1. Damp heat method
The production method of directly coating and hot pressing the veneer without drying is called the wet heat method.
This method is commonly used to produce plywood from blood gelatin and bean gelatin. Due to the moisture content of wet veneers typically being 60-120%, the moisture content of plywood after hot pressing is also high, usually between 30-40%, and the plywood is dried.
In this method, wet veneers are directly bonded, and there is no drying shrinkage loss or veneer processing loss when the veneers are dried, resulting in a high utilization rate of wood.
The process is simple, the equipment usage is small, and the factory area is small, so it has been widely used in the past.
However, due to the high internal stress of plywood after hot pressing, it is prone to warping, hair drying and cracking, and can easily cause "foaming" defects during the hot pressing process, so it is rarely used in production.
2. Dry cooling method
After drying the wet veneer (with a moisture content of about 10%), glue is applied and the manufacturing method is carried out using cold pressing at room temperature.
This method is used to produce plywood using soybean glue, casein glue, and urea formaldehyde resin glue for cold pressing (especially in the early stages of plywood industry development).
The moisture content of the plywood pressed by this method is about 20% or higher, so it also needs to be glued. The board of directors does it.
This method has a long production cycle, low efficiency, large working area, and consumes more adhesive compared to dry heat method. When using casein glue or soy glue, the water resistance of plywood is poor, and it is now only used in furniture manufacturing and some small factories.
However, the dry cooling method has the advantages of high wood utilization rate (low compression ratio, etc.), relatively simple equipment, no need for heating system, and low investment. Currently, many countries are developing cold cured synthetic resin adhesives that have relatively short curing times at room temperature. Efficient cold press machine.
Therefore, in the near future, the dry cooling method in plywood production is likely to regain its important position.
3. Dry heat method
After drying the wet veneer (with a moisture content of about 10%), apply glue and press the glue in a hot press (or pre press the adhesive sand particles in a cold press and then place them in a hot press). The manufacturing method of rubber pressure is called dry heat method. This method is applicable to various adhesives. It has short bonding time, high production efficiency, and high product quality. It has become the most important and common bonding method in plywood production.
