JP7582238B2 - Metal strip coil lifting device and method - Google Patents

Description

The present invention relates to a metal strip coil lifting device and method used when transporting a metal strip coil with a crane.

The most widely known methods for transporting metal strip coils are by conveyor or crane, with crane transport offering a high degree of freedom of movement and being an essential method for loading and unloading onto transport trucks.

In general, when transporting by crane, coil tongs installed on the crane are used as a means for transporting and moving the metal strip coil (hereinafter also simply referred to as coil). Here, the coil tongs 11 are a lifting tool that has a pair of L-shaped members 7 consisting of a vertical part 8 and a horizontal part (also referred to as hook parts) 9, as shown in FIG. 4, for example, and that inserts the hook parts 9 into the coil hole 10 (the core hole of the coil 20) from both sides and suspends the coil 20 by contacting (also referred to as abutting) the inner surface of the coil hole 10. The coil tongs 11 have an abutment surface 5, which is the surface of the hook parts 9 that abuts the inner surface of the coil hole 10. The coil tongs 11 also have a support frame 30 that supports the pair of L-shaped members 7 with a variable spacing, and the support frame 30 is suspended by a crane (not shown) and can be raised and lowered and rotated and moved in a horizontal plane.

When transporting coils, it is important to take care to prevent damage to the coil caused by the coil tongs, and the following proposals have been made regarding technologies to prevent this damage to the coil.

Patent document 1 discloses that multiple photoelectric sensors installed at the tip of the hook detect a position in the coil hole where the inner end hangs down and is not obstructed, and select this position as the appropriate insertion position for the hook. This prevents damage to the inner end of the coil due to contact with the hook.

Patent document 2 discloses that the surface of the hook portion is free to rotate. As a result, when attempting to lift a coil when the hook portion is not on a vertical line passing through the center of the coil, sliding friction is converted to rolling friction when the hook portion moves along the inner surface of the coil hole to the top end position of the coil hole, preventing scratches from occurring.

Patent document 3 discloses a protective device for transporting steel sheet coils, which is comprised of an inner surface protective part made of synthetic resin that contacts the upper part of the inner surface of the coil hole of the steel sheet coil, a side protective part made of synthetic resin that extends in the radial direction of the coil from one axial end of the inner surface protective part, and a magnetic attraction part that attracts the side protective part to the side of the coil. This prevents scratches and dents from occurring on the inner surface of the coil hole and the side of the coil.

Japanese Utility Model Application Publication No. 62-71180 Japanese Patent Application Publication No. 7-81868 Japanese Utility Model Application Publication No. 6-14173

Mechanical Engineering Pocket Book (JR edition), published in 1957, Ohmsha, page 77, table 2-23

In recent years, automation of coil transportation has been progressing, while the types of coils are becoming more diverse, with a wide range of coil widths from 500 to 2,000 mm, weights from 5 to 45 tons, and inner diameters (coil hole diameters) of 419 mm, 508 mm, 610 mm, and 650 mm.

When transporting coils using a crane, it is necessary to transport these coils in the same way at all times and while maintaining a consistent quality. However, when the inner diameter and weight of a coil are large, inserting the hook part of the coil tongs into the coil hole and lifting it with a crane causes linear scratches that run from the end of the coil hole in the coil width direction to the point where the hook part comes into contact, and extend in the axial direction of the coil hole.

Such linear defects occur even when there is no obstruction on the inner surface of the coil hole, and the technology in Patent Document 1 cannot prevent the occurrence of these defects.

In addition, these linear defects are caused by linear contact between the coil tongue and the inner surface of the coil hole, and occur even when the insertion position of the hook part into the coil hole is on a vertical line passing through the center of the coil, and cannot be prevented even with the technology of Patent Document 2.

In conventional coil tongs, the shape of the abutment surface of the hook portion is fixed and there is no way to change it.

Incidentally, in Patent Document 2, the shape of the contact surface that is free to rotate is fixed to the surface shape of a cylinder with a constant radius, and remains unchanged even when rotated.

