In recent years, more and more domestic barrel-making enterprises have adopted a new electrostatic powder coating process for the outer surface coating of steel barrels, which not only improves the surface quality of steel barrels, but also brings new ones to the production of steel barrels. problem. Although the drum powder coating process is small, there are many problems in the process. The main processes of powder coating are pre-treatment, electrostatic spraying and baking. The main process that affects quality should be a pre-treatment process. However, many manufacturers did not pay enough attention to it, resulting in many troubles. Some hidden dangers are not reflected in the short term. The more advanced technology and spent on pre-processing accounts for about 25% of the total cost.
Analysis of various problems arising from the production process. I think that the advanced level of equipment and the quality of raw materials play a decisive role in the quality of products. Both are indispensable. We, as engineering technicians, should establish consensus on this issue and must not be on the occasion of a new dusting production line. The only way to save money is to sum up. Using low-standard production equipment, processes, and materials will inevitably bring many problems for long-term production, and even produce high-quality products. Many manufacturers went to the powder coating production line, and soon the application was forced to be discontinued or replaced with new equipment, for the above reasons. We often see that the surface painting of foreign products is very beautiful, and one of the main reasons is that they continue to adopt advanced equipment and new materials and techniques.
In this sense, non-excellent equipment and coatings have no future for the powder coating equipment and coating manufacturers. This is especially true in the competitive conditions of hundreds of domestic powder spraying equipment and powder coating manufacturers. In Shaanxi alone, there have been nearly 10 equipment and powder coating production plants that have been converted or closed down.
Second, the analysis of the production of defects (a) pre-treatment:
1. Insufficient degreasing and rust removal First of all, I do not advocate the use of a two-in-one process that removes oil and rust. The two-in-one process itself is prone to this problem. Because the commonly used deoiling and derusting solution formulations are mutually exclusive, rather than complementary, it is difficult to come up with a reasonable two-in-one or three-in-one process (including phosphating). Another process uses a metal detergent to make oil, but it cannot remove oil completely. Because the degreasing effect of the metal cleaning agent is poor, generally only the grease floats on the surface of the metal body. To remove it, a mechanical force is also required. If there is no such mechanical force, the oil will not be completely seen. Metal cleaners are not suitable for industrial mass production.
I advocate the use of alkaline chemical degreasing. Alkali solution works well for removal of animal and vegetable oils as it produces saponification reactions. However, the removal effect of mineral oil is poor. To remove mineral oil, it is necessary to add emulsifiers. In addition, the washing quality has a great influence on the oil removal effect. The first is the water quality and the second is the water temperature. The third is to grade and flip, all three are good, only one purpose is to use pure water to clean the grease. The last level is best cleaned with deionized water.
2. Problems such as rough film of phosphate film Before steel powder is sprayed, it must be phosphatized. Foreign countries generally adopt the sand spray phosphating process. Many of the phosphating solutions we use are not ideal. This directly affects the quality of the phosphating film. The more common is the problem of phosphating film roughness. In this regard, I would like to analyze from three aspects: The first is to choose a good phosphating solution, which is the fundamental guarantee of quality. The first question involved is selecting the type of high, medium and low temperature? From the perspective of its history of development, the beginning is a high-temperature thick film type, which has now progressed to medium- and low-temperature film types. The domestic low-temperature phosphating solution, because the solution is not stable enough, maintenance is difficult, the adhesion of the phosphating film is poor, and some are not even water-resistant rinsing and so on, and are rarely used. Some low-temperature phosphating solution is ideal, but the price is more expensive. Although low-temperature phosphating is the development direction, it has yet to make new breakthroughs in achieving universal application. At present, Xianghe Phosphorus (Chengdu) Company has successfully solved the problem of normal temperature phosphating (passivation) powders and has already supplied them in bulk. At present, the commonly used medium temperature phosphating process. Followed by the selection of zinc system, iron system, zinc-calcium system and other phosphating solution? In contrast, I think the zinc-calcium phosphating solution is better, the spray coating requires a thin coating phosphate film to consider Iron is also a better choice. It has good heat resistance in addition to some of the advantages of the zinc system. Under medium temperature conditions, the hydrolysis is less, the sediment is less, the solution is easy to maintain, the mechanical strength is good, and the corrosion resistance is strong. When the film is thick, the crystallization is still very fine. Iron-based phosphatized iron films have poor corrosion resistance. In short, it is better to select the temperature zinc calcium system phosphating solution. The second is that the phosphating solution must be adjusted at any time, mainly adjusting the acidity ratio and the zinc content. Both of these factors have a direct influence on the film forming rate and the thickness of the crystal. It is necessary to periodically and irregularly analyze the solution according to the workload and make adjustments in time. There is no analysis data. Blindly replenishing the feed solution is unscientific. The third is to control the thickness of the film layer. Phosphate film has its best thickness. For example, the optimal film thickness of zinc and calcium zinc is 1.5-2 grams per square meter, while the iron film is 0.5-0.7 grams per square. In this range, rice has the best corrosion resistance. The finest grains, such as too thick, affect the flexibility and adhesion of the film, and the grains also become coarse. The problem that usually arises in production is that the phosphating film is thick. Here are some opinions on how to overcome the grain coarsening problem.
