Characteristics of powder spray guns for frictionally charged powder coatings

with the rapid development of powder coating in China, the wide application of electrostatic spraying technology, powder coating high-voltage electrostatic spraying equipment in china has developed rapidlyDomestic has a number of static spraying equipment manufacturing plants, the production of a variety of specifications and models of electrostatic spraying equipment and coating assembly linesIn many electrostatic spraying equipment production plant, Zhejiang Province, Huzhou new four-dimensional coating equipment factory (formerly: Huzhou electric wheat factory) in 1985 in the "National Society of Epoxy Applied Technology" Qiu Henian senior engineer under the guidance of the first successful development and formal mass production of a new type of powder paint spray gun - friction belt electric spray gunCompared with the high-pressure powder gun, which is commonly used at present, this spray gun has many characteristics and advantagesIn this paper, when applying friction-banded powder gun, the characteristics and functions of the two powder guns are compared, friction powder gun powder charge and electric fieldpowder coating in the friction powder gun charged, its charge does not come from the electrode tip corona discharge, but due to the powder and the gun wall of the special beads of polymer material collision, friction, contact, conjugates producedThat is, the use of friction starting principle to make the powder livea mixture of powder coating particles and air flows through the friction gun, using air flow pressure to spray out the muzzleThe charged powder particles form a space electric field, and the strength of the electric field is determined by the density of the space charge and the geometry of the electric field, i.ethe amount of charge of the powder particles, the proportion of powder in the mixture of powder, and the spray graphic of the spray gunThe mixture of air powder ejected by the spray gun, due to the reduction of air pressure and the repulsion of the same charge, the volume of the gas powder mixture gradually increases, the charge density decreases, and the electric field decreasesThe electric field of the friction gun is the strongest at the muzzle, and gradually weakens from the muzzle to the workpiece electric fieldThe direction in which the electric field is weakened is the same as the direction of airflow, and the direction of powder force is the same as that of the airflowsecond, friction electrostatic powder gun characteristics
friction powder gun has different from the high-voltage gun's live mode and electric field, so friction gun has its own characteristicsThese features show their characteristics and superiority in the electrostatic spraying process 1 The powder of the friction powder gun is charged by the powder friction with the gun wall, which determines that the friction gun does not need a high-voltage power supply - electrostatic generator in electrostatic spray Thus, save equipment investment 10 to 30%, especially for small test equipment, the proportion of savings is higher Although the energy consumption of electrostatic generator is not large, but over time, electrostatic generator energy consumption and maintenance repair costs are also considerable 2 It is safer to spray with a friction spray gun because there is no high-voltage electrostatic generator in the spray equipment A reasonable design of high-voltage electrostatic generator will not be personal injury or death accidents, but the stimulation of high-voltage electric shock will always make people nervous In addition, there is no metal electrode in the friction gun, and there is no spark discharge caused by the short circuit of the electrode in the spray and the gas powder mixture is introduced This is even more important when spraying in the inner wall of the pipe or in the inner cavity of the container 3 Spraying with friction spray gun is very convenient, one is friction gun does not connect to high-voltage cable, hand is convenient; 4 It is much superior to a high-pressure gun to spray small workpieces or complex surface-shaped workpieces with friction spray guns 5 There is no metal electrode in the friction spray gun, so there will be no powder accumulation on the electrode, which also avoids the powder on the electrode, ensuring that the surface of the powder layer is clean and flat 6 A thicker coating can be sprayed with a friction spray gun, which is not comparable to that of a normal high-pressure gun three, friction powder gun and high-pressure powder gun technical performance compared the two powder gun electric field
electrostatic powder gun performance is closely related to the electric field, to know the difference in the performance of the two guns, first compare the difference between the two types of gun electric field friction powder gun electric field is formed by the space charge of powder coating particles, and because the gun distance can be very small, so the electric field is more uniform The electric field of the high - pressure powder gun is a typical uneven electric field The electric field near the pole needle is very strong, the electric bit gradient is very large in the direction of the pole needle, near the workpiece The electric field is weak again In addition, the electric field range of the high-pressure powder gun is much larger than that of the friction gun 2 The current of the two powder spray guns electrostatic spray, the current output of the electrostatic generator is not carried entirely by the powder coating to the workpiece, or by the powder coating to the earth And a part of the current does not use powder coating as a medium to flow to the space outside the workpiece, the earth, the formation of the so-called ion wind current The powder gun of different structures, the ion wind current is different For friction allothic powder guns, the charge generated by friction is carried to the workpiece or the earth by powder coating, while the high-pressure powder gun has a strong ion air flow This is one of the reasons why spray is currently with a high-voltage gun, although the spray current is very large and the spray effect is not ideal 3 The spraying effect of the two powder guns it is difficult to compare the spraying effect of the two powder guns in a comprehensive way Only a few key indicators are compared here These results are deduced from the difference softer field difference between the two powder guns and have been confirmed by practice (1) coating thickness
