JPS6131947B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric induction heating method for heating a moving long metal material, such as a steel pipe, to a constant temperature.

Many electric induction heating devices have been published that uniformly heat a long metal material such as a steel pipe while moving it in its longitudinal direction. For example, Japanese Patent Publication No. 42-13674 discloses a uniform heating method using improved two-position control of the heating power source. Further, Japanese Patent Application Laid-Open Nos. 52-122941, 1982-122942, and 1977-122943 disclose devices for controlling the amount of power supplied to a heating induction coil.

In these known electric induction heating controls, the temperature of the material to be heated is detected and the amount of power supplied to the heating induction coil is controlled until a predetermined temperature is reached, and control is not performed within the same material to be heated. Ru. In these known electric induction heating controls, the control amount given is uncertain, and control is continued based on the measured temperature of the heated material exiting the heating induction coil in the control process. In addition, in these electric induction heating methods, since the temperature is controlled within the same heated material, the control is simple, and the control accuracy seems to be lacking.

The present invention reduces the height of the heating temperature increase between each heated material when giving a fixed temperature increase to each of the many heated materials that are sequentially sent to the heating inductor coil. The purpose is to keep the amount of temperature rise to a constant value.

In order to achieve the above object, in the present invention,
In induction heating using an inductor coil for a large number of materials to be heated belonging to one group, such as for each lot division, the
The difference between the pre-heating temperature and the post-heating temperature of the heated material in the group, that is, the deviation between the actual temperature increase amount and the target temperature increase amount, is determined, and the inductor coil supply power setting value for the already heated material is determined. , a supply power correction value obtained by multiplying the supply power value corresponding to the deviation by a predetermined gain is added as an adjustment value to determine the heating control operation amount for the heated material arriving at the inductor coil, or , when the set operation amount is determined for each heated material by uniformly determining the heating control operation amount for each of all the heated materials in the lot, the Ascertain the operation amount correction amount in the heating control of each part with respect to the initial setting operation amount of the heating material in any section from the tip to the tail end of the heated material, calculate the average value of these, and apply it to the current heated material in advance. A part or all of this average value is added to the assigned setting operation amount to determine the current initial setting operation amount for the material to be heated.

In order to prevent sudden fluctuations in the amount of temperature increase for each wire, the set operation amount is determined based on the deviation of the actual temperature increase from the target temperature increase of the material to be heated that has already been heated by the inductor coil as described above. It is preferable to determine the heating control operation amount for each subsequent heated material based on
In this case, the gain is used to smoothly smooth out the stepwise increase and decrease of the manipulated variable for each heated material over several or more materials, and to gently control fluctuations in the manipulated variable over many heated materials. This is to prevent rapid fluctuations in the amount of temperature increase from one tube to another.

It is preferable that the deviation is a smoothed deviation of a plurality of already heated materials so that the heating temperature increase amount of many materials to be heated converges to the target value. This smoothing method can be a simple averaging method, a weighted average of the deviations by giving lower weight to the past and higher weight to the closer to the present, an exponential smoothing method, or other smoothing methods. It is preferable to use the exponential smoothing method in order to sufficiently reflect the heating performance of the heated materials, to smoothly converge the heating temperature increase amount of each heated material to the target value, and because the calculation is simple. . In addition, in order to reduce individual fluctuations and stably converge to the target temperature increase for the entire lot, in addition to smoothing deviation, it is necessary to match gradual fluctuations in the temperature increase for many heated materials as a whole. , it is preferable to determine the amount of change in the manipulated variable by multiplying by an appropriate gain.

Such a heating control method of the present invention sets the first heating supply power for each lot based on the size and specification of the material to be heated, and for each material to be heated in that lot, A second heating supply power setting is performed for each heated material based on the actual temperature increase amount deviation for the material,
Furthermore, in heating control of each part of each heated material, each part is heated based on the correspondence between the temperature before heating of each part and the temperature increase target value, and/or the deviation of one already heated part is calculated. In the control of heating the whole lot, each material to be heated, and each part of each material to be heated to a constant temperature increase amount by three-stage heating setting or heating control, which controls the heating of the remaining part, (second heating supply power setting).

