Control points of cold depth of chilled cast iron camshaft and hardness of cam peach tip

1.Key points of cold depth control

(1) cold iron. In the early stage of product development, according to its own production process conditions, the camshaft foundry should design and manufacture the cold iron which is consistent with the product cam profile. Generally, the cold iron will not change after it is put into use. The greater the thickness of chill above the cam peach tip, the more conducive to the formation of cold depth. On the contrary, it is not conducive to the formation of cold depth. For example, for customer a and customer B products, the thickness of chill used in casting (as shown in Figure 1) is between 25-30 mm, and the thickness of chill is less than 25 mm, so the qualified rate of cold depth after batch production is low; The thickness of chill iron is more than 30 mm, which is not conducive to casting molding (molding around the cam will appear virtual).

(2) inoculation amount. After the cold iron is determined, the control of cold depth is mainly through the increase or decrease of inoculation amount. With the increase of inoculation amount, the cold depth decreases, while with the decrease of inoculation amount, the cold depth increases. At the same time, white test sample is used in front of the furnace to measure the white depth, so as to check and control the cold shock layer depth of the product. The inoculant is usually fesi75 special inoculant with stable quality, and the particle size is 3-8 mm. The inoculation amount is 3.0% – 4.5% of the weight of hot metal (varying with the batch of raw materials, burden ratio, inoculant batch, product, etc.).

(3) inoculation temperature (or hot metal discharge temperature). During inoculation, the temperature of molten iron directly affects the burning loss of inoculant, and also determines the cold depth of the cast camshaft blank. When the temperature of inoculated hot metal is high, the amount of inoculant burning loss is large, and the cold depth will increase; On the contrary, when the temperature of inoculated hot metal is low, the cold depth will be smaller. The tapping temperature of hot metal is usually controlled between 1560 ℃ and 1570 ℃, and the variation of this temperature is as small as possible.

(4) pouring temperature. The pouring temperature of chilled cast iron camshaft is usually controlled between 1360 ℃ and 1450 ℃. In the process of casting production, when the pouring temperature of hot metal is high, the cold depth of the camshaft blank is small. With the decrease of the pouring temperature of hot metal, the cold depth generally becomes larger.

(5) the width and top height of the product cam itself (as shown in Fig. 2) are also factors affecting the cold depth. The width of the cam is large, the top height is high, and the cold depth is easy to be small. In order to facilitate the formation of the cold shock layer, the width of the cam can be selected as the lower difference in the blank design; For the blank with high top height of cam, the thickness of chill should be larger.

2.Key points of cam peach tip hardness control

(1) cold iron. The wide width of chill is helpful to ensure the qualified rate of cam peach tip hardness. On the contrary, the hardness quality of cam peach tip after batch production is not stable, especially when “peach tip hardness a, B, C points ≥ 50 HRC” is required by customer a.

(2) deep cold. Generally, the hardness of cam tip increases with the increase of cooling depth. For example, the cold depth is 7 mm, and the hardness of cam peach tip is 50 HRC; When the cooling depth is 10 mm, the hardness of cam peach tip increases to 52 HRC. But sometimes there is a problem that the cold depth is very big, but the hardness of cam peach tip can not rise. For example, when the cold depth is 15 mm, the hardness of cam peach tip is 48 HRC or 45-48 HRC.

(3) cold shock white mouth purity (or transition region pockmark depth). The main reason is that the purity of chill chill is not high or the depth of transition zone is too deep. The higher the purity of chill, the more conducive to ensure the cam peach tip hardness qualified. To improve the purity of white iron, it is necessary to increase C and reduce Si, reduce the amount of recycled material, increase the pouring temperature, and control the temperature of circulating cold iron not higher than room temperature.