JPH102990A - Grapple for channel box - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grapple for a channel box of a spent nuclear fuel assembly having a relatively light weight, satisfactory operability and excellent grasping capacity. SOLUTION: A grapple has four gripping means 26a, 26b to 26d. The each means has a support pawl 38 having a part 38a engaged with one side of a channel box sidewall plate 14a of a spent nuclear fuel assembly, and cam pawls 50 rotatably provided around a predetermined axis 52 to operate between an engagement clamping position and a separation releasing position of the other side of the plate. The each pawl 50 grasps the corresponding channel box sidewall plate cooperated with the pawl 38 simultaneously at once in a clamping state. The each pawl 50 has a profile cooperating with the pawl 38 for the corresponding sidewall plate in the direction to drop from the state that the channel box is grasped to perform an automatic clamping operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a grapple or gripping device for a rectangular tubular channel box of a boiling water reactor (hereinafter, referred to as "BWR"), and more particularly to a rectangular tubular channel box suspended in a site bunker pool. The present invention relates to a grapple for a channel box used in an operation of moving the channel box in a state or cutting the channel box in a longitudinal direction at a corner thereof for volume reduction into two L-shaped cut pieces.

[0002]

2. Description of the Related Art In a boiling water nuclear power plant, a spent nuclear fuel assembly is disassembled and separated into a fuel body and a square tubular channel box for reprocessing in a spent fuel pool in a reactor building. . The channel box is transported into a site bunker pool located adjacent to the reactor building where gussets and spacers are removed and clips are stripped. Next, using a channel box cutting device installed in the site bunker pool, two of the four corners of the square tubular channel box are cut in the longitudinal direction at two corners opposite to each other in the diagonal direction to obtain two L-shaped or In a state of a chevron member, a plurality of these members are aligned and grouped and stored in a site bunker pool with reduced volume.

Channel box cutting devices known to those skilled in the art typically include a receiving support frame with a chute and a punching means (referred to as a "nibble") installed adjacent to and associated with the receiving support frame. There is). The square tubular channel box is lifted while being gripped by a grapple connected to a crane.
Conventionally used grapples typically have four gripping means each comprising a pair of movable gripping jaws which engage with the four side walls constituting the channel box, respectively, near the periphery of the channel box opening. . The pair of gripping jaws of the gripping means are operatively connected to a double acting pneumatic cylinder via a common single actuator rod and linkage. By operation of the pneumatic cylinder, the gripping jaws can be simultaneously opened and closed between an engagement tightening position and a releasing position for gripping the side wall plate.

When cutting a channel box in a site bunker pool, a channel box gripped and lifted by a grapple is positioned under water above a receiving support frame of a cutting device, and then lowered into the receiving support frame. One corner of the bottom end of the channel box reaches the nibble and is located between the female member of the nibble and the reciprocating male punch. While lowering the grapple, nibler punches the channel box at the corner from the bottom end to the top end in small steps upward along the corner, so that the punched holes are continuous,
This cuts the channel box longitudinally at the corners. Next, the channel box is pulled out of the cutting device, rotated 180 ° above it, lowered again into the receiving support frame, and the above procedure is repeated for the opposite corner. As a result, the channel box is 2
Cut into two L-shaped pieces or angled pieces. These L-shaped cut pieces do not fall because their side wall plates are gripped by the corresponding gripping means of the grapple,
Moreover, the L-shaped cut piece can be stably held without shaking.

[0005]

Each gripping means of the conventional grapple requires a very strong pneumatic cylinder to grip and lift a heavy channel box without dropping it. This is because used channel boxes are radioactive, and all cutting is done underwater, so it is essential to hold the channel box firmly so that it does not fall. By using a large pneumatic cylinder,
As a result, the grapple became larger and heavier, and the operability was poor.

[0006] Further, the gripping force of the pneumatic cylinder may be reduced due to the variation in the pressure of the pneumatic source, or the gripping jaw may open due to malfunction or human error, whereby the channel box or the L-shaped cut piece may be opened. Could fall off the grapple.

An object of the present invention is to provide an improved grapple that is relatively lightweight, has good operability, and ensures that the channel box does not drop accidentally.