use high-pressure powder gun, friction powder gun can be sprayed out a uniform coating However, it is difficult to spray a thick coating with a high-pressure electrostatic powder gun Anti-ionization (
also known as reverse-punch ) will appear when the powder layer is thickened when sprayed with a high-pressure macaroni gun A high-pressure powder gun spray test, in the surface of the powder layer not only appeared pits, hemp points but also appeared several rules of "snowflakes", its diameter is l
cm the size The anti-ionization of the powder layer destroys the gloss of the surface and the solidified coating even leaves pinholes Anti-ionization phenomenon is caused by the high-voltage electrostatic powder gun electric field is too strong There is no such strong electric field in the friction spray gun, so there is no anti-ionization A thick coating with a friction spray gun can be sprayed with a high surface quality (2) the adhesion of the powder coating
the powder coating layer that has not yet been thermally cured requires sufficient adsorption between the powder, otherwise the powder will fall off the powder layer This adsorption between powders is not a warehouse force produced by a free charge, but a gravitational pull between the bounding charges produced by the polarization of the powder particles The size of this gravity is determined by the intensity of powder polarization High-pressure electrostatic powder gun produces a strong electric field, high degree of powder polarization, the resulting binding charge density is large, the force between the powder gravity is large, the powder layer adhesion is large The powder layer sprayed with a high-pressure powder gun is placed for seven, ten or longer before the final cure, and the powder will not come off the powder layer The powder adhesion of the friction spray gun is smaller, but it can also fully meet the needs of spraying production, which has been confirmed by engineering practice (3) powder coating deposition rate powder coating deposition rate is a technical indicator determined by many factors, and is not a constant during spraying, the deposition rate will decrease with the thickening of the powder layer There is no uniform specification of sedimentation rate in our country, it is not strict to say that the sedimentation rate is high or low in general terms In order to correctly evaluate the advantages and disadvantages of electrostatic spraying equipment, we should develop a unified, we all recognize the technical specifications powder deposition rate of the two powder spray guns is not easy for careful and rigorous comparison However, it can be said that in the small amount of powder spray, close spraying, friction powder gun powder deposition rate is higher than high-pressure electrostatic powder gun, especially in small spray, surface shape complex workpiece is even more so (4) coating capacity
which is a technical indicator reflecting the production capacity of spraying equipment, is determined by the deposition rate of powder coating and the amount of powder spray If the two powder spray guns are similar in amount, the current coating capacity of friction spray gun produced by the new four-dimensional coating equipment factory in Huzhou can be compared with high-voltage electrostatic voltage of 40 to 60KV, spray distance of 200 to 300 mm when high-voltage electrostatic spray gun through the face of the two powder paint powder gun comparison, it can be said that: friction powder gun has many advantages, but friction powder gun can not completely replace high-pressure electrostatic powder gun The two powder guns each have their own advantages, characteristics and scope of application, in the powder coating production line can be complementary, designers in the design of coating assembly line should pay attention to this four, precautions according to the friction spray gun live principle and electric field, structural characteristics, in the use of friction spray gun should pay attention to the following points: 1 air to fully purify, dry, filter, no oil, no water, no dust This is the same as a high-pressure powder gun, but it should be more stringent 2 Friction spray to grab the live effect by the powder coating composition, performance and drying and other factors are greatly affected When spraying with different powder coatings, test spray should be carried out before the effect is good 3 Pay attention to the application scope of the powder supply of friction spray gun, the out-of-range will affect the effect of spraying 4 Friction spray guns produce two types of charge in the spray, one of which is taken away by powder and the other collected on the gun If this part of the charge is not directed to the earth in time, the gun body will have accumulated high voltage, but also affect the effect of the powder charge Therefore, when spraying with a friction spray gun, it must be