With the continuous development of calender industry, calendering technology has been gradually applied to leather, non-woven fabrics and bulletproof clothing materials. However, the existing steam heating and heat transfer oil heating methods can not meet the relevant technical requirements of temperature, so the heating methods need to be improved. Electromagnetic induction heating is a kind of heating method which fundamentally changes steam and heat transfer oil as heating medium. Its heating characteristics are high temperature peak value, fast speed and can reach above 400 ℃.

Soft calender is mainly composed of hot roll and soft roll, which is used for calendering finishing of various kinds of paper and paperboard. It can improve the smoothness, glossiness, bulk thickness, stiffness and strength of paper. The thickness of paper can also be adjusted through the controllable medium high soft roller of the calender. Usually, the main heating methods of hot roller are steam heating and heat conducting oil heating. The hot roller heated by steam uses cold cast iron roll with hollow surface. When steam enters and exits from the same side, the surface temperature of roller is not uniform, which affects the calendering quality of paper. The hot roller heated by heat transfer oil adopts the principle of three holes and one cycle, and holes are evenly drilled along the outer wall of the chilled cast iron roll, and the heat transfer oil heating makes the roller barrel. The outer surface temperature difference is small, so that the roller surface temperature is almost the same, which can achieve very good calendering effect, but the temperature can only reach about 200 ℃, so the application range is limited. With the wide application of leather, non-woven fabrics and bulletproof vests, the requirements of calendering technology become higher and higher, and the calendering temperature needs to be above 400 ℃. However, the heating mode of the existing calendering equipment can not meet the technical requirements. It is necessary to improve the heating mode of calendering equipment to fundamentally change the heating mode with steam and heat transfer oil as heating medium. Electromagnetic induction heating is an indirect heating method that converts electric energy into magnetic energy and then into heat energy through induction coil. Because the electromagnetic induction heating roller starts from the inside of the metal, so the heat conduction time will be very short, so it can be applied to calender roller heating.

After H.C. Oster discovered the current magnetic effect in 1820, many physicists tried to find its inverse effect and raised the question whether magnetism can generate electricity and whether magnetism can act on electricity. In August 1831, British physicist Michael Faraday became the first person to discover the phenomenon of electromagnetic induction, and constantly found and summarized the law of electromagnetic induction. The law of electromagnetic induction mainly says that the generation of induced electromotive force is due to the changing magnetic field in the area surrounded by a certain circuit, then there will be induced electromotive force at both ends of the circuit, and its size depends on the change rate of magnetic flux through the circuit. According to the principle of electromagnetic induction heating, induction heating is due to the energy conversion between electric energy and electromagnetic energy, and finally becomes the internal energy of metal materials to realize the heating of materials. This heating method is a kind of non-contact electromagnetic induction heating, which is relatively simple. The high-frequency alternating current in the heating coil generates an alternating magnetic field with the same frequency around the wire. Placing the heating roller with magnetic conductivity in the alternating magnetic field around the coil will form eddy current in the material due to electromagnetic induction. The eddy current makes the metal atoms in the magnetic field move irregularly at high speed. Atoms collide and rub with each other to produce heat energy so as to achieve the purpose of heating and it is used to heat calender roller to achieve calendering finishing effect on materials.

 The outer wall temperature distribution of Lianjing induction heating roller is uniform and the temperature value is high, which can reach above 400 ℃. It can meet the requirements of calendering technology for leather, non-woven fabric and bullet proof vest. It can also be adjusted by temperature sensor to realize constant temperature state. Electromagnetic induction heating not only has uniform heating and high heating temperature, but also helps to improve the temperature control accuracy of metal roller, realize the precision control and application of workpiece temperature, ensure the calendering effect, improve the production efficiency and quality, and meet the effective market demand.