What are the classifications of electric heating coils?

The heating principle of heating coils

1. The working principle of electronic heating is to use a thermistor probe placed in the water inside the cylinder to control the water temperature. The advantage of this type of heating rod is accurate temperature control, and its price is slightly higher than that of ordinary mechanical heating rods. If conditions permit, this type can be chosen, but the disadvantage is the complex structure of peripheral devices such as attached probe sockets.

2. The bimetallic plate type temperature control heating rod is the most common one on the market, which integrates temperature control. A bimetallic sheet is a combination of two different materials of bimetallic sheets using a special process. When the temperature changes, the metal sheet undergoes deformation due to its different expansion coefficients. A bimetallic sheet is placed inside the heating rod as a contact switch, which can automatically disconnect the contact after reaching the temperature for temperature control. The disadvantage is that the temperature control is not accurate. Generally, it will increase by several degrees with the increase of ambient temperature under the condition of constant set temperature. The internal bimetallic plates and their temperature control contacts of the constant temperature heating rod are the control core of this heating rod. Poor quality bimetallic plates are prone to fatigue during use, resulting in the bimetallic plates not being able to open or close the heating rod with temperature changes. In addition, poor quality contact opening and closing are also prone to ignition and adhesion, causing significant temperature fluctuations, and even cooking fish soup.

Recommended reading: What are the classifications of electric heating coils?

According to the different methods of electrical energy conversion, electric heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and medium heating.

Induction heating coil

The thermal effect formed by the induced current (eddy current) generated by a conductor in an alternating electromagnetic field causes the conductor itself to generate heat. According to different heating process requirements, the frequency of the AC power supply used for induction heating includes power frequency (50-60 Hz), medium frequency (60-10000 Hz), and high frequency (above 10000 Hz). Power frequency power supply is the commonly used AC power supply in industry, and the power frequency in the vast majority of countries around the world is 50 hertz. The voltage applied to the induction device by the power supply used for induction heating must be adjustable. According to the power of the heating equipment and the capacity of the power supply network, a high-voltage power supply (6-10 kV) can be used to supply power through a transformer; Heating equipment can also be directly connected to a 380V low-voltage power grid. The intermediate frequency power supply used intermediate frequency generator sets for a long time. It consists of an intermediate frequency generator and a drive asynchronous motor. The output power of this type of unit generally ranges from 50 to 1000 kilowatts. With the development of power electronics technology, intermediate frequency power supplies using thyristor frequency converters are now being used. This intermediate frequency power supply uses thyristors to first convert AC power into DC power, and then convert DC power into AC power of the desired frequency. Due to its small size, light weight, no noise, and reliable operation, this type of frequency conversion equipment has gradually replaced intermediate frequency generator sets. High frequency power supplies usually first use a transformer to raise the three-phase voltage of 380 volts to a high voltage of about 20000 volts, then use thyristors or high-voltage silicon rectifier elements to rectify the AC power into DC power, and then use electronic oscillators to convert DC power into high-frequency, high-voltage AC power. The output power of high-frequency power supply equipment ranges from tens of kilowatts to hundreds of kilowatts. The object heated by induction must be a conductor. When high-frequency AC current passes through a conductor, the conductor produces a skin effect, that is, the surface current density of the conductor is high, and the center current density of the conductor is low.

Induction heating can uniformly heat the object as a whole and heat the surface layer; Metal that can be melted; In the high-frequency range, changing the shape of the heating coil (also known as the inductor) can also allow for arbitrary local heating.