Views: 0 Author: Site Editor Publish Time: 2020-11-02 Origin: Site
The plywood that you usually see, such as three-plywood and five-plywood, is composed of the veneer. When the veneer peeling machine is peeling the veneer, the thickness of the peeling veneer must be determined according to the thickness of the finished plywood. However, in actual production, there is a vague understanding of the determination of the thickness of the veneer, and even a misunderstanding, the following is an explanation of this problem.
The thickness of the veneer can be divided into the nominal thickness of the veneer, the actual peeling thickness of the veneer, the thickness of the dry veneer, and the thickness of the veneer in the finished product. When measuring the thickness of the veneer at each stage, in order to obtain accurate values, it is necessary to have a dedicated person to use the same testing instrument, under the same operating essentials, after peeling, before drying, after drying, and after coating. Measure at the same measuring point in order to measure the thickness change of the veneer. It can be seen from the actual measurement results that the value measured before drying is slightly larger than that after rotary cutting. This is because the peeling veneer has partial rebound, that is, the veneer is compressed after being squeezed by the pressure ruler during the peeling, and part of the compressed amount is compressed into elastic deformation, and it will rebound after being placed for a period of time. And the size after drying, because the veneer shrinks in the dryer, the thickness becomes smaller than before drying (the moisture content of the veneer is controlled at 8%-12% after drying, and the size is basically unchanged during the placement process). After gluing, due to
The adhesive brings in part of the moisture, which causes the veneer to expand and increase in thickness. It is compressed during the autoclave process, which reduces the thickness of the veneer. Therefore, after the peeling, the veneer has undergone many changes in thickness.
Therefore, when determining the thickness of the peeling veneer, the peeling machine must consider the processing allowance in the thickness of the plywood, the amount of compression during the hot-pressing process, the shrinkage of the veneer during drying, and the thickness of the peeling The thickness deviation of the veneer, and the rebound and expansion of the thickness of the veneer should not be ignored.
When calculating the thickness of the veneer from the finished product, it is necessary to be clear here: the calculation of the compression is the thickness of the veneer after the glue is pre-pressed and glued, not the thickness of the veneer after drying. The calculation of the shrinkage rate should be careful not to use the moisture content to reach the dry shrinkage rate under absolute dry conditions. One more thing to be clear about the drying of the veneer is that the veneer is compressed by the pressure ruler when processed by the rotary cutting machine. The shrinkage rate given in wood science is the shrinkage rate of wood without compression. The compression rate of compressed wood is different from that of uncompressed wood. The determined shrinkage rate should be veneer The shrinkage rate after drying under the current drying process conditions of our factory because the drying process is different, the shrinkage rate is also different, it is best to verify the value of the shrinkage rate by field measurement, the factors that increase the thickness of the veneer after peeling There are rebound after peeling and expansion after gluing. The amount of rebound and expansion must be measured and mastered.
When determining the nominal thickness of the veneer (specified veneer peeling thickness), in addition to the thickness of the finished product, the amount of compression, and the amount of shrinkage, the rebound, and expansion of the veneer should be considered in the process after the peeling. Take it into consideration, otherwise, the determined nominal thickness of the veneer is thicker than required, which is easy to overlook.
After the above analysis, the nominal thickness of the veneer can be expressed as:
Nominal thickness of veneer = (finished product thickness + surface processing allowance)/number of plywood layers + compression of each layer of veneer-expansion of each layer of glued veneer thickness + thickness of veneer in the dryer shrinkage -Rebound on the thickness of the veneer after peeling.
When peeling a veneer, determine the feed amount according to the nominal thickness of the veneer (the feed amount refers to the distance that the peeler advances when the rotary cutter shaft is peeled for one round). At the same time, it is necessary to consider the amount compressed by the pressing ruler during the peeling process, that is, the nominal thickness of the veneer includes the amount compressed by the pressing ruler, and this pressing rate must meet the technological requirements. How to make the pressing rate meet the requirements? ? In addition to strictly operating in accordance with the operating rules when installing the rotary cutter pressure ruler, the pressing rate can also be corrected during rotary cutting. The correction method:
① With the knife door open, measure the peeled veneer to obtain the actual thickness of the peeled veneer without compression by the pressure ruler.
②Measure the thickness of the peeled veneer when compressed with a pressing ruler, and then extreme pressing rate.
③Compare the calculated pressing rate with the technological requirements, and then adjust the gap width of the knife. The amount of compression here can be understood as the difference between the amount of knife feed and the width of the knife door gap.
The rotary cutting machine determines the feed amount according to the nominal thickness of the veneer and the compression of the pressure ruler. However, due to various factors such as machine tool accuracy, equipment maintenance status, and processing technology, the actual veneer thickness and the required nominal thickness of the veneer ( Excluding the compression of the veneer by the normal pressure ruler, there is always a deviation. That is to say, the nominal feed amount and the actual exit thickness (measured by opening the knife door) are inconsistent. When determining the feed amount, it should be adjusted according to the actual situation. That is to say, if the thickness of the unscrewed veneer is larger than the adjusted feed amount, then the adjusted feed amount is smaller than the specified veneer peeling thickness to meet the requirements. For example, if the nominal thickness of the veneer is required to be 1.2mm, it may be adjusted to 1.1mmj to meet the requirement when determining the feed amount.
The specific thickness is more or less than the nominal thickness. Different rotary cutting machines have different rules. Generally, it takes many repeated experiments to adjust. The actual feed amount should be adjusted at the outer circle of the rotary wood section, that is, when the waste veneer is discharged, it should be adjusted to reduce the loss of wood.
Therefore, the peeling veneer should consider the processing allowance, compression, shrinkage, rebound, and expansion of the plywood thickness, otherwise, the plywood produced may be thicker than the required thickness. The above is the veneer produced by the veneer peeling machine. When determining the thickness of the reference.