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1 1 Classification of finger joints
The finger jointing gluing material is mainly made of small diameter material as raw material, and has a certain width, thickness and length made by a series of processes such as plate material preparation, drying, finger jointing, gluing and post-processing. It is a new type of substrate widely used in the construction industry, furniture industry and decoration industry. It can be divided into two categories according to its use.
1 1 1 Non-structural laminated timber
Non-mainly stressed parts, suitable for the decoration and furniture industry, can be used to make wall panels, ceilings, floors, furniture and other parts.
1 1 2 Structural glulam
Parts or products that are subject to major loads are mainly used in the construction industry, small and medium-sized engineering bridges, etc., for the production of large beams, columns, trusses, arched roofs, and irregular shaped load-bearing parts.
1 2 Characteristics of finger jointed laminated timber
1 2 1 Physical and mechanical properties Good finger jointed material is stable, the strength is 1~15 times of natural solid wood, and the ratio of strength to weight is large. The weight ratio of the dry wood with a bulk density of 0 3 8g/cm3 is 3 1 5 8 , while the steel is 57 7 , the aluminum is 70 3 , and the hard PVC is 42 5 .
1 2 2 The variation of the product format and section size is larger than that of other wood-based panels. The finger-jointed laminated material has a more flexible format and cross-sectional structure. The maximum cross-sectional area of ​​the product is over 1 square meter. The maximum size of the beam or truss exceeds 50 meters, and the maximum diameter of the wooden structure can exceed 70 meters, so it will be more adaptable to the market.
1 2 3 Good fire performance
The carbonized layer formed after combustion has a deflagration effect, and its carbonization rate is from 0 6 to 8 8 mm/min, and as the thickness of the carbonized layer increases, the carbonization rate decreases, and at a high temperature of 80 ° C, there is still 75% of the section. It is not carbonized, so its stagnation performance is better than steel, and the wood itself is easy to carry out “three-proof†treatment of “fireproofâ€, “insect-proof†and “waterproofâ€, which can improve its weather resistance and service life.
1 2 4 Good insulation performance
Low heat conduction, energy saving, and humidity control and temperature adjustment function. It is an ideal material for indoor use. For example, the conductivity of dry wood with a bulk density of 0 3 8g/cm3 is 0 0 95w/m·k and the conductivity coefficient of steel is The conductivity coefficient of concrete which is 45 times that of wood and whose bulk density is 2 2g/cm3 is 17 times that of the wood.
1 2 5 Low investment risk
Since the finger jointed laminated timber is an important substrate for the construction industry, the decoration industry, furniture and other industries, the product application field is broad, and its market adaptability and competitiveness are strong, which determines that the investment risk of the product is low.
2 Finger joints production technology research
The finger jointing production process mainly includes the following parts: the plate material preparation section, the drying section, the finger joint preparation section, the finger joint section, the glue joint section, and the post-processing section.
2 1 plate material preparation section
The equipment of this section is mainly composed of a sports car woodworking band saw, a rotary cutting machine, a main small band saw and a split circular saw, and a truncated circular saw. The board material preparation section is mostly located near the forest area, which is equivalent to an independent material workshop.
At present, China's timber equipment and production technology level generally lags behind the advanced level of foreign countries. The original Ministry of Forestry issued standards, the grade qualification rate should reach 95%, and the specification qualification rate should reach 84%, but most of the timber enterprises and workshops. If this requirement is not met, the qualification rate of the specification material is below 50%, and the grade qualification rate is 60% to 70%. Therefore, there is still a great potential for the improvement of the quality of the sawn timber. The material manufacturing process of small-diameter material is different from the traditional large- and medium-diameter material-making technology. There are differences in the equipment configuration and the sawing method. If the small-diameter material is sawed by the traditional method, the yield rate is only 30%. ~ 40%, and the special sawing method can achieve a yield of 50% to 60%, and can improve the comprehensive use value of wood.
There are four main types of sawing methods for small-diameter materials.
2 1 1 Orange petal sawing method
First, the small diameter wood is first cut into a certain length, and then spiraled into a cylinder. First saw into four open materials, and then into the orange petal shape, and then turn the orange petal shape upside down, along the length of the surface and face glue together, into any width of the laminated material (Figure 1) The sawing method can overcome the disadvantages of large-scale wooden tip sharpening. The material surface can be free from knots and other defects, and the structure is strong.
