WO2014061473A1

WO2014061473A1 - Resistive heating device

Info

Publication number: WO2014061473A1
Application number: PCT/JP2013/077108
Authority: WO
Inventors: 下津　晃治; 幸弘次田; 勝志大住
Original assignee: 株式会社アステア
Priority date: 2012-10-18
Filing date: 2013-10-04
Publication date: 2014-04-24
Also published as: JPWO2014061473A1

Abstract

The present invention aims to prevent localized overheating in a steel sheet and localized drops in temperature in other parts of the steel sheet due to the generation of stray currents, and to provide a resistive heating device that is lightweight and has a simple device configuration. Furthermore, the present invention aims to provide a resistive heating device that can uniformly heat a plurality of steel sheets at the same time. The resistive heating device for steel sheets has a plurality of electrode units comprising at least one insulating block (12), and an electrode (11) that supplies current (3) to a steel sheet (2). The resistive heating device for steel sheets is characterized by a part of the steel sheet being sandwiched by the electrode and insulating block forming one of the plurality of electrode units, an other part of the steel sheet being sandwiched by the electrode and insulating block forming an other of the plurality of electrode units, and current being supplied between the one and the other electrode units when the steel sheet is fixed by the insulting blocks and the electrodes.

Description

Electric heating device

The present invention is an energization heating device used when hot pressing a steel plate.

When hot pressing is performed, an electric heating device is used as one of means for heating the steel plate. In the electric heating apparatus, a steel plate is disposed between a plurality of electrodes, and the steel plate is heated by energizing between the electrodes. After heating, the steel sheet is brought into contact with a pressing mold and rapidly cooled. This heat treatment is called quenching. Quenching increases the hardness of the steel.

Patent Document 1 describes that an upper electrode (reference numeral 5) and a lower electrode (reference numeral 1) constitute one electrode unit. The electrode unit is energized in a state where it is disposed at both ends of the steel plate (FIG. 1 and the like). It is described that energization is stopped by lowering the lower electrode with a cylinder (reference numeral 2) and separating the steel plate from the upper electrode.

Patent Document 2 also describes that an upper electrode (reference numeral 4) and a lower electrode (reference numeral 5) constitute one electrode unit. In this device, the upper electrode is lowered by a load device (reference numeral 9). It is described that the elastic member 3 is arranged on the electrode support member, so that the electrode can be uniformly contacted with the steel plate. It is described that when the electrode and the steel plate cannot be uniformly contacted, it causes local overheating in the steel plate.

Patent Document 3 also describes that an upper electrode (reference numerals 51 and 52) and a lower electrode (reference numerals 51 and 52) constitute one electrode unit. When a steel plate is heated, the volume expands due to heat, and wrinkles may occur in the steel plate. In the present invention, as shown in FIG. 8, the upper and lower electrodes move to prevent the generation of wrinkles.

Japanese Utility Model Publication No.57-053594 JP 2009-142853 JP 2011-245535 A

In each of the energization heating devices of Patent Documents 1 to 3, the upper electrode and the lower electrode constitute one electrode unit, and the steel plate is heated by energizing between a pair of left and right electrode units. Common. As shown in FIG. 12, the present inventors have a configuration in which a steel sheet is sandwiched and fixed between an upper electrode and a lower electrode, which are generally used in the past. It has been found that the temperature of other portions of the steel sheet is locally reduced. That is, as shown in FIG. 12, since the voltage is applied to the upper electrode and the lower electrode by branching the power supply line from the same power source, the potential of the upper electrode and the lower electrode is theoretically Is the same. However, in reality, a slight potential difference is unavoidable. Where current should flow from one electrode unit to the other electrode unit via the steel plate, a small amount of current flows between the upper and lower electrodes of one electrode unit due to this potential difference (hereinafter referred to as this current). Is called stray current). Thereby, in the vicinity of the electrode, a part of the steel sheet is locally heated, or the temperature of the other part of the steel sheet is locally decreased.

