1. In the process of manufacture, installation and maintenance, the welding of pipeline is a key link in the refrigeration system of refrigeration and air conditioning, which is usually made of copper, aluminum and other Non-ferrous metal materials, more importantly, the impact on whether the system can work properly light problems, must cause great attention. 

2. The choice of solder refrigeration air-conditioning pipe is mostly copper (purple) pipe, commonly used solder types are copper phosphorus solder, silver copper solder, copper zinc solder and so on. In accordance with the characteristics of pipeline materials, the correct choice of solder and skilled operation to ensure the quality of welding. 2.1 welding of similar materials 

2.1.1 brazing of copper to copper may be done with phosphor copper solder or phosphor copper solder with low silver content, such as 2% or 5% silver-based solder. This solder is cheaper, has a good solution, uses caulking and wetting processes, and does not require flux.

 2.1.2 brass rod solders and appropriate fluxes can be used for copper-steel welding. When welding. After heating the solder to a certain temperature and inserting it into the flux, the flux will dissolve and adhere to the solder. But after welding, the residual flux near the weld must be cleaned with hot water or steam to prevent corrosion. It is best to use alcohol diluted in the use of welding flux into the surface of the weld, welding alcohol quickly evaporated to form a smooth film is not easy to lose, but also to avoid the danger of water immersion refrigeration system. 

2.2.2 phosphor copper solder or brass rod solder may be used for welding copper to iron, but a corresponding flux such as a mixture of Borax, boric acid or boric acid is also required. 

3. The size of the welding torch and the flame temperature are different when welding different materials and different pipe diameters. The flame size can be adjusted by two needle valves, flame adjustment according to oxygen, acetylene gas volume ratio can be divided into carbonization flame, neutral flame and oxidation flame three. 

3.1 types and characteristics of flame

3.1.1 the charring flame is characterized by the volume ratio of oxygen to acetylene less than 1, a little lack of oxygen, easy to bring carbon particles into the metal and affect the solder flow, smoke, the temperature is about 2700, can be used for the pipeline baking. 

3.1.2 the characteristic of the neutral flame is that the size of the flame core depends on the composition, consumption and flow rate of the combustion gas, the diameter of the nozzle hole of the torch determines the diameter of the flame core, and the flow rate of the mixed gas determines the length of the flame core, the flame of neutral flame is divided into three layers, the flame core is tapering, white and bright, the inner flame is blue-white, the outer flame gradually changes from lavender to orange and blue from inside to outside, and the temperature is about 3000 ~ 3500 °C, oxygen and acetylene gas volume ratio of 1:1.2 refrigeration air-conditioning pipe welding more use of neutral flame. 

3.1.3 the oxidation flame is characterized by the conical shape of the flame core, the obvious shortening of the flame length, the unclear outline, the dull colour and the shortening of the outer flame, the blue colour of the flame, and the sound produced when the flame is burning, the sound depends on the oxygen pressure, oxidation flame temperature is higher than the neutral flame, suitable for brass pipe welding. The nature of the flame is based on the type of metal being welded and its nature to choose, should pay attention to the scientific choice of use. 

3.2 before adjusting and igniting the flame, open the valves of the oxygen cylinder and the acetylene cylinder according to the operating rules, so that the indication of the low pressure oxygen meter is about 0.2ー0.5 MPA, and the indication of the acetylene meter is about 0.05 MPA. And then slightly open the oxygen valve of the torch. Then slightly open the torch on the Acetylene Valve, at the same time, from the back of the welding nozzle quickly ignition. Do not light the flame on the front of the nozzle to avoid flame-thrower. After ignition can be adjusted, the adjustment of the two valves is to adjust the proportion of oxygen and acetylene gas into the mixture of welding torch, so as to get different flame. 

3.3 welding should be carried out in strict accordance with the procedure, otherwise, will affect the quality of welding. 

3.3.1 preparation and Piping 

3.3.1.1 check the adequacy of the contents of oxygen and acetylene cylinders. 

3.3.1.2 check drawing requirements to ensure that all parts are complete and functional. 

3.3.1.4 ensure the pipeline light horizontal and vertical, pay attention to the direction of each valve.

 3.3.1.5 measure the length with tape measure according to the size and pipe diameter required on the drawing, and use the line marker several times. 

3.3.1.6 thicker copper pipe to be fixed, and then removed with a knife, to ensure that the cut level, not deformation. 

3.3.1.7 smooth the cut edges with a file and wipe with a cloth.

 3.3.1.8 the surface of the pipe to be welded shall be clean or flared. The flared mouth shall be smooth, round, without burrs and cracks, of uniform thickness. The joints of the copper pipe to be welded shall be cleaned with sandpaper and finally cleaned with a dry cloth. Otherwise, will affect the solder flow and welding quality. 

3.3.1.9 all fittings except copper and copper shall be cleaned with gauze or stainless steel wire brush before welding to reveal a bright metal surface. 

3.3.1.10 the copper tubes to be welded shall be placed on top of each other (pay attention to the dimensions) and shall be centered. 

3.3.1.11 the insertion depth and clearance of copper pipe joint and copper pipe are shown in table. (insert depth approximately equal to pipe diameter)

3.3.2 nitrogen-filled shielded welding

Above, there is no nitrogen protection

The above picture is filled with nitrogen to protect 

3.3.2.1 when welding should be welded pipe milk through low-speed nitrogen to prevent oxidation. 3.3.2.2 acetylene shall pass through the non-oxidizing welding generator to prevent oxidation of the outer surface of the welded object. 

3.3.3 copper pipe welding

3.3.3.1 when welding, the parts to be welded shall be preheated. When the copper pipe is heated to Fuchsia, remove the flame and place the solder against the welding joint. The solder will melt and flow into the welded copper. The temperature after heating can reflect the temperature through color, dark red: about 600 degrees Celsius; deep red: about 700 degrees Celsius; orange: about 1,000 degrees Celsius. 3.3.3.2 The gas welding flame shall not directly heat the electrode during welding. 3.3.3.3 protective measures shall be taken for parts which are easily deformed and damaged under high temperature conditions. If the angle valve, evaporator, condenser and so on must use the wet gauze to wrap the interface to carry on the welding again, regarding the solenoid valve, the expansion valve, the Liquid Mirror, the four-way valve, can disassemble must disassemble after the welding, can not disassemble the same take the above measure. 3.3.3.4 when the copper pipe is annealed after welding, the annealing temperature shall not be lower than 300 °C. 3.3.3.5 after welding, cool and clean the oxide and slag with dry nitrogen.

3.3.4 for dummy welding and Trachoma repair welding

3.3.4.1 in the process of pressure test found that welding leakage should be repair welding, repair welding to the system pressure test nitrogen release, after welding to re-test pressure. 3.3.4.2 repair weld the oxide layer on the front waist and wipe it off with Gauze. After repair welding, the oxide scale should be cleaned. After quenching in water, the copper pipe should be dried without water drops. 3.3.4.3 after all welds are completed, blow out the system with nitrogen gas. 

Source: The Web