7 Ways to Improve the Pickup Rate of Powder Coatings!

The powder coating rate of powder coatings can also be understood as the coverage rate of powder coating workpieces, and the powder coating powder coating rate is the most specific performance of its utilization rate

Ideally, we want 100% of the sprayed paint to be adsorbed on the workpiece, without any paint entering the recovery system

On the premise of ensuring the appearance and mechanical properties of the powder coating film, the unit powder consumption is the most important production cost control indicator for customers, so the powder coating rate of the powder coating is very important

So, what are the factors that affect the powder coating rate? How to improve the powder coating rate of powder coating? Let's discuss it together today

#Factors that affect the powder rate

The electrification of the powder coating itself

There are many factors that affect the powder application rate.

The ideal state is that when the powder is close to the workpiece to be sprayed, the combined force of the compressed air driving force, air resistance and gravity is 0, and the powder paint particles are only adsorbed to the surface of the workpiece under the action of electrostatic force

From this, we can infer that the factor that conventionally affects the powder coating rate is mainly the chargeability of the powder coating powder

Other influencing factors

In addition to the characteristics of the powder coating itself, the factors that affect the powder coating rate of the powder coating are also related to the type of spray gun and process parameters

The distance of the spray gun directly affects the powder application rate.
The closer the spray gun is to the workpiece, the better the powder application rate.
However, as the gun distance is closer, the phenomenon of reverse ionization and breakdown intensifies
.

The grounding of the workpiece also affects the powdering performance, and a good grounding is conducive to the adsorption of powder particles
.
In addition, the influencing factors include the shape of the workpiece, the density of the workpiece pendant, the position setting of the spray gun, and so on
.

#How to improve the powder coating rate

Controlling particle size and distribution of powder coatings

Since the particle size of the powder coating is related to the charge amount, the larger the particle size, the greater the charge amount.
If the particle size distribution of the powder coating is not uniform, the larger particle size will reach the surface of the sprayed object first, and the smaller particle size will appear.
The latter arrives or cannot be reached, which reduces the one-time powder application rate and is prone to problems with the appearance of the paint film
.

Therefore, it is necessary to control the particle size of powder coatings within a certain range, neither too large nor too small.
Each enterprise will formulate its own standards according to the needs of downstream customers.
Generally, the particle size is about 40-50 μm
.

Improve the chargeability of powder coatings

An appropriate amount of conductive additives is added to the formula of powder coatings (mechanism of action: the powder particles can be charged more), there is a strong electric field in the area between the high-voltage electrostatic spray gun and the workpiece, and the air is ionized to generate hundreds of millions of ions, the powder particles of the energizer are polarized when passing through this area, which can trap more negative ions and carry more charges
.
For parts such as the dead corners of the grooves, due to the weak Faraday effect, the powder particles with more charges can reach the surface of the workpiece by their own power, thereby improving the powdering of these parts
.

Increase resin content

In the composition of powder coatings, resin is a polymer compound, and its dielectric constant is the highest, and the dielectric constant of pigments and fillers is low
.

If there are more substances in the powder coating with high dielectric constant, the one-time powder rate will be increased during spraying, but at the same time, the cost will also be increased, and the coating company needs to configure the resin content according to customer needs
.

Reasonable selection of fillers

The fineness and dispersion of fillers are closely related to powdering
.
The precipitation powder is higher than that of general ultrafine heavy barium, and barium sulfate is better than calcium carbonate
.

Control of physical properties such as powder fluidity/moisture

The moisture content and powder fluidity of powder coatings in the manufacturing process are also closely related to the powder rate
.

Under the influence of equipment cleaning or weather and condensed water, the powder will contain more or less water, which will directly affect the fluidity of the powder and the surface of the coating film, and also reduce the powder coating rate.
Therefore, we need to reduce the water washing equipment.
, Control the humidity of the air inlet, reduce the production of high humidity weather and other means to reduce the water entering the powder
.

In addition, the use of flow aids such as fumed silica and alumina C to improve the fluidity of the powder is also an effective method to improve the powder loading rate
.
It should be noted that the type and fluidity of the flow aid need to be adjusted according to the powder coating production process, air temperature, humidity and customer equipment requirements
.

Choose the right spray gun

The size of the powder spraying rate of the spray gun is related to the type of spray gun, process parameters, the shape of the workpiece and the spraying method
.
When it comes to powder coating, the importance of one-time powder application cannot be ignored.
A good spray gun can achieve a rated powder application rate of 80%
.

In the case of spray guns, dense powders can block each other's charging paths, leaving the powder behind with no or very little charge
.

From the point of view of the spraying process, when the coating surface reaches electrostatic equilibrium, the powder particles coming from behind and the particles on the coating surface will repel each other, or even fall off by the opposite motion of ionization, and be recovered by the recycling equipment
.

Therefore, the amount of powder output should be measured according to the electrification capability of the spray gun, and more consideration should be given to whether these powders are fully electrified, and it should also be determined according to the shape of the sprayed workpiece and repeated experiments
.

Whenever the powder provided by a new supplier is replaced, a workpiece with a new shape is sprayed, or the production chain speed is changed, experiments should be carried out to determine the working voltage, output current, compressed air pressure, air outlet flow and workpiece hanging method, etc.
To optimize the process parameters, instead of simply increasing the voltage and increasing the air output
.

Reasonable spraying distance

In the case of static voltage determination, the electric field strength is inversely proportional to the distance between the poles
.
When the distance between the spray gun and the workpiece is too short, spark discharge will occur; if the distance is too far, the powder loading rate will be reduced
.

The relationship between spray gun distance and breakdown voltage is shown in the figure below.
It can be seen from the figure that when the electrostatic voltage is controlled at 60~90kV, the electrostatic spraying distance is more suitable between 250~350 mm
.

#summary

Powder coating rate is a technical index determined by many factors.
There is more than one fixed parameter in powder coating process.
In addition to the above factors, powder coating rate is also related to powder storage conditions, spraying process parameters such as construction voltage, gun distance It is related, and needs to be adjusted flexibly according to the problems in practical application
.