product manufactured by solidification of a melted metal inside a mold is called
a casting.
The molds can be:
A. Permanent (metal molds) – made from metals (cast iron, steel, copper, graphite or
another highly thermally conductive material), into which an entire series of castings can be
cast (30 to 250 pcs.) until its disposal due to change in shape, fracture etc. A general example
can be a cast iron permanent mold and a cast ingot product. Some parts of the molds
(thermally and mechanically loaded) can be fabricated from other materials and can be
changeable to increase lifetime of a mold.
B. Semi-permanent – can be used to cast more than 1 casting, but have shorter lifetime
than permanent molds. Manufactured from granular ceramic refractory mixtures. After each
casting they require service and drying (annealing).
C. Single-use – produced from sand mixtures and used for a single casting each. After
casting a mold is crushed and the mixture can be used to form a new mold (core).
Some modern methods use various combinations, e.g. the front part of a mold is equipped
with a thin sand mixture lining, e.g. to optimize cooling effect of a mold while maintaining its
high dimensional accuracy.
This text deals only with single-use molds providing the widest range of application for
various castings regardless their shapes, dimensions and weights. They are manufactured
from sand mixtures by ramming (pouring). Czech Republic is among the countries with
advanced foundry and engineering industries. It is among the 10 best foundry manufacturers
within Europe.
Characterization of molds according to type of cast material
The following text provides information about the average application of individual
technologies of molds and cores production for individual types of castings.
Grey and nodular cast iron
47% green-sand casting into bentonite mixtures
10% dry casting with application of natural or synthetic mixtures
10% self-solidifying mixtures based on water glass
23% mixtures with organic binders
10% special technologies including permanent molds
Malleable iron (white iron)
Cast exclusively into green-sand bentonite molds
Steel castings
42% green-sand casting into bentonite mixtures
7% dried and skin-dried natural sands and synthetic mixtures
8% mixtures based on water glass
43% technologies with organic binders
Non-ferrous metals alloys
78% pressure casting into metal molds
16% green-sand casting
6% mixtures for drying
The above mentioned proves the necessity to especially deal with single-use sand molds
(bentonite mixtures), into which majority of castings is cast in the entire world.
Categorization of molding mixtures
Pattern – prepared from new resources, rammed around a pattern model, in contact with a
molten metal.
Filling (regenerative) – filling the remaining volume of a mold flask (caisson when forming in
soil) or inner part of a core, prepared from a regenerative (already used) sand mixture.
Core – forming the entire volume or a front part (work surface) of a core. Prepared typically
from new resources. The requirements on quality are higher than for pattern sand mixtures
(higher resistance against penetration of metal, good disintegration ability after casting, longer
cores storage ability etc.).
Unified – is used for unified bentonite mixtures technologies, machine-production of molds
when the entire volume of a mold flask consists of one mixture (no double-layer form).
Already once (or multiple times) used mixtures prepared by processing after each casting
(cooling, moistening, revitalization).
Sand mixture – consists of two basic components:
Sand – granular material creating the main volumes of mixtures and molds and cores
scaffolds.
Binder – substance or a mixture of substances creating a binding system, providing to a green-
sand mixture the binding and plastic abilities necessary for forming, high-temperature
strength after hardening (drying) and good disintegration ability after casting.
A forming mixture can furthermore contain:
Water – for clayey and inorganic binders (cement, water glass).
Additives – substances improving properties of mixtures of the basic components. For
example, additives to improve disintegration ability after casting (bauxite, beech saw-dust),
surface quality (ground coal, activated flours, oils) etc.
Literature for further study
[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov
2008, 326 s. ISBN 978-80-89244-38-6.
[2] JELÍNEK, P. Pojivové soustavy slévárenských formovacích směsí (Chemie
slévárenských pojiv). Ostrava, OFTIS, 2004. 184 s. ISBN 80-239-2188-6.
7. MOLDING AND CORE MIXTURES
Time to study: 4 hours
Aim: After study of this chapter you will know
Basic components of forming mixtures
Basic types of forming mixtures
Basic regeneration procedures and their principles
Lecture
The basic component creating up to 98% of a mixture volume is sand.
The mostly used sand is a high-quality silica sand (SiO2), supplied washed and sieved.
Chromite has also found its important application in Czech foundry factories – for casting of
heavy castings. It features higher cooling ability and refractoriness, although its price is
approximately ten times higher comparing to silica sand. Other sands, such as zircon, olivine,
shale, chrommagnesite etc. are used in minority.
Binder, the component providing strength to a mold, is added in the amount of 1 – 10 %
depending on the type of the binding system.
A mixture can further contain water and other additives to improve its properties.
Mixtures with clayey binders
The most widely used clayey binder is bentonite (clay containing montmorillonite -
NaAl3MgSi8O20(OH)4), the water binding ability of which enables green-sand forming.
Bentonite mixture is the most widely used mixture for fabrication of forms in series – 60 to
70% of castings from cast irons and steels to 400 kg are cast into this type of forms.
Bentonite mixtures are regenerative – after removing of the casting, crushing of clusters,
removing of metal particles, mixing and necessary revitalization (addition of water, bentonite,
new sand, possible addition of carbon additives to improve surface quality of cast irons), the
mixture can be reused.
Chemically bound mixtures
Mixtures hardened by a chemical reaction of binder with hardening agent are not easily
recyclable. Before their reuse, it is necessary to remove from sand grains residuals of binder
and hardening products inhibiting chemical reactions during new application of a binder.
Moreover, high binder concentration causes undesirable increase in volume of gasses (casting
gaseous defects).