The first is to use a surface conditioner to refine the grains. That is, a surface modification process is performed prior to the phosphating of the workpiece, so that a layer of colloidal particles is adsorbed on the metal surface to form a layer of “activation centerâ€, and further phosphating is continued to grow on the “activation center†so that the phosphorized crystal can be obtained. Grains are noticeably thinner, especially prior to low-temperature phosphatization, which is an indispensable first-step treatment.
The second is to add grain refiners to the phosphating solution, such as calcium, nickel and other salts as improvers, and the best use of complex salts, the effect is better, while reducing the amount of low slag.
The third is passivation treatment after phosphating, so that the peak structure formed above the phosphate film, thereby enhancing the corrosion resistance, while increasing the adhesion of the coating.
The fourth is to adjust the acidity ratio and zinc content of the phosphating solution at any time. It has been discussed before.
(b) electrostatic spray:
1. Uneven spraying is mainly caused by uneven fluidization of powder in the powder bucket. The microplate should be replaced or the air supply system under the microplate should be adjusted so that the powder layer can be returned to the normal boiling state and eliminated. If the pressure is low, increase the pressure to eliminate it. Another possibility is the blockage of the pipeline, including the blockage of the venturi, the pipeline needs to be cleaned. If Venturi is often blocked, it is improper to use Venturi powder (such as brass, etc.) as a material, so long as it is changed to Poly Si Fo vinyl material, it can be solved. The blockage of the spray gun head can also be solved by the same method. If the powder is not a fluidized bed type, it is necessary to improve the stirrer or install a shaker to prevent the powder layer from appearing hollow and provide no paint.
2, powder on the powder rate is low:
(1) Low voltage or no high voltage is one of the main reasons. Need to increase the output voltage or repair the static generator.
(2) poor grounding of the workpiece, hook or low resistance; such as spraying the second time or greasy to not conductive, will make the lower resistance. When spraying the second pass with the ordinary spray gun, the workpiece must be preheated to about 104°C to perform thermal spraying, using the principle of hot-melt adsorption. The thermal spraying operation also facilitates the leveling of the powder. With the chameleon gun, the resistance of the lower layer can be overcome. The second pass of spraying can achieve cold spraying. It is based on the principle of using an additional plate to form a constant electrostatic field in the spray chamber.
(3) The excessive charge of the powder or the small amount of powder also affects the upper flour rate. The results of the epoxy-type powder test show that when the charged power amount of the powder is 1.6 microcoulombs/g, the upper dust rate can reach more than 95%. The corona discharge gun can only charge the powder 0.8-0.9 microcoulombs, so the powder rate is only about 85%. This number indicates the effect of the amount of charge on the rate of dusting. Therefore, the friction spray gun is not as good as the powder on the electrostatic spray gun. Generally, the control current does not need to be too large, and about 60 microcoulombs is enough. Otherwise, if the charge is too high, it may easily cause over-current and power-down. If it is too large, it will easily cause Faraday's screen effect. In general, it is the effect of the amount of charge on the powder rate and the small amount of charge. In addition to the difference in the self-reionization effect of different powder coatings, the main reason is that due to the failure of the high-voltage electrostatic generator, maintenance is required to restore the high pressure.
(4) Excessive air pressure: Will counteract the electrostatic attraction. The powder on the workpiece is blown off to reduce the rate of dusting. The experimental results show that when the air volume is 3 liters/second, the upper dust rate is about 95 percent. When air volume is added, the dust rate is increased for each additional litre/second of the powder air volume. Decrease by 2% to 3%.
