Quality Problems and Solutions in Plywood Production
In the production process of any kind of product, there will be some quality problems. There are many and complex factors affecting product quality, including the quality of raw materials, inadequate precision of processing equipment, or unreasonable processing arrangements. Of course, on the other hand, it is very important. The reason is human factors, such as: operator’s technical proficiency is not enough, operator’s sense of responsibility is not strong, operator’s mood fluctuation… Plywood production is no exception, there will be these situations.
In the production process, the product quality fluctuations caused by the above reasons need to be analyzed to find out, so as to solve in time to stabilize the product quality.
Quality of veneer joints
As the number of high-quality logs suitable for surface panel is decreasing, most plywood factories adopt gluing process to improve the yield of surface panel. The gluing quality of the sheet is related to the billet operation and plywood quality in the future. The quality problems, causes and solutions that may be encountered in gluing are as follows:
Quality problems: 1. The end of the veneer is uneven.
Reasons: improper sewing operation caused by the inconsistency of the ends of the veneers on both sides when feeding on the vertical tape splitter; or the inconsistency of the rectangle when the veneers are even.
Solution: Enhance the responsibility of the operator and improve the operation technology level; when veneer is edged, there should be a benchmark, and the veneer should not be cut into parallelograms.
Quality problems: 2. Too tight or too loose joints
Reasons: The inappropriate adjustment of the feeding extrusion roll of the sewing machine.
Solution: Adjust a pair of conical extrusion rolls under the working table of sewing machine to make them suitable.
Quality problems: 3. Insufficient adhesive tape
Causes: the tape is not fully wetted, the temperature of the heating roll of the sewing machine is too high or too low, and the pressure of the upper roll is not enough.
Solution: wet the tape fully with water; check the heating roll; increase the pressing force of the upper roll.
Quality problems: 4. The color or finish of the veneer is different.
Reasons: Material selection is inappropriate and the original matching is not achieved by the matching worker; the front and back of the two veneers are inconsistent, and the loose and tight sides are reversed in the operation of the splicing.
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 Blooms, the Defects, Causes and Solutions of core layup
Defect 1: Core-stacking Joint
Reasons: improper placement of the zero veneers during slab assembly; core plate dislocation caused by collision during slab removal.
Solution: Core veneer coated with glue should be put out for a while before billet formation; after billet formation, it should be pre-pressed to make the billet initially bonded together and not easy to shift; and improve the technology level of billet formation.
Defect 2: Edge missing and uneven edge of slab
Reasons: the length of core veneer is insufficient, the billet is not operated in accordance with the principle of “one side at one end”; the edge of the surface core veneer is defective.
Solutions: Strictly control the length of core board and the size of table board when purchasing; have a right angle base edge when forming blanks; strengthen production management, improve the skill and responsibility of operators. Use skilled workers as much as possible.
3. Quality Problems and Solutions of Pre-pressing
In the plywood production process, the quality problems of the pre-pressing process are mainly reflected in the unsatisfactory pre-pressing effect, the pre-pressing slab can not be formed, the pre-bonding effect can not be achieved, or the phenomenon of core separation after pre-pressing occurs. The defects, causes and solutions are as follows:
Defect 1. Pre-pressing effect is not ideal, and there is no good bonding between veneers.
Reasons: the viscosity of pre-pressing glue is not enough; the pre-pressing time is not properly mastered; the thickness of a pre-pressing plate is too large.
Solution: control the viscosity of the glue well, urea-formaldehyde glue should be 800-1400 cp, phenolic glue should be 1000-1800 cp; add flour or polyvinyl alcohol to increase the viscosity of the glue when mixing, and master the active period of the glue under different climatic conditions, so that the pre-pressing is in the period of resin transformation from stage A to stage B, pre-pressing. It is advisable to control the active period of the glue at about 2 hours. It is commonly said that the glue should be slightly “drawn” when the veneer is lifted from the pre-pressed slab.
In order to transmit the preloading pressure evenly to the width of each slab, it is better not to exceed 60 centimeters for the height of the slab to be preloaded at one time.
Defect 2: Core separation after preloading
Reasons: When the slab is moved into the pre-press, the core plate is distorted; the core plate used in the group slab is seriously warped and the edge is not straight.
Solution: In the production process, we should civilize the production operation, not be brutal; at the same time, we should pay attention to the core board of poplar isotachyte tree species should be leveled (softened) before use, and carry out secondary leveling, so that the surface is flat, the edge is straight.
4. Plywood Hot Pressing Quality Problems, Causes and Solutions; Plywood Hot Pressing Quality Problems, Causes and Solutions
Defects: 1. Low bonding strength or degumming
Reasons: the deterioration or concentration of adhesives is too low, or the amount of adhesives is too little; the moisture content of veneers is too high or the quality of veneers is poor; the ageing time of veneers after gluing is too long; the hot pressing temperature is low, or the hot pressing pressure is low, or the hot pressing time is short.
Solutions: timely inspection of the quality of adhesives, unqualified use; selection of suitable amount of glue according to different tree species and thickness of veneer; check whether the moisture content of the core board is within the required range before gluing; the shelf time of the post-gluing board depends on the climatic conditions; selection of appropriate hot press according to different products Art, do not always use the same hot-pressing parameters.
Defects: 2. “Bubble” or local opening
Reasons: after hot pressing, pressure reduction speed is too fast; slab moisture content is high; core board is partially glueless; veneer surface is partially greasy stained.
Solutions: strictly control the speed of pressure drop from equilibrium pressure to zero pressure; control the amount of glue coating; check the moisture content of the core board, not more than 10%, otherwise it is easy to open the glue bubbling; the resin-rich pine wood should be treated by hydrothermal treatment before rotary cutting, in order to extract some pine resin and turpentine.
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