Thomas M. Maloney
Thomas M. Maloney is Professor of Materials Science and Engineering and Head of the Wood Technology Section at Washington State University in Pullman. Washington, USA. He is the author of Modern particleboard and dry-process fibreboard manufacturing.
WOOD RESIDUES FOR PARTICLE BOARD chiefly from low-value tree species
With a small forest base, China must at present rely heavily upon foreign imports. An extensive reforestation/forestation campaign, if successful, could turn this situation around. In the interim, particle board - which can be made, in part, from non-wood residues - offers an attractive opportunity for developing the domestic wood products industry. In China today, particle board research and plant construction are thus moving ahead rapidly.
SUPPLYING A PARTICLE BOARD PLANT maximum wood utilization Is the goal
MANUFACTURING RESIN an extremely costly procedure
· The world's present production of particle board is about 40 million m3 a year. The industry has matured only in the past ten years, and its most rapid development has been in the industrialized nations. Together with the growth of this extremely practical form of utilizing wood in the manufacture of panels has come the development of new equipment, instrumentation and synthetic resins.
Particle board plants are especially attractive for countries with limited forest resources, since particle board is a product that can make maximum use of wood waste as well as of a variety of species that might not otherwise be profitably used. Such residues as flax and bagasse, for instance, can go into particle board. Therefore, forest-poor countries, industrialized and non-industrialized, would find these plants especially attractive. China, which has far too little forest to meet its wood needs, is one of, these, and thus the particle board industry there is in a period of rapid expansion.
In 1982 I had an opportunity to visit China as an FAO adviser in this field. What follows is a brief and partial summary of China's particle board industry, with a glimpse of what it is doing in the other panel board sectors, plywood and fibre-board. All the information was provided by the Chinese Academy of Forestry and is therefore official. An industry needs to be seen, first of all, in the context of a larger economy which includes the resources that are essential to its growth - or the scarcity of these same resources.
China today is in the midst of an extremely ambitious reforestation and forestation campaign. It remains to be seen whether or not the goals of this effort will be achieved. By the year 2000, the aim is that 20 percent of the country should be forested. Every Chinese citizen has been asked to plant a quota of at least four trees each year.
To understand how ambitious these targets are, it should be appreciated that at the time of the founding of the People's Republic of China in 1949, only about 8.6 percent of China's 9.6 million km- of land mass was forested. An extensive programme of tree-planting was undertaken, and as a result 12.7 percent of the country - 120 million ha - is now forested. Because of this. 50 million m3 of wood are currently available for the country's wood-using industries. In 1950 only 5 million m3 were available.
About 40 percent of the logs are used for lumber. They are mostly cut by very old mills, which are scheduled for modernization or replacement. In 1981, more than 100 000 people were employed in sawmills and wood-based panel; plants, with another 270 000 people working in furniture plants.
Table 1. Some current specification for particle board manufacture in China
|
Property |
Grade 1 |
Grade 2 |
|
Bending strength (kg/cm2) |
180 |
150 |
|
Internal bond (kg/cm2) |
4 |
3 |
|
Thickness swell (%) a |
6 |
10 |
a Water temperature 30 + 3°C, with the test taking four hours
Table 2. Estimated production of products and number of plants operating in China in 1982
|
Product |
Production in 1982 |
No of plants |
|
Sawnwood |
13.6 million ma |
unknown |
|
Plywood |
394000 m3 |
65 |
|
Fibreboard |
670000 m3 |
302 |
|
Particle board |
103000 m3 |
52 |
|
Furniture |
33 million pieces (1981) |
2100 |
Note: In China many factories have all three kinds of wood-based panel production lines The term plant as used here refers to that part of an integrated wood-products-manufacturing complex producing the particular panel product. Most of the plants are under the Ministry of Forestry but some are associated with the Ministry of Light Industry.
Most of China's wood-based panels are used for furniture. This is in contrast to the situation in the United States, Canada and other wood-using countries, where a high percentage of the panel products go into building construction.
A word should be said, first, about fibreboard and plywood industries.
China imported its first fibreboard mill in the 1950s, from Sweden. Since then, approximately 300 other plants have been built. All of them have been designed and built by the Chinese, and virtually all are of the wet-process type. A dry-process plant is operating in Shanghai.
