Development of induction heating technology and equipment（2）

New process of induction heating 

Induction heating technology is the main reflection of the level of induction heating technology, is the basis of technical development, advanced induction heating technology can effectively play the characteristics of induction heating, to achieve efficient, energy-saving local heat treatment.

(1) Longitudinal induction heating quenching half shaft longitudinal induction heating quenching has been used in the automobile and tractor industry.Half axis longitudinal heating is a single quenching.In Germany and the United States, there are special semi-spindle one-time quenching machine tools, which heat, correct and quench in one machine tool to improve productivity. The equipment with the same output of one-time quenching and continuous quenching covers an area of 40m2 and 115m2 respectively.

(2) The fatigue strength of crankshaft journal is doubled than that of normalcy after the crankshaft journal corner is quenched. This process has been adopted by Cummins and NH engine crankshafts manufactured in China.

(3) Low-hardenability steel gear quenching in China as early as in the 1970s, 55DT, 60DT, 70DT steel had been studied and preliminary results were obtained. Later, due to the instability of the hardenability of steel and other reasons, low-quenching steel did not continue to be used in production.Russian founder of low quenching steel 1992, k. 3 Щ Е П Е Л Я К О В С К Ц Ц Dr Come to China to give lectures, and to a steel mill investigate the condition of smelting low quenching steel, think that the factory fully equipped production low quenching steel condition.YB 2009-1981 "low hardenability with high quality carbon structural steel" in the control of alloy elements, unlike Russia (Russia), 1054-74, 58 (55 П П) steel elements content of Mn, Cr, Ni, Cu, the sum of the four elements required < 0.5% (mass fraction), and ti YB2009-8155 steel for the sum of three elements of Cr, Ni, Cu < 0.5% (mass fraction), it could be a key.

Russian low-quenched steel and control hardenability steel have been widely used in automobile, tractor rear axle gear, excavator gear, transmission cross shaft, rolling bearings for train cars, automobile plate spring and railway spiral spring, etc., and have obtained great economic benefits.

(4) Induction resistance quenching as is known to all, the gear of the steering rack is quenched by induction resistance method, and there are more than three imported machine tools in production in China.This process was applied to gear production by a British machine tool, and it was found that the gear basically did not deform after quenching and could then enter into the assembly process.

(5) The new equipment for fixed heating and quenching of crankshaft journal is called Gr ankproTM. Two fixed semi-annular heating sensors are used to replace the 8-character semi-annular rotating heating induction belt.This set of equipment can quench and temper the curved neck. Compared with the old technology, it has the advantages of energy saving, small floor space, small deformation of workpiece and long sensor life.

Induction heating power supply and technology

In terms of induction power supply thyristor to replace generator.In the early 1990s, the domestic thyristor power plant has mushrooming, everywhere, after the survival of the fittest competition, now the production plant has tended to stability.At present, thyristor power supply is developing to IGBT transistor power supply, and vacuum tube high frequency will develop to MOSFET transistor power supply, portable transistor super audio, high frequency power supply market competition is very fierce, its future will also be whose high quality, high technical level, who can stand firm.

At present, the domestic intermediate frequency power supply adopts parallel resonant inverter structure.Therefore, research and development in a larger capacity of parallel inverter of intermediate frequency power supply at the same time, the development of simple structure, easy to frequent starting series inverter intermediate frequency power source is the domestic problems to be solved in the field of medium frequency induction heating devices, especially in the applications of smelting, casting, series inverter power supply is easy to realize full under the condition of constant power output (reducing electricity tons of consumption) and more than one machine load power distribution control, more worthy of popularization and application.

In the range of superaudio frequency (10 ~ 100kHz), it is very difficult to develop the power supply in this frequency band due to the limitation of thyristor switching characteristics and other parameters.While in the 80 s, zhejiang university adopts thyristor frequency doubling circuit 50 kw / 50 KHZ ultrasonic frequency power supply is developed, using time division circuit is developed 30 KHZ thyristor super audio power, but the frequency doubling the double resonance loop coupling circuit load is nonlinear, time varying heating load parameters and the resonant circuit parameters matching debugging is very complex, and time division control circuit and main circuit structure is complex, inverter tube utilization rate is low, so didn't get good popularization and application.

From the 1970s to the early 1980s, people combined modern semiconductor microintegrated processing technology with power semiconductor technology, and developed a large number of fully controlled power electronic semiconductor devices (GTR, MOSFET, SIT, SITH and MCT, etc.), which laid a solid foundation for the development of all-solid-state super audio and high-frequency power supply.

