US3884065A - Straightening elongated articles - Google Patents

Abstract

This specification discloses a method and apparatus for straightening a bent elongated article of substantially constant cross-section in which the article is constrained to take up a straight configuration by holding it at both ends and applying a force to it by means of a die in a direction substantially at right angles to the longitudinal axis of the article intermediate its ends and the article is twisted about its longitudinal axis so that sufficient of the material of the article is plastically strained in torsion in order that when the article is released from constraint the article retains the straight configuration.

Description

United States Patent [191 Townend STRAIGHTENING ELONGATED ARTICLES [75] Inventor: Gordon Howard Townend,

Wolverhampton, England [73] Assignee: GKN Group Services Ltd.,

Worcestershire, England 22 Filed: Aug. 8, 1973 [21] Appl. No.: 386,799

[451 May 20, 1975 Primary Examiner-C. W. Lanham Assistant Examiner-M, J. Keenan Attorney, Agent, or Firm-A, Yates Dowell, Jr.

[57] ABSTRACT This specification discloses a method and apparatus for straightening a bent elongated article of substantially constant cross-section in which the article is constrained to take up a straight configuration by holding it at both ends and applying a force to it by means of a die in a direction substantially at right angles to the longitudinal axis of the article intermediate its ends and the article is twisted about its longitudinal axis so that sufficient of the material of the article is plastically strained in torsion in order that when the article is released from constraint the article retains the straight configuration.

3 Claims, 5 Drawing Figures STRAIGHTENING ELONGATED ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to methods and apparatus for straightening elongated articles of substantially constant cross-section.

2. Description of the Prior Art Various methods other than pure bending have been proposed for straightening elongated articles. Thus, for example, it is known to straighten longer articles, such as drill tubes, by applying localised bending moments to the tube while rotating the tube. The localised bending moments may be applied by moving a carriage longitudinally of the article, the carriage having pads or rollers for engaging the article as the article is rotated.

It is also known to apply a tensile force to an article in directions parallel to the longitudinal axis thereof to remove an axial bow or bend therein. A high tensile force is required since the force acts along a line not far removed from the centroid of the section at the point of maximum bow. The induced bending moment is therefore low and in order for the bending movement to be sufficient to straighten the article the tensile force may in many instances be so high as to cause permanent elongation of the article with a consequent reduction in cross section which is not permissible in many cases.

It has also been proposed to twist an elongated article when under tension to remove an undesired skew relationship between the ends of the articles.

In order to improve the mechanical properties of an elongated article such as a reinforcing bar, it has been proposed to cold work the article by twisting it about its longitudinal axis. During this twisting the bar may be under tension which is likely to cause the bar to elongate. While with an article such as a reinforcing bar, a small elongation and reduction in section is acceptable, this is not acceptable for smaller parts with small tolerances.

In French Patent Specification No. 860,100 there is described a method of cold working a bar to improve its mechanical properties by bending the bar into a bowed shape and then rotating the bar so that each section rotates about an axis which is generally tangential to the curve of the bow. The specification makes it clear that in order to improve the mechanical properties there must be plastic deformation which of course will accompany the cold working. The specification states that the plastic deformation may either be in bending or in torsion. Where the plastic deformation is in bending then both ends of the bar can be rotated at the same speed and after cold working the bar has to be restraightened if a straight bar is required. On the other hand, if the bar is bent within the elastic range and is subjected to plastic torsion, it is stated that one of the advantages of this arrangement is that restraightening of the bar is not necessary, the inference being that the bar will spring back to its straight position after the twisting has been completed.

Contrary to what is stated in the French specification we have surprisingly discovered that if an elongated article is subjected to plastic strain in torsion the longitudinal axis of the article will take a permanent set in the configuration which it has when the plastic deformation in torsion is effected.

It is an object of the present invention to provide a method of accurately straightening an elongated article without the reduction in cross-section and elongation discussed above.

