Generally, the hardness of cylinder liner in the qualified layer is hb225 ~ HB240, and the overall hardness difference of cylinder liner does not exceed hb30, but the hardness of black spot is lower than that in normal state, and the hardness value is only about hb210. Based on this, it can be envisaged that if the overall hardness of the cylinder liner is properly controlled to increase hb10 ~ hb15, the hardness value of the black spot part will also reach above hb225, and the hardness difference between various parts of the whole cylinder liner will be reduced, the black spot defect may be avoided. Therefore, in one production, the hardness of a batch of cylinder liners produced by a furnace is controlled above HB240. Take some cylinder liner test products with higher hardness and send them to the processing workshop. Compare them with the same batch of cylinder liners with original hardness control for processing and commissioning. See table for the results.
It can be found that both have about 10% of the black spot defect waste products, which proves that the overall hardness of the cylinder liner is not an inevitable factor causing the black spot defect.