[0008]

SUMMARY OF THE INVENTION In view of the above objects, the gist of the present invention is to provide a frame member which can be suspended and four side walls attached to the bottom of the frame member to form a square tubular channel box. A portion having four gripping means operable to grip the plate near the opening top edge of the channel box, each gripping means being attached to the frame member and engaging one side of the corresponding side wall plate. And a rotatable pivot about a predetermined axis so as to be operable between an engagement tightening position and a disengagement release position with respect to the other side surface of the side wall plate. A cam pawl adapted to grip the channel box side wall plate in a clamped state, wherein the four cam pawls are operatively pivotally connected to one end of a single actuator rod; The other end is integrally connected to a reciprocating piston of the hydraulic cylinder, and the four cam claws of the gripping means are simultaneously rotated toward the engagement tightening position via the actuator rod by the operation of the hydraulic cylinder. Each of the cam claws has a contour that exerts an automatic tightening action in cooperation with the receiving claws with respect to the corresponding side wall plate in the direction in which the channel box is to be dropped from the gripped state. The grapple for a channel box is characterized in that:

In the configuration of the present invention, even if the fluid pressure cylinder malfunctions, the channel box or the L-shaped cut piece will not fall off the grapple due to the automatic tightening action of the cam of the gripping means. Further, when the gripping means of the present invention is used, a small-sized fluid pressure cylinder can be used, so that the weight is reduced and the operability is improved.

[0010] Preferably, an interlock mechanism is provided for preventing the cam claws of the gripping means from being inadvertently released and the channel box from being released from the gripping state. The interlock mechanism engages with a lock block provided on a part of the actuator rod to limit the axial movement of the actuator rod, and allows the actuator rod to move axially by releasing from the lock block A hook attached to the frame member for rotation about a fixed axis between an unlocked position and an end operatively attached to the hook via a link device and axially relative to the frame member. It has an operating rod mounted for limited movement, and a compression spring which normally urges the operating rod so that the hook moves to the release position. The other end of the operating rod is connected to a crane. 2. The channel box according to claim 1, wherein when the frame member of the grapple is lifted by the crane via the operation rod, the hook rotates to the lock position against the urging force of the compression spring. Grapple. More specifically, when the cam box is in the disengagement / release position and the channel box is lifted without gripping the channel box, the hook of the interlock mechanism operates the actuator so that the cam hook does not rotate to the engagement tightening position. Engage the engagement block to limit the upward movement of the rod,
When the contact portion of the frame member contacts the top edge of the opening of the channel box, the hook is rotated to the unlock position by the action of the compression spring to enable the axial movement of the actuator rod, and the cam pawl is engaged and tightened. When lifting the channel box while holding the channel box in the position, the hook of the interlock mechanism engages the locking block to limit the downward movement of the actuator rod so that the cam pawl does not rotate to the release position. .

Preferably, a second compression spring is provided around the actuator rod so as to normally urge the actuator rod upward to maintain the engagement position of the cam pawl. When the cam pawl is rotated from the engagement tightening position to the release position, the operation of the fluid pressure cylinder causes the actuator rod to move downward against the urging force of the second compression spring to move the cam pawl to the release position. It has become.

Preferably, at the bottom end of the frame member, 4
A base plate having two cross-shaped arms is fixed, and receiving claws of the four gripping means are respectively rotatably pivotally mounted on the arms, and means are provided for limiting a rotation range of the receiving claws; The limiting means includes a stop screw housed in each arm and having a lower end engaged with the catch. Preferably, each of the receiving claws is a generally inverted U-shaped member, and one leg of U engages a side surface of a side wall plate of a corresponding channel box, and the predetermined rotation axis of the cam pawl is U-shaped. Is positioned on the other leg.

Preferably, a guide member located below the gripping means is fixed to the lower end of the frame member, and the guide member is configured such that each side wall plate of the channel box has a receiving claw of the corresponding gripping means and a cam nail. It has a portion that can be engaged with the inside of the corner of the side wall plate located on the diagonally opposite side of the rectangular opening end of the rectangular tubular channel box so as to be inserted therebetween.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the perspective view of FIG. 1, a grapple 10 constructed in accordance with the present invention is suspended through a rope by a crane (not shown) in a sight bunker pool and stands upright. Shown in alignment with the placed rectangular tubular channel box 12 (only the top is shown). Channel box 12 is shown separated from the spent nuclear fuel assembly, with gussets, spacers and clips removed. The channel box is composed of four side walls 14a to 14d, between which corners 16a to 16d are formed, respectively. The top edge of the rectangular opening of the channel box is constituted by the top edge or side of the side wall plate.