From another point of view, the configuration in which both of the electrode units that are in contact with the steel plate are electrodes is disadvantageous in the following points. That is, since an electric circuit and a power supply line for supplying power to the electrode are always connected to the electrode, the weight of the electrode increases and the electrode becomes large. After heating the steel plate with the electric heating device, at least one of the upper and lower electrodes is raised or lowered to remove the steel plate. At this time, if the upper and lower electrodes are heavy and bulky, the efficiency of the quenching operation is lowered. Furthermore, actuators such as hydraulic cylinders that move the upper and lower electrodes must improve the output according to the weight of the electrodes, which increases the manufacturing cost and the maintenance cost of the apparatus.

From another point of view, in order to improve productivity, it is conceivable that a plurality of steel plates are arranged in the width direction, and this steel plate is energized with the upper and lower electrodes in contact with each other. Again, in this case, if both the upper and lower members contacting the steel plate are electrodes, the steel plate is locally overheated or the temperature is locally lowered due to the stray current. In particular, when the upper electrode is a single long electrode and the lower electrode is also a single long electrode, it is difficult to uniformly contact a plurality of steel plates and the long electrode. Yes, the above-mentioned problem of stray current becomes even more apparent. The above-mentioned problems of manufacturing cost and device maintenance cost also occur.

An object of the present invention is to solve the problem caused by the stray current and to provide a light-weight and simple configuration energization heating apparatus.

The present invention is a steel sheet energization heating device (hereinafter sometimes simply referred to as a device) having a plurality of electrode units each composed of an electrode for supplying a current to a steel plate and at least one insulating block. To solve. One part of the steel sheet is sandwiched between an electrode constituting one of the plurality of electrode units and the insulating block. The other part of the steel plate is sandwiched between an electrode constituting the other of the plurality of electrode units and the insulating block. In a state where the position of the steel plate is fixed by the insulating block and the electrode, the steel plate is heated by energizing between one and the other electrode unit.

In the apparatus of the present invention, since the steel plate is sandwiched between the electrode and the insulating block, there is no possibility that stray current is generated. Since the steel plate is sandwiched between the electrode and the insulating block, it is firmly held during heating. Since the insulating block is used instead of the electrode, the area where the steel plate and the electrode are in contact decreases, but this can be ignored. For example, when electrodes are connected to the front sides of the left and right ends of the steel plate and insulating blocks are connected to the back sides of the left and right ends, the current flows mainly on the front side of the steel plate. The heat generated by energization is uniformly and quickly transmitted to the back side of the steel plate, so no problem occurs. For example, the electrode may be connected from the back side on the left side of the steel plate, and the electrode may be connected from the front side on the right side of the steel plate. In this case, an insulating block is brought into contact with the left surface and the right back surface.

Each electrode unit is provided with an actuator, the position of the electrode for supplying current to the steel plate is fixed in the vertical direction, and the insulating block is preferably configured to approach or separate from the electrode by the actuator. . If the position of the electrode is fixed in the vertical direction, it is not necessary to move a power supply line or an electric circuit associated with the electrode, so that work efficiency is improved. The electrode may be configured to be movable in the left-right direction according to the width of the steel plate. Examples of the actuator include a hydraulic cylinder and a pneumatic cylinder. If the rod is moved linearly by hydraulic pressure or air pressure and an insulating block is arranged at the tip of the rod, the insulating block can be moved in conjunction with the rod.

More preferably, each electrode unit is provided with an actuator, the position of the electrode for supplying current to the steel plate is fixed in the vertical direction, the electrode supports the steel plate from below, and the insulating block is attached to the electrode by the actuator. On the other hand, it is configured to approach or leave from above. In this case, the steel plate is suspended between the electrodes and energized in a state where the steel plate and the electrode are brought into close contact with each other so as to be pressed from above with an insulating block.

When quenching a plurality of steel plates at a time, the electrode unit may be configured as follows. That is, each electrode unit is composed of one electrode for supplying a current to the steel plate and a plurality of insulating blocks, and an actuator is arranged independently on each of the plurality of insulating blocks. In this case, one part of the plurality of steel plates is sandwiched between a plurality of insulating blocks constituting one of the plurality of electrode units and one electrode, and the other part of the plurality of steel plates is sandwiched between the other of the plurality of electrode units. It is sandwiched between a plurality of insulating blocks and one electrode. If it is within the range of the length of the electrode in the longitudinal direction, a single wide steel plate can be heated instead of a plurality of steel plates.