On the other hand, the technology of Patent Document 3 protects the inner and side surfaces of the coil with protective equipment made of synthetic resin, which can prevent scratches and dents, including the linear flaws. However, the protective equipment is attached to the coil, and requires labor to remove during automatic packaging of the coil, which reduces the efficiency of the coil packaging work.

In addition, in conventional coil tongues 11 (see FIG. 4), including the case of Patent Document 2, the shape of the contact surface 5 is such that the cross section perpendicular to the coil width direction is an arc, and the radius of curvature of the arc is fixed to a constant value less than the smallest value of the radii of curvature of the inner surfaces of the multiple coil holes 10 to be lifted.

In view of the above, the present invention aims to provide a metal strip coil lifting device and a method using the same that can prevent linear defects from occurring at the contact points between the inner surface of the coil hole and the hook portion of the coil tongs when transporting metal strip coils using coil tongs, without reducing the efficiency of the coil packaging work.

In order to solve the above problems, the inventors of the present invention have focused on the fact that linear defects occurring at the contact points between the inner surface of the coil hole and the hook portion occur when the coil inner diameter and weight are large, and have thoroughly investigated the cause of the occurrence of the linear defects. As a result, they have come to the following findings.
(a) The linear defects occur when the contact pressure at the contact point between the inner surface of the coil hole and the hook portion during coil transport exceeds the allowable stress, where the allowable stress means the yield stress, which is one of the material properties of the metal strip coil.
(i) Depending on the inner diameter of the coil to be lifted, the shape of the hook portion at the point where the hook portion abuts against the inner surface of the coil hole can be adjusted so that the abutment point transitions from line contact to surface contact, expanding the contact area, and the contact surface pressure becomes equal to or less than the allowable stress, thereby preventing the occurrence of linear defects.

The present invention was made based on the above findings and further studies, and the gist of the present invention is as follows.
[1] A lifting device for a metal strip coil, in which a hook portion of a coil tong is inserted into and abuts against a coil hole of the metal strip coil to lift the coil,
A metal strip coil lifting device comprising: a means for changing the shape of the abutment surface of the hook portion that abuts against the inner surface of the coil hole.
[2] The metal strip coil lifting device described in [1], characterized in that the means for changing the shape of the abutment surface is an attachment that is detachable from the coil tongue.
[3] The metal strip coil lifting device described in [2], characterized in that the attachment includes a plurality of abutment members, the abutment surfaces of which have a radius of curvature corresponding to the inner diameter of the metal strip coil.
[4] The metal strip coil lifting device according to [3], wherein the plurality of abutment members are rotatable abutment members each having a plurality of radii of curvature.
[5] The metal strip coil lifting device according to [4], characterized in that the plurality of radii of curvature are radii of curvature such that the contact surface pressure of the abutting surfaces is equal to or less than an allowable stress.
[6] The metal strip coil lifting device according to [4] or [5], characterized in that the attachment is provided with a motor that rotates the multiple abutment members.
[7] The metal strip coil lifting device according to any one of [1] to [6], characterized in that the metal strip coil is a steel strip coil having a coil weight of more than 15 tons.
[8] A method for lifting a metal strip coil, comprising inserting a hook portion of a coil tong into a coil hole of the metal strip coil and lifting the coil by abutting the hook portion,
A method for lifting a metal strip coil, comprising the step of changing the shape of the abutment surface of the hook portion that abuts against the inner surface of the coil hole.
[9] The method for lifting a metal strip coil according to [8], characterized in that the step of changing the shape of the contact surface includes a step of attaching and detaching an attachment to the coil tongue.
[10] A method for lifting a metal strip coil as described in [9], characterized in that the process of changing the shape of the abutment surface includes a step of changing the radius of curvature of the abutment surface with the attachment in accordance with the inner diameter of the metal strip coil.
[11] A method for lifting a metal strip coil as described in [10], characterized in that the step of changing the radius of curvature of the abutment surface in accordance with the inner diameter of the metal strip coil is a method of rotating a plurality of abutment members each having a plurality of radii of curvature.
[12] The method for lifting a metal strip coil according to [11], wherein the plurality of radii of curvature are radii of curvature such that the contact surface pressure of the abutting surfaces is equal to or less than an allowable stress.
[13] The method for lifting a metal strip coil according to [11] or [12], characterized in that the method for rotating the multiple contact members is by a motor.
[14] The method for lifting a metal strip coil according to any one of [8] to [13], characterized in that the metal strip coil is a steel strip coil having a coil weight of more than 15 tons.

