This is a brief talk about the problems that should be paid attention to in powder coating manufacturing equipment and production process.

1 Introduction:
powder coating as an efficient, energy-saving, resource-saving and environmentally friendly paint varieties, has been the world's attention, especially by China's attention. Although China's powder coating industry started late, but because of the attention of the country and the whole people, reform and opening up 30 years of rapid development, has now become the world's largest powder coating production, accounting for half of the world's total powder coating production. According to the relevant information, the output in 2008 was 720,000 t, and the output in 2009 is expected to increase by 15% over 2008 to more than 800,000

.the development of
powder coating industry also promotes the corresponding epoxy resin, polyester resin, curing agent, additives and other supporting raw materials industry development, but also promotes the development of supporting powder coating manufacturing equipment industry, now including foreign-funded enterprises, the vast majority of enterprises are using domestic powder coating manufacturing equipment, not only small and medium-sized production equipment and laboratory equipment can be manufactured, product quality has been greatly improved, a considerable number of sets of equipment exported to countries around the world each year. The quality of powder coatings depends not only on the quality of raw materials, but also on the control of powder coating manufacturing equipment and process conditions. As we all know, powder coating manufacturing equipment is mainly composed of high-speed mixers, extruders, cooling rollers, cooling belts, crushers, air grading grinding, cyclone separators and screening machines. From the production process considerations include: raw material weighing and high-speed mixer premixing process, extruder melt extrusion mixing, cooling roller and cooling belt cooling and crusher crushing process, air grading grinding and cyclone separator grading and screening machine separation process, product packaging process. There are many articles on the manufacturing equipment and production process of powder coatings, which are reported in many articles, and the following are specifically related to the problems that should be paid attention to in the production equipment and process control of powder coatings according to many years of production experience.
2 weighing and premixed
weighing are one of the most critical processes in powder coating manufacturing, and the selection of weighing utensil sensing and the accuracy of weighing processes are important factors in determining the accuracy of formulations and the quality of powder coating products. Therefore, according to the quality of the material in the formula, choose the appropriate amount of the measure for weighing, it is best to use the weighing convenient electronic scale, conditional conditions, in the weighing process should be reviewed. In order to weigh and feed in the convenience of large quantities of resin, titanium dioxide, nirconium sulfate and other raw materials, after reviewing the quality of the whole packaging of the material, can be the whole packaging of the material cast on the whole packaging feeding, the rest of the zeros for specific weighing. Weighed materials are premixed, and the equipment used in premixes is typically high-speed mixers and automatic mixers. The advantages of high-speed mixer is simple equipment, low price, easy to use, the disadvantage is that the equipment fixed in a place can not be moved at will, the bottom of the tank cleaning is not convenient, color change is also slightly troublesome. The advantages of automatic mixer is the high degree of equipment automation, cleaning and color change than high-speed mixer convenient, equipment can be moved, can be used for multiple extrused equipment;
In the use of premixed equipment, should pay attention to the following issues:
(1) carefully check the equipment, especially the motor rotation shaft and other parts of the sealing situation, timely eliminate the seal and connection of the material blockage or bonding problems.
(2) carefully clean the equipment to prevent interference and contamination of new materials.
(3) According to the material situation, select a good crushing time and mixing time.
(4) in order to mix the material evenly, the large particles such as epoxy and polyester resin are pre-crushed.
(5) For the same formula, the material order of each feed should be consistent, the mixing time is also fixed, in the formulation of less pigments and additives and other materials to avoid being placed in the mixing shaft core, as far as possible on the edge of the tank so that the material in the mixing dispersion is more uniform.
(6) in order to mix the material evenly, in principle, the amount of feed should not exceed 80% of the capacity of the mixing tank.
(7) from safety and hygiene considerations, mixing tank should be installed on the exhaust equipment, in the ingredients and mixing timely removal of dust generated.
3 Melt extrusion mixing and cooling crushing
In order for the various components in the powder coating formula to be evenly dispersed and the composition of each powder coating particle to be exactly the same, the premixed material needs to be melted out of the mixture with a extruder, so that the ingredients in the formula are better dispersed evenly. Because this process can be used to ensure that the composition of powder coating particles is consistent, thus ensuring the static spraying of powder coating charge performance and film performance stability, so the melt extrusion mixing process is the most important process to ensure the intrinsic quality of powder coating.
