Electromagnetic stirring device and continuous casting machine

Abstract

The invention provides an electromagnetic stirring device and a continuous casting machine. The electromagnetic stirring device comprises a first magnetizer, a fourth magnetizer, a second magnetizer and a third magnetizer; second electromagnetic stirring rollers with disconnected middle magnetic circuits are respectively arranged between the first magnetizer and the fourth magnetizer and between the second magnetizer and the third magnetizer; the second electromagnetic stirring roller is positioned on the edge of the first gap; and first electromagnetic stirring rollers of which the middle magnetic circuits are communicated are respectively arranged between the first magnetizer and the second magnetizer and between the third magnetizer and the fourth magnetizer. The four magnetizers and the two electromagnetic stirring rollers are optimized, a double-wing rotating magnetic field can be formed in the casting blank, the quality defects such as looseness, center shrinkage cavities, element segregation and cracks can be effectively reduced, and the quality of H-shaped blank products is improved.

Description

Technical Field

[0001] The invention relates to the technical field of H-beam continuous casting, and in particular to an electromagnetic stirring device and a continuous casting machine. Background Art

[0002] The technology of special-shaped continuous casting machine is an important technology in the development of modern steel industry. H-shaped continuous casting technology is a relatively typical special-shaped billet continuous casting technology. The current special-shaped billet mostly refers to H-shaped continuous casting billet. Since the shape of H-shaped billet is close to the final product, the production of H-shaped steel not only avoids the problem of unstable welding process quality, but also greatly reduces the rolling process, thereby greatly shortening the production process, reducing energy consumption, and fundamentally reducing production costs. The cross-sectional shape of H-shaped billet is relatively complex, so the equipment and process operation of the continuous casting process also have their corresponding particularities.

[0003] The existing H-beam continuous casting machine sector structure is as follows Figure 1 As shown, it includes flange support roller A, flange support roller B, web support roller C and web support roller D, and E is a schematic diagram of an H-shaped billet. During the production process, there is uneven temperature distribution inside the continuous casting billet, which often leads to major quality defects such as looseness, central shrinkage, element segregation, and cracks.

[0004] With the diversification and modernization of engineering construction design, the demand for large-scale steel sections will increase significantly, and H-beam continuous casting technology will increasingly demonstrate its important position in steel production. Therefore, it is of great significance to carry out in-depth research on H-beam casting quality control and process parameter optimization. Summary of the invention

[0005] In view of the shortcomings of the existing H-beam continuous casting machine, the purpose of the present invention is to provide an electromagnetic stirring device and a continuous casting machine to overcome the quality defects of the existing H-beam continuous casting technology.

[0006] The technical solution of the present invention is: an electromagnetic stirring device, comprising a first magnetic conductor and a fourth magnetic conductor spaced apart in the X direction, a second magnetic conductor and a third magnetic conductor spaced apart in the X direction, the first magnetic conductor and the second magnetic conductor spaced apart in the Y direction to form a first gap, the fourth magnetic conductor and the third magnetic conductor spaced apart in the Y direction to form a first gap; a second electromagnetic stirring roller with a disconnected intermediate magnetic circuit is respectively installed between the first magnetic conductor and the fourth magnetic conductor and between the second magnetic conductor and the third magnetic conductor; the second electromagnetic stirring roller is located at the edge of the first gap; A first electromagnetic stirring roller connected with an intermediate magnetic circuit is installed between the first magnetic conductor and the second magnetic conductor, and between the third magnetic conductor and the fourth magnetic conductor respectively; a second gap extending in the Y direction is provided inside the first magnetic conductor and the second magnetic conductor, and a second gap extending in the Y direction is provided inside the fourth magnetic conductor and the third magnetic conductor; the first gap and the second gap are connected; the first electromagnetic stirring roller is located at the edge of the second gap away from the first gap; The X direction and the Y direction are perpendicular to each other on the same top projection plane.

[0007] Preferably, the first magnetic conductor and the fourth magnetic conductor are symmetrically arranged in the X direction, the first magnetic conductor and the second magnetic conductor are symmetrically arranged in the Y direction, the second magnetic conductor and the third magnetic conductor are symmetrically arranged in the X direction, and the third magnetic conductor and the fourth magnetic conductor are symmetrically arranged in the Y direction.

