Patent Application
20150377556
The present application claims priority based on JP Patent Application 2013-018878 filed in Japan on Feb. 1, 2013, whose entire disclosure is incorporated herein by reference thereto.
The present invention relates to an infrared furnace, an infrared heating method and a steel plate manufactured by using the same, and especially relates to the infrared furnace and the infrared heating method which can heat one work in different temperature regions and the steel plate with which different strength regions are formed in one sheet.
In connection with needs growing to the weight saving aiming at the improvement in fuel consumption or collision safety of the body, the die quenching method has attracted attention as a production method of automobile parts. The die quenching method is a construction method which quenches a steel plate by carrying out rapid-cooling of the heated steel plate simultaneously with forming (molding) by means of press metallic dies.
In addition, as a method of heating a steel plate for quenching the steel plate, an infrared heating method has attracted attention. The infrared heating method is a method to make a work generate heat, by irradiating the work with infrared rays and making the work absorb infrared rays.
Moreover, as to parts for vehicles such as automobile parts, there is a demand to have strength variations within one part for saving steps of welding high strength parts and low strength parts to manufacture one part. As for such parts, there is an advantage that strength is secured by a high strength region while a low strength region is easy to process.
The patent literatures relating to the above Background are mentioned below.
Proposed in Patent Literature 1 is arranging a sheet material having a predetermined form between a steel plate and an infrared lamp(s), and setting at least a part of heating intensity distribution of a side not covered by a sheet material of a steel plate so as to differ from a heating intensity distribution of a side covered by the above-mentioned sheet material of the steel plate.
Proposed in Patent Literature 2 is an infrared heating device which irradiates the first region of a steel plate with more weak infrared rays and the second region of this steel plate with strong infrared rays.
Proposed in Patent Literature 3 is an infrared heating device which sets output intensity of all the infrared lamps to be turn on at a same rate while choosing the number of the infrared lamp to be turn on according to a target heating temperature of a steel plate.
Proposed in Patent Literature 4 is an infrared heating device which makes an output of lamp(s) of a predetermined sequence(s) low and an output of lamp(s) of other sequence(s) high, among a plurality of infrared lamps arranged in a matrix shape, in order to control the heating state of a steel plate for every region.
Proposed in Patent Literature 5 is a pressing method that starts press-forming of a steel plate in a state where the temperature of the remainder part of a steel plate is less than room temperature to Ar-1 transformation point while infrared heating a part of the steel plate not less than Ar-1 transformation point.
The following analysis is given by the present invention. The disclosures of the above listed literatures are each incorporated herein by reference thereto in their entirety.
For example, as for one sheeted steel plate, a low-temperature setting region thereof is equivalent to a portion which is not quenched, and a high-temperature setting region thereof is equivalent to a portion which is quenched. When a sheet material is arranged above this low-temperature setting region and the low-temperature setting region is entirely covered (shielded) at the time of infrared heating, there is a tendency that the temperature of the low-temperature setting region decreases than expected or a rising temperature takes a long time. Accordingly, there is a possibility that the high-temperature setting region cannot be fully quenched partially and a slowly changing part unavoidably formed between the high-temperature setting region and the low-temperature setting region may be formed more broadly than expected because the quantity of heat which flows into the low-temperature setting region from the high-temperature setting region becomes excessively large.
Therefore, there is a desire of an infrared heating method of a steel plate, contributing to laborsaving of a forming of the steel plate and simplification of forming apparatus while contributing to exact realization of the demanded temperature distribution.
In a first aspect, there is provided an infrared furnace which can heat a first region and a second region of a work in different temperature regions. The following means are provided:
a member which is positioned between the work and a plurality of infrared lamps apart from the work and the infrared lamps the work, to be arranged above a boundary region between the first and second regions.
In a second aspect, there is provided an infrared heating method for heating a first region and a second region of a work in different temperature regions. The following means are provided:
a member is positioned between the work and a plurality of infrared lamps apart from the work and the infrared lamps, and is arranged above a boundary region between the first and second regions;
an intensity of infrared rays caused to impinge onto the first region is relatively high; and
an intensity of infrared rays irradiating the second region is relatively low.