Figure 1 Orange petal sawing method
2 1 2 One of the trapezoidal sawing methods is to cut the small-diameter material into short wooden sections, and then spin them into a cylinder of the same diameter, and then use a band saw to obtain a curved side of the side, generally Three kerfs, the diameter is slightly larger, and the part is 5 kerfs. The upper and lower sides of the trapezoidal material are aligned with each other upside down, and the sizing side is put together to obtain a plate of a certain width (Fig. 2).
Figure 2 One of the trapezoidal sawing methods
2 1 3 The second method of trapezoidal sawing is to first saw the thicker edge board from the sides of the log, not to cut the edge vertically, but to cut the edge into a bevel (or milled edge) to become a sloped ladder. The material of the plate is trapezoidal, and the end of the material is an isosceles trapezoid. The wide end of the cut plate and the narrow end of the upper and lower faces are transferred together to form a plate of any width. It is especially suitable for small-diameter wood with large sharpness. It not only reduces the loss of wood during normal trimming, but also overcomes the disadvantages of large-scale wooden tip sharpening. The yield can be greatly improved, such as the end of the sheet. The head and the end finger are glued and can be made into plates of any length (see Figure 3).
Figure 3: The trapezoidal sawing method
In addition to the sawing method directly affecting the yield rate, the specification of the material grade, the quality of the sawing machine, the precision, and the elimination of defects before sawing are also extremely important, which will have an impact on the yield and quality of the sawn timber. 40 cm or more and 6 cm or more thick 2 5 to 3 2 cm
2 2 drying section
Compared with large and medium-diameter materials, small-diameter materials often have large differences in material properties. Small-diameter materials generally contain more inclusions and often have a core. The small-diameter material has a large growth stress, so its bending rate is large and the oblique texture is large. Therefore, the small-diameter material is prone to warpage deformation and cracking during the drying process. In order to ensure the qualified rate of the product after drying, a medium-low temperature dehumidification drying process is often used. Conventional high-temperature steam drying process, the waste rate of hard wide material exceeds 8%, the drop rate exceeds 6%, the wood loss is serious, and the heat pump type dehumidifying dryer can be controlled within 3% to 5%, but the dehumidification drying cycle is more Long, generally 2 to 25 times as much as conventional steam drying. The dehumidifying and drying process mainly includes two aspects: stacking method and drying standard. Since the effective drying volume has been determined when purchasing the dehumidifying dryer, the optimum kiln volume can be determined. The following are only the stacking method and the drying standard. Discuss it.
2 2 1 Stacking method
The wood surface is well ventilated, the heat dissipation is uniform, and the spacers and plates are evenly stacked.
Compartment thickness: 2 ~ 4 cm
Sheet thickness: 2 to 6 cm
Spacer width: 3 to 5 cm
Spacer spacing: 0 3 ~ 1 mm
The distance between the bottom of the pile and the ground: 10 ~ 15 cm
The distance between the pile and the top of the drying kiln: 80 cm.
2 2 2 Drying benchmark
In the production of laminated timber, it is best to use a medium temperature dehumidification dryer with a maximum temperature of 60 ° C. The drying process is theoretically divided into three stages, but the actual operation is a whole process.
(1) Preheating stage
At this time, the moisture content of the wood is more than 50%, which is higher than the fiber saturation point, and mainly free water.
Medium temperature: 45 ~ 60 ° C
Dry and wet bulb temperature difference: 1 ~ 2 ° C
Preheating speed: 2 ~ 2 5h / mm
Relative humidity: 80% to 90%
(2) Drying stage
The moisture content of the wood is reduced to 8% to 10%. At this time, the dry deformation is most likely to occur. Pay attention to controlling the moisture content gradient and the temperature and humidity in the kiln to ensure the drying quality.
Medium temperature: 3 5 ° C ~ 60 ° C
Relative humidity: 80% to 40%
Maximum temperature difference: 10 °C ~ 1 2 °C
(3) conditioning stage
When the water content in the center of the wood or near the center reaches the final water content, the water content gradient increases, resulting in increased stress and deformation. At this time, the temperature difference between the wet and dry bulbs should be reduced to increase the humidity in the kiln. Under normal circumstances, The humidity control time is about 24 hours, and the product qualification rate should be greater than 95%.
