Wood blockboards for construction fabricated by wood welding with pre-oiled dowels

Holding wood pieces together by rotationally welded dowels can be used to make blockboard panels with the dowels inserted in the side of the wood substrate slats. Pre-oiling the dowels with sunflower oil: (i) eases their insertion in the pre-drilled substrate, (ii) allows the insertion of dowels to a much greater depth by its lubricating action for welding, thus allowing more layers of wood to be joined and (iii) provides an improved water resistance to the welded joint. The strength of the joints prepared with this system is comparable to those already obtained with other welded dowel systems but with improved water resistance.     

Wood joints and laminated wood beams assembled by mechanically-welded wood dowels

Dowel welding by high-speed rotation was used to join two wood blocks and strong joints were obtained. Dowel angle to the surface of the wood blocks to be joined had a marked influence on the mechanical performance of the joint. When the dowel was inserted at 90° to the substrate, the dowel was subjected to and resisted a shear force only. When introduced at an angle such as 30° or 45°, the dowel was subjected to and resisted both shear and tension forces, resulting in better joint strength. The joint almost always failed by dowel fracture. The dowel/substrate interface was almost always stronger and did not break. Short two-layer beams joined exclusively by a series of welded dowels were prepared, tested in shear according to structural standards, and their performance was compared to those of solid wood and of glued laminated beams (glulam) of the same dimensions. The short two-layer beams prepared for testing met the Eurocode 5 standard requirements when the optimum dowel insertion angle was used. Then 2-m-long two-layer wood beams were prepared, with the two layers connected exclusively by a series of welded dowels, and tested in bending. Their maximum failure strength and stiffness in bending were determined. These beams outperformed both nailed beams and glued-dowel beams. All the beams had the same length and conformation. The number of nails necessary was double the number of dowels used.     

Wood Blockboards Fabricated by Rotational Dowel Welding

Holding wood pieces together by rotationally welded dowels can be used to make blockboard panels with the dowels inserted in the side of the wood substrate slats. The average results for both tensile and three-point bending tests indicate that a 20° dowel insertion angle yields strength results better than 10° and 0° insertion angles. Applied load vs deformation in the two types of tests showed that blockboard panel stiffness was greater for the panels with 20° dowel insertion angle.     

Parameter interactions in two-block welding and the wood nail concept in wood dowel welding

The interactions between parameters found to be determinant in wood dowel welding by high speed rotation have been evaluated. Of these, the interactions that proved to be the most significant, in descending order, were rotation rate/dowel moisture content, followed by rotation rate/ethylene glycol, and finally, at a lower level of significance, the interactions rotation rate/dowel temperature, wood grain direction/wood species and dowel temperature/wood species. Of the individual factors, once the most determinant factor already optimized in previous studies, namely the dowel/hole diameter difference, was fixed, the most significant were wood grain direction, dowel moisture content (dryness) and wood species. The optimized process yielded excellent strength results. The regression equations developed were able to predict the strength obtainable. The torque for insertion of the dowel in the substrate hole has been measured for several cases and the results are presented. In no cases the value of the torque needed for insertion was excessive and insertion was, therefore, easy. Wood joints composed of two pieces of timber held together by a dowel welded to both of them were assembled for the first time. Two further new concepts have also been advanced and tested: (i) the conical dowel, to maximize welding area and (ii) the concept of the wood nail in which a slightly conical fast-rotating hardwood dowel is inserted rapidly into a softwood substrate into which no hole has been pre-drilled. X-ray densitometry of the samples prepared with the latter approach showed some interesting mechanical interlocking features that might contribute to dowel bonding in softwoods.     

Wood joints by through-dowel rotation welding: microstructure, 13C-NMR and water resistance

Two-block wood joints were obtained by insertion and welding without adhesives of dowels by high-speed rotation. Their strengths were better than that obtained by poly(vinyl acetate) (PVAc) gluing. X-ray-microdensitometry analysis showed that a complete welding of the dowel to the substrate occurred and that a perfectly tight joint was formed. Isolation of the flow material allowed CP-MAS ¹³C-NMR analysis of its composition with possibly low interference from the constituents from the substrate. The flow material appeared to be composed of hemicelluloses, apparently xylans, and lignin. Scanning electron microscopy coupled with the NMR analysis results showed that microfibrils of cellulose, in both amorphous and crystalline states, torn from the wood surface during welding, as well as very small proportions possibly of recrystallized xylans and furanic compounds formed by heat transformation of the carbohydrates, were present. The geometry of the dowel joint allowed the joint to maintain up to 88% of its initial tensile strength after 24-h immersion in cold water.     