In a third aspect, there is provided a steel plate, particularly, based on the above second aspect, the following means are provided:
a first region in which rapid-cooling-forming and quenching are carried out after the above heating;
a second region in which cooling-forming is carried out but quenching is not carried out after the above heating; and
a slowly changing part having a width of 20 mm or less, unavoidably formed between the first region and the second region, having an intermediate characteristic of both regions.
Advantageous Effects of the Invention are mentioned below without limitations. The above each aspect contributes to laborsaving of the forming of the steel plate and simplification of forming apparatus while contributing to exact realization of the demanded temperature distribution.
Exemplary embodiments of the present invention can produce the following effects. In addition, in the following explanation, it is assumed that the infrared heating of the first region is carried out to a higher temperature than the second region, the first region is quenched by rapid-cooling-forming after infrared heating; on the other hand, the second region is not quenched.
(1) Since a member shields a boundary region between the first region and the second region, a portion, which adjoins the first region, of the second region is excessively irradiated with infrared rays, and it prevents this portion from being heated beyond the preset temperature range of the second region. Simultaneously, a falling in temperature of a portion, which adjoins the second region, of the first region is prevented.
(2) Since the member shields a work partially and minimally, it prevents the temperature of the second region from falling in excess. Accordingly, the temperature gradient near a boundary region becomes small, the quantity of heat per unit time propagating to the second region from the first region decreases, and a slowly changing part unavoidably formed between both regions and having an intermediate characteristic of both regions is formed as small as possible.
(3) Since the member's width can be formed narrowly, a support for the member becomes easy inside the infrared furnace.
(4) Since a temperature distribution having a temperature difference required for partial quenching for the work is formed in a heating step, a special step for giving a temperature difference to the work is not necessary and also a special apparatus for giving a temperature difference to the work is not necessary in a forming step.
(5) In that way, a temperature distribution required for one work is realized exactly, and further a strength distribution required for one work can be realized correctly.
It is preferable that the member is disposed along the boundary region so as to cover at least a part of the above-mentioned boundary region.
The member's width is set as preferably 3 to 60 mm, more preferably 5 to 50 mm, 5 to 30 mm, 5 to 20 mm, 5 to 10 mm.
The infrared furnace is preferably provided with one or some controllers which make(s) an output of one or some infrared lamps among a plurality of infrared lamps located in the first region side of the member higher than an output of one or some infrared lamps among a plurality of infrared lamps located in the second region side of the member,
Basically, an output rate of the infrared lamps by the side of the first region and the infrared lamps by the side of the second region may be set depending on a ratio of the preset temperature of the first region and that of the second region. An output intensity of the infrared lamp is controllable by adjusting the electric energy supplied or amount of the current flowing through the cathode emitting infrared rays.
In addition, in a direction in which the infrared lamps and the work oppose each other, a preferable relationship between a first distance between the member and the infrared lamps and a second distance between the member and the work is preferably in a range of the first distance/the second distance=1/9 to 9/1, and more preferably, 2/8 to 8/2, 3/7 to 7/3, 4/6 to 6/4.
Next, preferable other arrangement embodiments of a plurality of infrared lamps are explained. In the following embodiments, etc., the intensity of the infrared rays which impinges onto the first region of the work or with which the first region is irradiated is higher than the intensity of the infrared rays which impinges onto the second region of the same work or with which the second region is irradiated, depending on the arrangement relation of a plurality of infrared lamps.
Some infrared lamps are arranged relatively densely at the first region side of the member, and one or some infrared lamps is/are arranged relatively sparsely at the second region side of the member.
One or some infrared lamps is/are arranged relatively near the work at the first region side of the member, and one or some infrared lamps is/are arranged relatively far from the work at the second region side of the member,
Although the above-mentioned predetermined heat treatment is typically quenching, it may be other heat treatment(s) as long as it is a heat treatment required for heating the first region and the second region in different temperatures.
The above-mentioned member may be partially permeable of infrared rays. Since this member makes some infrared rays penetrate and the second region is also fully heated, the falling in temperature of the first region by the heat conduction from the first region to the second region is prevented.
The above-mentioned member may be of a mesh-like structure. Since the mesh part of this member makes some infrared rays penetrate and the second region is also fully heated, the falling in temperature of the first region by the heat conduction from the first region to the second region is prevented.
A material of the above-mentioned member for shielding (shading or covering) a part or entire of infrared rays can be selected from ceramics, heat-resistant board, heat-resistant iron sheet, heat-resistant silica, etc.
