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Single CoatMDF moisture content. MDF has a natural water content of typically 5 percent to 7 percent. The new system developed uses this as a means to make the board conductive. By quickly raising the surface temperature of the MDF to 200°F during a total dwell time of up to 2 minutes in a catalytic preheat oven, the board becomes conductive and remains so for up to 5 minutes after leaving the oven. Board temperature at application is 120°F to 150°F, well below the temperature at which the powder would fuse to the MDF. This method of applying the powder to the MDF is contrary to the convection process. In that process, the preheat lasts for some 15 minutes, virtually drying the board and raising the temperature to some 275°F at which point the powder will fuse to the board. By forcing the board to become conductive, however, the powder is easily attracted to the MDF at much lower temperatures, ensuring a high degree of transfer efficiency. The attraction causes powder to wrap around the board perimeter in a similar fashion to metal. Powder cure. Once the powder is evenly deposited on the board surface and around the edges, the board enters into a catalytic cure oven (Figure 2). Curing is complete within 5 minutes. The catalytic heaters within the oven are arranged in such a pattern as to drive the temperature of the powder on the edges through to cure as quickly as possible. This action has a number of benefits, the primary one being to seal off the edge to any out gassing that tends to happen along the edges of the board. By concentrating the IR towards these edges, the face of the board easily absorbs the required IR to flow and cure these flat areas. MDF has a natural tendency to expand when the relative humidity increases, especially at low ambient temperatures. Some MDF expands more than others. That’s why the powder on the edges has to be well-cured to reach the full physical properties of the coating. For a line running at 10 feet per minute, the typical oven length is 45 feet to 50 feet. Throughout the oven, some 50 heaters operate on 40 zone controls. Understanding the heating profile through temperature logging is critical to achieving good cures. A sample board has small lightweight thermocouples glued to the four edges and the flat top and bottom surfaces. This board is periodically sent down the oven to compare oven settings for peak temperature and duration. The Kyoto Protocol to the United Nations Framework Convention on Climate Change is an amendment to the international treaty on climate change, assigning mandatory emission limitations for the reduction of greenhouse gas emissions to the signatory nations. The objective is the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." As of December 2006, a total of 169 countries and other governmental entities have ratified the agreement (representing over 61.6 percent of emissions from Annex I countries). Notable exceptions include the US and Australia. Other countries, like India and China, which have ratified the protocol, are not required to reduce carbon emissions under the present agreement. There is still some debate about the usefulness of the protocol, and there have been some cost-benefit studies performed. From [www.wikipedia.org] | |
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MDF Powder Coat Systems, LLC | 300 Highpoint Ave., Portsmouth, RI
02871 | 401-683-7525 Email: jmartin@vulcan-mdf.com |
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