JP5639864B2 - Direct current heating method - Google Patents

Description

  The present invention relates to a direct current heating method for heating a plated steel plate by passing a direct current, for example, in hot pressing.

  For example, one method of heating a plated steel sheet during hot pressing is a direct current heating method (also referred to as a resistance heating method) in which a direct current is passed through the plated steel sheet. The direct current heating method is a method of heating the plated steel plate by utilizing the fact that heat is generated in proportion to the electric resistance of the plated steel plate through which an electric current flows, and can be used by converting electric power to heat without waste. There is an advantage that the temperature of the plated steel plate can be raised to the quenching temperature in a short time. The current passed through the plated steel plate may be either direct current or alternating current, but since commercial power is generally used as it is, alternating current is common. When alternating current is used, if the plated steel sheet is thick, an increase in electrical resistance due to the skin effect can be expected, so that the plated steel sheet can be heated more efficiently.

  Since the temperature of the plated steel plate to be hot-pressed is raised until the plated steel plate is quenched, there is a problem that the plating is temporarily melted and biased. For example, when an electric current is passed in the extending direction of the steel plate having a rectangular shape in plan view, the molten plating is biased toward the center in the width direction, and on the contrary, the plating in the vicinity of the side edge becomes thin. Plating is expected to prevent scale (oxide film) from being generated on the surface of the heated steel plate, or to work as a rust-proof film after hot pressing. It becomes impossible to prevent the generation of scale, and anti-rust performance after hot pressing cannot be expected.

  In Patent Document 1, since the molten plating moves and is biased by the influence of the magnetic field due to energization (attraction by Fleming's left hand rule) (Patent Document 1 [0007]), the current density is reduced when the plating is thick. On the contrary, when the plating is thin, a hot press molding method is proposed in which the current density is increased to prevent uneven plating. Specifically, the plating thickness and the current density are associated with a specific relationship (Patent Document 1 / Equation (1)), and a current equal to or lower than the current density determined according to the plating film thickness is passed. The hot press working method disclosed in Patent Document 1 has a maximum plating thickness of 22 μm because of a specific relationship between the thickness of plating and the current density (Patent Documents 1 and [0009]). Further, if the thickness of the plating is sufficiently small, the plating and the steel plate are rapidly alloyed, and uneven plating is effectively prevented (Patent Document 1 [0014]).

JP 2010-070800 JP

  As described above, the plating applied to the plated steel plate is expected to prevent the scale (oxide film) from being generated on the surface by heating or to act as a rust-proof film after hot pressing. There is no need for film thickness control. Rather, it is preferable that the plating film thickness is larger in order to achieve the above-described function sufficiently. Although plating is easy to control the film thickness, it is more difficult to control the film thickness than the electroplating method where the film thickness is relatively thin. It is preferable because the manufacturing cost can be reduced. From this, it is preferable that the plating applied to the plated steel plate is thicker, but in this case, the hot press molding method disclosed in Patent Document 1 is difficult to use.

  A careful examination of the effect of the magnetic field in direct energization revealed that the plating bias was only an effect of a portion of the magnetic field generated around the plated steel plate. The magnetic field generated in the plated steel plate directly energized in the extending direction is formed by magnetic flux generated so as to surround the cross section in the width direction of the plated steel plate. The magnetic flux generated in parallel with the front and back surfaces of the plated steel plate works on the molten plating with the Lorentz force pressed against the front and back surfaces, so that the molten plating is not moved. That is, the magnetic flux generated in parallel with the front and back surfaces of the plated steel plate does not significantly affect the plating bias.

  However, the magnetic flux generated upward or downward by winding the side edge of the plated steel plate (for example, if the upward magnetic flux is generated on the right edge side, the downward magnetic flux is generated on the left edge side) is the center in the width direction of the plated steel plate. The Lorentz force that moves toward the surface is applied to the molten plating. The Lorentz force becomes weaker as it moves away from the side edge of the plated steel plate, but the molten plating on the side edge moves toward the center in the width direction of the plated steel plate, It becomes like pushing sequentially toward the center in the width direction, and the plating is biased to the center in the width direction of the plated steel plate as a whole.

  Here, if the direct current is AC, the direction of the magnetic flux generated by winding the side edge of the plated steel plate is changed in a short time. It seems to push in the direction away from the center in the width direction. However, since the Lorentz force becomes weaker as it moves away from the side edge of the plated steel plate, the Lorentz force toward the center in the width direction of the plated steel plate is always greater than the reverse Lorentz force, resulting in molten plating. Moves toward the center of the steel plate in the width direction.