It is preferable that energy density of the infrared lamp(s) is high and the infrared lamp(s) emits near-infrared rays suitable for heating of the comparatively narrow range field. The preferable range of wavelength is 0.8 to 2 micrometers. In addition, it is also possible to use the comparatively long wavelength of infrared rays, in some cases.
As the infrared lamp(s), while lamps having various shapes can be used, especially among them, it is desirable to use a cheap and long-pipe-type with easy attaching to the infrared furnace. According to the present invention, even if the long-pipe-type is used, a sufficient characteristics change for one part can be formed.
As the work suitable for infrared heating, while various steel plates or sheets, for example, a boron steel plate or sheet, hot-dip galvannealed (GA) steel plate or sheet, and hot-dip galvanized (GI) steel plate or sheet are listed, other metal plates or sheets may be sufficient as long as partial heat treatment is possible.
Preferably, a plurality of infrared lamps are arranged at one surface side of the work, and a reflective surface reflecting infrared rays is arranged at the other surface side of the work. As for the reflective surface, like as a mirrored surface or a glossy surface, it is preferable that the infrared reflectance is high. The reflectance is preferably 60% or more, and more preferably, 70% or more, 80% or more, and 90% or more. The reflective surface can be formed from various metal plating, for example, gold plating, or silver plating, for example.
The other side of the work may be cooled locally by one or some cooling materials (or medium). Accordingly, the characteristic of the work can be changed in spot fashion.
It is preferable that a plurality of infrared lamps are arranged planar or in three dimensions, depending on the profile or desired characteristic distribution of the work.
The preferable steel plate as parts for vehicles comprises the first region in which rapid-cooling-forming and quenching are carried out after infrared heating, the second region in which cooling is carried out simultaneously with the first region but rapid-cooling is not carried out thus quenching is not carried out, and the slowly changing part having narrow width formed unavoidably between the first region and the second region and having an intermediate characteristic of both regions. It is confirmed that the width of the slowly changing part can be 20 mm or less and further 10 mm or less, and it is also possible to be 5 mm or less by optimizing conditions.
In addition, the above-mentioned respective embodiments can be suitably combined, as long as the effect of the present invention is achieved.
Hereinafter, exemplary embodiments of the present invention are explained, with referring to Drawings. In addition, reference signs of Drawings used in following explanation are additions for convenience to elements in Drawings in order to help understanding, without intention for limiting the present invention to the mode(s) as illustrated.
The infrared furnace 10 has a plurality of infrared lamps 1 opposing the work W, and a member 5 arranged above a boundary region B between the first region R1 and the second region R2. A plurality of infrared lamps 1 are arranged at one surface side of the work W. A reflective surface 3 reflecting infrared rays emitted from a plurality of infrared lamps 1 is arranged at the other surface side of the work. Alternatively, when a plurality of infrared lamps 1 are arranged below the work, the member 5 is arranged above a boundary region B in an area below the work W, and when the work W is provided in a standing posture and a plurality of infrared lamps 1 are arranged on the side of the work W, the member 5 is arranged above the boundary region B on the lateral side of the work W.
Furthermore, the infrared furnace 10 is provided with a controller 4 performing on-off control and output control of a plurality of infrared lamps 1. For example, among a plurality of infrared lamps 1, the controller 4 can make an output of one or some infrared lamps 1a located in the first region R1 side of the member 5 higher than an output of one or some infrared lamps 1b located in the second region R2 side of the member 5.
In addition, some controllers 4 may be provided one by one relationship with a plurality of infrared lamps 1, and the output intensity of the infrared lamps 1 may be adjusted individually. Moreover, when supporting, the work W by some pins from the bottom, it is preferable that a plurality of infrared lamps 1 are arranged on the upper side as shown in
Here, an effect resulting from installation of the reflective surface 3 is explained, referring to experimental results.
As shown in
A time to reach 900 degrees Celsius from room temperature was 31.4 seconds for single-sided heating, it was 29.6 seconds for both-sides heating and there was no significant difference in both the rate of temperature increase. Therefore, according to single-sided heating, it is recognized that the short enough time of temperature increase of the steel plate is obtained, attaining energy saving. Moreover, also in the case of single-sided heating, the temperature difference between the one surface side and the other side of the boron steel plate is controlled within 5 degrees Celsius, and this temperature difference is within a satisfactory level on temperature controlling.