In order to prevent the material from continuing to react chemically affecting the quality of the powder coating, the molten extruded material is cooled and finely crushed, generally using cooling rollers and cooling bands to cool to room temperature, and the crusher is used to break into 1mm ×5mm×5mm or so of paint sheets that can be finely crushed.
fusion extruder is currently the main domestic use of double screw extruder and reverusive single screw extruder, of which double screw extruder is more commonly used. Comparing the performance of the fusion mixing effect of the extruder, the easy cleaning of the equipment, the temperature control of the material, the performance of the reverberation single screw extruder is better than that of the double screw extruder, but the structure of the equipment is more complex, and the repair and replacement of the screw and screw fittings is better than Double screw extruder trouble, high requirements for processing materials (e.g. can not enter the metal foreign body) and the price of equipment is more expensive, etc. are the disadvantages of re-entry single screw extruder, so according to the requirements of the production of powder coating varieties to choose the type of cost-effective extruder.
With the technological progress of powder coating manufacturing equipment in China, the variety of equipment increases, product quality is also greatly improved, processing accuracy and production efficiency from the extruder alone is much higher than before, so the dispersion effect of powder coating has been improved, the same screw diameter production increased a lot. However, due to the reduction of the gap between the screws and the increase of the screw speed, the extrusion temperature of the material is significantly increased, from the original 120 degrees C to the current 140 degrees C or so. Therefore, the temperature control of extruders is higher, and the cooling of extruded materials is also higher. From the twin screw extruder, the general screw between the feeding section and the melting section of the solid to melt transition section of the maximum wear, need to consider this part of the screw material to choose a good wear-resistant material, and the use of easy to replace the module structure is very necessary. This extends the life of the equipment and ensures the stability of its use. Although the cooling of the single screw extruder can be controlled by the internal flow of water through the screw, the internal cooling technology of the screw of the twin screw extruder is very difficult. There have been units to test the method of water cooling inside the twin screw, but the stability of the screw seal and other issues have not been satisfactory solution. Therefore, the screw cooling technology of the twin screw extruder has not been satisfactory, which is the key problem to control the extruder extrusor material temperature.
addition, due to the increase of extruder speed, the production of extruder is increased, however, the noise of the transmission becomes erred and the impact of noise increase needs to be solved. As mentioned above, the temperature of extruded material in the extruder increases and the difficulty of controlling the extruded material temperature is a new problem. On the feeding funnel of the extruder, in order to prevent the material from overhead, it is best to install vibration or pulse device to prevent the material from breaking off, and it is necessary to maintain the stability of the feeding rate.
should pay attention to the following problems when using extruder:
(1) According to the powder coating variety, select the control temperature of extruder feed segment, melting section and ionization segment.
(2) when starting production, with the formula of materials or resin cleaning extruder, in order to prevent the film to produce mass (particles), after a period of time to use (or produce a certain amount) after regular use of PVC, polyethylene, rice, corn and other materials cleaning extruder, remove glue attached to the screw and screw, especially in the production of coating film appearance requires high varieties to pay more attention to this problem.
(3) according to the production capacity of the equipment, adjust the speed of the extruder main motor and the filling speed of the adder.
(4) From the chemical stability of the material, the internal material temperature of the extruder is sufficient to make the material melt and mix evenly, as far as possible at low temperature melting mixture, especially low temperature curing powder coating varieties, so that the extruded material temperature is kept at a lower temperature, to avoid chemical reactions in the extrusion process, thereby affecting the quality of the powder coating.
(5) When the extruder is stopped, the material containing curing agent in the screw must be introduced with the resin in the formula to prevent the material from curing in the screw and affecting the use of the equipment, and when the reboil is re-started, the resin material in the screw must be extruded from the material in the production formula, and the resin material must be placed separately, used in the clearing machine or treated as waste, to prevent these materials from entering the normal production product, interfering with the quality of the product coating appearance, etc.
(6) When using the extruder, regularly remove the attachment from the extruder extruder and part with the normal product. Because there are many gels in this attachment, if brought into the fine crushing process, it is easy to cause the mass (particles) of the coating film, so these materials and by-products are treated separately.
(7) In the temporary power failure, on the one hand, increase the cooling water to make the material in the extruder cool quickly, on the other hand, add a small amount of resin with a hand-shake rod rocking motor to launch part of the material, to prevent material curing in the extruder screw. In order to allow the extruded material to cool quickly and prevent the continuation of chemical reactions, it is generally pressed with a cooling roller into a paint sheet about 1mm thick and cooled, then cooled to room temperature with a cooling belt, and then broken with a gear crusher to a material that can be finely crushed. Cooling rollers are generally cooled by the inside of the roller through cooling water, depending on the water temperature in summer can be treated with frozen water or cooling tower cold water. There are many cooling methods of cooling belt, including water cooling, wind cooling, feng shui combined cooling, cooling with steel belt, track, mesh belt and other shapes, cooling belt structure has closed, open, etc. , each has its own characteristics, according to user requirements and environmental conditions to choose the appropriate cooling equipment and cooling methods.
