Plywood QC Inspection Checklist : Part 19 Defects and Solutions of Plywood in Hot Pressing

Plywood QC Inspection Checklist : Part 19 Defects and Solutions of Plywood in Hot Pressing

Defects and Solutions of Plywood in Hot Pressing

1 Bubble and local glue deficiency

Reasons for this:

1. The moisture content of veneer is too high or the drying is not uniform.

2. Excessive glue content 3. Excessive pressure-lowering speed or excessive hot-pressing temperature 4. Resin condensation degree 5. Insufficient hot-pressing time. Solutions: 1. Controlling moisture content of veneer in the range of 8-12%. 2. Controlling glue content to meet process requirements 3. The second stage of pressure-lowering speed should be slow. Hot-pressing temperature should be lowered appropriately 4. Checking resin quality 5. Appropriately prolonging hot-pressing time.

2. Low bonding strength or delaminated

Reasons for this:

1. The quality of glue is poor 2. The glue quantity is insufficient or the glue is not uniform 3. The aging time is too long. The glue has dried or aged too short. The glue does not form continuous film 4. The pressure is insufficient, or the temperature is too low, or the hot pressing time is too short 5. The burr groove of veneer is too deep. The spinning quality is poor 6. The methods to solve the problem of too high moisture content of veneer are as follows: 1. Check the glue quality 2. Pay attention to the glue quantity. Moderate and uniform 3. Mainly control aging time 4. Increase pressure temperature or prolong hot pressing time 5. Improve veneer spinning quality 6. Control veneer moisture content not to exceed the prescribed range.

3 permeation and bleeding

Reasons for this:

1. The veneer quality is too poor, the back crack is too large 2. The glue is too thin or the glue amount is too large. The aging time is too short 3. The solution to the problem of excessive temperature or pressure of hot pressing is: 1. Improving the veneer quality, reducing the back crack depth 2, increasing the glue concentration, reducing the glue amount, prolonging the aging time 3, reducing the hot pressing temperature or the unit pressure of hot pressing.

 

4. Core veneers voids and overlaps

Reasons: 1. The core veneer is not fully stretched, and the gap between manual core row is not grasped accurately.

 

2. Core veneer  movement dislocation 3, core veneer edge irregularity 4, core veneer edge with lotus leaf edge or crack solution: 1. Core veneer stretching or gelatinizing aging and then core row 2, core veneer dislocation 3, core veneer edge shear straight 4, improve core veneer rotary cutting and drying quality, prevent lotus leaf edge and crack

5 warp

Reason:

1. The structure and processing technology of plywood do not conform to the symmetry principle 2, the moisture content of veneer is not uniform 3, the temperature and pressure are too high to solve: 1. Pay attention to the symmetry principle 2, improve the drying quality of veneer 3, reduce the temperature and pressure properly.

6 Thickness does not exceed tolerance range

Reasons for this:

1. Excessive hot-pressing tension in each interval 2. Different veneer thickness 3. Inclination of pressure plate or plunger 4. Incorrect calculation of plywood embryo thickness or excessive pressure and temperature in hot-pressing process. Solutions: 1. Adopting one-pressure hot-pressing process as far as possible 2. Improving veneer quality 3. Press installation and adjustment to level 4. Adjusting plate embryo thickness and adjusting pressure Force and temperature

7 plywood indentation defects

Reasons for this:

1. The cushion plate indicates that the surface of the cushion plate is uneven 2. There are glue blocks or sundries on the surface of the cushion plate 3. Solutions for the interlayer solution of the clamping plate with veneer debris or sundries are as follows: 1. Inspection, replacement of the cushion plate 2, inspection of the cushion plate, cleaning up 3, and attention during embryo matching.

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