Referring to
The infrared heating method of the work W by this infrared furnace 10 is explained. The controller 4 shown in
With such infrared heating, the first region R1 is heated to a high temperature at which quenching is possible, and the second region R2 is heated to a low temperature at which no quenching is performed. The member 5 on the boundary region B prevents a portion which adjoins the first region R1 of the second region R2 from being excessively irradiated with the infrared light 2a having high intensity and being heated exceeding the preset temperature of the second region R2. Simultaneously, the excessive falling of temperature of the portion which adjoins the second region R2 of the first region R1 is prevented. Furthermore, since the member 5 shields the work W at a minimum extent, it prevents the temperature of the second region R2 from excessive falling than the preset. Accordingly, a temperature gradient taken across the boundary region B becomes small, the quantity of heat per unit time propagated to the second region R2 from the first region R1 decreases, and as shown in
Thus, in the infrared furnace 10, since highly precise temperature distribution is given to the work W, a special step for giving a temperature difference to the work W is unnecessary and also a special apparatus for giving a temperature difference to the work W is unnecessary in a forming step at a subsequent process.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Moreover, the member 5 arranged above a curved boundary region B of the work W is formed in a shape of a curve according to the profile of the first and second regions R1 and R2. According to the shape of the boundary region B or the member 5, as shown in
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
In addition, as the cooling material 7, using a temperature absorption member, such as a metal member enclosing ceramics and sodium, it can be contacted on the other side of the work W. Such a temperature absorption member may be used as a pin supporting the work W. Moreover, as the cooling material 7, water and air may be made to blow off from a nozzle arranged on the other side of the work W, and these may be used together with an above-mentioned metal member.
In addition, a number of exemplary embodiments explained above can be used together (or combined) as long as there are no directions.
Next, a desirable width of the member 5 as shown in
Referring to
Heating “a shadow-less-heating part” to a temperature of Ac-3 point or more, and securing the quenching ability in a subsequent forming step and from a view point of preventing the springback after the forming step, the temperature of the “shielding part” is preferably at a neighborhood of Ac-1 point or less; that is, it is preferable around 700 degrees Celsius.
As mentioned above, in order to provide a sufficient infrared shielding effect, the width of the member is preferably 5 to 50 mm, still more preferably 10 to 40 mm in the case where the member is infrared-shielding, and the width of the member is preferably 10 to 70 mm, still more preferably 20 to 70 mm in the case where the member is partially permeable of infrared rays.
Here, an example of an output adjusting method for an infrared lamp(s) according to the regional preset temperature (for example, about 400 to 900 degrees Celsius) is explained based on an experimental result. As a work to be subjected to infrared heating, a boron steel plate having 1.6 mm in thickness, 100 mm in length and 80 mm width was used, a thermo couple was attached at the center thereof, the intensity of infrared rays outputted from a plurality of infrared lamps was changed between about 50 and 100%, infrared heating was performed respectively, and the temperature change of a boron steel plate was measured, respectively.
Next, in the infrared furnace 10 as shown in
Moreover, as for comparison, except not using the above-mentioned shielding bar, the heating test was performed under the same conditions as the above (refer to the plot of “no member” in
Results of the above experiment 3 are shown in
As mentioned above, although exemplary embodiments, etc. of the present invention were explained, the present invention is not limited to the above-mentioned exemplary embodiments, etc., and the further modification, substitution or adjustment can be added, within a scope not deviating from the fundamental technical idea of the present invention.
The entire disclosures of the above Patent Literatures are incorporated herein by reference thereto. Modifications and adjustments of the exemplary embodiment are possible within the scope of the overall disclosure (including the claims) of the present invention and based on the basic technical concept of the present invention. Various combinations and selections of various disclosed elements (including each element of each claim, each element of each exemplary embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the overall disclosure including the claims and the technical concept. Particularly, any numerical range disclosed herein should be interpreted that any intermediate values or subranges falling within the disclosed range are also concretely disclosed even without specific recital thereof.
The present invention is used suitably for heat treatment or heat forming of automobile parts, for example, various pillars and side members or component parts for a door such as an impact bar.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-018878 | Feb 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2014/058655 | 1/30/2014 | WO | 00 |
