Uneven panels. Plant temperature. Glue application, improper stock preparation, press time and/or pressure can compromise the quality of laminated wood products. Here are five things that affect performance in panel-on-frame, veneer/solid core or high-pressure lamination – and what you can do to avoid them.
Cause #1 – Wood Stock is Uneven
Seeing a spotty bond across the panel? Maybe irregularities of an inner layer are transmitting (telegraphing) to the surface? The problem could be inconsistent stock thickness. Core thickness shouldn't vary more than +\- 0.005 inches across the gluing area. Spotty bonds might also indicate inconsistent glue spread and that it’s time to replace or re-groove your spreader rolls. By the way, if you need to sand the stock down, use an abrasive grit higher than 60.
Cause #2 – Plant, Wood and/or Glue Too Cold
Temperatures lower than an adhesive’s minimum use temperature can cause the glue to “chalk,” resulting in bright white squeeze-out or glue line – and a poor bond. Read the adhesive data sheet before gluing. For proper curing, you want the temperatures of the air, stock and adhesive to be above the minimum use temperature of the adhesive you are using.
Cause #3 – Improper Adhesive Spread
Excessive glue can cause panels to warp or glue bleed-through on face veneers. Too little glue can pre-cure. The rule of thumb is to apply 30-45 pounds of adhesive per 1,000 square feet of glue line. We recommend a mechanical glue spreader for even coating onto the substrate.
Cause #4 – Substrates Don’t Make Direct Contact
Proper pressure will vary with the material being glued and the size of the panel, but one fact holds constant: Direct contact of the gluing surfaces increases bond strength. Recommended pressures are: 30-80 psi for high-pressure laminates, 100-150 psi for solid core stock and 100-250 psi for all-veneer constructions depending on species of wood.
Cause #5 – Press Time Too Short
How long you press your panels varies with the adhesive you use, environmental conditions and the moisture content of the stock. Press times range from 30 minutes to two hours, but you can minimize yours through climate control in the plant and wood storage area. Keep the moisture content of wood substrates between six and eight percent before and after pressing.
You can see more about troubleshooting common lamination problems in our video,
Best Way to Prepare and Troubleshoot Laminated Joints. Our Technical Support Team also is at your service to solve any gluing problems you have, 1.800.877.4583 or IASTS@franklininternatinal.com.