Copper pipe also known as Red Copper Pipe. A type of Non-ferrous metal, which is a pressed and drawn seamless tube. Copper pipe has good electrical conductivity, thermal conductivity of the characteristics of electronic products as well as conductive parts and heat dissipation parts of the main materials, and become the modern contractor in all residential commercial housing water pipes, heating, cooling pipe installation of the first choice. Copper pipe corrosion resistance is strong, not easy to oxidation, and with some liquid substances not easy to chemical reaction, easy to Wei bend shape.

Copper pipe also known as red copper pipe is pressed and drawn seamless pipe. Copper Pipe light weight, good thermal conductivity, High low-temperature strength. Commonly used in the manufacture of heat transfer equipment (such as condensers) . It is also used for assembling low temperature piping in oxygen generating equipment. Small-diameter copper tubes are often used for conveying pressurized liquids (such as lubricating systems, oil pressure systems, etc.) and as pressure measuring tubes for instruments. Copper pipe is the modern contractor in all residential commercial housing water pipes, heating, cooling pipe installation preferred.

(1)Because copper pipe is easy to be machined and connected, it can save material and total cost, has good stability and reliability, and can be saved maintenance.

(2)Copper is lightweight. Copper tubes do not require the thickness of the Ferrous for the same inside diameter of the tube. When installed, copper pipes are less costly to transport, easier to maintain, and take up less space.

(3)Copper can change shape. Because copper tubes can be bent and deformed, they can often be made into bends and joints. Smooth bending allows the tubes to be bent at any angle.

(4)Copper is easy to connect. 

(5) Copper is safe. No leakage, no combustion, no toxic gas, corrosion 

resistance.

1.Selection of solder

Copper Tube is an important raw material for refrigeration equipment. It has two main uses: 1 making heat exchanger. Such as commonly used evaporator, condenser, commonly known as "two devices" , 2 production connection pipes and fittings. The 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.

1.1 welding of similar materials

(1) the brazing of copper to copper can be done with copper-phosphor solder or copper-phosphor solder with low silver content. This solder is cheaper and has good melt.

(2) for steel-to-steel welding, brass rod solders and appropriate fluxes can be used. When welding, the solders are heated to a certain temperature and inserted into the fluxes, so that the fluxes are melted and attached to the fluxes, but after welding must be near the residual flux brush clean, in order to prevent corrosion.

1.22 welding of different materials

(1) silver-copper solders and appropriate fluxes may be used for copper-to-steel or copper-to-aluminum welds. Residual fluxes near the welds 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) copper and iron can be welded with phosphor copper solder or brass rod solder, but the corresponding flux, such as a mixture of Borax, boric acid or boric acid, is also required.

2.Welding operation

The welding torch size and flame temperature are different for welding different materials and different pipe diameters. The flame size can be adjusted by two needle valves, flame adjustment is based on oxygen, acetylene gas volume ratio can be divided into carbonization flame, neutral flame and oxidation flame three.

2.1 types and characteristics of flame

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

 (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 welding torch determines the diameter of the flame core, while the flow rate of the mixed gas determines the length of the flame core, and the flame of the neutral flame is divided into three layers.) The flame core is tapered, white and bright, the inner flame is blue and white, the outer flame gradually changes from lavender to orange and blue from inside to outside, the temperature is about 3000 ~ 3500 °C, and the volume ratio of oxygen and acetylene is 1:1.2. Refrigeration and air-conditioning pipe welding more use of neutral flame.

 (3) oxidation flame, its characteristic is the flame core is conical,) , the length is obviously shortened, the outline is not clear, the color is dim, the outer flame is also shortened, the flame is blue, the flame combustion is accompanied by the sound, the sound size depends on the oxygen pressure, the oxidation flame temperature is higher than the neutral flame, is suitable for the 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 selection of use.

2.2 adjustment of flame

Before ignition, 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 ~ 0.5 MPA, and the indication of the acetylene pressure 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 oxygen and acetylene gas into the torch mixture ratio, so as to get different flame.

2.3 welding

When welding, should carry on the operation strictly according to the step, otherwise, will affect the welding quality. 

