Vacuum brazing technology has become a promising welding technology since 1940s. First appeared in the electronic industry brazed copper and stainless steel parts, and then applied to the aviation industry, atomic energy industry, in 1959 began to apply to the manufacture of stainless steel plate fin heat exchanger. Now, it is widely used in air separation equipment, petrochemical equipment, engineering machinery, vehicles, ships and household appliances and other industrial sectors of plate fin heat exchanger and cooler.
Because of its incomparable advantages, vacuum brazing technology has been rapidly developed and widely used in developed countries.
2、 Advantages of vacuum brazing
2.1. Vacuum brazing, because of the absence of flux, significantly improves the corrosion resistance of the product, eliminates all kinds of pollution, pollution-free treatment equipment costs, and has good safety production conditions;
2.2. Vacuum brazing not only saves a lot of expensive metal flux, but also does not need complex flux cleaning process, which reduces the production cost;
2.3. The wettability and fluidity of vacuum brazing filler metal are good, which can weld more complex and narrow channel devices. Vacuum brazing improves the product yield and obtains a solid and clean working surface;
2.4. Compared with other methods, the service life of furnace internal structure and fixture is long, which can reduce the maintenance cost of furnace;
2.5. There are 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 vacuum electric furnace. Designers can determine the required materials according to the use of brazing devices, among which aluminum and aluminum alloy are widely used.
3、 Application of vacuum brazing
3.1. Application of vacuum brazing in aeroengine
Abroad, the honeycomb sealing ring of jt9d engine made by Pratt Whitney company is made of ring and honeycomb sandwich by vacuum brazing; the main fuel pipe of the engine is composed of main pipe, multiple branch pipes and nozzle by vacuum brazing; the stainless steel heat exchanger of this engine is composed of more than 300 stainless steel tubes, clapboard and shell by vacuum brazing; the stator rings of stage 12 and 13 compressor of jt8d engine are composed of inner and outer rings And dozens of blades are made by vacuum brazing. The engine casing of Ge is composed of more than 240 Inconel alloy parts with thickness of 0.25-0.7mm, which are brazed in three steps. In China, Shenyang Liming Engine Company and Chengdu Engine Company respectively vacuum braze stator ring for Navy aircraft; Chengdu Engine Company vacuum brazes fuel main pipe and passes engine test.
Vacuum brazing furnace is the main brazing equipment in Aeroengine manufacturing. There are more than 200 vacuum brazing furnaces in the United States. In China, Liming Engine Manufacturing Company, Chengdu Engine Company and Beijing Institute of aeronautical technology developed medium-sized single chamber vacuum brazing furnace in 1970s. In 1964, Beijing Institute of Aeronautical Technology cooperated with Tianjin electric furnace factory to develop semi continuous vacuum brazing furnace. Xi’an aeroengine company imported horizontal vacuum furnace (furnace size 910 × 610 × 610 mm), Beijing Civil Aviation Ameco company introduced Epson bell type vacuum brazing furnace (furnace size 髟 2300 × 1300mm). All imported furnaces are controlled by microcomputer and program automatically System. Now, Shenyang Institute of vacuum technology, Beijing Institute of Aeronautical Technology, Shenyang Institute of vacuum application and other units have developed large-scale high-temperature vacuum brazing furnace which can be controlled by microcomputer and automatically controlled by program.
3.2. Application of vacuum brazing in construction machinery
Vacuum brazing small and medium bit is an example. It is widely used in metallurgy, geology, coal, water conservancy, railway, military and other construction. According to statistics, in 1978, about 10000 small and medium drill bits were consumed in China, and now the consumption is even larger, playing an important role in the national economic construction.
In 1978, Northwest Institute of mining and metallurgy began to develop small and medium-sized vacuum brazing bits. In 1980, it passed the technical appraisal made by the Ministry of metallurgy. In the 1980s, it had a production line with an annual output of 100000 small and medium-sized bits, and the products were supplied to hundreds of mines in China. Dozens of tests have been carried out in Damiao iron mine, Xiangdong tungsten mine, Meishan Iron Mine, Hongtoushan Copper Mine and Huatong copper mine. Different types of ore rocks have been drilled and tested by hard granite, difficult to drill hornstone and hard and abrasive massive magnetite with skarn. A comparative test of drilling granite with a diameter of 42mm is carried out on the spot with the same type of drill bit in Sweden. The average service life is more than 100m, reaching the level of Swedish drill bit. According to the investigation, the service life is increased by 1 to 1.5 times, bringing significant economic benefits to users.
