JPH0413072B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for joining steel billets in hot rolling, and in particular, to a method for joining steel billets in hot rolling, and in particular, a steel billet suitable for use in endless rolling in which hot finish rolling is continuously performed. Regarding the joining method.

[Prior Art] In conventional hot finish rolling, when steel billets are rolled one by one, the following problems arise due to unsteady parts at the leading and trailing ends of the steel billets. In other words, large variations in product dimensions such as poor biting at the tip of the billet, poor thickness between the tip and the rear end of the billet, and, for example, when the tip and rear ends of the strip pass through the finishing mill row. When rolling, the work rolls are likely to be flawed, leading to a decrease in rolling efficiency due to an increase in the number of roll replacements, and an increase in roll consumption.

Therefore, as a method for solving the above-mentioned problem, an endless rolling method has been proposed in which steel billets are joined before a finishing mill.

For example, JP-A-54-4842 proposes a method of joining a leading steel piece and a trailing steel piece by flash welding.

Furthermore, Japanese Patent Publication No. 59-37861 proposes a method in which a leading steel piece and a trailing steel piece are overlapped by a predetermined amount and pressed together using a press device.

Furthermore, Japanese Patent Application Laid-Open No. 138960/1983 proposes a method in which engaging uneven portions are formed that face each other on the end faces of a leading steel billet and a trailing steel billet, and both are rolled with a predetermined pressing force. There is.

Furthermore, JP-A-53-137057, JP-A-54-
31067 and JP-A-54-31068 propose a method of applying a chemical such as a metal oxide to the joint surfaces of a leading steel piece and a trailing steel piece to facilitate pressure welding of the two. There is.

[Problems to be Solved by the Invention] However, among the above-mentioned conventional techniques, the flashing solution method requires a very large welding area of the hot sheet bar material when the welding machine is moved together with the steel billet. It is predicted that the weight of the welding machine will be extremely large, for example, over 100 tons, and troubles in running the welding machine are predicted, which is not reasonable. Furthermore, the flash welding method requires fine control of the gap between the steel pieces, making it extremely difficult to put it into practical use.

In addition, the method of overlapping and pressing the running steel billet and the trailing steel billet is by using a looper installed between finishing stands,
Due to the bending deformation of the steel pieces due to the accumulation, there is a fear that the overlapping joint between the two steel pieces may peel off due to stress concentration that occurs starting at the point where the surface layers of the two steel pieces start to overlap.

In addition, in the case of the method of imparting irregularities for engagement to the end faces of the leading and trailing steel pieces, or the method of applying chemicals, special processing equipment is required before joining them. Providing these devices in a production line for steel billets that are passed continuously at high speeds will reduce the production efficiency, making it difficult to implement.

On the other hand, for the purpose of solving the above-mentioned conventional problems, the present applicant has proposed Japanese Patent Application No. 60-000713 (method for joining steel slabs in hot rolling).
The method already proposed by the present applicant is to match the rear end of the leading steel piece with the leading end of the trailing steel piece,
This is a method in which the abutting portions of both steel pieces are energized and pressed between two pairs of energizing rolls.

An object of the present invention is to enable more reliable joining of leading steel pieces and trailing steel pieces using simple equipment.

[Means for Solving the Problems] The method for joining steel billets in hot rolling according to the present invention is achieved by accumulating and retaining the unrolled portion of the preceding billet during hot finishing rolling before the finishing mill. , the rear end of the unrolled part of the steel billet is stopped and clamped by a clamping device consisting of a pair of upper and lower dies, and a pressing force is applied to the trailing steel billet by a pair of upper and lower rolls arranged in front of the clamping device. At the same time, the leading end of the trailing steel piece is passed through a guide placed between the clamp device and the roll, and is butted against the rear end of the leading steel piece between the guide and the clamp device. The abutting portions of the steel pieces are electrically heated and pressed together.

[Function] By the way, there are the following problems to be solved in joining hot steel pieces.

(a) Scale is generated on each end face of the leading and trailing steel pieces whose ends have been cut before joining, and this scale acts as a barrier and deteriorates the joining properties.
Measures are needed to eliminate the effects of scale.

(b) It is necessary to use a highly reliable and stable joining method.

(c) The preceding billet is being rolled in a finishing mill, and it is desirable to complete the joining in a short time.

(d) When accumulating steel slabs, there is a material problem in that austenite crystal grains become coarse due to bending deformation, so it is necessary to minimize the bending deformation that occurs in the steel slabs.

(e) When pressing the end faces of the leading and trailing steel pieces together, it is necessary to avoid buckling the steel pieces.

