Mon, 23 Jul 2018 02:22:53 +0000
Heat treatment techniques for vacuum furnaces
With the progress and development of industrialization, vacuum furnace plays an irreplaceable role in mold production, mainly used for ceramic sintering, vacuum smelting, electric vacuum parts degassing, annealing, metal parts brazing, and ceramic – metal sealing. The vacuum heat treatment of vacuum furnace can realize almost all heat treatment processes, such as quenching, annealing, tempering, carburizing and nitriding. In the quenching process, gas quenching, oil quenching, nitrite quenching and water quenching can be realized, and vacuum brazing, sintering and surface treatment can also be carried out. The vacuum furnace has high thermal efficiency, which can realize rapid temperature rise and cooling, no oxidation, no decarbonizing, no carburizing, can remove the phosphorus chip on the workpiece surface, and has the function of degreasing and degassing, so as to achieve the effect of surface brightness purification.
Generally speaking, the treated workpiece is heated slowly in the furnace, the difference of internal heat temperature is small, the thermal stress is small, and the deformation is small. The product pass rate is high. It can reduce the cost and has the function of degassing, thus improving the mechanical performance and service life. Good working environment, safe operation, no pollution and public hazards. The treated workpiece has no danger of hydrogen embrittlement, and has good stability and repeatability to prevent surface hydrogen embrittlement of titanium material and refractory metal shell. The development of vacuum heat treatment equipment and technology has been paid more and more attention to and applied widely.
Vacuum heat treatment is a comprehensive technology that combines vacuum technology and heat treatment. China divides the vacuum into low, medium, high and ultra-high vacuum.
Vacuum furnace and intermediate frequency electric furnace have a good development prospect in the field of thermal processing, which is used for induction heating of heat transmission, rolling, forging, pipe bending, heat treatment (quenching), welding and other processes. What are the heat treatment techniques of vacuum furnace and intermediate frequency furnace?
1. When treating titanium alloy in vacuum furnace, nitrogen should not be used as cooling gas, because titanium and nitrogen react at high temperature to form golden titanium nitride.
2. All the movable parts of the vacuum furnace are connected with o-type rubber ring seal, which is connected with water for cooling.
3. The workpiece shall be hardened in a vacuum state, and the vacuum quenching oil shall be used, which has a low saturated vapor pressure.
4. The maintenance of the vacuum furnace should be in the vacuum or pure nitrogen state to avoid inhalation and moisture absorption when not used at ordinary times.
5. The pressure lift rate of domestic vacuum furnaces shall not be greater than 1.33pa /h, and the standard of some foreign enterprises shall be 0.67pa /h
6. The vacuum heating is mainly radiation, and the workpieces should be kept apart in the furnace.
7. During the heating process, the workpiece and the materials in the furnace will be released to reduce the vacuum degree.
8. The heating temperature of vacuum tempering, vacuum annealing, vacuum solid solution treatment and vacuum aging is generally the same as that of conventional treatment.
The vacuum return furnace shall have a quick-cooling device. The pressure of cooling water should be greater than 0.2mpa and the flow should be adjustable.
10. Cooling gas: steel is generally made of 99.995 percent pure nitrogen, high-temperature alloys are made of 99.999 percent nitrogen or argon, and titanium alloys are made of 99.995 percent argon.
11. Heating: after putting into the workpiece, it is generally not heated until 6.67pa is pre-pumped.