JPH10180574A - Bolt replacing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method of replacing a tight fixed bolt without damaging its female threaded part. SOLUTION: Nearly in the center of a tight fixed bolt, a sack hole is formed till the tightly fastened portion 15, and this counterbored part 14 is cut away from the portion 15 by a cutting tool inserted into the sack hole. Owing to the left-hand threading of the sack hole, the counterbored part 14 of the bolt can be taken out by screwing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for replacing a bolt which is firmly fixed. This type of bolt replacement method is effectively used especially when it is difficult to access the bolt. For example, such a case occurs during a bolt change in a steam generator.

[0002]

2. Description of the Related Art Conventionally, this kind of problem has been solved by mechanically drilling a bolt firmly fixed to a thread. The disadvantage of this method is that the bore diameter must be precisely matched to the core diameter of the bolt when drilling. If the core diameter of the bolt is set to be too small, there may be a case in which a residual portion of the bolt that cannot be removed remains in the screw hole. If the diameter of the hole is only slightly larger than the core diameter of the bolt, the internal thread is damaged, and the coupling strength of the bolt is reduced. The danger of damage to the internal thread is particularly problematic in the case of relatively long bolt connections, as there is a problem in maintaining the original angular state of the screw hole during boring and ensuring the centering of the screw shaft with respect to the boring shaft. large.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for replacing a bolt which is firmly fixed so that a female screw portion is not damaged.

[0004]

This object is achieved by a method having the features of claim 1. Further advantageous embodiments of the invention are described in the dependent claims.

The gist of the present invention is a method divided into several working steps. As with the drilling of bolts, if the bolt has a head, the head of the bolt is first cut off and the remaining part of the bolt is drilled with a bore diameter that is clearly smaller than the core diameter of the bolt shaft. The boring of the bolt shaft is empirically performed at the threaded end of the bolt until just before the position where the bolt bites. The gist of the present invention is that the drilled bolt is divided into two parts at the position where it is firmly fixed. Since the outer part of the bolt is therefore held with relatively little force on the original thread, it can be removed by screwing. However, the tightly engaged inner part (remaining part) of the bolt generally remains in the original thread. For the separation, a cutting tool is inserted into the core hole of the bolt shaft, the cutting tool moving in the radial direction at the final position and dividing the drilled bolt into two parts. This separates the outer portion of the bolt shaft from the firmly secured portion and allows for easy movement within the female thread. With a bolt with a right-hand thread, the left-hand thread that is rotated into the core hole allows the outer portion of the bolt shaft to be removed by screw rotation.

Next, a new bolt shorter than the original bolt is screwed into the thread. This method is particularly suitable for fixing bolts having a relatively large length in calculation.

Due to the fact that the diameter of the core hole is smaller than the diameter of the bolt shaft, any inaccuracies in centering the core hole and maintaining the angular state are less affected than in the conventional method.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

As shown in FIG. 1, a column head 1 connected to a column 2 of a steam generator is connected to a steam generator 5 by bolts 3 via a pad 4 of the steam generator. FIG. 2 shows a three-dimensional view of a state in which it is difficult to approach the bolt 3 for fixing the column head 1 to the pad 4 of the steam generator.

A cross section of the bolt connection shown in FIG. 1 is shown in detail in FIG. Shown are headed bolts 3 that attach the column head 1 to a steam generator pad 4 via a caul plate 6. This configuration further comprises a washer 7 between the column head 1 and the bolt 3 head.
To prevent the bolted connection from coming off or loosening unintentionally. The position of the bite at the female thread normally formed at the end of the screw is shown at 8.

FIGS. 4 to 10 show the individual working steps of the method according to the invention. If the bolt has parts for stable seating, the parts are removed (for example, the washer 8 in FIG. 3 is cut off), and then, if the bolt has a head first, the parts shown in FIG. As shown in FIG. 5, a centering hole 10 is provided. Next, as shown in FIG. 6, the blind hole 11 is drilled to a position where the bolt is firmly fixed. In this blind hole, a left-hand thread 12 is cut in FIG.

In FIG. 8, a cutting tool 13, for example, a miniaturized chevron milling cutter is inserted into the blind hole, and is fed radially so that the remainder of the bolt 2 is immediately above the position where the bolt is firmly fixed. Divided into two parts. Therefore, as shown in FIG. 9, the bored portion 14 of the remaining bolt can be removed from the female screw portion. this is,
This is carried out by screwing in a screw tool 16 provided with a screw corresponding to the left-hand thread.
5 remains in the female thread.

