Special Casting Processes.pptx

Special Casting Processes
Centrifugal Casting
Semi centrifugal casting
Centrifuging
Die Casting
Gravity Die Casting
Pressure die casting
Hot chamber die-casting:
Submerged plunger die casting
Air blown or goose neck die casting machine
Investment Casting
Defects in Casting
Blow holes Casting Defects
Shrinkage
Crack
Inclusions
Lift and shift
Swell
Fins
Misrun and cold shut
Metal Penetration
Hard spot
Run out
Drop
Warpage

1. Special Casting Processes

2. Centrifugal Casting The mould is rotated and the molten metal is distributed to the mould cavity with centrifugal force. This process makes hollow product. Following are centrifugal process: True centrifugal casting process Semi centrifugal casting process Centrifuging process.

3. Centrifugal Casting True Centrifugal casting process: This process is also classified as horizontal, vertical or inclined at 70 to 90°. Horizontal axis machine : With this process better quality casting is achieved and speed control is also possible.

4. Centrifugal Casting (B) Vertical axis machine: The axis of rotation of mould is vertical. Here molten metal is poured from the top of axis of mould, so due to centrifugal force it will stick on mould wall. Small length castings are produced with appropriate thickness.

5. Centrifugal Casting 2. Semi centrifugal casting: The casting like symmetrical shape, pulley, wheel, disk, gear like big shape products manufactured. More than one casting achieved. Here vertical axis machine is used. In center the hub is provided to create hollow core.

6. Centrifugal Casting 3. Centrifuging: This process is used for non-symmetrical castings having intricate details and also for precision castings. The centrifugal force provides high-fluid pressure to force the molten metal into mould cavity. A number of similar components can be cast simultaneously.

7. Die Casting Die casting utilizes two blocks of heat resistant metal machined to meet along the plane of the parting line. Fine vents are cut to allow air to escape as the metal centers. Molten or semi molten metal is either poured under gravity or is forced under high pressure into a die and pressure is maintained till solidification stage.

8. Die Casting Gravity Die Casting: feeder is incorporated so that when the level of the metal in the feeder is above that at the highest point of the casting. head of liquid in feeder forces the metal into all parts of the mould cavity. Aluminum, Copper, Lead, Magnesium, Zinc products are produced.

9. Die Casting 2. Pressure die casting: In pressure die casting metal flows under high pressure Also as the die is metallic, the casting rate is high and thus mass production is possible. The following are the types of pressure die casting (A) Hot chamber die-casting (1) Submerged plunger die casting (2) Air blown or goose neck die casting (B) Cold chamber die casting.

10. Die Casting Hot chamber die-casting: Submerged plunger die casting: Generally 125 kg/cm2- pressure is applied. The castings from zinc, tin and lead alloys are produced having low melting temperature. When plunger comes down, ‘C’ port closes and required pressure is applied in ‘B’ chamber.

11. Die Casting (2) Air blown or goose neck die casting machine: with this process the metals having low melting temperature like lead, tin, zinc ore to be cast. In this machine the cast-iron goose neck chamber is used.

12. Advantages of die casting Advantages: Thin section (0.5 mm thickness) can be easily made. Impression or complicated design can be achieved on component walls. The production rate is high (300 per hour approx ). Die set can be used many times. All non-ferrous products are produced with this method. Better surface finish is achieved.

13. Disadvantages of die casting It is not economic for small quantity of production. It is used for only small casting (10 kg weight approx ). Initial cost is high for die and other equipment. Only non-ferrous products are casted. If proper care is not taken then the defects like blow hole can be possible.

14. Investment Casting This process is called the lost-wax process or precision casting. The following are the different stages (1) Die making (2) Making wax pattern (3) Precoating the wax pattern assembly (4) Investment the wax pattern in mould box (5) Removal of wax pattern (6) Pouring molten metal (7) Cleaning of casting

15. Advantages Investment Casting Very smooth surface of casting without parting lines are achieved. (2) Machining of intricate shape can be manufactured. (3) Die casting can be replaced when short runs are involved. (4) Castings are sound and have large grains as the rate of cooling is slow. (5) It represents the only method suitable for manufacture of precision shaped castings of high melting point metals which would cause too rapid die failures is normal die casting process.

16. Disadvantages Investment Casting (1) It is expensive process and hence is adopted only where small number of intricate and highly accurate parts particularly high melting point alloys are to be manufactured. (2) This process is suitable for small size parts. (3) This presents some difficulties when cores are to be used.

