Good pressing and laminating is essential to the quality of the finished product. Here are some troubleshooting tips for ensuring a good bond in the hot and cold pressing process.

Hot pressing
1 Experiencing 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 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.

4 Exhibiting a warpage of the 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.

5 Seeing 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.

Cold pressing
6 Total delamination with little or no substrate failure.  Probable causes: (1) Pre-cure (no glue transfer); (2) low pressure (poor contact); 3) short press time. Solutions: (1) Increase the glue spread; (2) increase pressure; (3) increase the pressure period.

7 Spotty bonds.  Probable causes: (1) Uneven surfaces; (2) worn spreader rolls. Solutions: (1) Calibrate cores to uniform thickness and/or increase pressure; (2) replace or re-groove rolls.

8 Glue bleeds through the face veneers. Probable causes: (1) Excessive glue spread; (2) excessive pressure; (3) wrong adhesive type. Solutions: (1) Reduce the glue spread; (2) reduce the pressure; (3) consult your supplier.

9 Telegraphing of core defects or banding. 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.

10 Warpage of panels. Probable causes: (1) Excessive or unequal adhesive spread; (2) unbalanced construction; or (3) excessive moisture. Solutions:  (1) Reduce the adhesive spread and/or make sure the top and bottom spread are equal; (2) check the grain orientation and the number of plies; (3) a 6-8 percent moisture content is recommended.

11 Brilliant white on glue squeeze-out and/or glue line. Probable cause: Chalking caused by low temperature. Solution: Raise the temperature of the plant, wood and adhesive above the minimum use temperature of the adhesive.

Source: Franklin Adhesives & Polymers. For more information call 800-877-4583 or visit FranklinAdhesivesAndPolymers.com. More gluing and pressing troubleshooting tips are available on Franklin Adhesives’ website.