Vacuum brazing technique refers to the heating of the workpiece in a vacuum chamber, and is mainly used for welding products that require high quality and easily oxidized materials. The vacuum brazing furnace includes a pressure vessel with a cylindrical side wall and a door. The size and position of the door are designed to close one end of the cylindrical side wall. The workpiece processing system is installed on the pressure vessel door to support metal workpieces for heat treatment or brazing. The workpiece processing system includes a device that rotates the workpiece during processing. The vacuum system can be connected to the workpiece so that the pressure inside the workpiece is lower than atmospheric pressure during the brazing process.
Overview
Vacuum brazing technology has become a very promising welding technology since the beginning of the 1940s. It first appeared in the electronic industry for brazing copper and stainless steel parts, and later applied to the aviation industry and the atomic energy industry, and in 1959 began to be applied to the manufacture of stainless steel plate-fin heat exchangers. Now, it is widely used in plate-fin heat exchangers and coolers in industrial sectors such as air separation equipment, petrochemical equipment, engineering machinery, vehicles, ships and home appliances.
Because of the unparalleled advantages of vacuum brazing technology, it has been rapidly developed and widely used in industrially developed countries in the world.
Advantage
Vacuum brazing, because it does not use flux, significantly improves the corrosion resistance of the product, avoids all kinds of pollution, pollution-free treatment equipment costs, and has good safe production conditions;
Vacuum brazing not only saves a large amount of expensive metal flux, but also does not require complicated flux cleaning procedures, which reduces production costs;
Vacuum brazing solder has good wettability and fluidity, and can weld more complex and narrow-channel devices. Vacuum brazing improves the yield of products and obtains a firm and clean working surface;
Compared with other methods, the internal structure of the furnace and fixtures have a long life, which can reduce the maintenance cost of the furnace;
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 a vacuum electric furnace. The designer determines the required materials according to the purpose of the brazing device, and aluminum and aluminum alloys are the most widely used.
application
Aircraft engine
Abroad, the JT9D engine honeycomb sealing ring of Pratt & Whitney, USA, is made of vacuum brazing ring parts and honeycomb sandwich core; the engine fuel main pipe is composed of a main pipe and multiple branch pipes and nozzles using vacuum brazing; this machine The engine stainless steel heat exchanger is composed of more than 300 stainless steel tubes, partitions, and shells by vacuum brazing; the JT8D engine 12 and 13 stage compressor stator rings are made of inner and outer rings and dozens of blades by vacuum brazing. The engine casing of GE in the United States is made by three-step vacuum brazing of more than 240 Inconel alloy parts with a thickness of 0.25-0.7mm. Domestically, Shenyang Liming Engine Company and Chengdu Engine Company vacuum brazed stator rings for naval aircraft; Chengdu Engine Company vacuum brazed fuel headers and passed engine test runs.
The 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, Liming Engine Manufacturing Company, Chengdu Engine Company, and Beijing Aviation Technology Research Institute developed medium-sized single-chamber vacuum brazing electric furnaces in the 1970s. In 1964, Beijing Institute of Aeronautical Technology and Tianjin Electric Furnace Factory jointly developed a semi-continuous vacuum brazing furnace. Xi'an Aero Engine Company introduced Ipsen horizontal vacuum electric furnace (furnace size 910×610×610mm), and Beijing Civil Aviation Ameco Company The bell-jar type vacuum brazing electric furnace from Ipsen Company (furnace size: 2300×1300mm) is introduced. The imported furnaces are all microcomputer temperature controlled and automatic program controlled.
Construction machinery
Vacuum brazing of small and medium drill bits is an example. Small and medium drill bits are widely used in metallurgy, geology, coal, water conservancy, railway, military and other construction industries. According to statistics, in 1978, the country consumed about 10,000 small and medium-sized drill bits, but now the consumption is even greater, playing an important role in the construction of the national economy.
The Northwest Institute of Mining and Metallurgy began to develop vacuum brazing small and medium-sized drill bits in 1978. 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 100,000 small and medium-sized drill bits, and the products were supplied to hundreds of mines nationwide. The drill bit produced by the company has also been tested dozens of times in Damiao Iron Mine, Xiangdong Tungsten Mine, Nanjing Meishan Iron Mine, Hongtoushan Copper Mine, Huatong Copper Mine and other places. Different types of ore rocks have been drilled, and they have withstood the tests of hard granite, difficult-to-drill angle rocks, and hard and abrasive massive magnetite-skarn. The φ42mm cross-shaped drill bit was compared with the same type drill bit in Sweden for drilling granite. The average service life exceeded 100m, which reached the level of the Swedish drill bit. According to the survey, the service life was increased by 1 to 1.5 times. Brings significant economic benefits.
Vehicle
Vacuum brazed plate-fin oil coolers are used in vehicles and ships. The plate-fin oil cooler has the characteristics of high heat transfer efficiency, compact structure and light weight. It is an updated product of today's diesel engine cooler and has been widely used in automobiles, tractors, marine diesel engines and other fields.
There are few manufacturers in China that produce this type of plate-fin oil cooler, and they all use silver-copper alloy welding, each costing 150 grams of silver, and the cooler made by the silver-free copper vacuum brazing process is not only for the country It saves a lot of precious silver and has good air tightness. The brazed products have passed the air pressure test of 10kg·f/cm2, and there is no air leakage or leakage. The cleanliness is high and the surface gloss is good. When used on diesel engines, its transmission The thermal performance meets the requirements of the "t·diesel engine plate-fin water-cooled oil cooler" promulgated by the Ministry of Machinery Industry. It is immersed in water for 115 hours without rust and corrosion on the surface and greatly reduces the production cost.