According to the present invention, the shape of the contact surface of the hook portion that comes into contact with the inner surface of the coil hole, for example the radius of curvature of the contact surface, is changed to increase the contact area of the contact surface in accordance with the inner diameter of the metal strip coil, and the contact surface pressure of the contact surface is adjusted to be equal to or less than the allowable stress, thereby preventing the occurrence of linear defects on the inner surface of the coil hole. In addition, by reducing the contact surface pressure on the coil tongue side, the frequency of repairs can be reduced.

FIG. 2 is a schematic diagram showing an example of a coil tongue used in the present invention. FIG. 4 is a schematic diagram showing another example of a coil tongue used in the present invention. FIG. 13 is a diagram showing an example of the relationship between the radius of curvature of the contact surface of the hook portion with respect to the coil hole and the calculated contact surface pressure (when the coil inner diameter is 650 mm). FIG. 1 is a schematic diagram showing an example of a conventional coil tongue.

The following describes an embodiment of the present invention with reference to Figures 1 and 2. In the following, the metal strip coil lifting device according to the present invention is also referred to as the present invention device, and the metal strip coil lifting method according to the present invention is also referred to as the present invention method.

[Metal strip coil]
The coil 20 to be lifted is, for example, a steel strip coil with a coil width of 500 to 2000 mm, a coil weight of 5 to 60 tons, and a coil inner diameter of 419 to 650 mm. The steel strip has a plate thickness of 0.4 to 3.2 mm, a material (steel material symbol) of, for example, SS400, SPCC, SPFC980Y, etc., and a yield stress of 100 to 600 N/ ^mm2 .
When the metal strip coil is a steel strip coil and the L-shaped member 7 and the abutting member 6 are made of steel, for a coil weight of 15 tons or less, the contact surface pressure is below the allowable stress in both the conventional method (where the radius of curvature of the abutting surface is a fixed value (200 mm) corresponding to the minimum coil inner diameter) and the present invention (where the radius of curvature of the abutting surface is changed according to the coil inner diameter), and no difference appears between the two in the effectiveness of preventing linear defects. A difference appears between the two in the effectiveness of preventing linear defects for coil weights exceeding 15 tons.
Therefore, in the present invention, from the viewpoint of the manifestation of the effect of preventing linear defects, the effect of the present invention is particularly exhibited in a metal strip coil having a coil weight of more than 15 tons.

[Device of the present invention]
The device of the present invention is a metal strip coil lifting device that inserts and abuts hook portion (horizontal portion) 9 of coil tongs 1 into coil hole 10 of coil (metal strip coil) 20 to lift the coil (metal strip coil), and has means 2 for changing the shape of abutment surface 5, which is the surface of hook portion 9 that abuts against the inner surface of coil hole 10 (Figs. 1 and 2). However, in the present invention, the abutment surface 5 of hook portion 9 includes the abutment surface 5 via means 2, as shown in Figs. 1 and 2.

[Coil tongue and hook part]
The coil tongs 1 according to the present invention are similar to the conventional coil tongs 11 (FIG. 4) in that they are hoists that have a pair of L-shaped members 7 each consisting of a vertical portion 8 and a hook portion 9, and that the hook portions 9 are inserted into a coil hole 10 from both sides and abut against the inner surface of the coil hole 10 to hoist the coil 20, and that they have a support frame 30 that supports the pair of L-shaped members 7 with a variable spacing, and that the support frame 30 is suspended by a crane (not shown) and can be raised and lowered and rotated and moved in a horizontal plane. The L-shaped members 7 are made of steel. The length L of the hook portions (the length of the abutment surface 5 in the coil width direction) is 100 to 200 mm.

[Means for changing the shape of the abutment surface of the hook portion]
The device of the present invention is characterized by having a means 2 for changing the shape of the contact surface 5 .
This makes it possible to adjust and change the shape of the contact surface to make it more of a surface contact and to increase the area of the contact surface so that the contact pressure is below the allowable stress, depending on the inner diameter of the coil to be lifted, as described above in the finding (i), thereby achieving prevention of the occurrence of linear defects.

