This document discusses airless spraying theory and techniques. It covers topics such as: - The physics of how materials atomize when forced through a small opening at high pressure due to overcoming surface tension. - Components of an airless spray system including pumps, hoses, guns and tips. - Factors that affect spray pattern such as viscosity, surface tension, density, tip size and pressure. - Techniques for proper spray application including overlap, gun angle, and adjusting for film thickness. - Troubleshooting tips for issues like insufficient atomization or coating sag. - Safety considerations like using properly rated hoses and keeping trigger locks engaged.

1. Theoretical & Technical Aspects

2. Agenda
About Airless Spraying
Coating Characteristics
Airless Spray Pump Components
Setup for Application
Quality Control
Safety

3. Spraying Theory
John William Strutt Rayleigh (1842 – 1919)
First put forward the theory that materials break up or ATOMISES (this is
what we see as a ‘fan pattern’) when forced to travel at great speed.
Therefore it is the SURFACE TENSION and not the VISCOSITY Which
governs how easily a fluid can be sprayed.

4. Spraying Theory
Viscosity
This is the resistance of a fluid to flow. Highly viscous or thick fluids flow less easily than low
viscosity or thin fluids.
http://www.planetseed.com/flash/science/lab/liquids/visco_exp/en/viscosity.swf
Surface Tension
This is the tendency of liquids to reduce their exposed surface to the smallest possible area.
The phenomenon is mainly due to cohesion, the attractive forces acting between the
molecules of the liquid.
In other words, we need to overcome the materials built in resistance to break into fine
particles in order to spray it.
Thixotropy
A fluid is said to be Thixotropic if its viscosity reduces when it is agitated or stirred i.e. it is
subjected to shear force.
Specific Gravity/Density
The specific gravity of a substance is a comparison of its density with that of water. A
substance with an S.G greater than 1 (water) is heavier than water and a substance with
an S.G. less than 1 is lighter than water.

5. Spraying Theory
SPEED is the key word !
By forcing a fluid through the spray tip, we cause it to rapidly increase
its speed, otherwise known as its ‘velocity’.
At a critical speed, governed by the surface tension of the fluid, the
friction caused by the collision of the fast flowing fluid with the
surrounding air molecules is sufficient to overcome its viscosity and the
fluid breaks up or atomises.

6. Spraying Theory
Airless spray utilizes equipment which creates high pressure (energy
source) within the fluid which then converts that pressure to velocity to
atomize the fluid.
The material then gains momentum as it leaves the spray tip, thus
delivering an even coating over a designated surface, by forcing it
through a small orifice.

7. Atomisation

8. Advantages of Airless Spray
High production rate
Pump can operate direct from the supplied container
Reduced overspray and blowback
Good coating uniformity
Better coating penetration and surface ‘wetting’

9. Disadvantages of Airless Spray
The major disadvantage of the airless spray is that the tip tends to clog
and can be dangerous to use or clean because of the high pressures
involved.
Because of the speed/outgoing pressure of the fluid, an accidental skin
injection is extremely dangerous, as we’ll see later on.
Again, because of the high pressure levels involved, operators must be
fully trained to operate the equipment and service it.

10. Airless Spray Equipment
Pump (s)
Fluid Lines
Gun
Spray Tips
Reservoir / hopper System

11. Airless Spray Pumps

12. Airless Spray Pump

13. Airless Spray Pump

14. Double Acting Reciprocating Pump
Displacement rod
Wet cup
Packing's
Displacement rod
Chrome cylinder
Piston ball
Inlet ball
Inlet seat
Piston
Cartridge
Built-in-filter
Filter cap
Filter cap
Cylinder pin
Outlet plug
Quick Access TM Intake

15. Double Acting Reciprocating Pump
Piston reciprocates when the trigger is pulled. One cycle consists of
upstroke and down stroke.
Upstroke
Down stroke
Material is sucked in and pumped out.
Material is pumped out.

19. AIRLESS SPRAY COMPONENTS

20. Spray Pump Strip Down

21. Plural Component Spray
Plural Component

22. Airless Spray Hose
Rated for high pressure - up to 517 MPa (7,500 psi).
Electrically continuous and grounded.
Check for damage and discarded if defective.
Tightly connected.
Length should not exceed 45m (150 ft.).

23. Fluid Hose Safety
Hoses should be stored in neat coils.
Before each use, check for any damage (kinks, scuffs).
Check chemical compatibility between cleaning material
and hose.
Hose connections should be tight.
Always check for electrical continuity.

24. Airless Spray Equipment
Fluid hoses provide the means of getting the fluid from the pump
to the spray gun.
1) ENSURE that only hoses with a pressure rating compatible
with the maximum output of the pump are used.
2) DISCARD any hose with kinks or outer sheath damage.
3) NEVER attach a hose without the use of the correct wrench.
4) NEVER disconnect a hose unless you are absolutely sure
the internal pressure has been relieved.

