" " wisno wood furniture finishing: Orange peels in the wood furniture finishing

Wednesday, April 28, 2010

Orange peels in the wood furniture finishing

Orange peels
Orange peel is an uneven film surface (seem as orange peel or orange skin looked) in the  finishing layer. Orange peel could be major issue in the film layer especially for high gloss and clean looked finish. It is caused by the application of clear coating that is not perfect in the wood finishing process. Actually, at every surface finishing layer, there is always orange peel when it is  viewed accurately (we can check it using a magnifying glass), but when the uneven surfaces can not be seen with the naked eye it will not be a problem. Orange peel would be a problem if it is obviously and too visible at the surface finish. Orange peel is clearly visible and will increasingly become a problem in finishing with at thick film layer and high gloss finishing, especially for the clean looked finish.In the low gloss and antique finish the orange peel may not obviously seem.

How to prevent the orange peels.
 
Orange peels is mainly caused by the application of clear coating that is not good, mainly because the atomization of finishing material that is not perfect. Orange peel is only an issue on the final top coat, on clear coating before last coat the orange peel will not be a problem  since it will be sanded and layered with another clear coating. In this case the good sanding before the last coat is very important. The imperfect sanding in the sealer or top coat coat that leave the orange peel in the layer before the last top coat will cause orange peel on the final coat. Therefore, to overcome and prevent the occurrence of orange peel is to fix both of these issues. 

Here are the things that can be done to prevent the occurrence of orange peel.
  • Avoid the application of clear coating that is too viscous.
Too viscous material is difficult to be atomized with the spray gun. While the good finish need the good atomization.  Spray gun as a tool for atomizing the material has a certain viscosity limitation to produce the perfect atomization.  For the air spray gun, usually  the maximum viscosity is about 14 sec with Nk # 2 cups or 21 sec by Zahn cup # 2 (see my previous article: viscosity of finishing material). For the hvlp gun, the lower  viscosity is required. to get the good atomization. Since that we need to check the material viscosity before application of a clear coating. If the viscosity material used is too high then we have to reduce the viscosity by thin it using the appropriate thinner. 
There are several types of spraying equipment  that is equipped with a heater to reduce the viscosity of the finishing materials by heating it. This tool can be used to apply finishing materials with thick layer, but we need to use the suitable finishing materials for applications with heater equipment. There are several brands of finishing materials that provide coating materials that are designed to be heated, but mostly the coating is not designed to be applied in this way.  The uses of regular coating to be heated application will lead to  a finishing problem. Therefore it must be ensured that we already using the appropriate material in the heater spraying equipment. 
  • Don,t apply clear coating too many layer in one time
Every time we apply a clear coating, we have to let it atomized and dry to get a good flow and film built. To keep get good film layer we need to let it dry and do sanding to prepare the good layer for the next application of a clear coating. Remember that for every clear coating application there will be an orange peel though it not visible, we need to cut the unevenness by do a good sanding. Apply a clear coating to the surface without sanding will add the orange peel on the surface to more and bigger, then the orange peel is visible by naked eye. 
Apply 1 or 2 wet coat, let it dry and do good sanding for every clear coating application. It is a good choice for better result then too many layer application1 time. It will make the clear coat drying faster and easier in the sanding to get the smooth surface. Too many application of clear coating will create a thick film with big orange peels and need long time to dry. After that  we have to spend lot of time and energy in the sanding process to cut the orange peel to make even and smooth surface. 
  •  Use a good paint thinner
The main function of the thinner coating on the mixing clear is to reduce the viscosity, since that when we add thinner, it must be ascertained that the paint thinner can fulfill its function. A thinner must contain enough solvent to do his function. One way to check thinner is to mix thinner with the paint and see the effect. Do a mixing of a clear coating with a thinner with a certain ratio, then check its viscosity. A good thinner will reduce the viscosity of the material quickly  with the small addition of thinner. Thinner with a less quality requires more amount of thinner to achieve the desired viscosity. While too much thinner in will reduce the solid content of the mixture of the material then the film resulted will be thin. To obtain the film with the desired thickness it will require more coating application and finally it will make finishing cost expensive.
  •  Do a good sanding before the final top coat application.
Each time we apply the clear coating, the underneath layer must be sanded good to get the  flat and smooth surface. The film that is uneven or still have the orange peel will produce uneven or orange peel film on the final surface when it is coated with clear coating on it. Since that before the final top coat application we need to make sure the surface already sanded well. Make sure the film surface is already flat, no orange peel, scratches or dirt before the last coat application. For the NC clear coating or other non reaction clear coating type, then a slightly imperfect sanding can still allowed, but for the chemical reaction clear coating such as: acid curing, or PU then sanding must be done perfectly to produce a smooth and even film coat..
  •   Be careful with the use of airless spray gun
Airless spray  is a tool that does not use compressed air for atomization of the material. The atomization produced by the airless spray gun is not as good as the atomization material with air spray gun. Since that reason actually for the better surface finishing, the final top coat should be applied with an air spray gun. Although with the selection and adjustment  of material and the proper adjustment of equipment, the airless spray gun is also widely used for top coat in many finishing industries with good results, but the use of air spray gun will be easier and safer for the final top coat application.


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