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1 Test materials and methods
1.1 Test materials and equipment Test materials: Fraxinus mandshurica, Juglans mandshurica and Piceajezoensis var. Komarovii. The sheet was processed into a sheet having a size of 192 mm × 100 mm × 20 mm (length × width × thickness), and the water content was 12%. The adhesive is selected from two-component aqueous polymer isocyanate, and the group distribution ratio is the main agent: crosslinking agent=100:15-20 (mass ratio) [2,3]. Equipment QD-100 press and self-made integrated wood fixture, RCT-2TR wood universal ability test machine.
1.2 Test method The manufacturing process of the integrated material is as follows:
Wood sawing → sheet → drying → longitudinal solution → (wood strip) flat, planing → cross section → wood block sorting → glue adjustment → wood block coating → blanking → cold pressing glue → laminated sawing → inspection
1.2.1 Gluing test Aqueous polymer isocyanate is a room temperature curing adhesive. Therefore, only the unit pressure A, the pressing time B and the coating amount C are selected as the change factors. The density of the long-white fish scale spruce material is relatively lower than that of ash and walnut, and the material is soft [4], so the unit pressure should be slightly lower. The pressing time and glue level of the three kinds of wood are the same, as shown in Table 1. The test was arranged according to the L9 (34) orthogonal table, and 4 samples were produced under each process condition.
1.2.2 Glue strength testing of glulam is carried out according to the Japanese Glulam Standard (July 2001, Ministry of Agriculture, Forestry and Fisheries Notice No. 991). (1) Immersion peeling test One sample of each tree species under different process conditions was taken, and two specimens with a length of 75 mm were cut out, that is, a total of 18 specimens per tree species group. The test piece was immersed in room temperature water for 6 h, and then placed in a (40 ± 3) ° C constant temperature oven for 18 h. After cooling, the adhesive layer was observed for peeling and the peel length was measured. Fig.1 Schematic diagram of the test of the rubber layer shear test F ig.1 Samplesizeforshearstrengthtesting (2) Shear strength test of the rubber layer Each tree species is taken from three samples under different process conditions in the orthogonal test, according to the Japanese laminated timber standard. It is stipulated that the test pieces are produced (see Figure 1), and six test pieces are made for each test piece, that is, a total of 18 test pieces under each test condition. Nine of them were used for the detection of the shear strength of the dry rubber layer. After being immersed in hot water of (63 ± 3) °C for 6 hours, the maximum load was measured after the wet shear failure. The shear strength of the rubber layer was calculated.
2 Test results and discussion
2.1 Impregnation and peeling test The glued test pieces of the three kinds of wood were not peeled after being soaked and dried, indicating that the impregnation and peeling test of the test piece met the qualification requirements of JAS non-structural laminated materials.
2.2 Dry and wet shear strength of rubber layer
2.3 Variance analysis of wet shear strength of three kinds of wood integrated gluing specimens Table 2 and Table 3 show that: (1) dry shear strength is within the scope of this test, dry shearing of three kinds of wood gluing specimens The average of the strengths all meet the requirements of the corresponding wood in the JAS non-structural laminated timber standard. Under the same conditions, the average dry shear strength of the specimens obtained from the 4th, 5th and 6th gluing tests of ash and walnut stalks and the 7th, 8th and 9th gluing tests of the long white spruce spruce were 15.17, respectively. 10.64 and 7.53 MPa, also meet the requirements of JAS. Under the same process conditions, the shear strength of the dry rubber layers of the three woods increases with the increase of wood density. (2) Suitable bonding process parameters: pressure 2.0MPa (ash, walnut), 1.5MPa (long white scale spruce); pressurization time 60min; coating amount 250g/m2. After the F test, the influence of the unit pressure was significant or highly significant, and the effects of the pressurization time and the amount of the glue applied were not significant. When the wood is glued, the pressure should be selected according to the nature of the adhesive, the amount of glue applied, and the wood species and surface characteristics. Within a certain range, the greater the pressure, the more glue that penetrates into the wood, the increased the bonding area, and the higher the bonding strength; if the pressure is too large, the adhesive will excessively penetrate into the wood structure, causing the glue surface to lack glue, and the bonding strength Instead, it fell. Within the scope of this test, the three kinds of wood bonding strength increased significantly with the increase of unit pressure. Due to the high density and hardness of ash, the effect of pressure on its strength is also the most significant. Because of its low density, the scale of spruce wood of Changbai fish is relatively small. In this test, the wet shear strength of the rubber layer increased with the extension of the pressurization time. The three levels of coating amount have little effect on the wet shear strength. Only the wet shear strength of the ash test piece increases with the increase of the amount of glue applied, which is due to the processing of the ash block during processing. The thickness variation is greater than the other two types of wood, and the ring hole material, the adhesive is easy to penetrate, and thus requires a larger amount of glue. But on the whole, the three levels of glue can meet the process requirements. When the amount of glue applied was 300 g/m2, some of the glue was squeezed out during the pressurization.
