Wood dowel bonding by high-speed rotation welding

摘要

High-speed rotation-induced wood dowel welding,without any adhesive,is shown here to rapidly yield wood joints of considerable strength.The mechanism of mechanically-induced highspeed rotation wood welding is shown here to be due,as already observed in vibration welding,to the temperature-induced softening and flowing of some amorphous,cells-interconnecting polymer material in the structure of wood,mainly lignin,but also of hemicelluloses and consequent high densifitation of the bonded interface.Wood species,relative diameter differences between the dowel and the receiving hole,and pressing time were shown to be parameters yielding significant strength differenceswhile relative orientation of the fibre grain of the dowel in relation to the fibre grain of the substrate,relative rate of rotation within a limited range and the use of rough or smooth dowels did not have any significant influence.X-ray microdensitometry and scanning electron microscopy were used to determine the limits of wood dowel welding by high-speed rotation.The type of parameters that had an influence on strength indicated that the strength values obtained,although often rather high,were often due to welding of only a limited part of the dowel to the substrate.This is due to the forcing of the dowel into a truncated conical shape by the pressure of insertion and the consequent disruption of bonding in some areas,Notwithstanding this effect,the welded contact area is sufficient to yield strength results comparable to or even slightly higher than that obtained by PVAc adhesive bonding.The use of dry dowels inserted hot in the substrate after preheating them at high temperature (100deg C) yielded consistently better results than that obtained with PVAc gluing.