Investment castings with internal defects,which are assembled in the equipments,will bring unpredictable hazard to production.It will not only shorten the service life,but also causing accidents.
The management's goal of investment casting foundry is to maximize profits.Therefore,it is necessary to improve the yield of investment castings.The yield of investment castings is the percentage of total weight of qualified castings and total weight of material which is input metal furnace.
According to casting material,size,the normal yield should be in below range:
iron investment castings small piece 60%~64%,middle piece 64%~70%,large piece 70%~80%.
Steel investment castings:50%~55%.
Nodular cast iron and alloy cast iron pieces:45%~50%.
aluminum die castings:50%.
In order to reduce casting defects and improve the yield of castings,casting defects must be effectively controlled.The first step is to have accurate judgment of defects.Thus it is necessary to understand various analysis methods of defects,including general and special analysis method.To determine the type of defect, analysis its causes,and puts forward prevention measures, at last implement it from the technology and management.
Analysis and study of casting defects is one of the key technology to improve casting yield.But the difficulty is not small.Main display in:a. involves broad scope, such as alloy, casting technology, molding materials, casting equipment and detection of production process,etc. b.the diversity of the reasons for the casting defects.A kind of defects can be caused by a variety of reasons, and a kind of reason may cause several kinds of defects.c.the conditionality of technical measures such as adopting some measures to prevent a particular type of defect,but it may lead to another kind of defect.d.It is difficult to control influence factors,like quality of raw materials, such as the air temperature and humidity.
Although the type of defect is the same,but for different casting alloy,the forming reason and preventing measures are distinct.For example,both iron carbon alloy and same shrinkage cavity defect,to cast steel parts,riser and cold iron should be adopted to prevent shrinkage defects.For the large thick wall nodular cast iron parts, can use the solidification process of graphite expansion, and using no riser casting to eliminate the shrinkage cavity defects. Therefore, we should analyse the specific situation in details.