25. Airless Spray Pressures
Range from 55 - 450 Bar (800 to 6,500 psi)
Most commonly use 100 - 240 Bar (1,500 to 3,500
psi).
Ensure you are using the correct hose for the capacity
of the airless pump that you are using!

26. Airless Spray Equipment
1. Spray Tip Safety Guard
2. Trigger Guard
3. Trigger with Safety Lock
4. Gun Filter
5. Gun Swivel Fitting
6. Safety Catch
7. Reversible Airless Spray Tip

27. Trigger Safety
The most important aspect of the spray gun is the safety
mechanism.
The most common type shown below, is a simple design
and prevents accidental release of high pressure fluid.
If You Are Not Spraying, Then The Safety Catch Must Be
Engaged, No Matter How Brief The Stoppage.

28. Trigger Safety
NEVER use a spray gun with a faulty safety catch.
Always make sure the gun is correctly rated for the
pressure that can be developed by the pump.
Do not use a low pressure rated gun on a high pressure
pump.
Ensure the gun is compatible with the pump being used.

29. Airless Spray Gun Safety
All airless spray guns must be fitted with a safety
guard to prevent accidental injection.
Never use a gun without a guard.

30. Using The Spray Gun
Arcing reduces penetration into the blast profile and
reduces the adhesion, as well as poor thickness control.

31. Using The Spray Gun
50% overlap provides uniform coverage.

32. Spray Gun Safety
KEEP THE SAFETY CATCH
ON AT ALL TIMES!
Only release it when you are wanting to
squeeze the handle and put product on the
job!
It’s a loaded gun!

33. Airless Spray Tip Components
Flow Rate
Spray Tip
Fan Width
Spray Tip
Flat Reversible

34. Spray Tips
Tip
Seal
Safety Guard
Tip Holder

35. Spray Tips
The tip aperture is elliptical in shape and the aperture size designation
does not refer to either the long or short axis length but to the diameter of
a round pattern orifice that would have the same cross sectional area and
flow rate.
Spray Tip Part Numbers
XHD
Type of spray tip
Refers to fan angle and width
add “0” to give 50o angle or
double “5” to give 10” fan width at
12” from the tip.
Last two digits refer
to the tip aperture size
in thousandths of an inch.
50°
12”
10”
523

36. Spray Tip Wear
Correct Pattern / Partially Worn Tip / Badly Worn Tip

37. Airless Spray Tip size
Coating
Tip Size
(inches)
Tip Size
(millimetres)
Fan Width
(inches)
Fan Width
(millimetres)
Low Viscosity 0.011 0.28 6, 8, 10 150, 200, 250
Industrial Primer 0.015 to 0.021 0.38 to 0.53 6 to 12 150 to 300
High Build 0.019 to 0.025 0.48 to 0.63 8 to 14 200 to 350
Flake Glass Systems 0.025 to 0.040 0.63 to 1.0 10 to 14 250 to 350

38. Spray Tip Selection
Film Thickness Requirement
Table of Independent Variables

39. Table of Independent Variables
XHD-313, desired FT= 150 µm. New requirement: 60°
fan angle.

40. Table of Independent Variables
Desired FT = 190 µm Spray trial with XHD-515
FT=145 µm

41. Troubleshooting
If the coating is failing to atomize you should check the
following:
Compressed air source
Material temperature
Flow rate at the gun without a tip
Spray tip size
(may need reducing or increasing)

42. Troubleshooting
Stall Out Test
Raise the pressure at the pump, trigger the gun and
check both strokes for even flow.
Upstroke fails
Down stroke fails
Note: Displacement rod should be continuously lubricated with a compatible TSL oil.
Check displacement rod packings
and top ball / top ball seat
Check pump inlet valve / bottom
ball / ball seat

43. Troubleshooting

44. Mixing
Settlement is likely to occur in
storage.
Mechanical mixing should be used
to agitate the base prior to adding
the catalyst / hardener.
Plan your mixing program.
If using a pot, change regularly to
avoid part cured material from being
drawn into the pump.

45. Spray Application
Apply coatings with correct spray technique.
Purge system before spraying.
Adjust gun to give correct spray pattern.
Overlap of 50% on passes.
Measure wet film thickness (brushed out).
Focus on difficult areas.
Do not ‘arc’ spray gun.
Complete within pot life of mixed coating.

46. Airless Spray Technique
Gun moves parallel to surface
50 % Overlap spray passes.
Trigger gun at each end of the pass.
Select tip size and fan angle to suit configuration of
work piece.