17. Defects in Casting Casting defects, their causes & remedies: (1) Blow holes Holes on casting surface is blow holes. This defect occur because of air comes out from surface. Causes: Moisture level is high in mould sand, improper baking of core. unnecessaryy carbonic binder, unwanted ramming, small vent hole, fine sand etc. Remedies: Proper moisture level, proper baking of core, proper use of binder, proper ramming, proper vent hole with vent rod, selection of sand particle.

18. Blow holes Casting Defects

19. Casting defects, their causes & remedies (2) Shrinkage When metal transfer from liquid to sold its volume will decrease. During this process if it will not get more molten metal then in the internal surface of casting voids are developed, that is known as shrinkage. Causes: Defective runner, gate and riser, molten metal's pouring temperature. Remedies : Proper arrangement of runner, riser and gate for proper directional solidification. If required, the design can be changed, maintaining proper molten metal temperature.

20. Shrinkage Casting Defects

21. Casting defects, their causes & remedies (3) Crack : Due to solidification metal shrinks in mould. The improper shrinkage develops stress on surface, due to that cracks propagates on surface also known as pull. Causes: Non availability of collapsibility property of mould and core, improper design, hard ramming of mould. Remedies: Collapsibility property can be improved, design can improved. properly ramming of mould.

22. Crack casting defect

23. Casting defects, their causes & remedies 4) Inclusions : Unwanted ingredients such as metal oxide, slag, sand particles give defects known as inclusions in metal castings. Causes: Improper gating system, improper pouring, low quality mould and core sand, improper ramming, impurity in metal charge. Remedies: By modifying gating system, turbulence free pouring, using good quality mould and core, proper ramming of mould sand, proper and pure metal charge should be used and by using oxide free molten metal crucible.

24. Casting defects, their causes & remedies (5) Lift and shift : Some part of casting gets distortion known as lift and shift. Causes: Improper alignment of pattern parts, improper support of core, improper clamping of mould box, improper strength of mould sand. Remedies: By aligning the mould box with help of dowel pin, properly supporting core in mould, properly clamping of mould box, providing proper strength mould and core sand. (6) Swell Due to molten metal the some part of mould cavity become large so the casting becomes larger than required which known as swell. Causes : Pressure of molten metal on surface, improper ramming of sand, low strength of core sand. Remedies: By properly ramming of sand, by increasing core strength so molten metal can easily flow in mould. (7) Fins Thin edge on casting known as fins. Generally it is on parting line. Causes: Improper clamping of mould b0x, improper arrangement of mould and core. Remedies: Properly clamping of cope and drag, proper assembly of mould and core.

25. Casting defects, their causes & remedies (8) Misrun and cold shut : Molten metal cannot reach in all the parts of mould, so this improper filled casting known as misrun. Molten comes from different sides, sometimes cannot mix each other. This defect known as cold shut. Causes: Defective design of gating system, low fluidity of molten metal, thin wall of casting, non-continues pouring of metal. Remedies: Modification of gating system, increasing temperature of molten metal, continuously pouring of molten metal, increasing porosity of sand. (9) Metal Penetration: Surface of casting becomes rough due to metal penetration. Causes: Bigger size of sand, less ramming, low strength of moulding sand and core, higher permeability. Remedies : Fine grain sand, proper ramming of mould sand, proper mixture should be used to increase moulding and core porosity. (10) Hard spot: Some part of casting solidifies very fast and that surface becomes tough, that known as hard spot. Causes: Bad casting design, improper métal composition, improper use of chills. Remedies: Proper design of castings so metal solidifies in same time, proper metal Composition, proper use of chills in design.

26. Casting defects, their causes & remedies (11) Run out: While pouring, molten metal comes out (leaks out) from casting known as run out. Causes: Defective mould box, defectively moulding process. Remedies Moulding box should be changed, modification in moulding process. (12) Drop: A drop occurs when cope surface cracks and breaks, thus the pieces of sand fall into the molten metal. Causes Due to either low green strength or improper ramming of the cope flask, improper reinforcement. Remedies: Proper mixing of binder for strength improvement, proper arrangement of steel rod for reinforcement in core and mould, proper ramming. (13) Warpage: After or before solidification casting may twist or change shape known as warpage. Causes: Improper design, lack of directional solidification, internal stress. Remedies: Proper design of casting to get directional solidification. By proper heat treatment the stress can be removed.