  From this, it is understood that the unevenness of the plating can be prevented if the side edge of the plated steel plate is wound to weaken the magnetic flux generated upward (or downward), and at least the Lorentz force caused by the magnetic flux can be reduced. Thus, for example, in hot press processing, in the direct current heating method in which the plated steel plate is heated by passing a direct current, the side edge of the plated steel plate is rolled upward (or so as to eliminate the problem of uneven melting of the plated plating) In order to develop a direct current heating method that reduces the Lorentz force caused by the magnetic flux generated downward), we examined it.

  As a result of the study, in the direct energization heating method in which the plated steel plate is heated by passing a direct current, the side edge that extends in the direction in which the current of the plated steel plate flows (hereinafter referred to as the side edge of the plated steel plate) A direct energization heating method characterized in that an auxiliary energizing plate having side edges extending across an insulating gap is arranged in the same plane as the plated steel plate, and an electric current having the same phase is applied to the plated steel plate and the auxiliary energizing plate. It is. Since there are a pair of side edges extending in the direction in which the current of the plated steel plate flows, the auxiliary energizing plate is used for each of the side edges.

  The direct current heating method of the present invention applies the same phase current to the plated steel plate and auxiliary current plate arranged in the same plane, and surrounds the cross sections in the width direction of the plated steel plate and auxiliary current plate. The magnetic flux of the direction is generated, the side edge of the plated steel plate is rolled up, and the magnetic flux generated upward (or downward) and the side edge of the auxiliary energizing plate in a positional relationship facing the side edge of the plated steel plate are rolled up. Cancels the magnetic flux generated downward (or upward) and weakens the magnetic flux generated by winding the side edges of the plated steel plate.

  The current passed through the plated steel plate and the auxiliary energizing plate may be direct current or alternating current. In-phase current means direct current or alternating current with the same frequency and no phase difference. When the current flowing through the plated steel plate and the auxiliary energizing plate is alternating current, the magnetic flux generated by entraining the side edge of the plated steel plate or the side edge of the auxiliary energizing plate in a positional relationship facing the side edge of the plated steel plate Since the magnetic flux generated by winding is changed in direction, it can always cancel each other by eliminating the phase difference at the same frequency.

  “The side edge of the plated steel plate extending in the direction in which the current flows” means the side edge of the plated steel plate parallel to the current to be supplied, and normally the current flows in the extending direction (longitudinal direction). It becomes the side edge of the direction. The purpose of heating and quenching the plated steel sheet in the hot press process is to be uniform in the extending direction. From this, it is customary that the steel plate in hot press processing is a rectangular in plan view extending in the same width so that the electric resistance in the extending direction is uniform, and “plated steel formed in a pair of left and right” The side edges extending in the direction in which the soot current flows are parallel.

  Auxiliary energizing plate has a side edge extending across the insulating gap with respect to the side edge of the plated steel plate means that the side edge of the auxiliary energizing plate on the side facing the side edge of the plated steel plate is the plated steel plate. It means that it is parallel to the side edge. Insulation gap means the distance between the plated steel plate and the auxiliary energizing plate that does not cause dielectric breakdown. You may comprise on both sides of a board. The side edge of the auxiliary energizing plate that is far from the side edge of the plated steel plate has the same current density in the direction in which the current flows, and the magnetic flux that surrounds the cross section in the width direction of the auxiliary energizing plate is even in the extending direction. Therefore, it is preferable to make the cross-sectional area of the auxiliary energizing plate constant so as to be parallel to the side edge of the plated steel plate.

  “Place the plated steel plate and the auxiliary energizing plate in the same plane” means that the planes of the plated steel plate and the auxiliary energizing plate are parallel and flush with each other, and the side edges described above are arranged side by side. Means that. In this case, if the magnetic flux generated by entraining the side edge of the plated steel plate and the magnetic flux generated by entraining the side edge of the auxiliary energizing plate in a positional relationship opposite to the side edge of the plated steel plate can be canceled out The auxiliary energization plate may be slightly shifted in the vertical and horizontal directions with respect to the plated steel plate, or may be inclined.