Mixtures with inorganic binders – the binder is water glass – alkalic silicate
(Na2O.mSiO2.nH2O). Hardening is imparted by a chemical reaction of the binder with an
externally supplied hardening agent (CO2 process). For self-solidifying mixtures, the agents
are usually various esters. Considering that the alkalic silicates hardening products (silicic
acid gel) feature high adhesion ability to the silica sand grains, their removal is more difficult
comparing to the below mentioned mixtures with artificial resins.
Mixtures with organic binders (artificial resins) – at present the most widely used binding
systems for fabrication of cores. Especially furan and phenol-formaldehyde resins are used to
fabricate whole molds. Their advantage is especially economic production – rapid preparation
and high quality of cores/molds (resulting in high-quality products) directly influence the
production cost. However, such economic advantages are accompanied by non-favorable
impacts on the hygiene in foundry working environments and on environment in general.
Usually 30 to 40% of side-products from organic resins applications are toxic gases or solid
thermal destruction side-products. A significant portion of the destruction products remains in
the reused “waste” mixture. The up-to-date development has been focused on decreasing in
the content of free monomers (phenol, formaldehyde, furfuryl-alcohol).
Regeneration of forming mixtures
The aim of regeneration is to remove residuals of binders (in various degrees of degradation
depending on heat transferred from the cast metal) and other impurities so that the sand can be
reused in another mold forming process.
REGENERATION OF MOLDING MIXTURES IS A TECHNOLOGICAL PROCESS
COMPRISING REGAINING OF A SIGNIFICANT PORTION OF SAND FROM AN
ALREADY USED MIXTURE FOR ITS REUSAGE IN NEW MOLDS AND CORES.
The intensity of regeneration necessary to remove residuals of binder and deteriorating
substances from sand grains depends on the type of used binder and its adhesion ability to the
sand grains surfaces. Therefore, various devices and technological steps have to be applied in
order to achieve the cleanest grains surfaces possible.
An already used mixture represents a highly chemically inhomogeneous dispersed system.
Sand grains are covered with a film of binder, which is, depending on the state of thermal
exposition, either in the original state (poly-condensed resin, silicic acid gel with other
hardening products, dehydrated clay) or in a state of complete thermal degradation (coke rests
of organic binders, silica glass, oolitic clay layer).
Degree of thermal degradation depends on:
Distance from a casting
Robustness of a casting
Thermal volume of a cast metal (alloy type, casting temperature)
Sand to metal ratio
Binder content
Regeneration processes
For selection of a suitable regeneration process, an entire set of factors has to be considered –
economic and ecological factors (expenses on regeneration, amount of wastes produced
during regeneration and their subsequent processing, cleaning of waste waters, etc.). It is
especially necessary to consider:
- The used binding system from the point of view of regenerating ability and sensitivity to
impurities in a regenerated mixture.
- Composition of the used “waste” mixture (one-component binding system or a
combination of various technologies – binding systems).
Three basic regeneration processes can generally be separated (BAT):
Literature for further study
[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov
2008, 326 s. ISBN 978-80-89244-38-6.
[2] JELÍNEK, P. Pojivové soustavy slévárenských formovacích směsí (Chemie
slévárenských pojiv). Ostrava, OFTIS, 2004. 184 s. ISBN 80-239-2188-6.
8. PROPERTIES OF MOLTEN METALS AND ALLOYS
Time to study: 6 hours
Aim: After study of this chapter you will know
Main processes occurring in a foundry mold
Basic calculations to design a gating system
Basic melting processes and their principles
Lecture
MECHANICAL REGENERATION
THERMAL REGENERATION
WET REGENERATION
To be able to properly design a production process for a casting it is necessary to be familiar
with the processes occurring in a mold and a casting.
Main processes influencing quality of castings.
crystallization and solidification mechanisms,
fluidity and mold filling,
shrinking during solidification,
solid state shrinking,
gasses in the metal and mold.
Crystallization mechanism
Pouring of a molten alloy into a mold results in cooling of the metal due to heat removal
through the mold walls. When the temperature drops to a certain value, the metal starts to
crystallize. The temperature at which the metal starts to crystallize is denoted as liquidus
temperature, while the temperature at which the crystallization is finished is denoted as
solidus temperature. These temperatures vary with varying content of additives (with
content of carbon for iron alloys). A line connecting the two temperatures is the liquidus-
solidus curve. The difference between the temperatures is the solidification interval. Pure
metals and eutectic alloys solidify at a single temperature (zero solidification interval). Most
alloys have a more or less wide solidification interval (Figure 6).
Metal crystals grow preferentially in the heat removal direction. According to the width of
solidification interval, the solidification can be progressive, dual-phase or volumetric. The
solidification intervals are schematically depicted in Figure 7.
Figure 6: Dependence of solidification start
and finish temperatures on chemical
composition of alloys.
Figure 7: Schematics of crystallization at
various solidification intervals. From left
a) progressive solidification, b) dual-phase
solidification c) volumetric solidification.
A set of locations, in which the alloy solidifies last, is called a thermal axis. Its location
depends on the shape of casting and heat removal mechanism. The thermal axis does not have
to necessarily be conformant to the geometric axis and is usually deviated from the geometric
axis in the directions of slower and quicker heat removals (Figure 8).
Monitoring of castings solidification can be performed using simple relations, according to
which the time for complete solidification of a casting (in the thermal axis) and solidification
from the walls of a casting can be calculated. The Chvorinov’s rule applies for solidification
time:
τ = k (R)2
where, τ-time of complete solidification of a casting [s], R-relative thickness (module) of a
casting [m], k-solidification constant,
where, V-metal volume in a casting [m3 ], S-cooled casting surface [m
2].
