Bubbling, delamination , warping, common problems of plywood hot pressing in China
1、 Bubbling and partial delamination
Causes:
1. The moisture content of veneer is too high or the drying is uneven
2. Too much glue
3. The pressure drop speed is too fast or the hot pressing temperature is too high
4. Insufficient resin condensation
5. Insufficient hot pressing time
Solution:
1. Control the moisture content of veneer in the range of 8-12%
2. Control the gluing amount to meet the process requirements
3. The speed of the second stage of depressurization shall be slow, and the hot pressing temperature shall be reduced appropriately
4. Check the resin quality
5. Properly extend the hot pressing time
2、 Low bonding strength or delamination
Causes:
1. Poor glue quality
2. Insufficient or uneven glue application
3. The aging time is too long, the glue solution has dried or the aging time is too short, and the glue does not form a continuous adhesive film
4. The pressure is insufficient, or the temperature is too low, or the hot pressing time is too short
5. The burr and groove of veneer are too deep, and the quality of rotary cutting is poor
6. The moisture content of veneer is too high
Solution:
1. Check the glue quality
2. Pay attention to the moderate and even amount of glue
3. Mainly control aging time
4. Properly increase the pressure and temperature, or extend the hot pressing time
5. Improve veneer peeling quality
6. Control the moisture content of veneer not exceeding the specified range
3、 Permeating glue
Causes:
1. The veneer quality is too poor, and the back crack is too large
2. The glue solution is too thin or the amount of glue is too large, and the aging time is too short
3. The temperature or pressure of hot pressing is too high
Solution:
1. Improve veneer quality and reduce back crack depth
2. Increase the concentration of glue solution, reduce the amount of glue coating, and prolong the aging time
3. Reduce hot pressing temperature or unit pressure
4、 Core plate lamination parting
Causes:
1. The core plate is not integrated, and the manual core arrangement gap is inaccurate
2. Core plate movement and dislocation during plate installation
3. The edge of core plate is uneven
4. There are ruffles or cracks at the edge of the core plate
Solution:
1. The core board shall be arranged after being integrated or coated and aged
2. Prevent core plate from dislocation during plate installation
3. Core plate edge shall be sheared and straight
4. Improve the core plate peeling and drying quality, and prevent ruffles and cracks
5、 Warpage
Causes:
1. Plywood structure and processing technology do not conform to the principle of symmetry
2. Uneven moisture content of veneer
3. Too high temperature and pressure
Solution:
1. Pay attention to the principle of symmetry
2. Improve veneer drying quality
3. Reduce temperature and pressure appropriately
6、 Tolerance range of plywood
Causes
1. Too many hot pressing sheets in each interval
2. The thickness of veneer varies
3. The pressing plate is inclined or the plunger is inclined
4. Incorrect thickness calculation of plywood veneer or excessive pressure and temperature in hot pressing process
Solution:
1. The hot pressing process of one piece and one press shall be adopted as far as possible
2. Improve board quality
3. Press installation and correction to be horizontal
4. Adjust the matching thickness of the plate blank, and adjust the pressure and temperature
7、 Plate surface indentation
Causes:
1. The base plate shows unevenness
2. Glue blocks or sundries are stuck on the surface of base plate
3. Pieces or sundries of veneer are sandwiched between layers
Solution:
1. Check and replace the base plate
2. Check and clean the base plate
3. Be careful when preparing embryos
For the defects such as low bonding strength, blistering and partial delamination of plywood during hot pressing, the following three points are mainly summarized: 1. The veneer quality is good, and the moisture content is low; 2. The hot pressing process should be reasonable; 3. The quality and use of adhesive shall be good.
However, due to the backward formulation and process of some rubber plants, and also because many rubber plants use little or no expensive organic modifiers such as polyvinyl alcohol and melamine in order to reduce production costs and obtain higher profits, especially those in non plywood base, the quality of urea formaldehyde adhesive is very poor, that is, thin glue, slow film formation, long prepressing time, poor bonding strength, low heat resistance and abrasion resistance, and high formaldehyde content.
Plywood plants only use a large amount of flour to eliminate the above disadvantages, which is not only poor in quality, but also high in cost. What are the good strategies for some advanced plywood plants?