  Specific examples of the auxiliary current-carrying plate may include an end material portion of a press-formed plated steel plate or another plated steel plate. When the end material part of the press-formed plated steel plate is used as an auxiliary current plate, a slit is provided on the side edge extending in the direction in which the current flows in the plated steel plate to form an insulating gap, and both ends in the extending direction are plated. It is good to connect with a steel plate to make an electrode connection plate shared with the plated steel plate. By providing the common electrode connection plate, it becomes easy to flow the same phase current through the plated steel plate and the auxiliary energizing plate.

  Moreover, when another plated steel plate is used as an auxiliary energizing plate, a plurality of plated steel plates are arranged in the same plane leaving an insulating gap between side edges extending in the direction of current flow. This is a direct energization heating method in which a plurality of plated steel plates are arranged in a direction orthogonal to the direction of current flow and directly energized at once, and is suitable for heating many plated steel plates at a time. Among the arranged steel plates, a separate auxiliary energizing plate is arranged on the side edge on the side where there is no adjacent plated steel plate located at both ends, or the end material is only for the side edge. It is better to leave the part and use it as an auxiliary energizing plate.

In the direct energization heating method for heating a plated steel plate by flowing a direct current using the present invention, an auxiliary energization plate having a side edge extending along a side edge extending in a direction in which the current of the plated steel plate flows, The direct energization heating method is characterized in that it is arranged in a parallel plane facing the plane of the plated steel plate with an insulating gap interposed therebetween, and a current of opposite phase is applied to the plated steel plate and the auxiliary energizing plate. The magnetic flux generated by entraining the side edges of the plated steel plate can be weakened by utilizing the canceling of magnetic flux, which is a characteristic feature.

  In the direct current heating method in which the planes of the plated steel plate and the auxiliary energizing plate are opposed to each other, currents in opposite phases are applied to the plated steel plate and the auxiliary energizing plate arranged in parallel planes, respectively. A magnetic flux in the opposite direction is generated so as to surround the cross section in the width direction of the steel plate. For example, a magnetic flux generated upward (or downward) by entraining the side edge of the upper steel plate is opposed to the side edge vertically. The side edge of the lower auxiliary energizing plate is rolled up to counteract the magnetic flux generated downward (or upward), and the magnetic flux generated by winding the side edge of the upper plated steel plate is weakened.

  The plated steel plates and auxiliary current plates arranged in parallel planes, for example, are arranged flush with the upper and lower parallel planes divided into upper and lower sides, and the side edges of the plated steel plates and auxiliary current plates are aligned in the horizontal direction. In order to align the side edges of the plated steel plate and the auxiliary energizing plate in the horizontal direction, it is preferable that the plated steel plate and the auxiliary energizing plate have the same shape in plan view. From this, the direct energization heating method uses the auxiliary energizing plate as another plated steel plate, and the side edges extending in the direction in which the current of the plated steel plate flows coincide with the direction orthogonal to the direction in which the plated steel plates are opposed to each other. It is also possible to arrange the plated steel plates in parallel planes facing each other across the insulating gap. In this case, two plated steel plates can be heated simultaneously by a single heat treatment.

  The present invention relates to a direct current heating method in which, for example, in hot pressing, a plated steel sheet is heated by direct current flow, a magnetic flux generated by winding a side edge of the plated steel sheet is entrained on the side edge of the auxiliary current plate. It is weakened by canceling each other with the magnetic flux generated in step 1, and the Lorentz force caused by the magnetic flux generated by entraining the side edges of the plated steel plate is reduced, thereby eliminating the problem that the molten plating is biased. In addition, the present invention can obtain the above effects regardless of the thickness of the plating, and can be used in combination with the invention of Patent Document 1, for example.

  In order to use the present invention, a separate auxiliary energization plate is required as compared with the conventional direct energization heating method. However, the addition of the auxiliary energization plate does not cause a great increase in labor and cost in direct energization heating. Further, for example, the auxiliary energizing plate can be easily added by using the auxiliary energizing plate as an end material portion of a press-formed plated steel plate or another plated steel plate. In particular, if the auxiliary energizing plate is made of another plated steel plate, there is an advantage that a large number of plated steel plates can be heated at one time without causing uneven plating.

  The direct current heating method, in which the plated steel plate and the auxiliary energizing plate are arranged in parallel planes and the current of opposite phase is applied, the plated steel plate and the auxiliary energizing plate are stacked in the direction perpendicular to the plane. It has the effect that the installation area of the direct current heating apparatus using the invention can be suppressed. Further, if the auxiliary energizing plate is made of another plated steel plate, the processing efficiency can be improved. Further, for example, if a configuration in which a plated steel plate and an auxiliary energizing plate or another plated steel plate are alternately stacked, the number of plated steel plates that can be heat-treated at a time increases, and the processing efficiency can be further improved. .

