The characteristics of powder coating friction electrostatic spray gun

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

2.
The current of the spray gun

In electrostatic spraying, the current output by the electrostatic generator is not completely increased by the powder or brought to the workpiece, or brought to the ground by the powder.
And a part of the current does not use the powder as a medium to flow to the space and the ground outside the workpiece, forming the so-called ionic wind current.
Different spray guns have different ion wind currents.
For the friction gun, the electric charge generated by friction is brought to the workpiece or the ground through the powder, 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 even though the spraying current is very large when spraying with a high-pressure gun.

3.
The spraying effect of the two guns

It is difficult to comprehensively compare the spraying effects of the two guns.
Only a few main indicators are compared here.
These comparison results are inferred from the electric field difference of the two guns and have been confirmed in practice.

①Coating thickness

Both high-pressure guns and friction guns can spray uniform coatings.
However, it is difficult to spray thick coatings with a high-pressure gun.
When spraying with a high-pressure gun, reverse ionization (also called reverse breakdown) will occur when the powder layer thickens.
In a spraying experiment with a high-pressure gun, not only pits and pits appeared on the surface of the powder layer, but also several regular "snowflakes" with a diameter of 1 cm.
The reverse ionization phenomenon of the powder layer destroys the smoothness of the surface and the gloss of the cured coating and even leaves pinholes.
The reverse 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 reverse ionization phenomenon.
With a friction gun, thick coatings with high surface quality can be sprayed.

②Adhesion

The uncured powder layer requires sufficient adsorption between the powders, otherwise, the powder will fall off from the powder layer.
This kind of adsorption force between powders is not the Coulomb force produced by free charges, but the same is the gravitational force between the bound charges produced by the polarization of the powder particles.
The magnitude of this gravitational force is determined by the polarization of the powder.
The high-voltage gun has a strong electric field and high powder polarization, resulting in bound charges

The density is large, the attraction between the powders is large, and the powder layer has a large adhesion.
The powder layer sprayed by a high-pressure gun will not fall off the powder layer if it is left for seven days, ten days or longer before it is cured.
The adhesion of the powder layer sprayed by the friction gun is smaller, but it can also fully meet the needs of spraying production, which has been confirmed by engineering practice.

③Powder deposition rate

The powder deposition rate is a technical index determined by many factors, and it is not a constant in spraying.
The deposition rate will decrease as the powder layer thickens.
There is no uniform standard for sedimentation rate in our country.
Generally speaking, it is not strict to say that the sedimentation rate is high or low.
In order to correctly evaluate the pros and cons of electrostatic spraying equipment, a unified technical specification that everyone recognizes should be formulated.

The powder deposition rate of the two guns is not convenient for careful comparison.
However, it can be said that the powder deposition rate of the friction gun is higher than that of the high-pressure gun when the powder spraying amount is small and the spraying is close, especially when spraying small parts and workpieces with complex surface shapes.

④Painting ability

This is a technical indicator that reflects the production capacity of spraying equipment, and is an indicator determined by the deposition rate and the amount of powder sprayed.
If the powder spraying amount of the two guns is similar, the coating capacity of the friction gun produced by Huzhou Electric Meter Factory can be compared with that of the high-pressure gun when the workpiece is 40-60KV and the spraying distance is 200-300 mm.

By comparing the two guns above, it can be said that the friction gun has many advantages, but the friction gun cannot completely replace the high-pressure gun.
Both guns have their own advantages and scope of application.
Designers should pay attention to this when choosing electrostatic spray guns.

Four, matters needing attention

According to the charging principle, electric field and structure 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.
This is the same as the high-pressure gun and should be more stringent.

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

3.
Pay attention to the scope of application of the friction gun's consumption of old powder.
Exceeding the scope will affect the spraying effect.

4.
The friction gun produces two kinds of electric charges during spraying, one electric charge is taken away by the powder, and the other electric charge accumulates on the gun body.
If this part of the charge is not guided to the ground in time, high voltage will appear on the gun body and it will also affect the charging of the powder.
Therefore, when spraying with a friction gun, the ground wire connected to the gun body must be reliably connected to the ground.
(Source: Global Coatings Network) (For more information, please log in: Global Coatings Network http:// )