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What are the applications of vacuum brazing of aluminum alloy?
There are four main brazing methods for aluminum alloy: dry air chloride flux brazing, salt bath brazing, nitrogen protection non corrosive flux brazing and vacuum non flux brazing. The main disadvantage of the dry air method and the salt bath brazing method is that the flux residue must be removed after welding because the residue has a corrosive effect due to the use of chloride brazing flux. The cleaning process needs to consume a lot of fresh water, which inevitably brings about environmental pollution. The problems of corrosion and contamination of residual flux urge people to do a lot of research on flux – free brazing technology. Vacuum aluminum brazing technology came into being.
Vacuum aluminum brazing is an advanced method of brazing in vacuum atmosphere without using brazing flux. Compared with traditional brazing methods with various fluxes, it has many advantages:
1.Solder flux and salt are not used, so there is no harmful gas generated during heating, so the post welding cleaning process is avoided, and the environmental pollution problem is eliminated.
2.Vacuum brazing is carried out under high vacuum condition, with complete degassing, no defects such as porosity and slag inclusion, and good and compact welds and joints can be obtained.
3.There is no corrosion problem caused by residual flux and salt on the workpiece due to incomplete cleaning, which can prolong the service life of the product.
4.The workpiece surface after vacuum brazing is clean and bright, and the appearance effect is good.
Because vacuum aluminum brazing technology has many advantages, it is widely used in the world today. At present, it has been cited to various industrial sectors such as aviation, aerospace, petrochemical, electronics, air separation, low temperature, vehicles, ships, refrigeration and refrigeration. The heat exchanger is an important aspect. Specific products include evaporator and condenser of automobile air conditioner, automobile radiator, oil cooler, intercooler, plate fin heat exchanger in air separation equipment, etc.
Automobile radiator or water tank:
The radiator core is made of flat tubes, radiator fins and end plates brazed in a vacuum furnace at one time. The flat tube is formed by seam welding of a composite plate with filler metal on one side after forming. The base material is LF21, and the filler metal is aluminum silicon magnesium alloy. The heat sink is not coated with solder, and the ribbon sheet is folded into a wavy shape with a special tape rolling machine and a hundred window type heat sink holes are opened. The radiator may consist of one or more rows of tubes.
The structure of the intercooler used on the truck is similar to that of the water tank, but its tube is a porous flat tube formed by extrusion, and there is no filler metal on the flat tube, while the radiator is a composite plate with filler metal. The welds between the flat tube and the end plate, and between the flat tube and the radiator can be brazed in a vacuum furnace at one time.
Air conditioning evaporator and condenser
The evaporator is generally of coil type. The pipe is a perforated flat pipe extruded from pure aluminum or LF21 aluminum alloy, which is bent into a serpentine shape by a special pipe bender. Heat sink made of composite sheet is put in the middle, and it is brazed in the furnace after assembly. The tubes and fins of the condenser are narrow, and the overall structure size is large. In addition, because the condenser must bear high internal pressure, the flat tube used by the condenser is usually thicker than the evaporator.
Vacuum brazing equipment
Vacuum brazing equipment is mainly composed of vacuum system and vacuum furnace. The vacuum system mainly includes vacuum unit, vacuum pipeline, vacuum gate, etc. Vacuum unit is usually composed of rotary vane mechanical pump and oil diffusion pump. To obtain high vacuum, an oil diffusion pump must be used, so that the vacuum degree can reach 133 × Vacuum at 10 ° mPa level.
The heating of the vacuum furnace is integrated with the brazing chamber, and the furnace wall is a double-layer water-cooled structure. Built in thermal reflective screen, composed of multilayer thin metal plates with smooth surface. Molybdenum sheet or stainless steel sheet is selected as the material to prevent the heat from radiating outward, reduce the heating of furnace shell and improve the heating efficiency. Heating elements are distributed in the reflective screen, and different heating elements are selected according to the rated temperature of the furnace: nickel Yijun and iron chromium aluminum alloys are generally used in medium temperature furnaces; The high-temperature furnace mainly uses molybdenum (1800 ℃), tantalum (2200 ℃), tungsten (2500 ℃) and graphite (2000 ℃). High heating efficiency, convenient and safe to use.
According to the process characteristics of aluminum alloy vacuum brazing, the design of vacuum aluminum brazing furnace should meet the requirements of the process on equipment in terms of vacuum degree, air leakage rate, temperature uniformity, etc. Therefore, the quality of brazing furnace selected in vacuum brazing is also a crucial factor. The RVB vacuum brazing furnace produced by SIMUWU has the advantages of good temperature control accuracy, high heating uniformity, and is an excellent product for aluminum alloy brazing process. On the premise of selecting appropriate process parameters, high quality vacuum brazing can be achieved.
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