FIG. 1 shows an exemplary configuration of an apparatus for implementing the present invention. In FIG. 1, reference numerals 1 ₁ , 1 ₂ and 1 ₃ are heating inductor coils, which are arranged along a transfer path 2 for a material to be heated 3 such as a steel pipe. 4 ₁ to 4 ₆ are temperature detectors, and detectors 4 ₁ , 3 ₃ and 4 ₅
are _{the incoming} temperatures _{T i1 ,}
It detects T _i2 and T _i3 , and the detector 4
₂ , 4 ₄ and 4 ₆ are inductor coil 1, respectively.
The temperatures T _p1 , _{T p2} , _and T _p3 of the heated material 3 are detected on the outlet sides of the heated materials 1 , 1 ₂ , and 1 3 . These temperature detectors 4 ₁ to 4 ₆ may be of almost any type, but radiation thermometers are usually used. When multiple sensors are installed in the circumferential direction of the pipe, the average value of their detected temperatures is used.

In this embodiment, the first inductor coil 1
₁ is arranged for constant temperature heating in order to always raise the outlet temperature T _p1 to a constant target temperature T ₁ despite the variety of inlet temperatures T _i1 , and the second induction Child coils 1 _{and 2} have inlet side temperatures T _i2
It is used for constant temperature rise heating to give a predetermined temperature rise (T ₂ - T ₁ ) to
₃ , a predetermined temperature rise (T ₃ − _{T 2} ) to the inlet temperature T _i3
It is used for constant temperature rise heating to give . Correspondingly, a heating control circuit that controls the heating power of each of the inductor coils 1 ₁ to 1 ₃ has almost the same configuration, but a heating control circuit that controls the heating power of the first inductor coil 1 ₁ for constant temperature heating. The control circuit uses the difference between the inlet temperature T _in1 and the target temperature T ₁ (T ₁ - _{T in1} ) as one input quantity, while the second and third inductor coils for constant temperature rise heating 1 ₂ and 1
The heating control circuit No. ₃ and No. 3 each use the set temperature increase amount (T ₂ −T ₁ ) and (T ₃ −T ₂ ) as one input amount.

The heating control circuit receives an electrical signal representing the inlet temperature T _i1 continuously or at intervals, and outputs a signal representing a time series average value T _in1 of T _i1 .
Average value calculation circuit 5 ₁ consisting of an integrating circuit with a predetermined time constant, etc. Average value calculation circuit 5 ₂ having a similar configuration and outputting a signal representing the average value T _pn1 of the outlet temperature T _p1 ; Target temperature setting A signal representing the target temperature T ₁ from the device 6 ₁ (for example, a potentiometer) and an average value T of the inlet temperature from the average value calculation circuit 5 ₁
Temperature increase target value setting circuit 7, which is composed of an operational amplifier, a differential amplifier, etc., receives a signal representing T _in1 as an input, and outputs a signal representing a temperature difference of (T ₁ - T _in1 ).
₁ ; With the signals representing T _in1 and T _pn1 from the average value calculation circuits ₅₁ and ₅₂ as inputs, and the signal representing (T ₁ −T _in1 ) from the setting circuit ₇₁ , (T _pn1 −T _in1 ) − (T ₁ − T _in1 ), that is, the actual average temperature increase amount (T _pn1 − T _in
1 ) A temperature rise amount deviation calculation circuit 8 ₁ consisting of an operational amplifier etc. outputs a signal representing the deviation from _the target temperature rise amount (T ₁ −T _in1 ); Smoothing circuit 12 ₁ that smooths over two or more heating materials, for example, several heating materials; This smoothed value is multiplied by the unit operation amount (operation amount required to change the temperature increase by 1 degree Celsius) and the gain for power control. A first correction amount calculation circuit 9 ₁ consisting of an operational amplifier, a function generator, etc., converts into a signal representing the change in the manipulated variable (this is the set manipulated variable of the material to be heated this time); A manipulated variable calculation consisting of an operational amplifier, etc., which adds all or part of the average value of the temperature increase control correction amount of each part to the initial setting manipulated variable in the previous heating control of the heated material, which will be described later. Circuit 10 ₁ ; Internal control circuit 13 ₁ that outputs a manipulated variable correction amount in response to the ever-changing difference between the pipe inlet temperature and its target temperature; Pipe tracking circuit 14 ₁ ; Average value calculation circuit 15 ₁ ; and the second
It is composed of a correction amount calculation circuit ₁₆₁ . In this heating control circuit, the temperature increase target value setting circuit 7
₁ , the temperature T on the inlet side of the first inductor coil 1 _1
in1 and target temperature T ₁ are input, which results in (T ₁ −
T _in1 ) becomes the target temperature increase amount, and therefore, even if the temperature T _i1 on the input side of the heated material 3 varies, heating control is performed to set the temperature on the output side as the target value T ₁ .