Each electrode unit preferably includes an elastic member between the insulating block and the actuator. The insulating block has a function of pressing the steel plate against the electrode. However, when the insulating block is pressed against the steel plate using an actuator, the pressing force may be excessive or a load may be applied locally. If an elastic member is arrange | positioned between an insulating block and an actuator, it can prevent that excessive pressing force and a local load are added to a steel plate. Examples of the elastic member include a coil spring, a leaf spring, and an elastomer block. The elastic member is disposed so as to expand and contract with respect to the moving direction of the insulating block.

It is preferable that an insulating block forms an insulating layer in the surface facing the steel plate of a block main body. Although the entire block may be made of an insulating material, the manufacturing cost increases because the insulating material is expensive. Furthermore, according to this configuration, since the material of the block main body does not necessarily need to be an insulating material, the block main body can be configured from an inexpensive material. Thereby, the manufacturing cost of an apparatus can be reduced. By covering the block body with an elastic insulator, an insulating layer can be formed on the surface of the block body facing the steel plate.

In the present invention, a steel plate is sandwiched and fixed between the electrode constituting the electrode unit and the insulating block. Since no current passes from the electrode to the insulating block, it is possible to suppress the occurrence of stray current. By suppressing the generation of stray current, the steel sheet can be heated uniformly.

If the position of the electrode is fixed in the vertical direction and the insulating block is moved closer to or away from the electrode by an actuator, there is no need to move a power supply line or an electric circuit associated with the electrode. By adopting this configuration, the device configuration can be simplified and the working efficiency can be improved.

If each electrode unit is composed of one electrode and a plurality of insulating blocks, and an actuator is arranged independently for each insulating block, the insulating block is independently approached or separated from one electrode. It becomes possible to do. If it does in this way, it is also possible to heat a some steel plate at once, and it is possible to heat the steel plate of various widths.

It is a perspective view which shows a mode that the steel plate is heated using an example (Example 1) of the electricity heating apparatus of this invention. It is a side view of the electric heating apparatus of FIG. It is a perspective view showing a mode that a steel plate is carried in to the electric heating apparatus of FIG. It is a perspective view showing a mode that a steel plate is carried out from the electric heating apparatus of FIG. It is a side view showing a mode that the electric heating apparatus which concerns on another Example (Example 2) is used. It is a side view showing a mode that the electric heating apparatus of another Example (Example 3) is used. It is a side view showing a mode that the electric heating apparatus of another Example (Example 4) is used. It is a side view showing a mode that the electric heating apparatus of another Example (Example 5) is used. It is a perspective view showing a mode that several sheets of steel plates are heated using the electric heating apparatus of another Example (Example 6). It is a perspective view showing a mode that one wide steel plate is heated using the electric heating apparatus of another Example (Example 6). It is the side view which showed typically the stray current produced by the clearance gap between an electrode and a steel plate. It is a side view showing a mode that the electric heating apparatus of a comparative example is used. It is a schematic diagram which shows the external appearance of the steel plate heated and cooled using the electric heating apparatus of Example 5. FIG. It is a schematic diagram which shows the external appearance of the steel plate heated and cooled using the electrical heating apparatus of a comparative example.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. 1 to 4 show an example (Embodiment 1) of the electric heating apparatus of the present invention. 5 to 10 show apparatuses according to the second to sixth embodiments.

As shown in FIGS. 1 and 2, the electric heating device 1 of Example 1 is composed of a pair of left and right electrodes. Each electrode unit is composed of one electrode 11 and one insulating block 12. The electrode 11 is disposed on the lower side and does not move in the vertical direction, but can be moved in the horizontal direction according to the length of the steel plate 2. The insulating block 12 is disposed on the upper side, and approaches or leaves the electrode 11 from above by an actuator. The left end of the steel plate 2 is sandwiched between a lower electrode 11 and an upper insulating block 12 constituting one of a pair of left and right electrode units. The right end of the steel plate 2 is sandwiched between the lower electrode 11 and the upper insulating block 12 constituting the other of the pair of left and right electrode units. The power source 113 is connected only to the lower electrode 11 via the feeder line 112.

