1.    Spotty bonds.

Probable cause: (1) low spread; (2) uneven core thickness; 3) low pressure; or 4) cold spots in the platen. Solutions:  (1) increase the adhesive spread; (2) calibrate the cores to a uniform thickness; (3) increase the pressure; or (4) check the bond line temperature with thermocouples.

2.    The glue bleeds through the face veneers.

Probable causes:  (1) excessive glue spread; (2) excessive pressure; or (3) the face veneers are high in moisture content. Solutions:  (1) Reduce the glue spread and/or use a higher viscosity adhesive; (2) reduce the pressure; and (3) dehumidify the plant during the wet seasons.

3.    Warpage of panels.

Probable causes: (1) Excessive or unequal adhesive spread; (2) high moisture content; (3) unbalanced construction; or (4) a high press temperature. Solutions:  (1) Reduce the adhesive spread and/or make sure the top and bottom spread are equal; (2) maintain a 6-8 percent moisture content in the material; (3) check the grain orientation; and (4) reduce the platen temperature.

4.    Telegraphing of core defects.

Probable causes:  (1) Excessive pressure; (2) uneven or variable thickness; or (3) foreign material on the core. Solutions:  (1) Reduce the pressure; (2) re-sand the core; and (3) pre-clean the core.

5.    Experiencing checking and cracking.

Probable causes: (1) The moisture content of the stock is too high or low; (2) improper conditioning; (3) the press temperature is too high; or (4) the press period is too long. Solutions:  (1) The stock should be between 6-8 percent moisture content and humidify the plant if it is below 25 percent relative humidity; (2) panels should be squarely stacked and weighted for 12 hours after removing them from the press;  (3) don’t use high temperatures to attain short pressure periods unless the moisture content is carefully controlled; and (4) remove the panels as soon as the press is opened.

6.    Steam blisters are visible.

Probable causes: (1) Excessive adhesive spread; (2) high moisture content; (3) high press temperature; (4) wet spots from non-uniform moisture; or (5) the press or assembly time is too short. Solutions:  (1) Reduce the adhesive spread and check the planers, blades and spreader rolls; (2) ensure materials are at 6-8 percent moisture content and dehumidify the plant in wet seasons;  (3) reduce the temperature; (4) avoid materials with worm holes, dents, knots and fillers; and (5) use a longer assembly time.

Source: Franklin Adhesives & Polymers. For more information call (800) 877-4583 or visit FranklinAdhesivesAndPolymers.com.