What is Powder Coating?
Powder coating is a method of applying powder to a conductive substrate where powder particles are given an electrical charge allowing them to deposit on substrates of the opposite charge when influenced by a direct current.
The resultant paint finish is of a high aesthetic standard affording strong durability, high impact resistance, high resistance to fading and resistance to corrosion and the effects of corrosive liquids and chemicals.
Over the years the process has been modified to remove all hazardous air polluting solvents together with virtually all volatile organic compounds. Equally, the process used by Profin contains no lead compounds or chromium in any format.
Powder coatings provide good adhesion to most conductive substrates, provided that the surface is properly cleaned, by removing any oil, grease and dust contamination, and that it is thoroughly dried.
Anticorrosion and durability depend upon the substrate, and type of pre-treatment used.
In order to present the components in a fit state for powder coating, they may first have to undergo a series of preliminary processes which are outlined in more detail on the subsequent pages.
Briefly the preliminary processes are as follows:
- Cleaning to remove all debris and lubricants from the components.
- Iron phosphating in order to change the surface and formulate a phosphate film on the surface which has the ideal grain configuration for painting.
- Followed by stoving through a gas fired oven.
- OR Zinc phosphating in order to change the surface and formulate a phosphate film on the surface which has the ideal grain configuration for painting.
- The powder coating painting operation itself.
- Followed by stoving through a gas fired oven.
In order to remove all debris, oils and contaminants, a series of different cleaners used in the first three process tanks.
These vary from a low strength ‘knock-off’ cleaner to a highly caustic powder cleaner to a full degreasing. The various cleaning methods used are effective on a wide variety of oils and greases. The high alkalinity of the caustic cleaners helps shift some types of soil although the level of caustic is not sufficient to de-rust effectively.
Occasionally oils and greases are encountered which cannot be removed by the three cleaners used. When this situation arises, the parts are degreased using either our cleaning plant or the iron phosphate and cleaning plant.
Trication Zinc Phosphate deposits a fine crystalline zinc phosphate at around 1 -3 grams/ M². The Trication formula comprises a mixture of zinc, manganese and nickel to make up the phosphate structure. The Nickel content is expressly excluded from the substances of concern list in the ‘End of Vehicle Life Directive – 200/53/EC’ This is due to the fact that currently there is no better way to phosphate automotive parts.
‘Tricats’ generally ‘sludge’ less than traditional calcium modified zinc phosphates and are favored by Honda, amongst others. Keeping the temperature low, if possible, helps minimise ‘mapping’ problems from uneven phosphate build up.
This process is in accordance with BS 3189 Type 4 and DEF STAN 03 – 11 Class IV
Iron phosphate deposits a fine crystalline phosphate surface at around 0.2-0.4 grams/M². The phosphate is applied by a spray process through a high-pressure on-line production spray line which has the added advantage of cleaning the parts as well as applying the phosphate.
The chemical used is a liquid material which is a combined coater (heavier coating weight phosphate) and cleaner solution designed to simultaneously degrease and pre-treat ferrous substrates prior to painting.
Special points of interest
- Salt spray resistance to a 500 hours as per ISO 7253
- Humidity resistance to a 1,000 hours in accordance with DIN 50017
- Adhesion in accordance with ISO2409 to GtO
- Persoz hardness in accordance with ISO1522 greater than 95
- Pencil hardness in accordance with ASTM D3363-92A at 3H
- Impact Resistance (direct/reverse) in accordance with ISO6272 to > 2.5 N.m.
- Conical Mandrel in accordance with ISO6860 giving 0 – 10 mm.
- Erichsen in accordance with ISO1520 giving > 5mm.
As previously stated, the process applies powder to the surface of the component by electrically charging the powder particles which, in turn, are then deposited onto the conductive substrate being the opposite charge.
The powder is applied using powder guns which are powered by air. Two spray booths are used in order to ensure full coverage by spraying both front and back of the components. This method ensures and even thickness of coat leaving a blemish free surface and cosmetically pleasing finish.
Directly following on from the powder coating process, the components are ‘stoved’ in an oven at 200ºc for approximately thirty minutes, thus giving the finish a highly durable hard skin.
Powder Coat Painting
Powder coat painting has been the preferred finish for conductive materials for many, many years. It has been used, and still is used, to coat components for domestic appliances, domestic radiators, metal office furniture, automotive parts and accessories, alloy wheels, toys, glass bottles and industrial machinery. Powder coatings are aesthetically pleasing, produce a uniform finish and can be custom formulated to produce a variety of finishes from high gloss to low gloss and in a variety of textures. Powder coat offers a number of advantages over other finishes such as:
- An extremely strong resistance to ageing and fading in strong sunlight.
- A blemish free surface with a high resilience to impact and scuffing.
- Improvements in bimetallic corrosion allowing for a wider use of construction materials in product design.
- Excellent chemical resistance.
- Extremely good adhesion qualities when sprayed over electrocoat.