Classification of Sand & Centrifugal Casting

BY-SHIVAM OMAR

CLASSIFICATION OF SAND

• According to their use in foundry moulding sand into classify following different types…• Green sand• Dry sand• Loam sand• Facing sand• Baking sand• Parting sand• System sand• Core sand

GREEN SAND

• It is sand used in the wet condition for making the mould. It is mixture of silica sand with 15-25% clay and 6-8% water

• As explained earlier green sand moulds are not dried and metal is poured in them in the wet condition.

• This sand is used for producing small to medium sized moulds which are not very complex.

DRY SAND

• Dry sand is the green sand that has been dried or baked after preparing the mould.

• Drying sand gives strength to the mould so that it can be used for larger castings

• If we dry the green sand mentioned above, then we get dry sand. the physical composition remains same, except for water content.

LOAM SAND• Loam sand is sand containing up to 50 % clay

which has been worked to the consistency of builder mortar.

• This sand is used for loam sand moulds for making very heavy castings usually with the help of sweeps and skeleton patterns.

FACING SAND• Facing sand is the sand which covers the pattern

all around it. The remaining box is filled with ordinary floor sand.

• Facing sand forms the face of the mould and comes in direct contact with the molten metal when it is poured.

• High strength and refractoriness are required for this sand.

• It is made of silica sand and clay without the addition of any used sand.

BAKING SAND• Backing sand is the bulk of the sand used to back

up the facing sand and to fill up the volume of the flask.

• It consists mainly of old, repeatedly used moulding sand which is generally black in colour due to addition of coal dust and burning on contact with hot metal.

• Because of the colour backing sand is also sometimes called black sand.

• The main purpose for the use of backing sand is to reduce the cost of moulding.

PARTING SAND• This sand is used during making of the mould to

ensure that green sand does not stick to the pattern and the cope and drug parts can be easily separated for removing the pattern without causing any damage to the mould.

• Parting sand consists of fine grained clay free dried silica sand, sea sand or burnt sand with some parting compounds.

SYSTEM SAND• This is the sand used in mechanized foundries for

filling the entire flask.• No separate facing sand in used in a mechanized

foundry.• Sand, cleaned and reactivated by the addition of

water and binders is used to fill the flask. Because of the absence of any fresh sand, system sand must have more strength, permeability and refractoriness compared to backing sand.

CORE SAND• Core sand is the sand used for making cores. This

is silica sand mixed with core oil. That is why it is also called oil sand.

• The core oil consists of linseed oil, resin, light mineral oil with some binders.

• For larger cores, sometimes pitch or flour and water may also be used to save on cost.

CENTRIFUGAL CASTING

• Centrifugal casting is a metal casting process that uses centrifugal force to form the cylindrical parts.• Its application are like jet engine, compressor cases,

petrochemical furnace tubes , many military product and other high- reliability product.

TYPES OF CFGL.CASTING• Various types of centrifugal casting methods are

in use. The main principle behind any centrifugal casting is metal that is poured in to a rotating mold exactly at center is thrown outward due to the action of centrifugal force.

• The main advantage of centrifugal casting is the impurities get accumulated exactly at the center. The types of centrifugal castings are…. 

1) True centrifugal casting2) Semi centrifugal casting3) Centrifuge casting

TRUE CENTRIFUGAL CASTING

This casting technique is employed when axis symmetrical objects with uniform diameter are to be produced. Core is not employed in these castings.

ADVANTAGE,DISADVANTAGE AND ITS APPLICATIONAdvantages of true centrifugal casting

1) Relatively very light impurities move inwards towards center. So they can be removed easily thus helping in producing sound castings. 2) Central core is not required for making a hole or pipe.3) Employment of gates and risers is not required.4) This technique is best suited for the mass production of symmetrical objects.5) Castings yield is very high in some cases it is even equal to 100%.Disadvantages of true centrifugal casting

1) Centrifugal castings require very high investments.2) Skilled labors are to be employed for this process.3) Only some shapes can be generate casting processed by thisApplications

1) Bearings for machines 2) Pipes3) Liners for IC engines4) Rings and other annular components

SEMICENTRIFUGAL CASTING

This is also similar to the true centrifugal casting but there is a modification in it. These castings consist of a central core. • Semi centrifugal casting is employed for casting

gear blanks, sheaves, and wheels etc. low spinning speeds can be used speeds ranging between 180 to 200 RPM is recommended.

• These castings are normally prepared in vertical machines.

• The mold cavity is arranged with in the mold so that its central axis is vertical and concentric with the axis of rotation.

ADVANTAGES• 1) In this number of molds can be stacked

together, one over the other can be fed by a common central sprue in order to produce more than one casting at a time.

• 2) Similar to true centrifugal casting it ensures purity and density of the product poorer structure forms the center of the casting so this can be machined off.

CENTRIFUGE CASTING• This type of casting method is used for casting

unsymmetrical castings in groups.• In these castings the axis of mold doesn’t

coincide with each other to induce the pressure on molds the casting rotated at the center.

• Feeding to the mold cavities is done by central sprue by the action of centrifugal forces. When castings are generated in multiple layers by placing one over the other then it is called stack molding.

ADVANTAGES1) Ensures better quality.2) Castings when generated on large scale will be economical.3) These castings generate high yield4) The castings obtained by this method cannot be satisfactorily obtained by other casting methods.5) Cleaning and fettling cost of the castings can be reduced.6) Rejection percentage is very low.