RU2792732C1 - Method for double-sided rotational friction welding, methods for producing cold-rolled steel strip and coated steel strip, device for double-sided rotational friction welding and installations for producing cold-rolled steel strip and coated steel strip - Google Patents

Abstract

FIELD: rotational friction welding.

SUBSTANCE: group of inventions relates to double-sided rotational friction welding and production of cold-rolled steel strip and coated steel strip using said welding. Two rotating tools are pressed against the butt section or overlapping section of the steel strips and moved in the direction of welding while rotating in opposite directions to each other. The area softened by the heat of friction is agitated with rotating tools to obtain a plastic flow and ensure that the steel strips are welded to each other. The end part of each of the two rotating tools has the shape of a round convex or concave curved surface. The height of said convex surface or the depth of the concave surface is chosen depending on the diameter of the end part of the tool. The end parts of the tool are made of a harder material than steel strips.

EFFECT: increase in the durability of a rotating tool while suppressing the occurrence of defects in the welded area.

14 cl, 14 dwg, 5 tbl

Description

Technical field

The present invention relates to a double-sided friction rotation welding method and apparatus for double-sided friction rotation welding of steel strips, in which steel strips are welded to each other by rotating two opposing rotating tools in opposite directions relative to each other while butt-welding or overlapping the rear end of a preceding steel strip with the front end of the next steel strip. The present invention also relates to methods for producing cold-rolled steel strip and coated steel strip using a double-sided friction friction welding method, and to plants for producing cold-rolled steel strip and coated steel strip.

State of the art

Patent Literature 1 discloses a method for welding a pair of workpieces such as steel strips by rotating both or one of the steel strips to generate frictional heat that softens the steel strips and mixing the softened portion to induce plastic flow.

However, the method described in Patent Literature 1 requires rotating workpieces such as steel strips, and thus limits the shape and size of workpieces such as steel strips.

A friction welding method other than that of Patent Document 1 is disclosed, for example, in Patent Document 2. In Patent Document 2, a rotary tool (which may be referred to simply as “tool” hereinafter) that has a probe (hereinafter referred to simply as “ pin"), made of a material much harder than blanks, such as steel strips, is inserted into the non-welded part of the steel strips, and the rotating tool is moved while rotating. In this method, heat and plastic flow generated between the rotating tool and the steel strips are used to continuously weld the steel strips to each other in the longitudinal direction. In the present description, the section in which the steel strips are butted or overlapped and which has not yet been welded will be referred to as the "non-welded section" in the following, and the section that has been welded and integrated will be referred to as the "welded section" in the following. .

As described above, the friction welding method described in Patent Literature 1 includes rotating the steel strips and welding the steel strips to each other using the heat of friction between the steel strips. The friction rotation welding method described in Patent Literature 2 includes welding steel strips to each other by rotating and moving rotating tools while the steel strips are fixed in place. Thus, the advantage of the friction welding method is that even if elements having a substantially infinite length are welded to each other, these elements can be solid-state welded continuously in the longitudinal direction of the elements. Since the friction rotation welding method is a solid state welding using plastic flow of metal caused by frictional heat generated between a rotating tool and steel strips, welding can be performed without melting the unwelded portion. In addition, the friction welding method has many advantages, such as less deformation after welding due to low heating temperature, fewer defects in the welded area due to no melting of steel strips, and no need for filler material.

The rotational friction welding method has a wide range of applications in the fields of aircraft, ships, railway vehicles and automobiles and other fields as a method for welding low-melting metal materials such as aluminum alloys and magnesium alloys. This is because such fusible metal materials are unlikely to provide a welded portion having satisfactory properties using the prior art arc welding method using the rotational friction welding method, but can provide a welded portion (joint) having high quality with high performance.

Using the friction rotation welding method for structural steel, mainly used as materials for structures such as buildings, ships, heavy equipment, pipelines and automobiles, avoids brittleness resulting from the segregation of impurities during melting and solidification, and embrittlement as a result of hydrogen penetration, which has been a problem in prior art fusion welding. At the same time, the microstructures of steel materials are less susceptible to change. For them, joint characteristics can be improved. In addition, agitation of the welding surface with a rotating tool can create clean surfaces, and the clean surfaces can be brought into contact with each other, so that another advantage can be expected in that no pre-treatment step is required, unlike diffusion bonding. As described above, the use of a structural steel friction welding process has many purported advantages. However, the use of the friction rotation welding method for structural steel still has problems with welding workability, such as defects in joints during welding and low welding speeds. Thus, the use of the friction rotation welding method for structural steel has been less popular than the use of the friction rotation welding method for low melting point metal materials. Examples of the aforementioned defects in joints include misalignment and weld failure on joint surfaces or in joints, especially immediately after welding.

The main defect generation factors in the friction welding method described in Patent Literature 2 include changes in temperature and plastic flow that occur in the thickness direction of the workpieces. In particular, in the case where the rotating tool is located only on the first surfaces of the workpieces, plastic flow sufficient to achieve a metallurgically preferred welding state can be obtained on the first side of the surface. However, the plastic flow on the second side of the surface is often insufficient, since in the non-welded area during welding, the temperature increase and shear stress loading are insufficient.

When the friction rotation welding method described in Patent Literature 2 is used for structural steel, in many cases, with low heat input and high welding speed, sufficient plastic flow cannot be obtained in the unwelded portion because the structural steel, which is a blank, has a high strength at high temperature. Thus, it is difficult to increase the welding speed while suppressing the occurrence of defects during welding.

As a means to solve such problems, for example, in Patent Literature 3-5, two-sided rotational friction welding methods are disclosed. In the method of two-sided rotational friction welding, two opposing rotating tools are pressed against the first surface and the second surface of the welded area of metal plates (blanks) to create a uniform and sufficient plastic flow in the direction of the thickness of the blanks. As a result, the welding speed can be increased and the occurrence of joint defects during welding can be reduced.

By the way, the steel strip production process requires continuous supply of steel strips to improve productivity and product yield. For a continuous supply of steel strips, it is necessary to weld the previous and subsequent coils together. In other words, the rear end of the preceding material (previous steel strip) is welded to the leading end of the next material (next steel strip), and the welded steel strips are continuously fed to pickling, cold rolling, continuous annealing, and continuous coating lines in a conventional process. This process allows steel strips to be rolled over their entire length under tension and allows precise control of the thickness and shape of the steel strips even at their front and back ends.

Due to the high alloying of cold rolled steel strips and advanced laser welding machines, instead of flash butt welding or other methods in the relevant field of technology, laser welding is becoming the main method of welding the predecessor material to the subsequent material. However, laser welding is a fusion welding and may have problems of brittleness due to impurity segregation during melting and solidification, and embrittlement due to hydrogen penetration. To solve these problems, it is considered effective to use the method of rotational friction welding, which is welding in the solid state. However, as described above, it is difficult to increase the welding speed while suppressing the occurrence of defects in conventional rotational friction welding, and thus conventional rotational friction welding cannot achieve the productivity required in the steel strip production process. As a means for solving such problems, for example, Patent Literature 4 describes a cold rolling mill using double-sided rotational friction welding.

In addition, the use of the friction rotation welding method for welding cold-rolled steel strip requires high strength and long service life of the rotating tool. The reason for this is as follows: the rotating tool needs to be repaired due to damage and wear. However, if weld failure is expected to occur with a high probability for this reason, it will be practically difficult to use the friction rotation welding method to weld cold-rolled steel strips together, although the positive effects described above occur.

A typical conventional friction welding method uses a rotating tool with a protruding probe at the end and center of its axis of rotation and a flattened protrusion around the probe, and this method includes: with a friend. Thus, the probe receives a large load during welding and is thus particularly prone to breakage and wear among the parts of the rotating tool.

Examples of methods for preventing breakage or other damage to probes include rotational friction welding using a rotating tool having a flat end without a probe, as described in Patent Literature 6-11.

List of sources

Patent Literature

PTL 1: Japanese Pending Patent Application Publication No. 62-183979.

PTL 2: Japanese Pending Patent Application (PCT Application Translation), Publication No. 07-505090.

PTL 3: Japanese Patent No. 3261433.

PTL 4: Japanese Patent No. 4838385.

PTL 5: Japanese Patent No. 4838388.

PTL 6: Japanese Patent No. 5185103.

PTL 7: Japanese Pending Patent Application Publication No. 2015-127063.

PTL 8: Japanese Pending Patent Application Publication No. 2003-181655.

PTL 9: Japanese Pending Patent Application Publication No. 2003-290936.

PTL 10: Japanese Pending Patent Application Publication No. 2004-195480.

PTL 11: Japanese Pending Patent Application Publication No. 2011-115846.

Disclosure of the essence of the invention

Technical task

However, the methods disclosed in Patent Literature 6 and Patent Literature 7 are aimed at strengthening the welded portion or strengthening the metal surface, and are not intended to be used for welding steel strips. Patent Document 6 and Patent Document 7 describe a rotary tool end having a smooth surface or a flat surface, but do not describe a rotary tool end having a concave or convex curvilinear shape for improving plastic flow. Also, Patent Document 6 and Patent Document 7 do not describe prior art rotary tools having a helical stepped portion extending in a direction opposite to the direction of rotation. Thus, the use of the aforementioned state-of-the-art rotary tools for welding steel strips to each other may result in insufficient plastic flow in the thickness direction, resulting in failure of the weld.

