JPH0361335A - Ring transformer for electrical heating of strip - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a ring transformer for electrically heating a running strip, particularly a relatively thin strip, in an apparatus for electrically heating a strip to a predetermined temperature for various purposes. Regarding.

(Prior art) One of the joint applicants of this application created an electrical heating device for running materials based on a new technical idea, and the invention directed to wire rods was published in Japanese Patent Application No. 61-272798 (Japanese Unexamined Patent Publication No. 63 -128
No. 125), and an invention directed to a band material was filed in Japanese Patent Application No. 300127/1983. For example, the inventions of both applications will be described with reference to FIG. 1 showing an apparatus for processing a strip material.A transformer 101 whose feeding passage passes through the inside of the ring of an annular iron core t1 is disposed close to both ends of the transformer 10 and is placed above the feeding passage. For example, a pair of rolls a contacts the strip W of
, b, and a conductive material 3.3 that electrically connects the both roll electrodes 21.22 via, for example, a slider S.
．． The relationship between the resistance R1 of the running heated belt material W between 22 and the resistance R2 of the conductive materials 3, 3 is set as R1>>R2, and by supplying power to the primary winding 12 of the transformer 10, both of the above-mentioned Conductive materials 3, 3 are placed on the strip W running between the roll electrodes 21 and 22.
This is an energization heating device that heats by inducing a secondary current with a return line of .

(Problems with the prior art) By the way, the current heating device does not cause any problems when heating a wire rod, but when heating a strip material, it is difficult to find a way to uniformly heat the inside direction. It occurred to me that there was a problem, and a solution to the problem was desired.

(Object of the Invention) The present invention has been made to solve the problems faced by the invention of the device for energizing a strip material as filed in the above-mentioned Japanese Patent Application No. 62-30.0127. It is an object of the present invention to provide a ring transformer for electrically heating a band material, which enables uniform heating in the width direction.

(Structure of the Invention) The present invention provides a transformer for a heating device that heats a strip material by energizing it, in which the winding weight of a primary winding wound around an iron core is set to be at least approximately equal to the width of the maximum width strip material to be heated. The gist is to become.

That is, in the band material heating using the energization heating apparatus 100 of FIG. 1, the energization heating is scheduled for the band material.

In Fig. 2, for example, the width (Ww) shown by the solid line as Wl is relatively small or medium, or the width (Ww) of the core 11 shown by the broken line as W2 is almost full width (Wwmax), or the width is intermediate between the above two. , etc.

Although there are various sizes, in the present invention, the width (Cw) is not 12゜, which is the width of the strip material W1 that heats the primary winding.
Almost equal winding weight (Cwmax) corresponding to the width (Wwmax) of the maximum medium band material W2, that is, (Wwmax #
Cwmax).

This setting is based on the width of the maximum width of the band material (Wwmax
), it may be set to be slightly larger, it may be set to the same width, or it may be set to be slightly smaller or medium.

(Function of the Invention) Originally, in heating by the current heating device 100, when heating a relatively thin strip W such as 9, for example, 2 mm or less, the inside of the strip (W w ) and the primary winding width (Cw ) if the relationship is (WW#CW), ideal uniform heating in the middle direction can be obtained, but by adopting the above configuration, the present invention has the above configuration, even if (Ww<Cw), uniform heating in the width direction can be obtained. It has the effect of ensuring uniform heating.

In addition, in the case of (Ww<<Cw) and when the plate thickness is particularly thin (for example, 1 mm or less), although it is said that the edge direction shows a slightly higher temperature than the center, the difference is small. , can be considered as uniform heating in relation to heat radiation.

(Progress until completion of the present invention) The present invention was completed through current density analysis during electrical heating, heat transfer analysis, and experiments using an actual machine.

The progress will be described below.

(1) Current density analysis during current heating: The current density distribution relationship induced in the heated strip W by the transformer IO during current heating was analyzed by computer using the finite element method.

Some of them are disclosed below.

Basic equation of electromagnetic equation In the above equation (11), assuming that the x-y two-dimensional field is isotropic and that A changes sinusoidally, equation (1) becomes as follows.

--------(2) however, A.

