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Blistering, degumming and warping of plywood, common problems in hot pressing of plywood

Blistering, degumming and warping of plywood, common problems in hot pressing of plywood

1、 Blistering and local degumming

The causes are as follows

1. Too high moisture content or uneven drying of veneer

2. Too much glue

3. Too fast decompression speed or too high hot pressing temperature

4. The condensation degree of resin is not enough

5. Insufficient hot pressing time

Solutions:

1. The moisture content of veneer should be controlled in the range of 8-12%

2. Control the amount of glue to meet the process requirements

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

4. Check the quality of resin

5. Extend the hot pressing time appropriately

2、 Low bonding strength or degumming

The causes are as follows

1. The quality of glue is poor

2. Insufficient or uneven gluing

3. The aging time is too long, the glue is dry or the aging time is too short, and the glue does not form a continuous film

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

5. The burr groove of veneer is too deep and the quality of rotary cutting is poor

6. The moisture content of veneer is too high

Solutions:

1. Check the glue quality

2. Note that the amount of glue is moderate and even

3. Main control aging time

4. Properly increase the pressure and temperature, or extend the hot pressing time

5. Improving the quality of veneer rotary cutting

6. Control the moisture content of veneer within the specified range

3、 Penetration

The causes are as follows

1. The veneer quality is too poor, and the back crack is too large

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

3. The temperature or pressure of hot pressing is too high

Solutions:

1. Improve veneer quality and reduce back crack depth

2. Increase the concentration of glue, reduce the amount of glue, extend the aging time

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

4、 Lamination separation of core plate

The causes are as follows

1. The core plate is not integrated, and the manual core clearance is not accurate

2. The core plate moves and dislocates during loading

3. Uneven edge of core plate

4. The edge of the core plate has a lotus edge or a crack

Solutions:

1. After the core board is fully tensioned or coated with glue, the core can be arranged

2. Prevent the core plate from dislocation during plate installation

3. The edge of the core plate is cut straight

4. Improve the quality of core plate rotary cutting and drying, prevent lotus leaf edge and crack

5、 Warpage

The causes are as follows

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

Solutions:

1. Pay attention to the principle of symmetry

2. Improving drying quality of veneer

3. Reduce the temperature and pressure appropriately

6、 Tolerance range of plywood

Causes

1. The number of hot pressing sheets in each interval is too large

2. The thickness of veneer varies

3. Press plate tilt or plunger tilt

4. The thickness calculation of plywood blank is incorrect or the pressure is too high and the temperature is too high in the hot pressing process

Solutions:

1. The hot pressing process of one sheet and one press should be adopted as far as possible

2. Improve the quality of veneer

3. Press installation and leveling

4. Adjust the plate thickness, pressure and temperature

7、 Surface indentation

The causes are as follows

1. The backing plate shows that it is uneven

2. There are rubber blocks or sundries on the surface of the base plate

3. Veneer debris or debris sandwiched between the layers

Solutions:

1. Check and replace the base plate

2. Check and clean the backing plate

3. Pay attention to embryo matching

For the defects such as low bonding strength, bubbling and local degumming of plywood during hot pressing, the following three points are summarized: 1. Better veneer quality and lower moisture content; 2. Reasonable hot pressing process; 3. Better adhesive quality and use.

Bubbling, degumming, warping, plywood hot pressing common problems how to solve?

However, due to the backward formulation and process of some glue factories, and in order to reduce production costs and obtain higher profits, many glue factories seldom use or do not use expensive organic modifiers such as polyvinyl alcohol and melamine, especially the glue factories in non plywood base, resulting in poor quality of UF glue, that is, thin glue, slow film forming, long preloading time, poor bonding strength, low heat and wear resistance, and high cost The content of formaldehyde is high.

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?

Some will choose in the factory and glue, the use of modifiers or additives to be modified. As for modification, there are no other than organic 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 booming inorganic modification has a certain threshold, but the price is relatively low, which has great potential for popularization and application. Of course, if it is made into high-grade plywood, it is best to give priority to organic modification, supplemented by inorganic modification This not only improves the grade of the board, but also reduces the cost of the board!

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