In the frequency band of high frequency (above 100kHz), foreign countries are in the transition stage from traditional vacuum tube power supply to transistorized all-solid-state power supply.Some Japanese companies use SIT, and the power level reached 1000kW, 200kHz, 400kW, 400kHz in the late 1980s.

In Europe and America, because SIT exists high-pass state loss (SIT works in unsaturated zone) and other defects, its high-frequency power devices are mainly MOSFET.With the modularization and large-capacity of MOSFET power devices, the capacity of MOSFET high-frequency induction heating power supply has been developed rapidly.Spain USES MOSFET current type induction heating power supply manufacturing level up to 600kW, 400kHz, Germany developed in 1989 current type MOSFET induction heating power supply level up to 480kW, 50 ~ 200kHz, Belgium I nductoEiphiac current type MOSFET induction heating power supply level up to 1000kW, 15 ~ 600kHz.In the 1990s, Zhejiang University developed 20kW, 300kHz MOSFET high-frequency power supply, which has been successfully applied to surface heat treatment of small cutting tools and thermal stress assessment of aircraft turbine blades.

At present, the induction heating power supply mainly adopts thyristor in the intermediate frequency band and IGBT in the ultra-audio frequency band, while in the high frequency band, MOSFET power supply is mainly developed internationally due to the defects such as high conduction loss in SIT.Although resonant inverter is adopted in induction heating power supply, which is beneficial to realize soft switch of power devices, induction heating power supply is usually of large power and has many special requirements for power devices, passive devices, cables, wiring, grounding and shielding.Therefore, the realization of high-frequency induction heating power supply still has many application basic technologies need to be further discussed, especially the advent of new high-frequency high-power devices (such as MCT, IGBT and SIT power devices), will further promote the development of high-frequency induction heating power supply.

Considering the large-capacity induction heating power supply from the point of view of circuit, the large-capacity technology can be divided into two categories: one is the series and parallel of devices;The other type is multi - bridge or multi - power series, parallel.In the series and parallel modes of devices, it is necessary to carefully deal with the problem of voltage sharing of series devices and the problem of current sharing of parallel devices. Due to the discreteness of the manufacturing process and parameters of devices, the number of series and parallel devices is limited, and the more the number of series and parallel devices, the worse the reliability of devices.More than one power supply series, in parallel technology is based on devices in series, in parallel technology further more effective means of capacity, with the help of reliable power supply technology in series, in parallel, in appropriate cases, stand-alone capacity can be obtained simply by running in series, in parallel way large capacity unit, each single just device of a unit (or a module).

Induction heating power supply inverter parallel inverter and series inverter, main series inverter output can be equivalent to a low impedance voltage source, when the two voltage source shunt, the amplitude, phase and frequency of the different between each other or fluctuations will lead to a large circulation, so that the current serious heterogeneity of the inverter device, therefore, the series inverter weaver expansion difficulties;For parallel inverter, inverter dc at the input big reactor can act as the current buffer between the parallel inverter, makes AG/DG at the input or DG/DG links have enough time to correct the deviation of dc current, achieve multimachine parallel expansion, transistor, super audio, high-frequency current shunt inverter structure is used in many parallel inverter is easy to be modular and large capacity is one of the main reasons.

Load objects of all kinds of induction heating power supply, power inverter and the load is an organic whole, generally USES the matching transformer connected power supply and load sensor, high-frequency, super audio power supply with the matching transformer from the magnetic material to the winding structure was further optimized to improve, at the same time, from the circuit topology can use 3 without the source element instead of the passive components, to cancel the transformer and achieve high efficiency and low cost.

Induction heating power supply, thyristor, transistor and vacuum tube type can be produced in China.Thyristor power supply has been used for many years.At present IGBT power supply because of its advantages more and more users are used.MOSFET power supply high efficiency, low voltage, but the price is higher, is gradually replacing the vacuum tube high-frequency power supply.Because of its low price and convenience, portable small high frequency power supply has been widely used in China and even entered the foreign market.

Uhf power supply (27.12mhz), which used to rely on imports, is now produced by at least two domestic enterprises, which have solved the needs of blade, saw blade and other special processes.

With the improvement of automatic control degree of induction heat treatment production line and the requirement of high reliability of power supply, the development of complete set of heating process equipment must be strengthened.At the same time, the induction heating system is developing towards intelligent control, and the induction heating power system with intelligent computer interface, remote control and automatic fault diagnosis and other control performance is becoming the next generation of development goal.