Each of the above problems (a) to (e) can be solved as follows by the present invention.

First, regarding issue (a) regarding scale that deteriorates bonding properties, we clarified the relationship between scale amount and bonding strength. The relationship is shown in FIG. 2, and it is observed that the bonding strength decreases rapidly when the scale thickness exceeds 15 μm. On the other hand, regarding the relationship between the amount of scale generated and the elapsed time, the experimental results shown in Figure 3 show that after just a few seconds after the new front is exposed,
It is observed that a scale of 10 μm or more grows. Therefore, for example, if we consider joining the leading and trailing steel pieces after cutting them with a crop shear, it is impossible to join them within a few seconds, and it is necessary to use a joining method that is insensitive to scale. It is necessary to provide As a result of various experimental studies, it was determined that the best method would be to join the scales in a molten state. In other words, the main component of the scale at high temperatures is FeO, whose melting point is
1371℃ (Journal of the Welding Society Vol. 45 (1976), No. 6, p. 471)
Therefore, in the present invention, by heating the abutting portions of both pieces of steel to a temperature higher than this temperature, it is possible to melt the scale and realize joining without the influence of the scale.

Next, there is problem (b) regarding a highly reliable and stable joining method. To ensure stable bonding, it is most reliable to bond in a stationary state. Performing the welding under static conditions is contrary to solving the problem (c) related to short time welding and the problem (d) related to minimizing the amount of billet accumulation, but if the welding can be completed within a few seconds, If this is possible, these problems (c) and (d) can almost be solved even if the parts are joined in a static state. For example, the billet speed at the entry side of the finishing mill is set to 60m/
If it takes 20 seconds to join, then 20m
storage device is required. If a common sense rigid looper is used for this purpose, about 5 rolls will be required. In experimental studies, after passing through the roll once,
A strain of 1.0 to 1.5% occurs in the steel billet, and with five rolls, a strain of 5 to 8% occurs in the steel billet, resulting in coarsening of austenite grains and deterioration of material properties. Furthermore, in such an accumulating device, there are naturally concerns that the temperature of the steel billet may drop due to contact between the roll and the steel billet, and that peeled scale may become entangled. However, if the bonding time is, for example, 5 seconds or less, the accumulated amount will be within 5 m, contact with the roll will be small, and the above-mentioned concerns will not occur. That is, in the present invention,
If the preceding steel pieces are accumulated and retained, and the trailing end is clamped by a clamping device, and the two pieces of steel are pressed against each other by heating with electricity while abutting each other, under conditions where the joining time is short and the amount of accumulation is small, It becomes possible to realize joining in a stationary state.

Next, regarding issue (e) regarding buckling of steel billet,
According to the present invention, it is possible to set the distance between the roll as the pushing device and the joint portion short, and it has been recognized that this makes it possible to prevent the occurrence of buckling.

[Example] FIG. 1 is a schematic diagram showing the implementation state of the present invention.

After the preceding hot-rolled steel billet 1 is descaled by a scale breaker 2, it is bitten into a finishing mill 3 and rolled at a rolling entry speed υ2. After the rear end crop of the preceding steel slab 1 is cut off, the preceding steel slab 1 is accelerated by the pinch roll 4 to a speed equal to or higher than the rolling entry speed υ2, and forms a loop between the pinch rolls 4 and 5. do. When the rear end of the preceding steel piece 1 comes between the clamp device 6 consisting of a pair of upper and lower molds and the butt guide 7, the pinch roll 4 is stopped, and at the same time, the hydraulic cylinder 8 is activated.
The upper and lower molds of the clamp device 6 are moved, and the rear end of the preceding steel piece 1 is clamped between these molds. At this time, the loop length of the preceding steel piece 1 becomes maximum.

On the other hand, after the trailing steel piece 1 is cut off at its rear end, the trailing steel piece 9 whose tip end is immediately cut off is rolled by a light reduction push roll 10 equipped with a torque limiter, and then rolled by a hydraulic cylinder 11. It then passes between the upper and lower molds of the guide 7 whose gap has been adjusted, and comes into contact with the rear end of the preceding steel piece 1. The guide 7 has a function of allowing the leading end of the trailing steel piece 9 and the rear end of the leading steel piece 1 to be smoothly butted together.

The light reduction push roll 10, which generates a predetermined torque by adjusting the torque limiter, applies a predetermined pressing force to the abutting portion of both steel pieces 1 and 9, and the light reduction push roll 10 is powered by a power source 12.
A large current is applied between the clamping device 6, and the steel pieces 1,
The abutting portions of No. 9 are pressed together. At this time, the current density
Under the conditions of 160 A/mm and a pressing force of 2 Kg/mm ² , the current application time is approximately 2 seconds, and the temperature at the joint rises to 1400°C.