In the heating control circuit, signals representing the first and second target temperatures _T1 and _T2 are sent from target temperature setting devices ₆₂ and ₆₃ such as potentiometers to the temperature increase target value setting circuit ₇₂ . is applied. Therefore, the heating control circuit sets the target temperature increase amount to a fixed amount (T ₂ −T ₁ ). Therefore,
The heating control circuit performs constant temperature increase control so that even if the temperature T _i2 on the inlet side fluctuates, the temperature on the outlet side is always T _i2 +(T ₂ −T ₁ ). The heating control circuit also performs constant temperature rise control in the same way. In addition, in FIG. 1, the target temperature setters 6 ₂ , 6 ₃ , 6 ₄ and 6 ₅ are shown to output signals representing the target temperatures T ₁ , T ₂ , T ₂ and T ₃ respectively, but This is tentatively displayed on the assumption that T _p1 = T _i2 = T ₁ and T _p2 = T _i3 = T ₂ , and each of these target temperature setters 6 ₂ to 6 ₅ is It may be set to output a signal indicating a predetermined temperature. This is because, in the second inductor coil ₁₂ , _a predetermined temperature increase amount T _p1 (in the diagram, _{T p1}
= T ₂ - T ₁ ), and in the third inductor coil ₁₃ , a predetermined temperature increase is applied to the temperature (T ₁ +T _p1 ) on the exit side of the second inductor coil. This is because it is sufficient to additionally heat the amount T _p2 (T _p2 = T ₃ - _{T 2} in the figure). In the embodiment shown in FIG. 1, the final target temperature is T ₁ +T _p1 +T _p2 . In addition, in the illustration, it is _T3 , and the relationship becomes _T3 = _T1 + _Tp1 + _Tp2 . However, the above is the first inductor coil 1
This is a case where it is assumed that the material to be heated 3 is not cooled while it is running between the second inductor coil and the second inductor coil, and between the second inductor coil and the third inductor coil. The influence of cooling can be compensated for by adjusting the set values of the target temperature setters 6 ₁ - 6 ₅ .

Next, to explain in more detail the functions of each of the above-mentioned components, the pipe tracking circuit ₁₄₁ detects the arrival of the tip and tail ends of the pipe, and detects the arrival of the tip and tail ends of the pipe, and determines the timing between them corresponding to the movement of the pipe. It issues a signal and instructs the average interval (sampling interval) to the average value calculation circuits ₅₁ and ₁₅₁ , and also instructs the internal control circuit ₁₃₁ to determine the tube end control timing and the temperature rise amount deviation of each part in the center of the tube. Instructs the calculation timing for modifying the manipulated variable based on the operation amount.

Internal control circuit 13 ₁ is a control circuit for eliminating temperature fluctuations in the length direction within one pipe. These include a feedforward control circuit that calculates a manipulated variable correction amount by multiplying by a constant coefficient, or a pattern control circuit that outputs a manipulated variable correction amount in a fixed pattern at both ends of a pipe. The output value of these changes within one line.

The average value calculation circuits 5 ₁ , 5 ₂ and 15 ₁ respectively receive the temperature measurement value by the thermometer (signal input continuously or intermittently at regular intervals) and the pipe tracking circuit 14 ₁ to calculate the operation amount correction amount of each coil. Input the signal in the interval specified by and calculate the average value. A good method for averaging is simple averaging, which is obtained by taking the integration (or integration) of the signals in the section and dividing it by the number of integrations (or integration time). The maximum average length is from the tip to the rear end of the pipe, but it is desirable to exclude unsteady parts (200 to 1000 mm) at both ends.

The second correction amount calculation circuit ₁₆₁ calculates the second correction amount ΔV ₂ from the operation amount correction amount average value V _D using the following equation.

