Formation of defects in crankshaft casting of large engine

Air conditioner

The cold air gap is the gap that penetrates or does not penetrate the casting, and the edge is rounded, which is caused by the poor fusion of the filling metal streams. According to the analysis of the causes of the cold air gap in conventional castings, the direct and indirect factors are: unstable pouring temperature and speed, unreasonable design of gating system, inappropriate hot metal composition and process, poor mold permeability, complex subcontracting process, and difficult control of hot metal quality. On the contrary, 80% of the defects of air-conditioning septum appear at the highest point of the mold. Based on the previous treatment methods of cold air barrier defects in castings, and by means of simulation analysis to improve the process, and after many times of product trial production experience summary, the effective solutions are proposed: increase the static pressure of hot metal filling, improve the exhaust scheme; optimize the gating system and melting process.

Sand holes

Sand hole refers to the hole in the casting which is wrapped with sand, sand block or other molding materials. The common causes of casting sand hole are: the floating sand in the mold cavity is not cleaned up before closing the box; improper operation in the closing process leads to mold collapse and sand dropping of the sand coating layer in the inner cavity; sand block and sand particles fall into the pouring system after the box closing; or slag inclusion in the coating, etc. However, the sand hole of the front product is mainly located at the end of the crankshaft, which exists on the surface of several main journal, connecting rod journal and balance weight. The main measures to solve the problem of sand hole are: optimizing the structure of sand box, improving the sand layer.

Scum hole

Slag hole is the product of some non-metallic inclusions, refractory high melting point alloys, metal compounds and so on in the mold cavity which solidifies on the casting. The causes are as follows: flux added and slag formed during molten metal melting; secondary oxidation and slag inclusion formed during molten metal pouring; MNS inclusions are formed by reaction with Mn element when the sulfur content of molten metal is too high. But in the production process, the cause of slag hole is the filter screen itself, so we should replace the filter screen to improve the slag hole problem.