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workshop by Handyman
Details to save down-time (13)
Gun handling is the key to successful spraying without correction check your settings on a test piece before painting
SPRAY PAINTING is not just a fast and easy way of painting without a brush. In order to save some of the down-time one can otherwise expect when the trainee takes up the paint gun. I will outline some of the tactics necessary when setting out to do a good class job with the minimum of mistakes.
First of all, do not confuse the professional spray gun with the aerosol touch-up tackle that is in so much demand — there is no comparison; the air-powered paint spray gun is an accurately made device. There are Other patterns such as the electrically vibrated diaphragm one, but the majority of good painters usually settle for the air-powered gun. When it is looked after it will give top-class service for years.
The trainee must be shown how to adjust the spreader valve to give the required fan pattern discharge, and how this setting must be balanced with the flow of fluid to suit the size and general contour of the workpiece to be sprayed. Here the aim is to provide atomization that will guarantee a uniform pattern.
Show him how over-atomization gives a broken, uneven pattern, often streaky in appearance, and how this wrong setting can shoot blobs of paint that form rings and sagged runs.
Demonstrate how to handle and trigger the gun, how to keep to straight uniform strokes with the gun upright and at the same distance from the work throughout each stroke. This the trainee should practise until he can handle the full weight without weaving about. Any weaving or whipping around will cause uneven work and streaks.
Paint can be wasted in quantity by not using the trigger at the right moment; demonstrate how and when to trigger during the stroke and how the edge of the area under spray should be banded in first to mate with the point where the gun is triggered for the general covering.
Gun handling is very much the key to successful spraying without waste or respray and corrections; and paint is easier to put on than to take off when it has sagged and run. Time spent in correct gun handling is time well spent. Probably all those who handle spray guns will have acquired the practice of having a test piece nearby before commencing the actual job; this test piece is most necessary in order to check the gun setting and see how the material will perform as it leaves the gun. The usual test piece is a section of steel plate mounted near the work; this will give visual confirmation of the settings made.
Check the temperature of the shop or booth, and let any newly arrived vehicle or workpiece have time to warm up to the booth temperature.
Once you have selected your paint and the correct thinners have been balanced out to the maker's instructions, set the air pressure as instructed and adjust the gun to the fully open position. Now apply three or four spray patterns on to the test piece at a nozzle distance of 8 to lOin, by opening the trigger fully for the three runs; give the test run four or five minutes to set and then examine carefully. Where the pattern has sagged at the bottom the thinners can be too slow, so select a faster one; where there is a dry spray appearance the thinners are much too quick and a slower solution is called for.
This test work is not down-time — it helps ensure that there is no down-time through corrective work when the actual job is started. This kind of practice makes craftsmen.
At the end of the exercise; service and clean the gun; the man who just turns off the air and parks the gun on the bench has little future in a good paint shop.
Never immerse the gun in a can of thinners as this kills the lubricant in the glands. Never use hard materials, wire, knife blades, etc. to clean out passages and holes in the nozzle. The container can be filled with clean thinners or solvent suitable for the paint just used; then use the gun normally and one or two refills should clean the internal passages. But on no account use caustic solutions inside the gun as these will destroy alloy parts.
Cleaning should begin the moment spraying is finished and before the thinner areas of paint can begin to harden inside the gun. Early cleaning is the quick and sure answer to a good start next day with no comebacks.
Glands and packings around the needle have to be kept pliant and lubricated — but use only your fingers when tightening and never a spanner.