For the internal quality of chilled cast iron camshaft casting, on the basis of controlling the chemical composition, the matrix hardness should be given priority. The matrix hardness should not only meet the technical requirements of customers, but also provide the basis for ensuring the tensile strength, and have good cutting performance for subsequent machining.
It is recommended in the technical specification for automobile engine camshaft that the hardness of the non chilled zone of the chilled camshaft (that is, the matrix hardness described in this paper) is 180-285 HBS.
As shown in the figure, the structure of the camshaft product itself is a long and thin shaft with several cams. The thickness is uneven. In addition, the cams of the cold shock camshaft need to be chilled by cold iron. Therefore, the hardness of the matrix on different parts of a camshaft is quite different. In order to meet the technical requirements and good cutting performance, at the same time to avoid shrinkage defects in large shaft diameter (a shaft diameter) during the casting process, the matrix hardness is usually controlled from the following aspects.
(1) a gate is set at the front end (left end) of the camshaft;
(2) matrix hardness test sample: cut from the large shaft diameter (a shaft diameter) at the front end of camshaft, that is, inspect the softest part of matrix hardness, and conduct sampling inspection on other parts;
(3) the inoculation amount should be controlled above 3 ‰;
(4) the unpacking time should not be earlier than 40 min after pouring, so as to avoid the high hardness of the matrix at the small shaft diameter of the product pouring end (right end) and poor processing;
(5) in case of deviation of matrix hardness, the content of C and Mn in hot metal can be slightly adjusted, and other alloy elements in hot metal can be slightly adjusted if necessary.
(6) some raw materials for smelting, such as pig iron and scrap steel, will contain Ti, which has a great influence on the hardness of the matrix. The interference of Ti can be offset by adjusting the content of Mn and Cr in the production process.
The internal control range of matrix hardness for customer a product and customer B product in a foundry. That is to say, by controlling and inspecting the softest part of the matrix hardness, the hardness of the non chilled area of the camshaft is not only qualified, but also has good cutting performance.