1. Dust removal of medium frequency electric furnace
Since the charge of the induction heating furnace usually contains dust and oil, the charge is added to the furnace and smoke is generated from the furnace mouth. If the charge contains galvanizing and its waste, the soot will also contain zinc or tin oxide. The soot generated in the induction furnace operation is harmful to the human body and the production environment, and is required to be discharged to the outside by a dust removal system. The amount of soot produced is related to the size of the furnace and the cleanliness of the charge. The dust removal system must have a large enough air volume to generate enough negative pressure at the furnace mouth. The dust removal system consists of an induced draft fan, a dust collector, a cyclone separator, a smoke temperature regulating device and a pipeline. In order to ensure that the temperature of the flue gas entering the precipitator does not exceed the value that the precipitator can withstand, the flue gas temperature adjusting device can adjust the amount of cold air incorporation to control the temperature of the flue gas entering the precipitator. The flue gas of the intermediate frequency electric furnace shall be discharged by the dust removal system to meet the requirements of the national standard GB9078-1996 “Emission Standard for Air Pollutants in Industrial Kilns”.
In order to capture the soot, the induction melting electric furnace is generally equipped with a furnace dust removal ring (see Figure 4) or a full-face dust removal furnace cover (see Figure 5). The ability of the furnace dust removal ring to capture soot is not as good as that of the whole cover type dust removal furnace cover, but it is suitable for electromagnetic suction cup or manual feeding, so it is used more on the furnace of ≤ 5t. The full-face dust-removing furnace cover has a good ability to capture soot, and it needs to be used together with the feeding car, and is usually used for a large-sized furnace.
For the dust removal of medium frequency electric furnaces, it is very important to select a dust removal system with excellent performance. However, the maintenance of the dust removal system is also very important. The dust collector and piping should be cleaned regularly to maintain the system's good dust removal effect.
2. Noise of medium frequency electric furnace
During the operation of the intermediate frequency electric furnace, the noise is mainly generated in the intermediate frequency power supply, the furnace body and the hydraulic pump. Second, the noise generated by transformers and pumps is relatively small. It is usually required that the noise on the furnace working platform, 1m away from the furnace body and 1m in height should be ≤85dB (after deducting background noise).
At present, the equipment layout of most medium frequency electric furnaces places intermediate frequency power supplies, furnace bodies, hydraulic pumping stations and pumping stations under the working platform (in the semi-subterranean pit), which reduces the noise at the operating station on the working platform. Improving the working environment of workers plays a big role.
When the furnace with high power density is running, the noise is relatively large due to the vibration of components such as induction coils and yokes. If necessary, the furnace structure can take some measures to reduce noise, such as the sound insulation of the inner wall of the furnace shell, the rubber cover of the repair hole cover, and the filling of the cavity of the structural part of the furnace body.
The hydraulic pump has a large noise during operation, so it should be stopped in time when not in use. For this reason, a stop button is provided on the hydraulic console, and the operator can stop the operation of the hydraulic pump in time, or configure the timer to shut down the hydraulic pump on time.
3. Harmonic problems of intermediate frequency electric furnace
Solid-state IF power supplies use thyristors, diodes, IGBTs and other electronic devices for rectification and inverter, which will cause harmonic interference to the power supply grid.
With the wide application of electronic devices such as electronic computers and numerical control machine tools, the requirements for power quality of power grids are getting higher and higher. In modern industrial production, various types of converter devices are used more and more, and the capacity is also increasing. The harmonics generated by it are injected into the power grid, causing the voltage waveform of the utility grid to be distorted, affecting the quality of the electrical energy, and threatening the safety and economic operation of various electrical equipment. To this end, the state has established the national standard GB/T14549-1993 "power quality, utility grid harmonics" standard. This standard specifies the allowable values for harmonics injected into the grid.
The harmonic interference generated by solid-state IF power supplies is mainly determined by the form of its rectifier circuit.
The voltage feedback series resonance type intermediate frequency power supply is rectified by a bridge type uncontrollable rectifier circuit, and the generated harmonics are smaller than the current feedback parallel resonance type intermediate frequency power supply.
In addition, the multi-phase rectification method, such as 6-phase 12-pulse rectification, 12-phase 24-pulse rectification, and the winding of the rectifier transformer take the equal measure, which can greatly reduce the harmonic interference of the intermediate frequency electric furnace.
4. The magnetic field of the intermediate frequency electric furnace
The alternating current passes through the coil of the induction heating furnace to generate an alternating magnetic field. The strength of the magnetic field depends on the power of the electric furnace. At present, the operating frequency of the intermediate frequency electric furnace is between 100 and 3000 Hz. This frequency is not the radio wave transmission frequency and generally does not cause interference to radio communications. However, if no technical measures are taken to limit the alternating magnetic field generated by the induction coil, the alternating magnetic field will cause the metal parts near the furnace to heat up, posing a hazard to workers operating on the furnace (especially for metal dentures). , metal artificial joints and other pieces of workers), so the intermediate frequency electric furnace needs to use a yoke to limit the magnetic field to divergence. The induction coil of the modern coreless induction furnace is surrounded by a plurality of yokes. The length surrounded by the yoke in the circumferential direction of the coil reaches 60% to 65% of the circumference of the coil. It is said that the production of medium-frequency coreless induction heating furnaces without yokes will cease in Europe.
