High frequency brazing of distributor

High frequency brazing of distributor

  Abstract: This article proposes a high-frequency induction brazing method for the liquid dispensing head used in air conditioners, and proposes the process flow and operation method for it, which improves the existing production process and solves the difficulty of the liquid dispensing head for induction The problem of brazing.

Keywords: Dispensing head Dispensing device Distributor Induction brazing

1. Overview of Dispensing Tip Induction Brazing

1.1 Overview of Dispensing Head

  The use of liquid dispensing heads in refrigeration systems is very common, especially in Freon systems with the use of thermal expansion valves that can automatically adjust the liquid flow to control the superheat of the evaporator outlet, and the liquid dispensing heads have been more widely used. In the distributed air conditioner, the liquid splitting head is one of the important components, which plays a key role in the heat exchange efficiency of the heat exchanger. At present, the existing air-conditioning liquid dispensing head usually includes a liquid inlet part at the upper end and a liquid dispensing part at the lower end. The middle through holes of the liquid part and the liquid separating part, and the lower end of the liquid separating part will be integrally formed with a plurality of liquid separating holes evenly distributed on the circumference. However, in actual use, it is often encountered that the evaporator has uneven liquid distribution due to ignoring individual factors such as the processing of the liquid dispensing head, the efficiency of the evaporator is low, or the resistance is too high, and the compressor discharge pressure is too high. It even caused many problems such as liquid back.

Figure 1 Dispensing head

1.2 Overview of induction brazing

  The welding seam is heated to the melting temperature of the alloy solder by electromagnetic induction heating method, but the metal being welded still has not reached the melting temperature at this time. The low melting point alloy adheres the two metals together through strong surface tension. Form a solid weld. The parts of the same or different materials can be welded together, the material saving effect is remarkable, and various needs can be met. Suitable for welding various magnetic materials such as steel, copper, aluminum, nickel, and special alloys. High-frequency induction local welding has high strength, no deformation, and comprehensive mechanical properties are better than other welding.

2. The overall frame of the induction brazing system

  The overall frame of the whole system includes 1 set of double-station welding station, 2 sets of high frequency welding machines, 2 sets of positioning tooling, 1 set of electric control system and 1 set of cooling system.

Figure 2 The overall frame of the induction brazing system

Figure 3 The equivalent physical map of the system framework

3. Process flow and selection

  Piping-upper workpiece-air cooling-welding heating-welding seam natural cooling-air cooling-take the workpiece.

  Welding power source selection-sensor selection-solder additives selection-tooling positioning design-auxiliary parts selection-welding parameters determination-cleaning after welding.

3.1 Selection of welding power source

  The diameter of the liquid dispensing head ranges from 10-120mm, and combined with the size of the capillary tube diameter, we finally chose the all-digital DIH-60 model dedicated to the welding of liquid dispensing heads as the welding power source.

Figure 4 DIH-60 welding power source

3.2 Sensor selection

Select the profiling sensor as its welding output terminal.

Figure 5 Sensor

3.3 Selection of solder additives

  The dispensing head has been determined by our company's process department to use a customized welding ring. Our company can provide solder additives process services, please inquire for details.

Figure 6 Solder

3.4 Tooling positioning design

  Induction heating welding is to place the welding part of the workpiece in an induction magnetic field for heating. The strength of the magnetic field in each part of the magnetic field is different, and there is a high requirement for the positioning repeatability of the workpiece. Therefore, it is necessary to design the corresponding tooling according to the specifications of each workpiece and the welding process at the same time. Our company can provide induction brazing tooling design services. Call us for details

3.5 Auxiliary selection

  In high frequency induction welding, the induction heating power supply needs to be cooled, and industrial chillers of corresponding specifications are required. Our company can provide different types of industrial chillers. Call us for details

Figure 7 Industrial chiller

3.6 Determination of welding parameters

  After our long-term high-frequency brazing research and a lot of customer experience, we chose the automatic heating mode in this model. The heating current of the automatic heating mode is divided into five sections. During this process, the characteristics of copper metal increase with the temperature. High resistance increases, and the Joule effect causes the heating rate to increase during the heating process. This is inconsistent with the welding process summarized by our research. Therefore, we use the method of gradual decrease in current to heat the welding part. In this way, the temperature of the welding part can be increased under the premise of uniform heating, and the workpiece can be prevented from overburning in the high temperature section. Finally, in order to ensure the integrity of the welding process, we set a small current for heat preservation afterwards to ensure that it reaches the penetration standard and has no porosity. And other technological standards.

Figure 8 Heating parameter setting	Figure 9 Display of operating parameters

3.7 Cleaning after welding

  Because of the use of special solders and additives, there is a small amount of residue on the surface of the dispensing head after soldering, and there is a certain degree of oxidation. It is only necessary to clean the surface residue and oxide scale with a cleaning agent.

4. Operation steps:

l Surface preparation: remove the oxide film and oil stains on the surface of the workpiece;

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

l Heating process: Using the previously set parameters, the operator only needs to press the start button, and the equipment will automatically execute the previously set parameters to accurately weld the workpiece, and stop heating after the welding is completed;

  Post-brazing treatment: Because of the use of special solders and additives, there is a small amount of residue on the surface of the dispensing head after welding, and there is a certain degree of oxidation, and only the cleaning agent is required to clean the surface residue and oxide scale.

5. Customer site pictures

Figure 10 Live picture

6. Energy consumption comparison

The welding process is equipped with equipment to reduce the dependence on manual technology. Ordinary operators can replace the certified flame welders, reducing the burden of safety and annual certification of the company.

In the case of small workpieces and fewer pipes, the advantage of induction brazing is not obvious. However, in the induction brazing process, the equipment is automatically welded without manual operation, and the welding time can be used to operate another equipment, so that one person can operate the double-station welding machine at the same time. This can further improve product quality.

According to the data in the above figure, the energy can save about 10.56-4.56=60,000 yuan per year, and the solder can save about 2/3.

7. Summary

  This article describes the four aspects of high-frequency induction brazing technology, process flow, operation method, and energy consumption comparison of the liquid-dispensing head in the air-conditioning pipeline, and focuses on copper metal, especially when the number of liquid-dispensing head holes is large. The difficulty of high-frequency induction welding is a solution based on all-digital induction heating technology, covering all aspects of welding before, during and after welding. And given detailed and effective data to prove that high-frequency induction brazing is superior to flame brazing in terms of environmental protection, energy consumption, and welding material consumption.