The grapple 10 includes a frame member 18 composed of a pair of side plates 18a and 18b parallel to each other. A flat connecting top plate 20 is secured to the top of the frame member, and a gripper assembly of the present invention, generally indicated at 22, is attached to the bottom of the frame member. The gripping assembly 22 preferably includes a base block 24 secured to the bottom end of the frame member, the base block being composed of four generally cross-shaped arms 24a-d (see FIG. 4). The gripping assembly 22 has four identical gripping means 26a-d operable to grip the side walls 14a-d of the channel box near the top edge of the opening, respectively.
including. Since the four grippers have the same configuration, one gripper 26a will be described in detail later.

Referring to FIGS. 1 and 2, an actuator rod 30 having one end integrally connected to a piston of a hydraulic cylinder, for example, a double-acting pneumatic cylinder 28, is provided in the frame member 18 so as to be reciprocally movable in the axial direction. Have been.
The other end of the actuator rod extends downward through the base block 24.
A connecting block 32 comprising a pair of arm segments 32a-d operatively connected to the gripping means 26a-d, respectively, is fixed (see FIG. 4). In addition, the grapple of FIG. 2 is shown in a normal state in which the lower part is rotated by 90 ° with respect to the upper part for convenience of description.

As can be seen in FIGS. 1, 2 and 3, the gripping means 26a is received in a recess 34 provided in the arm 24a and is pivotally mounted on the arm so as to be swingable about an axis 36. 38. The receiving pawl is preferably generally inverted U with a slit or opening 40 for receiving a corresponding channel box side wall plate, as described below.
It is a letter-shaped member. The slit entrance of the receiving claw 38 includes a guide ramp 42 that widens so as to receive the side wall plate in a guided state. The slit 40 is adjusted by adjusting the orientation of the receiving claw by operating the adjusting screw 44 which is inserted through the substantially middle portion of the arm and engages with the upper surface of the receiving claw.
Can be oriented perpendicular to the arm. A stop screw 46 is provided through the outer end of the arm. The bottom end of the stop screw terminates short of the upper surface of the receiving claw. The separation distance between the bottom end of the locking screw and the upper surface of the receiving claw determines the swing amount of the receiving claw. In a normal state, a compression spring 48 for urging the receiving claw 38 clockwise and pressing the upper surface thereof against the adjustment screw is provided around the stop screw. Thus, it will be appreciated that even if the opening top edge of the channel box is not exactly square, e.g., somewhat outwardly, the slit in the receiving pawl can receive the corresponding channel box side wall plate. One leg 38a of the inverted U-shaped receiving claw is attached to the side wall plate 14 of the channel box.
a to be engaged with the outer surface.

