Development of wooden-based nails for wooden pallet

Transcription

1 Development of wooden-based nails for wooden pallet Masafumi Inoue, Koji Adachi, Ken Kamachi, & Mami Yokoi Asian Natural Environmental Science Center The University of Tokyo, Japan Abstract We have been proposing wood-based connectors for timber structures, furniture or packaging manufacturing. Wooden connectors are considered to have some advantages in the following respects; - They do not have to be separated from waste wood during recycling or scraping - They can be cut by wood machinery together with wood members such as frames or panels when reusing - They do not cause metal stains or damages due to moisture condensation. - They are very light as the maximum density of wood is ca. 1.5 g/cm 3, which is 1/5 the density of steel. In this research, we will investigate on the possibilities of compressed wood or bamboo nail as fastener in wooden pallet and its adaptability to automatic nail driver. As a result, we could obtain high strength material more than 400MPa in MOR at density of 1.45 g/cm 3 by 53% compression of Madake bamboo. Drop impact resistance of the wooden flat pallet (1000x1000mm) with bamboo nails was almost same as that with iron nails. Keywords densified wood, bamboo, nail, pallet Paper WS-37 1 of 5

2 Introduction Most of the nails made from metal using wooden pallet for transportation. The wooden pallet production in Japan reached 55 million pallets (The required number of nails per unit pallet is 1 nails or more). Although metal nails have high reliabilities in toughness, durability and easy operation, cause a big problem in assorting required by material Re-use and Recycle. We have been using wood or bamboo nails as fasteners for traditional roofing, furniture and caskets in Japan. Recently, wood-based connectors such as a nail, wedge, dowels and mortisetenon joint have traditionally been used for timber structures (Chang et al. 07, Guan et al. 08, Inoue et al.03, Jensen et al. 01, Nakazono et al. 09, Nisiuchi et al. 03 and Shanks et al. 09). Since the development and spread of wood densification technology, several attempts to make densified wood nails (Inoue et al.03), dowels (Jung et al.08), and drift pins (Nakata et al.1997) have been reported. Wooden connectors are considered to have some advantages in the following respects; - They do not have to be separated from waste wood during recycling or scraping - They can be cut by wood machinery together with wood members such as frames or panels when reusing - They do not cause metal stains or damages due to moisture condensation. - They are very light as the maximum density of wood is ca. 1.5 g/cm 3, which is 1/5 the density of steel. In this research, we will investigate on the possibilities of compressed wood or bamboo nail as fastener in the wooden pallet for packaging manufacturing. Material and methods Manufacturing of wooden-based nails Madake bamboo (Phyllostachys bambusoides) and Japanese cedar (Cryptomeria japonica) flatgrain timber were used as the nail specimen. The inner part of column of the bamboo was shaved with a belt sander to make one side of the specimen flat. The air-dried bamboo and Japanese cedar timber were compressed to the radial direction in a platen press at 80 C by using a restrained jig for lateral deformation and then dried to fix the added deformation at 1 C for 8 hours. The densification degrees of the bamboo and Japanese cedar were 23% and 67%, respectively. The final density of Madake bamboo and Japanese cedar at the air-dried condition increased 1.21 and 1.18 g/cm 3 from 0.88 and 0.43 g/cm 3 of initial density respectively. The dimensions of the nail shank was 3.5 x 3.5mm (cross section) x 60mm (length) as shown in Figure 1(a). The nail tip was cut in the diamond point form and the tip length was 3.5mm. The nail head was made a flat-shaped like a pin nail. Paper WS-37 2 of 5