ΔV ₂ = bV _D , b is a constant: 0<b<1 Temperature increase target value setting circuit ₇₁ uses the average inlet temperature T _in1 (of the previous heated material) to set the target temperature T ₁ and A signal representing the difference θ*=T ₁ −T _in1 = target temperature increase amount is output. On the other hand, the circuit
, _... output a signal representing θ*=T ₂ −T ₁ =target temperature increase amount.

The temperature increase amount deviation calculation circuit ₈₁ calculates the average temperature increase value θ _n =T _pn1 −T _in1 , and further calculates the target temperature increase amount θ* and the average temperature increase value θ _n
From this, the temperature increase deviation Δθ=θ _n −θ* is determined, and a signal representing this is output.

First correction amount calculation circuit 9 ₁ and smoothing circuit 12 ₁
Here, as a method to reflect the temperature increase deviation of two or more past times in the first correction amount, for example, (1) smooth the temperature increase deviation Δθ for each time, obtain a smoothed value, and multiply this by a coefficient. , find the correction amount ΔV ₁ , or (2) ΔV ₁ = C ₁ (Δθ _{o -1} − Δθ _{o-2 ) from the previous temperature increase amount deviation Δθ o-1} and the temperature increase amount deviation Δθ _o-2 from the previous time. +C ₂ · Δθ _o-2 C ₁ , C ₂ : Calculate the correction amount ΔV ₁ using a formula consisting of appropriately set constants. In both cases, everything from the first to the previous run of the same lot is reflected in the manipulated variable V _S.

To explain the method (1) adopted in the example in a little more detail, as a smoothing method, exponential smoothing expressed by the following formula is simple and suitable _k-1 = α・Δθ _k-1 + (1-α) _{k-2 k-1} ; Smoothed value _k-2 due to previous deviation; 〃 〃 Δθ _k-1 ; Previous temperature increase deviation α; Exponential smoothing coefficient When calculating ΔV ₁ from 0<α<1 The coefficients used for are determined as follows. This coefficient is a product of two types of coefficients. One is the increase/decrease a ₁ in the temperature increase required to increase/decrease the temperature increase by unit temperature, which changes depending on the pipe size and other operating conditions, but may be set in advance. The other one is the adjustment gain a ₂ , which is usually 0 to 1.
This is to measure the stability of control by taking the values up to and avoiding removing all of the deviation only in the next time. In the end, ΔV ₁ is found using the following formula: ΔV ₁ =−a ₁ ×a ₂ ×.

In general, in a control method in which the initial setting manipulated variable V _S for each line is modified by the internal control circuit, in addition to the initial setting manipulated variable V _S , the internal control circuit outputs V _D (this output changes within one line,
V _D is the average value), and their sum V _T (=
V _S +V _D ) determines the amount of heat actually added to the material to be heated, and the temperature increase deviation Δθ occurs because there is a deviation in V _T .

However, when calculating V _S , the first correction amount Δ
Since the previous setting operation amount V _S is added to V ₁ , V _D is not taken into consideration at all.
Therefore, some kind of correction to V _D becomes necessary. Simply put, the first correction amount ΔV ₁ is added to the total operation amount V _T
There is also a method of calculating a new initial setting manipulated variable V _S by adding , but this is not necessarily appropriate. This is because while V _S captures the trends of several past lines, V _D is the amount of operation for the disturbance of only that one line, so these two cannot be made to be the same at any time.

Therefore, in the present invention, considering the temperature increase amount change Δθ' due to V _D , it is assumed that when V _D is 0, the temperature increase amount that was Δθ becomes Δθ − Δθ', and in contrast to this, the first Apply the calculation to find the correction amount of Δθ
Of -Δθ', Δθ is the source of the original first correction amount, and -Δθ' is the source of the second correction amount.
Now, if the unit operation amount (the increase or decrease in the operation amount necessary to increase or decrease the unit temperature of the temperature increase) is a ₁ , then Δθ'=V _D /a ₁ . Therefore, Δθ−Δθ′=Δθ−V _D /a ₁ . If we perform exponential smoothing with the coefficient α using this Δθ−Δθ′ as the temperature increase deviation, k=αΔθk+(1−α)Δk _−1′k =α(Δθk−Δθ′)+(1−α) _{Δk -1} , so ′=−αΔθ′. The first correction amount ΔV ₁ ′ is ΔV′ ₁ =a ₁ a ₂ {−(−αΔθ′)} =a ₁ a ₂ (−)+a ₁ a ₂ αΔθ′ = ΔV ₁ +a ₁ a ₂ α・(V _D /a ₁ ) = ΔV ₁ +αa ₂ V _D Therefore, the second correction amount ΔV ₂ is calculated as ΔV ₂ =bV _D , and the desirable value of b is αa ₂ . V _D is the output of the control circuit within one circuit (changes within one circuit).
Obtained on average within the book.