The techniques disclosed in Patent Literature 8-11 are directed to friction welding of metal plates and do not consider any application to the double-sided friction welding process. In other words, Patent Literature 8-11 does not disclose a proper relationship between the diameter of the end portion of a rotating tool and the thickness of metal plates to be welded to each other by bilateral friction welding. Thus, the methods disclosed in Patent Literature 8-11 may not provide a defect-free weld.

The present invention has been made in view of the above objects, and an object of the present invention is to provide a method for double-sided friction welding, methods for producing cold-rolled steel strip and coated steel strip, a device for double-sided friction welding, and a device for producing cold-rolled steel strip and coated steel strip, in which it is possible to increase the speed of welding using a rotary tool and improve the durability of a rotary tool, while the occurrence of defects in the welding section can be suppressed.

The solution of the problem

The essence of the present invention is described below.

[1] A double-sided friction friction welding method, which includes the following:

butt or overlap welding of the rear end of the previous steel strip and the front end of the subsequent steel strip

pressing two rotary tools located on the first surface and the second surface of the butt section or overlapping section of the steel strips against the butt section or overlapping section of the steel strips, and moving the rotary tools in the direction of welding while rotating the rotary tools in directions opposite to each other, so that unwelded the section of the steel strips is softened by the heat of friction generated between the rotating tools and the unwelded section of the steel strips, and the softened section is agitated by the rotating tools to obtain a plastic flow so as to weld the steel strips to each other, while:

each of the two rotary tools has an end part having the shape of a round flat surface, a round convex curved surface and a round concave curved surface; And

end pieces are made of a harder material than steel strips.

[2] In the method of double-sided rotational friction welding according to [1], each end portion has a helical stepped portion extending in a direction opposite to the direction of rotation.

[3] In the double-sided friction rotation welding method according to [1] or [2], the inclination angle α (°) at which the rotation axes of the two rotating tools are tilted back in the welding direction with respect to the normal to the surface of the unwelded portion of the steel strips, diameter D ( mm) of each end portion and the distance G (mm) between the end portions of two rotating tools satisfy formula (1) and formula (2) below:

0 ≤ α ≤ 3 … (1)

0.25 × t - 0.2 × D × sin α ≤ G ≤ 0.8 × t – 0.2 × D × sin α … (2)

where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap.

[4] In the method of double-sided rotational friction welding according to any one of [1] to [3], the diameter D (mm) of each end portion satisfies the formula (3):

4 × t ≤ D ≤ 20 × t … (3)

where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap.

[5] In the method of two-sided rotational friction welding according to any of [1] to [4], if the height of the convex curved surface of each end part is denoted by dv (mm), then the diameter D (mm) of each end part and the height dv of the convex curved surfaces satisfy formula (4):

dv/D ≤ 0.06 ... (4).

[6] In the bilateral friction welding method according to any of [1] to [4], if the depth of the concave curved surface of each end part is denoted by dc (mm), then the diameter D (mm) of each end part and the depth dc of the concave curved surfaces satisfy formula (5):

dc/D ≤ 0.03 ... (5).

[7] A method for manufacturing a cold-rolled steel strip, which includes: after welding the rear end of the preceding steel strip and the leading end of the next steel strip using the two-sided friction friction welding method according to any one of [1] to [6], performing cold rolling or perform cold rolling after pickling.

[8] The method for producing cold-rolled steel strip according to [7], which also includes performing annealing after cold rolling.

[9] A method for manufacturing a coated steel strip, which includes the following: after welding the rear end of the previous steel strip and the front end of the next steel strip using the double-sided rotational friction welding method according to any one of [1] to [6], performing a cold rolling, or performing cold rolling after pickling, and then performing annealing or coating.

[10] A device for double-sided rotational friction welding, including two rotating tools located opposite each other on a non-welded portion of two steel strips, and a control device that controls the operation of two rotating tools, in which:

the double-sided friction friction welding apparatus welds the steel strips to each other when two rotating tools are moved in the direction of welding, pressing against the non-welded portion of the butted or overlapping steel strips and rotating them in opposite directions relative to each other;

each of the two rotary tools has an end part having the shape of a round flat surface, a round convex curved surface and a round concave curved surface; And

end pieces are made of a harder material than steel strips.

[11] In the double-sided rotational friction welding apparatus according to [10], each end portion has a helical stepped portion extending in a direction opposite to the direction of rotation.

[12] In the method of bilateral rotational friction welding according to [10] or [11], the control device performs control so that the inclination angle α (°) at which the rotation axes of the two rotary tools are tilted back in the welding direction with respect to the normal to surface of the non-welded portion of the steel strips, the diameter D (mm) of each end portion, and the distance G (mm) between the end portions of two rotating tools satisfy the formula (1) and formula (2) below:

0 ≤ α ≤ 3 … (1)

0.25 × t – 0.2 × D × sin α ≤ G ≤ 0.8 × t – 0.2 × D × sin α … (2)

where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap.

[13] In the two-sided rotational friction welding apparatus according to any one of [10] to [12], the diameter D (mm) of each end portion satisfies the formula (3):

4 × t ≤ D ≤ 20 × t … (3)

where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap.

[14] In the two-sided rotational friction welding device according to any of [10] to [13], if the height of the convex curved surface of each end part is denoted by dv (mm), then the diameter D (mm) of each end part and the height dv of the convex curved surfaces satisfy formula (4):

dv/D ≤ 0.06 ... (4).

[15] In the two-sided rotational friction welding device according to any of [10]-[13], if the depth of the concave curved surface of each end part is denoted by dc (mm), then the diameter D (mm) of each end part and the depth dc of the concave curved surfaces satisfy formula (5):

dc/D ≤ 0.03 ... (5).

[16] A cold-rolled steel strip production plant, which includes: in addition to the two-sided friction welding apparatus according to any one of [10] to [15], a cold rolling section that cold-rolls welded steel strips or a cold rolling section which performs cold rolling of the welded steel strips after pickling in the pickling section.

[17] A cold-rolled steel strip production plant according to [16], which also includes an annealing section in which cold-rolled steel strips are annealed.

[18] An apparatus for producing coated steel strip, which includes the following: in addition to the two-sided friction welding apparatus according to any one of [10] to [15], a cold rolling section which performs cold rolling of the welded steel strips or a cold rolling section which performs cold rolling of the welded steel strips after pickling in the pickling section; an annealing section in which cold-rolled steel strips are annealed; and a coating section in which the annealed steel strips are coated.

Useful effects of the invention

According to the present invention, brittleness resulting from impurity segregation during melting and solidification and embrittlement due to hydrogen penetration, which have been problems in prior art fusion welding, can be avoided, and welding speed can be increased while suppressing the occurrence of defects.

According to the present invention, uniform plastic flow stimulated in the thickness direction of steel strips suppresses the occurrence of defects even in double-sided friction rotation welding at a high welding speed, giving a welded portion having sufficient strength.

In accordance with the present invention, it is possible to remove the probe, which preferably breaks and wears as a result of applying stress in excess of the load on the protrusion of the prior art rotary tool, which increases the durability of rotary tools for double-sided rotational friction welding.

Brief description of the drawings

In FIG. 1 is a schematic view illustrating the double-sided rotational friction welding method according to the present invention, which is an example of butt welding.

In FIG. 2 is a schematic view illustrating the double-sided rotational friction welding method according to the present invention, which is an example of overlap welding.

In FIG. 3(a) and 3(b) are schematic views illustrating a region that is agitated by friction with rotating tools, wherein FIG. 3(a) and FIG. 3(b) are respectively a plan view and a sectional view along the line A-A' shown in FIG. 3(a).

In FIG. 4(a) and 4(b) show the shape of a prior art rotary tool, and each includes a side view at the top and a top view at the bottom.

In FIG. 5(a) and 5(b) show the shape of a rotary tool according to the first embodiment of the present invention, and each includes a side view at the top and a top view at the bottom.

In FIG. 6(a) and 6(b) show the shape of a rotary tool according to the second embodiment of the present invention, and each includes a side view at the top and a top view at the bottom.

In FIG. 7(a) and 7(b) show the shape of a rotary tool according to the third embodiment of the present invention, and each includes a side view at the top and a top view at the bottom.

In FIG. 8(a)-8(c) show the shapes of the stepped portions of a rotary tool according to the present invention, where FIG. 8(a) is a plan view, and FIG. 8(b) and FIG. 8(c) shows sections taken along line B-B' in FIG. 8(a).

In FIG. 9 are diagrams illustrating an example of how to draw helixes forming stepped portions in accordance with the present invention.

In FIG. 10 are diagrams illustrating an example of how to run helices forming stepped portions in accordance with the present invention.

In FIG. 11 are diagrams illustrating an example of how to run helices forming stepped portions in accordance with the present invention.

In FIG. 12 are diagrams illustrating an example of how to run the spirals forming the stepped portions in accordance with the present invention.

In FIG. 13 are diagrams illustrating an example of how to run the spirals forming stepped portions in accordance with the present invention.

In FIG. 14 is a schematic diagram illustrating a method for welding steel strips (previous steel strip and next steel strip) to each other using the two-sided rotational friction welding apparatus according to the present invention, which is an example of butt welding.

Implementation of the invention

The present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

First, the method of double-sided rotational friction welding and the device for double-sided rotational friction welding according to the present invention will be described. In FIG. 1 shows an example of a butt-welding by a two-sided rotational friction welding method. In FIG. 2 shows an example of overlap welding by a two-sided rotational friction welding method.

