Wed, 26 Sep 2018 03:58:35 +0000
What is vacuum heat treatment furnace
It is a thermal equipment using vacuum heat treatment technology to process workpieces. Vacuum heat treatment technology is a combination of vacuum technology and heat treatment technology. All or part of the heat treatment process is carried out in vacuum. Vacuum heat treatment furnace has high thermal efficiency, can achieve rapid heating and cooling, can achieve no decarbonization, no oxidation and no carburization, can remove the scales on the surface of the workpiece, and also has the function of degreasing and degassing, thus achieving the effect of surface bright purification.
vacuum heat treatment furnace
Generally speaking, the heating of heat-treated parts in the furnace is relatively slow, the internal thermal temperature difference is relatively small, the thermal stress is also small, so it will be more easily deformed. So what’s the use of such a vacuum heat treatment furnace?
Vacuum heat treatment furnace is mainly used for annealing, tempering and carburizing of high chromium, rolls, steel balls and alloy steel and other mechanical parts. It can also be used for oil quenching, gas quenching, water quenching, nitrate quenching and so on. It can also be used for vacuum sintering, brazing and surface treatment.
Ordinary metal materials are heated in an air furnace because there is oxygen, carbon dioxide and water vapor in the air, and they oxidize the metal, so that the heated metal surface appears an oxide film or oxide scale, completely losing the metallic luster of the cause. At the same time, these gases react with carbon in the metal to decarbonize its surface and, if carbon monoxide or methane is present in the furnace, to carburize the metal surface.
In addition to those mentioned above, there are some metals with more active chemical properties that, when heated in an air furnace, absorb these gases in addition to oxides, nitrides, and hydrides, and diffuse into the interior of the metal, thereby deteriorating the properties of the metal materials, in order to solve this problem. In general, the workpiece will be treated before leaving a certain amount of machining allowance, after heat treatment through processing to remove the decarburization layer and oxide layer.
Vacuum annealing furnace, vacuum tempering furnace and vacuum quenching furnace are all called vacuum heat treatment furnace. The vacuum heat treatment process and the vacuum tempering process can be done on the same vacuum furnace. Vacuum annealing furnace and vacuum tempering furnace are usually referred to as vacuum chamber furnace or vacuum box type atmosphere furnace. The vacuum quenching process must be done on a dedicated vacuum quenching furnace. Standard vacuum box furnace with good sealing performance, can do vacuum or filled with inert gas, heat treatment in the furnace, tempered materials will hydrolyze. Vacuum box furnace can also do ordinary quenching, but it will hydrolyze normally as ordinary quenching furnace. If quenching is needed, hydrolysis must be made by vacuum quenching furnace. The price gap between the vacuum box furnace and the vacuum quenching furnace is very large because their structures are almost different.
Vacuum heat treatment furnace technical characteristics
Vacuum heat treatment furnace is a new heat treatment technology which combines vacuum technology with heat treatment technology. Vacuum environment refers to the atmosphere environment below an atmospheric pressure, including low vacuum, medium vacuum, high vacuum and ultra-high vacuum. Vacuum heat treatment actually belongs to atmosphere-controlled heat treatment. Vacuum heat treatment refers to all and part of the heat treatment process in a vacuum state. Vacuum heat treatment can achieve almost all of the heat treatment processes involved in conventional heat treatment, but the quality of heat treatment is greatly improved. Compared with conventional heat treatment, vacuum heat treatment can realize no oxidation, no decarbonization, no carburization, can remove the phosphorus chip on the surface of the workpiece, and has the function of degreasing and degassing, so as to achieve the effect of surface bright purification.
Vacuum high pressure gas quenching technology
Nowadays, vacuum high pressure gas-cooled quenching technology develops rapidly. New technologies such as negative pressure (< 1 65 After fire, the workpiece has good surface brightness, small deformation, high efficiency, energy saving and no pollution.
_vacuum high pressure gas-cooling quenching is used for quenching and tempering of materials, solid solution and aging of stainless steel and special alloys, plasma carburizing and carbonitriding, vacuum sintering, cooling and quenching after brazing.
When_is quenched by 6 105Pa high-pressure nitrogen, the cooling load can only be loose. High-speed steel (W6Mo5Cr4V2) can be hardened to 70-100mm, and high-alloy hot-working die steel (such as 4Cr5MoSiV) can reach 25-100mm.
When_is quenched by 10 105Pa high pressure nitrogen, the cooling load can be dense, which is about 30% ~ 4O% higher than that of 6 105Pa.
_is cooled and quenched with 20 105Pa superhigh pressure nitrogen or a mixture of helium and nitrogen. The cooling load is dense and can be bundled together. Its density is 80%~150% higher than that of 6 *105Pa nitrogen cooling. It can cool all high speed steel, high alloy steel, hot working die steel and Cr13% chromium steel and more alloy oil quenched steel, such as 9Mn2V steel of larger size.