As can best be seen in FIG. 4, the other leg 38b of the receiving pawl is composed of two mutually parallel segments between which the channel box side wall cooperates with the pawl leg 38a. A cam pawl 50 operable to grip the plate is provided. As shown, the cam pawl is also connected to the arm segment pair 32a of the connecting block 32.
It is located between. The cam claw 50 is rotatably pivotally attached to the leg 38b by a pin 52. As shown,
The cam pawl has an arcuate slot 54 and a substantially straight slot 56. Referring to FIGS. 2 and 3, a slot 54 is secured to the leg 38b and receives a pin 58 extending between the leg segments, and has an axis 52, described below.
The amount or range of the rotation of the cam claw 50 around is determined.
As will be appreciated by those skilled in the art, the cam pawl engages one end of the arcuate slot 54 in the engaged clamping position of FIG. 3 and engages the other end of the slot in the disengaged release position. When the cam pawl is operated from the engagement tightening position shown by the solid line in FIG. 3 to the disengagement release position shown by the imaginary line, the receiving pawl swings counterclockwise through a small angle as shown by the imaginary line. On the other hand,
The slot 56 receives the pin 60 fixed to the connecting block 32 and extending between the pair of arm segments 32a, so that the linear movement of the actuator rod and the rotating movement of the cam pawl can be performed smoothly and the components are not damaged. Like that. Thus, when the pneumatic cylinder 28 is actuated to raise the actuator rod, the cam claws 50 of the gripping means 26a to 26d simultaneously rotate around the axis 52 simultaneously via the connecting block 32, and move with respect to the side wall plates 14a to 14d. It will be understood that the engagement tightening position is obtained. The engagement and tightening positions of the cam claws are shown by solid lines in FIG. On the other hand, when the actuator rod is lowered, the cam claws 50 of the gripping means 26a to 26d simultaneously rotate around the axis 52 in the opposite direction simultaneously via the connecting block 32, and separate from the side wall plates 14a to 14d. I will be. The disengagement and release position of this cam pawl is shown in phantom in FIG. Each of the cam claws of the gripping means of the present invention has such a contour that the channel box side wall plate exerts an automatic tightening action in cooperation with the receiving claws in a direction in which the channel box side plate tends to fall from the gripped state shown by the solid line in FIG. It is important to have.

Referring again to FIGS. 1 and 2, even if the gripping force of the pneumatic cylinder is reduced due to a variation in the pressure of the pneumatic source or a malfunction or human error occurs, the channel box is prevented from being released from the gripping state. An interlocking mechanism 62 is shown. The interlock mechanism engages the upper and lower surfaces of a locking block 64 provided at an appropriate position along the length of the actuator rod 30 as shown in FIGS. First and second restrict axial movement of
The frame member is pivoted about a fixed axis 66 between a locked position of FIG. 5A and an unlocked position disengaged from the locking block to allow axial movement of the actuator rod as shown in FIG. Has a pair of hooks 68 attached thereto. More specifically, a pair of hooks 68 are located on both sides of the actuator rod and are adapted to engage the upper or lower surface of the opposing protrusion or wing of the locking block. The interlock mechanism further includes an operating rod 70 that supports the frame member through the top plate 20 of the frame member and is capable of limited axial movement.
Having. The upper end of the operating rod can be connected to the crane via a rope. The lower end of the operating rod is operatively attached to a hook 68 via a link device 72. The link device includes a link 78 connected to the hook 68 via an intermediate link 74 and rotatable about a fixed axis 76. The operating rod 70 is pivotally connected to a link 78 at reference numeral 80. In a normal state, a compression spring 82 for urging the operation rod upward is provided inside the top plate 20 of the frame member. In this configuration, the operating rod 7 is operated by a crane.
When the frame member 18 of the grapple is lifted through the hook 0, the hook 68 takes a locked position with respect to the locking block of the actuator rod against the urging force of the compression spring 82, thereby restricting the upward or downward movement of the actuator rod. It is supposed to. Reference numeral 84 denotes four legs which are attached to the operation rod so as to be adjustable in position and whose lower ends engage a chute of a channel box cutting device (not shown) to determine the lower limit position of the grapple with respect to the cutting device. .

With reference to FIG. 5, the operating state of the interlock mechanism will be described in more detail in relation to the handling state of the grapple and the operating state of the gripping means.

FIG. 5A shows the interlock mechanism 62 in the first lock position when the grapple is lowered toward the channel box for holding the lower channel box while being suspended via a crane. Is shown. In the first lock position, the cam pawl is in the disengagement release position due to the downward movement of the actuator rod due to the operation of the pneumatic cylinder, and the operation rod 70 is
2 pivots the link 78 clockwise about the axis 76, thereby rotating the hook 68 of the interlock mechanism clockwise about the axis 66, and the lower surface of the lower jaw 69 of the pair of hooks The actuator rod is simultaneously engaged with the upper surface of the protruding piece of the locking block 64. Thus, even if a malfunction of the pneumatic cylinder or an error of the operator occurs, the upward movement of the actuator rod due to these is prevented, and the released position of the cam pawl is maintained.

