WO2022059424A1

WO2022059424A1 - Heating device and metal material

Info

Publication number: WO2022059424A1
Application number: PCT/JP2021/030640
Authority: WO
Inventors: 公宏野際; 章博井手
Original assignee: 住友重機械工業株式会社
Priority date: 2020-09-18
Filing date: 2021-08-20
Publication date: 2022-03-24
Also published as: JP2023162459A

Abstract

This heating device is for heating a metal material to be shaped, and is provided with a heating unit for heating the metal material by means of electric heating. A zinc-containing plating layer is formed on the metal material. The heating unit carries out an alloying process for facilitating alloying of the zinc of the plating layer, and, after the zinc is alloyed as a result of the alloying process, heats the metal material to a temperature higher than the boiling point of the zinc.

Description

Heating equipment and metal materials

The present invention relates to a heating device and a metal material.

Conventionally, a molding device for molding a metal material is known. For example, Patent Document 1 below includes a molding die having a lower die and an upper die paired with each other, and a fluid supply unit for supplying a fluid into a metal pipe material held between the molding dies. The molding apparatus is disclosed. In such a molding apparatus, a heating apparatus for heating the metal material to be molded is used.

Japanese Unexamined Patent Publication No. 2009-220141

A heating device such as the above-mentioned conventional technique heats a metal material to be molded by energization heating. Here, since the heating device heats the metal material so as to have a high temperature, oxidation scale may be generated on the surface of the metal material due to the oxidation of the metal material. Therefore, by forming a plating layer on the surface of the metal material, the generation of oxide scale may be suppressed. However, when the heating device heats rapidly, zinc contained in the plating layer may evaporate and ignite, resulting in the generation of zinc oxide. Therefore, it has been required to suppress the generation of oxidizing compounds such as oxide scale and zinc oxide.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a heating device capable of suppressing the generation of an oxidizing compound on the surface of a metal material, and a metal material. be.

The heating device according to one aspect of the present invention is a heating device for heating a metal material to be molded, and includes a heating unit for heating the metal material by energization heating, and a plating layer containing zinc in the metal material. Is formed, and the heating part is subjected to an alloying treatment for advancing the alloying of zinc in the plating layer, and after the alloying treatment, after the zinc is alloyed, the temperature becomes higher than the boiling point of zinc. Heat the metal material to.

In the heating apparatus according to one aspect of the present invention, the heating unit performs an alloying treatment for advancing the alloying of zinc in the plating layer. Here, the boiling point of the alloy layer that has been sufficiently alloyed by the alloying treatment is higher than the boiling point of zinc. Therefore, after the alloying treatment, the heating unit heats the metal material so that the temperature becomes higher than the boiling point of zinc. Therefore, even if the temperature of the metal material becomes higher than the boiling point of zinc, the alloying of zinc is sufficiently advanced and the boiling point is high, so that the ignition of zinc can be suppressed. From the above, it is possible to suppress the generation of the oxidized compound on the surface of the metal material by suppressing the generation of zinc oxide while suppressing the generation of the oxide scale by the plating layer.

The heating unit may be heated so that the temperature of the metal material draws a temperature profile in multiple stages. In this case, the heating unit can heat the metal material so as to have an appropriate temperature profile depending on the progress of zinc alloying.

The heating unit may be heated so as to draw a temperature profile of the primary heating step, the holding step of holding the temperature, and the secondary heating step. In this case, the heating unit rapidly raises the temperature to the target temperature for the alloying treatment in the primary heating step, and keeps the temperature at the target temperature in the holding step to proceed with the alloying of zinc. Then, the heating unit can raise the temperature of the metal material to the final target temperature in the secondary heating step after the alloying treatment.

The heating unit may set the target temperature in the primary heating stage to 700 ° C or higher and 800 ° C or lower. In this case, it is possible to suppress the ignition of zinc while advancing the alloying of zinc while avoiding requiring an excessive heating time.

The metal material according to one aspect of the present invention contains alloyed zinc and has a plating layer having a boiling point higher than that of zinc.

