Defects and Solutions of Plywood in Hot Pressing

Defects and Solutions of Plywood in Hot Pressing

Bubble and local degumming

Reasons for this:

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

2. Excessive amount of glue

3. Over-fast pressure reduction or over-high hot-pressing temperature

4. The degree of resin condensation is not enough.

5. Insufficient hot pressing time

Solutions:

1. Control the moisture content of veneer in the range of 8-12%.

2. Controlling the amount of glue to meet the technological requirements

3. The speed of the second stage of depressurization should be slow and the hot-pressing temperature should be reduced appropriately.

4. Inspection of resin quality

5. Appropriate extension of hot pressing time

2. Low bonding strength or degumming

Reasons for this:

1. The quality of glue is poor.

2. Insufficient or uneven gluing

3. The aging time is too long, the gel has dried or the aging time is too short, and the gel does not form a continuous film.

4. Insufficient pressure, or too low temperature, or too short hot pressing time

5. Veneer burr groove is too deep and spinning quality is poor.

6. The moisture content of veneer is too high

Solutions:

1. Inspection of glue quality

2. Pay attention to the moderate and even amount of glue

3. Mainly control aging time

4. Increase the temperature of pressure or prolong the hot pressing time

5. Improving the quality of veneer spinning

6. Controlling the moisture content of veneer not exceeding the prescribed range

3. Permeability

Reasons for this:

1. The veneer quality is too bad and the back crack is too big.

2. The glue is too thin or the amount of glue is too large, and the aging time is too short.

3. Excessive temperature or pressure of hot pressing

Solutions:

1. Improving veneer quality and reducing back crack depth

2. Increasing glue concentration, reducing glue amount and prolonging aging time

3. Reduce the hot-pressing temperature or the unit pressure of the hot-pressing

4. Core laminated separation seam

Reasons for this:

1. The core plate is not fully stretched and the gap between manual core row is not accurately grasped.

2. Core plate movement and dislocation during loading

3. The edges of the core board are uneven.

4. Lotus leaf edge or crack at the edge of core plate

Solutions:

1. Re-core after core sheeting or gelatinizing aging

2. Prevent core plate dislocation during loading

3. Core plate edge shear straight

4. Improving the quality of spinning and drying of core plate to prevent lotus leaf edges and cracks

V. Warpage

Reasons for this:

1. The structure and processing technology of plywood do not conform to the principle of symmetry.

2. Non-uniform moisture content of veneer

3. Excessive temperature and pressure

Solutions:

1. Pay attention to the principle of symmetry

2. Improving drying quality of veneer

3. Appropriate reduction of temperature and pressure

6. Plywood of different thickness or beyond the allowable tolerance range

Reasons for this:

1. Excessive number of hot-pressing tensors in each interval

2. Veneer thickness varies

3. Plate inclination or plunger inclination

4. Incorrect calculation of plywood embryo thickness or excessive pressure and temperature in hot pressing process

Solutions:

1. Adopt one-pressure hot-pressing process as far as possible.

2. Improving veneer quality

3. Calibration of Press Installation to Level

4. Adjusting the thickness of blastocyst and adjusting the pressure and temperature

VII. Plate indentation

Reasons for this:

1. The cushion plate indicates unevenness.

2. Rubber or sundries adhering to the surface of the cushion plate

3. Veneer debris or debris clamped into the interlayer of the veneer

Solutions:

1. Inspection and replacement of cushion plate

2. Check the pad and clean it up

3. Be careful when mating embryos

For the defects of low bonding strength, bubbling and partial degumming of plywood during hot pressing, we mainly summarized the following three points: 1. veneer quality is good, and moisture content is low; 2. hot pressing process should be reasonable; 3. adhesive quality and use should be good. However, due to the backward formulation and technology of some rubber factories, and because many rubber factories, in order to reduce production costs and obtain higher profits, seldom use or do not use expensive organic modifiers such as polyvinyl alcohol and melamine, especially in non-plywood base rubber factories, the quality of urea-formaldehyde adhesive is very poor, that is, thin glue, slow film formation, long pre-pressing time, poor bonding strength, low heat resistance and wear resistance. Because of the high formaldehyde content, plywood factories only use a large amount of flour to eliminate the above disadvantages. Not only the quality is poor, but also the cost is high. What are the good strategies for some advanced plywood factories? Some of them choose to use modifiers or additives to modify the rubber in the factory. As for modification, there are no two kinds of modification: organic modification and inorganic modification. Organic modification is the most commonly used. Although the effect is the best, the cost is too high to be popularized and applied. At present, the flourishing inorganic modification has a certain threshold, but the price is relatively low. It has great potential for popularization and application. Of course, if we make high-grade plywood, it is better to give priority to organic and inorganic is the best supplement. This not only improves the grade of the board, but also reduces the cost of the board!

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