[attachment]
In the present invention, the means 2 for changing the shape of the contact surface 5 so as to transition the contact surface 5 from line contact to surface contact is preferably an attachment 3 that is detachable from the coil tongue 1 .
The attachment 3 that can be attached to and detached from the coil tongs 1 refers to a member that can be attached to and detached from the coil tongs 1.
The attachment is preferable because it reduces manufacturing costs and maintenance burdens compared to when the means 2 for changing the shape of the contact surface 5 is fixed to the coil tongue.
In this preferred embodiment, the hook portion 9 abuts against the inner surface of the coil hole via an attachment 3 attached to the coil tongue 1 .

[Multiple Contact Members]
When the shape of the abutment surface 5 is an arc in a cross section perpendicular to the coil width direction, as in the conventional case, the shape of the abutment surface 5 is uniquely determined by the radius of curvature of the arc. Therefore, in order to make the shape of the abutment surface 5 correspond to the inner diameter of the coil 20, it is preferable that the attachment 3 includes a plurality of abutment members 6, the radius of curvature of the abutment surface 5 of which corresponds to the inner diameter of the coil 20. This makes it possible to change the plurality of abutment members 6 according to the inner diameter of the coil 20 to be lifted, increase the contact area between the coil and the attachment, and keep the contact surface pressure of the abutment surface 5 below the allowable stress.

[Having multiple radii of curvature and being rotatable]
It is preferable that each of the plurality of contact members 6 has one of the plurality of radii of curvature. It is preferable that the radii of curvature of each of the plurality of contact members 6 are different from each other, so that the contact members 6 can correspond to various inner diameters of coils.
Each of the multiple abutment members 6 has an outer peripheral surface corresponding to the radius of curvature of a specific abutment surface 5, and the radius of curvature of the outer peripheral surface of each abutment member becomes the radius of curvature of the abutment surface 5 when each outer peripheral surface is oriented vertically upward and abuts against the inner surface of the coil hole 10.
As a result, one attachment 3 has a plurality of abutment members 6 each having a plurality of radii of curvature.

It is also preferable that the multiple abutment members 6 are rotatable. Here, rotation means rotation around the central axis of the hook portion 9. By making the abutment members 6 rotatable, the abutment members 6 can be rotated so that they face vertically upwards while the attachment 3 is attached, thereby appropriately changing the radius of curvature of the abutment surface 5. When the abutment members 6 are rotatable in this way, the work efficiency of coil transportation is improved compared to when the abutment members 6 cannot rotate, which is preferable. When the structure does not allow rotation, it is necessary to remove and reattach the attachment 3 in order to change the abutment members 6 to face vertically upwards.

1 and 2, the four radii of curvature of the outer circumferential surfaces of the four contact members 6 (6 ₁ to 6 ₄ ) are R1 = 200 mm, R2 = 240 mm, R3 = 285 mm, and R4 = 300 mm. The attachment 3 comprises a fixed portion 12 that detachably fits with the hook portion 9, and a rotating portion 13 that is coupled to the fixed portion 12 via a cylindrical roller 14 and rotates around the fixed portion 12, and the four contact members 6 (6 ₁ to 6 ₄ ) are fixed to four points in the circumferential direction of the outer surface of the rotating portion 13.

[Contact pressure and allowable stress]
It is preferable to appropriately select the radius of curvature of each of the plurality of contact members 6 such that the contact pressure of the contact surface 5 is equal to or less than the allowable stress. In this way, the contact member 6 is rotated in accordance with the inner diameter of the coil 20 so that the contact pressure of the contact surface 5 is equal to or less than the allowable stress, thereby preventing the occurrence of the linear flaws.