(1) the surface of the pipe to be welded shall be clean or flared. The flared end shall be smooth, round, without burrs or 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. 

(2) overlap and insert the copper tubes to be welded into each other (pay attention to the size) and align the centers of the tubes.

 (3) when welding, the parts to be welded must be preheated. When the copper pipe is heated to Fuchsia, the silver electrode is used for welding. Remove the flame and place the solder against the weld. Melt the solder and flow it into the welded copper. The temperature after heating can reflect the temperature by color. 

(4) it is best to use a strong flame rapid welding, as far as possible to shorten the welding time, in order to prevent the formation of excessive oxides in the pipeline. With the flow surface of the refrigerant oxide will cause dirty plug, or even make the compressor suffered serious damage. 

(5) when welding, when the solder is not fully solidified, must not shake or vibration copper pipe, otherwise the welding part will produce cracks and lead to leakage. (6) for refrigeration systems filled with R12, no welding shall be carried out without exhausting the R12 refrigerant, and no welding repair shall be carried out while the refrigeration system is still leaking, so as to prevent the R12 refrigerant from being exposed to open flame to produce toxic phosgene, poison the body.

3.Welding method of workpiece

3.1 phase diameter pipe welding, the refrigeration system for the same diameter of copper pipe welding, the use of casing welding. The welded pipe is expanded into a cup or a bell mouth, and another pipe is inserted. If the insert is too short, not only the strength and tightness will be affected, but also the flux will easily flow into the pipeline, causing pollution or blockage. If the gap between the inside and outside pipes is too small, the flux can not flow into the containment surface and can only be welded on the outside of the joint, then the strength will be very poor, if the fit clearance is too large, the flux will easily flow into the pipe, causing pollution or blockage. At the same time, it will cause leakage due to insufficient flux filling in the weld, which is not only of poor quality, and it's a waste of material. Therefore, it is very important to choose the appropriate insertion length and the gap between the two tubes. The reasonable size of the socket welding can be referred to table 2. 

3.2 welding of capillaries to copper tubes; welding of capillaries (throttling capillaries) to repair dry filters in refrigeration systems. When the capillary is welded with the dry filter or other pipes, the capillary heat capacity is very small because of the big difference between the two kinds of pipe diameters. In order to prevent the capillary tube from overheating, the gas welding flame should avoid the capillary tube and make it reach the welding temperature at the same time as the thick tube. A metal clip can also be used to hold a thick piece of copper on a capillary tube, so that the heat dissipation area can be appropriately increased to avoid superheating. 

3.3 for the welding of capillary and dry filter, the inserting depth of capillary should be controlled in the first 5 ~ 15mm, the inserting end of capillary and dry filter should be 5mm away from the end of filter screen, and the fit gap should be 0.06 ~ 0.15mm, as shown in Fig. 2. The tip of the capillary is preferably horseshoe-shaped at a 45 ° angle to prevent particles of impurities from sticking to the tip and clogging it. When the diameter difference between the two kinds of pipe, can also be used to dry filter forceps or pliers will be compressed outside the pipe, but can not be compressed (dead) capillary. The capillary tube is first inserted into the copper tube, and is compressed with a pipe clamp 10 mm from the end of the thick tube.

3.4 when the refrigerant tube is welded to the compressor tube, the depth of the refrigerant tube inserted into the tube must be 10mm. If the depth is less than 10mm, the refrigerant tube will easily move outward when heated, causing the flux to block the tube mouth. Welding Quality Inspection, in order to ensure the absolute no leakage of welding parts, after welding, should carry out the necessary inspection. 

(1) check whether the sealing performance of the welding place is good. After adding refrigerants or nitrogen to be stabilized for a certain time, it can be tested with soapy water or other methods. 

(2) in the refrigeration and air-conditioning operation, can not have because of vibration and welding crack (seam) phenomenon. 

(3) the pipeline should not be blocked by sundries during welding, nor should it be operated improperly to enter moisture.

 (4) the surface of the welding part should be clean and free of oil contamination when working on refrigeration and air conditioning. To sum up, in the process of copper pipe welding, if the operation is not appropriate, the defects such as virtual welding, melting and piercing, over-burning and burning through will easily occur.

 Source: maintenance