3. The problem of ignition during construction generally does not exist, because high voltage electrostatic generators are now mostly equipped with constant voltage and constant current protection circuits. Old-fashioned spray guns have a problem. The reason for the ignition is as follows:
1) The distance between the gun and the workpiece is too high and the powder has a large concentration in the electrostatic field, which is an important reason.
2) The internal resistance is small, resulting in excessive current.
3) The voltage is too high: Experiments show that the adsorption efficiency is nearly saturated when the field strength is 1 kV/cm. Since then, the field strength has increased by a factor of three and the coating efficiency has only increased by 3 to 5 percent. Therefore, the voltage is too high to be desirable, but it is easy to cause a fire. General control at 60kv is sufficient.
4, coating shrink pit:
1) Most of the situations are caused by the surface of the workpiece not being pulled out, and some are caused by the presence of oil in the compressed air. Because the oil point significantly affects the surface tension when the powder is cured.
2) The intrinsic elements of powder coatings, such as powders mixed with different manufacturers or batches, and the introduction of silica dust, will also affect the uniformity of surface tension during solidification, resulting in shrinkage pits.
5, coating pinhole blisters:
The gas under the coating reaches the surface of the coating during the drying process. The breakthrough is pinholes, and bubbles are too late to be excluded. The gas in the coating can be air, water vapor, or hydrogen (provided in the galvanized layer) or the like. The fundamental solution is to completely remove the gas before spraying. A small amount of gas that cannot be excluded can also be controlled by drying and spraying conditions to avoid pinholes or bubbles. According to calculations, it takes 26 seconds to remove the air from the coating and the temperature rises slowly in the safe melt leveling section (100-135 degrees Celsius) before the film begins to cure. Give enough exhaust time. Or take the method of dusting the workpiece after preheating, all have an effect.
6, coated with orange peel:
The main reason for the production of orange peel comes from the poor leveling of the powder coating itself. Construction also has an impact and is a secondary factor.
1) Leveling property of powder coating Mainly* The added leveling agent works. The leveling agent generally has two effects, namely wetting and leveling benefits: The wetting efficiency should be increased when the powder is around 100 degrees Celsius. For the leveling of the machine, the surface tension is as small as possible. The main effect of the leveling effect is greater than 150 degrees Celsius, the surface tension of the powder should be as large as possible to increase the leveling property. Leveling agents generally contain more than two materials for this reason.
2) The poor construction can also cause the orange peel phenomenon: once the coating is too thick or the baking temperature is too high, the orange peel will be obvious. Once again, the coating thickness should be about 60u. In addition, controlling the duration of the safe melt and leveling period is beneficial to the leveling of the powder coating.
7, electrostatic shielding effect:
When the workpiece of complex structure is dusted, the coating film is thin due to the electrostatic shielding (also known as Faraday) effect in the dead angle, and even the bottom cannot be covered. This effect is insurmountable with ordinary electrostatic spray guns. Friction spray can improve better. Some foreign electrostatic spray guns have basically overcome this effect and obtained a more uniform coating film. Chameleon spray guns, for example, are said to spray 3 mm deep grooves to obtain a more uniform coating. For the general electrostatic spray gun, some people advocate using the method of increasing the air pressure to overcome the static shielding effect. My practice has proved that, on the contrary, the gas should be smaller, because the powder at the blind corners would not have been adsorbed firmly, but the increase in air pressure would have caused the powder layer adsorbed to be blown away, which would not achieve the purpose of increasing the thickness of the coating. I analyzed that the chameleon could overcome the electrostatic shielding effect. In addition to auxiliary anodes, it is possible that there is a flow of air through the spiral body in the body of the gun. This increases the forward momentum of the powder without increasing the pressure and effectively solves the above-mentioned air pressure. The contradiction in size has received good results.
