What is veneer processing?

The process of changing geometry and repairing veneer defects. The purpose is to improve the utilization rate of wood and the grade of veneer and plywood. Veneer processing is mainly mechanical processing, including cutting, repairing, splicing, repairing cracks and other processes.

Veneer shearing

Cut the pieces of veneer before rotary cutting and the veneer strips after rotary cutting into veneers of a certain size, or cut off the material defects and processing defects that do not meet the quality standards such as decay, big knots, cracks and uneven thickness. Before 1960s, veneer was produced by cutting first and then drying. However, wet veneer is easy to crack and degrade during drying; The more times the veneer moves, the more serious the damage is. The edge of veneer is often wrinkled due to drying shrinkage, which makes the sewing process difficult, and the secondary trimming will reduce the yield. After the emergence of jet mesh belt dryer, veneer production mostly adopts the process of drying first and then shearing. It overcomes the shortcoming that veneer is cut first and then dried, and improves labor productivity and wood utilization rate. Veneer shearing equipment mainly includes mechanical driven shears and compressed air driven shears. Mechanically driven shears are simple in structure and easy to maintain. The disadvantage is that the action is slow, the veneer needs to stop feeding when cutting, and the productivity is low. The shearing machine driven by compressed air has a high shearing speed, and the veneer belt is still moving during shearing, so the productivity is high. (See veneer shears)

Veneer repair

The grade and yield of veneer can be improved by digging out defects such as knots on veneer and supplementing veneer with intact materials. The panel is dug and pasted by the pasting machine, and the punching, punching and pasting actions are completed in one station. The patch is rhombic or oval in shape, and its size is 0. 1 ~ 0.2 mm larger than the hole filling size, and it is not bonded with adhesive. The punch of the core plate repairing machine is large in size and often round or heart-shaped. In order to prevent the patch from falling off the veneer, perforated pressure sensitive tape or hot melt adhesive line is often used for sealing. When using mechanical digging and manual patch, first coat polyvinyl acetate emulsion around the patch, then embed the patch manually and iron it with an electric iron. Equipped with computer-controlled tracking patching equipment, it can automatically find defects such as knots and scars at any position of the veneer for patching. Using digging instead of shearing in the production of core board can effectively improve the utilization rate of wood and create conditions for the whole core board. (See veneer seam mending machine)

piece

Splicing the veneer with other veneers along its edge to form the required width or length. The splicing of veneers along the width direction is called flat seam, which is the most important process in veneer processing. Splicing of veneers along the length direction is called termination. In flat seam, the direction of veneer entering the plate is the same as the direction of fiber, which is called longitudinal flat seam; The direction of veneer entering the board is perpendicular to the fiber direction, which is called transverse splicing. The terminal is connected with butt joint, oblique joint and finger joint. In the plywood standard of China, it is not allowed to extend the veneer by butt joint, because this connection method is not firm, which seriously affects the strength of plywood.

In order to make the flat-fell seam tight, the edge of the narrow decorative panel should be straight. The narrow veneer produced by the dry-before-cutting process has a flat edge and can be directly used for sewing without trimming again. The veneer that is cut first and then dried should be trimmed, so that the edge of the board is straight before the flat seam can be carried out. Trimming equipment includes heavy shearing machine and veneer planer. Veneer flat-fell seam must be tight and firm, and can't be scattered during later processing and transportation. Therefore, rubber, adhesive tape, glue line and other adhesive materials are needed to strengthen the strength of flat-fell seam. The common methods of front and rear panels are: coating urea-formaldehyde resin on the edge of veneer, heating and curing the glue through the seam and heating area of paperless longitudinal sewing machine, and gradually splicing into the required format; When the veneer passes through the heating roller (or tube) of the longitudinal sewing machine, the perforated adhesive tape or nylon velcro tape is adhered to the seam on the back of the veneer. Using perforated adhesive tape will reduce the bonding strength of plywood by about 20%. The common methods of core board are: hot melt adhesive or hot melt adhesive line bonding; Pressure sensitive adhesive tape point bonding; Hot melt adhesive wire bonding; Nylon thread suture, etc. In plywood production, only the width of the core board is spliced on a horizontal splicing machine. (See Veneer Splicer)

Repair cracks

In the process of cooking, rotary cutting wood segments and veneer drying and transportation, the end cracks of veneer caused by improper operation need to be repaired. There are two kinds of cracks: closed and unclosed (cracks). All surface plate end cracks, whether closed or not, need to be repaired and sealed to avoid defective products. Close the crack or the crack where fingers can close together, stick the tape on the crack with an electric iron, or sew it with a hand-held tape sewing machine. If the crack is too big to be closed, fill it with a narrow veneer of opposite color and stick it firmly with the above method.

The management of veneer processing is also very important, and attention should be paid to veneer grading, veneer storage management and the balance of the number of face, back and core boards.