Three processes in plastic electroplating-electroplating surface treatment process.
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The electroplating surface treatment process is introduced as follows. Nowadays, an advanced electroplating surface treatment process generally includes three processes: heating, heat preservation and cooling, and sometimes there are only two processes: heating and cooling. These processes link up with each other and are uninterruptible.
There are many heating methods of metal heat treatment, the earliest is to use charcoal and coal as heat source, and then the application of liquid and gas fuel. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be heated directly or indirectly by molten salt or metal or even floating particles. When the metal is heated, the workpiece is exposed to air, which often occurs oxidation decarburization (that is, the reduction of carbon content on the surface of steel parts), which has a very adverse effect on the surface properties of parts after heat treatment. Therefore, metals should usually be heated in a controllable atmosphere or protective atmosphere, in molten salt and in vacuum, or by coating or packaging. Heating temperature is one of the important process parameters of heat treatment process. Selecting and controlling heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the metal material being treated and the purpose of heat treatment, but it is generally heated above a certain characteristic transition temperature to obtain high temperature structure. In addition, the transformation takes a certain amount of time, so when the surface of the metal workpiece reaches the required heating temperature, it is necessary to maintain the temperature for a certain period of time to make the internal and external temperature consistent and make the microstructure transformation complete. this period of time is called holding time. When using high energy density heating and surface heat treatment, the heating speed is very fast, so 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, cooling methods vary from process to process, mainly to control the cooling rate. Generally, the cooling rate of annealing is the slowest, the cooling rate of normalizing is faster, and the cooling rate of quenching is faster. However, there are different requirements for different types of steel. for example, air-hardened steel can be hardened at the same cooling rate as normalizing. Degree and toughness, a process that combines quenching and high temperature tempering, is called quenching and tempering. After some alloys are quenched to form supersaturated solid solution, the supersaturated solid solution is kept at room temperature or slightly higher temperature for a long time to improve the hardness, strength or electrical magnetism of the alloy. Such a heat treatment process is called aging treatment. The method of effective and close combination of pressure deformation and heat treatment to obtain a good combination of strength and toughness of the workpiece is called deformation heat treatment; the heat treatment in negative pressure atmosphere or vacuum is called vacuum heat treatment, which can not only make the workpiece non-oxidation, no decarburization, maintain the surface of the treated workpiece smooth, improve the performance of the workpiece, but also pass through the infiltration agent for chemical heat treatment.
Surface heat treatment is a metal heat treatment process that only heats the surface of the workpiece to change its mechanical properties. In order to only heat the surface of the workpiece and not transfer too much heat into the interior of the workpiece, the heat source used must have a high energy density, that is, a larger heat energy is given on the workpiece per unit area, so that the surface or local energy of the workpiece can reach high temperature for a short time or instantly. The main methods of surface heat treatment are flame quenching and induction heating heat treatment, commonly used heat sources such as oxyacetylene or oxypropane flame, induced current, laser and electron beam, etc.
Chemical heat treatment is a metal heat treatment process by changing the chemical composition, microstructure and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface of the workpiece. Chemical heat treatment is to heat the workpiece in a medium (gas, liquid, solid) containing carbon, nitrogen or other alloy elements (gas, liquid, solid) for a long time, so that the surface of the workpiece is infiltrated with elements such as carbon, nitrogen, boron and chromium. After infiltrating elements, other heat treatment processes such as quenching and tempering are sometimes carried out. The main methods of chemical heat treatment are Carburizing, nitriding and metallizing.
Heat treatment is one of the important processes in the manufacturing process of mechanical parts and dies. Generally speaking, it can ensure and improve the various properties of the workpiece, such as wear resistance, corrosion resistance and so on. The microstructure and stress state of the blank can also be improved to facilitate all kinds of cold and hot processing, for example, white cast iron can be annealed for a long time to obtain malleable cast iron and improve plasticity, and the gear adopts correct heat treatment technology. the service life can be increased by several times or dozens of times than that of the gear without heat treatment. In addition, cheap carbon steel has some expensive alloy steel properties by infiltrating some alloy elements, which can replace some heat-resistant steel and stainless steel, while almost all dies need heat treatment before they can be used.
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