The contact surface pressure of the contact surface 5 is calculated as P _max by the Hertz formula shown in formula (1) (see page 77 of Non-Patent Document 1).

where _Pmax is the contact surface pressure [N/ ^mm2 ], F is the load (coil weight per unit length of the hook portion) [N/mm], _d1 is the coil inner diameter (inner diameter of the metal strip coil) [mm], _d2 is 2 x radius of curvature of the contact surface [mm], _E1 is Young's modulus of the coil [N/ ^mm2 ], and _E2 is Young's modulus of the contact member [N/ ^mm2 ]. Here, the load F [N/mm] is calculated from the coil weight M [ton] and the hook portion length L [mm] (see Figure 1) by the formula F = 9800M/(2L). The hook portion length L is the length of the contact surface 5 in the axial direction of the coil hole.

On the other hand, the allowable stress is the yield stress, which is one of the material properties of the coil, as described above, and is known. Therefore, for each inner diameter of the coil, the relationship between the radius of curvature of the contact surface (= _d2 /2) and _the contact pressure _Pmax calculated by formula (1) is used to select multiple radii of curvature of the multiple contact members 6 from the range of the radius of curvature of the contact surface where the contact pressure Pmax is equal to or less than the allowable stress.

For example, when the coil inner diameter is small (minimum 419 mm) and large (maximum 650 mm), the radius of curvature of the contact surface is set to 200 mm, less than half of the minimum inner diameter as in the past, and the contact pressure is calculated using formula (1). The results are shown in Table 1 along with the input variables and allowable stress. Table 1 also shows the results of an investigation into the presence or absence of linear defects on the inner surface of the coil hole. The coil is a steel strip coil with the steel material designation SS400, and the contact member is made of steel.

From Table 1, it can be seen that when the radius of curvature of the abutment surface is 200 mm, when the coil inner diameter is 419 mm, the contact surface pressure is below the allowable stress and no linear defects occur, but when the coil inner diameter is 650 mm, the contact surface pressure becomes approximately three times the allowable stress and exceeds the allowable stress, causing linear defects to occur.
On the other hand, Fig. 3 shows the change in contact pressure when the radius of curvature of the abutment surface is changed for the maximum coil inner diameter (650 mm). As can be seen from Fig. 3, by increasing the radius of curvature of the abutment surface from 200 mm to 300 mm in accordance with the coil inner diameter of 650 mm, the contact area increases and the contact pressure is reduced to ^about 100 N/mm2, the same level as in the case of the radius of curvature of the abutment surface (200 mm) in accordance with the minimum coil inner diameter (419 mm) (see Table 1). In this way, by changing the radius of curvature of the abutment surface in accordance with the coil inner diameter, increasing the contact area, and keeping the contact pressure below the allowable stress, it is possible to prevent the occurrence of linear defects on the inner surface of the coil hole.

[Motor for rotating the contact member]
In the example of Fig. 1, the attachment 3 for changing the radius of curvature of the contact surface has a form in which the multiple contact members 6 are rotated manually, but in terms of workability and safety, a form in which the multiple contact members 6 are rotated automatically is more preferable. As exemplified in Fig. 2, this more preferable form of the attachment 3 includes a motor 15 for rotating the multiple contact members 6. The motor 15 may be any of an electric motor, an air motor, and a hydraulic motor, but it is particularly preferable to use a servo motor or a stepping motor that is capable of automatically stopping after starting and rotating the motor shaft by a predetermined angle in order to intermittently rotate the contact members 6 at a predetermined rotation angle.

[Method of the present invention]
The method of the present invention is a method for lifting a metal strip coil by inserting and lifting the hook portion of a coil tong into the coil hole of the metal strip coil, and is characterized in that it includes a step of changing the shape of the abutment surface of the hook portion that abuts against the inner surface of the coil hole.

The method of the present invention is preferably carried out using the device of the present invention. Therefore, the method of the present invention preferably includes a step of changing the shape of the abutment surface 5 of the abutment member of the hook portion of the coil tongue 1 (Figs. 1 and 2) rather than the coil tongue 11 (Fig. 4).

The process of changing the shape of the contact surface 5 preferably includes a step of attaching and detaching the attachment 3 to the coil tongue 1. The attachment 3 is mounted so that the hook portion 9 can contact the inner surface of the coil hole 10 via the attachment 3.

The process of changing the shape of the contact surface 5 preferably includes a step of changing the radius of curvature of the contact surface 5 with the attachment 3 in accordance with the inner diameter of the coil 20. In this step, an attachment 3 having multiple contact members 6 is used.

