Selección de materiales y métodos de soldadura para el revestimiento de superficies de sellado de válvulas
What is surfacing?
Surfacing belongs to the metal crystal combination of welding process methods, with the general characteristics of welding methods, but also has its special characteristics. Válvula sealing surface surfacing cemented carbide enhances the sealing surface of the valve sealing surface to prevent leakage to extend the service life. The advantage of surfacing is that it can give full play to the performance advantages of the metal material, save material, and extend the service life of the parts. Valve sealing surface surfacing carbide process of the physical nature, metallurgical process, and the law of the thermal process is similar to the general welding process.
Common valve sealing surface surfacing carbide methods
The sealing surface of steel valves are generally manufactured by surfacing. Metal materials used for valve surfacing according to the type of alloy are divided into four categories: cobalt-based, nickel-based, iron-based, and copper-based alloys. These alloy materials are made of electrodes, wires (including flux-cored wire), flux (including transition alloy-type flux) and alloy powder, etc., using manual arc welding, oxyacetylene flame welding, tungsten argon arc welding, submerged arc welding, and plasma arc welding and other methods of surfacing.
Selection of valve sealing surface surfacing material is generally based on the use of the valve temperature, working pressure, and corrosiveness of the medium, or the type of valve, sealing surface structure, sealing pressure and permissible pressure, or enterprise manufacturing conditions, equipment processing capacity and surfacing technology capacity and user requirements. It should also be used to optimize the design to meet the valve’s performance under the conditions, the choice of low price, simple production process, and high production efficiency of the sealing surface materials.
For valve sealing surface surfacing materials have only one form, or electrode or wire or alloy powder, and thus can only use a surfacing method. Some are made of electrode, wire, or alloy powder in multiple forms, such as stellitel 6 alloy, both electrode (D802), and wire (HS111) and alloy powder (PT2102), can be used manual arc welding, oxygen 2 acetylene flame welding, tungsten argon arc welding, wire plasma arc welding and powder plasma arc welding and other methods of surfacing. The choice of valve sealing surface surfacing material should consider the choice of the enterprise technology as a mature, simple process, high production efficiency surfacing method to ensure the realization of the sealing surface surfacing manufacturing performance.
Common valve sealing surface surfacing carbide methods are:
General fusion welding methods can be used for surfacing. According to the realization of the surfacing conditions, the valve sealing surface surfacing carbide method of welding rod arc surfacing, oxy-acetylene flame surfacing, submerged arc surfacing, gas shielded surfacing, plasma arc surfacing, and so on. Let’s take a look at the advantages and disadvantages of each of these surfacing methods.
Welding rod arc cladding
Welding electrode arc welding equipment is simple, easy to operate, suitable for on-site surfacing, adaptable, not subject to the limitations of the surfacing position and shape of the workpiece, can be surfaced in any position, and small or irregularly shaped parts are particularly suitable. With the development of welding materials and process improvement, the electrode arc welding application range is constantly expanding. Such as the application of welding rod arc melting self-melting alloy powder can obtain a shallow depth of fusion, surface flatness, and excellent performance of the surfacing layer. Valve sealing surface surfacing carbide using electrode arc welding is very common. The disadvantage of electrode arc surfacing is low productivity, high dilution rate, difficulty obtaining a thin and uniform surfacing layer, and poor production conditions.
Oxy-acetylene flame cladding
Oxygen-acetylene flame surfacing at low temperatures can get a small dilution rate, the surfacing layer surface is smooth and good quality, and are the current wear-resistant occasions mechanical parts surfacing commonly used process methods, valve sealing surface surfacing carbide is also often used to this method. Such as oxygen – oxygen-acetylene flame surfacing ironmaking industry blast furnace charge bell can make life 3 times. Oxygen-acetylene flame cladding is generally used for smooth surfaces with minimal trimming.
Submerged Arc Surfacing
Submerged Arc Surfacing is the process of covering the surfacing area with a layer of flux to ignite an electric arc between the surfacing workpiece and the welding wire. The surfacing workpiece, wire, and flux in the high temperature of the surfacing arc are partially melted in the flux layer under the formation of a closed cavity, and the arc burns in the cavity. In the cavity covered with melted flux layer shell, so that the cladding weld pool is isolated from the atmosphere, the formation of a good appearance of the cladding layer metal. Submerged arc surfacing is highly efficient, suitable for automated production, and is particularly suitable for large-area surfacing of vessel linings, etc. In addition to the use of wire, it can also be used with pole-submerged arc surfacing to improve the efficiency of surfacing.
Gas Shielded Surfacing
Gas-shielded surfacing can be done manually, automatically, or semi-automatically. According to the electrode used, the gas shielded surfacing can be divided into melting electrode gas shielded surfacing and non-melting electrode gas shielded surfacing. The heat of fusion electrode gas shielded surfacing is generated by the arc between the welding wire and the workpiece as one of the electrodes and the melting of the wire; non-melting electrode gas shielded surfacing is generated between the electrode and the weldment, and the heat of the arc melts the filler wire and the base metal, forming a molten pool of surfacing. According to the type of protective gas, gas shielded surfacing can be divided into CO2 gas shielded surfacing, argon shielded surfacing, and mixed gas shielded surfacing.
