US3807618A - Guide means for supporting a rod-shaped body having a nominally circular cross-section - Google Patents

Abstract

A device for guiding and supporting a rod-shaped body which is advanced longitudinally through the device and which has a circular cross-section. The device comprises an outer sleeve and an inner sleeve, which is axially movable with a tight fit in the outer sleeve and is formed at one end with an internal cylindrical surface for engaging the rod-shaped body. The cylindrical surface is provided by a plurality of tongues formed by incisions in the end portion of the sleeve. At the same end the inner and outer sleeves have cooperating inclined contact surfaces, which preferably are conical with different vertical angles, and spring means are provided between the sleeves for effecting a resilient engagement between the inclined contact surfaces of the sleeves and between the internal surfaces of the tongues and the rod-shaped body. The number of tongues is preferably an odd multiple of three.

Description

United States Patent [1 1 Agerup et al.

[11'] 3,807,618 [4 Apr. 30, 1974 GUIDE MEANS FOR SUPPORTING A ROD-SHAPED BODY HAVING A NOMINALLY CIRCULAR CROSS-SECTION [75] Inventors: Claes Christian Agerup; Torben Nielsen; Ole Olsen, all of Roskilde;

Hans Erik Gundtoft, Stenlose, all of Denmark [73] Assignee: Atomenergikommissionen,

Copenhagen, Denmark [22] Filed: July 11, 1973 [21] Appl. No.: 378,110

Primary ExaminerAllen N. Knowles Assistant Examiner-Gene A. Church Attorney, Agent, or Firm-Browne, Beveridge, De- Grandi & Kline ABSTRACT A device for guiding and supporting a rod-shaped body which is advanced longitudinally through the device and which has a circular cross-section. The device comprises an outer sleeve and an inner sleeve, which is axially movable with a tight fit in the outer sleeve and is formed at one end with an internal cylindrical surface for engaging the rod-shaped body. The cylindrical surface is provided by a plurality of tongues formed by incisionsin the end portion of the sleeve. At the same end the inner and outer sleeves have cooperating inclined contact surfaces, which preferably are conical with different vertical angles, and spring means are provided between the sleeves for effecting a resilient engagement between the inclined contact surfaces of the'sleeves and between the internal surfaces of the tongues and the rod-shaped body. The number of tongues is preferably an odd multiple of three.

8 Claims, 3 Drawing Figures PATENTEB APR 30 I974 W I E NTW I M GUIDE MEANS FOR SUPPORTING A ROD-SHAPED BODY HAVING A NOMINALLY CIRCULAR CROSS-SECTION BACKGROUND OF THE INVENTION The present invention relates to guide means for supporting a rod-shaped body having a nominally circular cross-section and which is advanced through the guide means in its longitudinal direction, especially but not exclusively for use in an apparatus for nondestructively testing tubes.

It is often requested that guide means of the type mentioned shall provide an extremely accurate centering of the supported body relative to a fixed centre line, for example the axis of a measuring head rotating around the body, irrespective of variations in the dimensions of the body including its cross-sectional shape within a given tolerance range. It is desirable moreover, that one guide means can be used for supporting bodies having different nominal diameters and that the movement of the body through the guide means takes place with low friction and without any significant risk of damage to its surface.

SUMMARY OF THE INVENTION According to the present invention there is provided a device for guiding and supporting a rod-shaped body having a nominally circular cross-section, and which is advanced in its longitudinal direction through the device, which device comprises a stationary outer sleeve and an inner sleeve axially displacable within said outer sleeve, which inner and outer sleeves over a part of their length have opposed cylindrical mating surfaces engaging with a tight sliding fit,

said inner sleeve having at one end thereof an internal, cylindrical or substantially cylindrical contact surface for engagement with the outer surface of said rod-shaped body and an external contact surface inclined with respect to the longitudinal axis of the device, said inner sleeve being formed at said end with a plurality of tongues separated by axially extending slits,

said outer sleeve having an inclined internal contact surface for engagement with said inclined external contact surface on said inner sleeve,

and spring means between saidinner and outer sleeve for urging said inclined internal and external contact surfaces on said sleeves into mutual axial engagement.

The employment of a slitted inner sleeve provided with tongues which, under the influence of the spring force, are able to move in unison towards and away from the surface of the rod-shaped body provides when the spring force is expediently selected a holding force which effectively counteracts tendencies towards lateral displacement of the body without restraining or braking its longitudinal movement through the device to any significant degree. The coaxial arrangement of the inclined contact surfaces and the outer sleeve ensures, in connection with the mutual centering of the two sleeves at the end of the device remote from the tongues, the best possible centering also in the case of deviations from the nominal rod crosssection.

