 |
|
|
|
|
Two Coat The two-coat process. The process previously described is the basic method of applying and curing powder for a one-coat system. From market pressures, it became essential to achieve a homogenous-looking substrate for both the edges and the flat surfaces. MDF has an end grain, and despite well routed profiles and sanded edges, the differences in MDF density across the end grain is difficult to hide. During the curing process, out gassing takes place. In addition, as the powder flows (and depending on the viscosity), it will “edge dive” in the less dense region in the center of the board, leaving a distinct area that telegraphs the coarser, less dense area through the finished coating (Figure 3). By simply applying a second coat, however, this area blends in perfectly with the rest of the surfaces. The challenge was to incorporate the two powder application booths and three ovens in a line process that was economical and not too distressing for the MDF with heat buildup. MDF is a porous medium. Consequently, its moisture equilibrium changes according to the climate. As the moisture percent increases within the board, slight increases in board thickness occur; conversely, the board will shrink as moisture is given up. To accommodate these small dimensional changes, the first coat takes on the properties of a formal powder prime coat, followed by the normal low-bake powder topcoat. In the two coat system, as the board cools down between exiting the prime cure oven and entering the topcoat booth, by simply wiping the primed edge with 220 sandpaper, any powder encapsulated fiber “nibs” are easily removed, ensuring a high-quality finish from the cured topcoat. The amount of inter-coat edge preparation depends on the degree of edge sanding done before coating and the finishing standard required. The two-coat process starts out as described with the prime coat applied to the preheated MDF panels, followed by a 3-minute cure. The board exits the oven at 330°F. An 5 – 8 minute cool down takes place via a power-and-free conveyor system, or the board simply keeps traveling down the line to the topcoat powder booth. (See Figure 4.) Within minutes, the board enters the final cure oven where both coats undergo a final co-cure. Before reaching the unload area, the board cools down for 30 minutes at ambient temperature or for shorter times by chilled forced air cooling. (See Figure 5.) In Line System Successful coating of MDF requires a three oven, two spray booth system. Line speeds may range from 8 to 20 ft. per min. The process starts with a Catalytic preheat oven through which the MDF boards pass. Once heated, the boards become conductive and receive the Powder Prime Coat. The primer is cured by the next oven in line and exits to a brief cool down and inspection in line area, before entering the final powder application booth. Once out of the top coat powder booth, the boards enter the final curing oven where the coating is baked to acheive the final properties. The process is unique, in that the majority of the moisture content is preserved within the MDF board. Additionally, the infra red energy only heats the outside of the board raising the surface temperature sufficiently to cure the powder, without compromising the integrity and physical properties of the MDF board.  Vulcan has a 300 foot conveyorized test facility with the full three oven / two coat process to demonstrate the MDF powder coating technology. Call for your appointment: 800-325-5422 Email: jmartin@vulcan-mdf.com Visit us on the web at: www.vulcan-mdf.com | |
|
MDF Powder Coat Systems, LLC | 300 Highpoint Ave., Portsmouth, RI
02871 | 401-683-7525 Email: jmartin@vulcan-mdf.com |
|