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What is the cooling method of forging plant when

by:Laike     2020-07-21
  Cooling process of crane wheel forging mainly includes cooling method and cooling time. Commonly used cooling media are water, oil and air. The cooling capacity and characteristics of these media have a great influence on the cooling process.

   The cooling capacity of water is the strongest among the three cooling media of water, oil and air. The circulation and agitation of water further improve the cooling capacity, and the water spray cooling capacity is more intense. The increase in water temperature reduces the cooling capacity in the high-temperature stage and does not change much in the low-temperature stage. Therefore, the water temperature of the forgings that require chilling cannot be increased. Impurities in the water will greatly change the cooling capacity of the water, and the cooling capacity of water varies from place to place. The cooling capacity of brine is greater than that of water.

  The cooling capacity of oil is smaller than that of water (especially in the low temperature stage), and the maximum difference is 28 times. In most cases, forgings require rapid cooling at high temperatures to ensure quenching, and slow cooling at low temperatures to reduce tissue stress. The method of using water quenching oil cooling in production is to use the feature that the cooling capacity of water is stronger at high temperatures and the cooling capacity of oil is weaker at low temperatures, and this goal is achieved. The change in temperature has little effect on the cooling capacity of the oil, so the oil temperature can still be used even if it is increased. The oil temperature in general production is between 20°C and 80°C. When the oil temperature is low, the viscosity is large, and the disadvantage of uneven cooling is easy to occur. The circulation of oil has little effect on its cooling capacity. The main purpose of circulating oil or moving the workpiece up and down in production is to make the forgings cool evenly and prevent the local oil temperature from rising too high.

How to determine the technological plan when forging crane wheel forgings?

   The cooling capacity of air is very low (especially in the low temperature stage). The cooling capacity of flowing air and still air is very different.

   The cooling capacity of water, oil, and air has a certain range of limitations, and can not fully meet the requirements of forgings for different cooling rates, so spray cooling is being widely developed.

   Due to the low plasticity of superalloys, various cracks often occur during forging. Especially ingots, due to the thick columnar crystals, are more prone to cracking when forging crane wheel forgings. The main causes of cracks are as follows.

   There are many harmful impurities. Pb, Bi, Sn, As, S, etc. are all harmful impurities in high temperature alloys. These elements have low melting points and are distributed on the grain boundaries in the alloy, which reduces the plasticity of the alloy.

   The content of some elements in the alloy is relatively high, they form brittle compounds in the alloy, and are distributed along the grain boundaries, so that the plasticity of the alloy is reduced.

  The quality of the surface and interior of the ingot is poor or there are some metallurgical defects in the bar (such as delamination of inclusions, residual shrinkage, looseness, point segregation, carbide accumulation, etc.), which causes cracking during forging.

  When heated in a flame furnace, the sulfur content in the fuel and furnace gas is too high, and the sulfur and nickel form a low-melting eutectic along the grain boundaries, which reduces the plasticity of the alloy.

The furnace temperature is too high, and the heating rate is too fast, especially when heating ingots and billets with large cross-sectional dimensions. Due to poor thermal conductivity of the alloy and large temperature stress, it is easy to cause cracking; the heating temperature is too high or the deformation temperature is too low; the degree of deformation is too high Large or excessive deformation speed; improper deformation process, excessive tensile stress and additional tensile stress.
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