The size and shape of crystals are significantly influenced by the heat removal mechanism.
The higher the heat removal, the finer the crystals and better mechanical properties of the
alloy. Therefore, casting to metal molds (chill casting, pressure casting) is preferred to casting
to sand molds. Nevertheless, castings cast into sand molds also exhibit thin surface layers of
fine crystals – die chill regions – featuring better mechanical properties comparing to the
central region.
Figure 8: Deviation of thermal axis at various
solidification conditions.
Figure 9: Fluidity testing
a) spiral - horizontal; b) tube – vertical.
Cooling rate decreases with increasing thickness of casting walls. Therefore, mechanical
properties of thick walls are worse comparing to thin walls. Crystallization of alloys can be
influenced externally by inoculation – addition of crystallization nuclei.
Fluidity and mold filling
Fluidity is not a physical property of a metal, such as e.g. viscosity and surface tension. It is a
technological property. It defines the ability of an alloy to fill the mold and is usually
expressed as a length of a cast channel with a certain cross-section under selected casting
conditions. To define fluidity, various casting tests are used. Examples of fluidity test castings
are shown in Figure 9.
Fluidity is not unambiguously given by a type of an alloy, but depends also on mold material
and casting method. The complete length of the filled cast metal can be calculated, but has to
still be proven by testing for specific casting conditions.
In order to fill the mold cavity with molten metal, a gating system is composed. This consists
of:
pouring basin,
down-sprue,
sprue well,
blind riser (slag collector)
gates to castings.
Figure 10 shows an axonometric projection of a gating system for castings from gray cast iron
(LLG). The gating system for steel castings in Figure 11 has different shape of pouring basin
and has a runner instead of blind riser.
Figure 10: Gating system
for gray iron castings.
Figure 11: Gating system for
steel castings.
Figure 12: Attachment of
gates to the molds: a) top;
b) bottom; c) step.
Besides the basic gating system shape, the casting gates positions can be top, bottom and step
according to their attachments to the molds (Figure 12).
A molten metal is poured from a casting ladle to the pouring basin.
The down-sprue is usually of a circular cross-section and gets narrower towards its lower
section to conform to the naturally narrowing shape of a poured metal.
The blind riser (slag collector) leads a molten metal to the gating runner and the individual
gates. It also serves as collector of impurities.
Gates connect the blind riser with the mold cavity.
Shrinking during solidification
Colling of alloys is accompanied by a reduction of their volumes – shrinking. This is a result
of a change of alloy density ρ, which increases with decreasing temperature. The types of
shrinking are shrinking of a molten alloy εVl
, shrinking during solidification ε
Vk and solid state
shrinking ε VS.
Figure 13 shows the process of shrinking for steels and cast irons. The main difference
between these two is in the crystallization mechanism. For cast irons, graphite particles
precipitate from the molten alloy and cause pre-shrinkage dilatation. This results in a smaller
total linear shrinkage of cast iron castings (1%), comparing to steel castings (2 %). For
foundry technology, shrinkage during solidification and solid state shrinking are the most
important since they cause shrinkage cavities and residual stresses, deformations and
fractures, respectively.
Shrinking during solidification depends on the cast material, solidification mechanism, mold
and casting designs. The difference between the volumes of the molten metal before
solidification and the solidified metal is called a shrinkage cavity (Figure 14). A large portion
of its surface consists of free dendritic structure. The main factor influencing shape and
location of a shrinkage cavity is the heat removal mechanism. Shrinkage cavities form in the
thermal center of a casting. Beside shrinkage cavities, shrinkage porosity can occur. This is a
less densely filled location – small cavities apparent on a cut or a fracture of a casting.
In order to compensate volume shrinking during solidification, the volume of the poured
molten metal has to be larger than the volume of the final casting. A reservoir from which a
molten metal is supplied is called riser. It is necessary to locate the shrinkage cavity to this
reservoir.
Locations in which the molten metal accumulates (comparing to surrounding walls) solidify
later. These are usually locations of walls attachments and connections. They are called
thermal nodes and are usual locations for formation of shrinkage cavities (Figure 15).
An approximate instrument for finding of thermal nodes is the method of inscribed spheres.
Spheres are inscribed into the cross-sections of casting walls on a drawing (i.e. double the
dimension of a circle diameter). The location with the largest circle is a thermal node, which
is then compensated with a technological addition (wedge). Alloys with wide solidification
intervals can exhibit formation of micro-cavities when individual growing dendrites enclose
islands of still molten metal. Small inner cavities then generate during solidification of the
molten islands.
To produce a well-done casting (Figure 17), solidification has to continue from the most
distant areas through the thermal axis to the riser, which has to solidify as the last part.
Figure 17: 1 - closed riser,
2 - open riser, 3 -
atmospheric core.
Figure 18: Shapes of
shrinkage cavities for
risers: a) unprotected; b)
covered with ash; c)
covered with exothermic
additive; d) with insulation
lining; e) with exothermic
lining.
Figure 19: a) without
chills; b) external shaped;
c) external flat; d) external
flat and shaped; e) internal
(horsenails); f) internal
(hooks).
Risers and chills
The riser – reservoir of a molten metal – has to solidify as the last part. Its positioning has to
ensure optimal filling of the molten metal into a certain area of the casting (feeding area).
According to their construction the risers can be open – opened into the upper plane of a
flask, and closed – hidden inside a mold (Figure 17).
Insulation and exothermal powders and linings are used to increase the riser solidification
time without increasing its dimensions (Figure 18). Shrinkage cavity volume remains the
same, while its shape changes.