FIG. 5B shows the interlock mechanism in the unlock position when the grapple is seated on the channel box. At the same time as the seat is seated, the lifting force of the operation rod is eliminated, and the urging force of the compression spring 82 causes the operation rod to move downward with respect to the frame member for a predetermined stroke, and the link 78 to rotate counterclockwise to move the hook 68 to the release position. So that the actuator rod can be moved in the axial direction. Next, when the actuator rod is moved upward by the operation of the pneumatic cylinder, the cam pawl can be brought into the engagement tightening position with respect to the channel box side wall plate.

FIG. 5C shows a state in which the grapple is lifted by the crane from the state shown in FIG. When the operating rod is pulled up by a predetermined distance, the hook 68 rotates clockwise around the axis 66 to thereby take the second locked position.
In the second lock position, the upper surface of the lower jaw 69 of the hook engages with the lower surface of the protruding piece of the locking block 64. Thus, even if a malfunction of the pneumatic cylinder or an error of the operator occurs, the downward movement of the actuator rod caused by the malfunction is prevented, and the engaging and releasing position of the cam pawl is maintained. In addition, the cam claw automatically exerts a tightening action on the side wall plate in cooperation with the receiving claw due to the weight of the channel box, so that accidental dropping of the channel box from the grapple is reliably prevented. Further, by utilizing the automatic tightening action obtained by the gripping means of the present invention, a smaller hydraulic cylinder can be used, and the compact and lightweight grapple is achieved.

Referring to FIGS. 1, 2 and 5, the actuator rod is arranged around the actuator rod 30 so as to rotate the cam pawl toward a position for tightening engagement with the channel box side wall plate. A compression spring 86 is shown, which constantly biases the base block 24 of the member upward. The spring force of the compression spring 86 urges the actuator rod upward even if the air pressure in the pneumatic cylinder is reduced for some reason and the pulling force on the actuator rod is reduced. Is sufficient to maintain Thus, it will be appreciated that the present invention provides an improved grapple which ensures that the channel box does not accidentally drop.

As shown in FIGS. 1 and 2, a guide member 88 including a pair of oppositely facing conical portions as a whole is attached to a frame member 1 by a mounting frame 90.
8 at the bottom. The guide member 88 as a whole is located below the gripping means. Guide member 8
8 is aligned with the rectangular opening end of the channel box so that the grapple is properly seated on the channel box, and each side wall plate of the channel box is inserted between the receiving claw and the cam claw of the corresponding gripping means. Help to be. In FIG. 1, the conical portion of the guide member 88 can be engaged with the inner right-angle portions of the side wall plate corners 16 a and 16 c located on the diagonally opposite sides of the rectangular tube-shaped channel box 12.

The use of the grapple of the present invention will be apparent to those skilled in the art from the above description, and will not be described. In addition,
The grapple of the present invention includes a conventional automatic display mechanism that informs an operator at the site bunker poolside that the channel box has been gripped and seated below the surface of the channel box. When the connecting block 32 is lifted up from the channel box side wall plate by the operation of the actuator rod and the cam pawl 50 rotates toward the engagement tightening position, the rod 94 moves upward via the connecting member 92 and is pivotally attached thereto. Related red display board 9
6 falls horizontally about axis 98, so that the operator can be informed of the gripping state. In addition, although not shown in the drawings, using a known mechanism, it is possible to operate between the vertical position and the horizontal position, and when the grapple is seated on the channel box side wall plate, the white color is turned to the horizontal position. It has a display panel 100.

[0027]

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state before a grapple of the present invention is seated on a channel box.

FIG. 2 is a schematic longitudinal sectional view showing the grapple of the present invention so that an internal structure can be seen by removing one side plate of a frame member.

FIG. 3 is a partially enlarged sectional view showing a grapple gripping means of the present invention.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

5A and 5B are diagrams showing an operation state of the interlock mechanism of the present invention, wherein FIG.
(B) is the unlocked position of the hook,
(C) is a schematic diagram showing the hook in a second locked position.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Grapple 12 Channel box 14a-d Side wall plate 18 Frame member 22 Gripping assembly 24 Base block 26a-d Gripping means 28 Fluid pressure cylinder 30 Actuator rod 32 Connecting block 38 Receiving pawl 40 Slit 44 Adjusting screw 46 Stop screw 50 Cam pawl 62 Interlock mechanism 64 Locking block 68 Hook 70 Operating rod 86 Compression spring 88 Guide member

