" " wisno wood furniture finishing: Dust spray problem in the wood finishing

Monday, May 23, 2011

Dust spray problem in the wood finishing

Dust spray is the rough surfaces caused by dust particles that attach to the finishing surface. In some severe cases the dust spray can appear as a surface with uneven gloss that can be looked like zebra. A thin dust spray in the unexposed part can be fixed by doing scuff sanding on the rough surfaces. But a severe dust spray on the wide and face surface especially with a high gloss, only can be revised by re sanding and re coat the whole surface.
The dust spray problem is mainly caused by the poor spray technique. The application of paint, top coat or sealer always need a wet and evenly coat layer to the overall surfaces. The uneven coat (dry spray) will produce a rough and uneven surface since there are dust attached to the surface. 


 the dry spray

The best way to avoid the problem of dust spray, is by doing a good spray technique. A proper spray technique will produce a wet coating layer to the entire surface evenly and result to an even and smooth finish. But even though the spray technique is seem as the main factor, in fact there are also some other factors which should be carried out to remedy the dust spray problem. There are some other factors that need to be considered such as: finishing material quality, spray equipment, the shape and size of the product and the finishing room. 

Here are the things that must be considered to avoid dust spray:
  • The finishing material
The finishing material has to be perfectly atomized when it is applied and layered to produce an even and smooth coating layer. To be perfectly atomized finishing material should have viscosity according to the type of spray equipment used. Check viscosity of each mixture of the finishing material before it is applied and make sure it is according to the specifications of the spray equipment. The h.v.l.p. spray gun usually requires material with low viscosity (14 second NK 2 cup), while the air spray gun and airless spray gun can work with a higher viscosity material (up to 18 second NK 2 cup). Each tool type and brand can have its own specifications, so we may need to do consultation with equipment suppliers and find the viscosity needed by the equipment. Then do the adjustment to the material in accordance with the spray gun to be used. Materials with too high viscosity can be thinned by add some thinner. Use an appropriate paint thinner to reduce the viscosity of the material. The good quality material finishing mixture is big help to get the good finishing result.
Instead of the proper viscosity of the finishing material also requires a proper drying time to avoid dust spray. A material layer should be wet quite long time to make sure the layer have enough time to receive the material dust spray during a spraying process. The wet layer will let the dust spray stuck is dissolved and merged with the surface layer and does not generate rough surface. Ideally a finishing layer of the first stroke spray gun is still wet until the last stroke is done. The coating layer must be remain wet until the last stroke of the spray gun movement, so the dust spray from the spray gun movement will be able to be accepted and mixed by surface finishing layer without causing a rough surface.
For a wide and big surface for example such as: big cupboard, or wide and long table it is sometimes rather difficult to be fulfilled. We may need to adjust the finishing material to dry slower. Add retarder to the mixture to slower the material drying time when we spray to the big objects.But we cannot set the drying time too long. Too long drying time will slower the finishing process. Too long drying time will also risk to affect the gloss and get problem with dust.
  •   The setting and selection of spray gun.
To produce a good coating material, we need a proper spray gun. To produce the perfect material coating, the spray gun has to produce the perfect atomization and send material to the surface evenly. We need a suitable tool to do it, the spray gun size need to fit with the surface area of ​​the object. Adjust the width spray according to the wide of surface object. Too narrow spray spreading width will require many strokes and be difficult to produce an even layer. Choose the type and size of spray gun according to the type of goods and the volume of work, The air spray gun can generate the most perfect atomization but we still need  the  proper size equipment. We cannot use the small cup gun to spray to the big volume job or big objects.  The air spray gun with pump or pressure port is better to be used since it can make a spraying can be done continuously. For big volume job the air assisted spray gun is good option since it is more effective tool to do the high speed spraying process.
  • The spray techniques
The poor spray technique is often the main reason of the failure of the finishing material application. This spray technique is a skill that need adequate training and exercising in a sufficient time to be mastered. To be success in the spray application we need operators with enough skill that can only be obtained with enough practice. The main principle in the spray coating is: the coating layer should be wet enough (as wet as possible) but do not let the finishing material sagging. It is more difficult to be obtained when we spray to objects with complicated forms such as: chairs, crib or a large cupboard. But with enough practicing then someone will be able to master the best spray technique  according to each model and item. As a basic knowledge of spraying technique please view it in our previous article: how to use spray gun correctly.
  • The finishing and drying room.
A rough surface finish can also be caused by dust that fall and stick to the surface while the layer is still wet. A good spray technique need a finishing with a wet layer, but if the wet surface is exposed to the air, there are may be some dust fall to the surface finish and generate as a rough surface. Therefore, we also need a finishing room and drying room that is clean and free of dust to place the wet coated product. 

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