Casting

Question 1

Factors that influence casting (3)

Answer 1

Correct investment
Type of machine
Design moulds

Question 2

What factors determine the correct investmenet?

Answer 2

Shrinkage

Thermal stability - investment material must be able to be at temperature needed to cast

Question 3

What can occur if the investment material does not have sufficient thermal stability?

Answer 3

Sulphide deposits = breakdown

Question 4

Why must investment be heated slowly?

Answer 4

They are insulators so cracks can form during heating

Question 5

How can you stop large pores forming in mould surface?

Answer 5

Use investment materials with mixed particle size

Question 6

Why should you not heat the metal too high above the liquidous line?

Answer 6

Greater chance of air incorporation = porosity = weakness

Question 7

What should be noted about investment base thickness?

Answer 7

Thick enough to provide stable mould

Too thick = poor air flow = cannot escape mould properly

Question 8

3 likely casting errors

Name them, the likely cause and how to avoid faults

Answer 8

Too small - not enough mould expansion, use correct temperature and investment materials

Too large = too much mould expansion = correct temperature and investment materials

Distorted = stress relief of wax pattern = warm wax thouroghly before creating pattern