Brazing is the use of lower melting point than the base material brazing material and the base material is heated together, in the case of the base material does not melt, the brazing material melted wetting and filling into the gap between the two base materials at the joints, the formation of brazing seams, in the gap, brazing material and the base material of each other to dissolve and diffuse, so as to get a solid combination.
Copper pipe brazing is the copper pipe, copper pipe fittings and melting point lower than copper copper phosphorus brazing material or tin brazing material together with heating, in the case of copper pipe, copper pipe fittings do not melt, heated to the brazing material melting, and then make the melted brazing material to fill into the gap of the socket, the cooling crystals to form brazing seams, and become a solid joint. Copper pipe brazing, socket gap is small, brazing material through the capillary effect to enter the brazing gap, and the capillary effect can only be formed when the liquid brazing material can wet the copper surface, otherwise the liquid brazing material will be under the action of surface tension, agglomeration into a ball, that is, the formation of the phenomenon of non-wetting. Therefore, the wetting of liquid brazing material on the copper surface is the key to whether the brazing material can flow into the brazing seam and fill the brazing seam. Practical experience tells us that the factors affecting the wetting of brazing material on copper surface are firstly the composition of brazing material and secondly the oxides on copper surface. Today's copper-phosphorus brazing material and tin brazing material on copper have quite good wettability, therefore, copper surface oxides are the main factors affecting the wetting, copper surface oxides will prevent the brazing material atoms and copper direct contact, so that the liquid brazing material on the surface of the formation of the copper surface does not wet, so copper pipe brazing, must remove the copper pipe and copper pipe parts brazing surface oxides, including oxides generated in the brazing process in order to So that the brazing material on the copper surface to maintain the necessary wettability, commonly used method is, brazing before the mechanical method to remove the oxides of the welding surface, and then choose the appropriate brazing agent to effectively remove the oxides generated in the brazing process. The above described as a simple principle of copper pipe brazing, as long as the brazing principle according to the requirements of the implementation of brazing, copper pipe brazing quality is guaranteed. Facts have proved that the copper pipe brazing technology is simple and convenient, a little construction experience in construction personnel, as long as the short-term training, you can master the copper pipe brazing skills.
Two, copper pipe brazing methods
1, copper pipe copper-phosphorus brazing
Copper pipe copper-phosphorus brazing belongs to the hard brazing, joints to a high degree of good temperature resistance, suitable for a variety of media, large and small-diameter copper pipe brazing connection, but due to the copper-phosphorus brazing material melting point of 710 ℃ or more, containing 5% of the silver of the low-silver copper-phosphorus brazing material melting point is also in the 640 ℃ or more, the brazing temperature is high, it must be used oxygen-acetylene flame or a flame of the same type. Oxygen - acetylene flame or oxygen - propane flame must be used as a heat source to meet the needs of brazing temperature and thermal power, especially when brazing large caliber copper pipe, but also need to be equipped with two gas torch, by two operators at the same time to heat, in order to control the heating temperature of the joints and joints in the ring direction and the length of the temperature uniformity, so that the melted brazing material uniformity. The melted brazing material evenly fill the brazing seam to ensure the quality of brazing.
Copper pipe brazing with copper-phosphorus brazing, not only the brazing material on the copper pipe and fittings with quite good wettability, and brazing material in the phosphorus can effectively remove the oxides produced in the process of brazing, so that the brazing material is always on the surface of the copper with sufficient wettability, so the brazing of copper and copper fittings brazing, just brazing before the brazing of the copper pipe and fittings brazing surface of dirt and oxides to remove, can be assembled directly to brazing, no need to add brazing agent. Add brazing agent, simple and convenient operation. Only when the copper pipe and brass fittings brazing, only need to brush or add brazing flux in the brass side, in order to remove the zinc oxide produced by the brass side, so that the brazing material on the brass surface to maintain the necessary wettability, to ensure the quality of brazing.
Copper tube brazing with low-silver copper-phosphorus brazing material brazing and silver-free copper-phosphorus brazing material brazing compared with the brazing temperature is low, brazing material fluidity is good, the quality of the easier to control and so on, so that the brazing operation is more convenient, higher efficacy. Although the cost of brazing material will be slightly increased, but the improvement of quality and efficacy reduces the labor consumption, the overall cost of the project has little impact, especially in the small diameter copper pipe brazing with low silver copper phosphorus brazing material is more reasonable.
