Hydraulic expansion machine is a special hydraulic expansion equipment used for the expansion and connection of tubes and tubesheet in the manufacturing of heat exchanger, condenser, high-pressure heater and other equipment. The use of hydraulic expansion technology has the advantages of low manufacturing cost, light labor intensity, short manufacturing cycle, uniform and reliable expansion quality, etc. Hydraulic expansion technology has been widely used in the manufacture of heat exchanger in petrochemical, electric power, boiler, nuclear power, refrigeration and other fields, greatly improving the quality and production efficiency of domestic heat exchanger equipment.
The connection between heat exchange tube and tube sheet mainly includes expansion joint, welding and expansion welding, and the expansion joint can be divided into mechanical expansion joint, hydraulic expansion joint, rubber expansion joint and explosive expansion joint. Domestic enterprises generally adopt the mechanical expansion joint method, which has high labor intensity and low work efficiency. When the heat exchanger with tube sheet exceeding 100mm cannot achieve full thickness expansion, and the actual expansion rate, pull off force, sealing pressure and other indicators are not directly related, the operator mainly determines the expansion tightness based on experience, and the expansion quality is greatly affected by human factors. Moreover, the lubricating medium used during expansion will penetrate into the gap between the tube and the tubesheet, which will adversely affect the subsequent welding quality.
In view of the above problems, Krips et al. developed the hydraulic expansion technology in the late 1970s. The technology has formed two divergences, one is the O-ring method, the other is the liquid bag expansion technology. With the O-ring method, an O-ring is set at both ends of the mandrel to seal the expansion medium. The expansion pressure is directly applied to the surface of the heat exchange tube through the central hole of the mandrel, so that the heat exchange tube is plastically deformed and connected with the tube sheet. The O-Ring method developed by Krips et al. Due to the poor dimensional accuracy of domestic heat exchange tubes, the deviation of tube wall thickness can reach ± 10%. The overseas O-ring expansion technology cannot expand the domestic heat exchange tubes, and the cost of imported high-precision heat exchange tubes is too high, which limits the promotion of this technology in China. The liquid bag type hydraulic expansion technology uses elastic hydraulic bags to isolate the expansion medium from the heat exchange tube, and the expansion pressure acts on the inner wall of the heat exchange tube through the liquid bag, thus avoiding the pollution of the pipe orifice caused by the O-ring expansion technology in the expansion process.
In view of the large size deviation of domestic heat exchange tubes, the domestic liquid bag type hydraulic expansion technology has absorbed foreign technology and continuously innovated to develop a new generation of hydraulic expansion machine suitable for China's national conditions, which has been widely used in the manufacture of heat exchangers in petrochemical, electric power, boiler, nuclear power, refrigeration and other fields.