A hot-pressing machine consisting of a plurality of hot-pressing plates for pressurizing and heating a plurality of groups of slabs. It is the most widely used host in wood-based panel industry. Full name is multi-layer heating hydraulic press. This equipment is also commonly used to press molded products and bent wood in wood processing industry.

The commonly used pressurizing media of hot press are petroleum-based hydraulic oil and water-based working fluid. The thermal medium for heating the workpiece usually adopts saturated steam, but also uses hot water, hot oil and organic heat medium. Use resistance heating or high frequency heating for special purposes. The steam injection method, which appeared in recent years, is suitable for heating thick workpieces.

the structure of the multi-layer hot press body is shown in the figure. Hot presses with many layers and large formats are generally accompanied by loading and unloading machines. Some hot presses also have simultaneous closing mechanisms. The machine takes the width size and gross tonnage of the processed products as the main performance parameters.

Rack

has frame type, column type and box type, and the first two types are common. High-pressure, large-tonnage hot presses mostly adopt column structure, such as 2-ton plastic veneer press, with a total pressure of 25 tons and a unit pressure of 7 MPa. Column structure adopts column structure, and there is a large space between columns, which is convenient for maintenance and installation, but it consumes a lot of metal materials and needs large mechanical processing equipment. Frame type is the most widely used structural form of small and medium tonnage hot press, with simple processing, such as BY214×8/8 plywood hot press, with total pressure of 8 tons and unit pressure of hot pressing plate of 2 MPa. The frame bears the total pressure of the press when working, so the accuracy and stiffness of the frame directly affect the working accuracy of the whole hot press, which is the key component.

Oil cylinder

is a hydraulic actuator, which bears great working pressure. Generally, the cylinder is made of cast steel or forged steel.

The working surface of plunger

requires good precision and smoothness, and the surface is plated with hard chromium to improve wear resistance and corrosion resistance. Some presses have an annular spray pipe at the top of the plunger to wash and cool the plunger. The sealing ring usually adopts V-shaped rubber ring, and the new hot press adopts U-shaped sealing ring made of polyurethane rubber, which has a long service life.

Hot pressing plate

must have sufficient strength and rigidity, and is usually made of thick steel plate. The upper and lower surfaces are required to be parallel, and the surface is smooth and smooth to ensure the quality of products. There are holes in the hot pressing plate for introducing heat transfer medium, and the circuit of the holes is specially designed to ensure the uniform temperature of the plate surface. Different pressed wood-based panel products have different panel temperatures, about 1 ~ 2℃.

heating system

according to different heat media, there are many types of heating systems, and the most commonly used one is steam heating system. The requirement of steam pipeline is that it can supply steam and exhaust waste gas normally and ensure sealing when the hot press is opened and closed. The common connecting pipes are telescopic pipe and crank arm pipe, which occupy a small area and have a simple structure, but are easy to leak; The elbow pipe has good sealing performance, but its size is large. Since the 197s, some hot presses have adopted metal braided hoses, which have good sealing performance but high price.

hydraulic system

the hydraulic system of the multi-layer hot press should meet the requirements of the pressurization curve made according to the process requirements, and provide a certain amount of pressure oil in each stage of closing, boosting, pressure maintaining and pressure relieving. Therefore, the hydraulic system is equipped with high-pressure pump, low-pressure pump, control pump, charging pump and various hydraulic valves, and the automatic working cycle of the pumps and valves is realized by electrical control. In order to meet various technological requirements, improve productivity and control the thickness of products, various technical measures can be adopted in the hydraulic system, such as pressure accumulator, variable oil pump, hydraulic servo technology and total stroke control.

Synchronization device

In order to ensure the synchronous lifting of the movable beam of the press, there are generally synchronization devices on the movable beam, including rigid guide type, connecting rod type, rack-and-pinion type, hydraulic balance type and electro-hydraulic balance type, among which rack-and-pinion type is the most widely used.

closing mechanism

The closing speed of large-scale multi-layer hot press is very high, and it is easy to cause the phenomena of air blowing out blanks and sucking in waste fibers when the hot pressing plate is opened and closed at high speed. Moreover, because the bottom hot pressing plate is closed early, the product will have the phenomenon of rubber pre-curing, and the closing mechanism can overcome these shortcomings. There are many types, such as elbow lever type, hinged lever type and tower wheel type, among which the elbow lever type simultaneous closing mechanism with hydraulic compensator is the most widely used.

loading and unloading machine

The multi-layer hot press with high layers must use loading and unloading machine, otherwise it will not form continuous and rhythmic production, and it is even more indispensable in the hot pressing process of fiberboard and particleboard. Loading and unloading machines are divided into two categories: non-pad type and pad type. There are many types of loading and unloading plates without pads, with synchronous belt trolley and pallet as the basic types.

Although there are single-layer flat press and continuous press in wood-based panel industry, it cannot affect the wide application and technical development of multi-layer hot press, which is still the most widely used main equipment in wood-based panel industry, especially in large production lines. The development trend of multi-layer hot press since 198s is as follows: ① Continue to develop to high-rise and high-speed. For example, the number of plywood presses is as high as 9, and the closing speed reaches 6 ~ 7 mm/s. In order to avoid the construction of high factory buildings and deep pits, horizontal multi-layer hot presses have also appeared. (2) The hot press is developing towards high precision. Adopting various mechanical, electrical and hydraulic measuring and sensing means, the working accuracy of the press and the quality of the products have been greatly improved. ③ The degree of automation has been continuously improved. For example, the press body, hydraulic system, loading and unloading machine and transportation equipment form an automatic control system with perfect performance and advanced control means. The new hot press is controlled by programmable controller and computer, which is the most automatic section in the wood-based panel production line.