Pre-treatment system

To remove surface pollutants such as dirt, oil, greases, rust from steel, galvanized steel, aluminum or plastic parts, the surfaces should be chemically pretreated in order to guarantee the adhesiveness of coating. We can provide various types of pretreatment to meet different applications:

Spraying pretreatment Suitable for single shape and bulk production, fully automatic painting line.

Dipping pretreatment Suitable for various shapes, materials and sizes of products and inner surface pretreatment.

Rolling wash pretreatment Suitable for sheet metal.

Waterfall pretreatment Suitable for aluminum profile pretreatment in fully automatic vertical line.

Powder Spray

The powder is applied with an electrostatic spray gun to a part that is at earth (or ground) potential. Before the powder is sent to the gun, it is fluidized:

– To separate the individual grains of powder and so improve the electrostatic charge that can be applied to the powder and

– So that the powder flows more easily to the gun.

Because the powder particles are electrostatically charged, the powder wraps around to the back of the part as it passes by towards the recovery system.

The purpose of the powder booth in electrostatic spraying is to ensure that powder from the application device stays inside the booth. This then offers the opportunity to collect the over spray and recover it .

It is the duty of plant designers to ensure that sufficient air movement is provided to accommodate in safety the amount of powder being handled at any particular time.

Spray Booth

An important element of the spray booth is the material of which it is constructed. Typically, booths are constructed of polypropylene, stainless steel, or coated steel panels. Some booths are a combination of materials. One unique design utilizes retractable polyethylene sheeting. Selection criteria include: effect on transfer efficiency (whether the booth material is conductive or non-conductive), clean ability (how strongly the powder is attracted to the booth wall), visibility in the spray area (translucence of the material), as well as strength, durability, and reparability given the size of the booth and specifics of the application.

Parts openings in a spray booth should be sized properly to allow clearance for the largest part to be coated. Openings for automatic and manual spray stations should allow sufficient access and be properly positioned for best coating efficiencies. Accommodations must be made for the induced air flows associated with spray equipment. Booth walls around such openings should be configured and contoured appropriately to minimize “dead zones” in the spray area where powder can build up.

Powder Recovery System

By collecting the powder, which passes by the job, and filtering it, the efficiency of the process can be increased to 95% material usage.

Curing Oven

The powder will remain attached to the part as long as some of the electrostatic charge remains on the powder. To obtain the final solid, tough, abrasion resistant coating the powder coated items are placed in an oven and heated to temperatures that range from 180 to 220 degrees C (depending on the powder). Under the influence of heat, a thermosetting powder goes through 4 stages to full cure.

MELT, FLOW, GEL, CURE

The final finish depends on accurate control of the oven temperature and on the following factors: The volume of circulating air is dependent on the required temperature, heat consumption and the temperature difference between the forward and return air. The temperature tolerance is ±5 °C. Heating – up and holding times are influenced by the mass of the internal oven components, such as intermediate walls, reinforcements and heat insulation. However, the nature of the work pieces, its density on the suspension system and the thickness of the material are also important criteria in designing the oven. Considerable care is therefore needed in the design of all detailed components of the oven.

Various oven structures have been developed , and the overall plant design and the space available will determine whether a continuous oven, a reverse oven or one of the many other types is advisable. Our experienced designer will always make his plant design flexible to conform to specific requirements. Another factor which also determines the surface quality is the amount of time the work piece is in the curing oven. When using a continuous oven with set production throughout rates, the temperature must be controlled within prescribed limits. Depending on the powder type, hardening is carried out at up to 250 °C.