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Safety First!
Read about airless
spray painting safety
In any airless spray application, a careful study to determine
correct spray techniques for each work piece configuration can save both time
and material.
A balanced combination of these three factors will generate
the best finish quality, with the least effort and the lowest cost.
Gun Position
Hold the airless spray gun with a firm, but comfortable
grip. Use the index and middle fingers to trigger the spray gun. The gun should
be a natural extension of the operator's arm. There are both two and four finger
guns.
Hose Position
Hold the gun in one hand and the fluid hose in
the other hand.
When using long hoses or when more flexibility at the gun
is needed, a small "whip-hose" hose can be installed between the end of the
supply hose and the gun. The whip-hose will allow the operator to move more
smoothly during the spray stroke.
Body Position
There are no set rules for body position, but
here are some recommendations. While facing the part, stand with your legs a
little wider than shoulder width. Pull the leg opposite the spray gun back slightly.
Use the forward foot to pivot during the spray strokes.
Distance
The fan angle and orifice size of an airless
tip affect the spray pattern. Gun tip distance from the work piece being sprayed
also affects the spray pattern. As the gun distance from the part increases,
the fan width becomes wider, eventually causing and overspray condition and
uneven coverage. A gun distance of approximately 12" produces the best coverage.
If the 12" distance must be exceeded, select a narrower fan width to retain
your efficiency. All airless tips are sized at the 12" spray distance.
Gun Position
Hold the gun perpendicular to the surface whenever
possible to reduce the chance of uneven paint coverage. Tilting the gun either
up of down will produce a heavy build-up of paint on the top or bottom of the
spray pattern. Arcing the gun causes a heavy coverage of paint on the left and
right side of the pattern. Both arcing and tilting the air spray gun also causes
an
angle at which the paint can bounce off the work piece surface.
Triggering
Triggering the gun controls an airless paint
system. The gun is either "full on" or "off", there is no partial triggering
or feathering. Timing the triggering movement is key to an even paint coverage
on the part. The gun stroke or movement should be started before triggering,
and release the trigger before the stroke ends. This method provides a "lead
and lag" for more
even coverage. Proper triggering also conserves paint and
prevents excessive material build-up at the beginning and end of
each stroke.
Overlapping
If the first stroke is begun on the left side
of the work piece, the gun is moved down at the end of that stroke and the second
stroke begins at the right side. A means of judging the amount of overlap is
aiming the spray gun directly at the bottom of the previous stroke. As spray
technique experience becomes more effective, the amount of spray overlap will
be reduced,
increasing the efficiency.
Spray Speed
The proper spray speed applies a full wet coat
application with each stroke without sagging. If the desired film thickness
cannot be obtained with a single pass because of "sagging", then two or more
coats can be applied with a flashoff period between each coat. The spray movement
should be at a comfortable rate. If excessive spray gun movement is necessary
to avoid flooding the work, then the fluid tip orifice is too large or the fluid
pressure is too high. If the stroke speed is very slow in order to apply full
wet coats, then the fluid pressure should be increased slightly or a larger
tip be used.
Rehearsing your spray strokes before doing the actual work
is a good practice for a new work piece and for a new operator. By rehearsing
the gun movement for a part, the operator can save paint with reduced overspray,
have less fatigue by using more effective gun movements and obtain a finer quality
of finish. This section examines various party configurations and
recommends
some spraying techniques using the least effort, with minimum paint waste, yet
providing the best quality of finish.
Banding
To reduce overspray on a work piece, use the
"banding" technique. Use a vertical stroke at each end of a large panel, rather
than trying to cover the ends with horizontal strokes. This reduces paint usage
and overspray.
The banding technique can also be used on the edges and outside
corners of some work pieces such as tables. Aim the spray gun at the leading
corner of the part. Use this same technique to spray the outside corner of a
box or cabinet.
Inside Corners
To apply an even coat of paint to an inside corner,
point the spray gun at an angle. To avoid double coating the same area, use
horizontal strokes to spray the area adjacent to the corner. Spray each side
of the corner separately. A vertical pattern is often used.
Outside Corners
To spray the outside of a corner, a straight-on
method can be used. The adjoining surfaces are then banded.
Small/Vertical Flat Surfaces
When spraying small, vertical flat work piece
configurations, the banding technique is used. Using a horizontal pattern, band
the edges of the part. After banding the edges of the part, finish the part
with horizontal strokes. First, spray the Class B side of a work piece (the
side that will not be finished), then spray the Class A (finished) side. If
there is any overspray turbulence, it will not appear on the Class A side of
the work piece.
Long/Vertical Flat Surfaces
Spray long vertical flat surfaces with horizontal
strokes in sections from approximately 18" to 36" wide. With practice, you will
find the distance most comfortable to your needs. As on small vertical flat
parts, use the same banding technique on each end of a long vertical flat part.
Use the same triggering technique as with a smaller panel, but overlap each
section approximately four inches.
Level Surfaces
When spraying a level or horizontal surface,
always start on the near side of the part and work to the far side of the part:
this technique allows the overspray to fall on the uncoated work. Some gun tilt
will be necessary.
Slender Parts
When spraying slender parts, choose a spray pattern
that fits the part to be finished. When using a vertical pattern, the spray
speed must be faster.
Round Parts
Small cylinder shapes, like furniture legs, are
best sprayed with a narrow spray pattern, using three vertical strokes. A vertical
pattern and stroke can be used, but the gun movement must be quicker to prevent
sags and runs.
Spray smaller or medium diameter cylinders with lengthwise
strokes. Spray large cylinders like a flat vertical surface, only with shorter
strokes.
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