(3) Control of baking curing conditions:
I would like to discuss three perspectives for your reference: 1. I don't advocate using far-infrared as the heat source for ovens or ovens. I should use ordinary electric direct baking or other heat sources for indirect cycle heating and baking. This is determined by the characteristics of the far infrared radiation. There are two main characteristics: First, it is directly absorbed by the workpiece to warm the workpiece. A layer of steel or aluminum with a thickness of about one millimeter has a far infrared absorption rate of about 75%. Therefore, the workpiece heats up rapidly, generally higher than the furnace temperature of 10-20 degrees, at the same time it will absorb the far-infrared radiation rate behind the workpiece is very low, resulting in a large temperature difference, the third layer of the workpiece is even worse. Therefore, the oven or oven cannot use far-infrared heat source. Another feature is that the general far-infrared ray radiation process advances radiantly. This determines that the radiation intensity at each point in the furnace is inversely proportional to the square of the distance from the element, which determines its The best baking distance is between 200-400mm. Thus, only the drying tunnel is suitable for far-infrared baking. 2, far-infrared components I advocate the use of opal quartz tube as a heat energy conversion carrier, it is best not to surface coating far-infrared conversion coating plate, tube and other components. The reason is that the former far-infrared conversion lifetime is theoretically infinite, while the latter's conversion efficiency is more than 20% per year. Attenuation not only does not save energy, but also wastes energy, because its thermal conductivity is lower than ordinary electric heat. 3, production of far-infrared infrared baking control temperature and time, should be determined according to the specific circumstances. It depends on the far-infrared furnace efficiency and thin workpieces. Powder types and other factors. An easy way to determine the control conditions is to use a test piece of similar thickness, measure the adhesive force and impact strength of the coating after curing to select the best control conditions, resulting in ills of baking over or under fire. We all have experience in production, powder coating requirements are harsh curing conditions, the choice of a very narrow range of fluctuations, a little beyond will cause brittle fracture or loss, must strictly control the temperature and time.
(4) Rework of defective products 1. General unqualified products: If there are dirty spots, virtual spray, flow plastics, scratches, etc., sandpaper dry grinding method can be used, and after grinding and drying, the whole method of re-spraying is carried out again. Rework. Can not be repaired by local refilling.
2, the product surface pits or bumps off the film and other defects, the entire coating film needs to be removed, wipe clean, the overall re-spray rework.
3, large areas of rickets or painted parts have been baked too hot, you need to remove the entire coating, wipe clean and then re-spray. Film stripping method: Available film remover, concentrated sulfuric acid can also be used. The former is a mixture of organic solvents, volatile, more expensive, but its non-corrosive materials, fast film. The basic mechanism is to destroy the binding force between the coating film and the body. Pieces fall off. I advocate using a film remover, which is cheap and slow to remove the film. Its mechanism is to directly destroy the epoxy coating and generate resin sulfonate. However, careless operation can cause excessive corrosion and lead to scrapped parts.
4. The defects of the coating film at the corners of the dead spot can be solved by the partial repair of the nitro lacquer or amino baking paint of the same color.
Analysis of various problems arising from the production process. I think that the advanced level of equipment and the quality of raw materials play a decisive role in the quality of products. Both are indispensable. We, as engineering technicians, should establish consensus on this issue and must not be on the occasion of a new dusting production line. The only way to save money is to sum up. Using low-standard production equipment, processes, and materials will inevitably bring many problems for long-term production, and even produce high-quality products. Many manufacturers went to the powder coating production line, and soon the application was forced to be discontinued or replaced with new equipment, for the above reasons. We often see that the surface painting of foreign products is very beautiful, and one of the main reasons is that they continue to adopt advanced equipment and new materials and techniques.
In this sense, non-excellent equipment and coatings have no future for the powder coating equipment and coating manufacturers. This is especially true in the competitive conditions of hundreds of domestic powder spraying equipment and powder coating manufacturers. In Shaanxi alone, there have been nearly 10 equipment and powder coating production plants that have been converted or closed down.
Second, the analysis of the production of defects (a) pre-treatment:
1. Insufficient degreasing and rust removal First of all, I do not advocate the use of a two-in-one process that removes oil and rust. The two-in-one process itself is prone to this problem. Because the commonly used deoiling and derusting solution formulations are mutually exclusive, rather than complementary, it is difficult to come up with a reasonable two-in-one or three-in-one process (including phosphating). Another process uses a metal detergent to make oil, but it cannot remove oil completely. Because the degreasing effect of the metal cleaning agent is poor, generally only the grease floats on the surface of the metal body. To remove it, a mechanical force is also required. If there is no such mechanical force, the oil will not be completely seen. Metal cleaners are not suitable for industrial mass production.
I advocate the use of alkaline chemical degreasing. Alkali solution works well for removal of animal and vegetable oils as it produces saponification reactions. However, the removal effect of mineral oil is poor. To remove mineral oil, it is necessary to add emulsifiers. In addition, the washing quality has a great influence on the oil removal effect. The first is the water quality and the second is the water temperature. The third is to grade and flip, all three are good, only one purpose is to use pure water to clean the grease. The last level is best cleaned with deionized water.