The method of double-sided rotational friction welding according to the present invention in butt or overlap welding of the rear end of the preceding steel strip with the front end of the next steel strip includes the following: two rotating tools are pressed, which are located on the first surface and the second surface of the butt section or overlapping section of the steel strips, opposite the butt section or overlapping section of the steel strips, and move the rotating tools in the direction of welding while rotating the rotating tools in opposite directions relative to each other. Then, the unwelded portion of the steel strips is softened by frictional heat generated between the rotating tools and the unwelded portion of the steel strips, and the softened portion is agitated by the rotating tools to generate plastic flow, whereby the steel strips are welded to each other.

As shown in FIG. 1 and FIG. 2, the bilateral friction rotation welding method according to the present invention uses a bilateral friction rotation welding apparatus including two rotating tools 1 and 8, a holding device (not shown) and a control device (not shown) which controls the operation of the rotating tools. 1 and 8. In the examples shown in FIGS. 1 and FIG. 2, one of the two steel strips 4 is the preceding steel strip located in front in the moving direction (not shown), and the other steel strip 4 is the next steel strip located behind in the moving direction.

The control device controls, for example, the inclination angle b of each of the rotary tools 1 and 8, the distance G between the end of the rotary tool 1 and the end of the rotary tool 8, the welding speed, the rotation speed and the direction of rotation of each of the rotary tools 1 and 8, as described. below.

Rotary tools 1 and 8 (the rotary tool located on the front surfaces of the steel strips, hereinafter referred to as the rotary tool 1 from the front side, and the rotary tool located on the rear surfaces of the steel strips, hereinafter referred to as the rotary tool 8 from the rear surfaces) are respectively located on the first surface (front surface) and the second surface (rear surface) of steel strips (blanks or welded elements) 4. Two steel strips 4 are located parallel to the center line 7 of the joint shown in FIG. 1 and FIG. 2 and are held by a holding device (not shown). On the non-welded section of two steel strips 4, located on the axial line 7 of the connection, the rotating tools 1 and 8 are moved in the direction of welding (the direction indicated by the arrow in the figures), rotating and pressing against the steel strips 4. The steel strips 4, thus softened due to frictional heat generated between the rotating tools 1 and 8 and the steel strips 4, and the softened area is agitated by the rotating tools 1 and 8 to create a plastic flow, whereby the steel strips 4 are welded to each other. In the following description, the section where the welding is completed will be referred to as welded section 5.

As shown in FIG. 1 and FIG. 2, the front surface rotary tool 1 and the rear surface rotary tool 8, which are opposite each other, rotate in opposite directions relative to each other as viewed from the front surface (or rear surface) of the steel strips 4. This allows the torque applied by the rotating tool 1 to the steel strips 4, and the torque applied by the rotating tool 8 to the steel strips 4 cancel each other out. As a result, the structure of the fixture holding the elements to be welded can be further simplified compared to the prior art rotational friction welding method in which the non-welded portion is pressed and welded using only one rotating tool located on one surface. In the examples shown in FIG. 1 and FIG. 2, the direction of rotation of the tool 1 rotating on the rake side is indicated by the arrow Ts, and the direction of rotation of the tool 8 rotating on the rear surface is indicated by the arrow Tb.

If the front surface rotary tool 1 and the rear surface rotary tool 8, which are opposite each other, rotate in the same direction, the speed of one of the rotary tools relative to the other rotary tool approaches zero. As a result, as the plastic flow of the steel strips 4 becomes more uniform, the plastic deformation decreases, and less heat is generated when the material is plastically deformed, making it difficult to achieve a favorable welded state. In order to ensure uniform temperature rise and uniform shear stress in the thickness direction of the steel strips sufficient to achieve a favorable welded state, it is effective to set the opposite directions of rotation of the rotary tool 1 on the front surface (first surface) and the rotary tool 8 on the rear surface (second surface) located opposite each other.

The type of welding of steel strips will now be described. Preferred examples of the type of welding of steel strips include butt welding and lap welding. As shown in FIG. 1, butt welding refers to the welding of steel strips, which includes pressing the rotating tools 1 and 8 to the butt section, including the end surfaces (adjacent surfaces) of two opposite steel strips 4 placed end to end without overlap, and moving the rotating tools 1 and 8 in the direction welding with rotating tools 1 and 8. As shown in FIG. 2, overlap welding refers to welding of steel strips in which the rotating tools 1 and 8 are pressed against the overlapping portion of two steel strips 4 with the end portions of the steel strips 4 at least partially overlapping each other, and the rotating tools 1 and 8 are moved in the direction of welding at simultaneous rotation of the rotary tools 1 and 8. Since FIG. 1 and FIG. 2 differ from each other only in the type of welding, and are the same in arrangement of devices, etc., the butt-welding example shown in FIG. 1.

Next will be described the rotary tools used in bilateral friction welding in accordance with the present invention. In FIG. 4(a) and 4(b) are diagrams illustrating a prior art rotary tool 20 including a probe. In FIG. 5(a)-8(c) are diagrams illustrating rotary tools 1 and 8 in accordance with the present invention. In FIG. 5(a)-5(c) show a rotary tool according to the first embodiment of the present invention. In FIG. 6(a) and 6(b) show a rotary tool according to a second embodiment of the present invention. In FIG. 7(a) and 7(b) show a rotary tool according to a third embodiment of the present invention. In FIG. 8(a)-8(c) show an example of a rotary tool according to the second embodiment, which has stepped portions on its end portion. In FIG. 4(a)-7(b), the upper part is a side view, and the lower part is a top view. Since the rake side rotary tool 1 and the flank side rotary tool 8 have the same shape, in FIG. 4(a) to 8(c) only show the rotary tool 1 from the rake side.

Now with reference to FIG. 4(a)-4(b), a rotary tool 20 including a probe (pin) 21, which is an example of the prior art, will be described. In FIG. 4(a) and FIG. 4(b) shows an example of a rotary tool 20 that includes a probe 21 on a projection 22. For example, in the example of a rotary tool 20 shown in FIG. 4(a), the rotary tool 20 has the following shape: the diameter of the projection 22 (protrusion diameter) is 12 mm, the diameter of the probe 21 (pin diameter) is 4 mm, the length of the probe 21 (pin length) is 0.5 mm, and the depth of the concave surface 0.3 mm. In the example of rotary tool 20 shown in FIG. 4(b), the rotary tool 20 has the following shape: a protrusion diameter of 20 mm, a pin diameter of 6.7 mm, a pin length of 0.7 mm, and a concave surface depth of 0.3 mm.

As shown in FIG. 4(a) and FIG. 4(b), the end portion of the prior art rotary tool 20, that is, the portion of the rotary tool 20 that comes into contact with the softened portion of the steel strip during welding, includes a projection portion 22 (the portion indicated by the diameter of the projection in FIG. 4 (a) and Fig. 4(b)) and probe 21 (the area indicated by the pin diameter in Fig. 4(a) and Fig. 4(b)). The projection 22 has a flat shape formed by a substantially flat surface or a slightly curved surface. The probe 21 is interrupted by a protruding portion 22 and protrudes substantially vertically to the steel strips (not shown).

The probe 21 is designed to improve the mixing characteristics near the center sections of the steel strips in the thickness direction by penetrating into the softened part of the steel strips closer to the center in the thickness direction during welding. However, there is a problem that the part of the probe 21 located closer to its end in the thickness direction (closer to the center of the thickness) is subjected to a stress greater than the stress perceived by the protrusion 22. Therefore, there is another problem in that that the rotating tool needs to be repaired due to damage and wear as described above.

The inventors of the present invention have made intensive studies. As a result, it has been found that the double-sided frictional welding method using rotary tools for double-sided frictional welding is able to suppress the occurrence of defects in the welded area and increase the welding speed without using the probe, which is particularly easy to break and wear due to the greater stress applied to it. .

As shown in FIG. 5(a)-7(c), the end of each of the rotary tools (rotary tools 1 and 8 located opposite each other) for bilateral friction welding according to the present invention is formed simply by the end part 11. Unlike the configuration of the rotary tool of the previous of the prior art, which is shown in Fig. 4(a) and FIG. 4(b), the end portion 11 of each of the rotary tools of the present invention does not include a probe 21. The end portion 11 of each of the rotary tools 1 and 8 has one of the following shapes: a flat shape 11a (see FIGS. 5(a)-5( c)), a convex curved shape 11b (see FIGS. 6(a) and 6(b)), and a concave curved shape 11c (see FIGS. 7(a) and 7(b)). Each end portion 11 has a circular cross section in plan view.

The end portions 11 of the rotary tools 1 and 8 (the front surface side end portion 2 of the rotary tool and the rear surface side end portion 9 of the rotary tool shown in Fig. 1 and other figures) are parts that come into contact with the steel strips. 4 and fluid areas (softened areas) of the steel strips 4 during welding. Thus, the end portions 11 of the rotary tools 1 and 8 are made of a material harder than the steel strips 4 in the high temperature environment to which the end portions 11 are subjected during welding. Thus, the rotating tools 1 and 8 can deform the steel strips 4 during welding while maintaining the shape of the end portions 11. As a result, high mixing performance can be continuously achieved and acceptable welding can be performed.

Vickers hardness testing methods at elevated temperatures can be used to compare hardness. The rotary tools 1 and 8 can be made so that only their end parts will have the above hardness, or all of the rotary tools 1 and 8 will have the above hardness.

