Production Technology of Plywood for Container Floor
Container transportation has been developing rapidly because of its advantages such as rapid handling, convenient transportation, small loss of goods and easy implementation of port transport mechanization. At present, the number of containers in the world has reached 100 million.
Container transportation is developing rapidly because of its advantages such as rapid handling, convenient transportation, small loss of goods and easy implementation of port transport mechanization. At present, the number of containers in the world has reached more than 100 million, and it is growing at the rate of 6% per year. The plywood used to expand, supplement and update the container floor is also more than 400,000 m3 per year. There are nearly 40 container factories in China. In 1997, the production capacity was 700,000 standard boxes per year, and the plywood needed was about 260,000 m3. At present, domestic plywood for container floor is mostly imported from abroad. If the domestic production of plywood for container floor can be realized, it will not only benefit the development of domestic plywood industry, but also save a lot of foreign exchange for the country.
The plywood used for container floor is a special plywood after epidemic prevention treatment. It must meet the international standards of health and epidemic prevention and the relevant physical and mechanical strength index requirements at the same time. The purpose of this project is to determine the production process and parameters of plywood for container floor which can meet the above requirements through experiments.
1 Materials and Methods
Veneer species and combinations: Dipterocarpus spp., Betula, Clone and Nanyang miscellaneous trees, Dryobalanops and Nanyang miscellaneous trees.
Size of veneer: small trial veneer is 800 mm x 800 mm x 1.85 mm; moisture content of veneer is less than 8%. The veneer for production test is 2 540 mm x 1 270 mm x 1.85 mm, and the finished product size is 2 440 mm x 1 220 mm x 28 mm.
Adhesive: Water-soluble phenolic resin made in China. The technical specifications are as follows: dark brown transparent viscous liquid with solid content of 50%-52%, viscosity of 120-200 Engrad degree (20 C) and free phenol content of less than 1%.
Filler: Common flour.
Preservatives: Imported SB-88 preservatives are used. Appearance is light brown liquid, containing rich coxim active ingredients, soluble in adhesives, and has good permeability to wood.
1.2 Test Method
Composition method: plywood is composed of 17 layers of veneer with equal thickness. The surface layer is composed of one layer of veneer with parallel grain, two layers of veneer with parallel grain and three layers of veneer with parallel grain. The middle layer is composed of common plywood with adjacent layer veneer with vertical texture.
Manufacturing process: veneer glue amount (double side) and plywood hot pressing process parameters are determined by orthogonal test of 4 factors and 3 levels. The other process parameters are determined by referring to ordinary plywood production process. Adhesives are formulated with a fixed ratio of resin to flour to preservatives = 100:10:2.6.
2. Process conditions and inspection standards
2.1 Process Flow
Preservative + Flour + PF Resin Mixing
Log cutting rotary cutting veneer drying finishing gluing billet hot pressing sawing sanding inspection storage
2.2 Test Method
The quality indicators of plywood for container floor are tested according to the following standards:
Appearance Size GB9846.3-88 “General Plywood Size and Tolerance Technical Conditions”;
Moisture Content GB9846.1-88 “Determination of Moisture Content of Plywood”;
Air-dry density: GB1 933-85 “Determination of wood density”;
Gluing Strength GB9846.12-88 “Determination of Gluing Strength of Plywood”;
Static Strength and Elastic Modulus ZBB 7006-88 Plywood for Concrete Formwork;
Quarantine Regulations for Freight Containers, Australia;
Bottom Strength GB 5338-85 “Technical Conditions and Test Methods for 1A, 1AA, and 1AX Universal Containers”.
3. Test results and analysis
3.1 Determination of glue amount and hot pressing process
Bonding strength is one of the main quality indicators of plywood used for container floor. The main influencing factors are glue amount, hot pressing time, hot pressing pressure, hot pressing temperature and the cross-influence of four factors. The four factors mentioned above were taken as factors, and three levels were selected for each factor. The experiment was carried out according to L9 (34) (Table 1). The way of forming blanks was the same as that of ordinary plywood. The test results are shown in Table 2.
