WHAT IS AIRLESS PAINT SPRAYING?
There are two types of paint spraying that are commonly used today, air and airless. In air spray compressed air is combined with the paint to achieve ‘atomisation’ – the breaking up of the paint into tiny droplets. This gives a superb finish (think of the finish on your car) but due to the high air:paint ratio, overspray can be extensive and is not easily controlled. By contrast, in airless spray atomisation is achieved by the paint being pumped with no added air through a very small nozzle (the spray tip). It is this total absence of any additional air that gives airless a huge advantage for the decorator – overspray is minimal, it can be easily controlled yet the standard of finish that can be achieved across a wide spectrum of coatings cannot be matched by either brush or roller application.
HOW DOES AN AIRLESS SPRAY PAINTING SYSTEM WORK?
Paint pumped through an airless sprayer becomes a fast moving high-pressure liquid stream that provides the energy necessary to overcome the viscosity of the paint (resistance to flow). This is sent down the hose to the gun and spray tip. The pressure generated by the sprayer is sufficient to force the paint through a small nozzle, or orifice (the spray tip). The surface tension (the force that bonds the surface of a liquid together) is overcome and the paint emerges as a solid stream (sheet) at an extremely high speed (at this point the force is sufficient to puncture human skin). When this solid stream comes into contact with the air, it becomes disrupted. This disruption breaks the fluid into fragments, these then become the tiny droplets that form the spray pattern.
GETTING IT RIGHT
To spray, you need a sprayer. Then there’s a gun, and a hose to link the two. It’s the gun that the spray tip fits into. Out of these components, the two that must be correct and must be compatible with each other are the sprayer and tip. As the size of tip increases, so does the maximum flow-through. It’s common sense, the larger the hole the more fluid can pass through it. Every machine has a maximum output – it’s one of the key numbers that any airless sprayer, irrespective of make can be compared by. What’s critical here is that the maximum flow of the tip does not exceed that of the machine.
Let’s take an example. A QTech QP019 is a great entry level professional machine. Its maximum flow is 1.9 ltrs/min. This means that the largest tip it can support is 0.021”, which has a maximum flow of 1.78 ltrs/min. Try to use a tip larger than this, and the results will be unsatisfactory. Why? Because the machine will not be able to hold the pressure required to fully atomize the amount of paint that can pass through the orifice. However, get the ‘formula’ right, and you’ll get a great set-up – the results will follow.