2, copper tube tin brazing
Copper tube tin brazing belongs to the lower brazing temperature of soft brazing, tin brazing material melting point are below 300 ℃, heating is convenient, but the joints of the brazing strength is low, and temperature resistance is poor, mainly used for φ2 ″ below the water as the medium of the copper tube.
Tin brazing can be used oxygen-acetylene flame or oxygen-propane flame as a heat source, can also be used propane-air flame or electric heating as a heat source, can meet the requirements of tin brazing temperature and thermal power.
Copper tube using tin brazing, although the tin brazing material has a good wetting of copper, but the copper surface oxides will prevent the tin brazing material atoms and copper direct contact, that is, the formation of the surface of the copper is not wetting. Therefore, tin brazing, not only the brazing surface of copper pipes and fittings need to be soldered to remove the dirt and oxides very clean, but also must add brazing flux to remove the oxides generated in the brazing process. Tin brazing compared with copper-phosphorus brazing, the biggest difference in addition to different brazing temperatures, mainly tin brazing material on the surface of the wetting of the copper surface as well as the combination of the surface of the copper, must be completed by the brazing agent to collaborate, that is, there must be a brazing agent in the front of the flow to remove the brazing surface oxides, tin brazing material in the back of the surface of the copper in a timely manner with the completion of the clean brazing connection with mutual solubility and diffusion, or else, the tin brazing material with the surface of the copper to see the formation of pseudo-welding. Therefore, tin brazing, although the brazing temperature is low, easy to heat, but the brazing surface of the cleanliness requirements are higher, the operator's skills, i.e., the operation of proficiency and temperature control ability to require more stringent.
Tin brazing of copper tubes currently has two connection methods, one is the use of conventional socket copper fittings, brazing by the operator from the outside of the tube to add brazing material to fill the gap to form a brazed joint. Another is the use of special copper fittings with brazing material ring, the fittings in the production, in the fittings at the mouth of the inner side of the press has a ring-shaped groove, and in the groove casting and fittings flush with the inner wall of the brazing material, brazing, the operator does not need to add brazing material, as long as the docking implementation of the heating to be the fittings in the groove of the brazing material to be dissolved to fill in the joints gap, the formation of brazed joints. Copper tube tin brazing should be used lead-free tin brazing material to prevent contamination of water quality, and shall not use the copper corrosion of ammonia-containing brazing agent.
Three, copper pipe brazing procedure
1, the outer surface of the copper pipe joints and fittings joints of the inner surface of the oxide film clean.
2, in the clean tube outer surface and the inner surface of the fittings evenly coated with paste or liquid brazing flux, using copper-phosphorus brazing material or low-silver copper-phosphorus brazing material brazing copper and copper tubes and copper pipe fittings can not be coated with brazing flux.
3, insert the copper tube into the pipe fittings, inserted to the end and rotate appropriately to maintain a uniform gap, if coated with brazing flux, should be extruded out of the seams of the excess brazing flux with a clean rag to wipe away.
4, with a gas flame on the joint to implement uniform heating, until heated to the brazing temperature, tin brazing, can also be used to heat the joint to the brazing temperature of electric heating.
5, with the brazing material contact was heated to a high temperature of the joint, in order to determine the temperature of the joint, if the brazing material does not melt, said that the temperature of the joint has not yet reached the brazing temperature, need to continue to heat the joint, if the brazing material can be quickly melted, said that the temperature of the joint has reached the brazing temperature, you can continue to heat the joint in order to maintain the joint at the brazing temperature of the joint above the side of the joint to the gap to add the brazing material, using the joint to add the brazing material, using the gas flame to implement uniform heating until heated to brazing temperature. Brazing material, the use of heat at the joint will be melted into the gap, until the brazing seam filled, do not use the flame directly melted brazing material coated on the surface of the gap.
6, remove the heat source, stop heating, so that the joint in a stationary state cooling crystallization, to prevent the molten brazing material cooling crystallization by vibration and affect the quality of brazing.
7, will brazing joints at the residue clean up, if necessary, can be painted varnish protection.
In short, thin-walled copper pipe brazing connection is a mature connection process, easy to operate, reliable quality, and suitable for buried laying. Therefore, in the copper pipe project, brazing connection is the most commonly used connection method. With the rapid development of the application of thin-walled copper pipe, suitable for different occasions of different needs of the copper pipe connection method is also increasing. For example: small-diameter copper pipe connection has a ferrule connection, there is a clamp connection, there is a plug connection, large-diameter copper pipe connection has a copper flange connection, there is a loose set of flange connection, there is a groove connection and so on. I believe that these connection methods will be the same as the brazing connection method, in the copper pipe project to get due application.
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