1, preparation
The first step in the production process of MDF is to prepare materials. The equipment mainly includes chippers, belt conveyors, screening machines, bucket elevators, storage silos, etc. The raw materials for the production of MDF are mainly wood fiber. It includes small-diameter wood, branchwood, fuel wood, and processing residues. The ideal raw materials for preparation are 60% to 70% of coniferous wood, 30% to 40% of hardwood The skin content should not exceed 5%.
2. Preparation of fibers
Fiber preparation is mainly fiber separation, which is the core link of MDF production process. Fiber separation equipment includes wood chip silo (or preheating silo), small hopper, hot mill, paraffin melting and applying device, and sizing metering device.
Fiber separation steps:
A: Hot grinding. The qualified wood chips are conveyed into the wood chip silo, and after being softened by cooking, the wood chips are conveyed to the mill body. The wood chips are compressed by a hot mill, and moisture is squeezed out of the wood chips with a higher moisture content.
B: Apply wax. The paraffin is heated and melted by the steam coil, and the molten paraffin is driven into the wood chip before entering the grinding chamber through the pump pipe, and after being separated into fibers, the paraffin is distributed evenly on the fiber surface.
C: Sizing. The urea-formaldehyde resin is fed into the double-metering tank through the filter and the glue pump, and then fed into the discharge pipe to sizing the fibers. The fibers in the discharge pipe are in a high-speed flow state, and the glue solution is atomized and sprayed evenly on the fibers surface. The glue tank can be added with a curing agent, formaldehyde trapping agent, etc. for stirring.
3.Dry
The main equipment of the drying process of the MDF production process is composed of a drying host, a drying pipe and a cyclone separator, a fiber conveying device, and a dry fiber silo. The hot mill discharge pipe sucks the wet fibers of the drying pipe and fully contacts the hot air. The fibers are suspended in the air duct and transported by the airflow. The fiber runs in the air duct for 4 to 5 seconds, and the moisture of the fiber is quickly evaporated to meet the requirements. Water content (8% ~ 12%).
4.Forming
Pavement molding is a very important process in the production process of medium density fiberboard. This process includes the main parts of slab pavement, pre-compression, edge alignment, cross section, etc. The requirements for the pavement process are: uniform and stable slab density The thickness is consistent, and the weight control of the slab on the unit area is continuous and consistent, with a certain degree of compactness.
5.Hot pressing
The hot-pressing process for domestic manufacture of medium and high-density fiberboard is an intermittent multi-layer hot-pressing process. Various process factors have an important impact on the performance of MDF.
A: Hot pressing temperature. The selection of the hot pressing temperature is mainly based on the type and performance of the board, the type of adhesive and the production efficiency of the press. The selection of the temperature mainly depends on the comprehensive factors of raw materials, tree species, fiber moisture content, adhesive properties, slab thickness, heating time, pressure and equipment conditions.
B: Hot pressing pressure. The hot pressing pressure changes during the hot pressing process. When pressing, the pressure gradually increases to meet the slab thickness requirements, that is, the pressure should be reduced, and the curing of the adhesive, the formation of various bonding forces between the fibers, and the evaporation of water are mainly It is completed in the low-pressure section. The pressure in the low-pressure section is generally 0.6 to 1.3Mpa.
C: Hot pressing time. The determination of the hot pressing time is mainly related to the properties of the glue and curing time, fiber quality, slab moisture content, thickness, temperature and pressure of hot pressing and other factors. Hot pressing time is generally expressed by the time required for a 1mm plate thickness.
D: Moisture content of slab. In the hot pressing process, the role of moisture in the slab is to increase the plasticity and thermal conductivity of the fiber. Therefore, the appropriate moisture content guarantees the quality of the board, which is generally controlled at about 10%. If it is too high, it will cause the density of the surface and core layer. The gradient increases, the bonding force between the fibers of the core layer is poor, and the water vapor is difficult to remove during depressurization and exhaustion, which causes bubbling and delamination in the board. If it is too low, the board surface is soft, the pre-cured layer is thick, and the board strength is reduced.