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Laminated veneer lumber (L VL) is a structural material in which the veneer is glued into the main component in the direction of the grain. It not only retains the natural characteristics of the wood, but also has many features not found in solid wood sawn timber in North America and Japan. Has been widely used in construction [1]. Plantation Chinese fir has a wide area of ​​planting in China, but due to its short growing period, the wood quality is worse than that of natural forest wood, and it has not been reasonably applied so far. The use of artificial forest fir to produce L VL can provide wood products with high use value for the society, and it is of great significance to solve the problem of rational and efficient utilization of small-diameter Chinese fir in plantation forest. In this paper, the relationship between the performance of L-VL of Chinese fir and the technological factors and the feasibility of making LVL were discussed, which provided a basis for the industrial production of LVL of plantation.
1 Materials and methods
1 . 1 material
Cunninghamia lanceolata (Cunninghamia lanceolata) was collected from the Jurong Xialin Forest Farm in Nanjing, with a DBH of 1500-1200 mm, a gas dry density of 0.33 g/cm3, a tree age of 1 to 13 years, and a MOR of 59. 7MPa, MOE is 850 0 MPa. PF resin solid content 52%; viscosity 2 3 0 s (20 ° C, coated -4 cups); p H value of 1 1.0; free phenol content of 3%.
1.2 method
1 . 2 . 1 Experimental design and data processing The three-factor quadratic orthogonal rotation combination design is used to arrange the experimental scheme [2]. The change space of the investigation factor is: hot pressing temperature (x1) 1 3 0 ~ 1 70 ° C; hot pressing time (x2) 0. 8 ~ 1. 2 min / mm plate thickness; hot pressing pressure (x3) 0 . 8 ~ 1. 8MPa.
According to the experimental results, the regression equation is solved, and the simplified regression equation is optimized by the composite method to obtain the optimal process parameters.
1 . 2 . 2 Process
(1) Rotary cutting and selecting the artificial forest fir wood section with a length of 1 m, a straight shape and a regular shape, and cutting with a BQ1 40 rotary cutting machine. The nominal thickness of the veneers is 1.4, 2. 1 and 3. 0 mm; the angle of rotation of the knife is 1 9°; the angle after cutting is 40′; the pressing ratio of the pressure ruler is 10% [3].
(2) Veneer quality measurement veneer thickness deviation and backside fracture rate. After the wood segment is rounded, the continuous veneer strip is taken: 1. 4 mm thick veneer is taken every 6 times; 2. 1 mm thick veneer is taken every 4 times; and 3.0 mm thick veneer is taken every 3 turns. Each block of a single board with a width of 200 mm and a length of 100 mm is taken.
It can be seen from Table 1 that the thickness deviation of the veneer plate is small according to the above conditions, which is in accordance with the thickness deviation range of the veneer of the manufacturer, but the crack on the back side of the veneer is large. And with the increase of the thickness of the rotary cutting veneer, the back crack rate increases significantly, and the average number of cracks decreases. Considering the influence of the crack rate on the back side of the veneer on the mechanical properties of the LVL and the thickness of the JAS on the thickness of the veneer, the hot pressing test is carried out using a veneer having a thickness of 2.1 mm.
(3) Drying of the veneer The veneer is cut into 40 0 ​​mm × 40 0 ​​mm, and dried in a constant temperature drying oven at (1 0 0 ± 5) °C until the water content is 5%. After cooling, the bag is sealed and stored.
(4) The rubberized blank is hand-coated, and the single-side coating amount is 200 g/m2. When the blank is formed, the tight side of the veneer is tight, and the loose side is loose, which is 14 layers. When the blank is assembled, the core material is assembled in a proportion similar to the position of the logs, to prevent warping deformation and to obtain higher strength properties.
(5) Pre-pressing aging pre-compression pressure 0. 8MPa, time 1 5min; aged 4h.
(6) The hot pressing hot pressing parameter [4] is carried out according to the setting scheme, and the thickness of the product is controlled by a thickness gauge. After hot pressing, the board was placed for 72 h trimming.