The metal material according to one aspect of the present invention contains alloyed zinc and has a plating layer having a boiling point higher than that of zinc. Therefore, even if the temperature of the metal material becomes higher than the boiling point of zinc during heating, the zinc is sufficiently alloyed in the plating layer and the boiling point is high, so that zinc is ignited. It can be suppressed. From the above, it is possible to suppress the generation of the oxidized compound on the surface of the metal material by suppressing the generation of zinc oxide while suppressing the generation of the oxide scale by the plating layer.

According to the present invention, it is possible to provide a heating device capable of suppressing the generation of an oxidized compound on the surface of a metal material, and a metal material.

It is a schematic diagram of the molding apparatus which adopted the heating apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the state when a nozzle seals a metal pipe material. It is an enlarged sectional view of the plating layer. It is a graph which shows the temperature profile of a metal pipe material. It is a table which shows the value of various parameters set in the heating of a heating part, and the generation state of zinc oxide when these values are set. It is a table which shows the value of various parameters at the time of raising a temperature with a one-step temperature profile in the heating of a heating part, and the generation state of zinc oxide at the time of setting these values. It is a figure which shows the structure of the heating part of the heating device which concerns on a modification.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, the same parts or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted.

FIG. 1 is a schematic view of a molding apparatus 1 that employs the heating apparatus 100 according to the present embodiment. As shown in FIG. 1, the molding apparatus 1 is an apparatus for forming a metal pipe having a hollow shape by blow molding. In this embodiment, the molding apparatus 1 is installed on a horizontal plane. The molding apparatus 1 includes a molding die 2, a drive mechanism 3, a holding unit 4, a heating unit 5, a fluid supply unit 6, a cooling unit 7, and a control unit 8. In the present specification, the metal pipe refers to a hollow article after the molding in the molding apparatus 1 is completed, and the metal pipe material 40 refers to a hollow article before the molding in the molding apparatus 1 is completed. The metal pipe material 40 is a pipe material of a steel grade that can be hardened. Further, among the horizontal directions, the direction in which the metal pipe material 40 extends at the time of molding may be referred to as "longitudinal direction", and the direction orthogonal to the longitudinal direction may be referred to as "width direction".

The molding die 2 is a mold for molding a metal pipe material 40 into a metal pipe, and includes a lower mold 11 and an upper mold 12 facing each other in the vertical direction (first direction). The lower mold 11 and the upper mold 12 are made of steel blocks. The lower mold 11 is fixed to the base 13 via a die holder or the like. The upper mold 12 is fixed to the slide of the drive mechanism 3 via a die holder or the like.

The drive mechanism 3 is a mechanism for moving at least one of the lower mold 11 and the upper mold 12. In FIG. 1, the drive mechanism 3 has a configuration in which only the upper mold 12 is moved. The drive mechanism 3 includes a slide 21 that moves the upper mold 12 so that the lower mold 11 and the upper mold 12 meet each other, and a pull-back cylinder as an actuator that generates a force for pulling the slide 21 upward. A 22 is provided, a main cylinder 23 as a drive source for downwardly pressurizing the slide 21, and a drive source 24 for applying a driving force to the main cylinder 23.

The holding portion 4 is a mechanism for holding the metal pipe material 40 arranged between the lower mold 11 and the upper mold 12. The holding portion 4 includes a lower electrode 26 and an upper electrode 27 that hold the metal pipe material 40 on one end side in the longitudinal direction of the molding die 2, and a metal pipe material on the other end side in the longitudinal direction of the molding die 2. A lower electrode 26 and an upper electrode 27 holding the 40 are provided. The lower electrodes 26 and the upper electrodes 27 on both sides in the longitudinal direction hold the metal pipe material 40 by sandwiching the vicinity of the end portion of the metal pipe material 40 from the vertical direction. Grooves having a shape corresponding to the outer peripheral surface of the metal pipe material 40 are formed on the upper surface of the lower electrode 26 and the lower surface of the upper electrode 27. The lower electrode 26 and the upper electrode 27 are provided with a drive mechanism (not shown), and can move independently in the vertical direction.

The heating unit 5 heats the metal pipe material 40. The heating unit 5 is a mechanism for heating the metal pipe material 40 by energizing the metal pipe material 40. The heating unit 5 is the metal pipe material in a state where the metal pipe material 40 is separated from the lower mold 11 and the upper mold 12 between the lower mold 11 and the upper mold 12. 40 is heated. The heating unit 5 includes the lower electrodes 26 and the upper electrodes 27 on both sides in the longitudinal direction described above, and a power supply 28 for passing an electric current through the electrodes 26 and 27 to the metal pipe material. The heating unit 5 may be arranged in the pre-process of the molding apparatus 1 and heated externally.

