Powder electrostatic spraying coating industry has developed rapidly in recent years is the new technology. It is the feature of environmental protection and energy saving, high efficiency, rich color, beautiful, coating of excellent physical and chemical properties, aluminum now almost throughout the home appliances, automobile and other industries, is the future trend of the development of coating industry. In the process of aluminum powder electrostatic spraying, coating grain defect is a common and causes more complex problems. In this paper, several years working experience, the author will cause and control measures of powder electrostatic spraying, communicate with colleagues to discuss. 1. The technological process Powder electrostatic spraying process is as follows: profile preview to skim - water - plasma water washing, chromium - water - plasma water to water control, drying and purging to spray powder coating, curing to inspection, packaging. 2. Coating particles causes and control measures 2.1 profile burr caused by the particles themselves big burr is mainly aluminum rod extrusion scale is not divided, the extrusion speed slightly faster result in cucumber, clearly feel sting when touch. Appear mixed black silicon and silicon carbon particles mainly due to insufficient heat, causing internal components not evenly distributed, the bar after making the aluminum extrusion. Such defects. Most of these particles diameter around 0.1 ~ 0.3 mm, spraying pretreatment can't remove, need to deal with alkali corrosion groove in front of the surface treatment of section processing. Control measures is to strengthen the aluminum substrate, control of the production process to avoid such problems.

2.2 shaped cavity saw material cause of aluminum particles of aluminum extrusion of aluminum profiles cavity after not clean, washed into the trough, after bath in circulation under the action of mixing, dispersion adhesion in different surface profile, the chromizing generated during chromizing with membrane become an organic whole, tightly attached on the chromium film, purging out, lead to larger outstanding coating particles larger particles (0.3 ~ 1.0 mm). Most of such particles plate shaped, with a file file off can be found in the process of particles coated with silver aluminum particles.

2.3 profile end remnants of particles

(1) aluminum extrusion sawing, spray cooling fluid mixed aluminum dust adhesion in the profile end, operator did not wipe clean up in time, lead to material aging cooling fluid into a glue dot, dry after pretreatment can't get rid of.

(2) sometimes after feeding on the profile label to show distinction. Sometimes, posted on the main decorative surface pre-treatment, after remove the label material residues is a little on the viscose. Before treatment bath can't clean profile end adhesion, hot air drying after firmly stick on the profile, such as the operator is not found in time, can cause local coating particles, particles such characteristics are gathering in profiles, on one end of a distribution in the area of the matchbox size range. Therefore, it is necessary to strengthen the quality control of substrate, strengthening the management of sawing. The profile end with a small clip clip tag, can completely solve such problems.

2.4 workshop, attached to the profile of the dust of the ground caused by particles

(1) the company's climate belongs to the northern climate, the floating dust in the air, profile or repair a little place, after chromium surfaces will fall on a layer of dust, purging may appear in large area not clean, not in place with uniform particles.

(2) the air is dry, the dust of the ground grain hardness is very high, on the ground when polishing embedded repair material or scratch the coating of paint film. If you do not clean up in time, can cause larger particles.

(3) cleaning mop the floor, the mud splashed down on the material, form the wet clay, closely attached on the surface profile after dried, very hard very dry, in addition to clean will cause not in time after spraying powder particles larger defects. Produce this kind of defect, the dust composition is SiO2, its surface tension and powder coating surface tension difference is big, so the formation of the particles sag into a small pit, was a highlight in the middle, easy to recognize, but is not easy to repair. Requirements for chromium good profiles and temporary not spray profiles must cover with cotton, avoid dust on the surface, also avoid dirty mud, water point contamination.

2.5 caused by floc particles

(1) cotton clothes, cotton or suede gloves must lead to linear defects. In production, filaments in contact with the end of the profile Angle, burr and so on can produce wire drawing, suspended on the profiles, powder coating curing process, the contraction between the film surface tension, lead to after powder produced linear defects. Therefore require operators wear rubber gloves or thin hard canvas gloves, synthetic chemical fiber clothes wear is not easy to generate filaments, and required before handling personnel scrape all profiles end curf MAO stubble, burr, prevent hang clothes rub silk thread, and spraying point discharge occurring in the drawing, to avoid such defects.

(2) powder curing of volatiles in curing furnace cooling crystallization of import and export for catkin, falling on the powder coating, again with powder melting solidification, due to the inconsistent flowing property, powder coating surface caused by a small group of large particles, particles crunchy texture, easy to scrape off with nails. Require regular purging flocculent volatiles of curing oven and furnace wall, furnace, clean hygiene, to avoid this kind of defect.

