Application of vacuum brazing technology

Abstract : The characteristics of vacuum brazing technology and its wide application in aeroengine, air separation equipment, engineering machinery, vehicle and ship and petrochemical industry are reviewed.

Key words : brazing vacuum application

I. Foreword

Vacuum brazing technology has become a promising welding technology since the 1940s. The first parts to braze copper and stainless steel in the electronics industry were later applied to the aerospace industry and the atomic energy industry. In 1959, they were applied to the manufacture of stainless steel plate-fin heat exchangers. It is now widely used in plate-fin heat exchangers and coolers in industrial sectors such as air separation plants, petrochemical plants, construction machinery, automobiles, boats and home appliances.

Due to the unparalleled advantages of vacuum brazing technology, it has been rapidly developed and widely used in industrialized countries around the world.

Second, the advantages of vacuum brazing

1. Vacuum brazing, because it does not use flux, significantly improves the corrosion resistance of the product, eliminates all kinds of pollution, pollution-free processing equipment costs, and has good safety production conditions;
2. Vacuum brazing not only saves a lot of expensive metal flux, but also does not require complicated flux cleaning process, which reduces production costs;
3. The vacuum brazing solder has good wettability and fluidity, and can weld more complicated and narrow passage devices. Vacuum brazing improves the yield of the product and obtains a firm and clean working surface;
4. Compared with other methods, the internal structure of the furnace and the fixture have a long service life, which can reduce the maintenance cost of the furnace;
5. Many materials suitable for vacuum brazing, such as: aluminum, aluminum alloy, copper, copper alloy, stainless steel, alloy steel, low carbon steel, titanium, nickel, Inconei, etc. can be brazed in a vacuum electric furnace, The designer determines the materials needed for the purpose of the brazed device, with aluminum and aluminum alloys being the most widely used.

Third, the application of vacuum brazing

1. Vacuum brazing application on aero engines

Abroad, the JT9D engine honeycomb sealing ring of the United States Puhui Company is made of vacuum brazing of the ring and the honeycomb core; the engine fuel main pipe is composed of the main pipe and the plurality of branch pipes and nozzles, which are vacuum brazed; The engine stainless steel heat exchanger is composed of more than 300 stainless steel pipes, partitions and shells by vacuum brazing; the JT8D engine 12 and 13 compressor stator rings are made of vacuum brazing from inner and outer rings and dozens of blades. The engine casing of GE in the United States is brazed by more than 240 steps of 0.25-0.7 mm thick Inconel alloy parts. Domestically, Shenyang Liming Engine Company and Chengdu Engine Company respectively vacuum brazed the stator ring for the naval aircraft; Chengdu Engine Company vacuum brazed the fuel main pipe and passed the engine test.

Vacuum brazing electric furnace is the main brazing equipment in the manufacture of aero-engines. There are more than 200 vacuum brazing furnaces in the United States. Domestically, Dawn Engine Manufacturing Company, Chengdu Engine Company and Beijing Aviation Technology Research Institute developed a medium-sized single-chamber vacuum brazing electric furnace in the 1970s. Beijing Aviation Technology Research Institute cooperated with Tianjin Electric Furnace Factory to develop semi-continuous vacuum brazing furnace in 1964. Xi'an Aero Engine Company introduced Ipson horizontal vacuum electric furnace (furnace size 910×610×610mm), Beijing Civil Aviation Ameco Company Introduced Ipsen's bell-type vacuum brazing electric furnace (furnace size 髟 2300 × 1300mm), the imported furnaces are controlled by microcomputer, and the program is automatically controlled. Now, Shenyang Vacuum Technology Research Institute, Beijing Aviation Technology Research Institute, Shenyang Vacuum Application Research Institute and other units have developed large-scale high-temperature vacuum brazing electric furnaces that can control the temperature of the microcomputer and automatically control according to the program.

2. Application of vacuum brazing on construction machinery

Vacuum brazing is a small example of small bits. Small and medium-sized bits are widely used in metallurgy, geology, coal, water, railway, military and other construction projects. According to statistics, in 1978, the country consumed about 10,000 small and medium-sized bits, but now it is used more and plays an important role in the national economic construction.

In 1978, the Northwest Institute of Mining and Metallurgy began to develop vacuum brazing medium and small bits. In 1980, it passed the technical appraisal by the Ministry of Metallurgy. In the 1980s, it has a production line with an annual output of 100,000 small and medium-sized bits. The products are used in hundreds of mines across the country. The drills produced by the institute have also been tested dozens of times in the Dumiao Iron Mine, Xiangdong Tungsten Mine, Nanjing Meishan Iron Mine, Hongtoushan Copper Mine, and Huatong Copper Mine. Different types of ore have been drilled, and they have withstood the test of hard granite, hard-to-cut horn rock and hard and abrasive massive magnetite skarn. The cross-shaped drill head of φ42mm and the same type of drill bit in Sweden are used to compare the drilling of granite in the field. The average service life is over 100m, which reaches the level of the Swedish bit. According to the survey, the service life has been increased by 1 to 1.5 times. Brought significant economic benefits.

