Valve sealing surface spraying alloy processing process mainly consists of four steps: valve spray welding before the preparatory work, surface pretreatment, valve spray welding, valve spray welding after treatment.
First, the valve spray welding before the preparatory work:
Spray welding materials, spray welding tools, spray equipment and process determination.
Before preparing the process should first understand the actual condition of the valve spray welding workpiece and technical requirements half of the analysis.
1, determine the thickness of the coating. Generally speaking, the valve spray welding must be machined, so the thickness of the coating should be reserved for processing allowances, but also take into account the thermal expansion and contraction of the valve spray welding.
2, the determination of the coating material. Selection is based on the coating material should meet the valve spray welding workpiece materials, with the requirements, technical requirements and working conditions, etc., respectively, to choose the combination of layer and working layer materials
3, to determine the parameters: pressure, powder particle size, gun and workpiece relative movement speed.
Second, the valve workpiece surface pretreatment.
Surface preparation, is to ensure that the coating and substrate bonding strength of the important processes
1, concave cutting treatment, the surface of the existence of fatigue layer and local serious strains of the groove marks, under the premise of strength allows, can be carried out Ao cutting treatment, for thermal spray welding to provide space to accommodate.
2, surface cleaning, remove oil, rust, paint layer, etc., so that the surface of the workpiece clean, oil paint can be removed with solvent cleaner, if the oil has penetrated into the substrate material, you can use flame heating to remove, the rust layer can be acid-impregnated, mechanically polished or sandblasted to remove.
3, surface roughening purpose is to enhance the combination of coating and substrate to eliminate the stress effect, commonly used in sandblasting, slotting car threads, brushing, and so on.
A: sandblasting is the most commonly used, sand can choose quartz sand, aluminium oxide sand, cold hard iron sand, etc., sand to sharp and hard for good, must be clean and dry, with sharp edges. Its size, the size of air pressure, sandblasting angle, distance, and time should be carried out according to the specific situation.
B: grooving, turning threads, roller flowers. Roughening of the surface of shafts, sets of parts, can be a slot, car screw mosquito processing, groove and thread surface roughness to RA6.3-12.5 is appropriate, the processing process does not add a coolant and moisturising agent, for the groove car threaded workpieces can be rolled on the surface of the pattern, but to avoid the sharp corners.
C: Higher hardness workpiece can be EDM brushed for roughing. However, thin-coated workpieces should be used with caution. The EDM brushing method is to use a fine nickel or aluminium wire as the electrode, and under the action of the electric arc, the electrode material is locally fused to the surface of the substrate, resulting in a roughened surface. Surface roughening after the presentation of the fresh surface, should prevent contamination, it is strictly prohibited to touch the hand, save in a clean, dry environment, roughing as soon as possible after the valve spray welding, general valve spray welding time of no more than two hours.
4, non-spray welding parts of the protection
Ball valve spray welding surface near the non-spray welding need to be protected, you can use heat-resistant glass cloth or asbestos and shielding up, if necessary, according to the parts switch to make the appropriate fixture protection, but note that the fixture material to have a certain degree of strength, and can not be used in low melting point alloy, so as not to contaminate the coating for the substrate on the surface of the bonding grooves, oil holes, etc. does not allow the spray welding of the parts, you can use graphite or chalk blocking flat or slightly above the surface. surface. After spraying to remove, pay attention to the coating to be bruised, the corners should be poured blunt.
Third, the valve sealing surface welding
Valve spray welding before preheating to one hundred to two hundred degrees, reduce the temperature difference. Small pieces can be preheated in the oven.
Spray combined with the layer of priming control between ten and twenty wire, spray powder with neutral or north carbonised flame, after sending a concentrated bright red fire beam, and blue-white smoke. If the end of the white bright colour, it means that there has been a phenomenon of injury should be adjusted flame or reduce the amount of powder sent, if the dark red, indicating that there is no melting through, increase the flame, control the amount of powder and flow rate. If the adjustment of the flame and the amount of powder is invalid, you can change the powder particle size Wyatt nickel content, change to coarse powder or powder with a large amount of nickel. Spray to be perpendicular to the valve spray welding surface, the distance in general control in 180-200MM.
Valve spray welding working layer: combined with the layer after spraying to use a wire brush to remove grey powder and oxide film, use iron powder with north carbonation flame, use copper powder should be used when the neutral flame, and use nickel powder between the two, depending on the composition and change. Distance control between 180-200MM, spray distance is too large, the melt temperature is reduced, slow down and insufficient energy, low bonding strength, loose organisation, spray distance is too small, the powder particles are not fused, the impact is strong to produce rebound, low deposition efficiency, bonding strength is also low. Relative moving speed is best in 70-150MM / S, often measured with a thermometer, more than 250 degrees should be suspended valve spray welding.
Cooling of the workpiece after spray welding: When cooling, the main thing is to prevent the coating from de-cracking and the workpiece from deforming. Especially for some special shapes, preventive measures should be taken, such as long shafts rotating on the machine tool while cooling naturally, or hanging them vertically for cooling.