In addition to the above-described configuration, in the present invention, the end portion 11 of each of the rotary tools 1 and 8 preferably has helical (helicoidal) stepped portions 12. of the tool 1, and the spirals (helicoids) forming the stepped portion 12 of the rotary tool 8 preferably extend in the direction opposite to the direction of rotation of the rotary tool 8. The number of spirals forming the stepped portions 12 is preferably 1 or more.

In the case of one or more spirals, the curves (radial curves) are formed so that they extend radially from the center of the end part 11 or the perimeter of the circular empty area in the center to the outer circumference of the end part 11.

If the number of spirals forming the stepped portions 12 is more than 6, the material flow improvement effect is reduced, and furthermore, the end portions 11 of the rotary tools 1 and 8 may break easily due to their complex shape. Thus, the number of helices forming the stepped portions 12 is preferably 6 or less. In the examples shown in FIG. 5(b), 6(b) and 7(b), as well as in the example shown in FIG. 8(a), the number of spirals is 4.

In order to prevent breakage of the end portions 11 of the rotary tools 1 and 8 while improving the fluidity of the material, the number of spirals forming the stepped portions 12 can be adjusted according to the diameter of each of the end portions 11. In particular, the number of spirals is preferably increased as the diameter of each of the end parts 11, and the number of spirals is preferably reduced as the diameter of each of the end parts 11 decreases.

In particular, the number of spirals is preferably 2 or less when the diameter of the end portion is less than 6 mm, and the number of spirals is preferably 3 to 6 when the diameter of the end portion is 6 mm or more.

How to conduct coils will be described using the examples shown in FIG. 9–13. In FIG. Figures 9-13 are top views of the end portion, and each of them shows the process of guiding the spirals in the end portion.

In FIG. 9, the number of spirals is 2, and in FIG. 9 shows an example of how two spirals can be drawn at equal intervals.

As shown in FIG. 9, first, from the starting points at point A and point B (see (1)) two semicircles (first semicircles) are drawn with a radius equal to the length of the line A-B. Then, outside the first semicircles, semicircles (second semicircles) are drawn with centers at points A and B and a radius equal to twice the length of the line A-B each (see (2)). Then, outside the second semicircles, semicircles (third semicircles) are drawn with centers at points A and B and a radius equal to three times the length of the line A-B each (see (3)). Similarly, semicircles (fourth semicircles) are drawn, each of which has a radius four times the length of the line A-B (see (4)). By repeating this process, two spirals can be drawn at equal intervals in the end part.

On each of the FIGS. Figures 10–13 show an example of how to draw spirals at regular intervals, where the number n of spirals is chosen from 3 ≤ n ≤ 6.

As shown in FIG. 10-13, regular n-sided polygons are drawn first. In the example in FIG. 10 a regular triangle is drawn, in the example in FIG. 11 is a square, in the example in Fig. 12 is a regular pentagon, and in the example in Fig. 13 is a regular hexagon. Arcs (first arcs) are drawn to the intersection points with lines extending from the sides of a regular n-sided polygon (see (1)) having centers at the vertices of each regular n-sided polygon and having a radius equal to the length of one side of a regular n-sided polygon. Then, outside the first arcs, to the intersection points with lines extending from the sides of a regular n-sided polygon (see (2)) draw arcs (second arcs) having centers at the vertices of each regular n-sided polygon and having a radius equal to twice the length of one side of a regular n-sided polygon. Then, outside the second arcs, to the intersection points with lines extending from the sides of a regular n-sided polygon (see (3)) draw arcs (third arcs) having centers at the vertices of each regular n-sided polygon and having a radius equal to three times the length of one side of a regular n-sided polygon. Similarly, arcs (fourth arcs) are drawn, each of which has a radius four times the length of one side of a regular n-sided polygon (see (4)). By repeating this process, n (3 ≤ n ≤ 6) spirals can be drawn at equal intervals in the end.

In case the number of spirals is 1, the spiral can be carried out by any of the methods shown in FIG. 9-13. If the number of spirals is 2 and two spirals are drawn at equal intervals, then the spirals can also be drawn in the manner shown in FIG. 11 or FIG. 13, in addition to the method shown in FIG. 9. If the number of spirals is 3 and three spirals are drawn at equal intervals, then the spirals can also be drawn in the manner shown in FIG. 13, in addition to the method shown in FIG. 10. In these cases, the number of spirals (number of lines) is adjusted by appropriate selection of the starting points shown in FIG. 9 or the vertices of the regular n-sided polygons shown in FIG. 10-13, according to the number of spirals.

Each of the stepped portions 12 is recessed from another surface (flat surface or curved surface) of the corresponding end portion. Such recessed stepped portions 12 cause the metal material, softened by frictional heat, to flow from outside to inside of the rotating tools 1 and 8 when the rotating tools 1 and 8 press and stir the steel strips 4. Accordingly, the rotating tools 1 and 8 can prevent the metal material from flowing out of the pressed portion. . This can promote plastic flow of the pressed portion, and can also prevent the thickness of the welded portion from being thinner than that of the base material, forming a smooth surface of the welded portion without burrs. The above beneficial effects of the stepped portions are achieved by forming the helical stepped portions 12 such that the stepped portions 12 extend in the opposite direction to the direction of rotation of the rotary tools 1 and 8. The rotary tools of the present invention preferably do not have a helical stepped portion at the center of their end parts or preferably do not have in the center of its end part a helical stepped section extending in the direction opposite to the direction of rotation.

Beneficial effects similar to those described above can be obtained by providing one or more helical stepped portions 12 extending in the opposite direction to the direction of rotation of the respective rotary tool.

Now with reference to FIG. 8(a)-8(c) the stepped portions 12 will be described more specifically. In FIG. 8(a) is a plan view of the rotary tool 1 (rotary tool from the front surface), which includes an end portion 11 having a convex curved shape 11b, and FIG. 8(b) and FIG. 8(c) shows sections taken along line B-B' in FIG. 8(a).

As shown in FIG. 8(a) in plan view, the stepped portions 12 extend in the direction opposite to the direction of rotation. In other words, the direction of the curve of each of the stepped sections 12 extending from the perimeter of the circle to the center of the circle is opposite to the direction of rotation of the rotary tool.

As shown in FIG. 8(a) in plan view, each of the helical stepped portions 12 forms a curve extending from a starting point near the center of the circle to the perimeter of the circle. The length of each spiral is preferably 0.5 turns or more, and 2 turns or less if the length of the outer circumference of the end portion 11 is one turn. The length of each helix can also be adjusted depending on the diameter of the end portion 11. The length of each helix is preferably increased as the diameter of the end portion 11 increases. The length of each helix is preferably reduced as the diameter of the end portion 11 decreases.

Specific examples of the stepped portions 12 include the stepped portions 12b shown in FIG. 8(b) and grooves 12c shown in FIG. 8(c). In the example shown in FIG. 8(b), the stepped portions 12b form substantially horizontal steps, so that the height of the steps gradually increases from the perimeter of the circle to the center of the circle, as on the convex curved surface of the end portion 11 of the rotary tool 1. To obtain the above-described beneficial effects, the present invention can be formed one or more spiral steps. In the example shown in FIG. 8(b), each formed stepped portion 12 has a helical shape in plan view as shown in FIG. 8(a).

Although not shown, if a rotary tool having a concave curved end portion includes stepped portions 12b on the concave curved surface, then the steps may be formed such that the height of the steps gradually decreases from the circumference of the circle to the center of the circle along the concave curved surface. .

In the example shown in FIG. 8(c), each groove 12c on the curved surface (convex curved surface) of the end portion 11 of the rotary tool 1 has a groove with a substantially U-shaped cross section to be recessed relative to the other surface. In order to obtain the above-described beneficial effects, one or more grooves 12c may be formed in the present invention. In the example shown in FIG. 8(c), each formed groove 12c has a long and narrow shape extending in a spiral in plan view as shown in FIG. 8(a). The above-described beneficial effects are achieved, for example, by using a V-shape or a swoosh-shape instead of a U-shape.

Although not shown, if a rotary tool 1 having an end portion 11 of a concave curved shape 11c or a flat shape 11a includes grooves 12c on the concave curved surface or flat surface, the grooves having a substantially U-shaped cross section may be formed in a similar way.

In addition to the configuration described above, the diameter D (mm) of the end portion 11 of each of the rotary tools 1 and 8 preferably satisfies the relationship represented by the following formula (3) in the present invention:

4 × t ≤ D ≤ 20 × t … (3)

where t is the thickness (mm) of each steel strip for butt welding of steel strips or the total thickness (mm) of steel strips for welding steel strips with an overlap.

By controlling the diameter of each end portion 11, the rotary tools 1 and 8 can uniformly and efficiently provide temperature rise and shear stress in the thickness direction of the steel strips 4. The diameter D of the end portion 11 of the rotary tool 1 is preferably adjusted according to the thickness of each of the steel strips 4 (total thickness t of steel strips 4 for overlap welding). In other words, it is expedient to set the diameter D (mm) of the end portion 11 of each of the rotary tools 1 and 8 according to the formula (3): 4 × t ≤ D ≤ 20 × t.

If the diameter D (mm) is smaller than 4×t (mm), uniform plastic flow in the thickness direction cannot be effectively obtained. If the diameter D (mm) is larger than 20 × t (mm), then the plastic flow region is unnecessarily expanded, and an excessive load is applied to the device, which is undesirable. The diameter D is preferably 5.5 x t (mm) or more, and preferably 14 x t (mm) or less.