FIG. 10 shows a modification of this method, in which the blind hole 17 is likewise provided up to the end of the bolt. In this case, the annular groove 19 is machined into a bolt to which the annular groove 19 is firmly fixed by a cutting tool. The annular groove may extend substantially to the original thread. In this case, such damage to the thread does not significantly affect the function of the thread.

In this case, it is assumed that the outer part of the bolt 18 thus separated from the remaining part is still firmly fixed and cannot be removed. Accordingly, another annular groove 21 is formed from the blind hole 17. This annular groove can also reach the original thread. Again, such localized damage does not adversely affect the function of the original thread when a new bolt is subsequently inserted.
However, in FIG. 10, the other annular groove 21 does not completely reach the original thread. With the aid of a screw tool 25 inserted into the left-hand thread 22, a torque is provided on the outer part of the bolt which is strong enough to divide the outer part into two new individual parts 23 and 24, but only the outermost part 24 has an annular groove. 2
It is transmitted by cutting off the other part 23 remaining at the position 1.

The part 23 is then left-threaded, so that the part 23 can likewise be removed with a screw tool. This part 23 has a relatively short axial length, i.e. the holding force of the tightly threaded thread is correspondingly small. In this way, the longer bolts are separated from the tightly engaged connection in individual parts. In that case, the tip inside the bolt remains on the thread.
However, it is also possible to remove them at these points. For example, if the bolt originally has a larger length in terms of calculation, i.e., has a longer thread than is necessary for the mechanical load of the bolt, it will fit into the bottom of the original thread. The remaining portion 20 can be cut by the cutting tool together with the original thread end.

That is, this method includes a cutting tool, a positioning hole,
It is only necessary to provide boring tools for countersunk holes and left-hand threads, and corresponding screw tools. In that case, the original thread retains its function almost without the need for special precision.

[Brief description of the drawings]

FIG. 1 is a sectional view of a steam generator supported on a column.

FIG. 2 is a three-dimensional layout of a part of FIG. 1;

FIG. 3 is a cross-sectional view of bolt connection when FIG. 1 is applied.

FIG. 4 is a cross-sectional view of a bolted joint in a state where a head is separated from a bolt shaft, showing one of operation steps for replacing a fixed bolt.

FIG. 5 is a cross-sectional view of a bolt coupling portion in a state where a positioning hole is formed in a bolt shaft.

FIG. 6 is a cross-sectional view of a bolt connection portion in a state where a hole is bored in a bolt shaft.

FIG. 7 is a cross-sectional view of a bolted joint in a state where a screw is cut on the inner surface of the bore of the bolt shaft.

FIG. 8 is a cross-sectional view of the bolted joint in a state where a cutting tool is inserted into a hole formed in the bolt shaft and the bolt is cut into two parts.

FIG. 9 is a cross-sectional view of the bolted joint in a state where the outer portion of the cut bolt is taken out.

FIG. 10 is a sectional view of a bolted joint in a modified example of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Prop head 3 Bolt or its head 4 Steam generator pad 6 Backing plate 7 Washer 8 Bolt biting position 9 Bolt shaft 10 Centering hole 11 Bag hole 12 Screw part 13 Cutting tool 14 External part of bolt 15 Internal bolt Part 16 screw tool 17 blind hole 19 annular groove 20 remaining bolt 21 other annular groove 22 screw part 25 screw tool

Claims (4)

[Claims] 1. The outer part of the bolt is cut off from the remaining fixed part (15) of the bolt and removed from the original thread by screw rotation, and then the remaining original thread part is removed. A bolt replacement method characterized in that a new bolt is screwed. 2. A blind hole (11) is provided substantially at the center of the bolt which is firmly fixed to the remaining portion (15),
The perforated part (14) is cut off from the remaining part (15) which is firmly fixed by the cutting tool (13) inserted into the blind hole (11), and then the perforated part (14) is removed. 2. The method according to claim 1, wherein the removal is performed by screw rotation. 3. The method according to claim 2, wherein the bolt heads which are securely fastened are removed before forming the blind hole. 4. A thread (1) having an opposite orientation to the thread of the bolt before removing the drilled portion (14) by screw rotation.
2) is cut into a drilled part (14), and the corresponding threaded part of a screw tool (16) is inserted into this opposite thread (12) and the drilled part (14) is turned 4. The method according to claim 1, wherein
The method described in one.