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The thickness of the veneer can be divided into the nominal thickness of the veneer, the actual thickness of the veneer, the thickness of the veneer, and the thickness of the veneer in the finished product.
In the measurement of the thickness of the veneer at each stage, in order to obtain accurate values, a person should use the same spiral micrometer, under the same operation method, after the rotary cutting, before drying, after drying, after coating, select Measurements are taken at the same measuring point to measure small changes in the thickness of the veneer. It can be seen from the actual measurement results that the value measured before drying is slightly larger than that after the rotary cutting, which is due to the partial rebound of the rotary-cut veneer, that is, the compression of the veneer after being pressed by the pressure gauge in the rotary cutting, the amount of compression Some of them are compressed into elastic deformation, and will rebound after being placed for a while. The size after drying, because the veneer is shrinking in the dryer, the thickness is made smaller before drying (the moisture content of the veneer is controlled to 8% to 12% after drying, and the size is basically unchanged during the placement process). After the veneer is glued, the veneer expands and the thickness increases due to the partial moisture of the adhesive. Compressed during hot pressing, which reduces the thickness of the veneer. It can be seen from the above that after the rotary cutting, the veneer has undergone several changes in thickness.
Therefore, when determining the thickness of the rotary cutting veneer, the rotary cutting machine should consider the machining allowance on the thickness of the plywood, the compression amount during the hot pressing process, the dry shrinkage in the thickness of the veneer when drying, and also consider the time of the rotary cutting. Veneer thickness deviation, and do not ignore the amount of rebound and expansion on the thickness of the veneer.
When calculating the thickness of the veneer from the finished product, it is necessary to clarify here that the calculation of the compression amount is the thickness after the veneer is pre-pressed and coated, and the thickness of the veneer is not the thickness of the veneer after drying. The calculation of the shrinkage rate should be careful not to use the moisture content to achieve the dry shrinkage rate under dry conditions. It is also clear that the drying of the veneer is that the veneer is compressed by the pressure bar during the rotary cutting, and the shrinkage rate given in the wood science is the shrinkage rate of the wood without compression, and is compressed. The shrinkage rate of wood and uncompressed wood is different. The determined shrinkage rate should be the shrinkage rate of the veneer after drying under the current process conditions of the dryer. Because the drying process is different, the shrinkage rate is also different. It is best to verify the dry shrinkage value by field measurement. The factors for the thickening of the veneer after the rotary cutting are the rebound after the rotary cutting and the expansion after the rubber coating. The amount of rebound and the amount of expansion should be measured to grasp the value.
When determining the nominal thickness of the veneer (the specified veneer thickness of the veneer), in addition to considering the thickness of the finished product, the amount of compression, and the amount of dry shrinkage, the process of rewinding and expansion of the veneer Considering it, otherwise the nominal thickness of the board is determined to be thicker than required, which is easy to ignore.
After the above analysis, the nominal thickness of the veneer can be expressed. for:
The nominal thickness of the veneer = (finished product thickness + surface processing allowance) / plywood layer number + compression of each veneer - the amount of expansion on the thickness of each veneer veneer + the thickness of the veneer in the dryer - the amount of rebound on the thickness of the veneer after rotary cutting
When cutting a veneer, determine the amount of infeed according to the nominal thickness of the veneer (the amount of infeed refers to the distance the rotor advances when the card cutter shaft rotates one revolution). At the same time, the amount of compression by the pressure gauge during the rotary cutting process should be considered. That is to say, the nominal thickness of the veneer contains the amount of compression by the pressure gauge, and this pressing rate must meet the requirements of the process. How to make the crush rate meet the requirements? In addition to the strict operation of the operating procedure when the rotary cutter is installed, the crush rate can also be corrected during the rotary cutting. Correction method: 1 When the knife door is opened, the unscrewed veneer is measured to obtain the actual thickness of the veneer without the pressure gauge compression. 2 Measure the thickness of the veneer veneer when compressed with a pressure gauge, and then calculate the crush rate. 3 Calculate the calculated crushing rate and the requirements of the process, and then adjust the gap width of the knife. The amount of compression can be understood here as the difference between the amount of feed and the gap width of the knife door.
The rotary cutter determines the amount of feed according to the nominal thickness of the veneer and the compression of the pressure gauge. However, due to various factors such as machine tool precision, equipment maintenance status and processing technology, the thickness of the veneer and the nominal thickness of the veneer are actually unscrewed ( There is always a deviation in the compression of the veneer from the normal pressure gauge. That is to say, the nominal amount of feed and the actual thickness of the veneer (measured by the open door) are inconsistent. When determining the amount of feed, it should be adjusted according to the actual situation. That is, if the thickness of the unscrewed veneer is larger than the amount of the infeed, the amount of the infeed is smaller than the thickness of the specified veneer to meet the requirements. For example, the nominal thickness of the veneer is required to be 1.20 mm, and it may be possible to adjust to 1.10 mm when determining the amount of infeed. The specificity is greater or less than the nominal thickness. Different rotary cutting machines have different laws. Generally, they have to be repeatedly tested before they can be adjusted. The adjustment of the actual feed amount should be carried out in the outer circle of the rotary wood section, that is, it should be adjusted when the board is scrapped to reduce the loss of wood.
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