The oxygen acetylene flame is used as the heat source for spraying, the effective temperature range is 2000~3000 C, the neutral flame or the weak carbonization flame is used, the particle flying speed is low, the lower effective temperature limits the range of the type of the butyl spray material. The material above 2500 C is not suitable for the oxygen acetylene flame spraying, which is mainly suitable for the repair of crankshaft, valve and other parts. Again.
1. oxygen acetylene flame spray (welding) equipment
It mainly includes spray gun, oxygen and acetylene supply device.
(1) spray gun. The spray gun is the main tool for thermal spraying. The small spray gun is mainly used for spraying and welding of small and medium parts and precision parts. The large spray gun is mainly used for the spray welding of large parts, and the production efficiency is high.
(2) oxygen and acetylene supply device. Oxygen is generally bottled oxygen and output through the decompressor. Acetylene should also be bottled to ensure stable gas supply and medium pressure acetylene generator.
(3) assistive devices. Generally include rotary devices, powder recovery devices and sifter screens, drying boxes, sandblasting or napping devices.
2, oxygen acetylene flame spraying (welding) gold powder
(1) alloy powders used for spray welding include nickel base, iron base, cobalt base, copper based alloy powder, and high chromium cast iron powder and mixed powder.
(2) spraying material. Most of the sprayed materials are powder like, and they are divided into two kinds of combined powder (combined powder) and working layer powder. The combination powder is aluminum coated nickel or nickel aluminum composite powder, and the combination powder is mainly used to improve the bonding strength of the coating. The work layer powder is mainly three categories of nickel base, iron base and copper base. In addition, there is a kind of "one-time spraying powder". It combines the powder and the working table with a good combination and good working performance.
3. spray and spray welding process
(1) powder spraying process. Spraying process: prepare a pre heating (200 c) spray combined powder and spray powder before spraying.
(1) preparation before spraying, including workpiece cleaning, pre processing and preheating.
Cleaning is using metal cleaning agent, alkali solution and so on to thoroughly clean the surface of the workpiece and the oil, rust and so on. For the long time contact with the lubricating oil, the oil is infiltrated into the tissue, and the oxygen acetylene flame is used to bake the oil.
The common methods for pre processing are car, grinding, sandblasting, shot peening and so on. The main purpose is to clean up the surface of the workpiece, remove all kinds of damage (fatigue layer and corrosion layer), original spray coating, electroplating coating, alloying layer, and modify the uneven wear surface. High bonding strength. Pre processing methods include car, grinding, sand blasting, etc.
The preheating can remove the moisture adsorbed on the surface of the workpiece and help to reduce the shrinkage stress in the cooling process, thus improving the bonding strength. The preheating temperature before spraying is not more than 200 c, and the micro carbonization flame can be used to preheat directly with the spray gun, in order to avoid the oxidation of the material.
(2) spray combined powder. After pretreatment, parts should be sprayed immediately, the thickness is 0.1 to 0.15 millimeters, and the spraying distance is 180~200 mm.
Spray work powder. The coating layer should be sprayed immediately after the layer is sprayed. The quality of the coating depends mainly on the quantity of powder feeding and the distance of spraying. The quantity of powder feeding should be controlled according to the size of the flame power. The quantity of powder delivery should be moderate. The quality of the coating will be reduced by the increase of the raw powder in the coating, too small and the productivity will be reduced. The spray distance is 180~200 millimeter. The distance too close will make the powder heating time and the workpiece temperature rise too high; the distance too far fork will cause the alloy powder to reach the workpiece surface speed and temperature, which will affect the quality of the coating. In addition, the powder injection should also be noted that the direction of powder injection should be perpendicular to the workpiece.
The spraying post treatment. The temperature of the workpiece after spraying is not high, which can naturally cool and not cause problems. The spraying layer is porous and porous. On the one hand, it can improve the lubrication between the surface of the workpiece by using this performance storage oil. When the coating is cooled, the workpiece can be soaked in the hot oil, and after the oil is filled, the other side can be refined. On the surface, the gap may also suck the abrasive medium to make the parent abrasive. Therefore, the coating should be sealed to protect the base material for the coating working in the abrasion condition. In general, paint and epoxy resin are used to brush the coating on the coating surface.
When the dimension accuracy and surface roughness of the sprayed coating can not meet the requirements, it is necessary to finish the finishing process. At the same time, turning or grinding can be used.
(2) powder spray welding process. Spray welding process: pre heat preparation, pre heating, spray protection powder (0.1 mm), powder injection, remelting - powder injection, remelting and spraying.
