High Adhesion Polymer Alloy (HAPA) plastic coating powders have been specifically designed to provide a long lasting, chemically and mechanically tough coating for both exterior and interior applications.

HAPA coatings are a superior choice when compared to the conventionally used PVC and polyester coatings. The coating has excellent adhesion to the base metal and is almost impossible to peel off.

Coating Method

1. Fabrication

The metal plate is de-greased, de-rusted, de-scaled, passivated and cleaned. Thin "wire loops" or hooks should be attached at suitable locations, for ease of handling the article, so as not to mar the product appearance. These are later cut off or removed after the entire operation is over.

2. Preheating

The bare article is heated in the oven at 250-300?C (480-570?F) for 5-10 minutes. The heating time and temperature depends on the mass of the article and the loading of the oven. This has to be practically ascertained to provide the desired production rates and coating thickness.

3. Coating

The heated article can be coated in two ways:

Spray Coating: The powder can be sprayed onto the article using electrostatic spray guns. The air velocity and amount of powder should be suitably adjusted so as to prevent over spray or bouncing back of the powder spray.

Dip/Fluidised Bed Coating: The heated article is dipped in a tray containing the powder and the powder is splashed on it or dipped in a fluidised bed of the powder for 2-5 seconds. The powder will stick to the hot article. Once the article is coated, care should be taken to ensure it does not rub or come into contact with any surface, to prevent damage to the coating.

At this stage, a rough powdery, but uniform coating on the article is obtained. The excess un-melted powder is shaken off with a slight jerky motion or light tapping. The coating thickness increases with the pre-heating temperature and dipping time.

4. Fusion Sintering

To smoothen out the powder and provide a glossy surface, the article is re-heated in the oven for 2- 3 minutes. The suggested temperature varies between 120-140?C. This causes the powder to melt, sinter and flow out. Excessive heating may cause the coating to discolour or sag. The article should be carefully taken out of the oven, without coating coming into contact with any other surface and allowed to cool in a clean dust free atmosphere. Sometimes water quenching is also resorted to, for wire products.

5. Inspection & Post Finishing

The thin "wire loops", attached earlier for handling the article, are carefully snipped off at the base so as not to mar the appearance. The article is inspected for pinholes or blemishes. These can be filled or repaired with a little powder with a small soldering iron or hot air gun.

Fundamental Notes

• The coating thickness increases with:
• Increase in temperature of the article
• Thickness of the wire, and
• Duration of dipping in the powder.

Product Composition & Colour Customisation

HAPA powders are free of heavy metals (lead, chrome, cadmium, mercury and arsenic) and conform to environmental standards like EN71 Part III, RoHS and REACH. All colours are matched as per internationally accepted RAL, Patone, NCS and IS standards. Customised colours and finishes are available.

(Rapid Engineering Co Pvt Ltd, Rapid Coat Division, Sahibabad, UP. Tel: 0120-2896655. Fax: 91-120-2896656. Email: anuj.gupta@rapidcoat.com)