SUMMARY OF THE INVENTION According to one aspect of the present invention I provide a method of straightening a bent elongated article of substantially constant cross-section comprising the steps of constraining the article to take up a straight configuration by holding the article at both ends and applying a force to the article in a direction substantially at right angles to the longitudinal axis of the article intermediate its ends and twisting the article about its longitudinal axis so that sufficient of the material of the article is plastically strained in torsion in order that when the article is released from constraint the article retains the straight configuration.

The invention is primarily concerned with the straightening of parts where high accuracy is required, for example, a total indicator reading of not more than 0.010 inches. TIR readings are obtained by placing a clock gauge in contact with the point of largest bow on the article and rotating the article, while it is supported at both ends, through 360. These readings are thus equal to twice the largest bow. More accurate straightening than this can easily be obtained using the invention.

The invention has been developed in connection with the straightening of bolt blanks before the blanks are threaded but is not limited thereto and can be applied to other articles such as connecting rod blanks.

A bent elongated article may possess a number of bend conditions. For example, the article may have a steady bend of large radius of curvature or a sharp bend of locally small radius of curvature. The article may also be bent in a single plane or may include a number of bends in different planes.

It is extremely difficult to provide an apparatus or a method which will straighten a bent elongated article including any one of the bend conditions described above and which is capable of giving the degree of accuracy of 0.010 inch TIR discussed above coupled with the capability of automatic operation to give the level of output necessary to make it commercially viable.

In order to illustrate this point, an example will now be given of the difficulties involved in straightening a bolt blank, by conventional bending methods, which possesses the simplest bend condition of a steady bend in one plane. The problem arises from the elastic recovery of the bolt blank material after it has been deformed. Thus, if one has a bent bolt blank it is insufficient merely to bend the blank to a straight configuration because when the forces bending the blank are released the blank will spring back to its bent configuration. It is thus necessary to overbend the blank so that after elastic recovery has taken place the longitudinal axis of the blank is straight. It is apparent that in order to straighten the blank the material thereof must be caused to flow plastically and one requires a considerably greater deflection of the blank to cause plastic flow than is required to actually straighten the blank. Thus, for example, to correct a deflection of, say, 0.020 inch at a point on the blank it may be necessary to deflect the blank by, say, three-eighths inch in order to obtain plastic flow of the material and then continue the deflection by the 0.020 inch to change the configuration of the axis. The actual straightening part of the deflection is therefore only a small part of the total deflection which is required and this makes for difficulties in practice in straightening.

The difficulties encountered in straightening an elongated article with a number of bends in different planes are even more complex as each bend must be straightened separately using the above bending technique.

I have found that by constraining an elongated article to take up a straight configuration and plastically straining the article in torsion when so constrained, the plastic strain induced by the torsion will effectively kill the elastic recovery of the article in bending so that the article will retain the straight configuration when released from constraint. It is not necessary that the article is plastically strained across its whole crosssection perpendicular to the longitudinal axis. The amount of the cross-section which is plastically strained must be sufficient to cause the article to retain the straight configuration when the constraint is released. It may be, for example, that the plastic straining of the outer half of the cross sectional area of the article is sufficient for this purpose.

The invention thus provides an efficient method of straightening an elongated article with bends in one or more planes. The method and apparatus in accordance with the invention can also readily be automated and are easily capable of producing the level of accuracy discussed above.

The method may be carried out by clamping the article at both ends, one end being clamped so as to hold it stationary and the other end being clamped so as to permit twisting of the article about its longitudinal axis, bringing a die into engagement with a portion of the article between the clamped ends so as to constrain the article to take up a straight configuration, and twisting said other end of the article when so constrained so as to plastically strain the article in torsion.

Although the deformation of the article in bending by the die will normally be within the elastic range, this deformation may in certain cases be plastic, for example, when the article is badly bent the forces exerted on the article by the die in constraining the article to take up a straight configuration may in fact result in plastic deformation of the article. However, for the reasons explained above, this plastic deformation in bending will not itself be sufficient to permanently straighten the bar.