2 3 Finger joint preparation section
After drying, the plate material is first cut off by high-speed cutting machine to eliminate all kinds of defects, and then thickened by double-sided planing and thickened, then enter the precision multi-saw saw for longitudinal section. The following problems should be paid attention to in this section. .
2 3 1 Strictly eliminate defects according to enterprise standards or user requirements, without taking the next process
2 3 2 Although it is a preliminary machining, it should also ensure the machining accuracy, the dimensional tolerance is within the standard range, the length is not limited, the thickness tolerance is less than ± 1 mm, and the width tolerance is less than ± 15 mm.
2 4 Finger jointing section
It mainly includes milling, gluing, pressurizing and four-sided planing. The first three processes can be completed in one-time on the automatic finger jointing machine. It can be manually fed and discharged. Four-sided planing requires four or more planes. Cutting machine to ensure processing accuracy.
2 4 1 Selection of tooth parameters
The tooth profile parameters include tooth length h, tooth tip width b, pitch t and slope θ, and the relationship between them is: tgθ=(t-2b)/ 2h
Tooth length h: domestically generally 10 to 12 mm, while Japan and the United States, etc.
The difference is fine, the structural laminated material is more than 12 mm, non-structural integration
The material is 5 mm.
Tip width b: generally 0 2 ~ 27 mm
Slope θ: generally 1 / 7 5 ~ 1 / 1 1
Pitch t: generally 3 to 4 mm.
These four tooth parameters are related to each other and affect each other. They should be considered in terms of finger joint strength, machining accuracy, and tool life.
2 4 2 Glue
Mechanically or hand-painted two liquid glue or other rubber type, the amount of glue is 2 50 ~ 300g / m2.
2 4 3 Pressurization
The finger joint strength increases with the increase of the pressurizing pressure. The pressure is related to the length of the gums and the water content. Generally, the short teeth are broad and the material is 80 to 140 kg/cm2, and the long teeth are connected: the coniferous material, 20~ 3 0kg/cm2, hardwood material 2 5～3 5kg/cm2 Lateral pressurization pressure: 2 0～3 0kg/cm2 Pressurization time: 4～6s Maintenance time: 2 4h
2 4 4 four-sided planer
In order to improve the quality of the glue and reduce the amount of sanding work, the finger joints must be cut in four sides. The planing margin and accuracy are as follows:
Width direction: 3 mm, accuracy 0 2 mm
Thickness direction: 2 mm, precision 0 2 mm
2 5 glue and post-processing section
2 5 1 glue fight
After the finger-joined materials are sorted by color difference and material type, firstly, the glue is applied on the glue applicator, the glue amount is 2 50 to 300 kg/cm 2 , and after 20 minutes of aging, the pressure splicing is performed on the jigsaw machine. , the parameters are as follows:
The pressing pressure is hard and wide: 1 2～1 5kg/cm2
Softwood: 7～10 0kg/cm2
Pressurization time: 30 to 50 minutes
Curing time after pressurization: 2 4h
The temperature is low, the pressurization time is prolonged, and the reverse is shortened. After curing, the post-processing can be carried out. The adhesive is made of two liquid or cold pressed urea-formaldehyde glue, and the export product generally requires water-based polyurethane glue. The integrated material produced by water-based polyurethane adhesive is popular in foreign countries mainly because it does not contain harmful substances such as formaldehyde and phenol. The adhesive layer is non-toxic and harmless after curing; water resistance, heat resistance and aging resistance are excellent; initial tack is strong, curing Fast speed and high adhesive strength.
2 5 2 Post-processing
The post-processing is mainly sanding, inspection, etc., using double-sided sanding, sanding allowance of 2 mm, graded according to surface quality.
3 Conclusions and recommendations
3 1 Finger jointed laminated timber is one of the most effective technologies for comprehensive utilization of small-diameter materials. As a new type of substrate, it has broad development prospects.
3 2 Finger jointing material technology and drying process are the key factors affecting production cost. Different diameter grades should adopt different sawing methods, and drying process parameters should be adjusted at any time according to actual conditions.
3 3 Further strengthen the development of domestic equipment and improve the cutting precision and automation strength of the products.
3 4 Try to establish national standards for finger joints to regulate market competition and guide production.
Nie Tao (Jiangxi Architectural Panel Research Institute Nanchang 3 3 0 0 0 1 )
1 Classification and characteristics of finger joints