SRS - Technical Centre: Problem Solving

Dark Rough Oxidised Casting - Causes:

1. Burn-out temperature too high
2. Oxidising flux being used
3. Metal over used and over heated

Flashing is shown as excess metal around the outside of the cast piece. These occur more often in the higher part of the structure to be filled with metal. They can form under pressure of the molten metal or may already be present in the mould and are aggravated by the metal which may be too hot

Burn-out temperature too high

Solution - Never exceed 730°C. If the temperature of the burn-out furnace is too high then the gypsum binder will start to break down and produce sulphur dioxide or trioxide. These will both produce a rough surface finish and also stain the castings.

Oxidising flux being used

Solution - Use only boric acid or borax flux. The use of an oxidising flux can stain or discolour the surface of the metal.

Metal over used and over heated

Solution - Refine metal and use correct casting temperature. If the metal is introduced too hot into the mould it will produce a rough surface which is blackish where the metal is thicker and holds the heat for the longest time.

» Download this problem solution - Dark Rough Oxidised Casting (PDF 80k)

» Technical Centre: Mixing | Burnout Cycles | Helpful Hints | Problem Solving | Datasheets | Stone in Place Casting | Stone in Wax Setting