[0008] Preferably, a non-magnetic mounting frame is connected between the first magnetic conductor and the fourth magnetic conductor, between the first magnetic conductor and the second magnetic conductor, between the second magnetic conductor and the third magnetic conductor, and between the third magnetic conductor and the fourth magnetic conductor.

[0009] Preferably, the first magnetic conductor comprises a first wall, a second wall, a third wall and a fourth wall which are bent in sequence, the first wall and the third wall are parallel to the same side of the second wall, the second wall and the fourth wall are parallel to the same side of the third wall, and a second gap is provided between the first wall and the fourth wall; the second magnetic conductor, the third magnetic conductor and the fourth magnetic conductor have the same structure as the first magnetic conductor; and a first gap is provided between the fourth walls in the same Y direction; The first electromagnetic stirring roller is connected to the first wall, and the second electromagnetic stirring roller is connected to the fourth wall.

[0010] Preferably, the length of the fourth wall is longer than that of the second wall.

[0011] Preferably, the electromagnetic stirring device further comprises a second electromagnetic roller, a third electromagnetic roller, a sixth electromagnetic roller, a seventh electromagnetic roller and a second connecting portion; One end of the second electromagnetic roller is mounted on the first magnetic conductor, one end of the third electromagnetic roller is mounted on the second magnetic conductor, and the second connecting portion is installed between the other end of the second electromagnetic roller and the other end of the third electromagnetic roller; the second electromagnetic roller, the second electromagnetic roller and the second connecting portion form one of the first electromagnetic stirring rollers; One end of the sixth electromagnetic roller is mounted on the third magnetic conductor, one end of the seventh electromagnetic roller is mounted on the fourth magnetic conductor, and the second connecting portion is installed between the other end of the sixth electromagnetic roller and the other end of the seventh electromagnetic roller; the sixth electromagnetic roller, the seventh electromagnetic roller and the second connecting portion form another of the first electromagnetic stirring roller.

[0012] Preferably, it further comprises a first electromagnetic roller, a fourth electromagnetic roller, a fifth electromagnetic roller, an eighth electromagnetic roller and a first connecting portion; One end of the first electromagnetic roller is mounted on the first magnetic conductor, one end of the eighth electromagnetic roller is mounted on the fourth magnetic conductor, and the first connecting portion is installed between the other end of the first electromagnetic roller and the other end of the eighth electromagnetic roller; the first electromagnetic roller, the eighth electromagnetic roller and the first connecting portion form one of the second electromagnetic stirring rollers; One end of the fourth electromagnetic roller is mounted on the second magnetic conductor, one end of the fifth electromagnetic roller is mounted on the third magnetic conductor, and the first connecting part is installed between the other end of the fourth electromagnetic roller and the other end of the fifth electromagnetic roller; the fourth electromagnetic roller, the fifth electromagnetic roller and the first connecting part form another second electromagnetic stirring roller.

[0013] The present invention also provides a continuous casting machine comprising the electromagnetic stirring device.

[0014] Compared with the related art, the present invention has the following beneficial effects: 1. The invention is optimized with four magnetic conductors and two electromagnetic stirring rollers, which can form a double-wing rotating magnetic field inside the ingot (at the intersection of the first gap and the second gap), which can effectively reduce quality defects such as looseness, central shrinkage, element segregation, cracks, etc., and improve the quality of H-beam products; Second, the electromagnetic stirring device can divide the first electromagnetic stirring roller and the second electromagnetic stirring roller into two groups, forming two rotating magnetic fields to act on the unsolidified part of the core of the flange casting, which conforms to the characteristics of the fan-shaped section of the H-beam continuous casting machine; 3. A second connecting part is installed in the middle of the first electromagnetic stirring roller, and a first connecting part is installed in the middle of the second electromagnetic stirring roller. When the magnetic field strength is large enough, connecting parts of different lengths can be replaced according to the distance between the two magnetic conductors to meet the H-beam continuous casting machine to produce different casting specifications, thereby improving the utilization rate of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of the fan-shaped segment of the existing H-beam continuous casting machine; Figure 2 A schematic diagram of the structure of the electromagnetic stirring device provided by the present invention; Figure 3 Schematic diagram of electromagnetic stirring flow field.

