JP3671722B2 - Hot slab sizing press method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot slab sizing press method, and more particularly to a hot slab sizing press method in which a hot steel slab, which is a material for hot rolling, is forged from the width direction of the slab by a die.
[0002]
[Prior art]
Hot-rolled steel sheets are usually manufactured from hot slabs by rolling or the like. In recent years, a sizing press technique for forging a hot slab from the width direction using a die having a tapered portion in the material-containing side direction has been developed for the hot slab. With this technique, it is reported that a practical product can be reduced in width by about 350 mm at the maximum.
[0003]
FIG. 8 shows a plan view of a part of a general mold used for a hot slab sizing press. In addition, although a metal mold | die consists of a pair of metal mold | die each arrange | positioned so that a hot slab may be pinched | interposed, only the metal mold | die of one side is shown for convenience.
The side surface of the mold 1 is mainly composed of a parallel portion 2 parallel to the material feeding direction, a tapered portion 3 inclined to the entry side with respect to the material traveling direction, and a transition region 4 between the parallel portion 2 and the tapered portion 3. It is a machined surface. Here, the angle θ of the tapered portion 3 with respect to the parallel portion 2 is often 10 to 15 degrees.
[0004]
Next, a method for sizing and pressing the steady portion of the hot slab using such a mold will be described with reference to FIGS. In this method, the mold is forged from the plate width direction of the hot slab by periodically changing the gap in the plate width direction of the hot slab.
[0005]
First, as shown in FIG. 9 (A), after the molds 1a and 1b are arranged in the direction perpendicular to the traveling direction of the hot slab 5, the hot slab 5 is sent to the mold side (before the n-th press). . Next, as shown in FIG. 9B, the hot slab 5 is pressed by the mold 1a and the mold 1b (during the n-th press). Subsequently, as shown in FIG. 9C, after the mold 1a and the mold 1b are separated from the hot slab 5, the hot slab 5 is fed by a predetermined amount (before the (n + 1) th pass press). In FIG. 9B, W indicates the width of the hot slab 5 before pressing, and w indicates the width after pressing.
[0006]
In addition to the method of FIG. 9, there is a material that moves continuously in the longitudinal direction during pressing, as in the flying type, and the mold moves in the longitudinal direction to reduce the relative speed with the material. .
[0007]
However, in the forging method described above, slip may occur during pressing, which is an operational problem. That is, when pressing from the state before pressing as shown in FIG. 10 (A), a phenomenon has occurred in which the hot slab 5 retreats without being pressed down as shown in FIG. 10 (B). By the way, when the slip occurs, the hot slab 5 is not subjected to the processing for the specified feed amount, so the number of presses must be increased, and the operation efficiency is lowered. Moreover, since slip marks remain on the surface of the hot slab 5, it also causes a reduction in the surface quality of the product.
[0008]
Japanese Utility Model Laid-Open No. 5-5201 discloses a press die that suppresses slip by increasing the coefficient of friction by forming grooves, protrusions and holes on the surface of the die in contact with the side surface of the slab. However, in the case of this device, there is a problem that the machining of the mold is expensive, and if the groove is worn, the mold cannot be used, so that the frequency of replacing the mold increases. In addition, since grooves and protrusions on the mold surface are transferred to the side surfaces of the material, there is a problem that it is liable to cause wrinkles.
[0009]
Japanese Patent Application Laid-Open No. 9-122706 discloses a slip detection method for a sizing press that detects slip from a press load and a feed amount of a transport roll and transports the material again so that a specified feed amount is obtained when the slip occurs. Has been. In JP-A-2-52106, JP-A-62-124057 and JP-A-6-210316, damage during slipping is minimized by eliminating or reducing the pushing force of the transport roll during pressing. A conveying method and an apparatus to be stopped are disclosed.
[0010]
However, in the case of these inventions, if a slip occurs, some damage to the material surface is unavoidable, and ideally, a pressing method that does not cause a slip without performing special processing on the mold surface is necessary.
[0011]
Moreover, from the point of view of operation, the production efficiency improves as soon as the sizing press is completed, and the temperature drop of the material during the sizing press can be prevented, so that the heat amount of slab heating can be saved and the product quality can be improved. Further, if the pressing speed of the sizing press is constant, the larger the material feed amount, the fewer the number of pressings and the more efficient. However, if the feed amount is large, the press load naturally increases. According to the literature (“Materials and Processes”, Vo19, No. 2, p288), when a die with a taper angle of 12 degrees is used, the feed amount (see FIG. 9) is appropriate to be about 400 mm. Yes, the feed rate cannot be increased any more in terms of the load capacity of the device.