The electrode 11 is a rectangular parallelepiped block having an electric circuit (not shown) therein, and the upper surface of the block, that is, the electrode surface is made of a copper plate. A current 3 is supplied with the copper plate of the electrode 11 in contact with the back surface of the steel plate 2. The weight of the lower electrode 11 in Example 1 is about 20 kg per piece. The length in the longitudinal direction of the electrode 11 is set longer than the width of the steel plate 2 to be heated. As the material for the electrode surface, a material having low heat resistance and low resistance during energization may be used. Examples of such materials include copper and silver. The electrode 11 is fixed on a base 111 formed of a nonconductive material. In Example 1, the base 111 is a rectangular parallelepiped that is slightly larger than the electrode so that the electrode can be stably supported. The base 111 is required to have insulating properties and heat insulating properties. In Example 1, the base 111 was formed of ceramic.

The insulating block 112 is obtained by forming an insulating layer 121 on the lower surface of a rectangular parallelepiped block main body 122 as shown in FIG. In order to press the steel plate 2 against the electrode 11 without a gap, the length of the insulating block 112 is set to be longer than the width of the steel plate 2. On the upper side of the insulating block 112, three coil springs 123 and a plate 124 for attaching the coil springs 123 are provided. The tip of the rod 125 of the hydraulic cylinder is connected to the central portion of the plate 124 in the longitudinal direction. Although not shown, the base end of the rod 125 is connected to a hydraulic cylinder. The rod 125 moves up and down in response to the hydraulic pressure. That is, the hydraulic cylinder and rod 125 function as an actuator.

When oil in the hydraulic cylinder or air in the pneumatic cylinder is heated, the control of the actuator is disturbed. Therefore, the insulating block 112 preferably has a heat insulating property in addition to an electric insulating property. In the first embodiment, the main body 122 of the insulating block is formed of stainless steel, and the insulating layer 121 is made of ceramic having excellent heat insulating properties. As the insulating layer 121, an elastic insulator having heat resistance described later may be used. The block body 122 may be made of iron in order to finish it at a lower cost.

The insulating block 12, the coil spring 123, and the plate 124 are moved up and down by the expansion and contraction of the rod 125. When the steel plate 2 is placed on the apparatus 11, as shown in FIG. 3, the rod 125 is contracted to separate the insulating block 12 from the left and right electrodes 11, and the steel plate 2 is placed on the left and right electrodes 11. Then, the rod 125 is extended to bring the insulating layer 121 of the insulating block 12 into contact with the steel plate 2. From this state, the rod 125 is further extended to compress the coil spring 123, and the steel plate 2 is evenly pressed by the repulsive force of the coil spring 123. Thereby, the steel plate 2 and the electrode 11 are closely adhered without a gap. If there is a gap between the steel plate 2 and the electrode, contact resistance is generated and the contact surface between the electrode and the steel plate may be locally overheated. Generation of contact current can be eliminated by pressing the steel plate 2 against the electrode 11 using the coil spring 123. In addition, as shown in FIG. 11, a current may be generated between one contact 113 and the other contact 114 of the steel plate 2 and the electrode 11. This causes the generation of stray current. If the steel plate 2 and the electrode 11 are brought into close contact with each other as described above, the generation of stray current can be prevented. After the heating of the steel plate 2 is completed, the left and right insulating blocks 12 are separated from the electrode 11 and the steel plate 2 is removed from the apparatus 1 as shown in FIG. The removed steel plate 2 is rapidly cooled to complete quenching. The steel plate 2 may be formed simultaneously with the rapid cooling.

As described above, when a gap is generated between the steel plate 2 and the electrode 11, stray current and contact resistance may be generated and the steel plate 2 may not be heated uniformly. Therefore, the shape of the electrode 11 may be changed as in the second to fourth embodiments shown in FIGS. The electrode 11 of Example 2 shown in FIG. 5 has a semicircular cross section, and this cross-sectional shape is continuous in the longitudinal direction of the electrode 11. The electrode 11 of Example 3 shown in FIG. 6 has a triangular cross section, and this cross sectional shape is continuous in the longitudinal direction of the electrode. In the apparatus of Example 2 and Example 3, since the contact point between the electrode 11 and the steel plate 2 is a line, there is no gap between the electrode 11 and the steel plate 2. The electrode 11 of Example 4 shown in FIG. 7 has a shape in which the upper right and upper left corners of the quadrangular prism are chamfered along the longitudinal direction thereof. Since the contact area between the electrode 11 and the steel plate 2 is larger than that of the electrode 11 according to Examples 2 and 3, the steel plate 2 can be supported stably. The apparatus 1 of Examples 2 to 4 has the same configuration as that of the apparatus 1 of Example 1 except for the shape of the electrode 11.