(7) Performance test Considering that the test piece has a small format, the sampling chart is designed by itself in combination with JAS Japanese Standard and ASTM American Standard.
In this test, where the dimensions of the test piece meet the requirements of JAS, the test is based on JAS. The remaining MOR and MOE test pieces that do not meet the requirements of JAS are referred to ASTM 1 991.
1 Materials and methods
1 . 1 material
Cunninghamia lanceolata (Cunninghamia lanceolata) was collected from the Jurong Xialin Forest Farm in Nanjing, with a DBH of 1500-1200 mm, a gas dry density of 0.33 g/cm3, a tree age of 1 to 13 years, and a MOR of 59. 7MPa, MOE is 850 0 MPa. PF resin solid content 52%; viscosity 2 3 0 s (20 ° C, coated -4 cups); p H value of 1 1.0; free phenol content of 3%.
1.2 method
1 . 2 . 1 Experimental design and data processing The three-factor quadratic orthogonal rotation combination design is used to arrange the experimental scheme [2]. The change space of the investigation factor is: hot pressing temperature (x1) 1 3 0 ~ 1 70 ° C; hot pressing time (x2) 0. 8 ~ 1. 2 min / mm plate thickness; hot pressing pressure (x3) 0 . 8 ~ 1. 8MPa.
According to the experimental results, the regression equation is solved, and the simplified regression equation is optimized by the composite method to obtain the optimal process parameters.
1 . 2 . 2 Process
(1) Rotary cutting and selecting the artificial forest fir wood section with a length of 1 m, a straight shape and a regular shape, and cutting with a BQ1 40 rotary cutting machine. The nominal thickness of the veneers is 1.4, 2. 1 and 3. 0 mm; the angle of rotation of the knife is 1 9°; the angle after cutting is 40′; the pressing ratio of the pressure ruler is 10% [3].
(2) Veneer quality measurement veneer thickness deviation and backside fracture rate. After the wood segment is rounded, the continuous veneer strip is taken: 1. 4 mm thick veneer is taken every 6 times; 2. 1 mm thick veneer is taken every 4 times; and 3.0 mm thick veneer is taken every 3 turns. Each block of a single board with a width of 200 mm and a length of 100 mm is taken.
It can be seen from Table 1 that the thickness deviation of the veneer plate is small according to the above conditions, which is in accordance with the thickness deviation range of the veneer of the manufacturer, but the crack on the back side of the veneer is large. And with the increase of the thickness of the rotary cutting veneer, the back crack rate increases significantly, and the average number of cracks decreases. Considering the influence of the crack rate on the back side of the veneer on the mechanical properties of the LVL and the thickness of the JAS on the thickness of the veneer, the hot pressing test is carried out using a veneer having a thickness of 2.1 mm.
(3) Drying of the veneer The veneer is cut into 40 0 ​​mm × 40 0 ​​mm, and dried in a constant temperature drying oven at (1 0 0 ± 5) °C until the water content is 5%. After cooling, the bag is sealed and stored.
(4) The rubberized blank is hand-coated, and the single-side coating amount is 200 g/m2. When the blank is formed, the tight side of the veneer is tight, and the loose side is loose, which is 14 layers. When the blank is assembled, the core material is assembled in a proportion similar to the position of the logs, to prevent warping deformation and to obtain higher strength properties.
(5) Pre-pressing aging pre-compression pressure 0. 8MPa, time 1 5min; aged 4h.
(6) The hot pressing hot pressing parameter [4] is carried out according to the setting scheme, and the thickness of the product is controlled by a thickness gauge. After hot pressing, the board was placed for 72 h trimming.
(7) Performance test Considering that the test piece has a small format, the sampling chart is designed by itself in combination with JAS Japanese Standard and ASTM American Standard.
In this test, where the dimensions of the test piece meet the requirements of JAS, the test is based on JAS. The remaining MOR and MOE test pieces that do not meet the requirements of JAS are referred to ASTM 1 991.
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