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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. Both the edge of the part and the top
surface is banded in figure 15. 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, spray as
shown in figure 16. 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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