2.3 Glue test specimen dry and wet shear strength comparison and strength preservation rate strength preservation rate /% = wet shear strength dry shear strength × 100 according to the average dry and wet shear strength of the test pieces listed in Table 2 The strength retention rate was calculated according to the above formula. The results are shown in Table 4.
It can be seen from Table 4 that the average wet shear strength of the three tree species is as follows: walnut 楸 > ash > Changbai fish scale spruce; the order of strength preservation rate is: walnut 楸 > Changbai fish scale cloud Cedar > ash. Studies on the swelling of wood have shown that both hygroscopic expansion and water swelling vary with species. In general, the density is higher and the expansion is higher [4], and the wood swelling is as anisotropic as the shrinkage [5]. Among the three tree species in this experiment, the density of ash is the largest, and there are cases where the radial and chord directions are randomly combined when the wood is glued. In addition, from the processing precision of the three tree species, the thickness variation range of ash is the largest, indicating that the processing precision of ash is poor. In the integrated gluing test of three tree species, the ash glued wood block After hot water treatment, the wood block has the largest amount of water swelling and the largest variation, which leads to the internal stress on the wood-adhesive interface of the ash, which affects the wet shear strength of the glued wood block, which is reflected in this test. The wet shear strength of the ash-glued wood block is greatly reduced, and the preservation rate is low. The data in Table 4 also shows that the three tree species of glued wood have a high dry and wet shear strength. According to the literature, the normal shear strength of birch glulam block with the same kind of adhesive can be as high as 23.8～24.6MPa, and the wet shear strength after repeated boiling treatment also retains 11.8～12.6MPa, and resorcinol resin glue. The adhesive properties of the adhesive are quite [2]. The other side reflects the good bonding strength and water resistance of the adhesive.
3 Conclusion
1) Ash tree, walnut meal and Changbai fish scale spruce 3 tree species are integrated with water-based polymer isocyanate adhesive, and the dip peeling test of the test piece meets the qualification requirements of JAS non-structural laminated timber.
2) Under the same process conditions, the average dry shear strength of ash, walnut and tarragon spruce is 15.17, 10.64 and 7.53 MPa, respectively, which are all corresponding to the corresponding tree species of JAS non-structural laminated timber. The dry shear strength requirement; the dry shear strength is positively correlated with the density of the tree species.
3) The average wet shear strength of the three tree species is ranked from large to small: walnut meal (7.45MPa), ash (6.05MPa), long white scale spruce (4.59MPa); strength preservation rate from large The order of the small ones is: walnut carp (66%), Changbai fish scale spruce (59%), and ash (47%).
4) The gluing test of 3 tree-type glulams showed that the unit pressure had a significant effect on the wet shear strength of ash and long-white spruce, and the effect on the walnut mites was highly significant; the pressing time and the amount of glue applied to the three kinds of wood The effects are not significant; the wet shear strength of the glulam block increases with the increase of the unit pressure, and increases with the prolongation of the pressurization time.
5) Under the conditions of this test, the preferred process conditions for the integrated bonding of three kinds of wood are: unit pressure 2.0MPa (ash, walnut), 1.5MPa (long white scale spruce); pressurization time 60min, coating amount 250g /m2.
Glulam, also known as glulam, is a material in which the plate or square is assembled in parallel fiber direction and glued in the length, width or thickness direction. It not only has the characteristics of natural wood, but also overcomes the natural wood. It is easy to warp, deform and crack. It is the same as wood I-beam and veneer lumber. It is widely used in construction, furniture and decoration in Europe, North America, Japan, Russia and other countries. industry. The history of producing glued wood in China is also earlier, but it is rarely used. In the past ten years, the integrated products have received increasing attention and the output has been rising. In addition, the production of laminated timber can be short-small material and small-diameter wood as raw materials, which not only can alleviate the contradiction between supply and demand of high-quality board and square materials, but also an effective way to improve the comprehensive utilization rate of wood and added value of products [1]. In this study, based on the performance requirements of Japanese JAS non-structural integrated materials, based on the relevant performance requirements of integrated wood for sliced ​​thin wood, the integrated bonding process and performance of the three tree species were tested.