1. Material preparation
The first step in the production process of MDF is material preparation. The mdf sheet manufacturer equipment mainly includes chippers, belt conveyors, screening machines, bucket elevators, storage bins, etc. The raw materials for MDF board production are mainly wood fiber raw materials, which include small-diameter wood, branch wood, firewood, and processing residues. The ideal raw materials for preparation are 60% to 70% of coniferous wood, 30% to 40% of hardwood, and tree The skin content should not exceed 5%.
2. Preparation of fiber
Fiber preparation is mainly fiber separation, which is the core link of the mdf panelling production process. The 8mm mdf equipment used for fiber separation includes wood chip silo (or preheating silo), small hopper, heat mill, paraffin wax melting and applying device, and sizing metering device.
Steps of fiber separation:
A: Hot grinding. The qualified wood chips are transported into the wood chip silo, and the wood chips are delivered to the mill body after being steamed and softened. The wood chips are compressed by the heat mill, and the water is squeezed out from the wood chips with higher moisture content.
B: Apply wax. The paraffin is heated and melted by the steam coil, and the melted paraffin is pumped into the wood chips before entering the milling chamber through the pump pipe. After being separated into fibers, the paraffin wax is more evenly distributed on the fiber surface.
C: Glued. The urea-formaldehyde resin passes through the filter and the glue pump into the double metering tank, and then the pump is input into the discharge pipe to sizing the fiber. The fiber in the discharge pipe is in a high-speed flow state, and the glue is atomized and sprayed on the fiber evenly. surface. A curing agent, formaldehyde trapping agent, etc. can be added to the glue tank for mixing.
3. Dry
The main equipment for the drying process of the 18mm mdf sheet production process consists of a drying host, a drying pipeline, a cyclone separator, a fiber conveying device, and a dry fiber silo. The discharge pipe of the heat mill sucks the wet fiber in the drying pipe and fully contacts the hot air. The fiber is suspended in the air pipe and transported by the air flow. The fiber runs in the air pipe for 4 to 5 seconds to quickly evaporate the moisture of the fiber to meet the requirements. Water content (8%~12%).
4. Forming
Pavement forming is a very important process in the production process of medium density fiberboard. This process includes the main parts of slab paving, pre-compression, edge alignment, cross-section, etc. The requirements for the paving process are: the slab density is uniform and stable , the thickness is consistent, the weight of the slab per unit area is controlled continuously and consistently, and it has a certain degree of compactness.
5. Hot pressing
The hot pressing process for domestic manufacturing of medium and high density fiberboard is an intermittent multi-layer hot pressing process, and various process factors have an important influence on the performance of 4x8 mdf.
A: Hot pressing temperature. The choice of hot pressing temperature is mainly determined by the type and performance of the board, the type of adhesive and the production efficiency of the press. The selected 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. The pressure gradually rises when the pressure is applied to reach the thickness of the slab, 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 It is completed in the low pressure section, and the pressure of the low pressure section is generally 0.6~1.3Mpa.
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, pressure and other factors of the hot pressing. The hot pressing time is generally expressed by the time required for 1mm plate thickness.
D: The moisture content of the slab. In the process of hot pressing, the effect of moisture in the slab is to increase the plasticity and thermal conductivity of the fiber, so the appropriate moisture content can guarantee the quality of the board, 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 core layer fibers is poor, and the water vapor is difficult to remove when the pressure is reduced, resulting in bubbling and stratification in the board. If it is too low, the board surface will be soft, the pre-cured layer thick, and the board strength will be reduced.