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Technology of Brazing and Soldering

  • The brazing process procedure includes the following steps:
  • The surface treatment of T. parts, including degreasing, removing the scale of the crucible, and sometimes plating the various metals that are beneficial for brazing.Assembled and fixed to ensure the mutual position of the workpiece parts.
  • The most sturdy configuration of the solder and flux locations allows the liquid solder to achieve the optimum orientation in complex brazing seams.
  • When the brazing material is not flowing on the surface of the workpiece, sometimes black is coated with a flow-blocking agent on the base material to regulate the flow direction of the brazing material.
  • IK does choose the process parameters of brazing, including brazing temperature, heating rate, holding time after the completion of the brazing joint, cooling rate, and so on.
  • Washing after brazing to remove solder residue that may cause corrosion or deposits that affect the shape of the seam.
  • If necessary, the brazing joint is also post-weld coated along with the entire workpiece, such as plating with other inert metal protective layers, oxidation or passivation, painting, etc.
  • The above steps are different for different brazing base materials.

Joint Types and Flowability of Molten Filler Metal in the Clearance

  • Brazed joints come in a variety of forms, and general handbooks and books on Vacuum brazing furnace are designed and drawn in detail. To sum up, there are only three basic brazing seams for sheet or pipe: section-section brazing seams (such as butt joints), surface-surface brazing seams (such as lap joints), and section-surface brazing seams (such as T joints). The brazing seams are often not single.
  • The molten solder flows in a straight line in the brazing joint. If the nature and relationship of the brazing material and the base material are not considered, the function of the flux is not considered, and the capillary capacity of the brazing seam plays a large role. The capillary capacity is in turn related to the type of brazing seam and the size of the braze gap. In general, a brazed joint having a small gap is more fluid than a straight seam having a large gap. However, it is not as small as possible, and the optimum value of the gap of the brazing seam is between 0.01 and 0.2 mm, and the specific value depends on the type of the base material. A larger brazed surface (larger overlap area) will have better bearing capacity.
  • The rolled sheet and the drawn tubing and the bar have quite different cross-sectional structures and surface textures. The cross-section structure of the rolled sheet is relatively loose and the grain boundary is clear; the surface structure of the rolled or drawn material is dense and smooth, and the grain is stressed and the grain boundary is tight. The degree of dissolution and infiltration of the brazing filler metal during brazing is significantly greater than the degree of dissolution and infiltration of the surface. 1 The flow of the brazing material in the surface-surface brazing seam is better than that in the cross-section brazing seam. The latter sometimes sees the mother’s brazing material spreading to the surface of the parent metal around the brazing seam without snagging. This is the case with a flat joint, and it is often impossible to form a joint with a corner.
  • Figure 1-27 shows several types of indium of the brazed joint. Figure l-27a shows the butt joint, that is, the section-section joint. This long-lasting brazing process + wei, the joint strength is also the worst, the advantage is that a smoother brazing surface can be obtained. This type of connection is rarely used except for the excellent bonding properties of the brazing filler metal and the base metal and the special needs.
  • In the usual sense of lap joints (see Figure 1-2b), it is not just a simple surface-spinning indium-structured braze joint. After the brazed joint is formed, it is obvious that there is a cross-section structure; rfD’T In addition to the section-surface indium brazed joint, it also has a surface-surface type structure; the pure surface-surface type joint is only 6 and 〖 in Figure 1-27; -27d also has the possibility of forming a cross-sectional type structure on the back side of the brazing seam.
  • The surface-surface joint has a large lap joint, which has a large bearing capacity; however, due to the large cross-sectional area of ​​the weld joint, the irregular flow of the molten solder often causes slag inclusion or void in the weld joint. In many cases, the brazing method is carried out by sandwiching the brazing foil into the brazing seam. The joint of Fig. l-27c has a relatively small fracture line of the brazing seam, and has a cross-section-surface and surface-surface mixing structure, which is the strongest capillary action in the brazing joint, and the nail material has the strongest flow capacity in the brazing joint. . The brazing material has an automatic slagging action when the K distance flows in the sew seam, and the joint has the best air tightness.
  • The combination or deformation combination of the basic types in Figure \-21 can evolve a variety of joints, for example, the flange joint of the tube and the plate is the deformation combination of Figure 1-27c; the sandwich structure or the honeycomb structure is the deformation of Figure 1-27e Combinations, etc.

