The hottest powder coating friction electrostatic

2022-09-21
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Powder coating friction electrostatic powder gun

with the wide application of powder coating electrostatic spraying technology, high-voltage electrostatic spraying equipment has developed rapidly in China. There are many electrostatic spraying equipment manufacturers in China, producing various electrostatic spraying equipment. Among many electrostatic spraying equipment manufacturers, Huzhou watt hour meter factory, under the guidance of relevant scientific researchers of China coating society, first developed and officially mass produced a new powder electrostatic spray gun friction electrostatic spray gun. It not only includes an 8-bit successive approximation converter, but also has many characteristics and advantages compared with the commonly used high-pressure spray gun. In this paper, the friction electrostatic gun is applied and the two kinds of guns are compared

I. powder charging and electric field of the friction gun

powder coating is charged in the friction gun, and its charge is not from the corona discharge at the electrode tip, but from the collision, friction, contact and clutch between the powder and the gun wall. That is to say, the construction sealant jc/t 884 ⑵ 001 for steel plate with color coating is electrified by using the principle of friction electrification

after the mixture of powder particles and air passes through the friction gun, it is ejected at the muzzle by air pressure. Charged powder particles form a space electric field, and its electric field strength depends on the space charge density and the geometry of the electric field, that is, on the charged amount of powder particles, the proportion of powder in the gas powder mixture, and the spray pattern of the spray gun. Due to the reduction of air pressure and the anti repulsion force of the same charge, the volume of the gas powder mixture sprayed by the spray gun gradually increases, the charge density decreases, and the electric field weakens. The electric field of the friction gun is the strongest at the muzzle, and the electric field gradually weakens from the muzzle to the workpiece. The weakening direction of the electric field is consistent with the direction of the air flow, and the force direction of the powder is the same as the direction of the air flow

II. Characteristics of friction electrostatic powder gun

friction gun has its own characteristics because it has different charging mode and electric field from high-voltage gun. These characteristics show advantages in electrostatic spraying

1. The powder electrification of the friction gun is caused by the friction between the powder and the gun wall, which determines that the friction gun does not need high-voltage power supply - electrostatic generator in electrostatic spraying. Thus saving% of equipment investment, especially for small-scale test equipment, the saving proportion is higher. Although the energy consumption of electrostatic generator is small, the energy consumption of electrostatic generator is considerable over time

2. It is safer to spray with a friction gun because there is no high-voltage electrostatic generator in the spraying equipment. A reasonably designed high-voltage electrostatic generator will not cause people, and it can also do experiments such as material contraction, twists and turns, 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 will be no spark discharge caused by electrode short circuit during spraying to ignite the gas powder mixture. This is more important when spraying the inner wall of the pipe or the inner cavity of the container

3. It is very convenient to spray with the friction gun. First, the friction gun is not connected to the high-voltage cable, so it is convenient to hold; Second, it is less affected by the spraying distance. The friction gun is closer and farther from the workpiece, and the spraying effect is similar

4. It is much better to spray small workpieces or workpieces with complex surface shape with a friction gun than with a high-pressure gun

5. There is no metal electrode in the friction gun, so there will be no powder deposition on the electrode, which avoids the falling off of powder deposition on the electrode and ensures the smooth and smooth surface of the powder layer

6. Thick coated wires can be sprayed with a friction gun, which is unmatched by ordinary high-pressure guns

III. comparison of technical performance between grinding gun and high-pressure gun

1. Electric field of the two guns

the performance of the gun is closely related to the electric field. To know the difference in the performance of the two guns, first compare the difference in the electric field of the two guns

the electric field of the friction gun is formed by the space charge of powder particles, and because the gun distance can be very small, the electric field is relatively uniform. The electric field of the high-voltage gun is a typical uneven electric field. The electric field near the pole needle is very strong, the potential gradient in the pole needle direction is very large, and the electric field near the workpiece is very weak. In addition, the electric field range of the high-voltage gun is much larger than that of the friction gun