Due to their distant locations, some thermal nodes inside a casting can only hardly be
connected to open risers and their connection to local closed risers is very costly. Such
thermal nodes are eliminated by increased chilling of the molten metal via application of
chills. According to their location, chills can be external (located on a casting surface) and
internal (located inside a casting).
Solid state shrinking
The cause for residual stresses, possible cracks, fractures or deformation is solid state
shrinking. Linear shrinkage results in change – decrease – in casting dimensions. The overall
linear shrinkage of a casting is usually around 1% for gray cast irons and tin bronzes, 1.5%
for brasses and aluminum alloys and 2% for white cast irons and steels. During design of a
pattern (mold), the shrinkage has to be considered and the patter has to be correspondingly
oversized. Addition for machining has to also be involved.
Shrinkage stress generates in the casting as a result of resistance of mold, cores etc. against
shrinking (by external forces). This stress typically results in generation of high-temperature
cracks. At higher temperatures, when the material is plastic instead of elastic, internal stress
releases via permanent deformation of dimensions.
During cooling of robust castings (cylinders, stocks etc.)
or castings with various walls thicknesses in the
temperature region of elastic-plastic deformations and
then in the region of completely elastic deformations,
internal thermal stress is generated as results of thermal
gradients. This stress then increase during further
cooling to room temperature. If the stress is higher than
tensile strength, cracks occur (with clean metallic
surface). Generation of internal stress in a casting is
schematically depicted in Figure 20.
Besides internal stress caused by non-uniform cooling of
a casting in solid state, transformation stress is generated
due to γ -> α Fe phase transformation in solid state
during which volume increases. A typical example is residual stress in Fe alloys.
Residual stress is very dangerous for castings, since it leads to deformations (especially
during machining), decreases loading ability (residual stress is added to external stress) and is
the cause of early fracture nucleation.
Thermal stress in a casting can be calculated:
±σ = E.α.(T1-T2)
where σ – stress [MPa], α – coefficient of thermal linear shrinkage [K-1
], E – elasticity module
of metal [MPa] and ∆T – temperature difference in two locations within a casting [K].
Generation of residual stress can be prevented by suitable casting construction (possibility of
a harmless stress release, uniform walls thicknesses, smooth changes etc.), suitable foundry
Figure 20: Generation of
deformations during shrinking.
technology (supple molds, early removal of a casting from the mold, reinforcement of high-
exposure locations by fins) and slow uniform casting cooling.
If inner residual stress after all generates in a casting, it can be released via either natural
release – aging (i.e. long-time storage, favorably at weather conditions) or annealing to
decrease internal stress.
Gasses in metal and mold
Gasses in mold and metal during casting are involved in several phenomena occurring at the
same time:
Dissolution of gases in a molten metal.
Generation of gases in a mold.
Flow of gasses towards a casting surface.
Removal of gases from a mold cavity.
Entry of gases into a molten metal.
Movement of gases inside a molten metal.
Separation of gases from a molten metal.
At a certain temperature, molten metals and alloys can dissolute certain amounts of gas.
Generally, the amount of gas which can be dissolved in a melt increases with increasing
temperature. Dissolubility of gases decreases with decreasing melt temperature and is
decreased significantly at the point of solidification.
Gases separated from a melt have atomic character and synthesize into molecules. They are
especially CO, N2 and H2.
Gases dissolve in pure iron exactly according to the Sieverts law. If a metal is completely
liquid and has low viscosity, gasses are released easily. Mechanical processes such as stirring
can be used to facilitate gasses releasing. An often used method is decreasing of partial gas
pressure above the melt level (vacuum extraction or blowing of inert gas into the melt).
Gases dissolved in a metal can cause generation of bubbles resulting in smooth-surface
cavities on the surface or inside a casting. Besides gases dissolved in a metal (endogenous
bubbles), gases penetrating into the metal from the mold during its filling with the metal
influence generation of bubbles as well (exogenous bubbles). Humidity of molding mixtures
can be very dangerous especially for green-sand molds generating a significant amount of
vapor. Organic binders and additives present in a molding mixture also disintegrate and
generate carbon oxides and carbohydrates.
Permeability of a molding mixture itself is not sufficient for removal of gases, vapor and air
from a sand mold. Therefore, channels for gases removal – gas vents and vent holes – are
usually formed in a mold.
Vent holes – the main gas removal channels – are always positioned in the top parts of
castings. Contrary to this, vents are usually cast through with a metal and can also serve to
control filling of the mold or sometimes as risers. The vent holes remove gases only from a
certain part of a mold. To achieve good gases removal, the mold has to have other degassing
channels – vents.
Vents are among molds formed also in cores and they together create the extract system of a
mold cavity. They are created by perforating a mold (core) above the pattern with a steel spike
of a diameter 3 to 12 mm, the perforations are to the depth of 5 – 20 mm above the pattern.
Vents are made from an external side when the pattern is still in the mold and are not cast
through with the metal. For metal molds, the gas channels are milled and drilled.
Melting and casting of metals
Foundry technologies work only with liquid metals, which have to be produced by melting
and subsequent heating to temperatures higher than Tm. A melt of a required composition is
prepared by melting of a batch, in which the metal part usually consists of recyclable material
(risers, parts of gates, vents), slag-forming resources, external waste, possibly alloying
elements. The non-metal part of the batch consists of slag-forming additions (limestone etc.)
and also fuel for shaft furnaces. Some melting technologies do not enable to influence the
composition of a molten metal. It is therefore necessary to carefully sort individual resources
according to the chemical composition of the batch, optimize the lumpiness and surface
cleanliness.