The output of the fibreboard plants ranges from 2 000 to 5000 tonnes a year, which is quite small. However, this size is well suited to areas with scattered forest resources. An advantage of the wet process is that little or no resin is i needed to bind the fibres together in the board, an important consideration since synthetic resins are costly. These resins are a significant part of dry-process manufacturing.
At present, one medium-density fibreboard plant is operating. It is a converted dry-process fibreboard plant at Zhuzhou in Hunan Province and is producing about 10 000 m3 a year. A large new plant using foreign technology is under construction in Fujian Province. It will produce 50 000 m3 a year. A third plant is under construction at the Guangha Lumber Mill in Beijing. It also will use foreign equipment. Several other fibreboard mills are reportedly in the planning stages.
Productivity in China's plywood plants is low. It takes 40-50 working hours to produce 1 m3 of plywood in the better mills, and 60-70 working hours in most mills. The majority of, the panels are fairly thin, in the range of 9 mm. Plans include improving plant production, particularly as new forest is brought into commercial use.
There have been approximately 11 particle board plants operating in China since the 1950s. These! plants are relatively small, producing about 20 m3 of board a day. Even the larger ones have been producing only about 30 m3 a day.
Of the original plants, three are of the extrusion type. One of these, purchased from Switzerland, uses a horizontal extrusion system based on the American Lane process. The other two are vertical extrusion systems, of the OKAL type from the Federal Republic of Germany.
The standard platen-type particle board plants built earlier are of, Chinese design, and all the equipment was also produced by the Chinese. Some of the newer plants, however, are using foreign equipment. The largest new plant, now producing 100 m3 a day of the highest-quality particle board in China, is a single-opening press line imported from the Federal Republic of Germany. Another plant, with a capacity of 100 m3 a day, is under construction in Guangzhou. The main production machines are also being imported from the Federal Republic of Germany, the remaining equipment being of Chinese manufacture.
Two other plants of 50 m3 capacity a day are at present undergoing trial runs. One is in Hangzhou and the other is in Wuhan. Both are entirely of Chinese design, and the equipment is also Chinese.
To expand the particle board industry, the Chinese are developing designs for three different sizes of plants: 25, 50 and 100 m3 a day. The smaller plants are being designed for construction in the smaller communities throughout the countryside. The larger ones are scheduled to be built near forested areas, although some are planned for urban locations.
China has developed its own industry to produce equipment for particle board and hardboard plants. Most of the equipment is made in Kunming. The particle board press is manufactured near Xian in Qian Xian County, while the pressurized refiner for hardboard is produced in Shanghai.
The particle board equipment includes a 12-knife drum flaker, a 26-knife counterrotating ring flaker, an impact mill, a rotary dryer of the bundle-tube type a short-retention-time continuous blender, a weight scale for use with the blender, two- or four-head formers, a belt precompressor, a seven-opening hot press for making 1480-by 2 620-mm boards, a caul-plate return conveyor, a speed-up conveyor, and a cut-off saw for mats. The hardboard equipment includes a defibrator pressurized refiner of the single revolving disc type, a refiner with a 600-mm-diameter disc, a Fourdrinier board-forming machine, a board conveyor, a depressurizing and diluting unit for removing ferrous metal from chips, a 15- or 17-opening hot press with platens of 1 150 by 2 250 mm, and a press loader and unloader.
China is now preparing to offer its equipment for sale to other countries.