If all inductor coils are controlled by the amount of temperature rise,
It is sufficient that the inlet temperature of the first stage (initial stage) coil and its target value match, but if there is a discrepancy, the difference will be carried over to the final stage heating temperature.
In order to prevent this, the heating control device shown in Fig. 1 does not use the temperature set as the target value of the inlet temperature of the first stage coil, but rather the average value of the inlet temperature of the previous heated object (the temperature of the material before heating). (equal to temperature). The temperature of the material before heating usually does not differ from one piece to another, so the next temperature and the previous temperature can be considered to be the same.

The first stage heating coil ₁₁ will be explained by taking an example.

The set inlet and outlet temperature target values are T ₀ *,
T ₁ *, and the average values of the entrance and exit temperatures of the previously heated material are T ₀ and T _1. If all coils are controlled by a constant temperature increase amount, the temperature increase deviation Δθ is Δθ = (T ₁ − T ₀ ) - (T ₁ * - T ₀ *), and if control is performed to make Δθ 0, then T ₁ = T ₁ * + (T ₀ - T ₀ *), and the outlet temperature T ₁ is the target temperature T ₁ * (T ₀ −
This will result in a deviation of T ₀ *). This deviation is carried over to the final stage. On the other hand, when the coil ₁₁ is subjected to constant temperature control as shown in Fig. 1,
Since T ₀ is used instead of T ₀ *, the temperature increase deviation Δθ is Δθ = (T ₁ − T ₀ ) − (T ₁ * − T ₀ ) = T ₁ − T ₁ *, so that Δθ is set to 0. Assuming that such control is performed, T ₁ =T ₁ *, and the outlet temperature T ₁ becomes equal to the target value T ₁ *.

Next, an example will be described. Inner diameter 370mm, coil rating 1000V, coil capacity 1200KW, coil length 700mm,
In the second stage coil ₁₂ with an energizing frequency of 330Hz,
The material to be heated is a pipe with an outer diameter of 244.5 mm and a wall thickness of 12.05 mm, and the target temperature increase value T ₂ - _{T 1} is 140℃ (T ₂ = 310
℃, T ₁ = 170℃).

For the third pipe, we calculated the initial setting operation amount (V _S ) = 510V. In the part excluding 1000mm at both ends of the pipe
The total operation amount and the inlet and outlet temperatures were sampled and measured every 500 mm, and the results were averaged. The total operation amount (V _T ) was 518V, the average inlet temperature was 169℃, and the average outlet temperature was 311℃. The smoothed value of the temperature increase up to the second tube was 8°C, the smoothing coefficient of the temperature increase was 0.5, the temperature increase amount to manipulated variable gain was 27, and the adjustment gain was 0.6.

From the above, the procedure for calculating the initial setting operation amount for the fourth pipe is as follows: Temperature increase deviation Δθ = (311-169) - 140 = 2℃, Temperature increase deviation smoothed value = 0.5 × 2 + 0.5 × 8 = 5℃, 1st correction amount ΔV ₁ = −0.6×2.7×5≒−8V, 2nd correction amount ΔV ₂ =0.3×(518−510)≒2V, 4th operation amount V _S =510−8+2= It is 504V.

Figure 2 shows the first lot of the same number as the numerical calculation example.
The actual values of the initial setting operation amount, total operation amount, temperature increase average value, and final heating temperature (7 coil outlet temperature) of the No. 2 coil ₁₂ described above up to the 20th coil are shown. From this, the optimum value for the manipulated variable of the Γ2 coil is approximately 510V.

ΓThe initial operating value of 550V was about 40V higher, resulting in a temperature increase deviation of about 10°C.

Γ However, by the third test, both the set operation amount and the temperature increase amount had settled down to good values.

