The Study Of Linear Vibration Welding Of Moso Bamboo

Welding technology is widely used in the plastic and automotive industries. However, the same technique has been employed to wood bonding without any thermoplastic material and any other binder just for more than ten years. And now, the equipment used for wood welding is the modified machine designed for plastic or metal welding. Linear welding of wood can give bonding results satisfying the relevant standards such as beech. Some of the parameters that influence welding of metals and plastics with the same type of equipment also influence wood welding:welding time, welding pressure, vibration amplitude, welding frequency and holding time and pressure. The optimized parameters are totally different for different kind of wood. Although the welding technology has been applied to a lot of woods, the bamboo has not been mentioned in this filed. The aim of this paper is to employ the environment-friendly, efficient and low cost technology to mo so bamboo.Owing to the wettability of bamboo outer and inner skin is not good, the gluing performance of bamboo by synthetic adhesives without removing the skin is bad. However, there is no such kind of problem in the welding technology because the outer and inner skin of the bamboo has been expelled out during the welding process. Response surface experiment design has been used to optimize the welding parameters of the moso bamboo inner-outer, outer-outer and inner-inner welding and the best average tensile bonding strength of them are6.23MPa,5.91and7.15MPa, respectively. The welding amplitude and welding pressure have significant impact on the final bonding strength, but the welding time of4-6s does not influence the strength significantly. The mechanism of mechanically-induced vibration welding has been shown to be due mostly to the melting and flowing of some amorphous, bamboo cells interconnecting polymer material under the about210℃generated on the welded surface. This caused partial detachment network of the bamboo fibers and formation of a fibers entanglement network in the matrix of molten cells and interconnecting materials which then solidifies after welding. Besides that, the analysis of TMA shows that some kind of cross-linking in the welded layer has happened and contributed to the final bonding strength.The temperature changes in the welding layer can be calculated by the following formulation: The prediction error of the model is less than5%and it is suitable to calculate the temperaturechange of the welding layer. The friction coefficient during the welding process can also becalculated by the model.After the4-6s welding, the temperature of the welded surface reaches the highest level andthe best bonding strength can be got if the welding stops right now. if the welding time is lessthan4s, the continuous and uniform welded layer cannot be got owing to the temperature and thebonding performance is not good. If the welding time exceed6s, the bamboo fibers are allexpelled out from the welded surface and excessive carbonation on the surface also decrease thefinal bonding performance. The holding time can influence the welded performance a lot. Whenthe holding time exceeds35s, the effect can be neglected. The holding pressure between2-3MPahas no significant influence on the final welded strength.The strong welded moso bamboo joints are not capable of satisfying the specifications forexterior joints as they show not very good resistance to water. These joints thus can only beconsidered for interior application such as for furniture and for interior grade wood joints. Butrosin, an environment-friendly, water repelled and low cost natural material, has been used toimprove the water resistance of the welded joints. The results show that the rosin modified jointcan be immersed in water after30days and the strength has not been lost.The bamboo end grain butt joint achieved by linear vibration welding is an interesting filedto study. Although the bamboo is easy to split, we do not find the same phenomenon in the endgrain welded process of bamboo which surely will come up in the low density wood welding.During the welding, the vascular bundles of the bamboo emerge from the welded surface andendure the welding pressure and the friction force protecting the end of the bamboo fromdeparting and making the welding go on. The melted material mainly is parenchyma cells. Thevascular bundles immerse and bend in the melted materials and then solidify to form a specialboding layer which is quite different from the welding along the bamboo fiber.