Modern engines have very strict requirements on cleanliness. For cylinder block (cylinder head) castings, only a few grams (g) of sand and foreign matters are allowed to remain in the water cavity, oil cavity, tappet chamber and other parts. Many enterprises have adopted secondary shot blasting, strong shot blasting, and even introduced advanced shot blasting equipment, such as squirrel cage or manipulator shot blasting, to fully achieve the cleanliness of the inner cavity It is still difficult to find, whether it is shell core or cold core, the situation is the same.
The cleanliness fails to meet the requirements, which is fundamentally due to the casting structure. During shot blasting of the above cavities, because the sand holes are few and small, the amount of iron shot can be projected into is limited, so the finish and cleanliness of the inner cavity are not as good as the outer surface of the casting, and the crankcase, cylinder surface and other parts. When the casting structure cannot be changed, only other factors affecting the cleanliness can be found.
1.1 the surface of sand core is in poor condition, such as loose filling, rough surface of sand core, mucous membrane, etc.
1.2 improper application, such as poor coating performance, improper glassiness, insufficient coating thickness, etc.
1.3 the existing strong shot blasting device can clean most of the inner and outer surface of the casting, but it is still insufficient for the narrow and complex water cavity and oil cavity.
2.1 improve and improve the quality of the surface of the sand core, for example, select the core material with good fluidity (rest angle < 29 °); reasonably set the vent plug and maintain it to be unblocked; apply the mold release agent with good quality to prevent the mucous membrane, etc., the purpose of these measures is to obtain the sand core with compact surface.
2.2 generally, the core shall be coated. The vitricity of the coating should be appropriate; the coating should have strong permeability; the coating should have a certain thickness (generally 0.2mm), and the sand particles can not be seen after the coating is dry; the selected coating has excellent anti sticking performance, which can form a low melting point sintering layer on the surface of the casting under the pouring temperature, and can be peeled off automatically due to the different shrinkage rate during the cooling process of the casting.
2.3 as mentioned in 3.0, efforts should be made to avoid the occurrence of vein defects. Once the veins appear, the cleanliness of the inner cavity of the casting becomes worse. See 3.2 for relevant measures.
2.4 for the internal cavity cleaning of castings, the mainstream technology at home and abroad is to adopt the powerful mechanical shot blasting method, which is in the form of squirrel cage shot blasting, manipulator holding shot blasting, etc. For this kind of shot blasting equipment, to maintain the additional current value, it is necessary to adjust the best shot angle. For the latter shot blasting method, it is also possible to set the program at the best incident angle for the inner cavity that is difficult to clean up and appropriately extend the shot time.
In addition, there are several ways to improve and improve the cleanliness of the inner cavity:
a. The reason for electro-hydraulic cleaning is that the castings to be cleaned are placed in the pool. During the high-energy discharge process, the high-pressure shock wave generated will shake off the sand adhered to the castings. Theoretically, the sand adhered to the cavities immersed by water can be cleaned up, but this method occupies a large area, consumes a lot of energy, has a long process (still need to empty the water in the cavities and dry the water traces), and has a large amount of maintenance There are also some safety problems.
b. The casting is roasted in the furnace before shot blasting. The effect of this way to improve the cleanliness of castings is still obvious, but it also has high energy consumption and long cycle. If coal is used as the fuel of heating furnace, the working environment is poor.
c. Some manufacturers not only use strong shot blasting, but also for water channel cavity or oil channel cavity for shot blasting. This method is the most effective way to improve the cleanliness of the inner cavity, and the highest level of cleanliness can be achieved. At present, there are only such general single machine products. It is still necessary to manually hold the shot peening head and extend it into the sealed workroom to aim at the relevant sand holes for spraying. The labor intensity is high and the environment is bad. It is expected that the special automatic shot peening equipment will be applied in the cylinder block (cylinder head) cleaning production line.