As described above, the shape of the rotary tool according to the present invention can be simplified by eliminating the probe required for the prior art rotary tool. A rotating tool may have greater durability. A rotary tool can be made in fewer steps and at a lower cost.

According to the double-sided rotational friction welding method of the present invention, using rotating tools in the thickness direction, uniformly sufficient temperature rise and sufficient shear stress during welding can be ensured. In other words, a uniform temperature increase in the thickness direction can be more efficiently achieved by promoting plastic flow by the welding method using the rotary tools of the present invention having the above configuration, compared to a uniform temperature increase that can be obtained by two-sided rotational welding. friction of the prior art. Thus, in order to perform welding of steel strips, a part of the welded portion is not subjected to excessive temperature rise, which prevents segregation embrittlement caused by segregation of the melting region due to exposure to high temperature and hydrogen embrittlement caused by increased penetration of hydrogen into the steel due to high temperature.

Next, the rotary tools according to the first to third embodiments of the present invention will be described in detail. It should be noted that in FIG. 5(a)-7(b) only show the rotary tool 1 from the front surface side.

First Embodiment

As shown in FIG. 5(a) and FIG. 5(c), each of the rotary tools 1 and 8 according to the first embodiment of the present invention has a round end formed from an end portion 11 having a flat shape 11a. Each end portion 11, having a flat shape, has an end surface that comes into contact with the steel strips and is formed by a single flat surface perpendicular to the axis of rotation of the corresponding one of the rotary tools 1 and 8. Unlike the rotary tool of the prior art, the end surface does not has a probe protruding towards the steel strips. As shown in FIG. 5(b), the end portion 11 of each of the rotary tools 1 and 8 may have one or more helical (helicoidal) stepped portions 12 extending in the direction opposite to the direction of rotation, as described above. The stepped portions 12 have stepped portions 12b or grooves 12c as described above.

The top view of Fig. 5(c) is a sectional view taken along the line B-B' shown at the bottom of FIG. 5(c). The stepped portions 12b are formed, for example, by slopes of substantially horizontal surfaces, as shown in FIG. 5(c). In other words, the groove portions are formed in the form of a checkmark. The spirals of the stepped portions 12b in FIG. 5(c) can be carried out, for example, in the manner shown in FIG. 10 described above.

Second Embodiment

As shown in FIG. 6(a) and FIG. 6(b), each of the rotary tools 1 and 8 according to the second embodiment has a round end formed by an end portion 11 having a convex curvilinear shape 11b, and the end of each rotary tool is convex. Although the prior art rotary tool includes a probe that protrudes towards the steel strips and is interrupted by a projection, each end portion 11 having a convex curvilinear shape has a continuous shape without a probe and forms an approximately uniform inclined surface. In other words, each end portion 11 having a convex curvilinear shape has an end surface that comes into contact with the steel strips and is formed by a single curved surface (parabolic surface, elongated surface, or spherical surface) protruding towards the center, and the end surface forms a curve having an approximately uniform radius of curvature in cross section, including the axis of rotation in the direction perpendicular to the steel strips. As shown in FIG. 6(b), the end portion 11 of each of the rotary tools 1 and 8 may have one or more helical (helicoidal) stepped portions 12 extending in the direction opposite to the direction of rotation, as described above. The stepped portions 12 have stepped portions 12b or grooves 12c as described above.

In the case where the end of each of the rotary tools 1 and 8 is formed by an end portion 11 having a convex curved shape 11b, the rotary tools preferably satisfy the relationship represented by the following formula (4), where dv is the height (mm) of the convex curved surface (convex surface), and D is the diameter (mm) of the end of the rotating tool:

dv/D ≤ 0.06 … (4)

If the end portions come into contact with the steel strips satisfying the formula (4) (i.e., the dv/D value is 0.06 or less), pressure can be effectively applied to the fluid portion. As a result, sufficient plastic flow for welding can be created by rotating rotating tools. If the ratio dv/D goes beyond the limits of formula (4) (i.e. the value of dv/D exceeds 0.06), then the front and back surfaces of the welded area become noticeably recessed, and the thickness of the welded area becomes noticeably less than the thickness of each of steel strips. Thus, it may be difficult to secure the connection strength, which is undesirable. In order to efficiently apply pressure to the fluid portion, the lower limit of the dv/D value is preferably 0.01 or more.

Third Embodiment

As shown in FIG. 7(a) and FIG. 7(b), each of the rotary tools 1 and 8 according to the third embodiment has a round end formed by an end portion 11 having a concave curvilinear shape 11c, and the end of the rotary tool is concave. Although the rotary tool of the prior art includes a probe that protrudes towards the steel strips and is interrupted by a projecting part, each end part 11 having a concave curved shape has a continuous shape without a probe and forms an approximately uniform inclined surface. In other words, each end portion 11 having a concave curvilinear shape has an end surface that comes into contact with the steel strips and is formed by a single curved surface (parabolic surface, elongated surface, or spherical surface) recessed towards the center, and the end surface forms a curve having an approximately uniform radius of curvature in cross section, including the axis of rotation in the direction perpendicular to the steel strips. As shown in FIG. 7(b), the end portion 11 of each of the rotary tools 1 and 8 may have one or more helical (helicoidal) stepped portions 12 extending in the direction opposite to the direction of rotation, as described above. The stepped portions 12 have stepped portions 12b or grooves 12c as described above.

In the case that the end portion of the rotary tool is formed by the end portion 11 having a concave curved shape, the rotary tool preferably satisfies the relationship represented by the following formula (5), where dc denotes the depth (mm) of the concave curved surface (concave surface), and D is diameter (mm) of the end of the rotary tool:

dc/D ≤ 0.03 … (5)

If the end portions come into contact with the steel strips satisfying formula (5) (i.e., the dc/D value is 0.03 or less), then the concave curved surfaces of the end portions are surrounded by softened metal to apply uniform pressure to the fluid portion. As a result, sufficient plastic flow for welding can be created by rotating rotating tools. If the dc/D ratio exceeds the range of formula (5) (i.e., the dc/D value exceeds 0.03), it is difficult to apply uniform pressure to the fluid portion described above, and it may be difficult to obtain sufficient plastic flow for welding, which is not preferred. In order to uniformly apply pressure to the fluid portion, the lower limit of the dc/D value is preferably 0.01 or more.

The shapes of the base portions of the rotary tools 1 and 8, with the base portions opposed to the end portions of the rotary tools 1 and 8, are not specifically limited, as long as the base portions can be attached to a double-sided friction friction welding apparatus known in the art.

Next, a preferred example of the two-sided rotational friction welding method using rotary tools 1 and 8 in accordance with the present invention will be described.

In the method of double-sided rotational friction welding, more favorable effects of increasing the durability of rotating tools, suppressing the occurrence of defects in the joint, and increasing the welding speed can be obtained by optimizing the following various parameters.

In the present invention, the inclination angle α (°) at which the rotation axes of the two rotary tools 1 and 8 are inclined in the welding direction with respect to the normal to the surface of the non-welded portion of the steel strips, the diameter D (mm) of the end portions 11 of the rotary tools 1 and 8, and the distance G ( mm) between the end portions of the two rotary tools 1 and 8 is preferably adjusted to satisfy formula (1) and formula (2) below.

(1) Tilt angle α (°) of rotating tools: 0 ≤ α ≤ 3 … (1)

In FIG. 3(a) and 3(b) are diagrams illustrating the area subjected to friction by rotating tools in accordance with the present invention. In FIG. 3(a) is a diagram illustrating the movement of the rotary tools 1 and 8 located on the front and rear surfaces of the steel strips 4 as shown in FIG. 1 in the welding direction in a top view from the front surfaces of the steel strips 4. In FIG. 3(b) is a sectional view taken along line A-A' in FIG. 3(a).

As shown in FIG. 3(b), during welding, the rotation axes of the rotary tools 1 and 8 (the rotation axis 3 of the tool on the front side and the rotation axis 10 of the tool on the rear surface) are preferably tilted back in the welding direction at an angle α° relative to a vertical line (normal) 6 that runs in a direction perpendicular to the steel strips 4. In other words, the rotary instruments 1 and 8 are preferably inclined so that the proximal ends of the rotary instruments 1 and 8 are further forward than the distal ends of the rotary instruments 1 and 8 in the welding direction. As a result, the load otherwise applied to the rotating tools 1 and 8 in the horizontal direction (bending direction) during welding can be dispersed into force components causing compression in the axial directions.

The rotary tools 1 and 8 must be made of a material harder than the steel strips 4 and may be made of a low impact material, such as ceramic, for example. In this case, the application of force to the rotary tools 1 and 8 in the direction of bending can locally concentrate the stress and in turn lead to breakage of the rotary tools 1 and 8. To avoid this situation, the rotation axes 3 and 10 of the rotary tools 1 and 8 are tilted under a predetermined angle (α°) as described above, so that the load applied to the rotating tools 1 and 8 can be taken as force components causing compression in the axial direction to reduce the force in the bending direction. As a result, the durability of each of the rotary tools 1 and 8 can be further increased.

The above-mentioned beneficial effects are achieved at an inclination angle α of 0 degrees or more. If the inclination angle α exceeds 3°, the front and back surfaces of the welded area may become recessed, which may adversely affect the strength of the joint. The tilt angle of the rotation axis of each of the rotary tools 1 and 8 is preferably 0 ≤ α ≤ 3.

The tilt angle α is more preferably 1° or more, and more preferably 2° or less.

