The effect of raw material quality on investment castings

1.Metal materials

Metal materials of Investment casting manufacturers mainly come from outsourcing materials,scrapped castings and casting riser. Outsouring materials is often in bulk,very few is pressed into tubular.So it is easy to confuse different material together,such as stainless steel 316 is mixed with stainless steel 304,ect.Therefore,investment casting manufacturers should purchase compressed into tubular materials as far as possible. Using spectrum analyzer for analysis on each batch purchased material.If possible,spot investigation should be made to raw material supplier to evaluate whether the material is under for identification,protection and isolated storage,etc.To investment casting foundry itself,we should remove rust,degreasing,deoxidization,clean and dry processing on scrapped castings and riser.And control compostion of S,P element.

2.Mould material

The main performance indicators of mould material are:Melting and solidification temperature interval,heat resistance,thermal expansion rate and shrinkage,strength,hardness, viscosity,liquidity,smearing and ash content,etc.General investment casting manufacturers are hard to examines the performance indicators. So, when choosing the supplier, as far as possible to choose some formal factories with relatively perfect quality management system.But we could test the shrinkage rate,which is one of the most important performance index.As shrinkage rate directly affects the dimension precision of casting and the quality of the shell.

3.Silica sol

Physico-chemical parameters of silica sol mainly include: the content of SiO2, density, content of Na2O, PH value, kinematic viscosity, colloid particle diameter,etc.These parameters mainly affect the shell strength, coating stabilit and coating powder liquid ratio.As the general investment casting enterprise is hard to test these physical and chemical parameters, so, on the one hand, we must strengthen the supplier selection, evaluation and validation, on the other hand, we should choose to use different specifications of the silicon sol on the surface layer and back layer, such as using S-830 silicon sol for  the surface, and choice S-1430 silicon sol for back layer.

4.Surface coating

Investment casting manufacturers generally choose zircon powder as the surface coating.When zircon powder contain oxide impurities, decomposition temperature will drops,amorphous SiO2 will be in precipitation, react with certain elements in metal, make the casting surface produces "pitting" defects,which will make casting surface quality worse. Moreover, zircon powder particle size and distribution also has a direct impact on powder casting liquid. Therefore, the choice of the supplier should be strictly controlled.