Hot pressing is a key process in particleboard production. Its function is to solidify the glue in the slab and pressurize the loose slab.
Consolidated into sheets of specified thickness. Its process requirements are:
① Appropriate moisture content. When the surface moisture content is 18~20%, it is beneficial to improve the flexural strength, tensile strength and surface finish.
Reduce the possibility of slab bubbling and delamination during pressure relief. The moisture content of the core layer should be appropriately lower than that of the surface layer to maintain appropriate plane tensile strength.
② Appropriate hot pressing pressure. Pressure can affect the contact area between shavings, sheet thickness deviation and the degree of glue transfer between shavings.
According to the different density requirements of the product, the hot pressing pressure is generally 1.2~1.4 MPa.
③ Appropriate temperature. Excessive temperature will not only decompose the urea-formaldehyde resin, but also cause the slab to partially solidify in advance when the temperature rises, resulting in waste.
④ Appropriate pressurization time. If the time is too short, the middle layer resin will not be fully cured, and the elastic recovery of the finished product in the thickness direction will increase.
The plane tensile strength is significantly reduced. The hot-pressed particleboard should undergo a period of humidity control treatment to bring the moisture content to a balanced state.
After sawing and sanding, inspect and package. However, hot stacking is not allowed after pressure relief, otherwise the brittleness of the plates will be increased.
Molding technology refers to the technology that forms a product in one operation. There are three mature processes. Hot molding can use less or no glue.
It relies on the activation and flow of lignin in a closed hot mold to act as a glue, but it requires cooling to demould, which consumes a lot of heat and has low productivity.
Gradually phased out. The box forming method uses a special press to pressurize the product, and then press it once to make the product, which is used to make packaging boxes.
To manufacture furniture accessories, interior decoration accessories, pallets and other products, the adhesive is mainly urea-formaldehyde resin, and the surface of the product is made of veneer or tree.
Grease impregnated paper is pasted and molded in one step. In addition, there are also molds used on the surface of the particleboard that has been made, or the formed slab that has not been hot-pressed.
The plate is pressed to form a flat molding method with a relief pattern, etc.