The reason why the Γ total manipulated variable changes somewhat violently for each line is probably due to the temperature disturbance that changes for each line.

As a result of performing similar control for each Γ coil, the final heating temperature was within ±4° C., which is a fully satisfactory result.

(If it were not controlled, it can be estimated that the temperature variation would be about ±10°C.)

In FIG. 1, the average of the inlet temperature T _i1 and the average of the outlet temperature T _p1 are first obtained, and from these values the average of the difference between the inlet temperature T _i1 and the outlet temperature T _p1 (T _pn1 -T _in1 ), the detection signals of the detectors 4 ₁ and 4 ₂ are applied to a difference calculation circuit such as a differential amplifier circuit to calculate the difference between the input temperature T _i1 and the output temperature T _p1 . (T _p1 - T _i1 ) is obtained, a signal representing this is given to the average value calculation circuit, and the average value (T _pn1 - T i1 ) is calculated.
T _in1 ) may be obtained and a signal representing this may be input to the temperature increase amount deviation calculation circuit.

Further, FIG. 1 shows a mode in which the first inductor coil performs heating control to the target temperature T ₁ and then the second and third inductor coils perform heating to a predetermined temperature increase amount.
In the heating control circuit, the target temperature setting device ₆₂ is omitted, and the signal representing T _i2 , which is the output of the detector ₄₃ , is used as a negative input of the heating amount target value setting circuit ₇₂ , and _T2 is set as the second target temperature. By doing so, the second
Heating by the inductor coil ₁₂ is a constant temperature control mode in which T2 is _{the outlet temperature despite fluctuations in the inlet temperature T i2 .} Similarly, the heating control circuit can also have a constant temperature control mode. In this way, when the second and third heating control circuits are set to a constant temperature control mode, the outlet temperatures T _p1 and T _p2 are respectively controlled in the heating control by the inductor coil arranged in the previous stage (upstream side). Even if there is a slight deviation from the target temperatures T ₁ and T ₂ , the deviation is compensated for in the subsequent stage, so it does not affect the final temperature (T ₁ +T _p1 +T _p2 or T ₃ ).

The heating temperature control circuit shown in FIG. The number of inductor coils may be any number greater than or equal to two, depending on the temperature difference between the temperature of the inductor and the final target temperature, the capacity of each inductor coil, and the like. The detectors 4 ₂ and 4 ₃ may be used in common (T _p1 = T _i2 in this case), or the detectors 4 ₄ and 4 ₅ may be used in common (T _p2 = T i2 ). T _i
3 ). When doing this, the average value calculation circuit 5
₂ and 5 ₃ and 5 ₄ and 5 ₅ each become one shared item.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an example of an electric induction heating device implementing the present invention, and Fig. 2 is a graph showing the relationship between the voltage applied to the inductor coil and the amount of temperature rise when the present invention is implemented. It is. 1 ₁ to 1 ₃ : inductor coil, 2: transfer path,
3: Heated material, 4 ₁ - 4 ₆ : Temperature detector, 6 ₁ -
6 ₅ : Target temperature setting device, 7 ₁ , 7 ₂ : Temperature increase amount target value setting circuit.

Claims (1)

[Scope of Claims] 1 A number of materials to be heated are sequentially passed through an inductor coil, and the heating of each portion of each material to be heated is controlled so that the amount of temperature increase in each portion or the temperature on the outlet side becomes a constant temperature increase amount. In order to do this, the amount of adjustment of the operation amount in the heating control of each part with respect to the initial setting operation amount of the material to be heated that has already been heated by the inductor coil is grasped in any section from the tip to the tail end of the material to be heated, and these changes are made. Induction heating is characterized in that the average value of is calculated, and all or part of this average amount is added to the set operation amount previously assigned to the current material to be heated, and the result is set as the initial setting operation amount for the current material to be heated. Control method. 2 The set operation amount of each heated material is determined by calculating the difference between the pre-heating temperature and the post-heating temperature of the heated material that has already been heated by the inductor coil, that is, the deviation between the actual temperature increase amount and the target temperature increase amount. 2. The induction heating control method according to claim 1, wherein a corrected operation amount obtained by multiplying the operation amount change corresponding to the deviation by a predetermined gain is added to the initial setting operation amount for the heated material.