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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

What should we do when problems occur in vacuum heat treatment?

First of all, vacuum heat treatment technology is a very widely used technology, which is widely used in aerospace, electronics and precision machinery. In the production of mold, it has outstanding advantages that ordinary heat treatment cannot compare with, because vacuum heat treatment has the advantages of no oxidation, no decarburization, and bright surface of the workpiece; It has the functions of degassing and purifying, which can improve the purity of materials, and improve the fatigue strength, plasticity, toughness and corrosion resistance of materials; The processed workpiece has no danger of hydrogen embrittlement, effectively preventing the surface embrittlement of titanium and refractory metal. The vacuum furnace has small quenching deformation and good stability and repeatability of heat treatment process. Safe operation, high degree of automation, good working environment, pollution-free. The future metal surface engineering will rely more on vacuum heat treatment technology, and the future is very broad.

However, in the actual production, it is often encountered that the workpiece heat treatment is not ideal. Generally, the following three problems are easy to occur: 1. Oxidation of stainless steel, molybdenum, titanium, tungsten and other materials during quenching, tempering and annealing of alloy die steel. 2. Uneven hardness and adhesion of workpiece after vacuum annealing. 3. Sensitive relay and high permeability alloy of magnetic amplifier widely used in radio and automatic control can not meet the design requirements.

The above two points are often caused by a variety of reasons. Let’s analyze the following:

1.Oxidation reasons affecting the surface brightness of vacuum heat treatment: the three major factors of workpiece, process and equipment are the main factors causing this problem. The three factors are summarized and analyzed as follows:

1) Workpiece

Workpiece material: the workpieces contain elements with strong oxygen affinity, such as Al, Ti, Si, Cr, V, etc. and elements with high vapor pressure, such as Mn, Zn, Cr, etc. In case of workpieces containing such elements, partial pressure control can be considered, and a small amount of nitrogen can be introduced as protective gas for vacuum heat treatment.

Dirt on the surface of workpiece, such as water, oil, oxide, etc.: for integral parts, plates and tubular parts with large shape and quality, they need to be cleaned and dried before processing. Pay attention to the cleaning and maintenance of the site and optimize the charging conditions of the workpiece.

2) Equipment elements

The vacuum pump capacity of the selected vacuum furnace is insufficient, the pipeline leaks, and the heating material or heating chamber is polluted. The cooling system and cooling medium of vacuum furnace are impure, containing water, uneven cooling and insufficient cooling capacity. High purity gas shall be used for the process.

The vacuum furnace shall be subject to regular leak detection, and the pressure rise rate shall not exceed 1.33 Pa/h through the cold furnace sealing detection. In addition, the existence of weak oxidation atmosphere in the heating chamber in the vacuum furnace will also cause the oxidation of the surface, which should be noticed. After the spectral analysis of the residual atmosphere in the vacuum furnace after 5 min and 40 min of vacuum pumping, it is found that after 40 5min of vacuum pumping, the atmosphere of the oxidation atmosphere in the furnace will be significantly reduced. Therefore, it can be considered to increase the vacuum pumping time to optimize the furnace atmosphere.

3) Discharge temperature

The furnace temperature of the vacuum heat treatment furnace has a significant impact on the brightness. If the oxidation is severe when the furnace is discharged at 500~300 ℃, the state and brightness of the sample surface are significantly reduced. If the furnace is discharged below 200 ℃, the brightness of the workpiece can exceed 70%.

2.Workpiece surface adhesion during vacuum annealing

Pure metals and metals in alloys will generate steam under certain temperature and vacuum heat treatment, which will cause surface element depletion and adhesion. The alloy elements Ag, A1, Mn, Cr, Zn that are easy to evaporate are easier to evaporate when the ambient pressure is lower, that is, the vacuum degree is higher and the heating temperature is higher.

Therefore, the heating temperature shall be appropriately reduced, the lower limit of temperature shall be reasonably selected, and the vacuum degree shall be reduced and controlled to 5 × 10-5Pa. The protective atmosphere is recharged with inert gas, and high temperature ceramics (better than magnesium hydroxide powder) are placed at the joint of the workpiece. It is especially important for superalloys, stainless steels and high-speed steels with high Cr content.

3.Effect on magnetic materials

Generally, when heating in a vacuum furnace with graphite structure materials, as long as the workpiece does not directly contact the graphite, the magnetic material will not change significantly. However, for magnetic conductive alloys with high requirements, the lower the carbon content, the better. When the basic composition is basically accurate, in a vacuum furnace with graphite felt insulation and graphite cloth as the heating element, the graphite will react with the leaked oxygen to generate CO, which has the effect of carburizing.

Therefore, when dealing with magnetic alloys, it is necessary to use a vacuum furnace with a metal heat shield and a metal heat generator, and ensure that the internal surface of the vacuum furnace is clean before use.

To avoid the above problems, it is crucial to the selection of equipment and manufacturers. If the manufacturing of vacuum furnace equipment is not up to the standard, and the manufacturer lacks the ability to solve problems, it will become very difficult to deal with heat treatment defects.

SIMUWU has a lot of experience in vacuum furnace manufacturing and heat treatment. Answering customers’ questions from the model selection stage, and responsible for the sales and after-sales service of the equipment. The RVGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tools and dies. The good vacuum system and temperature control system ensure the effective implementation of the vacuum heat treatment process. SIMUWU focuses on the manufacturing 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 gas quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.