Discussion on the importance of heating methods for multi-layer hot press machines

The heating system of the hot press is the most important part of the hot press system. Steam heating uses the latent heat of vaporization of steam to heat the hot press plate, while superheated water uses the sensible heat of superheated water to heat the hot press plate. After its heat is used up, superheated water can be repeatedly used by circulating and reheating. As hot water is circulated, the flow rate is relatively slow and the thermal efficiency is relatively high. Compared with steam, using superheated water as the heating medium is better, and the comprehensive utilization rate of thermal energy in the superheated water heating system is 40% -50%. In terms of temperature control, besides controlling the flow rate, superheated water heating can also adjust the temperature by changing the temperature of the circulating superheated water. Compared with steam heating, superheated water heating can more strictly control the temperature.

Due to the need to use high-pressure saturated steam to heat low-temperature water for superheated water heating, in addition to configuring a high-pressure hot water container, a high-pressure boiler is also required.

On the one hand, the mixing equipment is complex; On the other hand, the system pressure is still relatively high, and there are also high requirements for the sealing performance of the heating system; And hot water is prone to sedimentation and scaling, which has a corrosive effect on the heating system. In order to prevent scale and corrosion in the tank, pipeline, and hot press plate, it is best to use condensed water when heating with superheated water, at least soft water should be used.

Due to the use of superheated water and saturated steam as heat media, the heating of thermal oil requires operation under high pressure conditions, which increases the difficulty of equipment sealing and reduces heating stability. Therefore, seeking a high boiling point substance as a heat medium that can generate high temperatures under normal pressure or low pressure, has a large heat capacity, and is safe to use has always been a concern for people. In the 1930s, such a heating medium was found, which is high-temperature organic heat carrier, commonly known as thermal oil or hot oil. China began researching heat transfer oil heating technology in the early 1970s and was listed as a national energy-saving promotion project during the Eighth Five Year Plan period.

In the 1980s, heat transfer oil with the characteristics of high temperature and low pressure heat transfer was gradually applied in China's wood-based panel industry. Now this heating method has been widely used in such types of hot presses as medium density fiberboard hot press, particleboard hot press, low pressure short cycle veneer hot press, and particleboard molded product hot press. For low-pressure short cycle veneers, thermal oil is almost the only ideal heating medium for hot press machines; In the production of medium density fiberboard, thermal oil has gradually replaced hot water and saturated steam.