2. Problems such as rough film of phosphate film Before steel powder is sprayed, it must be phosphatized. Foreign countries generally adopt the sand spray phosphating process. Many of the phosphating solutions we use are not ideal. This directly affects the quality of the phosphating film. The more common is the problem of phosphating film roughness. In this regard, I would like to analyze from three aspects: The first is to choose a good phosphating solution, which is the fundamental guarantee of quality. The first question involved is selecting the type of high, medium and low temperature? From the perspective of its history of development, the beginning is a high-temperature thick film type, which has now progressed to medium- and low-temperature film types. The domestic low-temperature phosphating solution, because the solution is not stable enough, maintenance is difficult, the adhesion of the phosphating film is poor, and some are not even water-resistant rinsing and so on, and are rarely used. Some low-temperature phosphating solution is ideal, but the price is more expensive. Although low-temperature phosphating is the development direction, it has yet to make new breakthroughs in achieving universal application. At present, Xianghe Phosphorus (Chengdu) Company has successfully solved the problem of normal temperature phosphating (passivation) powders and has already supplied them in bulk. At present, the commonly used medium temperature phosphating process. Followed by the selection of zinc system, iron system, zinc-calcium system and other phosphating solution? In contrast, I think the zinc-calcium phosphating solution is better, the spray coating requires a thin coating phosphate film to consider Iron is also a better choice. It has good heat resistance in addition to some of the advantages of the zinc system. Under medium temperature conditions, the hydrolysis is less, the sediment is less, the solution is easy to maintain, the mechanical strength is good, and the corrosion resistance is strong. When the film is thick, the crystallization is still very fine. Iron-based phosphatized iron films have poor corrosion resistance. In short, it is better to select the temperature zinc calcium system phosphating solution. The second is that the phosphating solution must be adjusted at any time, mainly adjusting the acidity ratio and the zinc content. Both of these factors have a direct influence on the film forming rate and the thickness of the crystal. It is necessary to periodically and irregularly analyze the solution according to the workload and make adjustments in time. There is no analysis data. Blindly replenishing the feed solution is unscientific. The third is to control the thickness of the film layer. Phosphate film has its best thickness. For example, the optimal film thickness of zinc and calcium zinc is 1.5-2 grams per square meter, while the iron film is 0.5-0.7 grams per square. In this range, rice has the best corrosion resistance. The finest grains, such as too thick, affect the flexibility and adhesion of the film, and the grains also become coarse. The problem that usually arises in production is that the phosphating film is thick. Here are some opinions on how to overcome the grain coarsening problem.
The first is to use a surface conditioner to refine the grains. That is, a surface modification process is performed prior to the phosphating of the workpiece, so that a layer of colloidal particles is adsorbed on the metal surface to form a layer of “activation centerâ€, and further phosphating is continued to grow on the “activation center†so that the phosphorized crystal can be obtained. Grains are noticeably thinner, especially prior to low-temperature phosphatization, which is an indispensable first-step treatment.
The second is to add grain refiners to the phosphating solution, such as calcium, nickel and other salts as improvers, and the best use of complex salts, the effect is better, while reducing the amount of low slag.
The third is passivation treatment after phosphating, so that the peak structure formed above the phosphate film, thereby enhancing the corrosion resistance, while increasing the adhesion of the coating.
The fourth is to adjust the acidity ratio and zinc content of the phosphating solution at any time. It has been discussed before.
(b) electrostatic spray:
1. Uneven spraying is mainly caused by uneven fluidization of powder in the powder bucket. The microplate should be replaced or the air supply system under the microplate should be adjusted so that the powder layer can be returned to the normal boiling state and eliminated. If the pressure is low, increase the pressure to eliminate it. Another possibility is the blockage of the pipeline, including the blockage of the venturi, the pipeline needs to be cleaned. If Venturi is often blocked, it is improper to use Venturi powder (such as brass, etc.) as a material, so long as it is changed to Poly Si Fo vinyl material, it can be solved. The blockage of the spray gun head can also be solved by the same method. If the powder is not a fluidized bed type, it is necessary to improve the stirrer or install a shaker to prevent the powder layer from appearing hollow and provide no paint.