Melting furnaces can be heated using solid fuels (coke, anthracite), gaseous fuels (natural
gas), liquid fuels (black oil) or electrically. According to the construction and batch heating
method the furnaces can be:
cupola furnaces,
electric induction furnaces,
electric arc furnaces,
converters,
rotating gas furnaces,
resistance and fuel crucible furnaces,
flame furnaces,
gas shaft furnaces.
Literature for further study
[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov
2008, 326 s. ISBN 978-80-89244-38-6.
[2] ELBEL,T. a kol. : Vady odlitků ze slitin železa. Matecs, Brno 1992,339s.
9. TECHNOLOGICAL PROCESS OF CASTINGS PRODUCTION
Time to study: 6 hours
Aim: After study of this chapter you will know
Main steps of design of technological process of castings production
Basic principles of production process design
Basic melting processes and their principles
Lecture
Demand process
The design of casting production technology and processing of technical documentation have
to be performed based on “order acceptance decision-making” or “demand process”. The aim
of this process is to make the following issues clear before concluding an “Economic
contract” (or a different form of confirmation of a casting delivery):
- technological possibilities of production of a casting of the required parameters
- acceptability and justification of customer’s requirements
- economical acceptability
- possibility of time filling of the contract
The task of a technologist in this phase is to review suitability of the casting for production
conditions in the foundry, involving especially:
- conformity of the dimensions of the casting with parameters of the existing equipment
(flasks, maximum loads and lifting heights of cranes, openings of blasting machines and
annealing furnaces doors, melting aggregates capacities etc.)
- review of optimum construction of the casting from the technological point of view and
proposition of possible adjustments
- review of the ability to keep quality requirements
- review of optimum serial production from the point of view of time usage of equipment
- review of production risk
Casting production process
A production process consists of two consequential parts: casting production process and
pattern equipment production process.
In the foundry technological department, the basic casting production background papers are
prepared:
a/ foundry work flow drawing
b/ work flow card (usually having the official title "Casting production process”).
These background papers are then forwarded to the pattern technology department, where
drawings of the pattern and its production process are developed. Based on the work flow
drawing and card, the department of foundry production technological preparation (TVP)
prepares documentation for production of all the necessary instruments – drawings of metal
pattern plates, metal cores, reinforcements, templates, pads etc. Furthermore, according to the
custom practice in the foundry, the steps to produce molds, cores and other instruments (e.g.
reinforcements) can be prepared in detail.
Foundry work flow drawing
According to ČSN 01 3061 this is a drawing of components supplemented with data
necessary to produce the pattern and mold.
Among the most important data mentioned in the drawing are:
- shrinkage of the proposed alloy
- positioning of the casting within the mold, parting lines, additions, chamfers, pre-cast and
non-pre-cast openings
- positioning of gating system (including shapes and dimensions)
- data about pattern
According to the type and shape of a casting and relevant requirements, more data can be
mentioned in the foundry work flow drawing (e.g. free parts of a pattern, chills, risers,
forming pads etc.).
Shrinkage of cast alloys
Since shrinkage occurs during cooling of foundry alloys (e.g. metals), it is necessary to design
the pattern oversized by the shrinkage of the particular alloy. The size of linear shrinkage
depends on the type, chemical composition and structure of a casting, as well as on the
resistance against shrinking from the mold or construction of the casting itself. Since the size
of shrinking is influenced by many factors, its proper design is very difficult (it is often
necessary to consider empiric experience).
Values of free linear shrinkages for the most widely used foundry alloys are summarized in
Table 2.
Table 2: Linear shrinkage of selected alloys.
Alloy Shrinkage
/%/ Alloy
Shrinkage
/%/
Gray iron 9 – 10 Tin bronze 12 – 15
Inoculated cast iron 10 – 13 Aluminum bronze 15 – 20
Ductile iron 12 – 15 Brass 13 – 18
Malleable iron 15 – 18 Aluminum alloys 12 – 14
Steel from electric furnace 15 – 20 Magnesium alloys 12 – 13
Steel from SM furnace 13 – 18 Zinc alloys 12 – 15
Austenite steel 24 – 30 Pattern metal 3 – 4
On the work flow drawing, the shrinking data is marked in red and located (if possible) above
the corner stamp.
Note:
If a metal pattern, which has been formed using a “maternal pattern” is used, the maternal
pattern has to be designed for double shrinkage – first shrinkage for casting of the pattern and
the second for casting of the casting.
Position of casting within the mold
A suitable positioning of the casting within a mold is important for production of a casting of
a required quality by the easiest possible production process. Determination of the position
has to be based on a set of important principles:
A/ Among the principles based on technological aspects and thus respecting casting quality
are:
- functional (important) planes of cast iron castings with larger walls thicknesses have to be
located at the bottom part of the mold (purest metal); if there are more functional planes
within a casting or if the functional plane cannot be positioned as the bottom plane from
various reasons, it can possibly be designed as a side plane
- for castings from alloys with high tendencies to form shrinkages (e.g. steels), the positioning
of the casting has to enable correct positioning of risers and support directional solidification
B/ From the point of view of easy production, the following principles have to be met:
- the possibility of easy positioning and fixing of cores, fixing of cores into the top part of a
mold is not used (if possible), since this is very difficult to perform
- the possibility of uniform and the easiest possible ramming
- mold cavity, especially highly exposed locations, has to be accessible and enable possible
reparations
C/ From the economic point of view it is necessary to design the position of a casting so that
the area within the mold flask is used in the best way and usage of mold material is the
smallest possible.