The fluid supply unit 6 is a mechanism for supplying a high-pressure fluid into the metal pipe material 40 held between the lower mold 11 and the upper mold 12. The fluid supply unit 6 supplies a high-pressure fluid to the metal pipe material 40 which has become hot due to being heated by the heating unit 5, and expands the metal pipe material 40. The fluid supply unit 6 is provided on both ends of the molding die 2 in the longitudinal direction. The fluid supply unit 6 is a nozzle 31 that supplies fluid from the opening at the end of the metal pipe material 40 to the inside of the metal pipe material 40, and a drive that moves the nozzle 31 forward and backward with respect to the opening of the metal pipe material 40. A mechanism 32 and a supply source 33 for supplying a high-pressure fluid into the metal pipe material 40 via the nozzle 31 are provided. In the drive mechanism 32, the nozzle 31 is brought into close contact with the end of the metal pipe material 40 in a state where the sealing property is ensured during fluid supply and exhaust (see FIG. 2), and at other times, the nozzle 31 is brought into close contact with the end of the metal pipe material 40. Separate from. The fluid supply unit 6 may supply a gas such as high-pressure air or an inert gas as the fluid. Further, the fluid supply unit 6 may be the same device including the heating unit 5 together with the holding unit 4 having a mechanism for moving the metal pipe material 40 in the vertical direction.

FIG. 2 is a cross-sectional view showing a state when the nozzle 31 seals the metal pipe material 40. As shown in FIG. 2, the nozzle 31 is a cylindrical member into which the end portion of the metal pipe material 40 can be inserted. The nozzle 31 is supported by the drive mechanism 32 so that the center line of the nozzle 31 coincides with the reference line SL1. The inner diameter of the supply port 31a at the end of the nozzle 31 on the metal pipe material 40 side substantially coincides with the outer diameter of the metal pipe material 40 after expansion molding. In this state, the nozzle 31 supplies a high-pressure fluid to the metal pipe material 40 from the internal flow path 36. An example of a high-pressure fluid is gas or the like.

Returning to FIG. 1, the cooling unit 7 is a mechanism for cooling the molding die 2. By cooling the molding die 2, the cooling unit 7 can rapidly cool the metal pipe material 40 when the expanded metal pipe material 40 comes into contact with the molding surface of the molding die 2. The cooling unit 7 includes a flow path 36 formed inside the lower mold 11 and the upper mold 12, and a water circulation mechanism 37 that supplies and circulates cooling water to the flow path 36.

The control unit 8 is a device that controls the entire molding device 1. The control unit 8 controls the drive mechanism 3, the holding unit 4, the heating unit 5, the fluid supply unit 6, and the cooling unit 7. The control unit 8 repeatedly performs an operation of molding the metal pipe material 40 with the molding die 2.

Specifically, the control unit 8 controls, for example, the transfer timing from a transfer device such as a robot arm, and puts the metal pipe material 40 between the lower mold 11 and the upper mold 12 in the open state. Deploy. Alternatively, the control unit 8 may wait for the operator to manually arrange the metal pipe material 40 between the lower mold 11 and the upper mold 12. Further, the control unit 8 supports the metal pipe material 40 with the lower electrodes 26 on both sides in the longitudinal direction, and then lowers the upper electrode 27 to sandwich the metal pipe material 40, such as an actuator of the holding unit 4. Control. Further, the control unit 8 controls the heating unit 5 to energize and heat the metal pipe material 40. As a result, an axial current flows through the metal pipe material 40, and the electric resistance of the metal pipe material 40 itself causes the metal pipe material 40 itself to generate heat due to Joule heat.

The control unit 8 controls the drive mechanism 3 to lower the upper mold 12 and bring it closer to the lower mold 11 to close the mold 2. On the other hand, the control unit 8 controls the fluid supply unit 6 to seal the openings at both ends of the metal pipe material 40 with the nozzle 31 and supply the fluid. As a result, the metal pipe material 40 softened by heating expands and comes into contact with the molding surface of the molding die 2. Then, the metal pipe material 40 is molded so as to follow the shape of the molding surface of the molding die 2. When the metal pipe material 40 comes into contact with the molding surface, the metal pipe material 40 is quenched by quenching with the molding die 2 cooled by the cooling unit 7.