Methods for Heating

  • Any heat source that allows the workpiece to heat up under certain conditions can be used for heating during brazing. For example, flame heating, salt bath heating, gold W bath heating, resistance heating, induction heating, electric furnace heating, gas phase heating, infrared heating, laser heating, etc. U flame heating is the use of combustible gas (including liquid fuel vapor) to blow air or pure The flame after the ignition of oxygen is heated. Its heating temperature range is very wide, from the number of sprinklers to more than 3000t of oxyacetylene flames; The flame has a two-layer structure, and the outer blue light crown flame is an oxidizing flame. The combustion is the same, the temperature is the most turbulent, and the oxygen is rich. The excessive heating tends to oxidize the metal surface of the workpiece; the inner dark blue flame is the reducing flame, the temperature. Low, oxygen-deficient, carbon monoxide-rich, protects metals from oxidation. The excessively hypoxic flame is yellow, rich in free particulate carbon, and the metal alloy that is prone to carburization avoids this flame heating. The combustible gas combustion products are both CO 2 and high-temperature steam (hydrogen-oxygen flame only water vapor), and both the flux and the brazing material should be fully considered.
  • Salt bath heating is often referred to as salt bath brazing 13211286 [~. In fact, it uses molten flux as a heating medium. Under constant temperature control, the workpiece with the brazing material is immersed in a tank filled with molten flux, and the brazing material is melted to complete the brazing. The biggest advantage of this method is that due to the large heat capacity of the salt tip, the workpiece heating rate is extremely fast and the heating is very uniform, especially the brazing temperature can be precisely controlled, and sometimes even lower than the solid phase of the parent metal. Brazing under conditions u In addition to the special case, no additional flux is required. The disadvantage is that the residual flux on the post-weld cleaning workpiece is very troublesome, and the salt bath vapor and waste water are likely to cause pollution and the power consumption is also very high.
  • Metal bath heating actually uses the molten solder as a heating medium. After the constant temperature control, the assembled workpiece is coated with the flux, and the liquid tank of the molten solder is immersed to complete the brazing. The biggest advantage of this method is the ability to complete the brazing of multiple and complex brazing seams for large children at once. The disadvantage is that the surface of the T-piece will be completely filled with solder unless it is treated as a solder mask. Some radiators in the industry, such as brazing of heat exchangers in domestic water heaters, and wave soldering in the electronics industry, are examples of this type.
  • Resistance heating [2>1126< is the use of current through the brazed joint to generate heat to melt the solder. This type of joint requires tight assembly and pressure to allow current to pass. The advantage is that the temperature rises extremely fast; the disadvantage is that it is difficult to apply to joints of complex shapes.
  • Induction heating ~ is the use of high frequency or medium frequency induction current heating, the power output by the high frequency or intermediate frequency generator, through a well matched induction coil to the workpiece for heating. This heating method is different from all heating methods. Instead of the environment or medium transferring heat to the workpiece, the induction coil transmits island frequency or power frequency power to the metal workpiece, and the eddy current induced in the workpiece generates heat. It can be said that the solder is melted and spread by the method of heating the workpiece and the body. The main difficulty of induction brazing is the matching between the design of the induction coil (the copper tube coil of the internal cooling water) and the energy transmission between the workpieces. The advantage of induction brazing is that the energy transmission can be concentrated and the temperature rises extremely quickly, and the local joint can be brazed on a large system.
  • Electric furnace heating, commonly referred to as furnace brazing. This is the most widely used brazing method in which the furnace is heated by a resistance wire or other heating element to allow the workpiece to be brazed and heated. The furnace can be designed in various forms 1151 and can be supplied with an inert gas or other reactive gas to form a gas shielded braze or a gas flux braze. It can be made into a gas-tight furnace and brazed under vacuum conditions. It can also be used as a tunnel kiln with atmosphere protection and continuous brazing. Other heating methods, such as gas phase heating (steaming head method) , infrared heating (infrared heat source) Focusing on solder joints and laser heating with reflective condensers, these methods are mostly used for soft soldering in the electronics industry.