Gas shielded surfacing due to the protection of protective gases, to avoid the intrusion of air and impurity contamination, high quality surfacing, high deposition efficiency, and small heat-affected zone. Gas shielded surfacing belongs to open arc welding, can be observed in the welding surfacing layer, and can realize all-position welding, especially for alloy steel and special alloy surfacing.
Plasma Arc Surfacing
Plasma arc welding uses high-temperature plasma arc heating, a melting surfacing method, plasma arc heat concentration, temperature is very high, the center of the arc column temperature of 24000K or more. Therefore, plasma arc surfacing has a series of advantages, such as good performance of the surfacing layer, high bonding strength, good densification of the surfacing layer, controllable depth of the workpiece, low dilution rate of the surfacing layer, forming rules, and easy to realize mechanization and automation, manual operation is also relatively convenient. It is a very promising surfacing process.
Electroslag welding uses resistance heat to melt the cladding material and the base metal to form a molten pool of cladding method. Electroslag Surfacing can surface a large thickness at a time, have high deposition efficiency, and use solid wire, tubular wire, plate pole belt pole, etc., for surfacing. Electroslag surfacing is suitable for surfacing large-thickness surface shapes of simple large and medium-sized parts. However, the overheating in the surfacing process is serious, and the workpiece has to be heat-treated after surfacing.
Vibratory Arc Surfacing
Vibratory arc surfacing is a continuous vibration surfacing method using a fine wire to ensure the stability of the surfacing process under a small current. The parts are subjected to less heat; the small heat-affected zone can obtain a thin, flat, high-hardness surfacing alloy layer. Mechanical parts repair has been widely used, especially in automobiles, and tractor repair is more widely used. However, vibration arc surfacing has low productivity, general wear resistance of the surfacing layer, and low fatigue resistance of the repaired parts, for the repair of important parts is subject to certain restrictions.
High-frequency induction surfacing
High-frequency induction surfacing is a high-frequency current heating melts the surfacing material and the formation of the surfacing layer method. In high-frequency welding, the heating temperature is slightly higher than the melting temperature of the cladding material and lower than the melting temperature of the base metal. This can make the parts less heat and small deformation and make the cladding alloy and the base metal obtain a good metallurgical combination. High-frequency induction surfacing is easy to operate, has a shallow depth of melting, high productivity, and the thickness of the surfacing layer of 0.1 – 2mm in the wear-resistant mechanical parts of the occasion is widely used.
Laser cladding can achieve accurate control of heat input, thermal deformation is small, the chemical composition of the cladding metal and dilution rate is easy to control, and you can get a dense organization with good performance of the cladding layer. E-beam surfacing has high energy utilization, up to 30% or more, the heating of the substrate is not affected by the metal vapor, and the mechanical molten metal cooling speed is fast. The surfacing layer has good abrasion resistance, but the one-time investment in laser and electron beam surfacing equipment is large, the operating costs are high, and the efficiency is slow.
For valves working under high temperature and high-pressure conditions, the working conditions of the sealing surface are quite harsh, so the performance of the sealing surface has high requirements. Cemented carbide is the most commonly used material for surfacing valve sealing surfaces due to its excellent performance of high hardness, corrosion resistance, and high-pressure resistance. Through the above introduction of several surfacing methods, choose the appropriate way to surface according to the product characteristics.
Wrong area in the selection of valve sealing surface material
The sealing surface is the key part of the valve; its quality directly affects the valve’s service life. Reasonable choice of valve sealing surface material to improve the valve’s service life is one of the important ways. The valve sealing surface material selection should be avoided to go into the wrong area.
Misunderstanding 1: Valve sealing surface material hardness is good wear resistance.
Experiments show that the organizational structure of the metal material determines the valve sealing surface material wear resistance. Some of the austenite as the matrix plus a small amount of hard phase structure of the metal material, and its hardness is not very high, but its wear resistance is very good. Valve sealing surface with a certain degree of high hardness is to avoid the medium in the hard debris mat injury and scratches. With comprehensive consideration, the hardness value of HRC35 – 45 is appropriate.
Myth 2: Valve sealing surface material price is high performance.
The price of the material is its commodity characteristics, and the performance of the material is its physical properties; the two are not necessarily linked. Cobalt-based alloys in the metal cobalt from imports the price is higher, so cobalt-based alloy material prices are high. Cobalt-based alloys are characterized by high-temperature wear-resistant performance and are used in normal, medium-temperature conditions; the price/performance is relatively high. In the valve sealing surface material selection, the price/performance of the material is relatively low.
Myth 3: Valve sealing surface materials in a strong corrosive media co; corrosion resistance is good and must be adapted to other corrosive media.
The corrosion resistance of metal materials has a complex mechanism; a material in a strong corrosive medium corrosion resistance can be good, and the conditions of a slight change, such as temperature or medium concentration changes, the corrosion resistance is changed. For another corrosive medium, its corrosion resistance is greater. The corrosion resistance of metal materials can only be known through experiments; drawing on relevant information must understand the conditions to avoid unthinkingly drawing on them.