It is a perspective view showing an example of the direct energization heating method of the present invention which arranged a plating steel plate and an auxiliary energization board in the same plane. It is AA sectional drawing in FIG. It is a perspective view showing an example of the direct energization heating method of the present invention which used the end material extended in parallel with a side edge as an auxiliary energization board. It is a perspective view showing an example of the direct current heating method of this invention which used another plated steel plate as an auxiliary electricity supply board. It is a perspective view showing an example of a direct current heating method using the present invention in which a plated steel plate and an auxiliary energizing plate or another plated steel plate are arranged in parallel planes. It is BB sectional drawing in FIG.

  An embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, the direct current heating method according to the present invention includes, for example, a rectangular plated steel plate 1 that is long in the longitudinal direction and a plated steel plate having the same length as the plated steel plate 1 and a width. Auxiliary current-carrying plates 3 and 3 having a rectangular shape in plan view narrower than 1 are arranged in the same plane with an insulating gap 2 between the side edges 11 and 31 in a positional relationship with the plated steel plate 1 sandwiched in the short direction. A current I having the same phase is applied in the longitudinal direction of the plated steel plate 1 and the auxiliary energizing plate 3 by the electrodes 4 and 4 which are arranged and sandwiched between both ends in the longitudinal direction of the plated steel plate 1 and the auxiliary energizing plate 3.

  As shown in FIG. 2, the present invention applies a current I of the same phase to the plated steel plate 1 and the auxiliary energizing plate 3 arranged in the same plane, and each of the short sides of the plated steel plate 1 and the auxiliary energizing plate 3. Magnetic flux B in the same direction is generated so as to surround the direction (width direction) cross section, and magnetic flux B (downward thick arrow in FIG. 2) generated by winding the side edge 11 of the plated steel plate 1 downward, The magnetic flux B (upward thick arrow in FIG. 2) generated by winding the side edge 31 of the auxiliary energizing plate 3 is canceled out, and the magnetic flux B generated by winding the side edge 11 of the plated steel plate 1 is weakened. The Lorentz force F acting from the side edge 11 toward the center in the lateral direction is weakened. Although illustration is omitted, similar cancellation of the magnetic flux B occurs at the side edge 11 on the opposite side of the plated steel plate 1.

  In FIG. 2, a group of arrows representing the Fleming left-hand rule is the plated steel after the downward solid line arrow cancels out the magnetic flux B generated at the side edge 11 of the plated steel plate 1 before the downward broken line arrow cancels out. Each of the magnetic fluxes B acting on the side edge 11 of the steel plate 1 is represented, and the left broken white arrow indicates the Lorentz force F acting near the side edge 11 of the plated steel plate 1 before the magnetic flux B cancels out. The extracted arrows represent the Lorentz force F acting on the side edge 11 of the plated steel plate 1 after the magnetic flux B cancels each other. As understood from the group of arrows, since the Lorentz force F acting near the side edge 11 of the plated steel plate 1 is weakened, a situation in which the molten plating is biased by the Lorentz force F can be suppressed or prevented.

  The direct current heating method of the present invention may utilize the end material portion 12 of the press-formed plated steel plate 1 as shown in FIG. 3 instead of the auxiliary current plate 3 (see FIG. 1) described above. it can. In this case, a rectangular steel plate 1 in plan view that is long in the longitudinal direction, and rectangular end material parts 12 and 12 in plan view that are the same length as the plated steel plate 1 and narrower than the plated steel plate 1. Insulating gaps 2 are provided between the side edges 11 and 121, are arranged in the same plane, and are connected by electrode connection plates 122 formed at both ends in the longitudinal direction. 4, current I having the same phase is applied in the longitudinal direction of the plated steel plate 1 and the end material portion 12. When the direct current heating is intended for hot pressing, for example, the end material portion 12 and the electrode connecting plate 122 are cut off after the hot pressing.