[0016] In the accompanying drawings: 11, first magnet; 111, first wall; 112, second wall; 113, third wall; 114, fourth wall; 12, second magnet; 13, third magnet; 14, fourth magnet; 2, first electromagnetic stirring roller; 3, second electromagnetic stirring roller; 4, mounting frame; 5, first gap; 6, second gap; 21, first electromagnetic roller; 22, second electromagnetic roller; 23, third electromagnetic roller; 24, fourth electromagnetic roller; 25, fifth electromagnetic roller; 26, sixth electromagnetic roller; 27, seventh electromagnetic roller; 28, eighth electromagnetic roller; 31, first connecting portion; 32, second connecting portion. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. For the convenience of description, if the words "upper", "lower", "left" and "right" appear in the following, they only indicate that the upper, lower, left and right directions are consistent with the drawings themselves, and do not limit the structure.

[0018] like Figure 2 As shown, an electromagnetic stirring device provided in this embodiment includes a first magnet 11 and a fourth magnet 14 spaced apart in the X direction, and a second magnet 12 and a third magnet 13 spaced apart in the X direction. The first magnet 11 and the second magnet 12 are spaced apart in the Y direction. The fourth magnet 14 and the third magnet 13 are spaced apart in the Y direction. The X direction and the Y direction are perpendicular to each other on the same top projection plane. The first magnet 11, the second magnet 12, the third magnet 13 and the fourth magnet 14 are made of the same carbon steel material as the original flange support roller A, the flange support roller B, the web support roller C and the web support roller D. The four magnets form a closed effective magnetic path (such as Figure 3 As shown), the space is symmetrical and the attenuation is small, which prevents leakage magnetic field.

[0019] The first magnetizer 11 includes a first wall 111, a second wall 112, a third wall 113 and a fourth wall 114 which are bent in sequence. The first wall 111 and the third wall 113 are parallel to the same side of the second wall 112, and the second wall 112 and the fourth wall 114 are parallel to the same side of the third wall 113. The length of the fourth wall 114 is longer than the length of the second wall 112. The second magnetizer 12, the third magnetizer 13 and the fourth magnetizer 14 have the same structure as the first magnetizer 11. A second gap 6 is formed between the first wall 111 and the fourth wall 114. One end of the first gap 5 is formed between the fourth wall 114 of the first magnetizer 11 and the fourth wall 114 of the second magnetizer 12. The other end of the first gap 5 is formed between the fourth wall 114 of the third magnetizer 13 and the fourth wall 114 of the fourth magnetizer 14. A second electromagnetic stirring roller 3 with a disconnected intermediate magnetic circuit is installed between the fourth wall 114 of the first magnetizer 11 and the fourth wall 114 of the fourth magnetizer 14. A second electromagnetic stirring roller 3 with a disconnected intermediate magnetic circuit is installed between the fourth wall 114 of the second magnetizer 12 and the fourth wall 114 of the third magnetizer 13, and the middle part of the first gap 5 is formed between the two second electromagnetic stirring rollers 3.

[0020] The first electromagnetic stirring roller 2 connected with the intermediate magnetic circuit is respectively installed between the first wall 111 of the first magnet 11 and the first wall 111 of the second magnet 12, and between the first wall 111 of the third magnet 13 and the first wall 111 of the fourth magnet 14. The first magnet 11 and the second magnet 12 are provided with a second gap 6 extending in the Y direction, and the fourth magnet 14 and the third magnet 13 are provided with a second gap 6 extending in the Y direction. The first electromagnetic stirring roller 2 is located at the edge of the second gap 6 away from the first gap 5.

[0021] The first magnetizer 11 and the fourth magnetizer 14 are symmetrically arranged in the X direction, the first magnetizer 11 and the second magnetizer 12 are symmetrically arranged in the Y direction, the second magnetizer 12 and the third magnetizer 13 are symmetrically arranged in the X direction, and the third magnetizer 13 and the fourth magnetizer 14 are symmetrically arranged in the Y direction.

