What is finishing with valances and what are the conditions for a correct UV curing

Flooring and flat panels can be industrially finished on lines that include valving systems for applying the finishing materials and batteries of UV lamps for faster drying. These are very efficient lines, which can have several application sites followed immediately by UV lamps, placed consecutively. On these UV curing and waved finishing lines, the wood goes in white and comes out finished, maybe even packaged.

The advantage of the valved application is the significant reduction in the consumption of finishing materials

The advantage of using valances is the very small amount of material that is applied. The amount applied per coat is around 40-50 g/m², but can be as low as 5-7 g/m². The main requirement is that the panels are very well calibrated. Products that are applied by waving have a very high solids content, between 96% and 100%, thus the solvent emission is very low.

The application on the finishing line is done with a system of wickets, some to apply the material and others to dose it. The applicator valves are coated with a special rubber. The hardness of this rubber is given by a number determined by the Shore method and is an important piece of information for the lacquer supplier. The metering valve, used to regulate the amount of material applied, is made of metal.

The amount of material applied can be adjusted in 3 ways:

• of the distance between the applicator and dispensing valve,
• by adjusting the pressure on the object to be finished
• by adjusting the direction and speed of rotation of the metering valve.

Types of Valanced Applicators

Depending on the number and positioning of the valves, there are several types of systems:

• Applicator with reversible metering valve (standard and reverse mode). It is recommended for the application of stains, primers, varnishes and enamels. By rotating the metering valve in the opposite direction to the direction of rotation of the applicator (reverse mode), greater uniformity of the applied layer is obtained.
• Machine with a metering valve and an adjacent standard rotating valve. Used for applying paints.
• Machine with two applicator valves. The second applicator valve rotates in the opposite direction to the conveyor belt feed direction. It results in reduced consumption and a more even surface. It is mainly used for applying UV varnishes.
• Applicator with two applicator wands. Between the first and second application the material does not dry but turns into a gel. It is mainly used to improve adhesion between coats.

UV curing of waved materials

The applied material is cured by passing under UV lamps. Having a large body means there is no need for conventional dryers to remove the solvent before going under the lamps. Products with 100% body can go under the lamps immediately, those with a percentage of solvent need a flash-off time for the solvent to be removed. The solvent remaining after UV drying is seen as an opalescence in the film. UV curing cures the material instantly, the panoramas can be immediately sanded, stacked or packaged.

On such lines, you can also apply a bath. They must be viscous to be applied with the wand and the colors must be UV resistant.

Primer coats can be applied wet-on-wet. They are simply gelled by the lamps so that the layers adhere to each other, and sanding is done after the last coat has been applied and the entire film is fully cured.

UV lamp radiation sources

Two radiation sources are used for UV drying: Gallium (Ga) and mercury (Hg) lamps. Ga lamps have a wavelength longer than 420 nm and a lifetime of about 2000 hours. They are used to harden pigmented coatings and are often combined with Hg lamps.

Hg lamps have a wavelength of 200-380 nm and a lifetime of about 3000 hours. They are used for transparent materials. UV lamps need to be checked regularly because, over time, their power decreases and with it the drying efficiency.

Such industrial finishing lines are used by major manufacturers of parquet and finished panels for their very good productivity. They are automated lines where human input is very low.

I hope you find the information useful. Complementaries are, as always, welcome. And if you have any questions or queries, please leave them below in the space provided. I will be sure to reply.