On the work flow drawing, the position of the casting is marked in green by the letter U (up)
or T (top) and by an arrow in the direction of the part of the pattern formed into the top of the
mold (see table Č. XVI).
Parting line
Positioning of the parting line has the most significant influence on the design of pattern,
fabrication process of molds and cores, number of cores within a mold and also achievable
dimensional accuracy of the casting. It basically comprises a suitable partitioning of a mold
(usually also pattern) to enable:
- removal of parts of the pattern after ramming
- fixation of cores
- forming of a gating system
Design of the parting line has to be performed in accordance with the following principles:
a/ A mold should have only one parting line (if possible). Application of more parting lines
significantly complicates productions, especially for machine production.
b/ The parting line should be "in plane" (if possible), especially for manual forming. An
irregular parting line should be designed only in exceptional cases – for complicated shapes.
c/ The parting line should be designed to minimize the number of pattern parts – loose parts in
particular – and cores.
d/ During design of partitioning of a free pattern, sufficient strength and stiffness of individual
pattern parts have to be maintained.
e/ The parting line should be designed to enable usage of forming flasks available in the
foundry.
f/ Parts of the casting requiring dimensional accuracy have to be formed in a single mold part
to exclude the possibility of offset.
g/ The parting line should be designed to enable positioning of all the cores in the bottom part
and their possible check before assembling of the mold.
h/ The parting line should also enable easy removal of possible seams and leakings.
The parting line is marked in green on the work flow drawing and is highlighted by end
crosses.
Additions for machining of casting planes - ČSN 014980
An addition for machining is basically a layer of material on the external or internal plane of
the casting enabling achievement of dimensional accuracy and surface quality given on the
drawing of the component by machining.
The size of a particular addition for machining is given by:
a/ The degree of accuracy of the casting according to ČSN 01 4470 and therefore the
technology used to achieve the required degree of accuracy
b/ Basic dimensions of the casting
c/ Nominal dimensions of the casting
d/ Positioning of the machined plane within the mold
e/ Material of the casting
f/ Special requirements
Gating system
The gating system generally consists of riser, down-sprue, blind riser (runner) and gates. Its purpose is
to regulate a stream of melt from a ladle to the mold and to provide perfect filling of the mold cavity in
the shortest possible time (with minimal temperature drop) in the easiest way. The gating system has
to also collect slag and impurities, which could get into the casting with the metal, and regulate
thermal processes during casting solidification. Shapes of gating systems can significantly deviate
from the common shape depending on specific conditions (i.e. character of the casting).
Calculation of gating system
Optimal casting time– τ0 – can be calculated according to the following relation:
0 = s*(m0)1/2
/s/
where: m0 – raw casting mass /kg/ (mass of components including additions for machining,
gating system, vents, possibly risers), s – coefficient depending on casting wall thickness
cast iron: s = 1.53 for thickness 3 - 4 mm
s = 1.85 for thickness 4 - 8 mm
s = 2.20 for thickness 8 - 15 mm
s = 2.50 for thickness 15 - 30 mm
steel: s =1.1 thin-walled castings
s = 2 – 2.4 simple thick-walled castings
Mean ferrostatic pressure height – Hp – can be calculated according to the following
relation.
H =H – P2/2C /m
where: Hp - mean ferrostatic pressure height, H – height of down-sprue above the gate /m/, C
– height of casting /m/, P - height of casting above the gate /m/
According to the location of attachment to the gates, specific cases can occur (Figure 12):
a/ bottom attachment – P = C and Hp = H – C/2
b/ top attachment – P = O and Hp = H
c/ step attachment, for a case when P = C/2 is Hp = H – C/8
Casting speed (metal flow rate) can be calculated according to the following relation:
v = (2g Hp)1/2
/m.s-1
/
where: v – casting speed, Hp – mean ferrostatic metal pressure height /m/, g – gravity
acceleration /m.s-2
/, μ – coefficient of resistance
μ is selected: 0.27 – 0.55 for cast iron
0.30 – 0.41 for steel
0.60 – 0.70 for non-ferrous metals
Calculation of the gating smallest cross-section
For a pressurized gating system, the smallest cross-section is the cross-section of gates, calculated
according to the following relation:
O
O
Zv
ms
Τ
(m2)
where: Sz – total gates cross-section, mo – raw casting mass (kg), – density of the molten
metal (kg.m-3
), v – casting speed (m.s-1
), o – optimum casting time (s)
If relation 8 is substituted for casting speed and relation 6 is substituted for optimum casting
time into the relation for sz and all the constants are consolidated as coefficient x, the
following equation is generated:
Hp
mxs
O
Z (m2)
where: x – coefficient depending on casting wall thickness.
Determination of the coefficient x:
a) for simple castings:
wall thickness 3 - 4 mm x = 3.8
4 - 8 mm x = 3.2
8 - 15 mm x = 2.8
over 15 mm x = 2.4
b) for more complicated castings:
wall thickness 3 - 4 mm x = 5.8
4 - 8 mm x = 4.9
8 - 15 mm x = 4.3
Note:
If the designed gating system has more gates, then a cross-section of one of the gates is
determined by dividing of the total cross-section area sz by the number of gates.
Shape and dimensions of gates can be determined (if the cross-section is known) according to
Figure 21.
Figure 21: Basic types of gates for gating systems.
Determination of other gating system cross-sections:
The sz gates cross-section is the basic parameter for calculation of other parts of the gating
system.
For pressurized systems, the following condition applies: cross-section of the down-sprue in
its narrowest location sk > cross-section of the runner ss > cross-section of gates sz.
