Casting shrinkage defects in engine cylinder block and cylinder head

The structure of cylinder block (cylinder head) casting is complex, and the wall thickness is quite different. The thick and large parts with raised circular arc surface are inconvenient to take measures such as riser feeding in the process of large-scale water production. When other processes are not handled properly, these thick and large hot joints tend to produce concentrated shrinkage and deep shrinkage crack defects in serious cases

1 Reasons

1.1 at the root of the above-mentioned parts, the filling of the mold is not compact and the hardness / rigidity of the mold is insufficient. When the liquid iron solidifies and graphitization expands, the mold wall displacement occurs

1.2 high pouring temperature

1.3 large shrinkage tendency of casting liquid

2 Countermeasures

2.1 improve the fluidity of molding sand, control the appropriate compactness rate of molding sand, and add vent plug to the corresponding part of the model for the molding method of air impact molding or air flow pre compaction. After these measures are taken, the mold hardness / rigidity of the defect location can be improved, so that the mold wall displacement will not be caused by graphitization expansion when the high carbon equivalent molten iron solidifies, so that the riser free self feeding can be realized

2.2 under the condition that the filling requirements are met and defects such as pores are not allowed, the pouring temperature shall not be increased blindly (too high pouring temperature will also cause fire leakage, sand particles and other defects)

2.3 ensure that the molten iron has good casting performance, especially prevent the tendency of white mouth shrinkage

a) To control carbon equivalent (3.9-4.1%) accurately, the shrinkage tendency of molten iron will increase when it is lower than the lower limit, and the more likely shrinkage defects will appear in the above parts

b) During the low alloying treatment of high carbon equivalent liquid iron, the tendency of shrinkage increase should be controlled. Some alloy elements that increase the tendency of gray iron white mouth and shrinkage should be strictly used. For example, Cr, which will reduce the eutectic temperature and expand the solidification temperature range, should not exceed 0.035%

c) When the carbon equivalent (carbon content) is adjusted by the carburizer in the electric furnace, there must be sufficient time to absorb the carbon increase, otherwise the false phenomenon of carbon increase will appear. Such molten iron casting products will tend to shrink

d) It is necessary to control the content of some harmful elements such as P, Ti, V and so on, which will also increase the shrinkage tendency of molten iron