[0012]
[Problems to be solved by the invention]
The present invention has been made in consideration of such circumstances, and by forging the contact start surface of the hot slab and the mold as a transition region between the tapered portion and the parallel portion and a part of the parallel portion, Provided is a hot slab sizing press method capable of avoiding the occurrence of slips during pressing without mold processing, and enabling efficient pressing without increasing the press load even when the feed amount is increased. For the purpose.
[0013]
[Means for Solving the Problems]
The present invention uses the mold having a taper portion inclined in the entry side direction with respect to the traveling direction of the hot slab, and a die having a main working surface that is continuous with the taper portion and parallel to the traveling direction. In the sizing press method for forging a slab from the width direction, a contact start surface between the hot slab and the mold is a transition region between the tapered part and the parallel part and a part of the parallel part , and the main part of the mold A hot slab sizing press method characterized in that a lubricant is applied to at least a contact surface with a hot slab among processed surfaces .
[0014]
In the present invention, to apply the lubricant to the contact surface with at least hot slab in the main processing surface of the mold, also reduce the coefficient of friction when contacted by the parallel portion of the die slip Since it does not occur, it is based on the fact that it is very effective to reduce the load by using a lubricant. Here, as the lubricant, for example, a hot lubricant having a function of reducing a friction coefficient, such as a mixture of a solid lubricant such as graphite, molybdenum disulfide, and graphite with mineral oil (grease), or a mineral oil alone. Any type is acceptable. The location where the lubricant is applied may be applied to at least the contact surface with the hot slab among the main processed surfaces of the mold as described above. You may give it. It is not desirable to change the friction coefficient by grooving or the like on the mold surface because the mold surface can be transferred to the material and cause wrinkles.
[0015]
As a method of applying the lubricant, for example, for the taper portion of the mold, the material is forged, the gap of the mold is once opened, and the material is moved by a specified amount toward the forging of the next pass (feeding). In this case, the lubricant is sprayed from the entrance direction of the material toward the taper portion of the mold with a nozzle. On the other hand, about the parallel part of a metal mold | die, it apply | coats similarly from the exit direction of material. Similarly, it is possible to apply the lubricant to both the tapered portion and the parallel portion of the mold by injecting the lubricant from the end in the width direction of the mold.
[0016]
In the present invention, since the forged material extends in the input / output direction, it is desirable that the parallel portion of the mold has a length equal to or longer than the feed amount during pressing. In addition, the present invention is effective in preventing slippage, particularly when used in the steady portion of the press from the hot slab tip to the rear end through the steady portion.
[0017]
In the present invention, the taper angle of the taper portion of the mold is preferably 16 degrees or more and 30 degrees or less. Here, when the taper angle is less than 16 degrees, as described later, when the reduction amount is large (or when the material feed amount is small), the frequency of slipping increases. Further, when the taper angle exceeds 30 degrees, a phenomenon that the material is detached from the mold during pressing occurs.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors investigated the occurrence of material slip during pressing. As a result, it was found that slip occurred at the start of contact between the mold and the material (hot slab), and that slip did not occur when the reduction was advanced to some extent. Here, in the sizing press, due to the reduction amount, feed, and taper angle of the mold, the contact point between the mold and the material is a substantially parallel part of the mold (in the present invention, the parallel part of the mold and the inclination in the transition region). A portion within an angle of 5 degrees is referred to as a substantially parallel portion) or a tapered portion.
[0019]
FIG. 1 schematically shows the forces acting on the molds 1a and 1b at the start of contact when the contact start surfaces of the molds 1a and 1b are tapered portions. In FIG. 1, P is an external force that presses the molds 1a and 1b against the hot slab 5, N is a reaction force that acts on the molds 1a and 1b from the hot slab 5, and f is a hot slab 5 and the mold 1a, The frictional force acting between 1b is shown. In FIG. 1, in order for the molds 1a and 1b to continue forging without slipping, the frictional force f must be equal to the component force P‖ in the taper direction of the rolling force. When the component force P‖ exceeds the maximum static friction force μN, the molds 1a and 1b and the hot slab 5 start to slip. Therefore, if the non-slip condition is expressed using the friction coefficient μ and the angle θ between the hot slab 5 and the molds 1a and 1b, μ ≧ tan θ. In FIG. 1, W indicates the width of the hot slab 5 before pressing, and w indicates the width of the hot slab 5 after pressing.
[0020]
In hot forging, the contact state between the material and the mold is poor because of the roughened forged surface, and scale is generated on the forged surface, so the friction coefficient μ between the material and the die is low. Therefore, when the contact start surface is a taper portion of the mold, the slip occurrence frequency is increased.
