" " wisno wood furniture finishing: Cold check for the finishing layer.

Wednesday, August 7, 2013

Cold check for the finishing layer.

Cold check is one of the basic tests for the finishing layer for the furniture. Cold check is an examination to see the behavior of the finishing layer due to the temperature changes. When we make furniture products to be export for overseas destination, the test is the important tool to make sure the product will be safe during the shipment. The product from Asia will need about 3 month trip to be arrived at US or Europe and during this time there could be temperature fluctuation from day to night or weather changes. The temperature fluctuate during the journey may damage to the product. The cold check is the important tool to make sure the finishing is strong enough to pass the temperature changes during the shipment. In the series of finishing test, the cold check is usually done at the first time, before the adhesion and hardness test

crcack at the finishing


How to do the cold check test.
The cold check for finish layer usually is done to the sample finish panel. The test for big object needs freezer and oven with big room that is expensive. The small size panel is enough to examine the finishing system. If the sample panel is passing the cold check than we can consider that the finishing system is safe. The finishing process for the panel should be the same with the production process. 

Take finished panel as the sample for the finishing process. The finish must be completely dry and perfectly cured. Put the panel in the refrigerator and chill it to the temperature of 0 degrees Celsius for 1 hour, then take out the panel and put it in the oven and heat it to the temperature of 80 Celsius for 1 hour. Then take out the panel from the oven and check the panel. If there is any defect, crack or check at the panel then we stop the test. 1 time process of cooling and heating is called as 1 cycle. If there is no damage at the finishing layer, then we continue doing the cycle.
The test result is expressed by the number of cycles which is successfully passed by the sample without any damage. In the condition when there is no check found, then the test usually is ended at the 8th cycle.

The things to be considered to pass the cold check.
  • The quality of the finishing materials.
The good quality material is needed to make the strong layer of finishing. Most of finishing problem caused by the poor material. The poor material could be caused by the material itself or because the improper in mixing and application. Therefore we need to check the finishing materials before use them. Check the technical data, expire date and the guide how to use it. If we need to mix or cut the material make sure the proper thinner is used. Make sure we well agitate the mixture, check the viscosity and the physically look of the coating. 
Perform finishing process step by step and following the drying time of each material. Use the material with the same type from the first step to the end whenever possible. The finishing with full NC system will have less risk to have finishing problem compare with the NC on PU system or NC on Ac or NC on UV. If we use the combination coating then we need to make sure they are compatible each other. See our previous article: The compatibility of coating application.
  • Avoid too thick film.
The thicker finishing layer tends to have a higher risk to get crack problem. Use the coating in fair amount, it is also will safe the material usage. If the close pores finish needed, then we can apply wood filler to reduce the consumption of the coating. Do good sanding for every layer coating application. Make sure we don’t exceed the maximum thickness of the film finishing recommended. The NC finish is recommended to have maximum 4 mill dry film coating to avoid the crack problem. The PU and UV finish could have thicker film coating, but we should keep the finish thickness as less as possible.
  • The substrate condition.
Some cases of crack and checking at the finishing layer are caused by the substrate. The wood or wood product which has high moisture content will release it water and contract upon the heat. The wood contraction leads to the crack problem the will be seem as the finishing problem. Therefore always check the moisture content of the wood or wood products before start the finishing process, make sure it has dry before the finishing process is started.
Some natural sources such as: leather, pandanus, water hyacinth, sees grass and rattan are elastic and resulted to the crack problem. The special treatment are needed to handle the elastic substrates. We need the special finishing material and special process to accommodate the movement of the substrates

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