The apparatus 1 of Example 5 of FIG. 8 is demonstrated. The apparatus of the fifth embodiment has the same apparatus configuration as that of the apparatus 1 of the fourth embodiment shown in FIG. 7 except that the configuration of the insulating block 12 is different. The insulating block 12 according to the fifth embodiment covers the block main body 122 made of iron or stainless steel with an elastic insulator 126 having heat resistance, so that the insulating layer 121 is provided on the surface of the block main body 122 facing the steel plate 2. Forming. Since the elastic insulator 126 can be in close contact with the steel plate 2 without a gap, the steel plate 2 can be pressed against the electrode 11 without a gap as compared with a hard material such as ceramics. The block main body 122 is configured such that cracks are not generated from the corners by chamfering the corners. As the elastic insulator 126, a heat resistant cloth can be suitably used. As the heat-resistant cloth, for example, a nonwoven fabric obtained by needle punching heat-resistant fibers such as glass wool mat, ceramic blanket, rock wool or the like can be used.

A device 1 according to Example 6 in FIGS. 9 and 10 will be described. The apparatus 1 of Example 6 includes a pair of left and right electrode units. Each electrode unit is composed of one electrode 11 and two insulating blocks 12. The number of insulating blocks 12 may be increased according to the number of steel plates 2 placed on the device 2. Since the two insulating blocks 12 are provided with rods 125 connected to the hydraulic cylinders independently as actuators, the insulating blocks 12 are connected to the electrodes 11 for each steel plate 2 as shown in FIG. Can be approached or separated from each other. Therefore, a plurality of steel plates 2 can be heated together and can be heated every predetermined number. That is, it can cope with both mass production and small production. Further, as shown in FIG. 10, a single wide steel plate 2 can be heated. In the apparatus 1 of Example 6, since the width of the steel plate 2 that can be heated can be freely selected, the apparatus 1 can be used for quenching various parts. In this embodiment, the number of the insulating blocks 112 is two. However, if the width of each insulating block 112 is reduced and the number thereof is increased, the steel plates 2 and the electrodes 11 having various widths are provided. It becomes possible to make it adhere more reliably. Further, if the electrode 11 is made longer and the number of the insulating blocks 12 is increased, the wide steel plate 2 can be brought into close contact. The electrode 11 is connected to a power source 113 via a feeder line 112. The configuration of the insulating block 12 and the shape of the electrode 11 can be changed as in the first to fifth embodiments. The number of coil springs 123 may be changed as appropriate. The length of the electrode 11 is longer than those in Examples 1 to 5, but can be heated without any problem.

In the device 1 according to the sixth embodiment, one electrode 11 includes one power supply line 112 and one electric circuit. That is, since it is not necessary to prepare a plurality of feeder lines and a plurality of electric circuits for each steel plate 2 to be heated, the apparatus configuration can be simplified and the weight per electrode can be reduced.

Hereinafter, using the apparatus of Example 5 (FIG. 8) and the apparatus of FIG. 12, steel sheets corresponding to German Industrial Standard 22MnB5 were quenched. The steel sheet has a transformation start temperature (AC1) of 810 ° C. to 840 ° C. and a transformation completion temperature (AC 3) of 850 ° C. Two steel plates having the same thickness, width, and length are prepared and heated by the apparatus of Example 5 and FIG. In the apparatus of Example 5, a block body 122 prepared by chamfering a corner of a stainless steel block as an insulating block and wrapped with a glass wool mat having a thickness of 5 mm was used. The steel plate was fixed in close contact with the lower electrode so that a pressure of 4 kN was applied to the left and right ends of the steel plate from above the steel plate via rods and coil springs of a hydraulic cylinder. On the other hand, in the apparatus of FIG. 12, the steel plate was fixed by sticking the steel plate to the lower electrode so that the pressure of 4 kN was applied from the upper side to the left and right ends of the steel plate from above.

