When the wood segment is transported back and forth on the fixed axis, the rotary cutter is parallel to the wood fiber Du and cuts a layer of veneer along the surface of the wood segment circumference. There is a complex kinematic relationship between the rotary motion of the wood segment and the linear motion of the rotary cutter. The strip veneer is cut continuously by the rotary cutter from the wood section, and the thickness is equal to the feed amount of the tool holder when the wood section rotates for one cycle. There are many tree species suitable for rotary cutting into veneers in China, such as Pinus massoniana, Pinus yunnanensis, spruce, fir, Pinus massoniana, Larix gmelinii, Fraxinus mandshurica, Tilia, birch, Schima superba, Acer, poplar, Paulownia, etc. In addition, China also imported logs from Southeast Asia, such as Liu'an, abidong, Shanzhang and clonal.
Rotary cutting process
In order to improve the wood temperature and moisture content, the wood is softened, the plasticity is increased, the cracks on the back of veneer are reduced, and the veneer quality is improved. Because the bark is easy to block the knife door during peeling, and there is often sand and other debris in the bark which will damage the rotary knife, so the wood section must be peeled first and then peeled. In order to improve the output rate of the whole veneer, it is necessary to determine the rotary center position of the largest diameter cylinder on the rotary cutter before the wood section is rotated. The centering machine can meet the above requirements. Centering methods can be divided into mechanical centering machine and halo centering machine. Main process flow of veneer rotary cutting。
In 6442 veneer rotary cutting, there is another kind of semicircular veneer, which is formed by the cross-section of the cross-section (about 1 / 4 of the log) stuck on a special chuck. The veneer has a texture similar to that of a sliced veneer.
Rotary cutting parameters
In order to produce high-quality veneer with flat and uniform thickness, the most suitable cutting conditions should be ensured, such as the main angle parameters, cutting speed, the position of rotary cutter and the position of pressure gauge relative to the rotary cutter. These conditions are determined according to the wood species, wood section diameter, veneer thickness, wood hydrothermal treatment degree, machine tool structure and its accuracy. The main angle parameters of rotary cutting include grinding angle β, back angle α, cutting angle δ (∠δ = ∠α＋β) and feed angle K (∠k = 90 ° + ∠α). The position of the rotary cutter is determined according to the height h and feed angle K of the rotary cutter tip relative to the center line of the clamping shaft, which have a great influence on the quality of the veneer. The range of commonly used angle parameters is β = 17 ° to 23 ° and α = - 1 ° to + 1 ° and K = 89 ° to 91 ° respectively. The variation range of feed angle K can be controlled by adjusting the slope of auxiliary slide on the rotary cutter. The commonly used tool height h = - 0.5 ～ + 0.5 mm can be selected according to the thickness of veneer and the wear degree of the rotary cutter. The function of the pressure gauge is to apply appropriate pressure to the blade of the rotary cutter, which can prevent the wood splitting phenomenon ahead of the blade due to the force of the rotary blade, improve the surface finish of the veneer, reduce the back cracks, and make the veneer thickness more uniform. At the same time, the drying time of veneer can be shortened by pressing a part of moisture from the veneer. The installation and adjustment of the pressure gauge are based on the horizontal distance h between the pressure gauge and the rotary blade and the vertical distance V between the pressure gauge and the rotary blade. In order to avoid the bending of wood section due to the force of rotary knife, pressure gauge and shaft clamp, bending proof roller should be used when the diameter of wood section is less than 250mm, so as to improve the quality of veneer, reduce the diameter of wood core and increase the yield.
Rotary cutting equipment
Rotary cutting machine is the key equipment for manufacturing veneer. According to the operation requirements of rotary veneer, the main actions of rotary cutting machine are as follows: ① to block the wood section and put down the wood core, the shaft must have axial expansion movement; ② for rotary veneer, there must be coordinated movement between the rotation of the clamping shaft and the knife feed of the tool carrier, and a series of mechanisms for adjusting the thickness of the rotary cutting; ③ there should be fast feed in and back motion to improve productivity. Since it was formally used in French industrial production in 1840's, there have been many improvements in the structure and performance of the rotary cutter. For example, the hydraulic double bayonet can effectively reduce the diameter of wood core and improve the yield; the control circuit can realize constant linear speed rotary cutting; the pre selection and rapid change mechanism of veneer thickness are conducive to improving the production efficiency; the application of power roller and electronic computer The ideal of "core free rotary cutting" can be realized in the near future. (see veneer lathe)