  Moreover, it replaces with the auxiliary | assistant electricity supply board 3 (refer FIG. 1) mentioned above, and another plated steel plate 1 can also be utilized so that it may be seen by FIG. In this case, for example, a plurality of plated steel plates 1 having the same shape are arranged in the same plane with insulating gaps 2 provided between the side edges 11 and 11, and both longitudinal ends of all plated steel plates 1 are integrated. Currents I having the same phase are applied in the longitudinal direction of the plated steel plate 1 by the sandwiched electrodes 4, 4. Thereby, the adjacent plated steel plates 1 and 1 play the same role as the auxiliary energizing plate 3 (see FIG. 1) with respect to the other party. Here, the auxiliary energization plate 3 is arranged on the side edge 11 on the side where the adjacent plated steel plates 1 of the plated steel plates 1 located at both ends do not exist, as described above. End material portions may be left only on the side edges 11 on the side where the adjacent plated steel plates 1 of the plated steel plates 1 located at both ends are not present (not shown).

Direct electrical heating how to utilize the present invention, as seen in FIG. 5, for example, longitudinal direction and plated steel sheet 1 of rectangular shape as viewed in plan is long, the same in plan view shape as the plating steel plate 1 An electrode 4, 4, in which a certain other steel plate 1 is arranged in parallel planes with an insulating gap 2 between opposing planes, and the longitudinal ends of the steel plates 1, 1 are sandwiched together, A mode in which the current I having the same phase is applied in the longitudinal direction of the plated steel plates 1 and 1 may be employed. The insulating gap 2 is stably maintained by the insulating plate 5 interposed between the plated steel plates 1 and 1. Instead of another plated steel plate 1, an auxiliary energizing plate 3 having the same shape in plan view as that of the plated steel plate 1 may be used (in FIG. 5, reference numerals are shown in parentheses).

  When the plated steel plates 1, 1 are arranged in a parallel plane, as shown in FIG. 6, a current I having an opposite phase is applied to the plated steel plates 1, 1, and the short sides of the plated steel plates 1, 1 are respectively short. A magnetic flux B in the same direction is generated so as to surround the direction (width direction) section, and the magnetic flux B generated upward by entraining the side edge 11 of the upper steel plate 1 (upward thick arrow in FIG. 6) And the magnetic flux B generated downward by winding the side edge 11 of the lower plated steel sheet 1 (downward thick arrow in FIG. 6), and the magnetic flux B generated by winding the side edge 11 of each plated steel plate 1 And the Lorentz force F acting from the side edge 11 toward the center in the short direction is weakened. Although illustration is omitted, similar cancellation of the magnetic flux B occurs at the side edge 11 on the opposite side of the plated steel plate 1.

  In FIG. 6, the arrow group representing the Fleming left-hand rule is such that the upward or downward solid line arrows cancel the magnetic flux B generated at the side edge 11 of the plated steel plate 1 before the upward or downward broken line arrows cancel each other. Respective magnetic fluxes B acting on the side edges 11 of the plated steel sheet 1 are shown, and the left-pointed broken white arrow indicates the Lorentz force F acting near the side edges 11 of the plated steel sheet 1 before the magnetic fluxes B cancel each other. The solid white arrows pointing to the left represent the Lorentz forces F acting near the side edges 11 of the plated steel plate 1 after the magnetic flux B cancels each other. In the upper plated steel plate 1 and the lower plated steel plate 1, the direction in which the current I flows is reversed, so the direction of the generated magnetic flux B is also reversed, and only the Lorentz force F is directed in the same direction. .

1 Plated steel plate
11 Side edge of plated steel plate
12 End material part
121 Side edges of mill ends
122 Electrode connection plate 2 Insulation gap 3 Auxiliary energization plate
31 Side edge of auxiliary energizing plate 4 Electrode 5 Insulating plate I Current B Magnetic flux F Lorentz force

Claims (3)

In the direct current heating method in which the plated steel plate is heated by passing a direct current,
Auxiliary energizing plates having side edges extending across the insulating gap with respect to the side edges extending in the direction in which the current flows in the plated steel plate are arranged in the same plane as the plated steel plate, and are in phase with the plated steel plate and the auxiliary energizing plate. A direct current heating method characterized by passing a current of The auxiliary energizing plate is an end material portion of the formed plated steel plate. A slit is provided in the side edge extending in the direction in which the current flows in the plated steel plate to form an insulating gap, and both ends in the extending direction are plated steel. The direct energization heating method according to claim 1, wherein the electrode connection plate is connected to a reed and shared with the plated steel reed. The direct energization heating method according to claim 1, wherein the auxiliary energizing plate is another plated steel plate, and the plurality of plated steel plates are arranged in the same plane leaving an insulating gap between side edges extending in a direction in which a current flows.

Images