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Vacuum hardening furnace: mold heat treatment
Heating with medium temperature and high temperature salt bath furnace, and using low temperature alkali bath and nitrate salt bath for graded isothermal cooling and tempering were the main means of mold heat treatment in those days. However, there are many disadvantages in the heating salt bath furnace: the barium chloride raw material used is poisonous, and the waste gas and waste residues pollute the environment and so on.
Nowadays, many enterprises have kept pace with the times and use vacuum hardening furnaces to carry out vacuum heat treatment on molds.
Advantages of vacuum hardening furnace:
Vacuum hardening furnace has no waste gas, smoke, waste water, waste residue, and no environmental pollution. It is called bright heat treatment, clean heat treatment and green heat treatment. Vacuum hardening furnace heating workpiece without oxidation, decarburization, alloy element depletion, degreasing and degassing, vacuum purification, avoiding hydrogen embrittlement, can realize graded isothermal quenching, can control heating and cooling, and lay the foundation for automatic and flexible production.
Compared with salt bath furnace heating, vacuum hardening furnace is also insufficient in terms of rapid and local heating, because this operation is also required in some specific occasions.
Mold vacuum hardening process
Alloy tool steel, high-speed tool steel, stainless steel, bearing steel, etc. are suitable for vacuum high-pressure gas quenching and vacuum oil quenching heat treatment. Commonly used steel grades are Cr12MoV, 4Cr13, 9Cr18, Y10, GR steel, etc. The blanking, deep drawing, extrusion, bending, wire rolling, hot forging, warm forging, die casting and plastic mold parts made of these steel types have obtained stable and reliable structures and properties of rigidity and toughness through vacuum heat treatment, ensuring the improvement of mold quality. service life.
Horizontal double-chamber high-pressure gas quenching and oil quenching vacuum hardening furnace is more suitable for mold quenching. Parts with similar volume or wall thickness should be processed in the same furnace to set an appropriate and uniform holding time, including heating temperature, heating speed, and holding time , cooling rate and other heat treatment process parameters are very important to the performance of parts.
The temperature difference between the surface and the core of the part, and the uneven heating and cooling are the main reasons for quenching deformation and cracking. Quenching heating and subsequent heat preservation are for the full dissolution of alloying elements and the homogenization of austenite.
The vacuum quenching heating temperature should be set according to the data given in the relevant technical data. The upper limit is taken when secondary hardening and tempering stability is required, and the lower limit is taken when deformation and cracking are prevented. The residence time after the part reaches the vacuum quenching temperature is related to factors such as electric furnace power, furnace charging capacity, furnace charging method and part size.
It is feasible to estimate the holding time H with H=30+thickness/50x10min. When the vacuum quenching heating temperature exceeds 1000°C, it generally needs to be preheated twice: the first time is 580°C, and the second time is 850°C. The first preheating and holding time is twice the vacuum quenching holding time H, and the second preheating and holding time is about H/3.
When heating, if the vacuum is too high, the alloy elements in the material will volatilize. The physical quantities Pa (Pascal), bar (bar 1bar=105Pa) and Torr (Torr, 1Torr=133.322Pa) are commonly used to mark the vacuum degree. There is a certain difference between the three conversion relationship. A lower vacuum degree is used in the preheating stage, and a higher vacuum degree is used in the heating and holding stages, generally between 10-1bar, 10-2bar and 10-3bar. The cooling rate of high-pressure vacuum air quenching is related to the cooling water flow rate of heat exchanger; gas type, temperature and flow rate; gas pressure, air flow form and distribution; workpiece size and furnace loading. Studies have shown that the cooling rate of 10bar low-temperature nitrogen is 30%~40% higher than that of 6bar, and the cooling rate of 20bar is more than 80% higher than that of 6bar.
When vacuum oil quenching, good quality vacuum quenching oil should be selected, and the process improvement should be used to prevent carbon increase when the workpiece is cooled.
The purpose of vacuum tempering is to relieve stress and obtain the required structure and properties. Mold vacuum tempering is often carried out in a well-type furnace that is pre-evacuated and then back-filled with nitrogen protection.
Vacuum hardening furnace equipment selection: The vacuum hardening furnace produced by SIMUWU can meet the needs of manufacturing high-quality molds. Can be customized to include features such as rapid cooling systems, gas quenching, and temperature monitoring and control. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.
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