(2) Distance G (mm) between the ends of two rotary tools 1 and 8: 0.25 × t – 0.2 × D × sin α ≤ G ≤ 0.8 × t – 0.2 × D × sin α … (2)

where t is the thickness (mm) of the unwelded section of the steel strip 4, D is the diameter (mm) of the end portions of the rotary tools 1 and 8, and α is the angle of inclination (°) of the rotary tools 1 and 8. Here, t is the thickness (mm) of each steel strip for butt-welding steel strips or total thickness (mm) of overlapping steel strips for steel strip overlap welding.

In double-sided friction friction welding, it is important to control the distance G between the end portions of the opposing rotary tools 1 and 8 in order to uniformly ensure sufficient temperature rise and sufficient shear stress in the thickness direction during welding. In particular, the distance G between the end parts of the rotating tools 1 and 8 is preferably controlled (adjusted) within the formula (2) using the thickness t of the unwelded section of the steel strips 4, the diameter D of the end part of each of the rotating tools 1 and 8, and the inclination angle α of each from rotating tools 1 and 8.

For the butt welding shown in FIG. 1, the thickness t of the unwelded portion of the steel strips 4 refers to the thickness of one steel strip 4. For the overlap welding shown in FIG. 2, the thickness t of the unwelded portion of the steel strips 4 refers to the total thickness of the overlapping steel strips 4. The inclination angle α of each of the two rotary tools 1 and 8 may be the same. The end diameter D of each of the rotary tools 1 and 8 refers to the end diameter (pin diameter) of the end part 11 in cross section, including the corresponding axis of rotation in the direction perpendicular to the steel strips, where the end part 11 has a flat shape or a curved shape (concave or convex curvilinear shape) shown in FIG. 5(a)-7(b).

In the case where the rotary tools 1 and 8 are not inclined (i.e., the inclination angle α of each of the rotary tools 1 and 8 is 0°), the lower limit and the upper limit of the distance G between the end portions (reference numerals 2 and 9 in FIG. 3(b)) of the rotary tools 1 and 8 are set to 0.25 x t and 0.8 x t, respectively.

In the case that the rotary tools 1 and 8 are inclined (i.e., the inclination angle α of each of the rotary tools 1 and 8 is 0 < α ≤ 3), or in the case that the end diameter D of each of the rotary tools 1 and 8 is increased in order to increase the contact area between the end part of the rotating tool 1 and the front surfaces of the steel strips 4 and the contact area between the end part of the rotating tool 8 and the rear surfaces of the steel strips 4, the distance G between the rotating tools 1 and 8 must be reduced. In this case, as expressed by formula (2), the lower limit of G can be obtained by subtracting 0.2 × D × sin α from 0.25 × t, and the upper limit of G can be obtained by subtracting 0.2 × D × sin α out of 0.8 × t.

As described above, if the distance G between the end parts of the rotary tools 1 and 8 is adjusted within the formula (2), then opposite end parts of the rotary tools 1 and 8 are pressed against the front and rear surfaces of the steel strips 4 under sufficient load, and also in sufficiently stimulate heat generation and plastic flow in the welded area. As a result, plastic flow is uniformly promoted in the thickness direction, and a joint (welded portion) of good quality can be obtained. If the value of the distance G exceeds the upper limit in the formula (2), the end portions of the rotary tools 1 and 8 cannot press the front and rear surfaces of the steel strips 4 (blanks) with sufficient load, and the aforementioned beneficial effects may not be obtained. If the distance G value is lower than the lower limit in formula (2), the front and back surfaces of the welded area may become recessed, which may adversely affect the strength of the joint.

The value of the distance G is preferably (0.4×t-0.2×D×sinα) or more, and preferably (0.7×t-0.2×D×sinα) or less.

As shown in FIG. 3(b), the distance G corresponds to the shortest length in the vertical direction between the end surface of the rotary tool (front surface side side of the rotary tool) 1 and the end surface of the rotary tool (rear side side of the rotary tool) 8 that oppose each other.

Other welding conditions can be set in the usual way. For example, the rotation speed of each of the rotary tools 1 and 8 is preferably 100 to 5000 rpm and more preferably 500 to 3000 rpm in the double-sided friction rotation welding apparatus and the double-sided friction rotation welding method according to the present invention. At rotation speeds in these ranges, deterioration of mechanical properties due to excessive heat input can be suppressed while maintaining a favorable surface profile. The welding speed is preferably 1000 mm/min or higher, and more preferably increased to 2000 mm/min or higher.

For non-stop welding of steel strips, the welding method of the present invention can be preferably used for welding general structural steels and carbon steels such as JIS G 3106 welded structure rolled steels and carbon steels used in as a structural material of machines in JIS G 4051. The welding method according to the present invention can be successfully used for high strength structural steels having a tensile strength of 800 MPa or higher. Even in this case, the strength of the welded portion is 85% or more, preferably 90% or more, and more preferably 95% or more of the tensile strength of the steel sheet (base material).

The welded section of steel strips is subjected to bending or compression deformation during the production process. An Eriksen test is used to determine whether the welded area is correctly welded and is resistant to such deformation. In the Eriksen test, the area to be welded is clamped in a die, and a hemispherical punch is pressed into the area to be welded. The Erichsen test is used to measure the depth of indentation before cracks appear, and the indentation depth is used to evaluate the characteristics of the welded area.

In bilateral friction rotation welding of steel strips, a bilateral friction rotation welding apparatus is used, including two rotating tools 1 and 8 in accordance with the present invention, a holding device 13 (described in Fig. 14) and a control device (not shown) that controls the rotating tools as shown in Fig. 1 and other figures. The control device controls, for example, the inclination angle of each of the rotary tools 1 and 8, the distance between the end portions of the rotary tools, the welding speed, the rotation speed of the rotary tools so as to satisfy the welding conditions (1) and (2). In FIG. 14, the right side of the figure corresponds to the front side in the moving direction (the moving direction of the steel strip), and the left side of the figure corresponds to the rear side in the moving direction. The holding device 13 holds the front and rear surfaces of the previous steel strip 4a and the next steel strip 4b to fix both steel strips. Since the rotary tools 1 and 8 operate at a portion (butt portion) where the steel strips are opposite each other to move in the width direction of the steel strips (back to front direction in the figure), the steel strips are welded to each other.

According to the rotary tools 1 and 8 of the present invention, the durability of each of the rotary tools 1 and 8 can be increased as described above. If the end portions of the rotary tools have the above-mentioned shape, and the opposite rotary tools 1 and 8 rotate in opposite directions to each other, the steel strips are subjected to sufficient temperature rise and sufficient shear stress during welding. As a result, it is possible to prevent defects in the welded portion and increase the welding speed.

Next, methods and equipment for producing cold-rolled steel strip and coated steel strip according to the present invention will be described. The device for double-sided friction friction welding (double-sided friction welding method) according to the present invention described above can be used in a cold-rolled steel strip production plant (cold-rolled steel strip production method) and a coated steel strip production plant ( in the production method of coated steel strip).

In the prior art method for manufacturing cold rolled steel strip, the welded portion, the coiled coil, can fail on production lines. Recently, this has become a more significant task to be solved in the production of high-strength cold-rolled steel sheets. Applying the double-sided frictional friction welding technique of the present invention described above to producing cold-rolled steel strips and the like can prevent breakage and brittleness of the welded portions of the obtained cold-rolled steel strips or the like. and improve material properties by solving the prior art problem described above.

The plant for producing cold-rolled steel strip according to the present invention includes at least the double-sided friction welding apparatus described above and, if necessary, a pickling section, a cold rolling section, and an annealing section. The coated steel strip production plant according to the present invention also includes a coating section in addition to these sections.

The method for manufacturing a cold-rolled steel strip according to the present invention includes welding the rear end of the previous steel strip and the front end of the subsequent steel strip by double-sided friction welding described above, and then cold rolling the welded steel strip using a cold rolling machine (cold rolling process). ) for the production of cold rolled steel strips. If necessary, cold rolling may be preceded by pickling in the pickling section. The cold rolling may be followed, if necessary, by annealing the cold rolled steel strips (annealing process) using an annealing section.

In the method for manufacturing a coated steel strip according to the present invention, cold-rolled steel strips obtained after a cold rolling process and an annealing process are subjected to a coating process using a coating section to obtain coated steel strips.

The use of the double-sided friction rotation welding apparatus (and the double-sided friction rotation welding method) according to the present invention in the production of cold-rolled steel strip and coated steel strip can reduce the number of defects in the welded portion of the obtained cold-rolled steel strip and the coated steel strip produced, and can provide sufficient connection strength.

Examples

Operations and effects of the present invention will be described below using examples. The present invention is not limited to the following examples.

Bilateral rotational friction welding was performed using steel sheets having the thickness, chemical composition, tensile strength, and Vickers hardness shown in Table 1. In the examples, some steel sheets were lap welded and the remaining steel sheets were butt welded.

For butt welding, two steel sheets of the same type were placed next to each other to form joinable butt surfaces having no edge angle, i.e. without beveled edges, and having a surface similar to a milled surface. The rotating tools were pressed against the joint portion from both the first surface (front surface) and the second surface (rear surface) and moved in the welding direction, whereby the steel sheets were welded to each other.

For overlap welding, two steel sheets of the same type were positioned so that they overlapped each other, and rotating tools were pressed against the overlapping section of the steel sheets, both from the first surface (front surface) and from the second surface (rear surface), as a result of which the steel sheets were welded together. The welding length for one process was 0.5 m.

