Curtain Coater for Wood Finishing

Curtain coater is a machine for coating application that uses a continuous fluid flow system in the form of a "curtain" to wet and coat the surface. The coating liquid is flowed by using a special nozzle to produce a curtain of material, while the workpiece is run using an automatic conveyor through the curtain of liquid so that the surface of the workpiece is exposed to the flow of the flowing finishing material.

The curtain coater is one of the flat line finishing machines that can automatically coat finishing materials at high speed and high transfer efficiency. The efficiency is about 95%, almost the same as the roller coater. This curtain coater is one of the finishing machines in the flat line finishing process instead of the roller coaters and automatic spray machine. 

The advantage of the curtain coater

• Smooth coating layer

The coating layer is the result of the liquid that falls and flows over the surface. It won't leave marks like a roller coater. The coating layer will not be as perfect as the spray automatic spraying machine, but it is still better than the roller coater. In the UV coating or water-based coating flat line system, this machine is mostly used to apply the last coat that needs the smooth and even coating layer.

• High efficiency and high speed

The curtain coater is an automatic machine that is designed for high-volume production. When it is set up, it can do the finishing with high speed and consistency. It also gives the high efficiency of material application; the material transfer of this machine is about 95%, about the same as the roller coater.

• More flexible

This machine can process products with slight differences in thickness and sizes as long as they have flat surfaces. This machine can also be used to apply the materials that are dry at room temperature (without an oven), such as NC, water-based, and other 1-component materials.

Curtain coater

picture taken from : www.promas-woodworking.com

The disadvantages of the curtain coater

• Only do the flat product

Curtain coating is only suitable for flat-surface products; it cannot be used for 3-dimensional products or complicated products. Curtain coater even cannot be used for textured or wavy surfaces. The material flow from the curtain will fill the low areas and produce uneven coating.

• Cannot do the thick material 

The machine works by flowing the liquid, but it does not work for viscous material. The thick materials, such as filler, putty, or the high-solid coating, cannot be applied by this machine. Materials should be sufficiently dilute so that they can be pumped and flowed to form a curtain of coating. 

Main Components of Curtain Coater

• Reservoir tank: 

It is a tank or container as a place to store the finishing material liquid applied. An agitator can be installed into the tank to keep the material well mixed.

• Nozzle

A special nozzle is needed to flow the liquid material from the storage tank and form a curtain of the liquid.

• Pump circulation

Pump is used to flow the finishing material liquid from the tank to the nozzle with a continuous and stable flow

• Conveyor

A conveyor is used to place the workpiece and run it to pass through the curtain coater at a certain speed.

• Filtration system: 

A filter is needed to filter the liquid so that it is free from dirt and ensure that the material curtain is always clean.

• Control panel

The control panel is used to set and adjust the speed of the conveyor and the flow of finishing materials to regulate the thickness of the layer as needed.

• Oven 

To speed up the drying process, the oven can be installed at the end of the tool to speed up the drying process according to the material being applied. A UV lamp oven is installed to complement the curtain coater used for UV coating applications; a hot oven or infrared lamp can be installed if the finishing material applied is water-based paint.

How curtain coater works

The working principle of a curtain coater actually is quite simple but effective. Finishing liquid is pumped from the tank to the top of the machine and flows through the nozzle, forming a falling stream like a curtain. When the workpiece passes under the stream, its surface is immediately coated evenly. The thickness of the finishing layer is adjusted by adjusting the liquid curtain, conveyor speed, and concentration of the finishing liquid. After the coating process, the workpiece usually goes directly to the drying stage, either with an oven, UV curing, or other methods. The oven can be installed in series with the coating machine or can also be installed separately. In the continuous machine, the oven is installed after the coating machine; it is more usual for the water-based or UV coating. With the right settings, the object that comes out of the machine is already coated with dry paint.

The drying process can also be done in another room by taking the workpiece that comes out of the machine and placing it on a rack to be taken into the drying room. This system give more flexibility in the adjustment and can be used for NC, orbased systems that need longer time to dry

The working principle of the curtain coater is quite simple but effective. The finishing liquid is pumped from the tank to the top of the machine and flows through the nozzle, forming a falling stream like a curtain. When the workpiece passes under the stream, its surface is immediately coated evenly. The thickness of the finishing layer is adjusted by adjusting the liquid curtain, conveyor speed, and concentration of the finishing liquid. After the coating process, the workpiece usually goes directly to the drying stage, either by oven, UV curing, or other methods. The oven can be installed in series with the coating machine or can also be installed separately. With the right settings, the object that comes out of the machine is already coated with dry paint (usually for UV coating or water-based coating materials). The drying process can also be carried out in another room by taking the workpiece that comes out of the machine and placing it on a rack to be taken into the drying room.

Things to consider when using a curtain coater

• Model and shape of the item

The curtain coater can only be used for items with flat shapes. This machine cannot be used for items with complex shapes. Flat objects with slight variations, such as small grooves or slight textures, may be able to be coated with this machine. However, complex shapes such as 3-dimensional shapes, deep carvings, or wavy surfaces are not suitable for the curtain coater application.

• Production volume

This tool requires proper settings and adjustments to work properly. Settings are made according to the thickness of the material, the type of finishing material, and the desired thickness. Once the settings are made, it should carry out the production process for items with a large volume of work. When there is a change in the product and finishing material, then you will need to adjust the machine setting. You need to have big volume production to get the benefit of the machine. 

• Finishing quality

The curtain coater will produce a smooth and even coating, but it will still not be as good as the spray application. The quality of the coating produced may be acceptable for mass-produced products but may not be able to meet the demand for high-quality products.

Curtain coater is also limited to finishing processes with standard coating and cannot do finishing processes for special effects like spray guns. Therefore, make sure you know for sure the quality and appearance of the finishing you need before choosing to use this tool. Make sure the finishing you want can be done with this machine.

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