With the steel plates fixed in this way, a current of 12000 amperes was supplied to the steel plates fixed to both devices. After energizing for 7 seconds, the energization was stopped and the steel sheet was cooled. Then, the external appearance of the steel plate was confirmed visually. FIG. 13 shows one end portion of a steel plate heated by the apparatus of Example 5. The upward direction in the figure is the central direction of the steel sheet. The electrode was contacted along the broken line at the lower end of the steel plate. In FIG. 13, the hatched portion 41 did not change in color with the raw steel plate before heating. The portion 42 with wide hatching has a slightly yellowish color due to quenching. This yellow color is due to the steel plate being burnt, and indicates that it has been uniformly hardened. Although not shown in the drawings, the steel plate heated using the apparatus of Example 5 was uniformly colored yellowish except for both ends contacting the electrodes. When the temperature of the portion 41 that turned yellow during the heating of the steel sheet was measured, it was confirmed that the temperature was about 870 ° C., which exceeds the transformation completion temperature (AC3).

FIG. 14 shows one end portion of the steel plate heated by the apparatus of FIG. The electrode was installed along the broken line at the lower end of the steel plate. Even when heated by the apparatus of FIG. 12, in the region where the electrode was in contact, there was no change in color and color of the raw steel plate, and it was confirmed that this region was not quenched. However, it was confirmed that a black portion 43, a portion 44 changed from yellow to brown, and a portion 45 having the same color as the raw steel plate appeared around the electrode. In FIG. 13, the black portion 43 is painted black, and the portion 44 is cross-hatched. The black portion 43 was generated because the steel plate was excessively heated and the steel plate was burnt. The yellow to brown portion 44 is a portion that is not heated as much as the black portion 43 but is too heated and burnt. A portion 44 having the same color as that of the raw steel plate is a portion where heating is insufficient. As is clear from FIG. 13, it was confirmed that there were a mixture of a part that was heated too much and a part that was insufficiently heated around the electrode.

Next, the steel plate heated as described above was quickly conveyed to a press machine without being cooled, and heat was removed while forming with a press die to produce a door beam. In the door beam using the steel plate heated with the apparatus of Example 5, the door beam which has uniform intensity | strength over the whole beam was able to be manufactured. On the other hand, the strength of both ends of the beam is not uniform in the door beam using the steel plate heated by the apparatus of FIG. 12, and when the stress concentrates around the both ends, it easily deforms and exhibits the expected performance. I couldn't. Then, although the both ends of the steel plate were cut | disconnected and the door beam was manufactured, the yield of the steel plate fell.

1 Electric heating device 11 Electrode 111 Base 112 Feed line 113 Power supply 12 Insulating block 121 Insulating layer 122 Block body 123 Coil spring 124 Plate 125 Rod (actuator)
2 Steel plate 3 Current 31 Stray current

Claims

A current-carrying heating apparatus for a steel plate having a plurality of electrode units composed of an electrode for supplying current to the steel plate and at least one insulating block,
One part of the steel plate is sandwiched between the electrode and the insulating block constituting one of the plurality of electrode units,
The other part of the steel plate is sandwiched between the electrode constituting the other of the plurality of electrode units and the insulating block,
An electric heating apparatus for a steel sheet, wherein electricity is supplied between one and the other electrode unit in a state where the steel sheet is fixed by an insulating block and an electrode.
Each electrode unit is provided with an actuator, the position of the electrode which supplies an electric current to a steel plate is fixed to the up-and-down direction, and an insulating block is constituted so that it may approach or separate from an electrode with an actuator. 1. An electric heating apparatus for steel sheet according to 1.
Each electrode unit is equipped with an actuator, the position of the electrode for supplying current to the steel plate is fixed in the vertical direction, the electrode supports the steel plate from below, and the insulating block is from above with respect to the electrode by the actuator. The electric heating apparatus for steel plates according to claim 1, which is configured to approach or separate.
4. Each electrode unit comprises one electrode for supplying a current to a steel plate and a plurality of insulating blocks, and each of the plurality of insulating blocks is configured by independently arranging an actuator. The electric heating apparatus for steel plates according to any one of the above.
The steel sheet energization heating apparatus according to any one of claims 1 to 4, wherein each electrode unit includes an elastic member between the insulating block and the actuator.
The insulating heating device for steel sheet according to any one of claims 1 to 5, wherein the insulating block is formed by forming an insulating layer on a surface of the block body facing the steel sheet.