A: Magnetic vector potential Az: Z-direction component of magnetic vector potential Jo: Forced commutation density Joz: Z-direction component of forced current density μ: Magnetic permeability σ: Electrical conductivity ω: Angular frequency φ: Potential Expression (2) above (W b/m) (A/m2) (A/m2) (H/m) (υ/m) (rad/s) (V) Common analysis conditions and physical property (Wb/m) values are as follows. For example, take a steel strip that is a common strip material to be heated, and calculate the difference between the winding overlap or winding position of the primary winding and the current density distribution in the width direction of the strip material with a thickness of 2 mm. We calculated the correlation between

f = 60 (Hz) μc”6000 (relative magnetic permeability of the iron core) μ匈=1 (relative magnetic permeability of the primary coil) μ5=30 (relative magnetic permeability of the strip material) σs = (conductivity of the strip material); 20°C --------7, 7X
108200℃−・−・−4,0XIO” 750℃−−−−4,OXIO” However, the gap g between the primary winding and the strip material is 150 (mm).The coil current Joz is the average current of the strip material. Density is 1.5
It was set to be X106 (A/m2).

Figure 3 shows the analysis results when there is a relationship (Ww=Cw), (a) is a magnetic flux simulation diagram, and (b) is the current density J of the strip material corresponding to the above change in the strip material conductivity σS.
In the distribution map, line A is 7.7X10', line opening is 4.0X1
0' and line C are for the case of 1.0x10e, indicating that the current density J becomes uniformly distributed as the temperature rises.

Figures 4(a) and (b) show the case where (Ww<<Cw) and the conductivity σS of the strip material is 7.7X106, and the difference between the center and edge is the line i in Figure 3(b). Even when compared with the current density distribution, there is not much difference in the current density distribution.

Figures 5(a) and (b) show the case where (Ww>>Cw) and the conductivity σS of the strip material is 7.7X10'', and it is clear that the current density, I, between the center and the edge is unbalanced. ing.

Next, the analysis results when (Cwmax = Wwmax) and the conductivity σS of the strip material is 7.7X108 are shown in Figure 6 (a).
) and (b). There is an extremely small difference in the current density 5 distribution between the center and edge.

In addition, the current density deviation (edge-center/center) under each condition shown in FIGS. 3 to 6 is
Shown in the table.

From the above figures and Table 1, it can be seen that as the temperature rises, the distribution of current density J tends toward uniformity, and that the current density J decreases in areas where the primary twist lines do not correspond. (Wwma
x=Cwmax x) is the best.

It is understood that the deviation of the current density J is also extremely small when (Ww=Cw) and furthermore (ww<cw).

What can be said further is that the current density J deviation between the center and edge at the band material conductivity σs = 7.7X10', which corresponds to the initial stage of heating, is in the single digit range, and this degree of difference is only noticeable at the end of heating. It is presumed that this has little effect on ensuring uniformity of heating temperature in the middle direction.

B0 The present inventor further assumes that the strip materials having plate thicknesses of 4 mm and 6 mm (Ww=Cw), and that the strip material conductivity σS is 1 to 7.
7×10′, and the other conditions were the same as in the case of the plate thickness of 2 mm.

Figures 7 and 8 show the five current density distributions that are the analysis results. In each figure, (a) is the surface, and (b)
is the current density 5 distribution in the core, and in each figure the strip material conductivity σ
The case where S is 7.7×108 is shown as line A, the case where S is 4×106 is shown as a line opening, the case where S is 2×106 is shown as line C, and the case where S is lXl0' is shown as line 2.

Further, Table 2 summarizes the changes in the deviation of the current density J due to the changes in the conductivity σS of the strip material at the surface and core portions shown in each of the above figures.

Table 2 From the above figures and Table 2, even if the relationship (Ww=Cw) is maintained, the thickness of the strip material is 4 mm,
As the thickness increases to 5 mm, the conductivity of the strip material corresponding to the initial stage of heating σS = 7.7
The current density J distribution deviation between edges shows 10-digit percentage,
It is confirmed that this is extremely large compared to the case of the strip material with a thickness of 2 mm mentioned above, which had almost the same conductivity σS and was in the single digit range.

In electrical heating, the distribution of current density J becomes uniform as the temperature rises, but the accumulation of the current density 4 distribution during the temperature rise process determines the final heating result.
From the percentage shown by the 5 mm strip material, it is estimated that the relationship (Ww=Cw) causes a significant temperature difference in the final heating temperature between the center and edge. In other words, it can be concluded that the thicker the strip material is, the more difficult it is to uniformly heat it in the middle direction when (Ww<Cw), contrary to the case of a thin strip material.

