The entire manufacturing process consists of several key steps: fiber separation, slurry treatment, slab forming, hot pressing, and post-treatment. First, fiber separation, which is also known as pulping. This step involves breaking down raw materials into individual fibers. There are two primary methods for achieving this: mechanical and explosive. The mechanical approach further divides into thermal mechanical, chemical mechanical, and purely mechanical methods. For instance, the thermal mechanical method pre-treats raw materials with hot water or steam to soften the intercellular layers, making them easier to separate using mechanical force. Afterward, the material undergoes a refining process in a disc refiner to produce finer fibers. This method yields fibers with excellent interlocking properties and high water drainage, with a yield of up to 90-95% for softwood. However, excessive refining can shorten fiber length and increase specific surface area, leading to some loss in strength.
Meanwhile, the chemical mechanical method uses a small amount of chemicals like caustic soda or sodium sulfite to weaken lignin and hemicellulose before mechanically processing the material. The pure mechanical method simply grinds the soaked raw material directly into pulp, but it's less commonly used. The explosive method involves heating the raw material under high pressure for a short period to soften lignin and partially break down carbohydrates, followed by rapid decompression to blast the material into smaller fibers. Next, slurry treatment focuses on enhancing the final product's properties based on its intended use. Waterproofing, reinforcement, fire resistance, and防è…treatment are all part of this step. Hard and semi-hard fiberboards benefit from paraffin emulsion treatments to improve water resistance, whereas soft boards often incorporate both rosin and paraffin-rosin emulsions. These additives can be applied either in the slurry tank or via a continuous glue box. Reinforcement typically employs water-soluble adhesives that bond well with fibers during hot pressing, with phenolic resin glues being common for hard fiberboards. Fire-retardant agents like FeNH4PO4 and MgNH4PO4 are frequently added, and pentachlorophenol or its copper salts serve as preservatives. After treatment, the slurry may be dried or directly fed into a molding machine for wet forming if kept at the right consistency. Dry fiberboard production requires a moisture content of 6-8% for hot pressing and 40-60% after sizing, necessitating prior drying. Two-stage drying processes achieve these levels, first reducing moisture to 20% at 160-180°C, then to 6-8% at 140-150°C over approximately 12 seconds. Equipment options include straight tube, pulse, and jacketed types. Slab forming occurs via wet or dry methods. Softboards and most hardboards use the wet method, while medium-density boards and some hardboards opt for dry forming. Wet forming relies on low-concentration slurries that gradually dehydrate to form slabs. Methods include box-frame molding, long-net molding, and rotary-net molding. Box-frame molding involves pumping slurry into a bottomless frame placed on a mat, followed by vacuum and pressure dehydration. Long-net molding resembles paper-making machinery, where the slurry is poured onto a long net to form a wet slab by natural and vacuum-assisted dehydration, leaving it at 65-70% moisture. Rotary-net molding, inspired by paper technology, uses vacuum to deposit the slurry onto a circular net, which is then rolled to remove excess water and adjust slab thickness.
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