Abstract: The powder coating process, also called powder spraying, is a new type of coating process that has developed rapidly in recent decades. For the powder coating process, there is no doubt that powder saving is the top priority of cost control.
This article discusses five aspects of powder saving, namely: film thickness control, one-time yield, powder loading rate of profiles, management of recycled powder, and methods of hanging materials.
In short, electrostatic powder coating is a high-voltage generator supplying high voltage, the powder captures the charge and becomes a charged powder, which flies to the pre-grounded profile under the action of the airflow and electric field, adsorbs on the surface of the profile, and is baked and solidified by the curing oven to form a solid film layer .
From the principle of electrostatic powder coating, it is not difficult to see that the powder coating process is firstly related to voltage, because the voltage influences the strength of the electric field, thereby affecting the powdering rate;
It is related to the workpiece connecting the profile, the texture of the workpiece affects the conductivity of the profile, thereby affecting the powdering rate; it is also closely related to the equipment and the environment.
To understand and control the powder coating process to a certain extent, we will naturally focus on cost control, and the control of powder unit consumption is quite important.
Similarly, the amount of powder used is inseparable from several major factors that affect the powder coating process. Namely: voltage, work piece, equipment, environment and method, etc.
These factors that affect the unit consumption of powder can be refined and reclassified into five categories: film thickness control, one-time yield, profile powder loading rate, recycled powder management and material hanging methods.
1 Film thickness control
The most important way to save powder is to control the film thickness. The thickness of the film directly reflects how much powder is consumed. If the film thickness is too low, the bottom will appear, and too high will cause orange peel on the surface.
If the film thickness control range is divided in detail, according to the powder characteristics, it can be distinguished from sand grain powder and light powder. Generally, the average particle size of new powder powder is 37μm~43μm, and the particle size of sand grain powder is relatively large, and the powder coverage rate of the profile High, so the film thickness control can take down the lower limit, saving powder consumption to the greatest extent;
The particle size of the light powder is small, and the coverage of the powder on the profile is low. It should be sprayed as thick as possible to avoid flooding, especially the white light powder has high transparency. If the film thickness is not enough, it will easily turn blue, so the light powder should take the upper limit or In the upper limit.
The ideal film thickness control range is a goal and an expectation. It is easy to say but difficult to do. In order to achieve this goal, workshop managers must pay attention to it.
At the same time, the technicians must continue to supervise and monitor in real time, requiring the front-line production employees to operate according to the process, through the accumulation of experience in the powder coating process of various types of powders and profiles, and continuous summary, so that the technology can mature and finally meet our expectations.
2 One-off yield
There will inevitably be defective products in production, and there will also be various problems. These will reduce our one-time yield, requiring rework or even scrapping. Finally, repeated operation or secondary production will not only waste powder, but also waste Time, manpower and material resources.
In particular, the issue of batch size is a huge waste of powder and cost.
To ensure the one-time yield, first of all ensure that the equipment is in good condition. Otherwise, it may cause various problems.
For example, impurities in the surface treatment tank liquid will cause particles on the surface of the material, and if the curing furnace is not cleaned, there will be ash. If the spray gun is not cleaned thoroughly when changing the color, it will produce variegated colors. Therefore, the equipment must be cleaned and maintained regularly to ensure that the equipment is operating normally;
Then strictly control the product quality of each process, strengthen self-inspection, and ensure that defective products are not accepted or released;
Secondly, the operation must be standardized, all personnel must strictly abide by it, improve the management system, and penalize and warn those who do not follow the process and operate in violation of regulations;
In addition, targeted measures should be taken for dystocia models or models with frequent problems, and the process should be strictly controlled to prevent the same problems from recurring.
In short, all aspects of production must be highly valued, and no one can be ignored in order to effectively control the one-time yield.
3 Powdering rate of profile
The unit consumption of powder is directly related to the powder loading rate of the profile. Under the same time and powder flow rate, the higher and lower powder loading rates directly influence the use efficiency of the powder.
The powder loading rate of the profile is proportional to the voltage and current, and inversely proportional to the distance between the spray gun and the profile. Therefore, it is necessary to ensure a certain voltage and current intensity to enable the charged powder to be well absorbed on the surface of the profile.
The control of voltage and current should not be too high, otherwise it will cause electric shock marks on the surface, and it should not be too low, otherwise the charge of the powder will be small and the powdering rate will be reduced.
