Quality problems and solving methods in the production of plywood 胶合板生产过程的质量问题与解决方法
In the process of production, the product quality fluctuation caused by the above reasons can be found through the analysis, so as to solve the product quality in order to stabilize the product quality.
The quality problem of the veneer joints such as gaps and overlaps , or joint seam
The good quality logs are suitable for using to peel to the top/bottom surface core veneer are decreasing, most plywood production manufacturers have been trying to use diffierent kinds of veneer joint skills to improve or upgrade the veneer quality and grades ,such as scarf joint ,butt joint ,finger joint and stitched joint in order to improve the surface veneer quality levels rate. The quality of the core veneer is related to the quality of the veneer core lay-up ,the quality of the plywood. From the veneer joint methods and process ,we can find The quality problems, causes and solutions are as follows:
Quality problems: 1, Core Veneer edges are not in alignment and neat and straight ,the core veneer are not lined up .
Cause: the joint gaps/Overlaps were caused by improper operation,When feeding the veneer into the veneer joint machine , ,some of the veneer are not aligned on both sides ; or veneer edge is not rectangular and not neat before match them .
Solution: to strengthen the operator’s responsibility and improve the level of operation of the technical level; Veneer edges Alignment/Straight and Neat should have a benchmark, Can not accept to cut the core veneer into a parallel quadrilateral or other shapes .
Quality problems: 2, the joint seam is too tight or loose
Cause: Caused by the not good adjustment of The squeezing roller of the veneer joint feed sewing machine adjustment .
Solution: adjust the squeeze roller of the sewing machine to meet the requirements of the feeding .
Quality issues: 3, adhesive tape’Bonding strength is not good .
Cause: the tape is not fully wet, sewing machine heating roller temperature is too high or too low, the roll pressure is not enough.
Solution:Make sure the glue tape fully wet; check the heating roller; increasing roll pressing force.
Quality problems: 4, the face veneer color or finish is not consistent.
Solution: to improve the technical level of operators, more technical training, and strengthen the operator’s sense of responsibility.
Two, the quality of the veneer core lay-up prodcess,manufacturing defects and reasons and solutions .
Defect 1: core gaps
The reason: when making the core veneer lay-up if put the core veneer to incorrect place; Or when moving the veneer core platform( before hot pressing and cold pressing process )will cause dislocation of the core veneer .
Solution: After the dry veneer glued with glue ,can condition the core veneer for suitable the lay-up and then make the lay-up .After lay-up ,need to do the cold pressing process ASAP and make sure every layer of the core veneer glued together and can not accept the core veneer move or shift. Improve the technology and skill of the veneer core lay-up workers.
Defect 2: edge shortage defects, edges are not neat and aligned and lined up.
Reason: the core veneer length is insufficient, when doing the VC Lay-up operation are not in accordance with the “One side/edge must be lined up and aligned and neat ” principle to do; The top and bottom surface core veneer have edge defects.
Solution: strict to control the core veneer length and sizes, When doing the Veneer Core lay-up ,should have one benchmark that one right angle core veneer as the reference edge; strengthening production management, improve operation skills and sense of responsibility. Try to use skilled labor.
Three, the quality of Cold pre-pressing problems and Solutions
In the plywood production process, the Main quality problems of cold pressing process is the cold pressing effect is not ideal, the veneer core platform cannot be formed after cold pressing, can not up to the bonding effect, or have so much core voids and overlaps after cold pressing . The defects, causes and solutions of this area are as follows:
Defect 1, pre-pressing effect is not ideal, each layer of the core veneer is not very good adhesion.
The reason: the glue viscosity of prepressing is not enough; prepressing time is out of control, The quantity piece of the platform are overload and height is too high .
解决方法：制胶时控制好胶的粘度，脲醛胶应为800－1400cp,酚醛胶为1000－1800cp;调胶时可适量加入面粉或聚乙烯醇来增加胶的粘度，并 掌握好不同气候条件下调制胶液的活性期，使预压处在树脂由A阶段向B阶段转化的时期，预压胶的活性期控制在2h左右为宜，通俗说法为，预压好的板坯当揭起 单板时胶应略有“拔丝”现象。
Solution: control the glue adhesive viscosity when making the glue, urea-formaldehyde glue should 800-1400cp, phenolic glue is 1000-1800cp; when mixing the glue may add some wheat flour or polyvinyl alcohol to increase the viscosity of the adhesive, and master the modulating the activity of the glue with the different climatic conditions ,as the popular saying, when tear the presseed glued veneer core should be a slight “candied /drawing ” phenomenon ( When tear the glued veneer will have glue thread / spin filaments linked the adjacent glued veneer ) .
In order to make the pre-pressure evenly delivered to each veneer on the surface, therefore, the maximum height of the hot presing plates open size should not exceed 60 cm as well.For example ,no more than 30 pieces of 1220x2440x18mm plywood every time for cold pressing.
Defect 2: after the pre-pressing have the quality problems of overlapping core and core voids .
Reason: When move the core veneer platform into the pre-pressing machine, the core veneer are slip and shifted ; core veneer with serious warpage, did not cut straight edge and cause shear dislocation ,or did not make a good veneer core layup and downgraded the quality.
Solution:Train all the workers must be civilized production operation in the production process, can not act recklessly; pay attention to the fast growing wood poplar core veneer before use them ,make sure the core veneer flat and softening, leveling and two times edge trimming,To make the smooth surface, The edge are lined up and straight .
Four, plywood hot pressing quality problems, causes and solutions of plywood hot pressing quality problems, causes and Solutions
Defects: 1, low bonding strength or adhesive failure
The reason: Glue adhesive deterioration or concentration is too low, or few little amount of glue sprayed to the veneer or the glue is too thin , veneer moisture content is too high or the poor quality of veneer; Glued veneer conditioning time is too long; hot pressing temperature is too low , hot pressing pressure is not enough , or hot pressing time is too short .
Solution: check the quality of glue adhesive, unqualified can not be put into the production; The sprayed glue amount should be according to different wood species ,different quality and different thickness of the core veneer ; Check if the Moisture content before glue spraying /coating of the core veneer are in the range of requirements; The glued veneer condition time should be depending on the climatic conditions; according to different plywood product selection of suitable hot pressing process to decide the hot pressing parameter .
Defects: 2, “bubble” or local delamination