In both butt welding and overlap welding, two rotating tools were rotated in opposite directions relative to each other during welding. In other words, rotating tools rotate in the same direction when viewed from the front of the tools. Friction welding conditions are described in Table 2-1 and Table 2-2. Eight types of rotary tools were used in welding, with the cross-sectional dimensions and shapes shown in FIG. 4(a)–7(b). The "shape" column in Table 2-1 and Table 2-2 represents one of FIGS. 4(a)-7(b). These rotary tools were made from tungsten carbide (WC) having a Vickers hardness of 1090. In the examples of the invention, rotary tools were used that did not have a probe or helical stepped portion as shown in FIG. 5(a), FIG. 6(a) and FIG. 7(a). Since the spirals run clockwise in probeless rotary instruments having helical stepped portions as shown in FIG. 5(b), FIG. 6(b) and FIG. 7(b), in the examples of the invention, the rotation of the rotary tools was counterclockwise, and in the comparative examples, the rotation of the rotary tools was performed clockwise. The rotary tools corresponding to "staggered" in the "staggered section status" column in Table 2-1 and Table 2-2 are shown in FIG. 8(b) and rotary tools corresponding to "groove" are shown in FIG. 8(c). In the comparative examples, rotary probe instruments were used as shown in FIG. 4(a) and FIG. 4(b).

Table 1

Number Thickness
(mm) Chemical composition (wt.%) Tensile strength (MPa) Vickers hardness C Si Mn P S 1 1.6 0.3 0.21 0.69 0.012 0.003 1010 337 2 2.4 0.16 0.07 0.69 0.016 0.009 425 142 3 1.2 0.3 0.21 0.69 0.012 0.003 1012 339

The following evaluation was carried out using the obtained welded joint.

(I) Presence or absence of surface defects when examining the appearance of the joint

Inspection was carried out using sections of the obtained welded joints, which were welded at the welding speeds indicated in table 2-1 and table 2-2. The presence or absence of surface defects was determined visually by whether a groove-like region was observed in the unwelded state due to insufficient plastic flow, or whether a welded region was observed in a recess due to a too small distance G between the protruding regions of the welding tools. If a groove-like portion in an unwelded state or a welded portion formed by a recess was observed as a surface defect, the depth Dd (mm) of the surface defect was measured with a laser displacement meter and judged based on the following criteria.

Criteria

No: None of the surface defects described above were observed.

Acceptable: One of the above-described surface defects was observed, but the ratio (Dd/t) of the depth Dd (mm) to the thickness t (mm) of the steel sheets was 0.1 or less.

Yes: One of the above-described surface defects was observed, and the ratio (Dd/t) of the depth Dd (mm) to the thickness t (mm) of the steel sheets exceeded 0.1. Alternatively, the unwelded groove-like portion extends from the front surface to the rear surface. If the groove-like portion in the unwelded state extended from the front surface to the back surface, then the welding was considered unsuccessful, and internal defects and joint strength were not evaluated.

(II) Presence or absence of internal defects when examining cross-sections of joints

Inspection was carried out using sections of the obtained welded joints, which were welded at the welding speeds indicated in table 2-1 and table 2-2. Cross-sections were prepared by cutting sections at a position of 20 mm from the start of the weld, at a position of 20 mm from the end of the weld, and at an intermediate position between the ends to prepare specimens for testing. The presence or absence of internal defects was determined using an optical microscope (magnification: 10 times) by whether an unwelded state formed in the welded portion due to insufficient plastic flow was observed and judged based on the following criteria.

Criteria

No: An unwelded condition formed in the form of a tunnel was not observed in any of the three positions mentioned above.

Acceptable: An unwelded condition formed in the welded area was observed in one of the three positions mentioned above.

Yes: An unwelded condition formed in the welded area was observed in two or more of the three positions mentioned above.

Table 3 shows the results of determining (I) the presence or absence of surface defects by examining the appearance of the joint during a single welding with a welding length of 0.5 m and the results of determining (II) the presence or absence of internal defects by examining the cross sections of the joint. Table 3 also shows the tensile strength and indentation depth. The tensile strength was measured in a tensile test (JIS Z 3121) using tensile test specimens each taken from the obtained welded joints and having the dimensions of test specimen No. 1 specified in JIS Z 3121. The plastic deformation indentation depth was up to crack formation in the welded part was measured using an Eriksen instrument.

Table 3 shows that butt joints in Invention Examples 1-24 and lap joints in Invention Examples 25-27 were obtained with a defect-free weld condition even at high welding speeds of 1.0 m/min or higher, while inspecting appearance of the joint or examination of the cross-sections of each joint, no surface or internal defects were found. The joint strength was 95% or more of the tensile strength of the steel sheets serving as the base material, and the indentation depth before cracking in the welded portion was 5 mm or more according to the Erichsen test.

In the butt joints in Comparative Examples 1 to 3, welding was performed using rotating tools each without a probe and having helical stepped portions extending in a clockwise direction, while the direction of rotation of each of the rotating tools was set to clockwise. . In the obtained joints, surface defects and internal defects were observed; a defect-free welded state was not obtained. The strength of the joint was 70% or less of the tensile strength of the steel sheets serving as the base material, and the indentation depth before cracking in the welded part was 4 mm or less according to the Erichsen test.

In the lap joints in Comparative Example 4, welding was performed using rotating tools each without a probe and having helical stepped portions extending in a clockwise direction, while the direction of rotation of each of the rotating tools was set to clockwise. In the resulting joint, surface defects and internal defects were observed; a defect-free welded state was not obtained. The strength of the joint was 70% or less of the tensile strength of the steel sheets serving as the base material, and the indentation depth before cracking in the welded part was 4 mm or less according to the Erichsen test.

The butt joints in Comparative Examples 5 to 9 used rotary tools each having a pin, where D (diameter (mm) of the end portion of each rotary tool), (inclination angle (°) of each rotary tool) and G (distance (mm) ) between the end parts of two rotating tools) satisfy formulas (1), (2) and (3).

In the butt joints of Comparative Examples 5 to 9, a defect-free welding state was obtained even at high welding speeds of 1.0 m/min or higher, and no surface or internal defects. The bond strength and the Eriksen test were confirmed to be positive. However, it has also been confirmed that rotary tools exhibited poor durability.

In the lap joints in Comparative Example 10, a defect-free welding state was obtained even at high welding speeds of 1.0 m/min or higher, and no surface or internal defects were found by examining the appearance of the joint or by examining the cross sections of the joint. The bond strength and the Eriksen test were confirmed to be positive. However, it has also been confirmed that rotary tools exhibited poor durability.

Table 3

The presence of surface defects when examining the appearance of the connection The presence of internal defects when examining the cross sections of the connection Tensile strength (MPa) Eriksen test: indentation depth before a crack appears in the welded area (mm) Invention example 1 No No 1009 8.3 Invention Example 2 No No 1012 8.4 Invention Example 3 No No 1007 8.2 Invention Example 4 No No 1005 8.2 Invention Example 5 No No 1006 8.3 Invention Example 6 No No 1001 8.1 Invention Example 7 No No 430 8.8 Invention example 8 No No 433 9.0 Invention Example 9 No No 432 9.0 Invention example 10 No No 1005 8.1 Invention Example 11 No No 1002 8.2 Invention Example 12 No No 1000 8.0 Invention Example 13 No No 1012 8.3 Invention Example 14 No No 1015 8.3 Invention Example 15 No No 1007 8.1 Invention Example 16 No No 430 8.8 Invention example 17 No No 433 8.9 Invention example 18 No No 432 8.8 Invention example 19 No Acceptable 990 7.8 Invention example 20 Acceptable Acceptable 999 7.8 Invention example 21 Acceptable No 995 7.9 Invention example 22 No Acceptable 980 7.5 Invention example 23 Acceptable Acceptable 987 7.7 Invention example 24 Acceptable No 983 7.6 Invention example 25 No No 1011 5.5 Invention example 26 No No 1006 5.2 Invention example 27 Acceptable No 1002 5.2 Comparative Example 1 Yes (unwelded area) Yes 587 3.3 Comparative Example 2 Yes (unwelded area) Yes 274 2.5 Comparative Example 3 Yes (unwelded area) Yes 487 2.8 Comparative Example 4 Yes (unwelded area) Yes 657 2.1 Comparative Example 5 No No 1001 7.9 Comparative Example 6 No No 1003 8.0 Comparative Example 7 No No 997 7.8 Comparative Example 8 No No 424 8.7 Comparative Example 9 No No 422 8.7 Comparative Example 10 No No 995 4.2

Table 4 shows the number of repeated welding operations with a welding length of 0.5 m from the total number of welding operations, in which a defect-free joint was obtained with a probability of 90% or more, while an internal defect was not detected when examining the cross sections of the joint. As shown in Table 4, in the butt joints of Invention Examples 1 to 24 and the lap joints of Invention Examples 25 to 27, the number of welding operations in which a defect-free joint was obtained with a probability of 90% or more was 13 or more.

In the butt joints in Comparative Examples 1 to 3, welding was performed using rotating tools each without a probe and having helical stepped portions extending in a clockwise direction, while the direction of rotation of each of the rotating tools was set to clockwise. . In Comparative Examples 1-3, the number of welding operations in which a defect-free joint was obtained with a probability of 90% or more was 0.

In the lap joints in Comparative Example 4, welding was performed using rotating tools each without a probe and having groove-like stepped portions extending in a clockwise direction, while the direction of rotation of each of the rotating tools was set to clockwise. In Comparative Example 4, the number of welding operations in which a defect-free joint was obtained with a probability of 90% or more was 0.