3 (a) (b) (c) 3.5 stringer deck Figure 1. Shapes of nail and pallet, (a) wooden and bamboo nail and (b) wooden pallet by using bamboo nails (c) nail strike position of the wooden pallet. Manufacturing of wooden pallet Japanese larch (Larix kaempferi) at green condition was used as the wooden-pallet member. The size of deck board and stringer were 1 x x 1100mm and 50 x 90 x 1100 mm, respectively. The two-way wooden pallet fabricated in this study was 1100 x 1100 x 1 mm as shown in Figure 1(b). The pallet was a combination of the deck board and the stringer by using the bamboo nails. The nail-strike position was shown in Figure 1(c). The bamboo nails were drove into the pallet member by a compressed air nail gun, which was newly developed for wooden-based nails. A wooden pallet by using iron nails was fabricated as a comparison of the mechanical property. The pallets after fabrication were conditioned to an air-dry at room temperature. Bending test of wooden-based nail Nail shank specimens were submitted to a bending test to determine modulus of elasticity (MOE) and modulus of rapture (MOR). The span and loading speed were 14 times the thickness of specimens and 5mm/minutes, respectively. Corner drop test of wooden pallet Corner drop test was performed according to JIS Z The pallet was dropped from a fixed height of 500mm. Number of drops and impact surface were 3 times and the pallet corner, respectively. After every times of the drop, lateral stability and visual damage was observed. Results and discussion Bending property of wooden nail Figure 2 shows the effect of the final density after the densified process on MOR of nail shank. We could obtain high strength bamboo material more than 400MPa in MOR at density of 1.2g/cm 3 by the densified process. Despite the final density was lower, the MOR of the bamboo was higher than that of Japanese cedar. Paper WS-37 3 of 5

4 Fig.2 The effect of the final density after densified process on MOR of nail shank. Corner drop test of wooden pallet The bamboo nails were driven into the timber with the air nail gun without pre-drill-hole process. Table.1 shows the deformation ratio of diagonal point on the deck of wooden pallets after corner drop test. The both pallets with the iron and the bamboo nails passed the standard by JIS, the acceptability criterion was below 3%, for the rigidity against corner drop impacts. There was a little damage to the pallets after four times drops. The edge board near the fastener of the impact corner was split. The deformation of the pallets with the bamboo nails was recovered gradually. However, that with the iron nails was not recovered. Whereas the deformation of bamboo nails was viscoelastic behavior, that of iron nails was plastically one. Paper WS-37 4 of 5

5 Conclusions The bending strength of the bamboo nails reached about 400MPa by densified processing. The bamboo nails were driven into the timber with the air nail gun without pre-drill-hole process. The wooden pallet with bamboo nails passed the standard by JIS. Acknowledgement Part of this study was carried out in the project Sustainable production of woody biomass in tropical peatlands financially supported by JST- CREST. References Chang WS, Komatsu K, Hsu MF, Chen WJ (07) On mechanical behavior of traditional timber shear wall in Taiwan I: background and theory derivation. J Wood Science 53: Guan ZW, Kitamori A, Komatsu K (08) Experimental study and finite element modeling of Japanese ''Nuki'' joints II: Racking resistance subjected to different wedge configurations. Eng Struct 30: Inoue M, Mori T (03) High performance bamboo nail (in Japanese), Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan, C-1, Structures III, 222 Jensen JL, Koizumi A, Sasaki T, Tamura Y, Iijima Y (01) Axially loaded glued-in hardwood dowels. Wood Sci Technol 35:1/ Jung K, Kitamori A, Komatsu K (08) Evaluation on structural performance of compressed wood as shear dowel. Holzforschung 62: Nakata K, Sugimoto H, Inoue M, Kawai S (1997) Development of Compressed Wood Fasteners for Timber Construction I. Mechanical properties of phenolic resin impregnated compressed laminated veneer lumber. (in Japanese) Mokuzai gakkaishi 43: Nakazono M, Inai E, Hiroshima N (09) Tensile behavior of traditional wooden column base joint by plural nagahozosashi-komisen. (in Japanese) Journal of structural and construction engineering 638: Nisiuchi Y, Kanagawa Y, Fujiwara S, Goto J (03) Tension Strength of Post-Sill Joints Connected with Full Pinned Mortise-and-Tenon Joints, I. Effect of Various Joint Conditions on Maximum Loads and Yield Loads. (in Japanese) Zairyo 52: Shanks J, Walker P (09) Strength and stiffness of all-timber pegged connections. J Mater Civ Eng 21: Paper WS-37 5 of 5