3. Vacuum brazing in vehicles and boats

Vacuum brazed plate-fin oil coolers are used in cars and boats. The plate-finned oil cooler has the characteristics of high heat transfer efficiency, compact structure and light weight. It is a new generation of diesel engine coolers and has been widely used in automobiles, tractors, marine diesel engines and other fields.

There are only a few manufacturers of such plate-fin oil coolers in China, and they are all welded with silver-copper alloy. Each unit consumes 150 grams of silver. The cooler made of silver-free copper vacuum brazing process is not only a country. It saves a lot of expensive silver and has good air tightness. The brazed product is tested by air pressure of 10kg·f/cm2 without leakage and leakage. It has high cleanliness and good surface gloss. It is used on diesel engines. The thermal performance reached the specified index of the t· diesel plate-finned water-cooled oil cooler issued by the Ministry of Machinery Industry. It was immersed in water for 115 hours, and the surface was free from rust corrosion, which greatly reduced the production cost.
In 1984, the Czech Republic introduced a small continuous vacuum brazing electric furnace from the UK to produce a shovel-heater on the Skoda truck, with an annual output of more than 10,000 units. In 1971, Ford Motor Company began to use the true brazing process to produce aluminum radiator cores. Among the car radiators produced in 1984, aluminum accounted for 20%. Later, the aluminum radiator production lines of the two factories in the subordinates were technically transformed. It is estimated that after the technical transformation, it could reach 3 million units in 1985. Ford's technical transformation of the production line is due to the light weight of the aluminum radiator and good heat exchange performance. Therefore, the number of aluminum radiators used in Ford Motor Company's passenger cars, light trucks and covered trucks accounts for 90% to 95%.

Japan Furukawa Aluminum Industry Co., Ltd. has developed a new type of alloy (CF series) suitable for vacuum brazing automotive heat exchanger fins, which has been mass-produced. This new CF series alloy is added to aluminum, zinc and manganese. ~0.3% alloy of calcium. It can be used as a heat sink for heat transfer, and the new alloy improves corrosion resistance and service life. According to interest rates, aluminum for automotive heat exchangers accounts for 80% to 90% in Europe, 50% in the US, and 15% in Japan. Therefore, Japan's Furukawa Aluminum Industry Co., Ltd. has launched the CF series of new aluminum alloys, which will undoubtedly promote the aluminum alloy of Japan's automotive heat exchangers.

Now, there are more than 20 vacuum brazed parts on a single car. It can be seen that vacuum brazing technology has a great effect, good effect and wide application.

4. Vacuum-brazing on air separation equipment The plate-fin heat exchanger used on air separation equipment is mainly used for the production of oxygen, nitrogen, argon and rare gases. In the past, the plate-fin heat exchanger was mainly made by salt bath dip soldering. This process technology not only has large energy consumption, complicated process, but also strong corrosiveness, serious environmental pollution, high production cost and low product life. Vacuum brazing has many advantages over salt bath brazing, so the trend is that vacuum brazing will replace salt-soluble brazing.

In 1991, Hangzhou Oxygen Generator Factory introduced the design and manufacturing technology of large vacuum brazing furnace and aluminum plate-fin heat exchanger of American Stewart Warner Company. The heat exchanger that can be brazed is 1200×1200×6000mm, working pressure. Up to 8.4 MPa.

The first vacuum brazed turbine oxygen compressor impeller of Hangzhou Oxygen Concentrator Factory was tested at the three speeds of 14500, 16000 and 18060r/min, and the speeding three-minute test was carried out respectively. Only one blade with poor brazing quality was found. The rest of the seam is still good and the entire impeller is still intact.

The success of the vacuum brazing impeller greatly improves the manufacturing precision of the narrow runner of the plant, thus not only ensuring the design performance index, but also reducing the manufacturing cost, and also shortening the production cycle. The actual fabrication of vacuum brazing impeller technology will play an important role in promoting the technological advancement of China's air separation equipment industry.

Due to the many advantages of vacuum brazing, the British Marston company closed the salt bath brazing furnace at the end of 1983, and used the FVB-114-120-240 large vacuum brazing furnace produced by the British company Cossack to produce low temperature heat exchange. Device.

5. Application of Vacuum Brazed Plate-Fin Heat Exchanger in Petrochemical Industry

Vacuum brazing is widely used in petrochemical industry to manufacture floor-fin heat exchangers, such as: (1) petrochemical refinery gas recovery; (2) separation and recovery of natural gas and coke oven gas; (3) natural gas and petroleum Liquefaction of gas. The plate-fin heat exchanger has the advantages of large processing capacity, good separation effect, low energy consumption and high purity. Therefore, all countries in the world attach great importance to the development of vacuum brazing plate fin heat exchanger technology.

6. Vacuum brazing technology in other applications

Vacuum brazing technology for locomotive radiators, compressor intercoolers, freon and alkane, olefin refrigeration systems, excavator oil coolers, gas turbine regenerators, high power transformer radiators, and household appliances applications, Such as vacuum brazing household air conditioners and heat exchanger core strips of various electric heaters.