Thursday, 13 December 2007

Spray Painter

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The History and Development of Spray Painting


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For thousands of years the traditional tool of the painter was some form of brush. This remained the case until the 1920s. About this time many changes were taking place in paint technology. Cellulose paints were developed that were impossible to apply by brush. The spray gun was therefore developed to handle these improved, fast drying coatings. Spray painting using a spray gun, is a more advanced method of paint application, whereby a controlled stream of paint is directed onto a surface in the form of a fine mist.

In the early days, coatings were poor in build and opacity. They had to be applied in several thin coats, each taking many hours to dry. It took many weeks to paint a coach, but with the introduction of the motor car on a mass-produced scale, new techniques were required. Spraying has also facilitated the production of synthetic resins giving us high durability, fast drying coatings. Other developments include thermoplastic, waterborne and dry powder coatings, with application methods including airless electrostatic spray, and automatic equipment such as robot spray men.

There are various methods of spray application. The conventional spray method uses a spray gun which is a device for atomising paint, projecting a cloud of fine particles onto the surface to be coated. Conventional spray guns are fed the paint by different methods, such as gravity fed guns which have a small hopper on top of the gun, and suction fed guns which pull up the paint from a pot attached beneath the gun. Both of these methods have the advantage of being able to use very small amounts of paint, and can facilitate quick colour changes

Pressure feed spraying offers ease of maneuverability. Pump feed guns have no fluid pressure drop over long distances, and have less operator interference with materials. Airless paint spray application eliminates compressed air and its associated problems i.e. water, oil and dirt in the atomising source. The paint is atomised by utilising the hydraulic forces developed when a fluid at high pressure, and above critical velocity, is forced through a fine orifice. The spray angles and paint output are governed by the spray tip only, and there is no feathering as with a conventional spray gun. The gun is either on or off. The tip orifice is drilled out of tungsten carbide to withstand pressures of up to 3200 psi. This results in a high speed application, thicker films and less paint fog, which can lead to structured materials being used, and this method is especially valuable in open paint shop spraying. Electrostatic paint spraying, like airless spray, does not use compressed air for atomisation. With this method, charged paint particles are attracted to earthed articles, and also repelled from one another, to give a wide spray pattern and wrap around.

Spray painting has many advantages over brush application. It is approximately 5 times faster than brush application. There are no brush marks, which gives the finish more abrasion resistance, and is friction free because of its lack of ridges. Spray painting gives easier access and more complete coverage on difficult surfaces such as rivets, bolt-heads, wire mesh and radiators etc. It also facilitates more decorative effects such as blending and shading by the gradual fading of one colour into another.

It does have its limitations however, and it is important to realise that spray painting may not always be the suitable method of application. It would be more practical to use brushes on small cutting-in jobs, where masking would take time and money. There is considerable wastage of paint with spray painting, both in overspray exhaust, and also in certain spray lines, and the cost of equipment is quite considerable. Today almost every manufactured article owes its superior finish to the spray gun. Over the last 60 years, paint manufacture and application methods have completely revolutionised the way we see and appreciate our world.



Article Source: http://EzineArticles.com/?expert=Nigel_Le_Monnier


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