Among the components of the molding device 1 described above, the heating device 100 includes a heating unit 5 and a control unit 8 (heating control unit). The heating device 100 is a device that heats the metal pipe material (metal material) to be molded. Further, as described above, the heating unit 5 heats the metal pipe material 40 by energization heating. The control unit 8 controls the heating unit 5.

As shown in FIG. 3A, the metal pipe material 40 according to the present embodiment has a plating layer 43 formed on the surface (outer peripheral surface and inner peripheral surface). The plating layer 43 contains at least zinc as a component. The plating layer 43 can suppress the generation of oxidation scale due to the oxidation of iron, which is the base material of the metal pipe material 40, during heating.

Here, in the plating layer 43, a region in which the boiling point is sufficiently high due to sufficient alloying is referred to as "region E2", and a region in a state before sufficient alloying is referred to as "region E1". ". In FIG. 3, the area E2 is grayscaled. In the state before the start of heating, as shown in FIG. 3A, the entire area of the plating layer 43 becomes the region E1. Region E1 contains pure zinc before alloying. Furthermore, in the plating process for forming the plating layer 43, since the temperature of the plating layer is 440 to 460 ° C., iron may diffuse to some extent with respect to zinc. Therefore, the region E1 may contain an alloy layer of zinc and iron in a state where the iron content is low. Examples of the alloy contained in the region E1 include a ζ layer alloy having an iron content of about 6%, a δ1 layer alloy having an iron content of about 7 to 11%, and a Γ layer alloy having an iron content of 11% or more. The iron content of region E1 is less than 30%. The region E2 is a region in which a FeZn solid solution phase having a high iron concentration is generated by heating. The iron content of the alloy in region E2 is 30% or more. In the present specification, expanding the region of region E2 by advancing the alloying of zinc in region E1 is referred to as "alloying treatment". In the plating layer of region E2, the content of the mating metal for alloying with zinc is 30% or more.

When the alloying treatment is started by heating the metal pipe material 40, the zinc contained in the region E1 of the plating layer 43 is alloyed by the alloying reaction with the iron which is the base material of the metal pipe material 40. It becomes an alloy of iron and zinc. Alternatively, the alloy layer having a low iron content in the region E1 of the plating layer 43 has a high iron content due to further promotion of zinc alloying. As a result, in the middle of the alloying process, as shown in FIG. 3 (b), the region E1 and the region E2 are mixed in the plating layer 43. When the alloying treatment of the plating layer 43 is completed, the entire area of the plating layer 43 becomes the region E2 as shown in FIG. 3C. As described above, the heated metal pipe material 40 contains the alloyed zinc and has a plating layer 43 having a boiling point higher than the boiling point of zinc. The plating layer 43 in this state is a region E2 having a boiling point higher than that of zinc in the entire area.

Here, in order to sufficiently quench the metal pipe after molding, the heating unit 5 heats the metal pipe material 40 so as to have a temperature of Ac 3 points or more in order to cause austenite transformation during heating. There is a need to. That is, the target temperature of the heating unit 5 (the temperature reached by the metal pipe material 40) is about 900 ° C. to 1000 ° C. of Ac 3 points or more. On the other hand, the boiling point of unalloyed zinc is 907 ° C. That is, the final target temperature of the heating unit 5 is higher than the boiling point of zinc. On the other hand, the boiling point of fully alloyed zinc (an alloy of iron and zinc) in the region E2 after the alloying treatment is higher than the boiling point of zinc. That is, the boiling point of the alloyed zinc after the alloying treatment is higher than the final target temperature of the heating unit 5. Therefore, in the state where the region E2 of the entire area of the plating layer 43 is reached (the state shown in FIG. 3C), even if the heating unit 5 heats the metal pipe material 40 to the target temperature, the components of the plating layer 43 are formed. Can be suppressed from evaporating and igniting.

