Tribo powder spraying is based on physical principles that largely determine the final parameters of the spraying equipment. The spray gun manufacturer is faced with the challenge of designing an optimum design that will provide the best possible output, which is a sufficiently charged powder that exits the charging tube mouth in the required quantity and at a usable velocity. As the name suggests, tribo powder charging is based on the principle of friction.
Pistol PRSTEN 031 with base tube
The principle of tribo spraying is to attract a charged powder that lands on the grounded surface of the object to be sprayed. The ratio of the amount of powder trapped on the sprayed article to the powder that flies over indicates the efficiency of the spraying. This parameter is a guideline for the user and provides an important basis for calculating the cost of spraying. The powder particles are charged by friction against the walls of the charging parts of the spray gun tube. In simplified terms, the charge of the powder increases with the number of particles and the magnitude of the intensity with which they strike the charging surfaces. Higher powder charge means higher coating efficiency. It is therefore clear that the thinner the mixture of powder paint and air (transport medium), the higher the paint charge will be.
In practice, however, we usually need to spray the object as quickly as possible due to operating costs, so we require a higher volume of paint at the gun outlet. This goes against the aforementioned principle of increasing the charge. Here again, we need to look for a happy medium and an optimal compromise between maximum charge and maximum powder volume.
The spray gun in the picture is with a standard charging tube, which allows control of the shape of the output beam and is able to work from minimum power with high charging efficiency. The maximum output of the tube depends on the quality of the powder mass and its ability to acquire charge by friction. An experienced painter can easily recognize when further increasing the pressure at the gun inlet would not result in higher spray efficiency. Spraying efficiency decreases rapidly not only due to charge reduction, but also due to paint blowing off the object when the powder exit velocity is too high.
Up to three times more power
The special R14 spray tube has been developed for high performance. Thanks to the cleverly designed internal labyrinth through which the powder must pass, it is able to feed and charge larger amounts of paint. While 3 kg of powder per hour was achieved when spraying with the standard tube, the R14 atomizer tube delivered 10.5 kg.h-1. These values correspond to measurements made on the Ring 031 gun at an inlet pressure of 1.3 bar. Thus, the R14 atomizer tube allows spraying at more than three times the output, while the specific charge (charge/weight unit) dropped by a manageable 30%. If sprayed with a good quality powder that charges well, the loss in chargeability is negligible.
Charging tube with sprayer R14 and its parts.
In paint shops where tribo spraying equipment is used and high performance is emphasised – spraying simpler products in larger quantities – the R14 charging tube with spray nozzle will certainly find its application. Simple and quick cleaning is made possible by the easy disassembly of the atomizer, which simply slides onto the charging tube and no screwing is required. The shorter tube is characterised by easier handling due to less knocking torque. The R14 atomizer tube is suitable for all types of domestic powder paint spray guns. The advantage is also the interchangeability of the charging parts with other tubes.
Customized sprayers
The next picture shows sprayers designed for various purposes such as spraying large areas, pipe structures, spraying crevices between ribs, corners, and other hard to reach areas. Sprayers can be made to measure. They can be used for manual and automatic spraying. In addition to standard tubes with attachments, tribo guns are also fitted with special tubes for spraying the inside of pipes of different lengths and diameters according to the user’s needs.
All tubes have one common part – the charging insert. It is the largest contributor to the charge and also the one that wears out the most. The wear occurs at the inlet of the insert at the electrode through which the charge is discharged to the ground. The liner is double sided and if turned in time (before it has broken through the liner casing) it will double its life. The other parts of the tube can also be replaced individually according to their degree of wear.
Example of possible variants of sprayers
Example of possible variants of sprayers
In paint shops with a variety of sprayed goods, it is worth using multiple spray tubes with sprayers specialized for a particular type of surface. Changing tubes is quick and easy and spraying will be more efficient. Higher purchase costs are offset by reduced operating costs. In fact, wear and tear on charging parts is only related to their operating time, which decreases with the use of more tubes.
Ing. Petr Vančata
Published in MM Průmyslové spektrum: 2017/11