Main factors affecting the quality of veneers (1)
The quality of the veneer is related to the quality of the plywood. There are four indicators for evaluating the quality of veneers: veneer thickness deviation, that is, processing accuracy; veneer back crack; veneer back finish; veneer horizontal grain tensile strength. The first two of these indicators are the main ones. Because the cracks on the back side of the veneer are deeper and deeper, the back finish is poor and the tensile strength is small. The measurement methods and instruments of the first two indicators are relatively simple and easy to adopt in production.
There are many factors affecting the quality of a veneer, and the factors are interrelated, which is a more complicated problem.
1 process conditions
The general process conditions are the heat treatment temperature of the wood section, the water content, the grinding angle of the rotary cutter and the installation position (blade height, cutting angle and relief angle), the shape of the pressure gauge, the angle and the installation position (the percentage of the press, the pressure gauge relative to The horizontal and vertical distance of the blade), the degree of change of the back angle of the rotary blade, and the like. These parameters are well coordinated with each other to obtain a high quality veneer.
When cutting the small diameter wood, in order to avoid the phenomenon that the thickness of the veneer is thick at the two ends, the middle part of the rotary knife can be 0.1~0.2mm higher than the two ends.
The cutting angle of the rotary cutter should be evenly smaller and cannot be enlarged during the cutting process. For a diameter of 300 to 1100 mm, the change in the relief angle generally does not exceed 1 °. It is 3° at 800-200mm; the cutting edge of the knife should be parallel to the axis of the card axis. If it is skewed in the vertical plane, it will cause a change in the back angle along the length of the tool, and the skew in the horizontal plane will form a diagonal cut.
The percentage of crush is related to the thickness of the veneer, the tree species, the temperature after heat treatment of the wood, and the like. At present, the percentage of crushing commonly used tree species in China is as follows: 10%-15% for eucalyptus, 15%-20% for ash, and 15%-20% for pine.
The precision of the rotary cutter and the rigidity of a workpiece system
The veneers used to make wood laminated plastics and aerospace plywood are relatively thin (about 0.5 mm). If the accuracy of the rotary cutting machine itself is very poor, then the veneer that meets the quality requirements cannot be cut. Therefore, the veneers with different requirements should be completed by a rotary cutter with different processing precision.
The rigidity of a workpiece system is poorly cut, and when the cutter is rotated, the tool holder is deformed or the wood segment is bent, so that the quality of the obtained single board is poor.
When the wood section above 50 °C is cut, the heat energy in the wood section and the veneer is transmitted to the front edge of the knife blade and the pressure gauge. As a result of local uneven heating and thermal expansion deformation, the rotary cutter and the pressure gauge are deformed and bent, and the amount of deformation is large. As can be seen from Fig. 3-30, the original horizontal spacing is 2.5 mm and the vertical distance is 0.5 mm. Due to thermal deformation, the spacing in the middle becomes 2.Omm and 0. At this time, the thickness difference of the veneers that are unscrewed is very large, and both will become waste veneers. There are two current improvement methods: 1 pre-heating the rotary knife and the pressure ruler and then mounting on the tool holder; 2, the tool holder is equipped with a cooling system, and the heat obtained by the rotary knife and the pressure gauge from the wood segment is recycled with circulating cooling water. Take it away. Some tree species have a lot of sticky secretions, which can easily adhere to the blade when it is cold, which affects the rotary cutting. Therefore, some of the tool holders are equipped with a hot water circulation system so that the mucus does not stick to the rotary cutter, thereby improving the quality of the rotary cutting.
During the rotary cutting, since the wood segment has a reaction force against the tool holder, the result is that the blade beam and the pressure beam are deformed, and the rotary cutting condition is changed.
In order to maintain a stable pressing force, the modern rotary cutting machine is equipped with a cylinder, and the air pressure is used to maintain the pressure of the pressure gauge on the wooden section to ensure the quality of the rotary cutting.
In order to prevent the knife beam from retreating and excessively abrading the feed screw, a pneumatic device is installed at the rear of the knife bed to resist the reaction force of the wood segment to the tool holder, and the quality of the single plate is uniform.
3 machine wear and maintenance
There are many moving parts in the rotary cutting machine, but the relationship between the quality of the rotary cutting is large between the feeding screw and the nut (currently, the rotary cutting machine has adopted the hydraulic feeding system), the card shaft is oscillating radially, two cards The center of the shaft is not the same, the pressure beam and the beam are loose. Therefore, it is necessary to regularly check these vulnerable places and repair and maintain them in time.
The outside of the feed screw should be covered with a holster to prevent dust from falling into the screw and accelerating wear. The pressure beam is preferably supported on the blade beam without the support screw, but is coupled and supported by a slider; the pressure gauge preferably maintains its pressure against the wood segment with air pressure.
The large rotary cutting machine should not be cut through the short wooden section, otherwise it must be equipped with a central support.
The quality of the veneer is related to the quality of the plywood. There are four indicators for evaluating the quality of veneers: veneer thickness deviation, that is, processing accuracy; veneer back crack; veneer back finish; veneer horizontal grain tensile strength. The first two of these indicators are the main ones. Because the cracks on the back side of the veneer are deeper and deeper, the back finish is poor and the tensile strength is small. The measurement methods and instruments of the first two indicators are relatively simple and easy to adopt in production.
