gating system designing - foundry...

GATING

SYSTEM

DESIGNING

Feasibility of 2D drawing. Feasibility of Section thickness sensitivity with the help of 3D model .Ask customer to increase if below 5mm.

Feasibility of feeding location w.r.t. section thickness connectivity.

Identify hot spots and last cooling spot with the help of simulation .

Try to make casting in cope and maximum in drag.

Decide the parting line in a such way so that riser neck location can be provided easily.

Design the proved gating system on match plate first and then make cavity wise layout.

Knowledge of metallurgical and sand control.

Top view of sample casting

Side view of sample casting

Cut section of sample casting

Lay out of sample casting

Casting wt: 47.3 kg.

Considering 70% yield

Bunch wt:68.3kg {consider M:S ratio}

Pouring Time = √Bunch weight x 2.2

For Example :

Bunch weight is 68.3Kg x 2.2

√68.3x2.2 = 15Sec.

Flow rate = Bunch weight/pouring time

For Green Sand Casting – 4 to 5 kg

molten metal should pass in 1sec.

For Hand Molding casting - 6 to 7 kg

molten metal should pass in 1sec.

The purpose of gating system is

to allow the liquid iron to fill

mold cavity while, at the same

time ,screening out slag.

Gating

System

Types of Filter

Ceramic Pressed Filter

Extruded Filter

Foam Filter – 10PPI, 20PPI, 30PPI

Filters

The purpose of the risering

is to provide freedom from

defects potentially arising

from volume changes which

cooling and solidifying

graphitic irons

Selection of Riser/Sleeve

(Insulating & Exothermic)

Modulus of casting = Volume/Surface area

Modulus of Riser = 1.2 x Modulus of casting

Modulus of Riser Neck = 0.4 to 0.65 of

Modulus of casting

METALLURGICAL

CONTROL

Ferritic Grade Pearlitic Grade

400/18 500/7

450/10 550/6

450/12 600/3

700/2

800/2

900/2

Charge Ferritic Grade Pearlitic Grade

Pig Iron. 20%. 0%

CRCA 40% 60%

Home SGI RR 40% 40%

Charge Sequence - Pig Iron – Max.20% of the charge (Phosphorous below 0.02%,

Sulfur 0.015% & Ti less than 0.04% Mn 0.2%max,)

- Runner Riser (duly shot blasted) – 40% of the charge

- CRCA – 40% of the charge

- Graphite addition – as per calculation

- Silicon addition – as per calculation

- Spectro Sample Temperature – @1510 degree

- Furnace chemical analysis

- Carbon – 3.5 to 3.6%

- Silicon – 1.4 to 1.5%

- Mn – o.2% max

- Ph -0.02%max

- Cr – 0.04% max

- Sn – 0.01% max

- Ti – 0.04% max

- Cu – Depending upon grade

Charge Sequence

Desulfurization

As a general rule 1% CaC2

(calcium carbide) is needed to

reduce base sulfur content

from 0.1 to 0.01%

FeSiMg -Alloy FeSiMg alloys contains :

Magnesium – 5 to 7%

Si – 44 to 45%

Ca – 1.2 to 1.4%

Al – 0.8 to 1%

Br – 2 to 5% (produces uniform distribution of high nodule count in thin and heavy section)

Ce – 0.3 to 0.5%

Size of FeSiMg – 10 to 25mm

Addition : 1 to 1.2% of Liquid metal

Note : Don’t place in treatment ladle pocket until 15 to 20sec prior to tap, because alloy may fuse and stick to bottom and cause poor recovery

Cover Steel : 1% of liquid metal

The tap must be completed with in 50sec for 1Ton metal i.e. 20kg per second.

FeSiMg Treatment Base metal treatment temperature from 1530c to 1560c depending

upon section thickness of the casting.

Magnesium has boiling point about 1107c which is far lower than temperature of molten cast iron being treated. This together with high vapor pressure of magnesium at the treatment temperature prevent easy dilution of magnesium and result inconsiderable ignition and violence during the reaction.

Magnesium is also powerful desulphuriser element , so reacts with all sulfur present in the base metal before it become effective in changing graphite form, from flake to spheroid.

Magnesium reacts with sulfur /oxygen and form MgS which called dross (slag).

Specified range of residual magnesium to ensure the fully nodular structure is 0.035 to 0.045% of Mg . It should be noted that the major Mg is the total Mg i.e. it includes Mg combined as MgO , MgS and MgSiO3.

If the residual magnesium is too high i.e. above 0.06% there is strong risk of magnesium exerting its power tendency to promote carbide formation, porosity and dross.

Specification of Inoculation

75% Ferro silicon

1 to 1.2% Calcium

0.8 to 1% Aluminium

2 to 3% Br

INOCULATION

PRACTICE &

MICROSTRUCTURE

The metallurgical meaning of

the word “inoculation” is to

provide the melt with seeds

or “nuclei” onto which the

solid phases grow during

freezing.

Need for Inoculation

While pouring metal in mould, due to sudden change in

cooling temp i.e non equilibrium condition means from

1450 to 28 0r 30 degree room temp, under-cooling or

super cooling happens and because of there is chance of

difference in microstructure and there is chance of

carbide formation.

From inoculation nuclei , eutectic cell form in the metal

get warm and temp raised and come to equilibrium and

uniform cooling.

Stages of Inoculation

Stream inoculation size i.e 1 to 3mm for 500kg and 2 to

7 mm above 1ton

Late stream inoculation size 0.2 to0.5 mm

Use of Inoculation

For 10 to 40 mm ladle addition of 0.4 to 0.6%

For 3mm to 5mm ladle addition may be 0.8%

In case of late stream inoculation 0.1 to o.2 %

Effect of inoculation

Improve nodule count

Avoid carbide formation

Promoter graphite formation

Refining of microstructure

Reduce segregation tendency

Reduce shrinkage tendency

Improve machinability

Increase tensile strength

Increase ductility

Excess inoculation form more nuclei and because of this more graphite form.

Graphite has low density i.e 2.5 hence we get excess graphite on machine surface.

Grade wise Microstructure

DEFECT

ANALYSIS

Improper inoculation & Excess under cooling

Low silicon containing carbide

Excess Manganese , chromium , vanadium, Moly

Corrective action

Special causes:

Common causes: