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Rectifying strut and vacuum heat treatment process
The rectifying strut is an important part of the gas turbine. Its structure is relatively complex. It is a precision casting with an overall size of up to 800mm and a gross weight of 26kg with a relatively uniform wall thickness. Because of its special core structure, it brings certain difficulties to the precision casting production and heat treatment process. The casting material is made of high-temperature heat-resistant alloy, which is difficult to process and requires high heat treatment.
Vacuum heat treatment has the advantages of high quality, low energy consumption, no pollution (or less pollution), etc. It can effectively prevent the defects of the rolling die, improve the surface roughness and reduce the friction factor. Vacuum heating is carried out in the form of radiation, the heating is slow, the furnace temperature is uniform, the product deformation is small, and it also has a dehydrogenation effect, which is conducive to improving the strength of the rectifier strut, and the life of vacuum quenching can be increased by 3 to 4 times compared with salt furnace quenching. . Experiments were carried out on the parts quenched in vacuum furnace, box furnace and salt bath furnace. Their lifespans from high to low are: vacuum furnace, box furnace and salt bath furnace. The advantages of vacuum heat treatment can be seen.
Vacuum melting process
The shell is manufactured by the silica sol-ethyl silicate composite shell-making process. Then put it into a vacuum furnace, and vacuumize the furnace. Start the mechanical pump, Roots pump and diffusion pump in sequence. When the vacuum is less than 0.1Pa, the smelting power is not less than 40kW.
During the melting process, the material should be rammed in time to prevent local overheating of the alloy. The charge is strengthened and smelted to prevent the charge from boiling, splashing and the formation of nodules on the crucible wall. Such as boiling, argon gas should be flushed into the furnace, and when the crucible is hung on the wall or formed furnace nodules, it can be eliminated by shaking the crucible.
When the temperature is close to 1600 ℃, the power is cut off to measure the temperature. When it is close to the pouring temperature of 1560°C and the vacuum degree is not greater than 4×10~2Pa, the pouring starts. When pouring, it should be smooth, continuous and continuous flow. After pouring, it was parked in a vacuum furnace for 10 minutes to stabilize the temperature of the mold and the uniform solidification of the metal.
Vacuum heat treatment process:
Combined with foreign advanced technology, according to the principle of vacuum heating and its heating calculation and conventional heat treatment process, the vacuum heat treatment process curve formulated is as follows:
The purpose of solution treatment is to obtain a uniform supersaturated solid solution and control a certain grain size. The temperature of solution treatment is generally between 980 °C and 1250 °C, which is mainly selected according to the precipitation and dissolution laws of each alloy and the requirements for use. The cooling method of solution treatment is usually air cooling for alloys with a high degree of supersaturation.
The purpose of the aging treatment is to make the strengthening phase precipitate sufficiently and uniformly.
Key points of vacuum heat treatment:
Since the heating method in vacuum state is a single radiation heat transfer, the heating speed of the workpiece in the vacuum heat treatment furnace is slower than that of other heat treatment methods, and the thermal stress is small.
When heated in a vacuum state, the heat transfer rate is slow in the low temperature stage, and the heating rate is fast in the high temperature state. In addition, since most of the vacuum furnaces are of internal heating type, the heat storage of the furnace material is small, because the vacuum furnace heats up quickly, and the workpiece heats up relatively slowly, the so-called lag phenomenon occurs in the heating of vacuum heat treatment. The heating coefficient of vacuum heat treatment is larger than that of atmosphere furnace/salt bath furnace, which is about 2 to 3 times that of atmosphere furnace, and about 6 to 8 times that of atmosphere furnace. Therefore, a longer quenching holding time should be used.
Selection of vacuum heat treatment equipment:
This processing is carried out using the RVGQ vacuum air quenching furnace produced by SIMUWU. The surface gloss and strength of the parts meet the requirements, the production process is stable and reliable, and the degree of automation is high.
SIMUWU is a domestic enterprise that designs and manufactures vacuum tempering furnaces, vacuum air quenching furnaces, vacuum oil quenching furnaces, vacuum sintering furnaces, vacuum brazing furnaces and other products. The equipments produced by SIMUWU are exported to many overseas countries and are well received.
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