[0022] A non-magnetic mounting frame 4 is connected between the first magnetizer 11 and the fourth magnetizer 14, between the first magnetizer 11 and the second magnetizer 12, between the second magnetizer 12 and the third magnetizer 13, and between the third magnetizer 13 and the fourth magnetizer 14. The mounting frame 4 is made of stainless steel, and the original carbon steel frame support structure of the continuous casting machine sector needs to be changed to non-magnetic stainless steel.

[0023] The electromagnetic stirring device further includes a second electromagnetic roller 22 , a third electromagnetic roller 23 , a sixth electromagnetic roller 26 , a seventh electromagnetic roller 27 , a second connecting portion 32 , a first electromagnetic roller 21 , a fourth electromagnetic roller 24 , a fifth electromagnetic roller 25 , an eighth electromagnetic roller 28 and a first connecting portion 31 .

[0024] One end of the second electromagnetic roller 22 is mounted on the first wall 111 of the first magnet 11, one end of the third electromagnetic roller 23 is mounted on the first wall 111 of the second magnet 12, and the second connecting portion 32 is installed between the other end of the second electromagnetic roller 22 and the other end of the third electromagnetic roller 23. The second electromagnetic roller 22, the second electromagnetic roller 22 and the second connecting portion 32 form one of the first electromagnetic stirring rollers 2.

[0025] One end of the sixth electromagnetic roller 26 is mounted on the first wall 111 of the third magnet 13, one end of the seventh electromagnetic roller 27 is mounted on the first wall 111 of the fourth magnet 14, and the second connecting portion 32 is installed between the other end of the sixth electromagnetic roller 26 and the other end of the seventh electromagnetic roller 27. The sixth electromagnetic roller 26, the seventh electromagnetic roller 27 and the second connecting portion 32 form another first electromagnetic stirring roller 2.

[0026] One end of the first electromagnetic roller 21 is mounted on the fourth wall 114 of the first magnet 11, one end of the eighth electromagnetic roller 28 is mounted on the fourth wall 114 of the fourth magnet 14, and the first connecting portion 31 is installed between the other end of the first electromagnetic roller 21 and the other end of the eighth electromagnetic roller 28. The first electromagnetic roller 21, the eighth electromagnetic roller 28 and the first connecting portion 31 form one of the second electromagnetic stirring rollers 3.

[0027] One end of the fourth electromagnetic roller 24 is mounted on the fourth wall 114 of the second magnetizer 12, one end of the fifth electromagnetic roller 25 is mounted on the fourth wall 114 of the third magnetizer 13, and the first connecting portion 31 is installed between the other end of the fourth electromagnetic roller 24 and the other end of the fifth electromagnetic roller 25. The fourth electromagnetic roller 24, the fifth electromagnetic roller 25 and the first connecting portion 31 form another second electromagnetic stirring roller 3.

[0028] The second connection part 32 is a silicon steel sheet, which can connect the second electromagnetic roller 22 and the third electromagnetic roller 23, and the sixth electromagnetic roller 26 and the seventh electromagnetic roller 27. The first connection part 31 is a non-magnetic stainless steel, and it is necessary to disconnect the magnetic circuit between the first electromagnetic roller 21 and the eighth electromagnetic roller 28, and between the fourth electromagnetic roller 24 and the fifth electromagnetic roller 25. This disconnection and connection mode of the first connection part 31 and the second connection part 32 effectively reduces eddy current loss and hysteresis loss, and can maximize the magnetic field strength.

[0029] After the first electromagnetic stirring roller 2 and the second electromagnetic stirring roller 3 are powered by alternating current, the first electromagnetic roller 21, the second electromagnetic roller 22, the third electromagnetic roller 23, and the fourth electromagnetic roller 24 form a group. The fifth electromagnetic roller 25, the sixth electromagnetic roller 26, the seventh electromagnetic roller 27, and the eighth electromagnetic roller 28 form another group. The two groups simultaneously excite the rotating magnetic field to generate electromagnetic force, which directly acts on the liquid core of the wing to form a double-wing rotating magnetic field (such as Figure 3 as shown).