Shrink-Fitting and Dowel Welding in Mortise and Tenon Structural Wood Joints

Shrink-fitting, a common bonding technique in metal assemblies, was used for mortise and tenon wood joints. The joints had considerable strength. Shrink-fitting yielded joint strengths comparable to those obtained by using several welded dowels. Increasing the number of welded dowels, however, produced joints of higher strength than those bonded just by shrink-fitting. Combining in the same joint both dowel welding and shrink-fitting yielded joint strengths higher than those obtained by the individual techniques alone, and at the same time allowing decreasing the number of welded dowels needed.     

Accelerating vs Constant Rate of Insertion in Wood Dowel Welding

Dowel insertion rates whether accelerating or constant are determining parameters for the tensile strength of welded dowel joints. Dowel insertion at acceleration up to 4–7 m/s² appears to yield the best results at the lower dowel insertion speed, characteristic of welding by manual drills. Strength results for dowel welded joints of 24 mm depths of up to 2700 N/mm² have been obtained. Constant dowel insertion rates appear instead to yield best results when the insertion rate is much higher and can be better controlled, as it is the case for a computer controlled dowel insertion equipment. Strength results for dowel welded joints of 24 mm depths of up to 4700 N/mm² have been obtained for insertion rates of 18–20 mm/s and welding time as short as 1.2 s. The results indicate that at low to medium insertion rates, the greater is the acceleration the better are the results. At fast insertion rates the acceleration has only little effect. The predominant effect is that a short welding time yields a high strength joint.     

Zig-zag rotational dowel welding for exterior wood joints

A zig-zag pattern of rotationally welded dowels across the interface of a butt joint between two wood planks was shown to yield strong joints without any adhesive. Tests after 2 h in boiling water showed that the joints were able to resist both 2 h immersion in boiling water, as well as the subsequent oven drying. Some unusual densification patterns were observed by X-ray microdensitometry. X-ray microdensitometry analysis of densification patterns in the dowel and at the dowel/substrate interface indicate that further improvement and optimisation of this process should consider minimizing the compression rate at the end of dowel rotation as well as minimization of the insertion impact of the dowel to avoid interfacial microfissures that can sometimes develop.     

Performance of Dowel-Welded T-Joints for Wood Furniture

Comparison of two types of furniture joints namely step butt T-joints and mortise and tennon T-joints held together either by one or two welded or glued dowels showed that the shear strength results of welded dowel and glued dowel joints were comparable. For mortise and tennon T-joints there is, in general, no difference if the dowel is inserted at a 45° or 90° angle. Also there is no significant difference between welded and glued dowel joints stiffness values in both step butt and mortise and tennon T-joints of the same geometry. Also, there is no significant difference between dowels inserted at 45° or 90° for mortise and tennon T-joints. Glued dowel and welded dowel step butt T-joints behave quite differently from linear joints. Thus, in step butt T-joints a higher shear strength is obtained if a single dowel is inserted at 45° for both glued and welded dowels. Both shear strength and stiffness increase as the number of dowels increases, namely from one to two. The application of the welded joint technique to joints where the number of dowels is limited by the limited space in which they can be inserted, such as in furniture, can give shear strength results comparable to those obtained by gluing the same dowels. This is particularly the case for mortise and tennon T-joints.     

Determination of optimal wood-dowel welding parameters for two North American hardwood species

Rotational wood-dowel welding has been shown to rapidly produce wood joints of considerable strength without any adhesive. The technique offers an opportunity to increase productivity and reduce costs in the furniture industry. The objective of the study was to define optimal wood-dowel welding parameters for two North American hardwood species frequently used for indoor appearance products: sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). Optimized parameters for individually studied species were determined using a rotational wood-dowel welding machine designed for the technique. A comparative analysis of wood-dowel welding parameters was performed. The investigated parameters for both species were grain orientation, rotational speed, and insertion speed. Temperature profile measurements at the interface during rotational wood-dowel welding were also carried out. Optimal welding mechanical properties were determined from the dowel withdrawal strength using a standard tensile strength test. Results revealed a significant interaction between species, rotational speed, and insertion speed. Sugar maple produced wood joints with higher withdrawal strength than yellow birch. The best results for sugar maple and yellow birch were obtained with a rotational speed of 1000?rpm. A 25?mm?s^?1 insertion speed produced significantly stronger welded joints in sugar maple than at 12.5?mm?s^?1. For yellow birch, a 16.7?mm?s^?1 insertion speed provided the best results. Both species and rotational speed had a significant effect on peak temperature at the interface during welding. Peak welding temperatures with optimal parameters were 244 and 282?°C for sugar maple and yellow birch, respectively.     