2, powder on the powder rate is low:
(1) Low voltage or no high voltage is one of the main reasons. Need to increase the output voltage or repair the static generator.
(2) poor grounding of the workpiece, hook or low resistance; such as spraying the second time or greasy to not conductive, will make the lower resistance. When spraying the second pass with the ordinary spray gun, the workpiece must be preheated to about 104°C to perform thermal spraying, using the principle of hot-melt adsorption. The thermal spraying operation also facilitates the leveling of the powder. With the chameleon gun, the resistance of the lower layer can be overcome. The second pass of spraying can achieve cold spraying. It is based on the principle of using an additional plate to form a constant electrostatic field in the spray chamber.
(3) The excessive charge of the powder or the small amount of powder also affects the upper flour rate. The results of the epoxy-type powder test show that when the charged power amount of the powder is 1.6 microcoulombs/g, the upper dust rate can reach more than 95%. The corona discharge gun can only charge the powder 0.8-0.9 microcoulombs, so the powder rate is only about 85%. This number indicates the effect of the amount of charge on the rate of dusting. Therefore, the friction spray gun is not as good as the powder on the electrostatic spray gun. Generally, the control current does not need to be too large, and about 60 microcoulombs is enough. Otherwise, if the charge is too high, it may easily cause over-current and power-down. If it is too large, it will easily cause Faraday's screen effect. In general, it is the effect of the amount of charge on the powder rate and the small amount of charge. In addition to the difference in the self-reionization effect of different powder coatings, the main reason is that due to the failure of the high-voltage electrostatic generator, maintenance is required to restore the high pressure.
(4) Excessive air pressure: Will counteract the electrostatic attraction. The powder on the workpiece is blown off to reduce the rate of dusting. The experimental results show that when the air volume is 3 liters/second, the upper dust rate is about 95 percent. When air volume is added, the dust rate is increased for each additional litre/second of the powder air volume. Decrease by 2% to 3%.
3. The problem of ignition during construction generally does not exist, because high voltage electrostatic generators are now mostly equipped with constant voltage and constant current protection circuits. Old-fashioned spray guns have a problem. The reason for the ignition is as follows:
1) The distance between the gun and the workpiece is too high and the powder has a large concentration in the electrostatic field, which is an important reason.
2) The internal resistance is small, resulting in excessive current.
3) The voltage is too high: Experiments show that the adsorption efficiency is nearly saturated when the field strength is 1 kV/cm. Since then, the field strength has increased by a factor of three and the coating efficiency has only increased by 3 to 5 percent. Therefore, the voltage is too high to be desirable, but it is easy to cause a fire. General control at 60kv is sufficient.
4, coating shrink pit:
1) Most of the situations are caused by the surface of the workpiece not being pulled out, and some are caused by the presence of oil in the compressed air. Because the oil point significantly affects the surface tension when the powder is cured.
2) The intrinsic elements of powder coatings, such as powders mixed with different manufacturers or batches, and the introduction of silica dust, will also affect the uniformity of surface tension during solidification, resulting in shrinkage pits.
5, coating pinhole blisters:
The gas under the coating reaches the surface of the coating during the drying process. The breakthrough is pinholes, and bubbles are too late to be excluded. The gas in the coating can be air, water vapor, or hydrogen (provided in the galvanized layer) or the like. The fundamental solution is to completely remove the gas before spraying. A small amount of gas that cannot be excluded can also be controlled by drying and spraying conditions to avoid pinholes or bubbles. According to calculations, it takes 26 seconds to remove the air from the coating and the temperature rises slowly in the safe melt leveling section (100-135 degrees Celsius) before the film begins to cure. Give enough exhaust time. Or take the method of dusting the workpiece after preheating, all have an effect.
6, coated with orange peel:
The main reason for the production of orange peel comes from the poor leveling of the powder coating itself. Construction also has an impact and is a secondary factor.
1) Leveling property of powder coating Mainly* The added leveling agent works. The leveling agent generally has two effects, namely wetting and leveling benefits: The wetting efficiency should be increased when the powder is around 100 degrees Celsius. For the leveling of the machine, the surface tension is as small as possible. The main effect of the leveling effect is greater than 150 degrees Celsius, the surface tension of the powder should be as large as possible to increase the leveling property. Leveling agents generally contain more than two materials for this reason.