[0030] The characteristic of the magnetic field is that it will automatically select the shortest path with the smallest magnetic resistance in space to form a circuit. In order to make the first electromagnetic roller 21, the second electromagnetic roller 22, the third electromagnetic roller 23, and the fourth electromagnetic roller 24 form a closed effective magnetic path through the first magnetic conductor 11 and the second magnetic conductor 12, and at the same time make the fifth electromagnetic roller 25, the sixth electromagnetic roller 26, the seventh electromagnetic roller 27 and the eighth electromagnetic roller 28 form a closed effective magnetic path through the third magnetic conductor 13 and the fourth magnetic conductor 14, it is necessary to disconnect the magnetic path between the first magnetic conductor 11, the second magnetic conductor 12, the third magnetic conductor 13 and the fourth magnetic conductor 14. Therefore, a non-magnetic mounting frame 4 is installed between each magnetic conductor.

[0031] The first electromagnetic roller 21, the second electromagnetic roller 22, the third electromagnetic roller 23, the fourth electromagnetic roller 24, the fifth electromagnetic roller 25, the sixth electromagnetic roller 26, the seventh electromagnetic roller 27 and the eighth electromagnetic roller 28 all include an iron core and a coil wound around the iron core, and the iron core is connected to the magnetic conductor and the connecting part at the corresponding position.

[0032] like Figure 3 As shown, two rotating magnetic fields 51 and 52 are formed at the liquid center of the flanges on both sides of the ingot E through the action of the electromagnetic stirring rollers, which can even out the temperature and steel liquid composition inside the ingot E and reduce the quality defects of the H-shaped ingot. The electromagnetic stirring parameters are: current 200A ~ 600A, frequency 1Hz ~ 10Hz.

[0033] The present invention also provides a continuous casting machine, comprising the above-mentioned electromagnetic stirring device, which is connected by the bearing seat of the continuous casting machine support roller and the frame part of the adjacent sector segments.

[0034] The present invention proposes a magnetic circuit structure design method by replacing the middle part (first connecting part 31 and second connecting part 32) of the electromagnetic stirring roller and utilizing the structural characteristics of the fan-shaped segment itself, which can adapt to H-beam continuous casting machines of different models and specifications. Combined with the particularity of the production process of the H-beam continuous casting machine, the coil part of the electromagnetic stirring roller is combined to form a double-wing rotating magnetic field, which efficiently stirs the liquid core part of the billet, makes up for the shortcomings of the H-beam continuous casting process, and effectively improves the surface, subcutaneous and internal quality of the billet, such as middle cracks, center looseness, center shrinkage and center segregation. This technology has the advantages of high energy density, high cleanliness, high reliability, strong interchangeability, etc., which is of great significance for improving the quality of the billet and improving production efficiency, making steel products more competitive in the market.

[0035] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An electromagnetic stirring device, characterized in that: The invention comprises a first magnetic conductor (11) and a fourth magnetic conductor (14) arranged at intervals in the X direction, and a second magnetic conductor (12) and a third magnetic conductor (13) arranged at intervals in the X direction, wherein the first magnetic conductor (11) and the second magnetic conductor (12) are arranged at intervals in the Y direction to form a first gap (5), and the fourth magnetic conductor (14) and the third magnetic conductor (13) are arranged at intervals in the Y direction to form a first gap (5); a second electromagnetic stirring roller (3) with a disconnected intermediate magnetic circuit is respectively installed between the first magnetic conductor (11) and the fourth magnetic conductor (14) and between the second magnetic conductor (12) and the third magnetic conductor (13); and the second electromagnetic stirring roller (3) is located at the edge of the first gap (5); A first electromagnetic stirring roller (2) connected by an intermediate magnetic circuit is installed between the first magnetic conductor (11) and the second magnetic conductor (12), and between the third magnetic conductor (13) and the fourth magnetic conductor (14); a second gap (6) extending in the Y direction is provided in the first magnetic conductor (11) and the second magnetic conductor (12), and a second gap (6) extending in the Y direction is provided in the fourth magnetic conductor (14) and the third magnetic conductor (13); the first gap (5) and the second gap (6) are connected; the first electromagnetic stirring roller (2) is located at an edge of the second gap (6) away from the first gap (5); The X direction and the Y direction are perpendicular to each other on the same top projection plane.