Where the ends of the article must remain in some predetermined relationship to one another, for example in the case ofa connecting rod, then the article may be twisted in one direction to strain it plastically and then twisted back in the opposite direction also to obtain plastic strain and to bring the ends of the article back into the desired relative relation.

The invention also provides apparatus for straightening a bent elongated article of substantially constant cross-section comprising means for holding the article at both ends and a die arranged to contact the article intermediate its ends so as to apply a force to the article in a direction substantially at right angles to the axis of the article this constraining the article to take up a straight configuration, one of said holding means being rotatable and the other fixed so that the article can be plastically strained in torsion about its longitudinal axis when constrained by the die.

The die may be in two parts arranged to be brought into contact with the article from opposite sides thereof, the die parts being provided with formations which contact the article to constrain it but allow it to be twisted while constrained.

For example, if the article to be straightened is of circular cross-section the die parts may be provided with formations in the form of grooves of V-shaped crosssection which extend longitudinally relative to the article and which co-operate to define a closed channel of substantially square cross-section in which the article is constrained.

Conversely, if the article is square in cross-section it may be constrained in a closed channel which is circular in cross section.

One of the parts may be arranged to be brought into contact with a stop thus positioning said part in a predetermined position relative to the clamped ends of the article and the other die part may be arranged to be brought into contact with said one die part so as to constrain the article.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be described, by way of example, with reference to FIGS. 1 to 5 of the accompanying drawings in which:

FIG. 1 is a longitudinal section through part of an apparatus embodying the invention;

FIG. 2 is a sectional view on the line AA of FIG.

FIG. 3 is a view in the direction of the arrow B in FIG. 1 of one end of the apparatus shown in FIG. 1; and

FIGS. 4 and 5 are side and plan views respectively of the other end of the apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be described in relation to the straightening of a bolt blank which is indicated generally at 10 in FIG. 1 and which has a shank 11 of constant and circular cross-section and a bolt head 12 which is generally spherical.

The apparatus for straightening the bolt blank comprises a base plate 13 which carries at its right hand end a clamping block 14 mounted on a dove-tail crosssection slide 15. At the other end of the base plate a rotatable chuck 16 is mounted on bearing assemblies 17 and 18, see FIG. 4. Positioned intermediate the clamping block 14 and rotatable chuck 16 is a two-part die arrangement 19, see FIG. 2.

The die arrangement comprises two die parts 20 and 21 which are mounted on dove-tail cross-section slides 22 and 23 respectively which in turn engage corresponding dove-tail cross-section slides 24 and 25 which are secured to the base plate 13. As can be seen from FIGS. 1 and 2, the die parts 20 and 21 are arranged to be brought into contact with the bolt blank from opposite sides of the blank. Both die parts are provided with V-shaped cross-section grooves 26 and 27 respectively which extend longitudinally relative to the bolt blank and which co-operate to define a closed channel of substantially square cross section in which the bolt blank may be constrained into a straight configuration.

The die parts are moved on the slides 24 and 25 by hydraulic piston and cylinder arrangements (not shown), the movement of the die part 20 being limited by an adjustable stop 28. The V-shaped cross section groove 26 provided in the die part is deeper than the corresponding groove 27 provided in die part 21 and the outer surfaces 29 and 30 of the die part 21 are chamfered so as to enter the groove 26. The die part 21 is resiliently mounted on the slide 23 by a number of pre-loaded Belleville washer arrangements 31 spaced along the die part. Each Belleville washer arrangement comprises a stack of Belleville washers 32 encircling a bolt 33, one end of the bolt being screwed into the slide 23 and the headed end of the bolt being received in a recess 33a provided in the die part 21.

