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Drying of Veneers

Drying of Veneers

Topics
General
Drying Problems

General

Veneers are dried in three ways

  1. By simple air drying where climate is suitable. This method can be useful for moderate production provided it is well organised. Air drying is not specially suited to hot pressing of high temperature setting phenolic reins. However it is quiet suitable when urea formaldehyde bonding is used when supported by some limited axillary form of drying facilities.

  2. By compartment driers using convection heating which are somewhat similar in design to timber kilns.

  3. By mechanical driers that are provided with conveyers usually in the form of mesh belts or rollers, and are fitted with both convection and/or radiant type heaters (see Picture 1).

Picture 1:- Mechanical Drier (Courtesy of Dr. P.D.Evans)

.Big River Timbers in Australia dry there veneers for 16 minutes to a moisture content of 12 percent. This company uses steam heated dryers with fans which circulate the air through jet boxes which contain small holes.

Veneers to be dried in batch type kilns or in continues driers should be separated into groups having approximately the same drying characteristics, ie by species, thickness, heartwood or sapwood, and initial moisture content. Control of mechanical driers is by control of temperature, ventilation and conveyer speed. In large modern driers, elaborate loading and unloading facilities are frequently provided (see Pic.1).

Drying Problems

Spiral or twisted gain can give trouble in veneer drying by buckling or by cracking the veneer, if there is to much restriction during drying. Even if dried satisfactorily, thin plywood panels made from such distorted material are not truly balanced in construction and may warp(Baldwin 1981) . Some woods are prone to split in drying, particularly at the end edges of the veneer. Others show the abnormal shrinkage and distortion of collapse and, although this can be removed, it involves additional expenses and special precautions in drying.