That is, by carrying out the method of the present invention, the problems caused by the bonding time and the problem of deterioration of bonding strength due to scale are solved. The power supply part need not be limited to the upper roll of the light reduction pushing roll 10 or the upper mold of the clamping device 6 as shown in FIG. It's okay.

The pressed end faces of the steel slabs 1 and 9 are deformed by thickening in the plate thickness direction, but the clamping device 6 and guide 7
By providing relief as shown in FIG. 1, it is possible to prevent the occurrence of inconveniences.

In addition to power supply, the functions of the light pressing roll 10 include:
The purpose is to apply a pushing force to the trailing steel piece 9, and the weight determines how much the rolling reduction rate should be in order to obtain the necessary pushing force. The necessary pushing force varies depending on the current density and application time as described above, but it is required to be 2 kg/mm ² or more. FIG. 4 shows the relationship between the rolling reduction rate and the resulting pushing force. Since the pushing force varies depending on the friction coefficient μ between the roll and the steel billet, the value μ = 0.637 in the theoretical formula for normal hot rolling, and μ considering the safety factor.
The case where = 0.3 is shown. Even in the case of μ = 0.3, which is a condition where slippage is likely to occur, it is recognized that it is possible to secure a pushing force of 2 kg/m ² if the rolling reduction ratio is 3% or more.

Furthermore, there is a fear that the trailing steel piece 9 may buckle due to the pushing force between the reduction roll 10 and the guide 7. The deformed state is shown in the broken line in Fig. 1, and the rolling roll 10 and guide buckle a 40 mm thick and 1000 mm wide hot steel billet (Young's modulus...5000 Kg/m ² ) under a pressing force of 2 Kg/mm ² . The distance l between 7 is calculated as 3.6
m (Frustration Theory Coronasha, 1968). In this embodiment, even if the distance between the reduction roll 10 and the guide 7 is set within the above-mentioned 3.6 m, there will be no interference problem with the equipment, and buckling of the trailing billet 9 can be reliably prevented. Is possible. In some cases, a pinch roll for preventing buckling may be installed between the reduction roll 10 and the guide 7.

According to the embodiment of the present invention described above, it becomes possible to endlessly roll a steel billet in a hot finishing rolling mill,
It becomes possible to achieve high production yield and high productivity. In addition, it is now possible to supply a large amount of hot lubricating oil and perform tension rolling over the entire length of the strip, which was previously impossible, making it possible to improve roll consumption and easily realize thin rolling of materials that are difficult to roll (SUS, etc.). becomes.

[Effects of the Invention] As described above, the method for joining steel billets in hot rolling according to the present invention is achieved by accumulating and retaining the unrolled portion of the preceding billet during hot finishing rolling before the finishing mill. , the rear end of the unrolled part of the steel billet is stopped and clamped by a clamping device consisting of a pair of upper and lower dies, and a pressing force is applied to the trailing steel billet by a pair of upper and lower rolls arranged in front of the clamping device. while doing,
Pass the leading end of the trailing steel piece through a guide placed between the clamping device and the roll, abutting it against the rear end of the leading steel piece between the guide and the clamping device, and The abutting portions are electrically heated and pressed together. Therefore, it becomes possible to more reliably join the leading steel piece and the trailing steel piece with simple equipment.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of the implementation state of the present invention, Fig. 2 is a diagram showing the relationship between the scale thickness of the butt surface of the steel billet and the crimp strength obtained when it is rolled, and Fig. 3 FIG. 4 is a diagram showing the relationship between the elapsed time after cutting the steel piece and the scale thickness generated on the cut surface, and FIG. 4 is a diagram showing the relationship between the pinch roll reduction rate and the resulting pushing force. 1... Leading billet, 3... Finishing rolling machine, 4... Clamp device, 7... Guide, 9... Trailing billet, 1
0... Push roll, 12... Power supply.

Claims (1)

[Claims] 1. By accumulating and retaining the unrolled portion of the preceding steel billet in front of the finishing rolling mill during hot finishing rolling, the rear end of the unrolled portion of the billet is stopped and a clamping device consisting of a pair of upper and lower dies is used. A guide placed between the clamping device and the rolls applies a pressing force to the trailing steel piece with a pair of upper and lower rolls placed in front of the clamping device. A steel billet in hot rolling is characterized in that the steel billet is butted against the rear end of the preceding steel billet between the guide and the clamp device, and the abutted portion of both billets is heated with electricity to be pressure-welded. Joining method.