Warp is seldom a problem with composite panels when care is taken.
To prevent warp in flat laminated panels:
1. Store panels and laminates in reasonably uniform, protected warehouse conditions, avoiding extremes in temperature and humidity
2. Balance the overlay sheets by type and weight, and ensure they are evenly conditioned. The ideal is 70F (±5) and 35% (±5) RH for one week.
3. Be sure the grain and machine direction of the paper run the same way on both sides of the substrate.
4. Be sure that press conditions are set to properly cure both sides when using different papers.
5. Whenever possible, utilize a balanced construction with uniform temperature for both the top and bottom platens.
6. Use as few openings in the press as possible: too many openings may increase the precure by slowing the closing time.
7. Stack hot boards flat in covered piles and allow them to cool to 120F or less before sawing.
Causes of warp in veneered panels:
1. A very thin core with thick face veneers
2. Unbalanced glue spreads on the two sides of the core. Also too heavy a glue spread or too low glue solids content. Inadequate cure of the glue in the hot press can also cause problems.
3. Too heavy a glue spread or too low glue solids content. Or inadequate cure of the glue in the hot press
4. Pressing two thin panels in one opening or uneven heating of platens within or between openings.
5. Different moisture contents, species density or thickness of face veneers can unbalance the panels.
6. Overdrying in the press before, during or after pressing.
7. Unpiling and sawing the board before adequate cooling.
Source: Composite Panel Association, 703-724-1128. More information is available at CompositePanel.org.
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