The sealing surface of steel valves, as the key to the performance of the valve, is of vital importance in the manufacturing process. In order to enhance the performance of the sealing surface, the surfacing technology is usually used. Surfacing material according to the type of alloy is mainly divided into cobalt-based alloys, nickel-based alloys, iron-based alloys and copper-based alloys four categories. These alloy materials are processed into electrodes, wires (including flux-cored wire), flux (including transition alloy flux) and alloy powder and other forms, and through a variety of welding methods, such as manual arc welding, oxyacetylene welding, tungsten argon arc welding, submerged arc welding and plasma arc welding, etc., is accurately surfaced on the valve sealing surface.
When selecting the valve sealing surface surfacing material, a number of factors need to be considered. First of all, the use of the valve temperature, working pressure and corrosiveness of the medium is an important factor that can not be ignored. Secondly, the type of valve, the sealing surface of the structure of the form, sealing pressure and allowable specific pressure will also affect the choice of surfacing material. In addition, the enterprise’s manufacturing conditions, equipment processing capabilities, surfacing technology capabilities and the specific needs of users are also decisive factors. In order to meet the premise of the valve performance, priority should be given to the lower price, simpler production process, higher production efficiency of the sealing surface material.
It is worth noting that some surfacing materials have only one form, such as electrodes or wires or alloy powder, and therefore can only use a specific surfacing method. While some materials have a variety of forms, such as stellite l 6 alloy, both electrode (D802), and welding wire (HS111) and alloy powder (PT2102), and therefore can be used in a variety of cladding methods. In the choice of surfacing materials, enterprises should combine their own technical maturity, process complexity and production efficiency, choose the most suitable surfacing method to ensure the use of sealing surface performance.
The quality of the sealing surface is directly related to the service life of the valve. Therefore, a reasonable choice of valve sealing surface material is an important way to improve the life of the valve. However, in the selection process, some misunderstandings need to be avoided.
Myth 1: that the higher the hardness of the valve sealing surface material, the better the wear resistance. In fact, the wear resistance of the material is mainly determined by the structure of its metal organization. Some metal materials, although the hardness is not high, but wear resistance is very good. Valve sealing surface requires a certain high hardness, mainly to avoid being gasketed or scratched by hard debris in the medium. Comprehensive consideration, the hardness value between HRC35 ~ 45 is more appropriate.
Myth 2: that the higher the price of the valve sealing surface material, the better the performance. The price of the material and its commodity characteristics, while the use of performance depends on its physical properties. The two are not necessarily linked. For example, cobalt-based alloys due to cobalt metal from imports, the price is higher. But cobalt-based alloys are characterized by good wear resistance at high temperatures, if used at room temperature or medium temperature conditions, the price and performance ratio is relatively high. Therefore, in the selection of valve sealing surface materials, should give priority to the price and performance ratio of lower materials.
Myth 3: that the valve sealing surface materials in a strong corrosive media show good corrosion resistance, must be suitable for other corrosive media. Corrosion resistance of metal materials has a complex mechanism. A material in a strong corrosive medium may show good corrosion resistance, but a slight change in conditions (such as temperature or media concentration, etc.), its corrosion resistance may change. For another corrosive medium, the change in corrosion resistance may be greater. Therefore, the corrosion resistance of metallic materials can only be known experimentally. When drawing on relevant information, it is necessary to understand the relevant conditions, do not blindly follow the trend.
In summary, steel valve sealing surface surfacing technology is a complex and delicate process. Reasonable choice of surfacing material and surfacing method, avoid selection of the wrong area, is to ensure that the valve performance and service life of the key.
Steel valve sealing surface surfacing technology analysis