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[Procedure amendment]

[Submission date] July 2, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

Claims (8)

[Claims] 1. A suspendable frame member, and four side wall plates attached to the bottom of the frame member and constituting a rectangular tubular channel box, each of which is operable to grip near an opening top edge of the channel box. A pair of gripping means, each gripping means being attached to a frame member and having a receiving claw having a portion engaging with one side surface of a corresponding side wall plate, and engaging fastening to the other side surface of the side wall plate. A cam claw provided rotatably about a predetermined axis so as to be operable between the position and the disengagement release position, and adapted to grip the corresponding channel box side wall plate in a tightened state in cooperation with the receiving claw; The four cam pawls are operatively pivoted to one end of a single actuator rod, the other end of which is integral with the reciprocating piston of the hydraulic cylinder. And the four cam claws of the gripping means are simultaneously rotated toward the engagement tightening position via the actuator rod by the operation of the fluid pressure cylinder, and each of the cam claws is gripped by the channel box. A grapple for a channel box having a contour that exerts an automatic tightening action in cooperation with a receiving claw on a corresponding side wall plate in a direction in which the grapple is to be dropped from a set state. 2. An interlock mechanism is provided for preventing the cam claws of the gripping means from being inadvertently released and the channel box from being released from the gripping state, wherein the interlock mechanism is a part of the actuator rod. Locked between a locked position that engages a locking block provided on the vehicle and limits axial movement of the actuator rod and an unlocked position that separates from the locking block and allows axial movement of the actuator rod A hook attached to the frame member so as to rotate about the axis, and an operating rod one end of which is operatively attached to the hook via a link device and is attached to the frame member so as to be freely movable in the axial direction. A compression spring that normally urges the operating rod so that the hook moves to the release position, and the other end of the operating rod is a clay. The hook is pivoted to a lock position against the urging force of a compression spring when the frame member of the grapple is lifted by a crane via an operation rod. Grapple for channel box as described. 3. When the cam box is in the disengagement / release position and the channel box is lifted without gripping the channel box, the hook of the interlock mechanism operates the actuator rod so that the cam pawl does not rotate to the engagement tightening position. When the abutment portion of the frame member abuts on the top edge of the opening of the channel box, the hook is rotated to the unlock position by the action of the compression spring, thereby restricting the upward movement of the actuator. When lifting the channel box while allowing the rod to move in the axial direction and holding the channel box with the cam pawl at the engagement tightening position, the hook of the interlock mechanism
3. A grapple for a channel box according to claim 2, wherein said engaging means engages with said locking block to limit downward movement of said actuator rod so that said cam pawl does not rotate to the release position. 4. In a normal state, a second compression spring is provided around the actuator rod so as to urge the actuator rod upward to maintain the engagement and tightening position of the cam pawl. When rotating from the position to the release position, the operation of the fluid pressure cylinder moves the actuator rod downward against the urging force of the second compression spring to move the cam pawl to the release position. The grapple for a channel box according to any one of claims 1 to 3, wherein: 5. A base block having four cross-shaped arms is fixed to the bottom end of the frame member, and receiving claws of the four gripping means are pivotally mounted on the respective arms so as to be rotatable. 2. A grapple for a channel box according to claim 1, further comprising means for restricting a rotation range of the claw. 6. A grapple for a channel box according to claim 5, wherein said restricting means includes a locking screw housed in each arm and engaging with a receiving claw. 7. Each of the receiving claws is a member having an inverted U shape as a whole, and one leg of the U is engaged with a side surface of a side wall plate of a corresponding channel box, and the predetermined rotation axis of the cam claw is provided. 7. The grapple for a channel box according to claim 1, 5 or 6, wherein the grapple is positioned on the other leg of the U. 8. A guide member located below the gripping means is fixed to a lower end of the frame member, and each side wall plate of the channel box is provided between the receiving nail and the cam nail of the corresponding gripping means. The grapple for a channel box according to claim 1, characterized in that the grapple has a portion which can be engaged with an inner portion of a corner of a side wall plate located on a diagonally opposite side of a rectangular opening end of the rectangular tube-shaped channel box so as to be inserted into the channel box.