Based on the above points, the control contents of the heating unit 5 by the control unit 8 will be described. The control unit 8 controls the heating unit 5 to perform an alloying process for advancing the alloying of zinc in the plating layer 43, and after the alloying process, the metal pipe is set to a temperature higher than the boiling point of zinc. The material 40 is heated. When the control unit 8 starts heating the metal pipe material 40, the plating layer 43 is in the state shown in FIG. 3A, and as the heating time advances, it is sufficient as shown in FIG. 3B. When the amount of zinc alloyed with the above increases and the alloying process is completed, the state shown in FIG. 3C is obtained. The control unit 8 controls the heating unit 5 so that the temperature of the metal pipe material 40 is equal to or lower than the boiling point of zinc before the alloying treatment of the plating layer 43 is completed. Then, it is preferable that the control unit 8 is in a state where the zinc alloying treatment is completed (the state shown in FIG. 3C) before the temperature of the metal pipe material 40 reaches the boiling point of zinc.

The control unit 8 controls the heating unit 5 so that the temperature of the metal pipe material 40 draws a temperature profile in a plurality of stages. The temperature profile indicates a graph formed by plotting the relationship between the time from the start of heating and the temperature of the metal pipe material 40.

A specific example of the temperature profile drawn by the control of the control unit 8 will be described with reference to FIG. 4 (a). FIG. 4A is a graph showing an example of a temperature profile. The horizontal axis shows the elapsed time from the start of heating of the heating unit 5. The vertical axis shows the temperature of the metal pipe material 40. As shown in FIG. 4A, the control unit 8 controls the heating unit 5 so as to draw a temperature profile of the primary heating step, the temperature holding step, and the secondary heating step. As shown in FIG. 4A, the primary heating step is performed between the start of heating (0 seconds) and the time t1, and the temperature of the metal pipe material 40 rises at a predetermined heating rate. The control unit 8 controls the heating unit 5 so that the metal pipe material 40 reaches a predetermined target temperature T1 when the primary heating step is completed. The holding step is performed between time t1 and time t2, and keeps the temperature of the metal pipe material 40 constant for a predetermined holding time. Next, the secondary heating step is performed between the time t2 and the time t3, and is a step in which the temperature of the metal pipe material 40 rises at a predetermined heating rate. The control unit 8 controls the heating unit 5 so that the temperature of the metal pipe material 40 rises at a predetermined temperature rise rate and reaches the final target temperature T2. When the final target temperature T2 is reached, molding is performed, so that the temperature of the metal pipe material 40 drops rapidly.

As parameters set for the control of the control unit 8, the temperature rise rate in the primary heating stage, the target temperature in the primary heating stage, the holding time in the holding stage, the rising speed in the secondary heating stage, and the target in the secondary heating stage. The temperature (final target temperature) can be mentioned. The specific values of these parameters can be appropriately adjusted in consideration of the heating conditions and the total heating time. For example, the control unit 8 may set the heating rate in the primary heating step to 50 to 150 ° C./sec. By setting the temperature within this range, the target temperature can be reached at an early stage. The heating rate in the primary heating step may be set to a value higher than the heating rate in the secondary heating step. The control unit 8 may set the target temperature in the primary heating stage to 700 ° C. or higher and 800 ° C. or lower. By setting it in this range, it is possible to suppress the ignition of zinc while advancing the alloying of zinc while avoiding requiring an excessive heating time. The control unit 8 may set the holding time of the holding step in the range of 10 to 30 seconds. The control unit 8 may set the heating rate in the secondary heating step to 5 to 150 ° C./sec. As described above, the control unit 8 may set the target temperature of the secondary heating step to about 900 ° C. to 1000 ° C., which is a temperature of 3 points or more of Ac.

Next, the operation / effect of the heating device 100 according to the present embodiment will be described.

