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The Functioning of a Spray Gun

Setting up and using a spray gun involves basic knowledge of how the device works, so that it is possible to judge when it is working correctly, and to determine what kind of air cap and other accessories you need. One thing that you must determine is what air cap is necessary for spraying the type of paint you are planning to use to coat your car. If the central orifice is too small for the thickness of paint you are using, it will clog – like trying to force toothpaste through a pinhole – while if it is too large, the spray pattern will be too loose and thin to create a good coating on the metal.

You can learn the size of air cap orifice needed by using a viscosity cup. These cups are small metal or plastic containers with an almost funnel-like design. Fill the cup with the paint, primer, clear coat, or whatever you are planning to use, then time the period it takes for the substance to drain out of the cup through its bottom hole.

Compare this to the chart that was supplied with the viscosity cup and you will know the viscosity of the paint. Note that viscosity is only measureable with any accuracy while the temperature of the paint or other substance is between 65˚ and 75˚ Fahrenheit. Heat above 75˚ F will make the paint a bit runnier than it would be at ordinary room temperature, while lower readings will make the paint sluggish and result in an inaccurately high viscosity reading. Once you have determined the viscosity, you will be able to find the type of air cap you need, possibly in consultation with paint store personnel.

The wing ports or horn ports – those openings on each side of the air cap which feature their own diagonally-aimed air orifices – send a converging blast of air towards the jet of air and aerosol paint that is being projected from the spray gun’s main orifice when you are shooting. Without these wing ports, the spray would jet out in all directions, forming a broad cone and producing only fitful, unpredictable coverage.

However, the air from the wing ports compresses the spray into a tall, flattened, vertical oval which paints a stripe of the vehicle’s surface thoroughly and evenly, producing the high-quality results needed for car painting. All of the orifices must be kept clean to keep the spray pattern correct.

Spray pattern might appear to be an unimportant detail to the layman, but in fact, any distortion will lead to irregularities in the thickness of the paint on the car’s surface. Too thick paint may run or even crack as it dries, while too-thin paint will be vulnerable over time. It behooves you to periodically test your spray gun’s spray pattern before making use of the device, to ensure that it is still working properly.


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