Study Of New Technology To Prevent The Shrinkage Of Ductile Iron Fittings

As a result of the solidification characteristics of ductile iron - mushy solidification mode, shrinkage is not only its inherent defects, but also it is difficult to eliminate if we use the traditional treatment process. In the production we often use the method such as increasing cold iron or cold iron plus water and so on, then the shrinkage can be driven from the surface into the casting. After machining, shrinkage will not be exposed, but as for the improvement of casting quality requirements, the customer has requirements not only for the state of castings appearance, but also for the intrinsic quality of the castings, And conduct nondestructive testing of the casting. Then this hide-house casting shrinkage will be found. Therefore, eliminating the shrinkage defects of the casting fundamentally is the hope target of the enterprises in the future.This issue deeply studied the solidification characteristics of ductile iron and the shrinkage of the formation mechanism. In order to eliminate the shrinkage defects of the casting fundamentally to improve the overall quality of Ductile Iron Castings ,this issue adopted a new technology.In this article we use varieties of alloy composition to make lots of ductile iron Complex eliminating shrinkage agent. Add them to different test blocks; and use the ultrasonic nondestructive testing technology detect the changes of Shrinkage defects within the specimen; observe Macro-organization of its cross section; use Metallurgical Microscope to Observe and analysis the Changes in its microstructure, and determinate Brinell hardness,Strength and elongation of the test blocks.The results show that: C-type eliminating shrinkage agent play a key role during eliminating shrinkage in the casting. Each 4.6kg 5028 stove plate, adding 2.4g C-type eliminating shrinkage agent can eliminate the casting shrinkage defects completely ; each 35kg test block crankshaft ,lay place , in both sides of the casting bottom each adding 6g C-type eliminating shrinkage agent , and top with the plus side riser , can eliminate the casting shrinkage defects completely. And after adding eliminating shrinkage agent, it does not affect not only the degree of graphite ball,strength and hardness of the casting and the number of pearlite, but also can Refine grain in local Casting.