MUFFAKHAM JAH COLLEGE OF ENGINEERING

AND TECHNOLOGY

Title : Casting Technique

Md Naseeruddin Shah 1604-11-736-072

Casting Technique

Contents History

Need of casting

Classification of casting

Sand casting

Special casting methods

Casting defects

Inspection of casting

Reference

HistoryOrigins back to around 3,600 B.C

at Mesopotamia

Bronze was melted and poured into a mould.

Good flow property of Iron at 1150 degree C have enabled the casting of iron.

Need Of CastingCan produce a wide variety of metal components with

complex geometries.

Castings of great size and weight can be produced.

Classification Of Casting ProcessSand Casting

Special Casting Methods

Permanent Mould Casting

Pressure Die Casting

Centrifugal Casting

Investment Casting

EquipmentsCope and dragSandPatternMolten metal

Sand Casting

Governing Equations

Bernoulli's principle : For an inviscid flow of a non-conducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

Continuity Equation : Mass entering is equal to mass leaving

Mould making :

Moulding sand consists of three basic elements

1) Silica sand particles (75-80%) : Used for producing required strength of mould

2) Clay (15-20) : Used for producing bond between the sand particles.

3) Water or sodium silicate (6-8%) : Used for initiating the formation of bond between the sand particles

Properties of moulding sand

1) Porosity property : The ability of escaping the air or gases through the moulding sand

2) Cohesiveness property : The ability to form bond between same material particles.

3) Adhesiveness : The ability of bond formation of sand particles with other materials

4) Refractoriness : The ability of withstanding higher temperature without loosing its strength and hardness.

5) Collapsibility : The ability of breaking the mould with little amount of force

6) Flowability : The ability of flowing of moulding sand into each and every corner of the mould.

PatternPattern is the replica of casting to be made.

Pattern size = casting size ± allowances

Allowances

1) Shrinkage allowance : Shrinkage of metal during cooling

2) Machining allowance : The extra material provided on the pattern

3) Draft allowance : Making the vertical surface of pattern into incline

4) Shake allowance : Provided to avoid the damages during removing of pattern

5) Distortion allowance : Distortion of shape due to differential cooling

Gating SystemIt is the provision made for the molten metal to enter into the cavity

Elements of gating system

•Pouring basin

•Sprue

•Sprue base well

•Runner

•Ingate

•Mould

Special Casting Methods

Permanent Mould Casting

Casting is obtained by pouring the molten metal in permanent metallic dies, as the metal is not refractory its use is limited to low melting point metals like aluminium, zinc, magnesium, copper, lead and its alloys.

Pressure Die Casting

• One die is fixed and another movable, a nozzle is connected to goose neck which is immersed in molten bath.

• Metal is injected into the die cavity by moving the plunger down.

• After solidification the dies are opened and casting is ejected

Centrifugal Casting

• Axis symmetrical castings can be produced (cylindrical)

• Huge size casting can be produced

• Core is not required

• Uniform distribution of mass

Investment Casting

Casting Defects

1. Blow holes : It is smooth almost spherical bubble inside the casting.

2. Shrinkage cavity : It is flat rough cavity formed due to improper design of gating system.

3. Hot cracks : Smooth edged single cracks formed due to differential contraction of the casting

4. Cold cracks : Sharp edged branched cracks formed due to improper handling of castings

5. Misrun : It is incomplete casting resulting from incomplete filling of mould

6. Cold shut : It is incomplete fusion of two streams of liquid metals7. Runout : Leakage of molten metal from parting plane.8. Mis match : It is due to improper matching of cope and drag

parts of the casting

Inspection of Casting

1. Visual Inspection : Common defects such as rough surface, shifts, surface cracks can be detected by a visual inspection of casting

2. Pressure Test : The pressure test is conducted on a casting to be used as a pressure vessel.

3. Magnetic Particle Inspection : It is practised to check for very small voids and cracks at or just below the surface of a casting of a ferromagnetic material.

4. Dye-Penetrant Test : This method is used to detect invisible surface defects in a nonmagnetic casting. The casting is sprayed by a dye containing a fluorescent material. The surface to be inspected is then wiped,dried and viewed in dark.

5. Ultrasonic Inspection : An oscillator is used to send an ultrasonic signal through the casting . The signal is transmitted through the casting and any discontinuity will reflect the signal back.

References

• Production Technology by ACE• http://www.custompartnet.com/wu/SandCasting•http://thelibraryofmanufacturing.com/metalcasting_basics.html• http://www.castingstechnology.com/