Performance of Dowel-Welded Wood Furniture Linear Joints

Comparison of three types of furniture joints such as scarf joints, step butt joints and dovetail joints held together either by one or two welded dowels, glued dowels and steel nails showed that the dowels always gave better shear strength and greater stiffness than the steel nails. The results of welded dowels and glued dowel joints were found to be comparable. The application of the welded joint technique to joints where the number of dowels is limited by the narrow space in which they can be applied, such as in furniture, can give results comparable to those obtained by gluing the same dowels.     

Vibration welding of heat-treated wood

Vibration welding of wood that has been preheated according to an industrial two-step process indicates that such wood can be welded and can yield welded joints of good strength. The joint strength is, however, markedly lower than obtained when welding non-heat-treated timber. In general, weld strength of the timber is poor if welding is done on hydrothermolyzed wood. The strength results are instead much better if welding is done at the end of the complete heat treatment process, i.e., after the dry heat step. The weld lines of heat-treated wood show entangled cells where there is none or very little of the molten matrix intercellular material usually observed in welded timber. Furthermore, in weldlines obtained after hydrothermolysis an increase in rigidity and brittleness of the wood cells is observed. Hence, the wood cells are not entangled at all or very little. Both observations indicate that heat treatment has affected the main melting region of the wood, namely the intercellular material. As most of this material is already either lost or heavily cross-linked during heat treatment, only little of it is now available to melt and bind the wood surfaces during vibrational wood welding.     

聚乙烯管道热熔对接焊接头性能的分析

测试和分析了聚乙烯管道热熔对接焊接头的结晶度、硬度、拉伸性能和冲击性能，并与基材的性能进行了比较。结果发现，焊接接头区域内的结晶度高于基材部分的结晶度。焊缝的拉伸强度和硬度也均高于基材，而冲击强度低于基材。     

耐热钢15CrMoR的焊接工艺研究

针对某公司的高压加氢反应器产品,对厚度为38mm的15CrMoR进行了焊接工艺评定。焊接方法采用钨极氩弧焊(GTAW)打底+焊条电弧焊(SMAW)填充盖面,焊后进行热处理。对焊接接头的拉伸强度、弯曲、冲击及硬度等性能进行了测试。测试结果表明,焊接接头的拉伸强度可达510 MPa以上,侧弯180°后未见裂纹产生;在-20℃的条件下,焊缝的冲击功可达46J以上,热影响区的冲击功可达42J以上;焊缝的平均硬度值为176HBW,热影响区的平均硬度值为190HBW。各项性能均可满足要求。     

The effect of edge banding thickness of white oak bonded with different adhesives on withdrawal strengths of beech dowels in composite materials

Dowel joints are widely used in furniture frame construction as a load-bearing connection structure, as well as a simple locator for parts. Joints constructed with dowels were subjected to withdrawal, bending, shear, and tensile forces. The aim of this study was to determine the withdrawal strengths of 6, 8, 10 mm diameter beech dowels embedded into matching holes drilled into the edges of medium-density fiberboard (MDF) and particleboard (PB) with solid wood edge banding of white oak with 5, 10 and 15 mm thickness, bonded with hot-melt, poly(vinyl acetate) (PVAc) and Desmodur-VTKA (D-VTKA), a polyurethane-based one-component adhesive. The effects of edge banding thickness, dowel dimension, type of composite material and type of adhesive used for edge banding on the withdrawal strength were determined. According to the interaction results from the Duncan test the highest withdrawal strength (7.019 N/mm²) was obtained in beech dowels with 6 mm diameter for MDF with solid wood edge banding of white oak with 10 mm thickness bonded with the hot-melt adhesive. Should the dowels be subjected to withdrawal, it is advised that a beech dowel should be used for MDF with solid oak edge banding with 10 mm thickness bonded with a hot-melt adhesive in furniture production and decoration applications.     