The results of Table 2 show that: (1) according to the magnitude of range, the factors affecting bonding strength are glue amount, hot pressing pressure, hot pressing time and hot pressing temperature in turn; (2) among the four factors, the third level is the most favorable for bonding strength, that is, when the amount of glue is 420 g/m2, hot pressing time is 30 min, pressure is 1.4 MPa, and temperature is 145 C, the bonding strength of plywood is the highest; (3) Considering that the bonding strength is guaranteed. Under the premise of 0.7MPa, the smaller the amount of glue coating, the lower the cost, the shorter the hot pressing time, the higher the production efficiency, the smaller the hot pressing pressure, the less the wood compression loss and the lower the hot pressing temperature, the less difficult the operation is. Therefore, the fifth set of test conditions should be selected for reasonable process parameters: 400 g/m2, 28 min, 1.4MPa, 135 C.
3.2 Selection of Surface Single Slab Block Structure
In order to improve the static bending strength and elastic modulus of plywood parallel to the texture direction of the surface plate, this experiment adopts the method of forming blanks whose surface is arranged in the same direction by several layers of veneers and the texture of the surface plate, in order to strengthen the strength along the texture direction of the surface plate, i.e. the combination of one layer, two layers and three layers of veneers is selected respectively to press the glue for the container bottom plate.
From Table 3, it can be seen that the static bending strength and elastic modulus of plywood can meet the requirements when using three-layer parallel veneer in three kinds of surface veneer structure combinations, which are consistent with that of plywood used for container floor in Japan, Korea, Malaysia and other countries.
3.3 Selection of Tree Species
At present, plywood imported from Korea and Malaysia is made of clones. Most of the structural boards used in concrete formwork in China are made of Nanyang miscellaneous wood, and some special plywood (such as springboards for sports and Aeronautical boards) with high strength in China are made of birch wood. In view of the above situation, this experiment selected four combinations of tree species for comparative test. According to the technological parameters determined by the orthogonal test, the mechanical properties of 17 plywood with a pressing width of 800 mm * 800 mm and a surface of three-layer laminated veneer composite structure were compared (Table 4).
From the results of Table 4, the plywood used for container floor made of four species of wood and their combinations all have good mechanical properties and meet the requirements of product use, among which clone and birch plywood are the best. Considering the high price of imported clone timber, birch is also restricted by the cutting of the state. For example, clone or camphor veneer is used as the surface board and Nanyang miscellaneous veneer is used as the core board, which is low in cost and meets the requirements of use and is a more reasonable combination mode.
3.4 Preservative dosage
According to Australian Quarantine Regulations for Freight Containers, the retention of SB-88 in plywood must be more than 2.8kg/m3. Because of the high price of preservatives, they should be used as little as possible on the premise of ensuring the retention of preservatives. Experiments show that resin, flour and preservatives can be formulated at 100:10:2.5 based on the average coating amount of 400 g/m2 and the process loss of adhesives by 3%. If the insurance factor is taken into account, the ratio of 100:10:2.6 can be used in production.
3.5 Productive test
Productive batch tests were carried out on the basis of small scale tests. The size of the product is 2 440 mm *12 20 mm *28 mm, clone for surface board and Nanyang miscellaneous wood for core board. Three layers of parallel veneer on the surface and each layer of veneer in the middle are arranged in a crisscross texture arrangement. The mixing ratio is the same as the small test, and the glue amount and hot pressing process are carried out according to the fifth group of process parameters determined by the small test.
Product inspection is carried out by the relevant state departments. Inspection items:
(1) The retention of preservatives was 2.91 kg/m3 determined by the National Health and Quarantine Administration, which met the requirements of the Australian standard of 2.8 kg/m3.
(2) The maximum permanent deformation of plywood is determined by Shekou Ship Inspection Bureau. The product inspection value is 1.0 mm, which is lower than the requirement of national standard 3.0 mm.
(3) The appearance dimensions are determined by the technical departments of the manufacturers such as Shekou Container Co., Ltd. The results are shown in Table 5.
(4) The National Center for Quality Supervision and Inspection of Physical and Mechanical Properties of Wood-based Panels was completed. The results are shown in Table 6.
1) The main performance indexes of plywood for container floor can meet the quality standards of similar products abroad and the relevant national standards at home under the conditions of 400 g/m2 glue coating, 135 C, 1.4 MPa, 28 min hot pressing and other ordinary plywood production processes.
2) The three-layer parallel-grain structure of clone veneer on the surface and Nanyang miscellaneous veneer on the other layers are combined with ordinary plywood structure, which can meet the special requirements of static strength and modulus of elasticity of container floor and greatly reduce production costs.
3) Adhesives are formulated according to resin:flour:preservative ratio of 100:10:2.6 and the amount of glue applied is strictly controlled to ensure the retention of necessary preservatives.