In the molding apparatus 1 as shown in FIG. 1, a high-strength molded product is molded by quenching at the same time as molding. Here, in order to perform sufficient quenching, it is necessary to heat to a temperature of Ac 3 points or more in order to cause austenite transformation at the time of heating. However, when the metal pipe material 40 is heated at a high temperature, the base material of the metal pipe material 40 is oxidized, which may generate an oxidation scale on the surface. In order to suppress the generation of such an oxidation scale, a plating layer 43 is formed on the surface of the metal pipe material 40. However, the boiling point of zinc contained in the plating layer 43 is relatively low at 907 ° C., and it easily ignites when vaporized during heating. When zinc evaporates and ignites in this way, zinc oxide is eventually generated. In particular, in the space on the inner peripheral side of the metal pipe material 40, the concentration of vaporized zinc is higher than that on the outer side, so that it is easy to ignite at a lower temperature and the amount of zinc oxide generated tends to be large. There is. If the zinc oxide generated in this way adheres to the molded product, there is a problem that the post-process such as painting is hindered, so that a step of removing the zinc oxide is required and the cost increases. Further, if zinc oxide is sprayed in the surrounding atmosphere in a powder state, a problem in the working environment occurs, and a removal device on the device side is required, which also increases the cost.

When the final target temperature T2 is set and the temperature rise rate is set to a constant value, for example, the temperature profile as shown in FIG. 4 (b) is obtained. Then, the conditions as shown in FIG. 6 are set as the temperature rising rate and the target temperature. In addition, FIG. 6 also shows the result of whether or not zinc oxide was generated. As shown in FIG. 6, when the temperature rising rate is set high, it is confirmed that zinc oxide is generated.

On the other hand, in the heating device 100 according to the present embodiment, the control unit 8 controls the heating unit 5 to perform an alloying process for advancing the alloying of the plating layer 43. As a result, the heating unit 5 performs an alloying process for advancing the alloying of the plating layer 43. Here, the boiling point of the alloy layer that has been sufficiently alloyed by the alloying treatment is higher than the boiling point of zinc. Therefore, after the alloying treatment, the heating unit 5 heats the metal pipe material 40 so that the temperature becomes higher than the boiling point of zinc. Therefore, even if the temperature of the metal pipe material 40 is higher than the boiling point of zinc, the alloying of zinc is sufficiently advanced and the boiling point is high, so that the ignition of zinc can be suppressed. From the above, it is possible to suppress the generation of the oxidized compound on the surface of the metal pipe material 40 by suppressing the generation of zinc oxide while suppressing the generation of the oxide scale by the plating layer.

Here, as shown in FIG. 6, it is confirmed that the generation of zinc oxide can be avoided by setting the target temperature low and setting the temperature rise rate low. In other words, if the temperature rise rate is kept low, alloying will proceed while the temperature is rising, and by the time the temperature rises to the boiling point of zinc, zinc alloying will be completed and zinc will ignite. Be prevented. However, if the heating rate is kept low, the heating time for energization heating (“total heating time” shown in FIG. 4) becomes long. In addition, the upper limit of the final target temperature is also limited, and the control range of the allowable heating temperature becomes small.

On the other hand, the control unit 8 controls the heating unit 5 so that the temperature of the metal pipe material 40 draws a temperature profile in a plurality of stages. As a result, the heating unit 5 heats the metal pipe material 40 so that the temperature of the metal pipe material 40 draws a temperature profile in a plurality of stages. In this case, the heating unit 5 can heat the metal pipe material 40 so as to have an appropriate temperature profile according to the progress of zinc alloying. This makes it possible to raise the temperature to the final target temperature after the alloying of zinc is completed, while keeping the total heating time short.

The control unit 8 controls the heating unit 5 so as to draw a temperature profile of the primary heating stage, the holding stage for maintaining the temperature, and the secondary heating stage. As a result, the heating unit 5 heats so as to draw a temperature profile of the primary heating step, the holding step of holding the temperature, and the secondary heating step. In this case, the heating unit 5 promptly raises the temperature to the target temperature of the alloying treatment in the primary heating step, and keeps the temperature at the target temperature in the holding step to proceed with the alloying of zinc. Then, the heating unit 5 can raise the temperature of the metal pipe material 40 to the final target temperature in the secondary heating step after the alloying treatment. As a result, it is possible to improve the certainty of suppressing the generation of zinc oxide while keeping the total heating time short.

The control unit 8 sets the target temperature in the primary heating stage to 700 ° C or higher and 800 ° C or lower. As a result, the heating unit 5 sets the target temperature in the primary heating stage to 700 ° C. or higher and 800 ° C. or lower. In this case, it is possible to suppress the ignition of zinc while advancing the alloying of zinc while avoiding requiring an excessive heating time.

