RU2039420C1 - Method for induction heating of flat metal products - Google Patents

Abstract

FIELD: heating methods. SUBSTANCE: method involves induction heating of products to temperature T by means of two flat inductors between which heated product is placed. Inductors are applied for period T to voltage supplied by central power supply. Upper inductor is movable in order to adjust space between it and heated product so that cosφ of inductors is near one. Heating is performed in three steps: first step involves setting minimal possible space and power supplied to circuit of upper inductor is half of maximal value P_max/2. Space between upper inductor and product is increased during second step so that minimal power in circuit is P_max/2. During third step power is kept at level P_min. During all steps power supplied lower stationary inductor is kept at level P_max/2. EFFECT: increased functional capabilities. 6 dwg

Description

 The invention relates to electrothermics and can be used in high-performance induction heating processes before metal forming.

 A known method of controlling the surface heating of workpieces [1] Heating is carried out by periodically repeating stages in two stages, on the first of which the workpieces are heated by connecting a power source, and on the second, the temperature is aligned over the workpiece cross section by turning off the power source, at both stages the surface and center temperature are controlled workpieces and when these temperatures are equal and they reach the lower permissible limit of the final temperature, the workpiece is unloaded from the furnace. In order to reduce the marriage by the unevenness of heating in transient conditions during heating in methodological furnaces, the average temperature of all the workpieces is determined at the beginning of the heating stage of the last stage and the power source is turned off when the average temperature reaches the final value.

 The disadvantage of this method is the limited heating performance.

A known method of heat treatment of metal products in an inductor [2] Produce heating products by connecting the inductor to the full supply voltage for a given time, then turn off the inductor and maintain the product for the time required to equalize the temperature over the cross section, and the heating is carried out with a change in the frequency of supply and support at this cosφ is close to unity. In order to increase the productivity of the process, heating is carried out in three stages, at the first of which the supply frequency is maintained at f _max , at the second stage, the frequency is gradually reduced to f _min , at the third frequency is maintained at f _min .

 A significant disadvantage of the heat treatment method is the limited productivity and uniformity of heating products. Another disadvantage is the difficulty of implementing frequency regulation caused by electromechanical or valve converters, as well as a change in the thermophysical properties of the heated products.

а P_min выбирают из соотношения P_min<

P_maxпричем Р_max определяется по соотношению
P_max=

где C удельная теплоемкость изделия;
m масса изделия.The essence of the heating method lies in the fact that when heating flat metal products to a predetermined temperature T _back , in which two flat inductors built into the production line, between which the heated product is located, are connected to the full supply voltage of a centralized source for a given time t _n , and the upper movable inductor controls the gap between it and the product with cosφ inductors close to unity, the heating is carried out in three stages, the first of which sets the minimum possible clearance and maintains the power in the circuit of the upper inductor is half the maximum P _max , at the second stage the gap is increased exponentially until the minimum power P _min in the circuit is reached, at the third stage, the power is maintained at P _min , while the power in the circuit of the lower stationary inductor is all stages of heating are maintained at

and P _{min is} selected from the relation P _min <

P _max and P _max is determined by the ratio
P _max =

where C is the specific heat of the product;
m mass of the product.

 In FIG. 1 is an illustration explaining a method for induction heating flat metal products; in FIG. 2 the law of changing the gap between the upper inductor and the heated product; in FIG. 3 program for changing the power in the circuit of the upper inductor; in FIG. 4 diagram of the distribution of temperature fields over the thickness of the workpiece; in FIG. 5 device for implementing the proposed method; in FIG. 6 design of inductors for implementing the proposed method.

 A device that implements the proposed method comprises an upper inductor 1, a lower inductor 2, an electric motor 3, a reducer 4, a heated product 5, a roller table 6, a power adjuster 7, a power regulator 8, a speed regulator 9, a current regulator 10, a controlled thyristor converter 11, an armature circuit 12 and the mechanical inertial part 13 of the electric motor 3, the integrating link of the gearbox 14, the transfer coefficient 15 of the inductor, the current sensor 16; speed sensor 17; power sensor 18.

 Inductors contain the first 19 and second 20 multi-position switches. The upper inductor 1 is movable, and the lower inductor 2 is stationary. Between the inductors 1 and 2 is a heated flat metal product 5. To move the upper inductor relative to the product, an electric motor 3 is used, on which shaft a speed sensor 17 is located. The electric motor 3 by means of a reducer 4 with a ball screw pair moves the inductor 1. The heated product 5 enters the heating zone along the roller table 6. The power sensor 18 measures the power in the circuit of the upper inductor 1.