47. Airless Spray Technique
With any spray applied coating it is essential that correct technique is used, but it is particularly
important with Polyglass as the large nozzle requirement and dense flake structure may cause
sag when Polyglass is incorrectly applied.
Polyglass should be applied by the wet on wet multi-pass technique as follows:
(1) Before spraying job surface, set pump pressure to give good spray pattern and atomisation
at the LOWEST ACCEPTABLE PUMP PRESSURE. Remember the higher the pressure,
the shorter the pot life and the longer the thixotropic recovery time on the surface.
(2) When a suitable pattern and atomisation have been achieved, start work by spraying
vertical passes (spraying from top to bottom/bottom to top). Do not try to achieve full
wetting out of the surface at a single pass, but mist coat the area with several vertical
passes until at least 90% coverage is achieved. Move to the adjacent area and carry out
the same procedure, then return to the previously vertically sprayed area and with
horizontal passes, build up the coating thickness. After building this area, return to the
adjacent area with horizontal passes. Check wet film with suitable gauge and, where
necessary, build film thickness by alternate vertical and horizontal passes until desired wet
film is achieved. On completion, move to the next adjacent area to be coated, again starting
with vertical passes.
REMEMBER GOOD INITIAL WETTING WITH VERTICAL PASSES IS ESSENTIAL FOR
BUILDING THICK FILMS WITH THIS PRODUCT.

48. Airless Spray Fingering
Increase the pressure until the “Fingers” just disappear.
The Unit is then set at the ideal pressure for atomisation.

49. Coating Techniques
Stripe Coat
Extra coat applied to cover sharp edges, welds, and
vulnerable areas.
Full Wet Coat
Maximum wet film application.

50. Pausing During Spray Application
Engage Safety Catch.
Remove & Clean Spray Tip.
Flush System.
De-pressurise.
Turn Off The System.

51. Finishing a Spray Application
Engage safety catch.
Remove spray tip.
Flush system.
De-pressurise – Reduce pressure to zero.
Open the system pressure drain valve.
Clean spray tip.
Strip & rebuild ‘wet end’.

52. Application Quality Control
Wet-Film Thickness
(WFT) checks.
Dry-Film Thickness
(DFT) checks.

53. Environment / Climatic Measurement
Air Temperature
Thermometer
Steel Temperature
Magnetic gauge or electronic surface gauge (laser is good but
can be easily confused by shiny surfaces!)
Humidity and Dew point (Calculated)
Steel Temperature Must be >3°C above Dew point.

54. Application - Inspection
During application;
Product batch number recording
Start / finish of coating
Overcoat windows
Environment conditions
Surface and air temperature
Relative humidity and dew point
Coating thickness
Problems…

55. Inspection of Spray Application
Monitor equipment and materials
Observe preparation and mixing
Observe application technique
Measure results
Record all inspection outcomes, including visual
observations.

56. Workmanship
Pinholes (in this case outgassing)

57. Workmanship
Improper Thickness
Sagging

58. Workmanship
Fish Eyes
Blistering

59. Workmanship
Particulate Contamination

60. Solvents
Highly flammable and may cause dizziness with over
exposure.

61. Personal Protective Equipment

62. Some General Precautions
Eliminate all fire and explosion hazards.
Ground all equipment and accessories.
Always engage the safety catch if the gun is left idle.
Always have a Safety Data information available.

63. Airless Spray Safety
The high pressure fluid that exits the gun is sufficient
enough to penetrate human skin.
Correct solvent PPE must be worn before using
cleaning solvents.
You should avoid spraying cleaning solvents

64. Airless Spray Safety
Do not leave pressurized unit unattended.
Use only high-pressure-rated hose and identical
fittings.
Always lock the gun when not actively spraying.
Observe safety guidelines.

65. Airless Spray Safety
Because of the risk of fire / explosion, always ensure
that all equipment and product drums are all earthed at
all times, and that any couplings have continuity straps
fitted.
NEVER use plastic containers that contain product or
solvents that feed the pump (Metal buckets are
essential).

66. Injection Injury

67. Injection Injury
A relatively small injury could be
very serious.

68. Airless Spray Safety
Should an injection injury occur;
Injured person should be taken to hospital immediately.
The person(s) should take with them the literature
(MSDS) on the material they have been injected with,
and recommendations for treatment.

69. Injection Injury: looking at Statistics
1) Injection injuries happen most commonly to men aged
21 to 59.
2) Over 75% of injections are to the index finger not holding
the gun.
3) The second most common injury site is the fleshy area
below the thumb of the hand not holding the gun.
4) Oil based products cause more injury than water-based,
but both can cause rapid tissue death.

70. Treating Injection Injuries
1) Injury site may appear to be a small puncture, but it can
lead to amputation or death.
2) Other complications include infection, chronic pain and
permanent contraction of the injured limb.
3) The injured site shall be treated as a serious injury,
leading to surgery in most cases.
4) Physical and occupational therapy is critical after the
treatment to help restore the injured area as much as
possible.

71. STAY SAFE !