2) The poor construction can also cause the orange peel phenomenon: once the coating is too thick or the baking temperature is too high, the orange peel will be obvious. Once again, the coating thickness should be about 60u. In addition, controlling the duration of the safe melt and leveling period is beneficial to the leveling of the powder coating.
7, electrostatic shielding effect:
When the workpiece of complex structure is dusted, the coating film is thin due to the electrostatic shielding (also known as Faraday) effect in the dead angle, and even the bottom cannot be covered. This effect is insurmountable with ordinary electrostatic spray guns. Friction spray can improve better. Some foreign electrostatic spray guns have basically overcome this effect and obtained a more uniform coating film. Chameleon spray guns, for example, are said to spray 3 mm deep grooves to obtain a more uniform coating. For the general electrostatic spray gun, some people advocate using the method of increasing the air pressure to overcome the static shielding effect. My practice has proved that, on the contrary, the gas should be smaller, because the powder at the blind corners would not have been adsorbed firmly, but the increase in air pressure would have caused the powder layer adsorbed to be blown away, which would not achieve the purpose of increasing the thickness of the coating. I analyzed that the chameleon could overcome the electrostatic shielding effect. In addition to auxiliary anodes, it is possible that there is a flow of air through the spiral body in the body of the gun. This increases the forward momentum of the powder without increasing the pressure and effectively solves the above-mentioned air pressure. The contradiction in size has received good results.
(3) Control of baking curing conditions:
I would like to discuss three perspectives for your reference: 1. I don't advocate using far-infrared as the heat source for ovens or ovens. I should use ordinary electric direct baking or other heat sources for indirect cycle heating and baking. This is determined by the characteristics of the far infrared radiation. There are two main characteristics: First, it is directly absorbed by the workpiece to warm the workpiece. A layer of steel or aluminum with a thickness of about one millimeter has a far infrared absorption rate of about 75%. Therefore, the workpiece heats up rapidly, generally higher than the furnace temperature of 10-20 degrees, at the same time it will absorb the far-infrared radiation rate behind the workpiece is very low, resulting in a large temperature difference, the third layer of the workpiece is even worse. Therefore, the oven or oven cannot use far-infrared heat source. Another feature is that the general far-infrared ray radiation process advances radiantly. This determines that the radiation intensity at each point in the furnace is inversely proportional to the square of the distance from the element, which determines its The best baking distance is between 200-400mm. Thus, only the drying tunnel is suitable for far-infrared baking. 2, far-infrared components I advocate the use of opal quartz tube as a heat energy conversion carrier, it is best not to surface coating far-infrared conversion coating plate, tube and other components. The reason is that the former far-infrared conversion lifetime is theoretically infinite, while the latter's conversion efficiency is more than 20% per year. Attenuation not only does not save energy, but also wastes energy, because its thermal conductivity is lower than ordinary electric heat. 3, production of far-infrared infrared baking control temperature and time, should be determined according to the specific circumstances. It depends on the far-infrared furnace efficiency and thin workpieces. Powder types and other factors. An easy way to determine the control conditions is to use a test piece of similar thickness, measure the adhesive force and impact strength of the coating after curing to select the best control conditions, resulting in ills of baking over or under fire. We all have experience in production, powder coating requirements are harsh curing conditions, the choice of a very narrow range of fluctuations, a little beyond will cause brittle fracture or loss, must strictly control the temperature and time.
(4) Rework of defective products 1. General unqualified products: If there are dirty spots, virtual spray, flow plastics, scratches, etc., sandpaper dry grinding method can be used, and after grinding and drying, the whole method of re-spraying is carried out again. Rework. Can not be repaired by local refilling.
2, the product surface pits or bumps off the film and other defects, the entire coating film needs to be removed, wipe clean, the overall re-spray rework.
3, large areas of rickets or painted parts have been baked too hot, you need to remove the entire coating, wipe clean and then re-spray. Film stripping method: Available film remover, concentrated sulfuric acid can also be used. The former is a mixture of organic solvents, volatile, more expensive, but its non-corrosive materials, fast film. The basic mechanism is to destroy the binding force between the coating film and the body. Pieces fall off. I advocate using a film remover, which is cheap and slow to remove the film. Its mechanism is to directly destroy the epoxy coating and generate resin sulfonate. However, careless operation can cause excessive corrosion and lead to scrapped parts.
4. The defects of the coating film at the corners of the dead spot can be solved by the partial repair of the nitro lacquer or amino baking paint of the same color.