Quality problems and solutions in plywood production process ,inspection,quality control,sourcing,import,export,buying guide

Quality problems and solutions in plywood production process

In the production process of any kind of product, there will be some quality problems, and there are many and complex factors affecting the product quality, including: the quality of raw materials, processing equipment accuracy is not enough Of course, the other important reason is human factors, such as: the operator’s technical proficiency is not enough, the operator’s sense of responsibility is not strong, and the operator’s mood fluctuates…… Plywood production is no exception, there will be these situations.

In the production process, the fluctuation of product quality caused by the above reasons can only be found out through analysis, so that it can be solved in time to stabilize product quality.

1、 Quality problems of veneer joint

As the number of high-quality logs suitable for making veneer is decreasing, most of the plywood factories adopt gluing technology to improve the yield of veneer. The gluing quality of the surface plate is related to the later assembly operation and the gluing quality. The possible quality problems, causes and solutions in gluing are as follows:

Quality problems: 1. The end of the single board assembled is uneven

Causes: improper splicing operation, misalignment of the ends of the two sides of the veneer when there is feeding on the tape splicing machine in the longitudinal direction, or non rectangle when the veneer is flush.

Solution: strengthen the operator’s sense of responsibility and improve the level of operation technology; there should be a benchmark when the single plate is flush, and it is not allowed to cut the single plate into parallelogram.

Quality problem: 2. The seam is too tight or loose

Cause: improper adjustment of the feed squeeze roll of the seaming machine.

Solution: adjust a pair of tapered extruding rollers under the worktable of the seaming machine to make them suitable.

Quality problems: 3. The tape is not firmly pasted

Causes: the tape is not fully wet, the temperature of the heating roller of the seamer is too high or too low, and the pressure of the upper rolling rod is not enough.

Solution: wet the tape with water; check the heating roller; increase the pressing force of the upper roller.

Quality problems: 4. The color or finish of the veneer is inconsistent.

Causes: the panel matching workers did not select the materials properly and did not match the original one; the front and back of the two boards were inconsistent during the panel matching operation, and the loose and tight surfaces were reversed.

Solution: improve the technical level of operators, carry out more technical training, and strengthen the sense of responsibility of operators.

2、 The quality problems of the green parts the defects, causes and solutions of the green parts

Defect 1: core separation

Causes: improper placement of parts and single plates during slab assembly; core plate dislocation caused by collision during slab moving.

Solution: the core plate coated with glue shall be put for a while before forming the blank; after forming the blank, it shall be pre pressed to make the slab initially bonded together, which is not easy to move; the technical level of forming the blank shall be improved.

Defect 2: edge missing, slab edge uneven

Cause: the length of core plate is insufficient, and the principle of “one side and one end are aligned” is not followed during the operation of blank assembling; the edge of surface plate is damaged.

Solution: strictly control the length of the core plate and the size of the surface plate when purchasing; have a right angle datum edge when assembling the blank; strengthen the production management and improve the operator’s skills and sense of responsibility. Try to use skilled workers.

3、 Quality problems and solutions of Preloading

In the plywood production process, the quality problems of the pre pressing process are mainly reflected in the poor pre pressing effect, the slab after pre pressing can not be formed, the pre bonding effect can not be achieved, or the core separation phenomenon occurs after pre pressing. The defects, causes and solutions are as follows:

Defect 1. The preloading effect is not ideal, and the veneer of each layer is not well bonded.

Reasons: the viscosity of the prepressing adhesive is not enough; the prepressing time is not mastered properly; the thickness of the plate stamp for one prepressing is too large.

Solution: the viscosity of the glue should be well controlled, the urea formaldehyde glue should be 800-1400cp, the phenolic glue should be 1000-1800cp; When mixing glue, flour or polyvinyl alcohol can be added properly to increase the viscosity of glue, and the active period of mixing glue liquid under different climate conditions can be well controlled, so that the prepressing is in the period of resin transformation from a stage to B stage, and the active period of prepressing glue is controlled at about 2 h. The popular saying is that when the pre pressed slab is lifted, the glue should be slightly “drawn”.

In order to transmit the preloading pressure evenly to the breadth of each slab, it is better that the height of each preloading plate should not exceed 60 cm.

Defect 2: core separation after preloading

Cause: the core plate is staggered when the slab is moved into the precompressor; the core plate used for slab assembly is seriously warped and deformed, and the edge is not cut straight.

Solution: in the process of production, civilized production and operation should be carried out, and it is not allowed to do anything rashly; at the same time, attention should be paid to the leveling treatment (softening) of the core plate of the same speed wood tree species of Italian poplar before use, and the secondary trimming should be carried out to make the surface flat and the edge straight.

4、 Plywood hot pressing quality problems, causes and Solutions

Defects: 1. Low adhesive strength or degumming of adhesive layer

Cause: the adhesive is deteriorated or the concentration is too low, or the glue amount is too small; the moisture content of the veneer is too high or the veneer rotary cutting quality is poor; the aging time of the veneer after gluing is too long; the hot pressing temperature is low, or the hot pressing pressure is small, or the hot pressing time is short.

Solution: check the quality of the adhesive in time, do not use it if it is unqualified; select the appropriate glue amount according to the different species and thickness of the single board; check whether the moisture content of the core board is within the required range before the glue application; the time of the board after the glue application depends on the climate conditions; select the appropriate hot pressing process according to different products, do not use the same hot pressing parameters.

Defects: 2. “Bubbling” or partial opening

Causes: after hot pressing, the pressure reduction speed is too fast; the moisture content of slab is high; the core plate is partially lack of glue; the surface of single plate is partially stained with grease.

Solution: strictly control the speed of pressure drop from equilibrium pressure to zero pressure during hot pressure reduction; control the glue application amount; check the moisture content of core plate, which shall not exceed 10%, otherwise it is easy to open the glue and bubble; before the resin rich pine is peeled, it shall undergo hydrothermal treatment to extract part of the pine resin and turpentine oil.

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