The cooling capacity of the double chamber gas cooled quenching furnace with a separate cooling chamber is better than that of the single chamber furnace of the same type. The cooling effect of 2 * 105Pa nitrogen cooled double chamber furnace is equivalent to that of 4 * 105Pa single chamber furnace. But the running cost and maintenance cost are low. The level of China’s basic material industry (graphite, molybdenum, etc.) and supporting components (motors) needs to be improved. Therefore, in order to improve the quality of 6 *105Pa single chamber high pressure vacuum protection, the development of double chamber pressurized and high pressure gas-cooled quenching furnace is more in line with the national conditions of our country vacuum high pressure gas-cooled isothermal quenching shape complex larger workpiece from high temperature continuous rapid cooling is prone to deformation and even cracks. Salt bath isothermal quenching has been used in the past. Is it possible for gas cooled isothermal quenching in a single chamber vacuum high-pressure gas quenching furnace? Fig. 1 is the result of quenching two groups of overlapped carbon structural steels in a single chamber high-pressure gas-cooled quenching furnace with convective heating by different cooling methods. A set of curves in the diagram are the result of continuous cooling with high purity nitrogen at 6 *105Pa pressure after heating at 102O C (alternating wind direction from top to bottom, switching once in 40s). The other group is controlled cooling of the surface and core of the sample at 370 C. From the comparison of the two curves, it can be seen that the time when the heart temperature passes through 50O (?) is only about 2 minutes. From the surface control cooling to the temperature of the heart reaches 370 degrees, it needs 27min. Therefore, it is feasible to conduct isothermal gas cooling quenching in a single chamber vacuum high pressure gas quenching furnace.
Vacuum nitriding technology
Vacuum nitriding is to use a vacuum furnace to heat iron and steel parts as a whole, fill a small amount of gas, at low pressure to produce active nitrogen atoms infiltration and diffusion into the steel to achieve hardening; and plasma nitriding is produced by flashlight discharge of active N ions bombardment and only heating the surface of iron and steel parts, chemical reactions occur to form nuclei. Chemicals achieve hardening.
In vacuum infiltration, when the vacuum furnace is exhausted to a higher vacuum of 0.133Pa (1 x 10-3 Torr), the workpiece is raised to 530-560, and ammonia or NH3+CXHY+N2O compound gas is injected into the workpiece, and the feeding quantity of various gases is accurately controlled. The furnace pressure is controlled at 0.667Pa (5Torr), and the gas on the workpiece surface can be accelerated at low pressure. Volume exchange, active N elements (or N, C) come from chemical reactions and NH3 (or cracking of NH3 and CXHY at 500-570 C). After holding for 3-5 h, they are cooled rapidly by inert gases in the furnace. The hardened layer with 20-80 micron depth and 600-1500 HV hardness can be obtained from different materials.
Vacuum nitriding is known as vacuum exhaust nitrocarburizing. It is characterized by the activation and purification of metal surface by vacuum technology. During the whole heat treatment process of heating, heat preservation and cooling, impure trace gases are discharged, and pure composite gases containing active substances are fed in, which makes it possible to adjust and control the surface layer structure, improve the quality and improve the efficiency. X-ray diffraction analysis shows that the compound layer in the vacuum nitriding layer is epsilon single phase structure, and no other brittle phase (such as Fe3C, Fe3O4) exists, so it has high hardness, good toughness and good distribution. The hardness and material composition of the “white layer” single-phase EPI compound layer are related. The higher the Cr content in the material is, the higher the hardness is. The hardness can reach 1200 HV at Cr13%, 1500 HV at Cr18% and 1700 HV at Cr25%. The wear resistance of single phase epsilon compound layer without brittle phase is higher than that of gas nitriding and carburizing structure. However, the existence of the “white layer” is also unfavorable to some dies and parts, which is easy to cause cracks in the early forging stage of the forging die, and easy to produce pinholes in welding repair. Another advantage of vacuum nitriding is that by controlling the type and amount of compound gases containing active materials that are fed into the furnace, almost no compound layer (white layer) can be obtained, but only 0.1-1mm diffusion layer of the structure. This may be due to the formation of 0.l33Pa (1 x10-3 Torr) after the exhaust gas from a vacuum furnace. Another reason is the structure formed by the diffusion of the composite gas with active substances into the steel in a short time. The advantages of this structure are excellent heat shock resistance and cracking resistance. Therefore, for the hot working dies which are tempered at high temperature, such as high speed steel or 4Cr4MoSiV (H13) steel dies, the comprehensive properties of high surface hardness, good wear resistance, good heat shock resistance, crack resistance and toughness can be obtained; but the anti-occlusion, anti-cladding and melting damage properties of the dies are not good enough when only the diffusion layer is formed. Due to the different service conditions and performance requirements of dies or mechanical parts, it is necessary to adjust the structure and properties of the surface layer during surface heat treatment. Vacuum nitriding is not only used in tools and dies, but also has obvious effect on improving the performance of precision gears, wear-resistant and corrosion-resistant mechanical parts and springs, and the materials acceptable to be treated are more widely.
Vacuum cleaning and drying technology currently heat treatment is inseparable from cleaning and drying processes, especially oil-cooled heat treatment of various types, cleaning and drying task is more onerous, more difficult. The cleaning agent used in the world is halogen cleaning agent. Developed, such as the proportion of halogenated detergent used in Japan, as shown in Table 1. Among them, three chloroethane and Freon are prohibited from using ozone depleting substances. Other halogen compounds are also restricted because of their harmful effects on the environment, people and animals. So various countries are studying various alternative cleaning and drying technologies.