For this reason, the powder should also have good electrical conductivity, so that under a certain voltage and current intensity, it can be ensured that the powder has enough electricity to be adsorbed on the surface of the profile.
When it comes to electrical conductivity, one thing that cannot be ignored is the cleaning of auxiliary equipment. Because we know that the principle of electrostatic spraying is simply to use the pole needle of the spray gun head as the electrode, and the high voltage generator is supplied with high voltage. When the powder is sprayed from the spray gun, the charge is captured and becomes a charged powder. The charged powder is adsorbed by the attraction of the electrostatic field. Profile surface.
Therefore, under the action of a certain electric field force, the electrical conductivity of the hanger, the hanger, and the chain will directly affect the powder loading rate of the charged powder. Therefore, these auxiliary equipment should be cleaned regularly, and should not be covered with grease and dust, otherwise it will affect the conductivity of the profile and reduce the powdering rate.
The distance between the spray gun and the profile should also be controlled. If the distance is too close, it will produce gun marks. If the distance is too far, it will reduce the powdering rate. Adjust the best distance. Adjust the distance between the spray gun and the profile according to this optimal distance to ensure the profile. Under the premise of surface quality, it can effectively increase the powdering rate.
4 Recycled powder management
The recovered powder is the powder that is not sprayed on the workpiece after the powder is sprayed once, and is recovered by the special recovery equipment.
The main feature is that the content of coarse and fine powder is higher than the normal powder ratio, and the large particle size of coarse powder may cause surface particles. The fine powder is easy to agglomerate and easily cause powder spitting. Moreover, the recycled powder has poor fluidity and poor powder loading, so it is generally not recommended Spray directly.
However, the amount of recycled powder produced is huge, and if it can be used, the powder savings will be very considerable.
For how to use recycled powder correctly and reasonably, the management of recycled powder is very important. Generally, the following points should be included:
1) The general recycled powder cannot be sprayed directly. It should be mixed and matched with new powder. The mixing ratio should be determined according to the surface effect and quality requirements;
2) The use of recycled powder should be used as early as possible, and it is best to mix it with new powder while producing it. Generally, if the recycled powder is stored for more than three months, check whether the powder has agglomerated;
3) For flat products, if the surface requirements are relatively high, an appropriate mesh should be used after sieving;
4) For metal powder products, pay attention to the same proportion when adding recycled powder to avoid color difference;
5) In the mixed color powder, the coarse powder in the general recycled powder has more components, and it is required to select a suitable screen before sieving;
6) When using a larger proportion of recycled powder, appropriate additives can be added to improve the fluidity and powdering rate of the powder;
7) Maximize the first powder application rate and reduce the production of recycled powder, such as increasing the hanging density of the workpiece, maintaining a good grounding, and adjusting the spray gun conditions and positions.
The above are just the basic principles in the management of recycled powder. The specific situation should be analyzed in detail. The use of recycled powder must not be ambiguous or careless, because any carelessness will cause bad batches, so that the recycled powder will not be effectively used. Also wasted new fans and wasted cost.
5 Hanging method
The amount of powder used and the surface effect are also closely related to the way of hanging the material. If the hanging material is improper, it will waste powder, and if it is heavy, it will produce batches of defective products, which is a great waste of powder and cost.
The position of the punching and hanging material should be determined according to the material model and decorative surface. Make sure that the decoration faces the spray gun. For materials with slots and corners, the slot angle should be aligned with the gun. The first thing to consider is to meet the condition that the slot angle does not show the bottom. Under control the film thickness to spray.
If the material is improperly linked, causing the gun at the corner of the slot to be backed, then the corner of the slot is exposed and needs to be reworked. The powder sprayed on the front is wasted;
If the slot angle is facing the gun obliquely, it will make the powder rate at the slot angle position low, and more powder is needed to ensure that the slot angle position does not reveal the bottom, and the film thickness on the other sides will be very high, and the powder will also be wasted.
Before producing each model, the density of the hanging material should also be carefully considered, because the density of the material hanging will increase the powdering rate, but it may also cause the side film thickness to be low and cause the bottom;
On the contrary, if the density of the hanging material is too thin, the powdering rate will be reduced, and the side film thickness may be too high to cause orange peel. Therefore, it is necessary to conduct a detailed analysis of most common types of materials to select the best hanging material density to form a standard.
Lean production is the goal of each of our companies, and it is also our responsibility. It is very important for cost control. For the powder spray production workshop, powder saving is the core of cost control, and of course it is also the direction that we need to focus on and work hard.