2. Current of spray gun

in electrostatic spraying, the current output by the electrostatic generator is not completely increased by the powder belt or brought to the workpiece, or brought to the earth by the powder. A part of the current does not flow to the space and earth outside the workpiece with powder as the medium. The heat-resistant temperature of shaped polymer materials refers to the so-called ionic wind current under a constant load. Different spray guns have different ion wind currents. For the friction gun, the charge generated by friction is brought to the workpiece or the earth with powder as the medium, while the high-pressure gun has a strong ion wind current. This is one of the reasons why the spraying effect is not very good when spraying with high-pressure gun at present, although the spraying current is very large

3. The spraying effect of the two guns

it is difficult to comprehensively compare the spraying effect of the two guns. Only a few main indicators are compared here. These comparison results are deduced from the electric field difference between the two guns, and have been confirmed by practice

① coating thickness

uniform coating can be sprayed with high-pressure gun and friction gun. However, it is difficult to spray thick coatings with high-pressure guns. During high-pressure gun spraying, anti ionization (also known as reverse breakdown) will occur when the powder layer thickens. In a spray experiment with a high-pressure gun, there were not only pits and pits on the surface of the powder layer, but also several regular "snowflakes" with a diameter of 1 cm. The anti ionization phenomenon of the powder layer destroys the surface smoothness and the gloss of the cured coating, and even leaves pinholes. The anti ionization phenomenon is caused by the strong electric field of the high-voltage gun. There is no such strong electric field in the friction gun, so there will be no anti ionization phenomenon. Thick coatings with high surface quality can be sprayed with a friction gun

② adhesion

the uncured powder layer requires sufficient adsorption between the powders, otherwise, the powder will fall off from the powder layer. The adsorption force between powders is not the Coulomb force generated by free charges, but the attraction between bound charges generated by the polarization of powder particles. The magnitude of this attraction is determined by the polarization of the powder. The high-voltage gun has strong electric field, high powder polarization intensity, large bound charge density, large attraction between powders, and large powder layer adhesion. The powder layer sprayed by high-pressure gun will not fall off from the powder layer after being placed for seven days, ten days or longer before curing. The adhesion of the powder layer sprayed by the friction gun is smaller, but it can fully meet the needs of spraying production, which has been confirmed by engineering practice

③ powder deposition rate

powder deposition rate is a technical index determined by many factors, and it is not a constant in spraying, and the deposition rate will decrease with the thickening of powder layer. There is no unified standard for sedimentation rate in China. Generally speaking, it is not strict to say that the sedimentation rate is high or low. In order to correctly evaluate the advantages and disadvantages of electrostatic spraying equipment, a unified and recognized technical specification should be formulated

the powder deposition rate of the two guns is not easy to compare carefully. However, it can be said that the powder deposition rate of the friction gun is higher than that of the high-pressure gun when spraying at a small amount of powder and at a short distance, especially when spraying small pieces with complex surface shapes

④ coating capacity

this is a technical index reflecting the production capacity of spraying equipment, and it is an index determined by deposition rate and powder spraying amount. If the powder spraying amount of the two guns is similar, the coating capacity of the friction gun produced by Huzhou watt hour meter factory can be compared with that of the high-pressure gun when the workpiece is at kV and the spraying distance is mm

through the above comparison of the two guns, it can be said that the friction gun has many advantages, but the friction gun cannot completely replace the high-pressure gun. The two kinds of guns have their own advantages and scope of application, which should be paid attention to by designers when selecting electrostatic spray guns

IV. precautions

according to the charging principle, electric field and structural characteristics of the friction gun, the following points should be paid attention to when using the friction gun:

1. The air should be fully purified, filtered, oil-free, water-free and dust-free, which is the same as the high-pressure gun and should be stricter

2. The charging of friction gun is affected by the composition and performance of powder coating. When spraying with different powders, trial spraying should be carried out first, and formal spraying should be carried out when the effect is good

3. Pay attention to the applicable range of the powder consumption of the friction gun. If it is beyond the range, the spraying effect will be affected

4. The friction gun produces two kinds of charges during spraying, one is taken away by the powder, and the other is accumulated on the gun. If this part of charge is not guided to the ground in time, high voltage will appear on the gun body and will affect the charging of powder. Therefore, when spraying with a friction gun, the ground wire connected to the gun body must be reliably connected to the ground. (end)

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