C0 In addition to the above-mentioned current density analysis, we also conducted a parallel analysis of the conduction state of heat generated depending on the current density, that is, a heat transfer analysis. Cwm
If it is set to a x=Wwmax x), then (WW<C
The results show that uniform heating in the middle direction of the strip material satisfying the relationship W) is guaranteed.

(2) Experimental Example: Next, the inventor conducted a heating experiment using the electrical heating device 100.

For the experiment, the core width was 520 mm in the middle direction, the primary winding width was 400 mm, and the gap between the strip material and the primary winding on one side was 15 mm.
Using a 0mm transformer, steel strips of various widths were passed through the transformer as specimens, heated with electricity in a stationary state, and when at least a portion of the specimen was heated to 500°C, the inside of the transformer near the exit was measured. The surface temperature was measured using a thermocouple. The width of each specimen (Ww>, the plate thickness t and the winding weight of the primary winding (C
W) Relationship 9 Heating specifications and temperature measurement results are shown in Table 3.

From Table 3 and the same table, when the thickness of the specimen is 1 mm or less, the width of the specimen (
The relationship between Ww) and the winding weight (CW) of the primary winding is (Ww<C
It has been confirmed that no uneven heat occurs even with w), and the uneven heat is slight when (Ww<<Cw), and as the thickness of the specimen increases, the uneven heat tends to increase. It was done.

The above experimental results confirmed the above computer analysis results, and proved that the present invention is extremely effective in uniformly heating a relatively thin strip material in the mid-direction.

(Other Examples) The above experimental examples were conducted under a stationary state in order to ensure accuracy of temperature measurement. However, in the case of line production in which the strip is heated to a predetermined temperature while running, the running speed should be set so that the strip runs between both roll electrodes 21 and 22 for the heating time described in the experimental example. Of course, the same results as in the experimental example can be obtained.

In addition, although the above analysis and experimental examples were about steel strips, if the material has a different electrical conductivity σ from that of the steel strip, the electrical conductivity σ
The band width WW: There are large and small ranges in which uniform heating is possible in the middle of the roll, but based on the results of many other analyzes and experiments in addition to the disclosed analysis and experiments, it is qualitatively the same. It has also been confirmed that there is a trend.

(Effects of the Invention) By carrying out the present invention, it is possible to uniformly heat various medium-sized belt materials from the smallest to the largest to be heated in the middle direction when heating relatively thin strip materials. This makes it possible to eliminate the need to prepare various medium-sized transformers or transformers with primary winding weights depending on the width of the strip material, and therefore equipment costs are kept to a minimum, and production costs are accordingly reduced. The cost can be kept extremely low, and the effects of the present invention are enormous.

[Brief explanation of drawings]

Fig. 1 is a front view of an electrical heating device to which the present invention is applied, Fig. 2 is a sectional view taken along the line X--X of Fig. 1 showing an embodiment of the primary winding of the transformer of the present invention, and Figs. 3(a) to 3). FIG. 6(b) shows the results of computer analysis for heating a 2 mm thick strip material, and (a) and (b) in each figure
are the magnetic flux principal nigression diagram and the current density distribution diagram, the seventh
Figures (a) to 8(b) show a plate thickness of 4 mm and a plate K6.
These are the results of a computer analysis using a strip material of mm as the heating target, and (a) and (b) in each figure are current density distribution diagrams on the surface and core. 100---1---------Electrification heating device 10
−・・−−1−−−−−−・−・−(Ring) transformer 11−・・・−1～−−・−・−・−Iron core 12−−−−
−−−−−−−−−−−−−−−Primary winding 21.22・
-1---・Roll electrode

Claims (1)

[Claims] A transformer in which a feed passage passes through the ring of a circular iron core, roll electrodes that are arranged close to both ends of the transformer and in contact with the strip material on the feed passage, and a conductive material that electrically connects the two roll electrodes. In a transformer of a heating device that heats a strip running between both roll electrodes by supplying power to the primary winding of the transformer to induce a secondary current with the conductive material as a return wire, A ring transformer for electrically heating a band material, characterized in that the winding width of the primary winding which is wound in multiple turns is set to be at least approximately equal to the width of the maximum width band material to be heated.