|
Particle board: what is it? Particle board is the generic term for a panel manufactured from lignocellulosic materials (usually wood), primarily in the form of discrete pieces or particles, as distinguished from fibres, combined with a synthetic resin or other suitable binder and bonded together under heat and pressure in a hot press by a process in which the entire interparticle is created by the added binder, and to which materials may have been added during manufacture to improve certain properties. Particle boards are further defined by the method of pressing. When the pressure is applied in the direction perpendicular to the faces, as in a conventional multiplaten hot press, they are defined as flat-platen-pressed; and when the applied pressure is parallel to the faces, they are defined as extruded. The composition board industry, including hardboard, insulation board, particle board (extruded and platen-pressed), medium-density fibreboard, cement-bonded board, and moulded products, is of very recent origin. No one has been able to coin a good, descriptive term acceptable to everyone for this relatively new branch of the forest products industry. These products were conceived in the laboratory and brought to fruition through laboratory research endeavours as well as pilot-plant development programmes. Thus, these industries are tied very closely to science and technology. Products made from comminuted wood materials in the shape of fibre, shavings and the many other possible types of particles have special appeal, as they can be - and mostly are - made from woodworking waste, noncommercial or low-value tree species, and agricultural wastes. Future considerations indicate that bark, forest-industrial and municipal refuse, and other agricultural wastes will go into similar building products. This development is also ecologically sound, as previously wasted material is now and will be going into useful products, thereby conserving our natural resources. Relatively small amounts of energy and petrochemical derivatives are needed for this industry. Composition board products do, at present, require small amounts of other raw materials such as synthetic resin adhesives, but these are conserved because minor amounts are needed in a board or product consisting primarily of wood. Development of adhesive systems from paper-industry wastes or other plant sources now seems likely. It does not make ecological sense to produce buildings entirely of non-renewable resources such as plastic or metal when wood is available. Present commercial products of comminuted wood have some very desirable characteristics: availability in large sheets, smooth surfaces, uniformity in properties from sheet to sheet, and freedom from localized defects. However, such products have been largely excluded from primary structural uses because they have been unable to approach the longitudinal stiffness, dimensional stability, and long-term load-carrying ability of sawn lumber or plywood. Changes in construction design can accommodate many of the present products, but this has not occurred to any extent yet. Adapted from Modern particleboard and dry-process fibreboard manufacturing by T.M. Maloney |
PREPARING THE MATS an upgrading of China's technology
GAUL PLATES ON HIGH-DENSITY OVERLAY LINE: an expansion of Chinese particle board
The Institute of Wood Industry in the Chinese Academy of Forestry is the national research centre for all types of forest products. Until recently, its research efforts in the area of composition boards of all descriptions were somewhat limited because of the lack of equipment. However, the laboratory has been rapidly developed within a very short period. The particle board, laboratory, in particular, should be one of the better ones in operation.:
The laboratory is already built, and laboratory equipment is being, installed. This equipment includes machines imported from the Federal Republic of Germany. Key pieces of equipment are a drum flaker, a ring flaker, a chipper, a screen, a blender, an air-classifying mat former, and a hot press. Some new testing equipment has also been purchased to complement the testing machines already in place.
As mentioned previously, the major use of particle board in China is for furniture. Extensive research work is planned to upgrade the quality of the product being used for furniture as well as to bring other species of wood and non-wood agricultural waste into use as particle board raw material.
At present, there is no standard conditioning established for testing. However, a new standard is close to being completed, and conditioning procedures will be established for the various tests. Also included in the new testing standard will be edge- and face-screw-holding measurements. At present, there is no testing for linear expansion.
VENEER OVERLAY ON PARTICLE BOARD finding products besides furniture
As China gains more wood resources through its reforestation efforts and through international trade, it plans to consider a number of other products similar to particle board for manufacture. These include moulded particle board, oriented strand board, and composites of veneer and particles. The composite of veneer and particles could be extremely important in expanding China's panel production for furniture.
For the most part, the species available for use in manufacturing particle board for furniture are relatively dense. This can make it extremely difficult to provide boards with very smooth surfaces. As noted earlier, plywood production is fairly low because of a lack of veneer. The veneer, however, does provide a very good substrate for the surface of panels used in the furniture industry. The combination of veneer for panel faces and the relatively high-density particles for panel cores offers the possibility of stretching the supply of veneer and producing better panels for furniture than when considering particles alone. Also of interest is the use of particle-board-type components for various types of building construction. All this is being investigated elsewhere in the world at present, and certain products are already in production. China wants to investigate as many products as possible to see whether they will fit into the domestic building market and whether their manufacture would be the most advantageous use of forest resources.
As China opens its door to other countries, trading not only goods but knowledge, a great expansion of the particle board industry is expected. New technology is being developed within the country, other technology is being adopted as it is developed elsewhere in the world, an important new laboratory is starting operation to enhance particle board development, and a broader knowledge of the uses of particle board for materials other than furniture is developing throughout the country. In addition, extensive work is being performed on synthetic resins and other bonding systems to enhance the bonding of the resins to the wood and to develop lower-cost bonding systems. There is no doubt of China's will to rapidly expand its particle board industry.