As can be seen from FIG. 2, the pre-loaded Belleville washer arrangements 31 force the die part 21 away from the slide 23 and leave a gap 34 therebetween. By chamfering the die part 21 and resiliently mounting this die part on the slide 23 the two-part die arrangement is made self-aligning as when the die part 21 contacts the die part 20, the chamfered surfaces 29 and 30 enter the groove 26 and the resilient mounting of the die part 21 allows this part limited freedom to move vertically and also to rotate relative to the other die part 20 about an axis substantially parallel to the bolt blank so that the two die parts automatically align themselves so as to constrain the bolt blank in the desired manner. The piston and cylinder arrangement which brings the die part 20 into contact with the stop 28 is arranged to exert a greater force than the piston and cylinder arrangement which brings the die part 21 against the die part 20. This ensures that the die part 20 always provides the fixed reference for the die part 21.

The clamping block 14 includes a lower jaw 35 and an upper jaw 36 which is mounted for vertical sliding movement on slides 38. The lower jaw 35 extends further towards the chuck 16 than the upper jaw 36 thus providing a ledge 53 which extends beyond the upper jaw 36. The clamping action is provided between the upper and lower jaws by an hydraulic piston and cylinder assembly 37 which is connected to the upper jaw 36 and which raises and lowers the upper jaw. An hydraulically operated ejector 39 is provided for assisting in the removal of the bolt blank from the apparatus when the headed end of the blank is released from the chuck 16. The ejector comprises a push rod 40 which is aligned with the end of the bolt blank, the push rod being arranged to contact the bolt blank and push it onto the ledge 53 when the headed end of the bolt blank is released following a straightening operation.

As previously stated the clamping block 14 is mounted on a slide 15 of dovetailed cross-section. This allows the apparatus to be used to straighten bolt blanks of varying lengths, as the distance between the chuck 16 and clamping block 14 is readily adjustable by sliding the clamping block 14 on the slide 15 and locking the clamping block in the required position by clamping means, not shown.

The rotatable chuck 16 is secured to an outer shaft 41 by an internally threaded retaining ring 42 which engages a screw-threaded shoulder 43 provided on the outer shaft. The outer shaft is supported on axially spaced bearing assemblies 17 and 18 which are carried by a housing 44 which is secured to the base plate 13. As can be seen from FIGS. 4 and 5, the chuck 16 is provided with a key-hole shaped access aperture 45 through which the head 12 of the bolt blank may be inserted. When in position in the chuck 16, the head 12 of the bolt blank is clamped against part-sperical surfaces 46 provided in the chuck by an inner shaft 47 which extends within a bore 48 provided in the outer shaft 41 and is supported in this bore by plain bearings 49 which allow the inner shaft limited freedom to move within the outer shaft so as to align itself correctly with the head of the bolt blank. The end of the inner shaft is recessed so as to co-operate with the head of the bolt blank and the inner shaft is pressed against the head of the bolt blank by a hydraulic piston and cylinder assembly 50 which rotates with the outer shaft 41.

The outer shaft 41 is rotated by a rack 51 which cooperates with a pinion 52 carried by the outer shaft. The rack 51 is moved by a hydraulic piston and cylinder assembly 53.

The apparatus described above operates as follows: The head 12 of a bolt blank 10 is placed in the chuck l6 and the end of the shank 11 of the blank is placed on the ledge 53 provided on the lower jaw 35 of the clamping block. The hydraulic piston and cylinder assembly 51 is then actuated so as to clamp the head of the bolt blank in the chuck 16 and to push the end of the bolt shank further onto the lowerjaw 35. Piston and cylinder assembly 37 is then actuated to bring the upper jaw 36 into clamping engagement with the end of the shank. The die part 20 is then advanced the bolt shank 10 until the stop 28 is contacted. The other die part 21 is then brought towards the die part 20 until the chamfered surfaces 29 and 30 enter the groove 26 in the die part 20 and the die parts automatically align themselves as previously described. By adjusting the position of the stop 28 prior to the commencement of the straightening operation, the die parts 20 and 21 can be arranged to constrain the bolt blank 10 to take up a straight configuration.

