Views: 1 Author: Site Editor Publish Time: 2022-08-08 Origin: Site
Vacuum heat treatment is a metal heat treatment process in which the metal workpiece is heated below 1 atmosphere pressure (that is, under negative pressure). Among them, the vacuum environment in which the vacuum heat treatment is located includes low vacuum, medium vacuum, high vacuum and ultra-high vacuum. Compared with conventional heat treatment, vacuum heat treatment technology can realize no oxidation, no decarburization, and no carburization at the same time.
Vacuum heat treatment can realize almost all heat treatment processes, such as quenching, annealing, tempering, carburizing, nitriding, gas quenching, oil quenching, nitrate quenching, water quenching, etc. Sintering, surface treatment, etc.
Taking advantage of the phase transformation characteristics of metals in a vacuum state, the thermodynamics and kinetics of solid-state phase transformation do not change in a vacuum that is only 0.1 MPa away from atmospheric pressure. At the same time, under the action of vacuum degassing, the physical and mechanical properties of metal materials can be improved. When heated in a vacuum state, elements on the surface of metal workpieces will evaporate. The vacuum degree required by the metal to achieve non-oxidative heating, the surface purification effect, and the realization of less and no oxidation and less dehydration.
The vacuum heat treatment furnace has high thermal efficiency, can achieve rapid heating and cooling, can achieve no oxidation, no decarburization, no carburization, can remove phosphorus chips on the surface of the workpiece, and has the functions of degreasing and degassing, so as to achieve the effect of bright and clean surface. Make the mold relatively bright.
Generally speaking, the workpiece to be processed is heated slowly in the furnace, the internal heat temperature difference is small, and the thermal stress is small, so the deformation is small, the product qualification rate is high, and the hardness of the workpiece after vacuum heat treatment is 3-5 times that of ordinary heat treatment. For some high-value precision workpieces, such as large precision molds, it is particularly important. Vacuum heat treatment greatly improves its service life. The final result is that the company used 10 precision molds a year, but now only needs to use 2-3 precision molds. Enterprises greatly save production costs and improve economic efficiency.
The workpiece to be treated has no danger of hydrogen embrittlement, and the surface hydrogen embrittlement of titanium and refractory metal shells is prevented, and the stability and repeatability of the vacuum heat treatment process are good.
Compared with the working environment of ordinary heat treatment, the working environment of vacuum heat treatment is better, the operation is safe, and the vacuum heat treatment technology has no pollution and pollution, which is internationally recognized as "green heat treatment".
1. Water-cooling device, furnace shell, furnace cover, electric heating element conduction treatment (water-cooled electrode), intermediate vacuum insulation door and other components of the vacuum heat treatment furnace all work under vacuum and heating conditions. Working under such extremely unfavorable conditions, it is necessary to ensure that the structure of each component is not deformed or damaged, and that the vacuum sealing ring is not overheated or burned. Therefore, each component should be equipped with a water cooling device according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and have a sufficient service life.
2. Use low voltage and high current: In the vacuum container, when the vacuum space is within the range of several Torr to lxlo-1 Torr, the energized conductor in the vacuum container will produce a glow discharge phenomenon at a higher voltage. In the vacuum heat treatment furnace, serious arc discharge will occur, burning electric heating elements, heat insulation layers, etc., resulting in major accidents and losses. Therefore, the working voltage of the electric heating element of the vacuum heat treatment furnace generally does not exceed 80-100 volts. At the same time, effective measures should be taken in the structural design of the electric heating element, such as avoiding pointed parts as much as possible, and the distance between the electrodes should not be too small and narrow to prevent the occurrence of glow discharge or arc discharge.
3. Most heating and thermal insulation materials can only be used in a vacuum state: the heating and thermal insulation linings of vacuum heat treatment furnaces work under vacuum and high temperature, so these materials have high temperature resistance, low vapor pressure, and radiation effects. Well, the thermal conductivity is small and other requirements. Antioxidative properties are not required. Therefore, the vacuum heat treatment furnace widely uses tantalum, tungsten, molybdenum and graphite as heating and heat insulation materials. These materials are easily oxidized in the atmospheric state, therefore, conventional heat treatment furnaces cannot use these heating and insulating materials.
4. Strict vacuum sealing: The vacuum heat treatment of metal parts is carried out in a closed vacuum furnace. Therefore, obtaining and maintaining the original air leakage rate of the furnace, ensuring the working vacuum degree of the vacuum furnace, and ensuring the quality of the vacuum heat treatment of the parts are important. very important meaning. Therefore, a key problem of the vacuum heat treatment furnace is to have a reliable vacuum sealing structure. In order to ensure the vacuum performance of the vacuum furnace, a basic principle must be followed in the structural design of the vacuum heat treatment furnace, that is, the furnace body should be airtightly welded, and at the same time, the furnace body should be opened as little or no holes as possible, and the use of dynamic Sealed construction to minimize the chance of vacuum leaks. The components and accessories installed on the vacuum furnace body, such as water-cooled electrodes and thermocouple lead-out devices, must also be designed with a sealed structure.
5. High degree of automation: The reason why the degree of automation of the vacuum heat treatment furnace is high is because the heating and cooling of metal workpieces require dozens or even dozens of actions to complete. These actions are performed inside the vacuum heat treatment furnace, which is inaccessible to operators. At the same time, after some actions such as heating and heat preservation, the quenching process of the metal workpiece requires six actions and should be completed within 15 seconds. To complete many actions in such a rapid condition, it is easy to cause the operator's tension and constitute a misoperation. Therefore, only higher automation can accurately and timely coordinate actions according to the program.