значение. Первый этап интервала нагрева заканчивается при достижении температурой верхней поверхности изделия Т_пов ⁽¹⁾ ≥ 1,1 Т_зад (фиг. 4). На втором этапе (фиг. 2) интервала нагрева (t₂-t₁) зазор увеличивают до минимального значения Р_min мощности в контуре индуктора 1. На третьем этапе интервала нагрева (t_н-t₂) мощность в контуре индуктора 1 поддерживают минимальной на уровне P_min. Мощность в контуре индуктора 2 на трех этапах интервала нагрева поддерживают постоянной на максимальном значении

.Интервал нагрева заканчивается (фиг.4) по достижении температурой нижней поверхности изделия Т_пов ⁽²⁾ 0,9 Т_зад и наступает интервал выдержви (t_в), необходимый для выравнивания температуры центра Т_ц с температурами Т_пов ⁽¹⁾, Т_пов ^{(2 )}и температурой слоя, прогретого выше Т_зад изделия, при котором централизованный источник питания полностью отключен. Интервал выдержки заканчивается по достижении температурами Т_ц, Т_пов ⁽¹⁾, Т_пов ⁽²⁾ равенства на уровне Т_зад ±ε
Устройство, реализующее предлагаемый способ, работает следующим образом. Токовый контур (фиг. 5), в составе 10-12,16, настроен на технический оптиум и компенсирует электромагнитную постоянную времени якорной цепи Т_я. Переходный процесс в контуре определяется малой постоянной времени токового контура Т_m ^т. Регулятор 10 тока имеет пропорционально-интегральную зависимость выходного напряжения от входного. Скоростной контур в составе 9, 13,17, настраивается на технический оптиум и компенсирует электромеханическую постоянную времени Т_м механической инерционной части 13 электродвигателя 3. Переходный процесс в контуре определяется удвоенной малой постоянной времени скоростного контура Т_m ^c. Регулятор 9 скорости пропорционального типа стабилизирует скорость электродвигателя 3 на заданном уровне и задает уровень напряжения входного сигнала регулятору 10 тока. Контур мощности, в составе 8, 14, 15, 18, настраивается на симметричный оптиум и компенсирует учетверенную малую постоянную времени контура мощности Т_m ^p. Переходный процесс в контуре определяется удвоенной малой постоянной времени контура мощности Т_m ^p. Регулятор 8 мощности пропорционально-интегрального типа стабилизирует мощность в контуре индуктора 1 на заданном уровне и задает напряжения входного сигнала регулятору 9 скорости.For optimal heating of the product to T _backside, the heating interval is carried out in three stages (figure 2), adjusting the power P (figure 3) in the circuit of the inductor 1 with a gap h between it and the heated product. At the first stage of the heating interval (t ₁ ), the gap is minimum h _min , and the power in the circuit of inductor 1 has a maximum

value. The first stage of the heating interval ends when the temperature reaches the top surface of the product T _pov ⁽¹⁾ ≥ 1.1 T _back (Fig. 4). In the second stage (Fig. 2) of the heating interval (t ₂ -t ₁ ) the gap is increased to a minimum value of P _min power in the circuit of the inductor 1. In the third stage of the heating interval (t _n -t ₂ ) the power in the circuit of the inductor 1 is kept at a minimum level P _min . The power in the circuit of the inductor 2 at three stages of the heating interval is kept constant at the maximum value

. The heating interval ends (Fig. 4) when the temperature of the bottom surface of the product T _pov ⁽²⁾ reaches 0.9 T _back and there is a holding interval (t _in ) necessary to equalize the temperature of the center T _c with temperatures T _pov ⁽¹⁾ , T _pov ^{(2 )} and the temperature of the layer heated above T _{backside of the} product, in which the centralized power source is completely turned off. The exposure interval ends when the temperatures T _c , T _pov ⁽¹⁾ , T _pov ^{(2) are} equal at the level T _ass ± ε
A device that implements the proposed method works as follows. The current circuit (Fig. 5), consisting of 10-12.16, is tuned to technical optium and compensates for the electromagnetic time constant of the anchor circuit T _i . The transition process in the circuit is determined by the small time constant of the current circuit T _m ^t . The current controller 10 has a proportional-integral dependence of the output voltage on the input. The _high -speed circuit, consisting of 9, 13.17, is tuned to the technical optium and compensates for the electromechanical time constant T _{m of the} mechanical inertial part 13 of the electric motor 3. The transient in the circuit is determined by the doubled small time constant of the high-speed circuit T _m ^c . The proportional type speed controller 9 stabilizes the speed of the electric motor 3 at a predetermined level and sets the voltage level of the input signal to the current controller 10. The power circuit, consisting of 8, 14, 15, 18, is tuned to a symmetrical optium and compensates for the quadruple small time constant of the power circuit T _m ^p . The transient in the circuit is determined by the doubled small time constant of the power circuit T _m ^p . The proportional-integral type power controller 8 stabilizes the power in the circuit of the inductor 1 at a predetermined level and sets the input voltage to the speed controller 9.