2. The electromagnetic stirring device according to claim 1, characterized in that: The first magnetic conductor (11) and the fourth magnetic conductor (14) are symmetrically arranged in the X direction, the first magnetic conductor (11) and the second magnetic conductor (12) are symmetrically arranged in the Y direction, the second magnetic conductor (12) and the third magnetic conductor (13) are symmetrically arranged in the X direction, and the third magnetic conductor (13) and the fourth magnetic conductor (14) are symmetrically arranged in the Y direction.

3. The electromagnetic stirring device according to claim 1, characterized in that: A non-magnetic mounting frame (4) is connected between the first magnetic conductor (11) and the fourth magnetic conductor (14), between the first magnetic conductor (11) and the second magnetic conductor (12), between the second magnetic conductor (12) and the third magnetic conductor (13), and between the third magnetic conductor (13) and the fourth magnetic conductor (14).

4. The electromagnetic stirring device according to any one of claims 1 to 3, characterized in that: The first magnetic conductor (11) comprises a first wall (111), a second wall (112), a third wall (113) and a fourth wall (114) which are bent in sequence, the first wall (111) and the third wall (113) are parallel to the same side of the second wall (112), the second wall (112) and the fourth wall (114) are parallel to the same side of the third wall (113), and a second gap (6) is provided between the first wall (111) and the fourth wall (114); the second magnetic conductor (12), the third magnetic conductor (13) and the fourth magnetic conductor (14) have the same structure as the first magnetic conductor (11); and a first gap (5) is provided between the fourth walls (114) in the same Y direction; The first electromagnetic stirring roller (2) is connected to the first wall (111), and the second electromagnetic stirring roller (3) is connected to the fourth wall (114).

5. The electromagnetic stirring device according to claim 4, characterized in that: The length of the fourth wall (114) is longer than the length of the second wall (112).

6. The electromagnetic stirring device according to any one of claims 1 to 3, characterized in that: It also includes a second electromagnetic roller (22), a third electromagnetic roller (23), a sixth electromagnetic roller (26), a seventh electromagnetic roller (27) and a second connecting portion (32); One end of the second electromagnetic roller (22) is mounted on the first magnetic conductor (11), one end of the third electromagnetic roller (23) is mounted on the second magnetic conductor (12), and the second connecting portion (32) is installed between the other end of the second electromagnetic roller (22) and the other end of the third electromagnetic roller (23); the second electromagnetic roller (22), the second electromagnetic roller (22) and the second connecting portion (32) form one of the first electromagnetic stirring rollers (2); One end of the sixth electromagnetic roller (26) is mounted on the third magnetic conductor (13), one end of the seventh electromagnetic roller (27) is mounted on the fourth magnetic conductor (14), and the second connecting portion (32) is installed between the other end of the sixth electromagnetic roller (26) and the other end of the seventh electromagnetic roller (27); the sixth electromagnetic roller (26), the seventh electromagnetic roller (27) and the second connecting portion (32) form another of the first electromagnetic stirring roller (2).

7. The electromagnetic stirring device according to any one of claims 1 to 3, characterized in that: It also includes a first electromagnetic roller (21), a fourth electromagnetic roller (24), a fifth electromagnetic roller (25), an eighth electromagnetic roller (28) and a first connecting portion (31); One end of the first electromagnetic roller (21) is mounted on the first magnetic conductor (11), one end of the eighth electromagnetic roller (28) is mounted on the fourth magnetic conductor (14), and the first connecting portion (31) is installed between the other end of the first electromagnetic roller (21) and the other end of the eighth electromagnetic roller (28); the first electromagnetic roller (21), the eighth electromagnetic roller (28) and the first connecting portion (31) form one of the second electromagnetic stirring rollers (3); One end of the fourth electromagnetic roller (24) is mounted on the second magnetic conductor (12), one end of the fifth electromagnetic roller (25) is mounted on the third magnetic conductor (13), and the first connecting portion (31) is installed between the other end of the fourth electromagnetic roller (24) and the other end of the fifth electromagnetic roller (25); the fourth electromagnetic roller (24), the fifth electromagnetic roller (25) and the first connecting portion (31) form another second electromagnetic stirring roller (3).

8. A continuous casting machine, characterized in that: It comprises the electromagnetic stirring device as described in any one of claims 1 to 7.

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