How to apply viscose varnish

If the paint to be applied is viscous, the first thought is to thin it so that it can be applied. Not a bad idea. There are varnishes and paints that, if not properly thinned before application, will produce a film that looks like orange peel. But there are other types of viscous varnishes where dilution is not the solution. These are thixotropic products which have particularly high viscosity. It can be applied vertically (sides of furniture, doors, windows, fences, gazebos) without appearing leaking lake. By dilution they lose this property. In addition, the addition of solvent will lead to a reduction in the solid content (solid body) and the applied layer will be thin and thin. The conclusion is that they should be used as they are with spray guns or special pumps for such products. Let's see what the ways of spraying varnishes are.

I have chosen to present this to you on various difficulty levels of the device. The idea is that you don't need to be in a factory to be able to do a quality varnish application on the product. I've seen many times how pieces of furniture or other wooden objects, done very well, are ruined when lacquer is applied at the end. My point is that you can have a good performing spray gun even if you have a shop where you work alone. There are machines for all levels and I will show you 3 of the possibilities below.

1. Spraying solutions of vascular materials for workshops, when application is done occasionally, not in a continuous flow.

Viscous materials need pressure or a larger nozzle to be applied. If spray pumps are used this pressure is provided. However, if the use of viscous products is occasional, the investment in a pump is not worthwhile. The simplest solution in this case is to use guns with large nozzles of 2.8 or 3. These allow the material to come out of the gun at air pressures of 4.5-5 atm. Using compressed air with higher pressure is not a solution because it leads to losses and a poor quality film.

The Sames Kremlin have found an ingenious solution to the problem. They combined free-fall and pressure application technology. That is, they created an overpressure in an ordinary barrel gun to push the lacquer out of the gun.

At first glance it looks like the same thing as increasing pressure which I just said is not a solution, but it is not. If the pressure of the compressed air were to increase, it would create a cloud of fine particles and lead to large losses of material (a lot of lake in the atmosphere). Also, because of the strong jet of air it would result in a veiled film.

In the pressurised cup gun proposed by Falk Consulting - Sames Kremlin dispenser - an overpressure is created inside the cup using a small hose that introduces compressed air. The overpressure pushes the sludge and forces it out through the narrow nozzle and the compressed air with the usual pressure of 4.5-5 atm turns it into fine particles. These will form a thick, orange-peel free, unglazed film.

It is a very suitable solution for those who use viscous materials (e.g. outdoor water-based varnishes) at a workshop level. The result will be very good compared to the investment.

2. Spraying of viscous products in case of constant production.

The Falk Consulting solution in this case are airmix pump Sames Kremlin with high compression ratio. A minimum pressure of 70 barr is required to apply a viscous material. For pumps this means a compression ratio of min 15:1.

The principle is as follows: the high viscosity product is pushed through a very small nozzle which leads to pre-atomisation. The finer this pre-atomisation, the better the film will look in the end.

Spraying can also be done with airless or normal systems, but the airmix system is recommended for its advantages. Airmix is a Sames Kremlin brand application system which sums up the qualities of the other two systems. Unlike the airless system, the airmix system has an adjustable nozzle radius which allows a significant reduction in losses. The system is very suitable for application on narrow surfaces such as window frames.

With airless, the radius is changed only by changing the nozzle. It is suitable for large-area application where the risk of wastage is low and productivity is important. The airless system is little used (approx. 10% of the total) because of the specific production (furniture, narrow elements, windows, etc.).

3. Application with automatic lines and spray robots

This is how it is applied in factories where the production volume is very high. Spraying is part of a finishing line where the object goes in finished white and comes out ready to be packaged.

The principle remains the same as with pumps, i.e. you need a system that can 'push' the viscous lake. It's all about compression ratio and smaller nozzles for finer sprays. Airmix guns are generally used and only when large areas are involved are airless guns used.

In the case of finishing lines, it is not just the guns but the whole line configuration. Parameters such as object size, type of finishing materials, drying time, viscosity, etc. are taken into account. The guns are mounted on automatic arms (robots) that make rotational, translational or shape-reproducing movements (anthropomorphic robots). The finishing lines are specific to each manufacturer and are practically made to order.

In conclusion, regardless of the size of the production, it should be known that a film looks better the more finely divided (smaller nozzle) the material is applied. The size of the nozzle is inversely proportional to the pressure applied and the more viscous the product, the higher the pressure must be.