Design Of Welding Equipment For Cu-Al Pipe Joint Used In Refrigeration Plant

Along with the improvement of living standard, people have found them more dependenton refrigeration plants such as refrigerator and air-condition in every way of life. Heatexchanger is the most important part and its performance directly influences the refrigerationeffect. It has large volume and usually takes up more than half weight of the whole plant.Thus to develop new recuperator with cramped construction and good thermal transmissionperformance is of special significance. In recent years, the tendency employing Al pipesinstead of Cu pipes has become popular in manufacture of evaporators and condensers.However, copper pipes are unsubstituted in some pipelines and how to join A1 pipes and Cupipes is to be solved. There are many problems when joining these two metals due to theirproperties. At the present time rosin joint and leakage are often detected in most weldingmethods employed in China. Thus a kind of welding equipment that solves the problemsduring welding of Cu-Al pipe with lower cost is needed urgently.The functional analysis approach was first employed to analyse the equipment, 8 betterdesign proposals were acquired using morphology matrix. Optimal proposal was confirmedby the fuzzy evaluation method. Ultimately a pneumatic upset butt welder with theapplication of PLC was designed exclusively used for Cu-Al joint of refrigeration plants inthis paper.On the basis of the weldabilities of Cu and Al, the butt joint style was designed for thepurpose of avoiding appearance of brittle eutectic. The butt welded electrode had beendesigned according to the physical characteristics of Cu and Al. Chromium-copper andchromium-zirconium-copper alloys were employed as electrode materials, semi-circle jawand hydrocooling were adopted in design of electrode. The clamp force and upset force were calculated in response to the yield strength of Al,accordingly the pneumatic system was contrived.The welding transformer was devised based on analysing the primary electric powersystem and operation system. Key parameters were: rated capacity P(50kVA); secondaryvoltage regulating stage number(16); secondary voltage regulating range(2～12V); loadpersistencerate(20%). Based on analysis of Cu-Al pipe welding process, the sequence chartwas designed. The CPU221 PLC of S7-200 series was preferred qua core control unit,ultimately the Cu-Al pipe welding process program was compiled.