Lianjing developed an electromagnetic induction heating roller for fiber sizing in order to meet the requirements of fiber drawing and setting at high temperature,. Lianjing's induction heating roller has many advantages working at high temperatue: with fast heating, uniform heating, simple temperature control, energy saving and environmental protection.

Hot roller is an important equipment for fiber post-treatment, which is widely used in heat setting and tension heat setting equipment. The general heating methods of hot roller are steam heating and heat conducting oil heating. With the continuous development of China's chemical fiber industry, there are higher requirements for the heating temperature and heating uniformity of the hot roller. According to the market demand, the induction heating roller developed by Shanghai Lianjing has incomparable advantages over the traditional heating method.

Background

Thermal drawing is an essential process of fiber post-treatment. The traditional steam and heat transfer oil heating rods can no longer meet the requirements because of the requirement of improvement of heating temperature, heating uniformity, environmental protection and reducing the labor intensity of operators. Both steam heating and heat transfer oil heating have problems such as uneven temperature of heating roll surface, temperature not meeting the process requirements, and leakage of steam and heat transfer oil seriously affect the environment. However,  induction heating roller eliminates the potential danger of steam leakage and leakage injection, which can ensure the temperature of heating roller is uniform and the temperature control is accurate, which can protect the environment and reduce the labor intensity of maintenance.

Basic principle of electromagnetic induction heating

As shown in above figure, induction heating transforms electrical energy into heat energy inside metal by induction coil. The induction coil doesn't contact  the heated metal directly, and the energy is transmitted by electromagnetic induction. In addition, it should be pointed out that the principle of induction heating is the same as that of eddy current and heating caused by eddy current in general electrical equipment. The difference is that eddy current is harmful in general electrical equipment, while induction heating is heating by using the thermal effect of eddy current.

In this way, the induced electromotive force produces an induced current (eddy current) in the workpiece to heat the metal. The relationship between heat and current resistance is as follows:

Q＝∑I2Rt

Q is the heat generated by the current passing through the resistance (J); I is the effective value of the current (A); R is the equivalent resistance of the workpiece (Ω); t is the time when the workpiece is energized (s).

It can be observed from the above formula that the induced electromotive force and heating power are related to the frequency and magnetic field strength. The greater the current flowing through the induction coil, the greater the magnetic flux generated. Therefore, increasing the current in the induction coil can increase the eddy current generated in the workpiece; similarly, increasing the working frequency will increase the induced current in the workpiece, so as to increase the heating effect and make the metal temperature rise faster. In addition, the size of eddy current is also related to the cross-section size, cross-section shape, conductivity, permeability and penetration depth of metal.

The whole process of induction heating can be summarized as follows: firstly, the electric energy is converted into magnetic energy by induction coil, and the alternating magnetic field generates the alternating electromotive force with the same frequency. After the alternating electromotive force acts on the metal object, it forms a closed circuit, and generates current eddy current on the metal surface, realizing the conversion from magnetic energy to electric energy. When the magnetic line of force in the magnetic field passes through the conductive metal material, numerous small eddy currents will be generated in the metal body, which makes the metal material itself generate heat fastly, so as to heat the metal object directly.

Brief introduction of electromagnetic induction heating roller technology

Induction heating technology has many advantages, such as low energy consumption, high thermal efficiency, fast temperature rise and high temperature control accuracy, so it is widely used in many industries. In Europe, the United States, Japan and other developed countries, " induction heating technology" is known as green energy, which has been greatly promoted by the government. Shanghai government has also encouraged the application of high-power induction heating technology. At present, the application of induction heating technology in injection molding machine, extruder, film blowing machine, granulator and other fields has been applied and widely recognized.

Induction heating roller is mainly used in medicine, packaging, printing, textile, nonwoven and other fields. This technology completely subverts the traditional heating method of heat transfer oil, cancels the oil heater, oil pump, circulating pipeline, rotary joint and other components required by the heat transfer oil heating system. Only a reasonably designed circuit is needed to convert the power frequency alternating current into high-frequency alternating current, and transmit it to the pre laid high-frequency induction coil inside the roller body, and generate high-frequency alternating magnetic field near the coil. The surface of the roller body is heated by induction, so as to achieve the purpose of heating the roller body. Taking the diameter of Ф 400 * 1800 hot pressing roller used in non-woven fabric processing as an example, the energy-saving effect is obvious. The actual power consumption per hour is only about 8kw. H, which is far lower than that of the heat transfer oil system above 20kW. H per hour.

Generally, compared with heat transfer oil heating roller, induction heating roller has incomparable advantages, mainly reflected in the following aspects:

1) Uniform roller surface temperature: Using instant heating and high-end temperature control means, the whole surface temperature of electromagnetic induction heating roller can be controlled within ± 1.0 ~ 2.0 ℃, and can be controlled within ± 0.5 ℃ in places with high requirements, which can fundamentally change the problems of large temperature difference and temperature lag caused by oxidation and coking of heat transfer oil, and ensure the stability of product quality.

2) Clean and environmental protection: the induction heating roller no longer uses heat transfer oil as heat conduction medium, which fundamentally eliminates the environmental pollution and potential safety hazard caused by the evaporation and leakage of heat transfer oil. The production environment is cleaner and the possibility of oil vapor pollution on the product surface is avoided.

3) High efficiency and energy saving: under normal conditions, the assembly power of the induction heating roller is reduced by more than 30% compared with the traditional heat transfer oil heater. At the same time, its heat utilization efficiency is higher, which can reduce the heat loss to the greatest extent, and the energy consumption can be reduced by more than 30% - 50%. All the energy consumption generated by the hot oil circulating pump will also be saved, and the comprehensive energy saving rate is often as high as 50%.

4) Easy operation and maintenance: electromagnetic induction heating roller no longer needs a series of accessories such as external heater, complex oil pipeline, joint, oil pump, etc., and the fault points are greatly reduced. At the same time, it can save a lot of replacement and maintenance costs. The practice of many industries has proved that the average time between failures of electromagnetic induction heating roller is more than 10000 hours. 

Control system and electromagnetic radiation

The heating control center of electromagnetic heating roller includes induction heating control system and temperature regulation control system. The induction heating control cabinet is placed close to the electromagnetic heating roller, and the temperature control system is integrated in the induction heating control cabinet. The radiation of  induction heating roller is very small. The electromagnetic intensity is 0.7 MV / M and the magnetic field intensity is 0.009 MA / m at a distance of 30 mm from the roller, which is far below the control limit of GB 8702-2014 "electromagnetic environment control limits". In actual production, it is easy to operate, safe and environmentally friendly.

Conclusion

With the continuous development of China's chemical fiber industry, there are more and more different kinds of fibers, especially the development of special fibers in recent years, the temperature control requirements of post-treatment are very strict, and high temperature is required.
Common steam heating and heat transfer oil heating can not fully meet the process requirements. The maximum temperature of electromagnetic induction heating in Lianjing can reach 400 ℃, and the operation is convenientand  safe, temperature control is accurate, uniform heating and environmental protected. The induction heating roller will become the main way of chemical fiber drafting in the future.

Product parameters