Ventilation

• Air circulation during application and drying is important for the drying and curing process, as air will transport the solvents away.

• For tanks and closed compartments: Air is added from the top of the tank at the same time as air mixed with solvents is drawn out from the bottom (solvents are heavier than air). The air drawn into the tank should be dry and temperate, but somewhat lower in temperature than the steel surface. If the air used for ventilation is warmed, the surface of the paint film will dry more rapidly, resulting in entrapment of solvents which in turn will lead to blistering and poor adhesion. During application of paint, the ventilation/dehumidification rate is normally high, in order to ensure rapid removal of solvents from the coating and the tank, but it should not be so high that surface (skin) drying occurs.

• The concentration of solvent fumes must be maintained below the lower explosion limit. (See section 7.5. and section on Safety, Health and Environment)

• If the wind is too strong during application it may result in dry spraying, porous film and in addition a very high paint consumption. (Wind carries paint away from the substrate).

Figure 7.6

Good ventilation is essential to have good drying and curing conditions.

G ood practice

B ad practice

Salts and contaminants

Salts, oil, grease, dust, abrasive and other contaminants that can precipitate on the surface to be painted must be avoided. Contaminants can come with the atmosphere (marine and industrial) or by other work / trades carried out close by. To prevent contamination of the surface the surfaces to be painted must be sealed off. Any existing salt must be washed away with fresh water and other contaminants such as oil and grease, with a suitable detergent.

• Salt may cause osmotic blistering

• Oil and grease will give reduced adhesion between the substrate and the paint

7.5. Safety aspects during application

Because airless spray systems operate at high pressure you need to give special attention to safety during operation. Two safety considerations are paramount:

• Fluid sprayed from the gun is propelled with sufficient force to penetrate a mans skin and cause very serious damage.

• The entire system is pressurised so that hose ruptures or leaks at fittings can result in dangerous high pressure spray.

Some important safety practices should always be born in mind:

• Never point the gun at any part of your own body or at another person.

• Do not make adjustments to the equipment set-up, such as changing nozzles or fittings without first shutting off the pump, releasing the system pressure and securing the gun.

• Do not remove the tipguard during operation. The tipguard is there so that you cannot put your finger close to the tip and inject paint under your skin.

• Always engage the trigger lock when the gun is not being used.

• Always make sure the fluid hose is in good condition before spraying.

• Do not use standard hardware on an airless system; only high pressure fittings.

• High pressure hose is required for fluid flow. The hose must never be bent or kicked.

• Airless spray equipment must be grounded to prevent static sparking.

• Do not spray solvent through the nozzle tip because this can build up static electricity and cause explosion or fire.