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Induction Brazing Solutions For HVAC Industry

Composition of air conditioning accessories

  Air conditioning accessories include circuit control boards, wire controllers, manifolds, refrigerants, electronic expansion valves, motors, compressors, liquid mirrors, and ball valves. High-frequency induction brazing technology is mainly used for high-frequency induction brazing in automotive air-conditioning pipe fittings.

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Introduction to Induction Brazing

First step: surface preparation, remove the oxide film and oil film on the surface of the workpiece;

Second step: workpiece positioning, the workpiece is positioned, supported, and fixed to ensure that the relative position of the workpiece and the inductor remains unchanged during mass production, and the brazing material is made into a ring and added to the part to be welded;

Third step: heating parameter setting, control the brazing temperature and heating speed by adjusting the heating current and heating time;

Fourth step: post-brazing treatment, directly put the workpiece into water or clean it with other chemicals;

Brazing points - pre-welding treatment

  Before brazing, oxides, grease, dirt, etc. on the surface of the workpiece must be carefully removed, because the molten solder cannot wet the surface of the uncleaned part, nor can it fill the joint gap. Cleaning part surfaces include:

Clean up oil stains: Oil stains can be removed with organic solvents. Commonly used organic solvents are alcohol, carbon tetrachloride, gasoline, trichloride, dichloroethane, and trichloroethane.

Removal of oxides: Mechanical methods can be used to remove oxides on the surface of parts, such as files, metal brushes, sandpaper, sandblasting, etc.; chemical erosion; electrochemical erosion.

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Introduction of brazing flux

  In order to meet the requirements of joint performance and brazing process, the solder generally meets the following basic requirements;

1). Appropriate melting temperature range, usually its melting temperature is lower than that of the base metal;

2). It has good wetting properties and spreading properties at brazing temperature, and can fully fill the joint gap;

3). The physical and chemical interaction with the base metal should ensure a firm bond between them;

4). The composition is stable, minimizing the burning loss or volatilization of elements at the brazing temperature, and containing less or no rare metals and precious metals;

5)It can meet the requirements of physical, chemical, and mechanical properties of brazed joints.

  According to the different brazing materials used, brazing is generally divided into:

(1). Soldering – the liquidus temperature of the solder is lower than 450℃;

(2). Brazing – The liquidus temperature of the solder is higher than 450°C.

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Fit clearance

  In the brazing process, the selection of joint gaps is very important. A reasonable joint gap is not only related to the capillary action of the molten solder, which in turn affects the flow in the weld but also the structural formula formed by the solidification of the molten solder in different gaps is different. When a large gap is used, the grains will grow without direction, and the large grains will affect the strength of the joint; while when a small gap is used, there is a grain layer along the width of the brazing seam, the gap is reduced, and the amount of solidified metal is reduced. , so that smooth plane grains can be formed after solidification, and the strength of the weld is improved. According to the material of the workpiece and the selected brazing material, the gap of the liquid-separating head is selected to be 0.05-0.15mm, so that the capillary effect can be fully exerted and the strength of the welded joint can be ensured.

Solder placemen

  In most brazing, the solder should be pre-placed on the joint. When placing the solder, the gravity of the solder and the capillary action of the gap should be used as much as possible to promote the filling of the gap. The solder must be close to the joint. It can be sucked into the gap by capillary action. For tight-fit and large lap length joints, make a solder seating groove in the joint.

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Apply flux

In order to increase the flow of the solder, it is sometimes necessary to apply flux. The function is to remove the oxides on the surface of the solder and the base metal, and to protect the solder and the liquid solder from oxidation during the brazing process, and to improve the wettability of the liquid solder to the solder.

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Assembly and Positioning

  There are many ways to fix parts by brazing. For parts with small size and simple structure, simple fixing methods can be used, such as relying on self-weight, tight fit, spring clips, positioning pins, etc.

  For parts with complex structures, special fixtures are generally used for positioning. The requirements for the brazing fixture are that the fixture material should have good high-temperature resistance and oxidation resistance, the fixture and the part material should have a similar thermal expansion coefficient, the fixture should have sufficient rigidity, but the structure should be as simple as possible, and the size should be as small as possible. The fixture not only works reliably but also ensures high production efficiency.

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Cleaning after brazing

  Most of the flux residues corrode the brazed joints and also hinder the inspection of the welds, which need to be cleaned up. The flux rosin does not corrode and does not need to be removed. The active flux residue containing rosin is insoluble in water and can be removed with organic solvents such as isopropanol, alcohol, gasoline, trichloroethylene, etc. Fluxes composed of organic acids and salts are generally soluble in water and can be washed with hot water. The flux consisting of inorganic acids is soluble in water and can also be washed with hot water. The borax and boric acid flux residues used for brazing are basically not soluble in water and are difficult to remove. Generally, sandblasting is used to remove them.

The most important problems in high frequency induction brazing

  • Possible problems include too large spread, outflow, and interruption of current inside the weld.
  • But the above problems have reasons and can be solved.
  • The most difficult problem to solve is the auxiliary problem.
  • Unlike flame brazing, high-frequency induction brazing does not have the flow-assisting effect of flame welding. Must rely on auxiliaries for flow.

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