For example, various parameters were set to the values shown in FIG. 5, and the state of zinc oxide generation was confirmed. As shown in FIG. 5, when the target temperature in the primary heating step is 500 ° C. or lower, the generation of zinc oxide is suppressed, but the total heating time tends to be long. On the other hand, when the target temperature in the primary heating stage is 600 ° C. or higher and 700 ° C. or lower, zinc oxide is generated by vaporizing and burning zinc before alloying proceeds. Therefore, in these temperature ranges, it is necessary to lengthen the total heating time by, for example, keeping the temperature rise rate low. On the other hand, if the target temperature is set and maintained at a temperature higher than the above range and lower than the boiling point of zinc, the high temperature promotes the alloying of zinc, and the subsequent heating also causes the vaporization of zinc. It is suppressed and the generation of zinc oxide can be prevented. This makes it possible to shorten the total heating time.

The metal pipe material 40 contains alloyed zinc and has a plating layer 43 (see FIG. 3C) having a boiling point higher than the boiling point of zinc. Therefore, even if the temperature of the metal pipe material 40 becomes higher than the boiling point of zinc during heating, zinc is sufficiently alloyed in the plating layer 43 and the boiling point is high. Ignition can be suppressed. From the above, it is possible to suppress the generation of the oxidized compound on the surface of the metal pipe material 40 by suppressing the generation of zinc oxide while suppressing the generation of the oxide scale by the plating layer 43.

The present invention is not limited to the above-described embodiment.

For example, what kind of temperature profile the control unit 8 controls the heating unit 5 is not particularly limited. For example, the control unit 8 may omit the holding step. For example, as soon as the target temperature of the primary heating step is reached, the process may shift to the secondary heating step. Further, the control unit 8 may control the heating unit 5 so as to draw a multi-stage temperature profile. For example, in the holding stage, the temperature does not have to be completely constant, and the temperature may be gradually increased. As a result, the temperature profile may be such that it has three heating stages.

Further, if the control unit 8 heats the metal pipe material 40 so that the temperature becomes higher than the boiling point of zinc after the zinc is alloyed, the control unit 8 is as shown in FIG. 4 (b). The heating unit 5 may be controlled to draw a step temperature profile.

In the above-described embodiment, the mold used in the molding apparatus for STAF has been described as an example. However, the type of the molding apparatus in which the mold according to the present invention is adopted is not particularly limited, and any molding apparatus may be used as long as it is a type for molding a heated metal material. Further, the shape of the metal material is not limited to the pipe, and may be a plate-shaped metal material or the like.

In the above-described embodiment, the heating unit 5 heats the metal pipe material 40 inside the mold. Instead of this, a heating unit 5 that heats outside the mold may be adopted. For example, as shown in FIG. 7, the holding portion 4 may have a robot arm 130 that moves the metal pipe material 40 from the outside of the molding die 2 between the lower die 11 and the upper die 12. Further, the robot arm 130 may have a heating unit 5 for heating the metal pipe material 40 while holding the metal pipe material 40. The robot arm 130 is provided with an upper electrode 131 and a lower electrode 132 at the tip thereof. The robot arm 130 sandwiches and holds the metal pipe material 40 between the electrodes 131 and 132, and can energize and heat the metal pipe material 40 by the electric power from the power supply cable 133.

5 ... heating unit, 8 ... control unit (heating control unit), 40 ... metal pipe material, 43 ... plating layer, 100 ... heating device.

Claims

A heating device that heats the metal material to be molded.
A heating unit that heats the metal material by energization heating,
A plating layer containing zinc is formed on the metal material, and a plating layer is formed.
The heating unit is a heating device that performs an alloying treatment for advancing the alloying of zinc in the plating layer, and after the alloying treatment, heats the metal material so that the temperature becomes higher than the boiling point of zinc.
The heating device according to claim 1, wherein the heating unit heats the metal material so that the temperature of the metal material draws a temperature profile in a plurality of stages.
The heating device according to claim 2, wherein the heating is performed so as to draw a temperature profile of a primary heating step, a holding step for holding a temperature, and a secondary heating step.
The heating device according to claim 3, wherein the heating unit sets the target temperature of the primary heating stage to 700 ° C. or higher and 800 ° C. or lower.
A metallic material containing alloyed zinc and having a plating layer having a boiling point higher than that of zinc.