Clayman: Casting Slip Faults

FAULTS IN CASTING
Everybody who casts suffers from time to time from some form of problem. Of course other factors besides slip properties can cause casting faults, but usually they can be easily noticed, for example, wet moulds causing slow casting, careless filling causing "pinholes" or "casting-spot" etc.

The table shown below gives a brief description of each of the common problems and the suggested remedies. This only gives the direction in which to move and it must be up to each person to determine how far they need to go.

If your cast is suffering from flabbiness and you stepped up your deflocculent addition to correct this, only to find you began to get brittle ware with casting spot. You would know you had gone too far. Therefore our table may assist you in recognising and rectifying common problems. Thixotropy is the property of casting slips thickening when they are left to stand.

Fault	Description	Cause	Remedy
Bad draining	Slip failing to drain from narrow sections	Fluidity too low, or thixotrophy too high	Increase water addition or increase deflocculent addition
Brittleness	Difficult to fettle or cut	Thixotrophy too low	Decrease deflocculent addition
Casting-spot	Discoloured patch appearing on the mould side of the article after firing	Thixotrophy too low	Decrease deflocculent addition
Cracking	Small cracks where handles join the body of the article	Thixotrophy too low	Decrease deflocculent addition
Flabbiness	Softs casts difficult to handle without distortion	Thixotrophy too low	Increase deflocculent addition
Pinholing	Small holes just beneath the surface on the mould side of the article	Fluidity too low	Increase water addition
Slow casting	Casting time too long	Fluidity too high, or thixotrophy too low	Decrease water addition, or decrease deflocculent addition
Wreathing	Small uneven ridges on the slip side of the article	Thixotrophy too low	Decrease deflocculent addition