Formation of White Dots in Forging and Pressing
The appearance of white dots in the forging process is caused by the rapid heating and cooling of the material. This can occur during the manufacturing process when the material is exposed to high temperatures, allowing heat to escape quickly and form a white dot in the heated area. While they may look like small blemishes on the surface of the material, they typically do not affect its strength or purity.
White dots form when atoms of material are pushed and pulled by their compounds due to high temperatures, allowing them to separate and then recombine. By adding an oxidizing agent such as oxygen, the material is heated and cooled rapidly, causing material to expand and contract quickly. This in turn causes white dots to form on the surface of the material. This can especially occur in forging and pressing processes, as the rapid and uniform compression of the material during these processes can cause atoms to break apart and recombine in the heated area, producing white, crystalline shapes.
White dots are typically seen in pressurized stainless steel, carbon steel, copper, brass, and other materials. The presence of these dots is usually not associated with any changes in the shape or properties of the material. However, if the white dots are excessive, this may indicate the materials purity has been compromised and should not be used.
White dots form in the presence of oxide particles in the atmosphere, as they can cause variations in the temperature of the material. This can be due to the lack of proper temperature control during the forging or pressing process. Additionally, the heat transfer rate of the material is a major factor, as slow heat transfer can cause variations in the temperature of the material, increasing the chances of white dots forming. The surface of the material can also contribute to the formation of white dots, as rough surfaces can cause the material to heat unevenly, leading to areas of rapid heating and cooling.
There are several methods used to prevent and reduce the formation of white dots. These include using a proper forging or pressing speed, ensuring proper temperature control, ensuring uniform and efficient heat transfer, and using a smoother surface finish. Additionally, using lubricants and coolants can reduce the chances of excessive overheating, reducing the risk of white dots forming due to oxide particles in the atmosphere and a high heat transfer rate.
In conclusion, white dots are a common occurrence during the forging and pressing processes and are typically small blemishes on the surface of the material. This is caused by the rapid heating and cooling of the material, which can be due to the presence of oxide particles in the atmosphere and an inefficient heat transfer rate. While it is not usually associated with any changes in the materials shape or properties, it should be monitored to ensure it does not reach excessive levels. By adopting proper forging and pressing speed, temperature control, and heat transfer rate, as well as using lubricants and coolants, the chances of the formation of white dots can be effectively mitigated.