In the butt joints in Comparative Examples 5-9, welding was performed using rotating tools each having a pin. The number of welding operations in which a defect-free joint was obtained with a probability of 90% or more was 10 or less.

In the lap joints in Comparative Example 10, welding was performed using rotating tools each having a pin. The number of welding operations in which a defect-free joint was obtained with a probability of 90% or more was 10 or less.

As described above, the use of rotating tools each without a probe and having helical stepped portions results in joint defects or welding strength problems if the helical stepped portion spirals run in the same direction as the direction of rotation of the rotating tools. . It turned out that rotating tools, each of which has a pin, showed low wear resistance.

Table 3 shows that the results of experiments under the same conditions, the use of rotating tools, each of which has helical stepped sections, increases the strength of welds, except for the presence or absence of helical stepped sections, which are pairs of examples of the invention, that is Invention Examples 1 and 4, Invention Examples 2 and 5, Invention Examples 3 and 6, Invention Examples 19 and 22, Invention Examples 20 and 23, and Invention Examples 21 and 24.

The results of Inventive Examples 19 and 22, in which experiments were carried out under conditions not satisfying formula (5) below, show that conditions above the range of formula (5) can affect the provision of plastic flow sufficient for welding and can lead to internal defects, although no surface defects were found. In other words, if the rotating tools each having a concave surface further satisfy the condition of formula (5), then the occurrence of surface defects and internal defects can be more effectively suppressed to provide a joint having sufficient strength.

dc/D ≤ 0.03 … (5)

The results of Inventive Examples 20 and 23, in which the experiments were carried out under conditions below the lower range of formula (3), show that conditions below the lower range of formula (3) can affect the provision of uniform plastic flow in the thickness direction and can lead to surface or internal defects, although surface defects and internal defects are rated as "acceptable". In other words, if the rotating tools each having a flat surface further satisfy the condition of formula (3), then the occurrence of surface defects and internal defects can be more effectively suppressed to provide a joint having sufficient strength.

4 × t ≤ D ≤ 20 × t … (3)

The results of Inventive Examples 21 and 24, in which experiments were carried out under conditions not satisfying formula (4), show that conditions above the range of formula (4) can affect the surface shape of the welded portion and can lead to surface defects, although surface defects and internal defects are rated as "acceptable". In other words, if the rotating tools each having a convex surface further satisfy the condition of formula (4), then the occurrence of surface defects and internal defects can be more effectively suppressed to provide a joint having sufficient strength.

dv/D ≤ 0.06 … (4)

Table 4

The number of welding operations in which a defect-free joint was obtained with a probability of 90% or more Invention example 1 16 Invention example 2 18 Invention Example 3 21 Invention Example 4 15 Invention Example 5 15 Invention Example 6 19 Invention Example 7 13 Invention example 8 14 Invention Example 9 17 Invention example 10 16 Invention example 11 15 Invention example 12 20 Invention example 13 18 Invention Example 14 21 Invention Example 15 24 Invention Example 16 15 Invention example 17 16 Invention example 18 17 Invention example 19 16 Invention example 20 15 Invention example 21 23 Invention example 22 14 Invention example 23 14 Invention example 24 18 Invention example 25 15 Invention example 26 16 Invention example 27 15 Comparative Example 1 0 Comparative Example 2 0 Comparative Example 3 0 Comparative Example 4 0 Comparative Example 5 10 Comparative Example 6 8 Comparative Example 7 10 Comparative Example 8 7 Comparative Example 9 9 Comparative Example 10 8

List of reference positions

1 rotary tool on the rake side

2 end of the rotating tool from the front surface

3 axis of rotation of the rotary tool from the side of the front surface

4 steel strip

4a preceding steel strip

4b next steel strip

5 welded area

6 vertical line in the direction perpendicular to the steel strip

7 central connection line

8 rotary tool back side

9 end of the rotating tool from the rear surface

10 axis of rotation of the rotating tool from the rear surface

11 end part

12 step section

12b stepped section

12c grooved section

13 holding device

G distance between end parts of rotating tools

α tilt angle of the rotating tool

D diameter of the end of the rotating tool

t steel strip thickness

Claims (39)

1. The method of bilateral rotational friction welding, including: butt or overlap welding between the rear end of the preceding steel strip and the front end of the subsequent steel strip pressing two rotary tools located on the first surface and the second surface of the butt section or overlapping section of the steel strips against the butt section or overlapping section of the steel strips, and moving the rotary tools in the direction of welding while rotating the rotary tools in directions opposite to each other, so that unwelded the section of the steel strips is softened by the heat of friction generated between the rotating tools and the unwelded section of the steel strips, and the softened section is agitated by the rotating tools to obtain plastic flow so as to weld the steel strips to each other, while: each of the two rotating tools has an end part in the form of a round convex curved surface or a round concave curved surface, and said end pieces are made of a harder material than steel strips, moreover, if the height of the convex curved surface of each end part is denoted by dv (mm), then the diameter D (mm) of each end part and the height dv of the convex curved surface satisfy the formula (4): dv/D ≤ 0.06, (4) moreover, if the depth of the concave curved surface of each end part is denoted by dc (mm), then the diameter D (mm) of each end part and the depth dc of the concave curved surface satisfy the formula (5): dc/D ≤ 0.03. (5) 2. The method of claim 1, wherein each said end portion has a helical stepped portion extending in a direction opposite to the direction of rotation. 3. The method according to claim 1 or 2, in which the angle of inclination α (°), at which the axes of rotation of the two rotating tools are tilted back in the direction of welding relative to the normal to the surface of the non-welded section of the steel strips, the diameter D (mm) of each end part and the distance G (mm) between the end portions of two rotating tools satisfy formula (1) and formula (2) below: 0 ≤ α ≤ 3, (1) 0.25 × t – 0.2 × D × sin α ≤ G ≤ 0.8 × t – 0.2 × D × sin α, (2) where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap. 4. The method according to claim 1 or 2, wherein the diameter D (mm) of each end portion satisfies the formula (3): 4 × t ≤ D ≤ 20 × t, (3) where t is the thickness (mm) of each steel strip for butt welding of steel strips or the total thickness (mm) of overlapping steel strips for welding steel strips with an overlap. 5. A method for producing a cold-rolled steel strip, including: after welding the rear end of the previous steel strip and the front end of the next steel strip using the method of bilateral rotational friction welding according to any one of paragraphs. 1-4 perform cold rolling or perform cold rolling after pickling. 6. The method according to claim 5, wherein the annealing is carried out after cold rolling. 7. Method for the production of coated steel strip, including: after welding the rear end of the previous steel strip and the front end of the next steel strip using the method of bilateral rotational friction welding according to any one of paragraphs. 1-4 cold rolling is performed or cold rolling is performed after pickling, and then annealing and coating are performed. 8. A device for bilateral rotational friction welding, containing two rotating tools located opposite each other on the unwelded section of two steel strips, and a control device that controls the operation of two rotating tools, while: said two-sided rotational friction welding apparatus welds steel strips to each other when two rotating tools move in the direction of welding against the unwelded portion of the butted or overlapping steel strips and rotate in opposite directions relative to each other; each of the two rotating tools has an end part having the shape of a round convex curved surface or a round concave curved surface; and said end parts are made of a harder material than steel strips, while if the height of the convex curved surface of each end part is denoted as dv (mm), then the diameter D (mm) of each end part and the height dv of the convex curved surface satisfy the formula (4): dv/D ≤ 0.06, (4) while if the depth of the concave curved surface of each end part is denoted as dc (mm), then the diameter D (mm) of each end part and the depth dc of the concave curved surface satisfy the formula (5): dc/D ≤ 0.03. (5) 9. The apparatus of claim 8, wherein each said end portion has a helical stepped portion extending in a direction opposite to the direction of rotation. 10. Apparatus according to claim 8 or 9, wherein the control device controls such that the angle of inclination α (°), at which the axes of rotation of the two rotating tools are tilted back in the direction of welding relative to the normal to the surface of the unwelded section of the steel strips, diameter D (mm) of each end portion and the distance G (mm) between the end portions of two rotary tools satisfied the formula (1) and formula (2) below: 0 ≤ α ≤ 3, (1) 0.25 × t – 0.2 × D × sin α ≤ G ≤ 0.8 × t – 0.2 × D × sin α, (2) where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap. 11. The device according to claim 8 or 9, in which the diameter D (mm) of each specified end part satisfies the formula (3): 4 × t ≤ D ≤ 20 × t, (3) where t is the thickness (mm) of each steel strip for butt welding steel strips, or the total thickness (mm) of overlapping steel strips for welding steel strips overlap. 12. Installation for the production of cold-rolled steel strip, containing in addition to the device for bilateral rotational friction welding according to item 8 or 9, a cold rolling section, which performs cold rolling of the welded steel strips or a cold rolling section, which performs cold rolling of the welded steel strips after etching in the etching section. 13. Plant according to claim 12, also comprising an annealing section configured to anneal the cold rolled steel strips. 14. Installation for the production of coated steel strip, containing in addition to the device for bilateral rotational friction welding according to claim 8 or 9, a cold rolling section that cold rolls the welded steel strips or a cold rolling section that cold rolls the welded steel strips after pickling in the pickling section, an annealing section configured to anneal the cold-rolled steel strips, and a coating section configured to coat the annealed steel strips.

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