The mutual ratio of these cross-sections varies for various foundry alloys. The following
rations are usually selected for gray cast iron castings:
Sk : Ss : Sz
2 : 1.5 : 1 for larger and medium castings
1.4 : 1.2 : 1 for simple and fine castings
1.11 : 1.06 : 1 for fine-walled castings
According to the casting and cast alloy types, it is possible to determine the sz and sk cross-
sections using the mutual ratio of the cross-sections.
Shape and dimension of the blind riser can be determined using Figure 22.
Figure 22: Shape and dimension of blind riser.
The down-sprue is of a circular cross-section. For pressurized systems, the sk cross-section
(i.e. cross-section of down-sprue in the location of attachment to the blind-runner) increases
towards the pouring basin. The chamfer, by which the widening is ensured, is usually 1° - 2°.
Pouring basin – absorbs the first impact of a metal during casting from a ladle and regulates
its flow into other parts of the gating system. It also ensures a constant casting speed during
filling of the mold and collects slag carried from the ladle by the stream of a molten metal.
The basic shape of a pouring basin is depicted in Figure 23a. However, various pouring basins
shape modifications can occur in practice – see Figure 23b-e.
Figure 23a: Basic pouring basin shape. b) H0 – level of cast opening entrance c)
Plugs, partitions and possibly strainers (see Figure 23b-d) reduce the danger of intrusion of
slag into other parts of the gating system and therefore to the mold cavity.
Plugs – reduce the danger of slag intrusion at the beginning of casting – i.e. in the most
important time period from the slag separation point of view. Plugs are controlled either
manually (for large castings) or automatically.
Funnels (Figure 23e) – do not separate slag and can therefore be applied for bottom-
attachment type of casting.
Pouring basins are formed in the mold either manually, pressed-in or “external” (i.e. formed
in an additional flask outside the main mold).
d) e)
Figure 23d-e: Various types of pouring basins.
On the work flow drawing, the gating system (shape and dimensions) is drawn in red,
possibly blue, color.
CORE
Vents and their calculation
Vents together with natural gas permeability of molding mixtures and exhaust vent holes
perforated into the molds serve to exhaust air and gas generated during casting and
solidification of the molten metal. They are positioned at the highest locations in the molds
and their number is determined according to their size (possibly shape).
The shape of a vent is depicted in Figure 24. Their cross-section is usually circular and
increases towards its outlet from the mold. The chamfer, by which the widening is ensured, is
usually 4° - 8°.
Figure 24: Positioning and shape of vents.
The following simple relation is applied to calculate the smallest vent cross-section sy (i.e.
cross-section in the location of attachment to the casting):
Sv = 1,5 . Sk (m2)………………...11
where: Sv – total vents cross-section, Sk – cross-section of down-sprue – see chapter 2.2.2.1
(m2).
Note:
If more vents are designed for a casting, then the cross-section of a single vent is determined
by dividing of the total vents cross-section area sy by the total number of vents.
On the work flow drawing, the vents (including dimensions) are drawn in red or blue.
Risers
For alloys which tend to form shrinkage cavities (e.g. steels), it is necessary to involve risers.
The riser is basically a container of metal providing metal filling for the solidifying casting.
The molten metal in the riser solidifies as last. Therefore the shrinkage cavity does not form
in the casting but in the riser, which is removed during subsequent machining.
Note:
Calculation of risers and technological principles for their design are described more in detail
in the recommended literature.
On the work flow drawing, the risers (shape, dimensions, number) are drawn in red or blue.
Work flow card
It is in principle a text part of a foundry process. It completes marks drawn in the foundry
work flow drawing and contains more information necessary for production, costs calculation
and control of technological flow in a foundry. The information and method of their
denotation in a work flow card vary substantially in individual foundries and depend
especially on the organization of production in the foundry and method of utilization of the
background papers.
The following details are in particular mentioned in work flow cards: material and weight of
the casting, shrinkage size, complete pattern, used forming machines, flasks sizes, casting
temperature and time. Furthermore, type and consumption of molding mixtures, molds,
conditions for cooling of the casting, cleaning method, heat treatment and delivery conditions.
VŠB-TU Ostrava
Department of
metallurgy and foundry
Ostrava Poruba
CASTING PRODUCTION
PROCESS
Model no.:
Drawing no.:
Casting title Mold
Number of produced
castings Molding mixture
Material of the casting Composition:
sand
Delivery conditions
binder
Casting weight: [kg]
additives
Usage of molten metal [%] Cores
Shrinkage of pattern
equipment [%] Molding mixture
Pattern Composition:
sand
Cores binder
Free risers additives
Number of castings
within a flask
Drying of molds and
cores
Dimensions of molding
flask: upper x / [mm]
Dimensions of molding
flask: lower x / [mm] Chills external
Mold stiffness Chills internal
Surface treatment Casting temperature [°C]
Schematics of the casting:
Production process elaborated
by:
Date: Study group:
Literature for further study
[1] HAVLÍČEK, F. Konstrukce odlitků, učební pomůcka, VŠB-TU Ostrava, 1995
[2] BEDNÁŘ, B. Technologičnost konstrukce odlitků, Univerzita J.E. Purkyně, ÚTŘV, Ústí nad
Labem, 2004
[3] HERMAN, A., SVÁROVSKÝ, M., KOVAŘÍK, J., ROUČKA, J. Počítačové simulace ve
slévárenství, učební texty ČVUT Praha, 2000
[4] GOODRICH, G.M. Iron Castings Enginering Handbook. American Foundry Society.
