English 
Multilayer hot press is also a kind of plywood machine. The multi-layer hot press is characterized by high production efficiency, wide thickness range, and easy control and adjustment of equipment. However, its structure is complex and large, and it must be equipped with a board loading and unloading system. Generally, a cold press is also required, and the board thickness tolerance is large and the hot pressing cycle is long. The main technical performance indicators of the hot press are: hot press size (length x width x thickness) (mm), number of layers of the hot press, distance between the hot press plates (mm), nominal pressure (MN), closing speed (s), Heating medium, number of cylinders, cylinder diameter (mm), predetermined working pressure of hydraulic system (MPa), external dimensions (length x width x height) (mm)) and net weight (t) of the main machine. The production output of the hot press mainly depends on the number of layers and the size of the hot press. Different products have different hydraulic systems for the hot press. For example, in the production of plywood, the nominal pressure of the hot press can be lower. The heating medium is heated by hot water, but oil heating is increasingly used recently. Steam heating is difficult to maintain the constant high temperature required for the entire platen surface. Using oil as the heating medium, the heat press can be heated to more than 200 without difficulty, thereby reducing the pressure of the pressurization.
In the original working position, the pressing plates of the hot press are all turned on, and the top layer of the plate loading machine is on the horizontal plane of the slab conveyor. When the slab is sent to the loading machine via the conveyor, the loading machine rises one layer, so that each layer rises one layer. When each layer is loaded with slabs, the loading machine (or other devices) will The billets are fed into the hot press together. Then, the oil cylinder of the hot press machine closes the hot press plate through the downward movement, and hot presses the slab. While hot pressing, the loading machine quickly descends to the level of the top layer and the slab conveyor, and continues to load the slab. When the hot pressing is over, the hot pressing machine is turned on and the plate loading machine is just in place. The loader (or other device) sends the slabs into the hot press again, and at the same time, pushes the pressed plates out of the hot press, and sends them to the unloader (or use a special method on the unloader to pull the plates out of the hot press. press). The hot press is closed again, the plate loading machine is quickly lowered, and the plate unloading machine moves to the next layer to unload the pressed plates. This repeated action forms continuous automated production.
In order to make the hot pressing conditions of each layer of the slab in the hot press be consistent, and do not eject the shavings or fibers in the slab during fast closing, a simultaneous closing device should be used. At the same time, a key problem of the closing device is to compensate the hot plate between The thickness of the blank changes. If this thickness change cannot be compensated, stress will be generated in the supporting device of the corresponding hot press plate. This stress can usually be balanced by oil pressure compensation.
Thickness gauge is the main working element to control the thickness of each layer of particleboard. Generally installed on both sides of each layer of hot pressing plate. At present, most domestically produced hot presses use thickness gauges or add four-corner limit control devices. However, the thickness gauge is made of steel, and long-term use or improper control of the hydraulic system can easily cause damage to the hot plate. Therefore, some current hot presses use a positioning controller, that is, an LVDT linear displacement sensor, to control the total distance of the hot press, and the thickness gauge only serves as an auxiliary control thickness. Install 4 sets of position controllers at the four corners between the fixed beam and the movable beam of the hot press. The controller is composed of a position measuring rod, a fine adjustment mechanism, a differential transformer, a travel switch, a timer, etc. Each small hole at the lower end of the positioning rod represents the basic thickness of the designed board. It is positioned by a cone inserted in the manhole, and then fine-tuned with a handwheel, so that the positioning rod can be linearly adjusted within a given range. Any precise size required within the range. When the press is closed, the conical part of the upper end of the positioning rod rises, contacts the differential transformer, and makes it displaced. The differential transformer sends out an electrical signal due to the displacement, and the total height between the movable beam and the fixed beam is adjusted by the PC control system, thereby controlling the thickness of the slab between each layer of hot pressing plate at each stage.
Each type of hot press has its own advantages in the production of plywood. Only by choosing a hot press that suits you can the production efficiency be improved.