While the bolt blank is so constrained, the chuck 16 is rotated by the actuation of the piston and cylinder assembly 53. This subjects the bolt blank to torsion, the rotation of the chuck 16 being arranged to be sufficient to plastically strain sufficient of the cross-section of the bolt blank so as to cause the blank to retain its straight configuration when released from constraint by the die parts 20 and 21.

Following the twisting of the bolt blank, the piston and cylinder assemblies 50 and 37 are retracted so as to release the ends of the bolt blank and the die parts 20 and 21 are drawn away from the blank. The ejector 39 is then actuated to assist in the removal of the bolt blank from the chuck and clamping block.

The precise shape of the chuck 16, the two-part die arrangement 19 and the clamping block 14 is determined by the shape of the article which it is desired to straighten. The apparatus described above can thus be used to straighten a variety of articles by employing a suitably shaped chuck, two-part die arrangement and clamping block or by replacing the chuck 16 by an appropriately shaped clamping means which is capable of the necessary rotation.

Where the ends of the article to be straightened must remain in some predetermined relationship to one another, for example in the case of a connecting rod, then the article may be twisted in one direction to strain it plastically and then twisted back in the opposite direction also to obtain plastic strain and to bring the ends of the article back into the desired relationship.

Experimental results obtained using the apparatus described above to straighten bolt blanks are shown in Table I below. The table shows the total indicator readings (TIR) obtained before and after the bars had been straightened by twisting through an angle of 120.

TABLE I.

TlR VALUES (inches) Before Straightening After Straightening To give some indication of the efficiency of the invention a similar set of bolt blanks were straightened by plastically straining the blanks in tension. The blanks were subjected to a 0.2 per cent tensile strain and the results achieved as set out below in Table II.

TABLE II.

TlR VALUES (inches) Before Straightening After Straightening I08 .022 103 .025 100 .007 .092 .O l 7 apparatus for straightening a bent elongated article which, as can be seen from Table i, are capable of working to a very high degree of accuracy.

The apparatus described above may easily be arranged for automatic operation by providing a mechanical handling device to place the head of the bolt blank in the chuck l6 and the end of the bolt shank l 1 on the ledge 54 and to remove the bolt blank from the chuck and ledge when the straightening operation has been completed.

I claim:

1. A method of straightening an elongated article having a bent portion of substantially constant crosssection comprising the steps of clamping the article at each end so as to hold one end stationary while the other end is clamped so as to permit the end to be twisted about the longitudinal axis of the article, bringing a die into engagement with said portion of the article so as to constrain said portion of the article to take up a straight configuration without preventing twisting thereof about said axis, and twisting said other end of the article about said axis while said portion is so constrained to plastically strain sufficient of the material of said portion in torsion whereby when said portion is released from constraint said portion retains its straight configuration.

2. A method as claimed in claim 1 comprising bringing two die parts into engagement with said portion of the article from opposite sides thereof in order to constrain the article.

3. A method as claimed in claim 2 comprising bringing one of the die parts into engagement with a stop, thereby positioning said part in a predetermined position relative to the clamped ends of the article, and bringing the other die part into contact with said one die part so as to constrain said portion of the article.

Claims (3)

1. A method of straightening an elongated article having a bent portion of substantially constant cross-section comprising the steps of clamping the article at each end so as to hold one end stationary while the other end is clamped so as to permit the end to be tWisted about the longitudinal axis of the article, bringing a die into engagement with said portion of the article so as to constrain said portion of the article to take up a straight configuration without preventing twisting thereof about said axis, and twisting said other end of the article about said axis while said portion is so constrained to plastically strain sufficient of the material of said portion in torsion whereby when said portion is released from constraint said portion retains its straight configuration.

2. A method as claimed in claim 1 comprising bringing two die parts into engagement with said portion of the article from opposite sides thereof in order to constrain the article.

3. A method as claimed in claim 2 comprising bringing one of the die parts into engagement with a stop, thereby positioning said part in a predetermined position relative to the clamped ends of the article, and bringing the other die part into contact with said one die part so as to constrain said portion of the article.

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