There are many factors affecting the quality of a veneer, and the factors are interrelated, which is a more complicated problem.
1 process conditions
The general process conditions are the heat treatment temperature of the wood section, the water content, the grinding angle of the rotary cutter and the installation position (blade height, cutting angle and relief angle), the shape of the pressure gauge, the angle and the installation position (the percentage of the press, the pressure gauge relative to The horizontal and vertical distance of the blade), the degree of change of the back angle of the rotary blade, and the like. These parameters are well coordinated with each other to obtain a high quality veneer.
The vertical distance h (mm) value of the rotary cutter relative to the card shaft is shown in Table 3-7.
Table 3-7 Vertical distance of the rotary cutter relative to the card axis (h value)
Tool holder type wood section diameter (mm)
There are no auxiliary slides above 300 and 300 or more auxiliary slides when μ=0; μ=30'
μ=3° 0～+0.5
0 to a 0.5
—0.5～一1.0 0～+1.0
0 to a 1.0
—0.5～一1.5
Table 3.7 Rotary Knife Note: μ is the auxiliary chute tilt angle.
When cutting the small diameter wood, in order to avoid the phenomenon that the thickness of the veneer is thick at the two ends, the middle part of the rotary knife can be 0.1~0.2mm higher than the two ends.
The cutting angle of the rotary cutter should be evenly smaller and cannot be enlarged during the cutting process. For a diameter of 300 to 1100 mm, the change in the relief angle generally does not exceed 1 °. It is 3° at 800-200mm; the cutting edge of the knife should be parallel to the axis of the card axis. If it is skewed in the vertical plane, it will cause a change in the back angle along the length of the tool, and the skew in the horizontal plane will form a diagonal cut.
The percentage of crush is related to the thickness of the veneer, the tree species, the temperature after heat treatment of the wood, and the like. At present, the percentage of crushing commonly used tree species in China is as follows: 10%-15% for eucalyptus, 15%-20% for ash, and 15%-20% for pine.
The precision of the rotary cutter and the rigidity of a workpiece system
The veneers used to make wood laminated plastics and aerospace plywood are relatively thin (about 0.5 mm). If the accuracy of the rotary cutting machine itself is very poor, then the veneer that meets the quality requirements cannot be cut. Therefore, the veneers with different requirements should be completed by a rotary cutter with different processing precision.
The rigidity of a workpiece system is poorly cut, and when the cutter is rotated, the tool holder is deformed or the wood segment is bent, so that the quality of the obtained single board is poor.
When the wood section above 50 °C is cut, the heat energy in the wood section and the veneer is transmitted to the front edge of the knife blade and the pressure gauge. As a result of local uneven heating and thermal expansion deformation, the rotary cutter and the pressure gauge are deformed and bent, and the amount of deformation is large. As can be seen from Fig. 3-30, the original horizontal spacing is 2.5 mm and the vertical distance is 0.5 mm. Due to thermal deformation, the spacing in the middle becomes 2.Omm and 0. At this time, the thickness difference of the veneers that are unscrewed is very large, and both will become waste veneers. There are two current improvement methods: 1 pre-heating the rotary knife and the pressure ruler and then mounting on the tool holder; 2, the tool holder is equipped with a cooling system, and the heat obtained by the rotary knife and the pressure gauge from the wood segment is recycled with circulating cooling water. Take it away. Some tree species have a lot of sticky secretions, which can easily adhere to the blade when it is cold, which affects the rotary cutting. Therefore, some of the tool holders are equipped with a hot water circulation system so that the mucus does not stick to the rotary cutter, thereby improving the quality of the rotary cutting.
During the rotary cutting, since the wood segment has a reaction force against the tool holder, the result is that the blade beam and the pressure beam are deformed, and the rotary cutting condition is changed.
In order to maintain a stable pressing force, the modern rotary cutting machine is equipped with a cylinder, and the air pressure is used to maintain the pressure of the pressure gauge on the wooden section to ensure the quality of the rotary cutting.
In order to prevent the knife beam from retreating and excessively abrading the feed screw, a pneumatic device is installed at the rear of the knife bed to resist the reaction force of the wood segment to the tool holder, and the quality of the single plate is uniform.
3 machine wear and maintenance
There are many moving parts in the rotary cutting machine, but the relationship between the quality of the rotary cutting is large between the feeding screw and the nut (currently, the rotary cutting machine has adopted the hydraulic feeding system), the card shaft is oscillating radially, two cards The center of the shaft is not the same, the pressure beam and the beam are loose. Therefore, it is necessary to regularly check these vulnerable places and repair and maintain them in time.
The outside of the feed screw should be covered with a holster to prevent dust from falling into the screw and accelerating wear. The pressure beam is preferably supported on the blade beam without the support screw, but is coupled and supported by a slider; the pressure gauge preferably maintains its pressure against the wood segment with air pressure.
The large rotary cutting machine should not be cut through the short wooden section, otherwise it must be equipped with a central support.
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