PATTERN MOULDING & CASTING

  • PATTERN ALLOWANCES: -
  1. Shrinkage or contraction allowances: - 
Types: - a. Liquid Shrinkage- Liquid to Solid
b. Solid Shrinkage- Solid to solid
(Contraction in solid shrinkage is less than the contraction in liquid shrinkage)

This type of contraction eliminated by adding to external dimension and subtracting the internal dimension.

Least shrinkage allowance for brass
Maximum shrinkage allowance for lead


2. Draft Allowance: -

Tapper form of vertical wall for easy and clean withdrawal of the pattern.

Value is generally 1/2 to 2°.

3. Machining Allowance: -

4. Distortion or Camber Allowance: -

5. Rapping or Shaking Allowance: -



  • TYPES OF PATTERN: -

1. SOLID OR SINGLE PIECE PATTERN -

Used for simple shapes and low quantity production.


2. SPLIT PATTERN -


3. MATCH PLATE PATTERN -

Used on machine moulding for quantity production of casting.

At a time, can be mounted several pattern.


4. COPE AND DRAG PATTERN -

Required accurate alignment by guide and location pin.


5. LOOSE PIECE PATTERN -

This type of pattern are used when any projection is difficult to remove or can't be drawn out.


6. SWEEP PATTERN -

In this type, 2D pattern is used to produce symmetrical 3D pattern.


7. GATED PATTERN - 

Runner is the integral part of the pattern.

Eliminated the hand cutting process of the runner.


8. FOLLOW BOARD PATTERN: -

Support the over hanging part of the pattern.


9. SKELETON PATTERN: -

Used for produce large pattern.

Minimize the material consumption for pattern.

IMPORTANT HAND TOOLS USED IN FOUNDRY SHOP: -

1.   SHOVEL: -

Pan fitted with a wooden handle.

Used for mixing and moving the sand.

 

2.   RIDDLE: -

Used for cleaning moulding sand.

Specified by the diameter of frame and mesh no.

 

3.   RAMMER: -

Used for packing and ramming the sand.

Types – a. Hand Rammer, b. Peen Rammer, c. Floor Rammer, d. Pneumatic Rammer

 

4.   VENT WIRE: -

Used for pierce holes in the rammed sand.

 

5.   SLICK: -

Used for repairing and finishing the mould surface after removal of pattern.

 

6.   LIFTER: -

Used for smoothing and cleaning out depression in the mould.

Used for scoop sand deep in the mould.

 

PROPERTIES OF MOULDING SAND:-

1.   REFRACTORINESS: - Withstand the high temperature of molten metals.

2.   GREEN STRENGTH: - Sand contains moisture is termed as green sand.

3.   DRY STRENGTH: - After pouring molten metal green sand convert in to dry strength, at this stage it should retain the mould cavity and at the same time withstand the metastatic forces.

4.   HOT STRENGTH: -

5.   PERMEABILITY: - Gas evolving capability.

6.   GRAIN FINENESS NUMBER: - It can be determine by conducting shieve shaker test.

7.   FLOWABILITY: -

8.   COLLAPSIBILITY: -

9.   ADHESIVENESS: -

10.  COHESIVENESS: -

11.  TOUGHNESS: -

 

 

SL. NO.

MACHINE

USED FOR

1

UNIVERSAL TESTING MACHINE

Testing green strength.

2

SAND MULLER

Mix and prepare moulding sand.

3

CUP TEST

Testing formability.

4

CHARPY TEST

Testing toughness.

5

KNOOP TEST

Testing micro hardness of the material.

6

SPIRAL TEST

Fluidity (of molten metal)

 

TYPES OF SAND: -

1.   GREEN SAND: - 2.6% of moisture.

2.   DRY SAND: - When moisture of moulding sand evaporates.

3.   FACING SAND: -Used near the mould cavity.

More clay and fine silica sand.

4.   PARTING SAND: -Used to avoid shrinking of the moulding surfaces with other surfaces.

5.   LOAM SAND: - 50% clay and 18% moisture.

6.   BAKING SAND: - Used at the extreme end of the mould.

Already used sand can be used as baking sand.


ADDITIVE USED IN MOULDING SAND: -

1.   WOOD FLOUR/ SAW DUST: - Improve green strength and collapsibility.

2.   STARCH AND DEXTRIN: - Used to improve resistance to deformation of the mould and improves the skin hardness of the mould.

3.   IRON OXIDE AND ALUMINIUM OXIDE: -

4.   COAL DUST, SEA COAL, and SILICA FLOUR: -Improves surface finish and resistance to metal penetration.