Heat treatment of conveyor chains
Heat treatment is one of the important processes in chain manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and chemical composition of the conveyor chain workpiece, but changes the microstructure inside the conveyor chain links. It is characterized by improving the intrinsic quality of the workpiece, which is generally not visible to the naked eye.
The heat treatment process generally includes three steps, heating, heat preservation and cooling. Sometimes there are only two processes heating and cooling. These processes are interconnected and uninterrupted.
When the conveyor chain links are heated, workpieces are exposed to the air, the oxidation and decarburization often occur(that is, the carbon content on the surface is reduced), which has a very adverse effect on the surface. Therefore, the chain links usually should be heated in a controlled atmosphere or protective atmosphere, in vacuum.
The heating temperature is one of the important parameters of the heat treatment process. Choosing and control of the heating temperature are the main issues to ensure the quality of the heat treatment. The heating temperature depends on the metal material and the purpose of the heat treatment. The workpiece usually is heated above the phase transition temperature to obtain a high-temperature structure. In addition, it takes a certain time to reach the required heating temperature, it must be maintained at this temperature for a period of time to ensure the internal and external temperatures consistent and the microstructure changes completely. This period of time is called the holding time.
When using high-energy density heating and surface heat treatment, the heating speed is extremely quick, there is generally no holding time, while the holding time of chemical heat treatment is often longer.
Cooling is also an indispensable step in the heat treatment process. The cooling method varies with different technologies, mainly controlling the cooling rate.
Chain links heat treatment process can be divided into two categories: overall heat treatment and surface heat treatment. According to the different heating medium, temperature and cooling method,each category can be divided into several different processes. The same workpiece adopts different heat treatment processes to obtain different structures and thus have different properties.