The step of changing the radius of curvature of the contact surface 5 in accordance with the inner diameter of the coil 20 is preferably a method of rotating a plurality of contact members 6, each having a plurality of radii of curvature. In this method, an attachment 3 is used as the member 4, which includes a plurality of rotatable contact members 6, each having a plurality of radii of curvature. By rotating these abutment members 6 and orienting the outer circumferential surface of any one of the abutment members 6 vertically upward, the radius of curvature of the contact surface 5 can be changed.

The multiple radii of curvature are preferably set to a value that makes the contact surface pressure of the contact surface 5 equal to or less than the allowable stress. For this purpose, an attachment 3 is used in which the multiple rotatable contact members 6 have a curvature radius that makes the contact surface pressure of the contact surface 5 equal to or less than the allowable stress.

The method of rotating the multiple contact members 6 is preferably by a motor 15. For this purpose, an attachment 3 having a motor 15 that rotates the multiple contact members 6 is used.

Also, as mentioned above, from the viewpoint of the manifestation of the effect of preventing linear defects, it is preferable that the metal strip coil 20 be a steel strip coil with a coil weight of more than 15 tons.

The present invention was carried out using steel strip coils (plate thickness = 0.4 to 3.2 mm, coil width = ₅₀₀ to 1800 mm) with coil inner diameters d ₁ of d ₁₁ = 419 mm, d ₁₂ = 508 mm, d ₁₃ = 610 mm, d 14 = 650 mm, coil weights M of 15 tons, 30 tons, 45 tons, and 60 tons, and steel material code SS400, as examples of the present invention.

In the present invention, the device shown in Fig. 2 was used, in which the coil tongs 1 were made of steel, the contact member 6 of the attachment 3 was made of steel, and the radius of curvature of the upper end surface of the hook portion 9 when the attachment 3 was not attached was 200 mm as in the conventional case (Fig. 4). The radii of curvature R1 to R4 of the outer peripheral surfaces of the contact members ₆₁ to ₆₄ were 200 mm, 240 mm, 285 mm, and 300 mm as described above, the hook portion length L was 170 mm, and the motor 15 was a stepping motor. The Young's modulus of the steel strip and the contact member 6 was 205,000 N/ ^mm2 . The allowable stress (yield stress) σ _max of SS400 was 235 N/ ^mm2 . The radii of curvature _R1 to R4 were selected from the radii of curvature (= _d2 / ₂ ) of the contact surfaces at which the calculated value of the contact surface pressure _Pmax according to formula (1) is approximately 100 N/ ^mm2 or less, which is significantly lower than the allowable stress _σmax (235 N/ ^mm2 ), when the coil inner diameter d1 is _d11 to d14, respectively. The contact members ₆₁ to ₆₄ are then associated with the coil inner diameters _d11 to _d14, respectively.

When lifting the coil, attachment 3 is attached to hook portion 9, and before hook portion 9 is inserted into coil hole ₁₀ , the radius of curvature of abutment surface 5 is changed by rotating abutment member 6 with motor 15 so that the outer peripheral surface of the corresponding abutment member (any of ₆₁ to ₆₄ ) faces vertically upward depending on whether the coil inner diameter is d11 to _d14 , and then hook portion 9 is inserted into coil hole 10 to lift coil 20.

On the other hand, in the present invention example, a device was used in which the attachment 3 and motor 15 were removed from the coil tongs 1 (Figure 4), and the rest of the device was the same as in the present invention example, making it the conventional example. In the conventional example, the coil 20 is lifted without attaching the attachment 3 to the hook portion 9.

After the coils according to the present invention and the working examples were transported by crane, the inner surface of the coil hole was visually observed to check for the presence of the linear flaws. The results of the investigation are shown in Table 2. Table 2 also shows the calculation conditions and results of the contact pressure according to formula (1), as well as the results of a comparison between the contact pressure and the allowable stress.

As can be seen from Table 2, in all of Inventive Examples 1 to 16, the contact surface pressure P _max was equal to or less than the allowable stress σ _max , and no linear flaws were observed.