(1) pre injection process includes cleaning, pre processing and preheating of the workpiece. Before spray welding, special rough treatment is not required. The preheating temperature is higher than that of the spray. It can improve the wetting of the parent material after the melting of the powder and reduce the stress between the spray welding layer and the parent material. But the preheating temperature should not be too high to prevent the material from oxidizing. The preheating temperature of the workpiece is 250~300 degrees centigrade, and the stainless steel workpiece can be properly improved. The preheating temperature should be properly reduced for small pieces, thin parts or materials with oxidizing elements. In order to reduce the oxidation of the base material, the preheating flame is suitable for a micro carbon flame. It is best to spray a thin layer of alloy powder (0.1 millimeters) on the face surface immediately after preheating. Effective prevention of oxidation.
Spraying and remelting. When spray welding, powder injection and remelting treatment are closely linked. According to the order of operation, they can be divided into one step or two steps.
One step is the simultaneous operation of powder and remelting. When the workpiece is preheated and protected by the alloy powder of the spray layer, the workpiece continues to be heated. When the pre sprayed powder begins to moisten, the powder feed switch is pressed intermittently and the alloy powder is melted. The movement of the flame is determined according to the melting condition and the requirement for the melting of the spray welding layer. Speed. At the same time, the flame is moving forward, and then the powder is intermittently and melted. In this way, the powder and remelting are carried out alternately until the surface of the whole workpiece is sprayed. Only one torch is used in operation.
Because the one step method has less heat input to the workpiece, the deformation of the workpiece is small and the effect on the structure of the material is little. At the same time, the utilization rate of the powder is also high. It is easy to get the thickness of the required spray welding layer. This process is more suitable for small workpiece, or the workpiece is large, but it needs small area of spray welding.
The two step method is two steps of powder spraying and remelting. In fact, the process of preheating, powder injection and remelting is carried out separately, and the same spray gun is not used, or even the same heat source is not used. The work is pre heated to the workpiece in large area or overall preheating. After the pre protection layer is sprayed, it continues to be heated to about 500, and then the whole The thickness of each layer of powder is not more than 0-2 millimeter on the surface, and the thickness and uniformity of the spray layer can be controlled by multiple layers of powder. After the thickness is expected, the powder is stopped and then remelting. The interval time should not be too long to save the heat needed for remelting, and reduce the possibility of surface cracks and shelling. In the two step process, remelting is a key process, which has a great influence on the quality of the whole spray welding layer. First, use a high power soft flame, and increase the flow of oxygen and acetylene without increasing its pressure, in order to prevent the molten surface from being too high and too big to blow the molten surface. If the coating is blown, the thickness of the spray welding layer is uneven. Secondly, the neutral flame or the weak carbon flame should always be used in the remelting process. When the coating is fused, the surface will show a bright and smooth "mirror reflection" phenomenon, and then the flame can be transferred to the other parts until the whole coating is fused. For the thicker spray welding layer, it can be sprayed second times after remelting. To third times, the final thickness of the spray welding layer can be controlled to 2~3 mm. When the thickness of the spray layer is measured in the hot state, the factor of 20% to 25% shrinkage after cooling is taken into account.
A cylindrical workpiece can be operated on a lathe. The line speed of the surface of the workpiece is adjusted to 220 meters per minute to make the spray welding layer melt evenly. For large work pieces, a special large remelting gun can be used. Some small plane pieces can be remelted in an electric furnace or remelting with high frequency heating. The temperature can be accurately controlled so that it can be obtained. Better spray welding layer.
(3) after spray treatment. The thermal expansion coefficient of the spray welding alloy is larger, and the improper cooling will produce deformation and even cause cracks. Usually, the long shaft type workpiece will be easily deformed when cooling. This kind of deformation is generally uncorrected. This not only affects the precision of the parts, but also makes the thickness of the spray welding layer uneven. In order to reduce the deformation, the deformation must be reduced. Take appropriate technological measures, such as the slender shaft parts can not stop immediately after remelting on the machine tools. When the surface temperature of the workpiece is reduced to 300~400 degrees C, it will be removed from the machine tool, vertical or suspended, otherwise the bending deformation will occur because of the self weight.
In order to avoid the crack, the general rigidity is not large and the martensitic transformation does not occur in the cooling process. The cooling after remelting does not need special treatment. When the workpiece is large, it should be put in the heat insulation material. For the high quench steel, it is better to anneal isothermal and then slow cooling.
According to the needs of the workpiece, the spray welding layer can be grinded and fined.