[0021]
By the way, when the angle of the taper portion is 15 degrees or less and the reduction amount is large or the feed amount of the material is small, the taper portion of the die is temporarily formed by forging the material surface once forged by the taper portion of the die. Since contact frequently occurs from the part, the frequency of slipping increases.
[0022]
Further, in the experiments by the inventors, slip did not occur until the taper portion of the mold was inclined by about 5 degrees. This is presumed to be because the component force in the incoming direction of the rolling force is small. However, if the inclination of the taper portion is 5 degrees or less, the contact length in the longitudinal direction between the hot slab and the mold becomes very large, and the vertical direction (in the case of the plate thickness direction) of the load increase or forging is increased. This is not practical because it increases deformation.
[0023]
On the other hand, when the contact start surface of the mold and the hot slab 5 is a parallel part of the mold as shown in FIG. 1, the component force in the taper part direction of the rolling force does not work. Does not occur. Further, according to the experimental results of the inventors, slip does not occur even if the parallel part of the mold has an inclination of about 5 degrees, and therefore, from the part where the inclination angle is within 5 degrees in the transition region from the parallel part to the tapered part. No slip occurs even when contact is started. Therefore, in the present invention, as described above, the parallel part of the mold and the part within the transition angle within 5 degrees in the transition region are collectively referred to as a substantially parallel part.
[0024]
This condition is the same even when the feed amount is larger than the material contact length at the taper portion of the mold. Further, the method according to FIG. 2 is effective in preventing slipping, particularly when used in the steady portion of the press from the hot slab tip to the rear end through the steady portion. Furthermore, when contacting from the parallel part of the mold, slip does not occur even if the friction coefficient is reduced, so it is very effective to reduce the load by applying a lubricant to the main machining surface of the mold. is there.
[0025]
Next, the present inventors investigated a change in press load when the angle of the taper portion of the mold was changed by a laboratory experiment using lead. FIG. 3 is a characteristic diagram in the case of a steady portion press load when using a die having a taper angle of 12 degrees and 20 degrees, using a material having a plate thickness of 32 mm × plate width of 150 mm × length of 300 mm and a reduction amount of 30 mm. Indicates. In FIG. 3, the horizontal axis indicates the contact length between the mold and the material. However, if the taper angle of the mold is large with the same feed amount, the contact length with the material is shortened. The contact lengths are almost the same. Accordingly, the feed amount is increased as the taper angle of the mold is increased.
[0026]
As a result, it was found that if the contact length between the material and the mold is equal, the press loads are almost the same regardless of the taper angle. In addition, the inventors conducted a similar experiment in the range of a material plate width of 80 to 220 mm (plate thickness is constant at 32 mm), a taper angle of the mold of 8 to 45 degrees, and a reduction amount of up to 50 mm. The result was obtained.
[0027]
For this reason, the larger the taper angle of the mold, the larger the feed amount and the more efficient the pressing. FIG. 4 shows the number of times it took to press the entire length of the experimental material at the time of FIG. 3, but the number of presses is smaller when the taper angle of the mold is large and the feed amount is 20 degrees. However, it has been found that if the mold angle is 30 degrees or more, the phenomenon that the material is detached from the mold during pressing occurs, which is not preferable (upper limit of the taper angle of the mold).
[0028]
However, when the taper angle of the mold becomes large, if the feed amount is small, contact with the material starts at the taper portion and slips as described above, which is not preferable. Therefore, when the load (= contact length) is equal to that of the conventional sizing press (mold taper angle 12 degrees + feed 400 mm) and the parallel part of the mold has the minimum taper angle required to start contact, slip occurs. The minimum feed amount to avoid this was calculated. FIG. 5 shows the result.
[0029]
As shown in FIG. 5, in order to prevent the slip at the time of pressing and perform the press with the same load as before, a mold having an angle larger than the slip limit taper angle shown in FIG. 5 is used and the minimum feed amount of the mold is used. It is clear that pressing may be performed with the above feed amount. Currently, the sizing press that is actually used has a reduction amount of about 350 mm at the maximum. Therefore, when a die having a taper angle of 16 degrees or more is used and a feed amount in which a slip does not occur, for example, when the die taper angle is 16 degrees, The feeding amount may be 600 mm or more. If the press is performed with this feed amount, the press time becomes about 2/3 of the conventional (feed amount of 400 mm), and the efficiency increases by about 50%. However, the minimum feed amount that does not slip depends on the taper angle of the mold and is not specified here.