In contrast, in the conventional examples, namely, Conventional Examples 2, 3, and 4 in which the coil inner diameters were 508 mm, 610 mm, and 650 mm when the coil weight was 60 tons, Conventional Examples 7 and 8 in which the coil inner diameters were 610 mm and 650 mm when the coil weight was 45 tons, and Conventional Example 12 in which the coil inner diameter was 650 mm when the coil weight was 30 tons, the contact surface pressure P _max exceeded the allowable stress σ _max , and linear defects were observed in all of them.

In Conventional Examples 14, 15, and 16, in which the coil inner diameter was 508 mm, 610 mm, and 650 mm when the coil weight was 15 tons, the contact surface pressure P _max was equal to or less than the allowable stress σ _max , and no linear defects were observed, as in the present invention examples. Therefore, when the coil weight is 15 tons or less, instead of changing the rotation angle position of any of the contact members 6 ₁ to 6 ₄ corresponding to the coil inner diameter to the upper end position of the hook portion 9 in the present invention examples 11 to 14, the same effect can be obtained by keeping the rotation angle position of the contact member 6 ₁ fixed at the upper end position of the hook portion 9, or by detaching the attachment 3 from the hook portion 9.

In this way, it has been demonstrated that the present invention can prevent the occurrence of linear defects by changing the radius of curvature of the contact surface according to the inner diameter of the coil being lifted, keeping the contact surface pressure below the allowable stress.

1 Coil tongs (present invention)
2 Means for changing the shape of the contact surface 3 Attachment 5 Contact surface (contact surface of the hook portion that contacts the inner surface of the coil hole)
6 Contact member (the subscripts 1 to 4 are given for individual identification)
7 L-shaped member 8 Vertical portion 9 Hook portion (horizontal portion)
10 Coil hole 11 Coil tongue (conventional)
12 Fixed part 13 Rotating part 14 Cylindrical roller 15 Motor 20 Coil (metal strip coil)
30 Support frame

Claims (8)

In a lifting device for a metal strip coil, a hook portion of a coil tong is inserted into a coil hole of the metal strip coil and abutted against the coil hole to lift the coil,
a means for changing a shape of a contact surface of the hook portion that contacts the inner surface of the coil hole,
The means for changing the shape of the contact surface is an attachment that is detachably attached to the coil tongue,
the attachment includes a plurality of contact members, the radius of curvature of the contact surface of which corresponds to the inner diameter of the metal strip coil;
A metal strip coil lifting device, characterized in that the plurality of abutment members are a plurality of rotatable abutment members each having a plurality of radii of curvature. 2. The metal strip coil lifting device according to claim 1 , wherein the plurality of radii of curvature are radii of curvature that make the contact surface pressure of the contact surface equal to or less than an allowable stress. 3. The metal strip coil lifting device according to claim 1 , wherein the attachment includes a motor for rotating the plurality of contact members. The metal strip coil lifting device according to any one of claims 1 to 3 , characterized in that the metal strip coil is a steel strip coil having a coil weight of more than 15 tons. A method for lifting a metal strip coil, comprising inserting a hook portion of a coil tong into a coil hole of the metal strip coil and lifting the coil by abutting the hook portion,
changing a shape of a contact surface of the hook portion that contacts an inner surface of the coil hole;
The step of changing the shape of the contact surface includes a step of attaching and detaching an attachment to the coil tongue,
the step of changing the shape of the contact surface includes a step of changing a radius of curvature of the contact surface by the attachment in accordance with an inner diameter of the metal strip coil;
A method for lifting a metal strip coil, characterized in that the step of changing the radius of curvature of the abutment surface in accordance with the inner diameter of the metal strip coil is a method of rotating a plurality of abutment members, each of which has a plurality of radii of curvature. 6. The method for lifting a metal strip coil according to claim 5 , wherein the plurality of radii of curvature are set so that a contact surface pressure of the abutting surfaces is equal to or less than an allowable stress. 7. The method for lifting a metal strip coil according to claim 5 or 6 , wherein the method for rotating the plurality of abutting members is by a motor. The method for lifting a metal strip coil according to any one of claims 5 to 7 , characterized in that the metal strip coil is a steel strip coil having a coil weight of more than 15 tons.

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