Enhancing the Exterior Performance of Wood Joined by Linear and Rotational Welding

Application of rosin, a wood derived, non-toxic, natural, inexpensive and easily and abundantly available natural material, to the wood faces to be joined by either linear vibration welding or rotational dowel welding has shown to greatly enhance the water resistance of welded wood joints. The method of application has been shown to have a marked effect on the results, with the application and drying of a diluted rosin solution to the wood surfaces before welding yielding the best results. The considerable improvement in water resistance does not still allow classification of the joints as fully exterior grade. However, dowel welding can now be used for protected exterior joints due to a combination of rosin waterproofing and joint geometry. Welded dowel joints holding together for longer than 455 days immersion in water indicate this to be the case. Rosin-treated linear vibration joints held together well in excess of 30 days but retained a measurable strength, in the best case, only up to 18 days water immersion. The wood anatomy and chemical reasons for the effect of rosin were determined by X-ray microdensitometry and CP–MAS ¹³C-NMR analysis.     

L450/316L不锈钢复合钢管对焊缝焊接接头组织性能研究

对壁厚(10+2)mm的L450/316L复合管进行了对焊试验,打底焊及过渡焊采用管内外充氩保护的GTAW焊,填充及盖面焊采用手工电弧焊,并对其焊接接头进行拉伸、刻槽锤断、弯曲、冲击、晶间腐蚀试验评价对焊焊缝的性能,采用光学、扫描电镜(SEM)及能谱分析(EDS)对焊接接头的冲击断口、显微组织及合金元素的进行扩散分析。试验结果表明:接头力学性能良好,耐晶间腐蚀性能较好;焊缝不锈钢层主要有奥氏体、铁素体组成;过渡层组织较细小,可以防止不锈钢层金属中合金元素被扩散层稀释;扩散层组织主要为马氏体、少量的残余奥氏体;合金钢层组织为先共析铁素体、针状铁素体、粒状贝氏体和及少量珠光体。     

Submerged friction stir weld of polyethylene sheets

The objective of this research work is to join polyethylene sheets using submerged friction stir welding by varying rotation speeds and traverse speeds. The effects of process parameters on macrostructure, microstructure, and mechanical property are investigated. The result indicates that the tensile strength increases at first and then decreases with the increase of rotation speed and traverse speed. The maximum tensile strength value of underwater welded joint is 12.3 MPa which is higher than normal weld joint. The microstructure of joint is investigated by using metallurgic microscope and laser scanning confocal microscope. The major microdefect of the interface is crack and air bubble. The result of differential scanning calorimetry which is used to measure the crystalline content of materials indirectly shows the crystalline content of parent material, heat affected zone, thermomechanically affected zone, and weld nugget approximate are 54.5%, 54.0% 51.1%, and 48.2%, respectively. The chief reasons of decrease in the tensile strength are formation of crack and air bubble and the decrease of crystalline content. The analysis of small angle X‐ray scattering indicates that the long period of weld regions decreases comparing parent material. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41059.     

Factors affecting the joint strength of ultrasonically welded polypropylene composites

Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and resultant high quality joints. An experimental study, based on the Taguchi orthogonal array design, is reported on the effect of different processing factors on the joint strength of ultrasonically welded composites, including weld time, weld pressure, amplitude of vibration, hold time, hold pressure, and geometry of energy director. Three materials were used in the study: virgin polypropylene, and 10% and 30% glass‐fiber filled polypropylene composites. Experiments were carried out on a 2000‐Watt ultrasonic welding unit. After welding, the joint strength of the composites was determined by a tensile tester. For the factors selected in the main experiments, weld time, geometry of energy director and amplitude of vibration were found to be the principal factors affecting the joint property of ultrasonically welded thermoplastic composites. Glass‐fiber filled polymers required less energy for successful welding than the non‐filled polymer. The joint strength of welded parts increased with the fiber content in the composites. In addition, a triangular energy director was found to weld parts of the highest strength for virgin polypropylene and 10% glass‐fiber filled polypropylene composites, while a semi‐circular energy director was found to weld the highest strength parts for 30% glass‐fiber filled composites.     

Comparative potential of alternative wood welding systems,ultrasonic and microfriction stir welding

Two alternative welding systems were evaluated for wood welding. Ultrasonic welding produces joints of good strength but it appears to be applicable only to thin wood pieces. It does not appear that further possible process improvement could bring the joint strength to a structural level. Microfriction stir welding does show potential for welding continuously wooden plates without any limitation on length of wood pieces. The strength of the weld obtained was low due to the limited depth of the weldline. Optimisation of parameters is necessary. A drawback at present appears to be the limited thickness of the wooden pieces that can be welded. X-ray micro densitometry, scanning electron microscopy and optical microscopy showed that the main difference compared to the other techniques is that in the microfriction stir weld, there is a veritable welded line of molten material. This molten material comes from the wood in contact with the rotating steel cylinder, which has flowed down in the micro gap between the two pieces of timber where it has bonded by solidifying.