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Heating mode determines the level of roll

2020-08-19 14:33:24

Roller is a great invention of mankind. Most of the rollers on the machine do not need to be heated, but a few need. We call them heating rollers.

Heating roller is widely used in paper making, printing,  copying, textile, rubber, plastic, chemical fiber and other industries, such as preheating, drying, shaping, laminating, embossing, etc. It is mainly used for heating and hot processing of all kinds of polymers. The roller is heated in a certain way, and the roller heats the product by conduction.

According to the different heating methods, heating roller can be divided into two kinds: fluid heating and electric heating. Among them, fluid heating mainly includes three kinds of media: thermal oil, water and steam; electric heating is mainly divided into direct heating by electric heating rod and induction heating.


Thermal oil heating roller

This is one of the most commonly used heating rolls, and most of the heating rolls in use are heated by thermal oil. The advantages are relatively simple structure and low cost. The disadvantage is that it is easy to scale after some time, which will result in uneven temperature; due to the nature of the thermal oil itself, the temperature cannot be too high (generally less than 250 ℃). It needs to be connected with an external oil pump for circulation and connected to the roller through the rotary joint, which not only wastes energy but also has the potential of oil leakage.


Water heating roller

The roller structure of water heating roller is similar to that of thermal oil heating roller, and the cost is also low. Limited by the water temperature (no more than 100 ℃ in open system), it is difficult for the roller surface temperature to exceed 80 ℃. If the ordinary tap water is used, the inner wall of the roller also has the problem of scaling, and the external water pump circulation has additional energy waste.


Steam heating roller

The steam heating roller passes the steam into the roller for heating through the external steam pipe connected with the rotary joint. The roller has simple structure and low cost. Similarly, due to the rapid rise of steam pressure with the increase of temperature, the roller temperature is not too high (generally less than 180 ℃). With the restrictions on the use of boilers, the number of steam heating rollers is rapidly decreasing.


Electric heating roller

Electric heating mostly uses the electric heating rod as the heat source. Therefore, in theory, the roller can be heated to a very high temperature.

Almost all electric heating rod in electric heating roller is not in full contact with the roller, so there are two ways of heat transfer: conduction and radiation. If the problem of reasonable heat transfer is not handled properly, the uniformity of roller temperature is often poor. For this reason, many manufacturers have oil holes on the roller wall to fill the heat transfer oil into the holes. In this way, the roller temperature can be more uniform through the soaking effect of the thermal oil. However, if the heat consumption is particularly large, the uneven phenomenon will still be very serious. In addition, there will be safety problems when filling heat-transfer oil. Many news have been reported that rollers cracked due to thermal expansion of thermal oil.


Induction heating roller

       Induction heating roller, with the most sophisticated technology, is invented by Tokuden of Japan in 1964. After more than 50 years of development, the company still monopolizes the advanced heating roller market. The induction heating roller with independent intellectual property rights in China was successfully developed by Shanghai Legion in 2009. Induction heating roller can not only achieve high temperature (above 400 ℃), but also clean and energy-saving. Good temperature uniformity can also be achieved after embedding good temperature equalization technology. Therefore, induction heating roller is an ideal heating and processing tool for many advanced materials. Meantime, due to the complex structure, its cost is also very high. This is the biggest obstacle to the wide application of induction heating roller.


According to the product of Shanghai Legion, the advantage of induction heating roller is as follow:

Structure diagram of induction heating roller of Shanghai Legion

The unique energy distribution technology enables the roller to achieve efficient heating while maintaining the surface temperature uniformity within ± 0.5 ℃.


电磁加热辊结构示意图.png

Working principle of induction heating roller 

The heating coil in the roller shell is connected with an external power control module.After being powered on, the alternating current of 50 Hz / 60 Hz is converted into DC voltage, and then the DC voltage is converted into high frequency voltage output with frequency of 20-40kHz through the power control module. The fast-moving high-voltage current produces a high-speed magnetic field in the inner coil of the roller shell.After the magnetic field generated in the coil contacts with the metal roller, the internal part of the heating roller gathers and cuts the alternating magnetic line of force and produces alternating current (eddy current). The eddy current makes the iron atoms of the heating roller shell move irregularly at high speed, and the atoms collide and rub with each other to generate heat.

In short, the principle of induction heating is to use the conversion between electricity, magnetism and heat to achieve the effect of heating the object itself.


Features of induction heating roller

Wide temperature range

Roller shell is heated in electromagnetic field, withthe temperature range in 50~420℃.


High-precision temperature control, anduniform surface temperature distribution

Special energy distribution technology isemployed in Legion induction heating roller,whichensures uniform surface        temperature within ±0.5℃.

Special temperature distribution can also bedesigned according to customer's requirement


Compact structure, space saving

Electricity is the only power source for LEGION® induction heating roller. So there is no need for additional facilities or specialconstruction. The equipment requires minimal spaceand is easy to operate.

Clean, and less maintenance operation

Without thermal oil, vapor or combustible material to leak, the work environment keeps clean and safe. Friendly human-computer interaction screen, one button operation.Communication protocol support: ModBus/TCP, ModBus RTU/ASCII RS-485 ,EtherNet-IP etc.

Lower energy consumption

Heated by induction method, the heat utilization rate is very high. Compared with oil heated roller,energy consumption rate reduces about 50%, and over 70% in some industries.

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