Effect Of Impregnation Technology Of UF On The Dimensional Stability And Assembly Performance Of Chinese Firfor The Components

Chinese fir as one of the main fast-growing forests of southern species and it has a huge amount of stock. Due to its short growth period results in the low density material properties, mechanical strength is poor, which severely limits its scope of application and use value, especially in the field of furniture industry.It is an effective way to increase the mechanical strength of wood by using resin to impregnated, but affected by the permeability of the impregnated resin, for the larger size of the treated material, its internal and external impregnation increment is not uniform. Therefore, using this material processed wood products prone to deform the parts, while directly toimpregnate modification for the processing parts not only can overcome this shortcoming, but also no need to reprocess for the treated parts. In addition, it can use the material efficiently and save the treating cost.In the view of this, the experiment mainly study on impregnated technology to the dimensional stability and assembly performance for the parts of Chinese fir, which aim to increase the added value of the impregnation process for fast-growing Chinese fir and to promote its industrial application.The main results of this paper are as follows:(1)Impregnated treatment process hardly changes the size and shape of the parts. Although there will be a slight shrinkage on the parts' surface, the collapse depth within 2mm which can be eliminated through the grinding process and the parts will not be warped. Therefore the treatment do not affect the assembly performance of the parts.The best scheme for the smallest size changing of the impregnated parts is: the initial moisture content of wood is 10%, concentration of resin is 45% and the impregnation pressure is IV 0.8MPa.(2)The following optimal combination is obtained by orthogonal test and variance analysis:For the weight gain, the initial moisture content of wood is 0%,concentration of resin is 45% and the impregnation pressure is 0.8MPa; for the dimensional change percentage, the initial moisture content of wood is 10%, concentration of resin is 45% and the impregnation pressure is 0.8MPa; for the collapse depth, the initial moisture content of wood is 5%, concentration of resin is 45% and the impregnation pressure is 0.8MPa; the initial moisture content of wood, concentration of resin and the impregnation pressure had no significant effect on the warpagefor the parts.(3)The moisture content of the parts which modified by resin from the dry to achieve the equilibrium state, the moisture absorption rate and swelling rate are smaller than the material. In the experiment, the different weight gain rate of the impregnated parts will be selected to compare, the higher weight gain rate of parts is, the better moisture resistance is. And in both sizes of radial and tangential direction are less swelling.(4) The parts from the balance state to the process of dry material, the both shrinkage in radial and tangential direction of the impregnated parts is smaller than the material. We also select the different weight gain rate of impregnated parts for comparison and the conclusion is consistent with the conclusion of the swelling rate in both size of radial and tangential. For the higher weigh gain rate of the parts, its structure will be more strengthen. Therefore, it can resist the shrinkage of wood to a certain extent.(5)According to the second chapter, take the most significant process parameters of the weight gain rate in the test result to impregnate the parts. In the scope of the experiment, for the material parts, the length of tenon is extremely significant to the the gripping force result, while the width of the tenon and the interference fit do not show the significant.Its best scheme is: length of tenon is 25 mm, the width of tenon is 25 mm and the interference fit is 0.8mm; for the impregnated parts, the length of tenon and the interference fit is significant to the result, and the width of tenon has no significant. The best scheme is: length of tenon is 25 mm, the width of tenon is 25 mm and the interference fit is 0.4mm.(6) In the scope of the experiment, for the material parts, the width of tenon and the length of it have certain influence to the bending strength result,while the interference do not show significant; for the impregnated parts, only the width of tenon has certain influence to the result, the interference fit and the length of tenon do not show significant. The best scheme of the parts is: length of tenon is 20 mm, width of tenon is 25 mm and the interference fit is 1.2mm.(7)In the scope of the experiment, the fir parts which impregnated by the urea-formaldehyderesin, when its weight gain rate reach 39%, the griping force has increased by 23%; While its weight gain rate reach 74%, the bending strength has increased by 18%. The data shows that the weight gain rate is more significant on the griping force. Therefore, the optimal scheme of griping force should be adopted when the modified material applied in practice.