A device having a slotted inner sleeve as defined above is known in a somewhat similar construction from the so-called collets used in machine tools. With a collet, however, it is a question of solving a substantially different technical task, viz. to'obtain the maximum gripping force on a workpiece for the transmission of substantial torques whereas, according to the present invention, it is desirable to achieve an optimum of centering accuracy with. as small gripping forces as possible to ensure the freedom of axial movement of the rod-shaped body. Furthermore, the axial and radial movements of the slotted sleeve in a collet are positively controlled and are considerably greater than in the device according to the invention since they have to ensure that the workpiece is alternately completely released and clamped immovably.

It is also known to employ radially slotted and externally conical bearing sleeves for rotary, axially fixed shafts, in this case, however, the construction of the sleeves is also determined by quite a different technical task, viz. to ensure automatic compensation for bearing play due to wear of the relatively rotating bearing surfaces of the shaft and the sleeve.

The contact surfaces of the sleeves may be conical and the vertex angle of the internal sleeve may be smaller than that of the contact surface of the external sleeve. This feature effectively counteracts tendencies towards jamming between the two sleeves in the contact surfaces, which would render the advancing of the supported body difficult in the'case of local dimensional variations.

With a view toensuring a maximum ofcontact area for the mutual centering of the two sleeves, the mating surfaces between the external and the internal sleeve may extend from the endremote from the slotted end of the internal sleeve and, at least, forward to the base or root end of the tongues.

Preferably, the number of tongues on the internal sleeve is odd and in particular it may be an odd multiple of three, by preference nine. Particularly when the supported bodies are seamless, rolled tubes, the crosssectionalshape is often slightly triangular due to the mode of manufacture and such a cross-section will become optimally centered when the number of tongues is divisible by three. It has been-found, however, that also oval cross-sections are centered with avery high degree of accuracy by employing an odd number of tongues. Generally speaking, the centering accuracy is improved the greater the number of tongues is, however, for practical reasons it will rarely be expedient to employ more than nine tongues-also because the improvement in accuracy which it is possible to achieve by employing a still greater number is relatively minor.

When the advance of the rod-shaped body through the device is always in the same direction, the slotted end of the internal sleeve may be located at the trailing end of the guide means, as seen in the direction of movement. This feature reduces the risk that the axial friction force between the body and the guiding surface of the tongues pull the internal sleeve more strongly towards the contact surface on the external sleeve which would lead to a self-intensifying increase of the gripping force and, hence, of the friction.

The invention will be explained in greater detail below with reference to the accompanying schematical drawing, in which FIG. 1 is a longitudinal section through an arrangement for non-destructive testing of tubes, wherein the tube is guided and supported in two devices constructed in conformity with a preferred embodiment of the present invention,

FIG. 2 is a detailed view on a larger scale of a portion of the tube and the internal sleeve of one of the guide means, partly in section along line Illl in FIG. 3, and

FIG. 3 is a view of the sleeve illustrated in FIG. 2 seen from the right-hand end.

The measuring arrangement depicted in a purely schematical manner in FIG. 1 comprises a stationary housing composed of two axially spaced housing portions 1 arranged inmirror-image relationship to one another, and a rotating, annular measuring head 2 located between and supported by the housing portions. The measuring head 2 may be provided with measuring apparatus (not shown) for measuring, monitoring or otherwise testing a tube -3 shown with dotted lines and being pulled continuously or intermittently through the housing 1,1 past the measuring apparatus. Examples of measuring apparatus in question are described in the co-pending Danish patent application No. 5086/70, for measuring the external and internal diameters and the wall-thickness of the tube and/or for detecting possible defects in the tube.

