How to choose your spray gun. Advantages and disadvantages of the most used systems

The production of furniture or other wooden objects involves, on the one hand, the making of the object itself and, on the other, its finishing. I have often noticed that a lot of energy and resources are expended to achieve the first part as close to perfection as possible, but unfortunately the finishing part is almost neglected. I say unfortunately because it is the finish that the eye falls on first and a missed finish negates all the effort put into the woodworking. The quality of the finish is as much about the quality of the finishing products as it is about the correct choice of gun for spray application.

The application gun is part of an application system. This system can be chosen to increase the quality of the finish, but also to improve the efficiency of the whole process. A good choice of spray system:

• reduce the cost of finishing materials
• increase productivity
• reduce pollution
• reduce material losses
• meets environmental protection requirements.

Several basic systems are used to finish wood, each with its advantages and disadvantages. Let's take them one by one.

CONVENTIONAL sprayingis the most flexible and adaptable method of covering wood. It consists of spraying the material through the nozzle of a gun with compressed air at a pressure of 3-5 bar. When the tank is above the nozzle, the material used falls out of the gun by gravity and when the gun is below the nozzle the material is absorbed from the pressurised tank. The amount of material is regulated by the supply of compressed air.

Advantages: uniform coverage, possibility to use different materials, good quality, simple method of adjusting jet width and material consumption.

Disadvantages: low productivity, high solvent consumption (low viscosity materials must be used), considerable loss of material during spraying (65-75%).

High Volume Low Pressure (HVLP) spraying has a change from conventional spraying in that the pressure of the compressed air coming out of the gun is no more than 0.7 bar. The modification was made in order to reduce high material losses.

Advantages: uniform coverage at low pressure, good quality, easy adjustment of nozzle and material consumption, material savings compared to conventional spraying.

Disadvantages: low productivity, high solvent consumption (use only with low viscosity products).

AIRLESS or high pressure spraying is achieved using a high-pressure pump that presses the material without compressed air (the material is not mixed with air), passing it through the nozzle at a pressure of 90-360 bar. The jet width can only be adjusted by replacing the nozzle of the gun.

Advantages: high productivity, possibility to use high viscosity coating materials, reduced material losses, material transfer efficiency

Disadvantages: difficult jet adjustment (by changing the nozzle), low coating quality compared to HVLP

AIRMIX® sprayingis a combination of low-pressure and high-pressure spraying. The material is passed through the nozzle at a lower pressure than in the airless method (20-120 bar). The pressure of the compressed air used to adjust the jet is no more than 1.5 bar. The method is a compromise that combines the advantages of low-pressure and high-pressure spraying and is the most widely used method to achieve a very good quality coating.

The method is one of the medium-pressure methods, like the AAA (Air-Assisted Airless) system, but it has much better results. AIRMIX is a registered trademark of Sames Kremlin, created by the Kremlin in 1975. The concept has been a tremendous success, transforming an ordinary technology into a worldwide industry standard. In time, Kremlin also developed the second generation of Airmix guns - Gun Aircap Adaptation - which achieves jet adjustment without changing the nozzle, saving time and money. Guns and spray systems Sames Kremlin are distributed in Romania by Falk Consulting.

Another application system - described in a separate article - is electrostatic spraying.

In conclusionEach system has its advantages and disadvantages, and the choice must be made in such a way as to achieve maximum benefit. It is important to remember that:

• Conventional spraying is chosen when productivity is not a priority, consumption is low, materials used have low viscosity.
• HVLP is a good choice for small workshops that want a reduction in material loss, don't need productivity, and the materials applied have low viscosity.
• Airless application is used when productivity is a priority and when applying viscous materials. It is a good choice for protective applications and less so for high quality ones.
• Airmix offers good material transfer efficiency while resulting in very good surface quality. It is one of the best choices, but not recommended when paints contain larger particle sizes, when productivity is not a requirement or workload is low, or when painting hard-to-reach areas.