Calculation of casting cooling time

Calculation of casting cooling time

In order to prevent the castings from being deformed, cracks and other defects due to excessive cooling after pouring, and to ensure that the castings have sufficient strength and toughness during sand cleaning, the castings should have sufficient cooling time in the mold. Continuously produced castings should be designed with sufficient cooling section length to ensure the cooling time of the castings.

The in-mold cooling time of the casting is related to the weight, wall thickness, complexity, alloy type, mold properties, production conditions and other factors of the casting.

1. Cooling time of cast iron in sand mold

The cooling time of iron castings in the sand mold is determined according to the temperature when unpacking, and the following data can be referred to: general castings are 300-500 °C; castings that are prone to cold cracking and deformation are 200-300 °C; Castings are 800-900°C. Immediately after opening the box, remove the pouring riser and remove the sand core, and then put it into the hot sand pit or cool it slowly in the furnace.

1. The cooling time of iron castings in the sand mold can usually be selected by referring to Table 11-2-1 and Table 11-2-3.

2. The in-mold cooling time of heavy iron castings can be calculated according to the following empirical formula.

k is the ratio of the weight of the casting to its contour volume. The larger the k value, the thicker the wall thickness of the casting and the longer the cooling time. The formula for calculating k is

Second, the cooling time of steel castings in the sand mold

The steel castings for hydraulic sand cleaning, shot blasting and pneumatic tool sand cleaning should be cooled to 250-450 ℃ in the sand mold. Falling sand above 450°C may cause casting deformation and cracks. Refer to Figure 11-2-1 and Figure 11-2-3 for the cooling time in the sand mold.

When using the above three diagrams, the following points should be noted:

(1) When the weight of carbon steel casting exceeds 110t, on the basis of checking the cooling time value corresponding to 110t according to Figure 11-2-2, the cooling time will be increased by 1-3h for each additional 1t of weight.

(2) When the weight of ZG310-570 and alloy steel castings exceeds 8.5t, the cooling time can be doubled compared to the cooling time value of carbon steel castings checked according to Figure 11-2-1 and Figure 11-2-2.

(3) Thick-walled castings (such as anvils, etc.) with simple shapes and uniform wall thickness can be loosened (or pryed) 20-30% earlier than the cooling time specified in the figure. Such castings may also not be heat treated in the furnace, cooled naturally in the pouring pit, and the holding time is calculated as 1.5-2t per 24h.

(4) For castings with complex structure, large difference in wall thickness, and prone to cracks, the cooling time should be extended by about 30% compared with the value specified in the figure.

(5) For some castings in pit shape, it is necessary to lift the cover box or loosen the sand mold in advance, which will increase the cooling rate, so the cooling time can be shortened by 10%.

3. Molding temperature of non-ferrous alloy castings

Molding temperature of non-ferrous alloy castings can be found in Table 11-2-4.