[0030]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
In this embodiment, as shown in FIG. 8, a case where a die having a one-stage taper portion is used is shown. FIG. 6 shows the relationship between the die taper angle, the feed amount, and the reduction amount when this one-stage die is used. In FIG. 6, (A) shows the case where the reduction amount is 50 mm, (B) shows the case where the reduction amount is 100 mm, and (C) shows the case where the reduction amount is 150 mm. In the range indicated by the arrow in FIG. 6 (the upper range of the curve), the press could be performed without causing a slip at the time of pressing, but the slip occurred outside the range shown in the figure (the lower side of the curve in FIG. 6). In some cases, the press was not always stable. In addition, considering the case where only the mold angle is changed while the feed amount and the reduction amount are constant, the press load decreases as the mold angle increases. Therefore, the press load can be reduced by performing pressing within the range shown in FIG. There is also an effect.
[0031]
Further, the load reducing effect when the friction coefficient is reduced by applying the lubricant to the parallel processing portion, the taper portion and the entire main processing surface of the main processing surface of the mold under the press conditions within the scope of the present invention is investigated. As a result, the load reduction ratios in the parallel portion, the tapered portion, and the entire main machining surface were 10%, 20%, and 30%, respectively. Also at this time, slip does not occur, and it is possible to reduce the load by the lubricant while maintaining the stability of the press.
[0032]
Further, when the deformation shape when the mold angle is 20 degrees and 12 degrees is examined, the dogbone shape under the condition A (see FIG. 3) with the same contact length is compared as shown in FIG. Therefore, it is possible to efficiently perform a sizing press because of a large feed amount without slipping with a load equivalent to the conventional one while maintaining the width reduction efficiency. In FIG. 7, curve (A) shows a case where the taper angle is 12 degrees, and curve (B) shows a case where the taper angle is 20 degrees.
[0033]
In the above-described embodiment, the case where the taper portion on the entry side is a single-stage mold has been described. However, the present invention is not limited to this. It can also be applied to molds with multiple steps.
[0034]
【The invention's effect】
As described above in detail, according to the sizing press method of a hot slab according to the present invention, the contact start surface of the hot slab and the mold is forged as a transition region between the tapered portion and the parallel portion and a part of the parallel portion. Thus, it is possible to avoid the occurrence of slip at the time of pressing without processing a special mold. Therefore, operational problems due to the occurrence of slip can be avoided. In addition, considering that the taper angle of the mold is gradually increased from outside the scope of the present invention with the same reduction amount and the same feed amount, the present invention is a direction in which the taper angle of the mold is increased, so that the press load is reduced. It also becomes. Furthermore, since it is not necessary to perform special processing on the mold surface, the mold processing cost is reduced, and the complicated control required when slipping does not have to be performed.
In addition, slipping does not occur even if the lubricant is applied to a part or the whole of the main machining surface of the mold to reduce the friction coefficient of a part or the whole of the main machining surface, so that the stability of the press is maintained. It is possible to reduce the load. Furthermore, the efficiency of the sizing press can be drastically improved by using a mold having a mold angle of 16 degrees to 30 degrees and using a feed amount that does not slip.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram when a taper portion of a mold starts to contact a material.
FIG. 2 is an explanatory view of a forging method according to the present invention.
FIG. 3 is a characteristic diagram showing the relationship between the press load and the mold contact length when the taper angle of the mold is 20 degrees and 12 degrees.
FIG. 4 is a characteristic diagram showing the relationship between the number of presses and the mold contact length when the taper angle of the mold is 20 degrees and 12 degrees.
FIG. 5 is a characteristic diagram showing a relationship between a reduction amount to a material, a slip limit taper angle, and a necessary minimum feed amount.
FIG. 6 is a characteristic diagram showing the relationship between the taper angle of the mold, the feed amount, and the reduction amount.
FIG. 7 is a characteristic diagram showing the relationship between the thickness of the material and the position in the material width direction when the taper angle of the mold is 12 degrees and 20 degrees.
FIG. 8 is a plan view of a general mold shape used for forging a hot slab.
FIG. 9 is an explanatory view showing a conventional forging method in the order of steps.
FIG. 10 is an explanatory diagram of slip generation by a conventional forging method.
FIG. 11 is an explanatory diagram of a two-stage taper mold.
[Explanation of symbols]
1, 1a, 1b ... mold,
2 ... Parallel part,
3 ... transition region,
4 ... Tapered part,
5 ... Hot slab.

Claims (2)

The hot slab is formed in a width direction by using a mold having a tapered portion inclined in the inward direction with respect to the traveling direction of the hot slab and a main machining surface that is continuous with the tapered portion and parallel to the traveling direction. In the sizing press method for forging, the contact start surface of the hot slab and the mold is a transition region between the tapered portion and the parallel portion and a part of the parallel portion , and the main processing surface of the die A hot slab sizing press method comprising applying a lubricant to at least a contact surface with a hot slab. The hot slab sizing press method according to claim 1, wherein a taper angle of the taper portion is 16 degrees or more and 30 degrees or less .

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