Metal hose joint structure and brazing characteristics


Metal hoses are widely used in thermal power plants for […]

Metal hoses are widely used in thermal power plants for transportation of dry fuel oil, insulation oil, and turbine oil. Due to the high pressure and temperature of the medium conveyed by the hose. Therefore, if leakage or de-soldering occurs at the welding site, serious accidents will occur. There are two layers of inner and outer metal hoses. The inner layer is a small φφφ20 x 2mm hose. The outer layer is a woven fine steel wire mesh. The two layers are made of 1Cr18Ni9Ti. Among them, the hose mainly plays the role of sealing, and the fine steel wire mesh plays the role of strength protection. There are currently three types of hoses produced by the manufacturer (spiral integral, roll-welded and brazed). Due to the high temperature and pressure that the metal conveying hoses on the utility boilers are subjected to during operation, they are often subject to bending stress. Therefore, it is recommended to use spiral integral hoses. After the hose is delivered to the site, a short stainless steel pipe joint is installed in the hose, and a stainless steel outer ring is added to the thin steel wire and brazed. The brazed seam must ensure the tightness and pressure of the pipe during work. The brazing structure has the following characteristics: The shape of the wall of the brazing joint is more complex, including corrugated, fine steel mesh, etc., as shown in Figure 1. In order to ensure the tightness and bearing capacity of brazed joints, the quality of brazing is high, and it has sufficient stability in mass production. Due to the thin and thin corrugated hose and thin wire mesh, manual brazing with an oxyacetylene flame is extremely likely to cause overheating. If it exceeds 830 ° C, it will produce stable chromium and oxen oxide and will not be easily removed, making brazing almost impossible It is required to prevent oxidation during brazing. In the welding production practice, due to the influence of its special hooks and unpublished factors, it is often difficult to meet the design and process requirements by using oxygen-oxygen fast brazing. To properly solve this problem, we adopt a new arc brazing process. That is, when the arc welding of the melting electrode is performed under the protection of an inert gas, the arc is located between the workpiece and the melting electrode, and a protective gas surrounds the arc. The solder serves as an electrode for the arc.
The filler metal is continuously fed from the welding gun into the brazing area to form a brazing joint. Fused arc welding is characterized by a low melting point of the solder (2% ring silver solder has a melting point of 8600 ~ 900 ° C), high mechanical strength, and a small heat-affected zone. There is no need to use a flux that may cause corrosion during brazing. No cleaning is required after welding. The equipment is easy to operate. It is easy to realize automation.