The operation of the device when changing the load moment M _n on the shaft of the electric motor 3 is as follows. With an increase in M _n on the motor shaft, the feedback signal from the sensor 17 decreases, and the error at the input of the controller 9 increases. The output voltage of the speed controller 9 increases, increasing the input voltage level on the current controller 10, the output voltage of which increases. The voltage at the output of the converter 11 increases and the speed of the electric motor 3 is restored accurate to statism. The device works similarly when reducing the load moment on the shaft of the electric motor 3.

 The operation of the device in the process of induction heating is as follows.

The centralized power supply is turned on at full voltage. The power adjuster 7 sets the input voltage signal corresponding to the maximum power level in the circuit of the inductor 1 to the input of the power regulator 9. There is a voltage at the outputs of elements 9-11 and the motor 3, rotating, brings the inductor 1 through the reducer 4 to the heated product 5 to the maximum power value P _max / 2 in the circuit of the inductor 1. The drive turns on when the voltages from the power setpoint 7 and power sensor 18 are equal . When switching the power setter 7 to the input voltage signal corresponding to the minimum power level in the circuit of the inductor 1, the input signal from the regulator 8 decreases, which leads to a decrease in the output voltages from elements 9-11 and the inductor 1 moves away from the heated product 5 to the minimum value of P _min power in the inductor circuit 1. The drive is turned off when the voltage is equal from the power setter 7 and the power sensor 18.

 In order to economically consume the active power of the supply voltage when changing the range of heated products, the inductors are made with multi-position switches 19 and 20, allowing you to include the required number of internal and external turns of the inductors, depending on the overall dimensions of the heated products.

Heat cycle endurance annular cylindrical steel blank with 850 mm outer diameter 250 mm inner diameter and 145 mm in height and ¹¹⁰⁰ C is characterized by the following parameters. The UPI2-500 / 1N induction unit with a frequency converter ППЧВ-500-1,0-6000 with control along the excitation circuit is used as a centralized power source for two ring spiral inductors with an external diameter of 1000 mm and an internal diameter of 250 mm. At the first stage of the heating interval, a maximum 1/2 P _max 250 kW power is maintained in the inductor circuit 1. This stage ends at time t ₁ , when the upper surface of the product reaches a temperature equal to T _POV ⁽¹⁾ 1.1 T _ass 1310 ^о С The time t ₁ is 6.3 minutes Then the gap between the upper inductor and the product is increased and the power in the circuit of the inductor 1 is reduced to a level of P _min 166 kW for t ₂ -t ₁ 8 s, after which the power in the circuit of the upper inductor is maintained at a level of P _min 166 kW, for t _n t ₂ 1.50 min. The range of the gap lies in the range of 10-100 mm. The power in the circuit of the lower inductor at three stages of the heating interval is maintained at 1/2 P _max 250 kW for t _n 8.00 min. The point in time t _n is recorded on reaching the bottom surface of the product temperature T _dressing ⁽²⁾ 0.9 T _backside 990 ^o C. At this end three phase heating interval of duration t _n. At a temperature equalization interval of 1.5 minutes _in duration, the centralized power supply is completely turned off. The end of the entire heating cycle products shutter is fixed when reaching a temperature equal surfaces and articles center at 1100 ± 40 ° ^C. The duration of the heating cycle t is determined by the product extract _n + t _in + 8.00 9.50 1.5 min at a heating accuracy ( ± 40 ^° C). Comparison of the proposed control method with frequency control shows that the minimum cycle time heating the exposure of the specified workpiece, when controlling the frequency of the supply voltage and accuracy (± 45 ^about C) is 18.2 minutes Thus, the cycle time at the stated heat exposure heating method is reduced an average of 10 minutes while heating achieving quality (± 40 ° ^C). As a drive for moving the upper inductor, a UVZ-21 motion reproducing device is used, manufactured by the Novosibirsk Electromechanical Plant with a type 1EM8-012 drive having a rod force with a locked rotor 8KN. The drive electric motor has a power of P 1.3 kW, rated current I _n 23A, supply voltage U 45.5 V. The annual economic effect of the introduction of the method and device for its implementation is about 494,100 rubles. due to a significant reduction in metal waste and a decrease in the number of defective products.

Claims (1)

METHOD FOR INDUCTION HEATING FLAT METAL to a predetermined temperature T _{s and d,} in which two planar inductor integrated into the process line, between which is arranged to be heated product connects to full voltage centralized power source for a predetermined time t _n, and the upper movable inductor controlled gap between them and the product with cosφ inductors close to unity, characterized in that, in order to increase the productivity of the process and increase the uniformity of heating, heating is performed in three stages apa, the first of which is set the minimum possible clearance and maintain the power in the loop of the upper inductor at half maximum P _{m a x,} in a second step the gap increase exponentially until the value of the minimum power P _{m i n} in the circuit in the third stage power maintained at P _{m i n,} wherein the power circuit of the lower stationary inductor at all stages of the heating is maintained at P _{m a x} / 2, and P _{m i n} is selected from the relation P _{m i n <m and} 1/3 _x P ,
and P _{m a x} is determined by the ratio

where C is the specific heat of the product;
m mass of the product.

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