types of sands used in moulds

7/31/2019 Types of Sands Used in Moulds

1/20


2/20

Green sand Dry sand Loam sand Synthetic sand

Core sand Parting sand Facing sand Backing sand

Sharp sand System sand Heap sand Oil and molasses sand


3/20

Green sand is an aggregate of sand, bentoniteclay, pulverized coal and water. The largestportion of the aggregate is always sand, which canbe either silica or olivine.

It contains about 5% water and 15 to 30% clay. Moulds and cores can be both made of green sand. Since this sand contains moisture, it is necessary to

prevent defects like voids by controlling thepermeability and moisture content.

Green sand moulds are poured in green condition. Green sand is preferred for producing simple,

small and medium size casting.


4/20


5/20

Green sand mould(cavity) when dried resultsin dry sand mould.

Depending upon the dried mould wall

thickness, it can be called skin dry mould ordry mould.

Since dry sand contains less water content, theamount of venting is even less than thatprovided in the green sand mould, but it willlet the mould gases escape.


6/20

Moulds may be

a) Dried by heating the same at about 3500F.b) Skin dried by a torch. Unlike full drying, it is a

localized drying process


7/20

Dry sands moulds possess

a)greater strength and rigidityb)Thermal stability

Dry sand moulds do not cause defects whichoccur due to the moisture content of thesands(i.e pinholes,etc)

Large and heavy castings are produced in drysand moulds


8/20

Loam sand contains much more clay whencompared to normal sand.

The clay content is in the order of 50% or so.

The ingredients of loam sand may be fine sands,finely ground refractories, clays, graphite andfibrous reinforcement.

A typical loam sad mixture consists of:-

a)silica sand 20 volumes

b)clay 5 volumes

c)manure 1 volume

d)moisture 20%


9/20

PREPERARTION

The material is mixed (with water) to aconsistency resembling mortor.

Loam dries hard

Moulds for casting large bells are made up ofbrick frame work and lined with loam sandand dried.

Sweep or skeleton pattern may be used forloam moulding.


10/20


11/20

Synthetic sand consists of:-

Natural sand(base) with or without clay.

Binder(bentonite).

Moisture. Thus a synthetic sand is a formulated sand.

Sand formulation is done to acquire certaindesired properties not pocessed by naturalsands.

Synthetic sands are used for casting steel,ferrous and non ferrous alloys.


12/20

Parting sand consists of dried silica sand, seasand and burnt sand.

Parting sand when sprinkled

a)over the rammed drag avoids the sticking ofdrag with cope.

b)over the pattern avoids its sticking with thegreen sand and makes the pattern withdrawal

easier.


13/20

Dry parting substances Fine dried sand Charcoal, ground bone and lime stone. Lycopodium -a yellow vegetable matter

Tripolite- a silicate rock Ground nutshells(walnut) Talc(magnesium silicate) Calcium phosphate

Liquid parting substances Petroleum jelly mixed with oil, paraffin and stearic

acid.Dry parting compounds are used on wood and weton metal patterns


14/20


15/20

Facing sand is fresh and specially prepared moldingsand which covers the pattern from allround and thenthe ordinary floor sand is used to fill the remaindermolding box.

Facing sand comes in direct contact with the moltenmetal being poured and therefore it should possessmuch improved properties as compared to ordinarymolding sand.


16/20

A sharp sand need not necessarily have sharpgrains.

A sharp sand is one which is substancially free

of bond.


17/20

System sand is one which is used in mechanicalsand preparation and handling system.

In mechanical sand preparation and handling

units(i.e mechanical foundries) no facing sandis used; rather the completely otherwise usedsand is cleaned and reactivated by the aditionof water, binders and special additives.

this is known as system sand.


18/20

It is a sand put on the floor as a heap when it isprepared for use.


19/20


20/20

Thank you!!

types of sands used in moulds

Documents