Investment casting is mainly made up of mold making,wax pattern production,shell making and other processes.Wax pattern is the shape that wax injected into the cavity of mold.To obtain investment casting parts with high size accuracy and surface finish,wax pattern itself should have high size accuracy and surface finish.So it is very important to make high quality wax patterns.Now we would like to discuss the factors that affect the quality of wax patterns.
1.Impurities in the wax pattern
In investment casting production process,if we do not deal with the filtration treatment well,it will easy to mix water or inpurities in it,which will result in defects of wax patterns.If the moisture in wax does not ruled out completely and get into mold,cause the wax pattern containing a certain amount of moisture.Then the surface quality of wax pattern is poor and cause internal hole defects,seriously affect the intensity of the wax models.See figure 1.If the wax material mixed in solid impurities,will also cause adhering sand or hemp pit in the casting surface.
2.The serving time of wax material
The wax material used in our steel foundry is medium temperture wax material,which is produced by overseas company.When this kind of wax material circulates for a long time,some components of wax material will be volatilized and decomposed.The liquidity will be dropped and sharinkage rate increases,these are all associated with metamorphism of stearic acid in wax material.
3.1 temperature of wax injection
When the temperature of the wax pattern is higher than 58 ℃, the surface of wax models will be smooth,and when the wax pattern lower than temperature 51℃, the shrinkage of wax pattern is small, but the surface becomes obviously rough, even produce flow mark on the surface of wax pattern.So if we improve the temperature of wax injection,the surface of wax pattern will be gradually smooth,but the corresponding shrinkage rate also increased. After mold material is injected into the mold, close to the surface of the mould will first form a layer of frozen layer,with high injection wax temperature, shrinkage rate increases, thus reducing size precision of wax pattern,so the wax injection temperature is unfavorably exorbitant.
3.2 Pressure of wax injection
With wax injection pressure increases,shrinkage rate of wax pattern line is declined obviously. With low wax injection pressure,pressure inside the wax pattern is small,the contraction of the surface solidified layer is large ,produce obvious shrinkage mark on the corner of wax patterns, the thickness of wax pattern becomes thinner, thus wax injection pressure shoulds not be too small.So when injecting wax,wax pattern must ensure that the pressure (3--4 mpa)