In 1984, the Czech Republic introduced a small continuous vacuum brazing electric furnace from the United Kingdom to produce shovel heaters on Skoda trucks, with an annual output of more than 10,000 units. The Ford Motor Company of the United States began to use the real brazing process in 1971 to produce aluminum radiator cores. Aluminum radiators accounted for 20% of the auto radiators produced in 1984. Later, the two subordinate factories produced aluminum radiator production lines for technical transformation, and it is estimated that after technical transformation, it will reach 3 million units in 1985. The reason why Ford had to carry out technological transformation on the production line was that the aluminum radiator was light in weight and had good heat exchange performance. Therefore, in passenger cars, light trucks, and trucks with roofs manufactured by Ford Motor Company, 90% to 95% of aluminum radiators are used.
Japan Furukawa Aluminum Industry Co., Ltd. has developed a new type of alloy (CF series) suitable for vacuum brazing of automotive heat exchanger fins, and has been mass-produced. This new CF series alloy is made of aluminum, zinc, and manganese with 0.2 ~ 0.3% calcium alloy. It can be used as the heat sink of the heat exchanger. The new alloy improves the corrosion resistance and service life. According to information, aluminum materials for automotive heat exchangers account for 80% to 90% in Europe, 50% in the United States, and 15% in Japan. Therefore, Japan's Furukawa Aluminum Industry Co., Ltd. only launched the CF series of new aluminum alloys, which will undoubtedly promote the aluminumization of Japanese automobile heat exchangers.
At present, there are more than 20 vacuum brazing parts on a car, which shows that the vacuum brazing technology has great effect, good effect and wide application.
Air separation equipment
The heat exchanger is mainly used for the production of oxygen, nitrogen, argon and rare gases. In the past, plate-fin heat exchangers were mainly manufactured by salt bath immersion brazing. This process technology not only consumes a lot of energy, but also has a complicated process. It is also highly corrosive, causing serious environmental pollution, high production costs, 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 Generator Factory introduced the design and manufacturing technology of large vacuum brazing furnace and aluminum plate-fin heat exchanger from American Stewart Warner Company. The heat exchanger that can be brazed is 1200×1200×6000mm, and the working pressure is 1200×1200×6000mm. The highest can reach 8.4MPa.
The first vacuum brazed turbine oxygen compressor impeller of Hangzhou Oxygen Plant was tested at three speeds of 14500, 16000, and 18060r/min. The three-minute overspeed test was carried out. Only one blade with poor brazing quality was found to be broken. Seam, the rest are in good condition, and the entire impeller is still intact.
The success of the vacuum brazed impeller greatly improved the manufacturing accuracy of the factory's narrow runner impeller, thus not only ensuring the design performance indicators, but also reducing the manufacturing cost, and at the same time shortening the production cycle. The actual breakthrough of vacuum brazing impeller manufacturing technology will play an important role in promoting the technological progress of my country'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 adopted the FVB-114-120-240 large vacuum brazing furnace produced by the British Consac Company to produce low-temperature heat exchange. Device.
Petrochemical
Vacuum brazing is widely used in the petrochemical industry to manufacture floor-fin heat exchangers, such as: (1) gas recovery in petrochemical refineries; (2) separation and recovery of natural gas and coke oven gas; (3) natural gas, petroleum Liquefaction of gas. Because the plate-fin heat exchanger has the advantages of large processing capacity, good separation effect, low energy consumption and high purity. Therefore, countries all over the world attach great importance to the development of vacuum brazed plate-fin heat exchanger technology
Air separation equipment
The heat exchanger is mainly used for the production of oxygen, nitrogen, argon and rare gases. In the past, plate-fin heat exchangers were mainly manufactured by salt bath immersion brazing. This process technology not only consumes a lot of energy, but also has a complicated process. It is also highly corrosive, causing serious environmental pollution, high production costs, 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 Generator Factory introduced the design and manufacturing technology of large vacuum brazing furnace and aluminum plate-fin heat exchanger from American Stewart Warner Company. The heat exchanger that can be brazed is 1200×1200×6000mm, and the working pressure is 1200×1200×6000mm. The highest can reach 8.4MPa.
The first vacuum brazed turbine oxygen compressor impeller of Hangzhou Oxygen Plant was tested at three speeds of 14500, 16000, and 18060r/min. The three-minute overspeed test was carried out. Only one blade with poor brazing quality was found to be broken. Seam, the rest are in good condition, and the entire impeller is still intact.
The success of the vacuum brazed impeller greatly improved the manufacturing accuracy of the factory's narrow runner impeller, thus not only ensuring the design performance indicators, but also reducing the manufacturing cost, and at the same time shortening the production cycle. The actual breakthrough of vacuum brazing impeller manufacturing technology will play an important role in promoting the technological progress of my country'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 adopted the FVB-114-120-240 large vacuum brazing furnace produced by the British Consac Company to produce low-temperature heat exchange. Device.
Petrochemical
Vacuum brazing is widely used in the petrochemical industry to manufacture floor-fin heat exchangers, such as: (1) gas recovery in petrochemical refineries; (2) separation and recovery of natural gas and coke oven gas; (3) natural gas, petroleum Liquefaction of gas. Because the plate-fin heat exchanger has the advantages of large processing capacity, good separation effect, low energy consumption and high purity. Therefore, countries all over the world attach great importance to the development of vacuum brazed plate-fin heat exchanger technology.
Other aspects
Vacuum brazing technology is used in locomotive radiators, compressor intercoolers, Freon and alkane, olefin refrigeration systems, excavator oil coolers, gas turbine regenerators, high-power transformer radiators, and household appliances. Such as vacuum brazing the heat exchanger core strips of household air conditioners and various electric heaters.
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