sand casting 2011

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SAND CASTING

• Sand casting is one of the earliest forms of casting practiced due to thesimplicity of materials involved. It still remains one of the cheapest ways tocast metal because of the same simplicity.

• In this casting process a pattern is made in the shape of the desired part.This pattern is made out of wood, plastic or metal. Simple designs can be

made in a single piece or solid pattern.

• The patterns are then packed in sand with a binder , which helps to hardenthe sand into a semi-permanent shape.

• Once the Sand mold is packed, the pattern is removed leaving a hollowspace in the sand in the shape of the desired part.

• The pattern is intentionally made larger than the cast part to allow forshrinkage during cooling.



• Cores can then be inserted in the mold to create holes and improve the

casting's net shape.

• Two piece molds are clamped together and melted metal is then poured into an opening, called RUNNER. If necessary, vent holes, called RISERwill be created to allow hot gases to escape during the pouring.

• The pouring temperature of the metal should be a few hundred degreeshigher than the melting point to assure good fluidity, thereby avoidingprematurely cooling, which will cause voids and porosity.

• When the metal cools, the sand mold is removed and the workpiece isready for secondary operations, such as machining & plating.

• Sand casting is the least expensive of all of the casting processes.



3200 B.C. Copper is the oldest known casting material in existence, is

cast in Mesopotamia.

Basically history of metal casting started from Neolithic period(6000 – 1800 BC).

645 B.C. China was the earliest known sand moulding country.

500 A.D. Cast crucible steel is first produced in India,

but the process is lost until 1750 when Benjamin Huntsman

reinvents it in England

History



Between 1875 and 1940, cast iron cookware manufacturers

periodically refined their casting techniques to produce extremelywell-made products.

Products made between 1900 and 1940 were both slightly thicker andmore finished in their appearance.

During same time, the manufacturing included a series of polishingsteps that produced pieces with glass-like surfaces.

The development of new technologies and an increased demand forcast parts gave tremendous impulses to the metal casting industry .

During 19 century iron casts was not only limited to the creation of cookware and decorative objects but was also used for the productionof machine parts and articles of daily use.



Parting line



Two Main types of sands

"Green sand" is a mixture of wet silica sand, clay, moisture and other locallyavailable additives.

The “Air set sand" method uses dry sand bonded to materials other thanclay, using a fast curing adhesive. When these are used, they are collectivelycalled "air set" sand castings to distinguish these from "green sand" castings.

Molding sands are natural bonded (bank sand) and synthetic (lake sand),which is generally preferred due to its more consistent composition.

With both methods, the sand mixture is packed around a master "pattern"forming a mold cavity.

The sand mixture is tamped down as it is added, and the final moldassembly is sometimes vibrated to compact the sand and fill any unwantedvoids in the mold.

Air-set molds often form a two-part mold having a top and bottom, termedCope and drag.



Greensand is an olive-green colored sandstone rock which is commonly

found in narrow bands, particularly associated with bands of chalk andclay worldwide; it has been deposited in marine environments at various

times during Earth history, such as during the Jurassic and Cretaceous

periods.

greensand

the name is due to its unfired or green state, not its color

http://en.wikipedia.org/wiki/Sandstone

http://en.wikipedia.org/wiki/Rock_(geology)

http://en.wikipedia.org/wiki/Chalk

http://en.wikipedia.org/wiki/Clay

http://en.wikipedia.org/wiki/Marine_(ocean)

http://en.wikipedia.org/wiki/Earth

http://en.wikipedia.org/wiki/Jurassic

http://en.wikipedia.org/wiki/Cretaceous

http://en.wikipedia.org/wiki/Geologic_time_scale

http://en.wikipedia.org/wiki/Geologic_time_scale

http://en.wikipedia.org/wiki/Cretaceous

http://en.wikipedia.org/wiki/Jurassic

http://en.wikipedia.org/wiki/Earth

http://en.wikipedia.org/wiki/Marine_(ocean)

http://en.wikipedia.org/wiki/Clay

http://en.wikipedia.org/wiki/Chalk

http://en.wikipedia.org/wiki/Rock_(geology)

http://en.wikipedia.org/wiki/Sandstone



Making of green sand:

Simply put, it is a mixture of sand, bentonite clay, and a bit of

water.

*The bucket contained nine inches of sand,

*one inch of bentonite

to achieve a 10% bentonite mixture, and mixed the to dry for about

ten minutes.

added about 32 oz water in six ounce (coffee cup)

increments, mixing constantly between additions, over a period of

several hours when the sand started to display "pack ability”



REQUIREMENTS TO SAND

• Ability to retain mould shape during

packing and pouring.

• High temperature stability.

• Permeability for the gases liberated from

the mould and solidifying metal.

• Silica sand with additives is used for sand

casting.



Patterns materials:

• In order to be used repeatedly patterns are made of relatively tough materials.

• Wood • Metal

• Plastic

• A parting (release) agent is applied on the pattern

surface in order to provide easy removal of thepattern from the mould.



GATING SYSTEM

It includes

Pouring cup

spruce

Riser

Runner Gas vents



GATING SYSTEM.

• In a sand casting mold the most important

thing is the GATING SYSTEM.

• The set of channels through which a molten

metal flows to the mould cavity is called

gating system.



TERMS

• Pouring cup and sprue - receive the poured

melt.

• Runner – a channel through which the melt

is supplied to the gates(through this molten

metal enters the mold cavity)

• Riser – a cavity connected to the gatingsystem feeding the casting when it is

shrinking.



• Vents – air within the mold cavity and

gases formed when a molten metal

contracts the mold surface are removed

through the vents.

• Cores – a separate insert to form the

interior cavities of a casting (usually madeof sand.



Patterns/Masters

• Patterns are commonly made larger than the

casting because of the shrinkage effect.

• Shrinkage allowances are usually 1-2%.

• The pattern surfaces are never made

perpendicular to the mould parting surface.



ADVANTAGES OF SAND

CASTING• Low cost of mould materials and

equipment.

• Large casting dimensions may be obtained.

• Wide variety of metals and alloys (ferrous

and non-ferrous) may be cast (including

high melting point metals).



DISADVANTAGES

• Rough surface.

• Poor dimensional accuracy.

• High machining tolerances.

• Coarse Grain structure.

• Strength of the product is lower then

machined and forged products.

• Thin products cannot be produced



The process is used to make medium to

large parts such as

• valve bodies

• Plumbing fixtures

• Locomotive components• Construction machinery

sand casting 2011

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