2.6 linked with clear net caused by particles In powder electrostatic spraying, linked with polishing cleaning is a very important working procedure, main guarantee has good electrical conductivity. Linked with clear when grinding, can produce a lot of paint at the end of the slag, iron, debris, and due to the resin for powder coating, friction collision itself when knock is electrostatic adsorption on the hanging fixture. If there is no timely hanging fixture in compressed air purging is clean, when powder spray gun will air purging the debris falling on the powder layer. To meet after high temperature curing furnace, automatic electrostatic adsorption of the larger particles, paint slag drop, cause local coating material surface particle defects. All defects such an obvious characteristic is focused on the hanging, hanging point on both sides. Due to debris from hanging above floating down, so the basic distribution on profiles of the above, in the following few, it is easy to identify.

2.7 profile repair caused by granular powder spraying process, some profile because of minor flaws need to grind the repair paint again. In repair grinding melted coating can be created, some of the larger inclusions granules in coating, some fragments by static adsorption on the material, at the end of the compressed air can blow off the surface debris, Mosaic cannot blow off bits. If not carefully remove all these adhesion, can cause defects repair parts with obvious particles. To this end, to rub gently with the fine sandpaper, polished by hand feel after polishing parts smooth grinding burrs generated can be () after the smooth, then repeated with a wet towel to wipe, then use the wind blow dry, so as to remove all adhesion of grinding material, to ensure repair paint.

2.8 particles caused by equipment system is not clean

(1) spray gun head, nozzle, electric acupuncture, mesh size, big cyclone wall, close to the valve cone pipe, casing pipe and the suction powder, powder on the harden layer, if not timely clean, powder spraying under air scour produce small particles onto the powder layer, after curing form significantly larger particles in the coating surface. Clear requires periodic inspection, especially at high temperature in the summer to double check the cleaning, avoid to produce this kind of problem.

(2) curing the dust and debris inside the furnace air filter mesh, as well as aging such as chopped fiber filter, if not timely check clean replacement, will the filamentous defects in the coating surface. Such defects long shape, generally with the hand a little bit hard to rub, or use a sandpaper gently rub off these particles, return repair paint more easily, also don't need to be very laborious.

(3) in production, girder catenary system lubrication mos2 RCC, such as dust, powder, rail scrap iron sludge, in curing furnace falls through curing furnace, hot air blowing, falling on the melting curing coating, this kind of oily sludge in curing will float on the coating surface, after curing in the coating surface form small black particles. The granule is soft, fell, but the black point dye around in black. Due to the sludge from falling off the catenary, so the profile distribution also face on one side. With sandpaper gently rub off the black coating, the return repair paint more easily. To prevent such problems require regular (weekly) clean up the girder catenary, outside the stove with compressed air blowing off girder oil dirt, blowing off catenary orbit, roller bearing on the sludge, iron and other dirt.

2.9 powder coating quality caused by particles

(1) mix powder coating curing harden small particles, the cause is a powder coating factory screw extrusion is not clean, lead to a small half harden curing powder particles into powder, cause there was a large powder particles. These particles can be seen everywhere in the coating, and the uniform distribution, almost the same size. Determine such defects, as long as powder spraying equipment and material surface can be cleaned up. Such defects occur rarely, need not special prevention, as long as the master methods.

(2) packing and powder coating temperature not completely down, powder paint their poor performance, low glass transition temperature and pressure during transit, be affected with damp be affected with damp, can produce large harden. There is something wrong with the use of such powder coating will lead to generate large particles on coating, at the same time accompanied by convex powder, accumulation, fat side, defects such as orange peel, and back to repair the paint is difficult. Preventive measures is to choose the good reputation of powder coatings manufacturers, powder coating when unpacking the case by hand grasp, and pore size of 300 microns screen check. Hand grasp a powder coating, then loosen, whether powder caking, if powder is easy to loose open,, no problem; If you have uneven size of the cluster is not. If screen out the particles, the powder coating must not be used.

3. The conclusion In the process of powder electrostatic spraying, coating grain to form factor is more than these, as long as we are used to shape, size, color, texture, formation of site characteristics should be carefully observation, analysis, test, and the corresponding solving measures, must be able to control this kind of defect, to produce high quality products.