Schaumburg, Illinois, USA, ISBN 0-87433-260-5, 2006, 418s.
10. CLEANING AND FINISHING OPERATIONS, FINAL CHECK,
DEFECTS OF CASTINGS
Time to study: 4 hours
Aim: After study of this chapter you will know
Individual processes for cleaning of castings
Basic principles of quality check
Basic defects of castings
Lecture
Cleaning of castings
After casting, the casting has to cool down to temperature enabling further manipulation. The
necessary cooling time depends on material, weight and shape of the casting and material of
the mold. After cooling, the casting (usually called raw casting) can be removed from the
mold. This is easy for permanent molds. For non-permanent molds, a special step called
releasing from the mold has to be performed.
Releasing of a casting from the mold
Cooled castings can be released from molds either by impacts (shaking-out) or by tension or
press (pulling or pressing out). Manual shaking-out consists in impacting the flask or casting
with a hammer. Mechanical shaking-out can be performed using vibrators or shaking grids.
Pulling or pressing out is used especially for casting to permanent molds and can be
mechanized and robotized.
Raw cleaning of castings
Shaking-out enables removal of a significant portion of mold material. Nevertheless, burnt-on
sand particles on the surface of the casting and rests of cores usually remains un-removed.
Raw cleaning of castings is performed manually by pneumatic hammers or in cleaning drums
and chambers. These devices enable removal of burnt-on and core sand by milling or jetting
of steel or cast-iron pellets – blasting.
Removal of down-sprues and risers
Down-sprues, risers and vents have to be removed from raw cleaned castings. The removal
process depends on the material of the casting. For fine castings from non-ferrous metals, the
down-sprues and risers are usually cut-off using circular saws. For brittle gray iron castings,
the down-sprues and risers can be broken-off. For steel castings, cutting is performed using
torches with oxygen-acetylene or oxygen in combination with natural gas.
Final cleaning and treatment of castings
Final cleaning comprises modifications of final appearance and dimensions of the casting to
conform to the dimensional and shape requirements. These steps are often performed
manually by chopping and grinding. Eventually, final blasting with a fine blasting agent can
be performed. Castings from iron alloys are protected with basic anticorrosion coatings.
Heat treatment of castings
Foundry castings are often finally heat treated. Since heat treatment is an individual
technological field, it is not mentioned in detail in this text.
Final inspection of castings
After cleaning, the castings are inspected. At first, they are inspected visually on their
surfaces. After this step, the castings are measured. In some cases, the customer also demands
inspection of internal quality by non-destructive testing. For separately cast or additively-cast
samples from each melt (or also each piece), chemical composition and mechanical, possibly
physical, properties are inspected.
Deviations (non-conformations) of the following are denoted as defects:
appearance,
shape,
dimensions,
weight,
structure,
uniformity (homogeneity) and
agreed conditions and standards.
Acceptable defects do not influence the applicability of the casting and have to be either
permitted or at least must not be interdicted.
Non-acceptable defects are usually namely stated and their occurrence signifies a non-
conformant product – spoilage.
Removable defects are defects, which can be removed by suitable technologies – additional
steps have to be performed by the foundry at its own expenses.
Defects (non-conformities) in castings
Various systems have been elaborated to classify casting defects. A relatively simple
classification, based on the international atlas of defects, is included within the still valid ČSN
42 1240 standard, which classifies defects of iron alloys castings into seven individual
categories.
Defects of iron alloys castings, the categorization of which into seven defect classes and
groups together with their classification, explanation of main causes and proposals for their
elimination in foundry industry, have also been summarized by Elbel. His basic classification
of classes, groups and types of casting defects is depicted in Table 3.
Table 3: Separation of foundry defects into classes, groups and types.
Class
of
defects
Title of class of defects Group of defects Title of group of defects Number
of types
100 Shape, dimensional 110 Missing part of the casting without fracture 8
and weight defects 120 Missing part of the casting with fracture 3
130 Deviation of dimensions, inaccurate shape 4
140 Deviation of weight -
200 Surface defects 210 Burning-on 3
220 Expansion scabs 3
230 Erosion scabs 4
240 Veining -
250 Eutectic Sweat -
260 Flash 3
270 Irregularities of casting surface 7
280 Painting Defects -
300 Defects of material continuity 310 Hot Cracks 3
320 Cold Cracks -
330 Failure by mechanical damage 2
340 Failure from unconnected metal 2
400 Voids 410 Gas Holes 5
420 Pinholes -
430 Blowholes 3
440 Shrinkages 6
500 Macroscopic inclusions 510 Slag inclusions 2
and macrostructural defects 520 Non-metal inclusions 6
530 Macro-segregations and segregations 4
540 Cold Shots -
550 Metallic inclusions -
560 Defective fracture -
600 Microstructural defects 610 Microcavities 3
620 Inclusions -
630 Incorrect grain size -
640 Defect o mikrostructure -
650 Hard spots -
660 Inverse chill -
670 Surface Decarburization -
680 Other defects of mikrostructure -
700 Defects of chemical 710 Incorrect chemical composition -
composition and properties 720 Deviations from mechanical properties -
of castings 730 Deviations from physical properties -
740 Wrong homogeneity -
Literature for further study
[1] Havlíček, F. Konstrukce odlitků, učební pomůcka, VŠB-TU Ostrava, 1995
[4] Goodrich, G.M. Iron Castings Enginering Handbook. American Foundry Society.
Schaumburg, Illinois, USA, ISBN 0-87433-260-5, 2006, 418s.
[2] ELBEL,T. a kol. : Vady odlitků ze slitin železa. Matecs, Brno 1992,339s.