Application Equipment Techniques

Conventional - Gravity Feed

Gravity Spray Guns
Fluid flows under force of gravity
Ideal for small applications detail finishing
Use small quantities of paint.
No fluid pick up tube is required.

Conventional - Suction Feed

Compressed air creates low pressure area at air cap siphoning the paint from the pot

Suction(pot) gun
It is possible to mix paint in pot.
Easily controllable
Suitable in low production rate operations

Conventional – Pressure Feed
Material is pressurised in pot and pressure forces material through fluid tip and air cap where atomisation occurs.
Typically between 1 – 3 bar pot pressure.
Allows gun to be used at all angles without fluid starvation.
Allows spray for long periods without refilling.
Lightweight and Manoeuvrable
Clean up increases solvent usage
Set up more critical than suction/gravity.

HVLP Sprayguns

High Volume Low Pressure H.V.L.P.
These sprayguns were introduced several years ago, to increase the transfer rate of the paint and to reduce overspray.
They work by using high volumes of compressed air at low pressures, therefore it is important to have a good, high volume compressor, and no restrictions in the air line

Electrostatic
Types – Airless Air Assisted / Pressure Feed
Settings 20-85 K
Paint savings 25-30%
Faster application times
Improved appearance

Airless Sprayguns

Material flow controlled by pump pressure and tip selection.
Atomises material by means of shear (typical 1800-2500 psi)
Suitable conventional material in aerospace and High solids industrial material.

Air - Assisted Airless Spray

Atomises material similar to airless but air is introduced at air cap which creates fine atomisation.
Rapid application rates.
Good finish achievable.
Low DFT even with high solids.
Suitable for large areas.(Air craft exterior)
Large volume of solvent for cleaning
Tips block easily

Fluid tips and Air caps
Five basic considerations when selecting tip and air cap.

1.Type and model of gun.
2. Air supply.
3. Type of material (viscosity)
4. Size of object to be painted.
5. Speed material will be applied and finish required / DFT.

Atomisation
Spray pattern consistent with size of object.
Combination of finest atomisation with smallest pattern.

Air Transformer & Filter
Usually fitted in the spraycabin,
to remove oil, dirt and moisture from the compressed air
to precisely regulate the quantity of compressed air delivered to the spraygun

Air Transformers

The Air Line
The correct internal diameter of air line will deliver the correct pressure.
The length of air line will also have an effect on the pressure delivered.
Air lines should be flexible, and removed from the spraycabin prior to heating

Gun Set Up. Fluid Flow Rate
Always use sprayguns that will produce the proper film capacity, when they are correctly adjusted.
Most production type guns are set to pass between 80 - 400 ml of material per minute.This depends on the article to be sprayed

Method – Airless Air Assisted/Pressure feed. 关闭气压
Shut off atomising air.
Pull trigger for 15 seconds and dispense material into graduated container
Multiply contents x4 to give flow rate over 1 minute.

Static Spray patterns
Clean paper on vertical wall.
Set Target distance (6 inches from paper)
Turn air cap through 180.
Pull trigger 3 secs.
Run out should only be across the shoulders.
Turn through 180 set fan width.

The spraygun technique
Gun Distance
About 150-200 mm from work
Too close or too far:
     runs and sags
    dry spray or over spray
Poor Triggering
The gun should be triggered properly
If not, paint will build up on overlap causing
    runs and sags
    heavy edges

Poor Technique may Result in:
Runs and sags
Dry spray / Poor Appearance
Film faults, e.g. ‘popping’
Angle of Gun
Spray gun should be vertical to the work
Tilting or arcing the gun dramatically may cause uneven and dry finish
Except ‘Fade Out’ repairs, gun is deliberately arced at the end of the repair

Spray Gun Speed
Comfortable speed
Wet but not overly wet
Too fast causes dry uneven spray
Too slow causes runs and sags
Incorrect Overlap
Overlap each pass about 50%