3.3. Application of vacuum brazing in vehicle and ship
On board vacuum coolers are used to braze the engine oil. Plate fin oil cooler has the characteristics of high heat transfer efficiency, compact structure and light weight. It is a new generation of diesel engine cooler, and has been widely used in automobile, tractor, marine diesel engine and other fields.
There are few manufacturers producing this kind of plate fin oil cooler in our country, and they all use silver copper alloy welding. Each cooler needs 150g silver. The cooler made by silver free copper vacuum brazing technology not only saves a lot of valuable silver for the country, but also has good air tightness. The brazed products have no air leakage and leakage phenomenon after air pressure test of 10kg · f / cm2, with high cleanliness and smooth surface It has been used in diesel engine, and its heat transfer performance has reached the standard of “t · diesel engine plate fin water cooling oil cooler” issued by the Ministry of mechanical industry. After being immersed in water for 115 hours, the surface has no rust and corrosion, and the production cost is greatly reduced.
In 1984, Czechoslovakia imported small continuous vacuum brazing electric furnace from Britain to produce shovel heater on Skoda truck, with an annual output of more than 10000 sets. In 1971, Ford Motor Company began to produce aluminum radiator core by true brazing process.
Aluminum accounted for 20% of the automobile radiators produced in 1984. After the technical transformation of the aluminum radiator production lines of two subordinate factories, it is estimated that after the technical transformation, it will reach 3 million units in 1985. The reason why Ford wants to carry out technical transformation of the production line is that the aluminum radiator is light in weight and has good heat exchange performance. Therefore, 90% to 95% of the passenger cars, light trucks and vans manufactured by Ford Motor Company use aluminum radiators.
A new type of alloy (CF Series) for vacuum brazing automotive heat exchanger fins has been developed by Guhe Aluminum Industry Co., Ltd. of Japan, and has been produced in large quantities. The new alloy of CF series is composed of aluminum, zinc and manganese added with 0.2-0.3% calcium. It can be used as heat sink of heat exchanger. The new alloy improves corrosion resistance and service life. According to information, 80% – 90% of aluminum materials are used in automobile heat exchangers in Europe, 50% in the United States and 15% in Japan. Therefore, Japan’s Guhe Aluminum Industry Co., Ltd. has just launched CF series new aluminum alloy, which will undoubtedly promote the Aluminization of Japanese automobile heat exchanger.
Now, there are more than 20 vacuum brazing parts on a car. It can be seen that vacuum brazing technology has great effect, good effect and wide application.
4. The application of vacuum brazing in air separation equipment.
The plate fin heat exchanger used in air separation equipment is mainly used for the production of oxygen, nitrogen, argon and rare gas. In the past, the plate fin heat exchanger was mainly made by salt bath impregnation brazing. This technology not only has large energy consumption, complex process, but also has strong corrosivity, serious environmental pollution, high production cost and low product life. Vacuum brazing has many advantages over salt bath brazing, so the development trend is that vacuum brazing will replace salt solution brazing.
In 1991, Hangzhou oxygen plant introduced the design and manufacturing technology of large vacuum brazing furnace and aluminum plate fin heat exchanger made by Stewart Warner company of the United States. The brazed heat exchanger is 1200 × 1200 × 6000mm, and the maximum working pressure is 8.4mpa.
The impeller of the first Vacuum Brazed turbine oxygen compressor in Hangzhou oxygen plant was tested at 14500, 16000 and 18060r / min, and the overspeed test was carried out for three minutes respectively. Only one blade with poor brazing quality was found to be cracked, the rest parts were still in good condition, and the whole impeller was still intact.
The success of vacuum brazing impeller has greatly improved the manufacturing precision of narrow channel impeller in the factory, which not only ensures the design performance index, but also reduces the manufacturing cost and shortens the production cycle. The development of Vacuum Brazed impeller manufacturing technology will play an important role in promoting the technical progress of air separation equipment industry in China.
Due to the advantages of vacuum brazing, maltton company closed down the salt bath brazing furnace at the end of 1983, and adopted fvb-114-120-240 large vacuum brazing furnace produced by Concord to produce low temperature heat exchanger.
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 exchanger, such as: (1) gas recovery in petrochemical refinery; (2) separation and recovery of natural gas and coke oven gas; (3) liquefaction of natural gas and petroleum gas. The plate fin heat exchanger has the advantages of large capacity, good separation effect, low energy consumption and high purity. Therefore, many countries in the world attach great importance to the development of vacuum brazed plate fin heat exchanger technology.
6. Application of vacuum brazing technology in other aspects
Vacuum brazing technology is used in locomotive radiator, compressor intercooler, freon and alkene refrigeration system, digging oil cooler, gas turbine recuperator, high-power transformer radiator, and household appliances, such as vacuum brazing of household air conditioner and various electric heaters