The following issues should be noted when selecting and using cooling equipment: the production capacity of the
(1) extruder should be matched with the production capacity of the cooling equipment, especially during the summer high temperature season, the production capacity of the cooling equipment should meet the requirements of the extruder production capacity.
(2) the diameter, length, width of the cooling belt, length and other equipment parameters to fully meet the extruded material cooling to break the required temperature, especially in the summer high temperature season production and production temperature requirements.
(3) according to the product coating appearance quality requirements, choose closed or open cooling equipment. For the production of powder coatings for household appliances with higher coating appearance requirements, it is best to choose a closed cooling system, which is conducive to preventing the effect of dust and other pollutants in the environment on the quality of powder coatings, especially on the appearance of coating cleanliness and mass (particles) and so on.
(4) from the stability of powder coating product quality considerations, the general temperature of broken materials should not exceed 35 degrees C, preferably below 33 degrees C, especially in summer production environment temperature is higher, pay attention to the temperature of broken materials should not be too high, to prevent powder coating products too high temperature and affect the storage stability of powder coatings.
(5) from the efficiency of fine crushing, the thickness and size of the broken paint piece should not be too large.
(6) extrusion after cooling and in the process of crushing friction easy to produce static electricity, in order to prevent the equipment with static electricity, all equipment should be grounded, especially the paint chip moving material tank should also do a good job of grounding, to prevent static electricity on the human body stimulation and cause accidental injury.
4 Fine crushing and grading screening
after melting out of the mixed crushed material, in order to achieve the static powder coating requirements of the powder coating particle size distribution, but also need to use air grading grinding (commonly known as ACM grinding) fine crushing, and then with cyclone separator separation to remove ultra-fine powder coating, and then used sieve equipment to remove the coarse powder coating, to get suitable for powder coating static coating products. Fine crushing process is an important link to ensure the particle size distribution of powder coating and the effect of electrostectrulation powder coating. In this process, the performance of air grading grinding is the key equipment to determine the particle size distribution of powder coatings. If the performance of the equipment is good, the particle size distribution of powder coating is suitable for static powder coating requirements, coarse powder and ultra-fine powder content is small, the product yield is very high, reaching more than 96%. In air grading grinding, crushed material is graded by sub-grinding, powders that meet the set granularity requirements enter the cyclone separator for separation, and crude powders that do not meet the requirements remain in the air grading grinding for re-crushing. Into the whirlwind separator powder, the isolated ultra-fine powder sent to the cloth bag filter for recycling, coarse powder to the screen powder machine for separation; Throughout the fine crushing and screening process, the fan acts as a conveyor.
The following issues should be noted when using air grading grinding:
(1) the production capacity of air grading grinding should be matched with the production capacity of extruders, especially taking into account the actual problems of the decline in air grading capacity in summer due to the influence of temperature.
(2) air grading grinding production capacity should also be matched with the production capacity of sieve powder machine.
(3) air grade grinding powder coating particle size distribution to meet the requirements of electrostitive powder coating, through the air grading grinding of the main grinding motor speed, sub-grinding motor speed, the adjustment of the acceleration motor speed to control the particle size distribution of powder paint, but also through the separation effect of cyclone separators, the size of the fan door and other parameters to control the content of ultra-fine powder, the general content of ultra-fine powder should not exceed 2%.
(4) Because the temperature affects the crushing effect of powder coating, especially in summer and winter particle size distribution is larger, the specific performance in the production volume, in order to ensure the particle size distribution of powder coating is stable, in different seasons to determine the particle size distribution, and timely adjustment of powder coating particle size distribution is close, so that powder static coating effect does not change significantly.
(5) in the summer workshop environment temperature is higher, affecting the fine crushing effect of the broken paint, it is best to install a cooler at the air grade grinding air inflect, reduce the temperature of the crushing material and crushing equipment, to ensure that the temperature of the crushed products is less than 35 degrees C, to prevent powder coating lumps, to ensure the looseness of powder coating and storage stability. If there are conditions, the production workshop using central air conditioning is better.
(6) For powder coating finished products to add additives such as loose agents, etc. , in the past generally used from the air grade grinding air inflection, this method is conducive to the dispersion of additives evenly, but easy to make the additives pumped into the cloth bag filter, the loss of additives is serious;