The wet veneers with high moisture will increase the time of hot press, and make bubbles inside of plywood sheets. It will also affect the spread of glue on the veneer surface and cause other quality problems.
Veneer dryer can remove moisture from veneers sheets and decrease the moisture content to a controlled level which is suitable for gluing and pressing process.
What’s the types of veneer dryer?
As one of the key process in veneer production, the veneer drying takes the whole production to next high quality level. It can dry veneer with thickness of 0.3-5mm. The hot air in the hot blast stove is injected into the upper and lower bellows by the fan, and then the hot air is blown to the upper and lower sides of the veneer through the nozzle of the upper and lower bellows, so that the two surfaces of the veneer are evenly heated and dried The effect.
According to the heat transfer mode, veneer dryers can be divided into contact type, radiation type, air convection type and composite type.
1.The contact dryer is to contact the veneer with the steel plate with heat to achieve the effect of drying. Its advantage is high thermal efficiency. there are some advantages for this type of dryer, such as dry veneer formation, high thermal efficiency, drying speed, energy saving more than 36% of drying heat.
2.Radiation dryer uses infrared, far infrared, microwave as heat source to dry veneer, which has high cost. At present, the infrared veneer drying is still under test. Some people think that it is possible to use a large number of infrared dryers that are heated with combustion gases.
3.Air convection dryer transfers heat to veneer by convection of hot air, such as general mesh belt dryer.
4.Composite dryer is a combination of the above heat transfer methods for veneer drying, common roller type belongs to this type.
For example, roller dryer heat transfer is a convection-contact compound heat transfer. In another example, an infrared drying device can added in front of an ordinary dryer feed end to speed up veneer drying process. And the microwave drying also can be used to improve the quality of drying veneer.
There are also two veneer dryer delivery method: roller dryer and mesh belt dryer. At present, most mills in china used belt dryer and compound heat transfer roller dryer instead of hot press dryer.
The mesh belt dryer is easy to operate and use less steel, but the flatness of drying veneers are not best, mesh belt easily damaged and need more maintenance.