Tube 3 which is advanced in the direction of arrow 4 in FIG. 1, is supported by two guide means 5 embodying the present invention and mounted at opposite ends of housing 1,1. Each guide means comprises an outer or external sleeve 6'which is immovably secured in the housing portion 1 in question and which, at one end,

has a conical, internal contact surface 7. An inner or internal sleeve 8, which is shown in greater detail in FIGS. 2 and 3 is, throughout the greater part of its length, externally cylindrical with a diameter that makes a tight sliding fit in a bore 9 in the external sleeve 6 behind its conical surface 7. At its foremost end, sleeve 8 is formed with an external conical contact surface 10 which, by preference, is somewhat more slender than surface 7. By way of example, the vertical or apex angle of surface 7 may be approximately 24, while the apex angle of surface 10 is approximately 18. One end of a helical compression spring 11 abuts against the bottom of bore 9 and the other end of the spring abuts against the rear end of sleeve 8, which thus is urged forward to effect engagement between conical surfaces 7 and 10. When the inclinations of these surfaces differ as mentioned above, it will in practice only be the foremost edge of contact surface 10, which may be slightly radiused or chamfered, which engages the internal contact surface 7.

From its foremost, externally conical end, sleeve 8 is slotted by means of a number of incisions 12, totalling nine in the embodiment shown, which extend parallel to the axis of the sleeve and are angularly equispaced, whereby a corresponding number of longitudinal, resilient tongues 13 are formed between the incisions. The foremost end of each tongue is internally formed as a portion of a supporting surface 14 which in the undeformed state of the tongue is circular-cylindrical and the diameter of which corresponds to the nominal diameter of tube 3. Behind surface 14, the internal cavity of the sleeve is radially enlarged so that tube 3 passes unimpededly through this part of the sleeve, in-

eluding a central aperture in its bottom wall which engages with spring 11.

As mentioned above, the solid part of the wall of sleeve 8 behind the bottom of incisions 12 has a tight sliding fit in bore'9 of the external sleeve 6. This ensures an accurate centering of sleeve 8 relative to sleeve 6 and, hence, relative to housing 1 and to the rotating measuring head 2. The evenly. distributed contact surfaces 14 on tongues 13 ensure a correspond ingly accurate centering of tube 3. In order to avoid the risk of tongues 13 jamming in bore 9 in response to an expansion of the tongues it may be expedient to provide the corresponding section of the length of sleeve 8 with a slight clearance relative to bore 9. Since the contact between surfaces 7 and 10 is preferably limited to a circumferential line as a consequence of the difference between the vertical angles of the two surfaces one of said surfaces could be replaced by a stepped cylindrical surface, whose circumferential edge would then engage and interact with an opposed conical surface on the other sleeve.

It is expedient to make the external rigid sleeve 6 of metal and, if the devices are to operate in water, which often is the case with the kind of measurings referred to above, a sufficiently resistant metal should be used, e.g., brass or-stainless steel. The resilient inner sleeve 8 may be fabricated from a suitable plastics material having a relatively low friction coefficient, for example, polytetrafluoroethylene.

Measurings made upon tubes or other rod-shaped bodies supported and guided by devices of the type described above have shown that the centering accuracy of the device is very high even after prolonged periods of use which,'inter alia, is assumed to be connected with the circumstance that the wear on the relatively movable components thereof is relatively slight as only relatively minor spring forces are required to keep the internalv sleeve suitably constrained around the tube and, at the same time, the wear is uniformly distributed over the area of the contact surfaces, both the surfaces on the sleeves themselves and those on the internal sleeve and the rod-shaped body that is advanced through the sleeve.

What we claim is:

1. A device for guiding and supporting a rod-shaped body having a nominally circular cross-section and which is advanced in its longitudinal direction through the device, said device comprising a stationary outer sleeve and an inner sleeve axially displaceable within said outer sleeve, which inner and outer sleeves over a part of their length have opposed cylindrical mating surfaces engaging with a tight sliding fit,

said inner sleeve having at one end thereof an internal, cylindrical or substantially cylindrical contact surface for engagement with the outer surface of said rod-shaped body and an external contact surface inclined with respect to the longitudinal axis of the device,

said'inner sleeve being formed at said end with a plurality of tongues separated by axially extending slits,

said outer sleeve having an inclined internal contact surface for engagement with said inclined external contact surface on said inner sleeve, and spring means between said inner and outer sleeves for urging said inclined external and internal contact surfaces on said sleeves into mutual axial engagement.

2. A device as claimed in claim 1, wherein said inclined internal and external contact surfaces are conical and the vertical angle of the internal surface is greater than the vertical angle of the external contact surface.

3. A device as claimed in claim 2, wherein the vertical angle of the internal surface is approximately 24 and the vertical angle of the external surface is approximately 18.

4. A device as claimed in claim 1, wherein said cylindrical mating surfaces of said inner and outer sleeves extend from the end remote from said slitted end of the inner sleeve and, at least, to the root ends of the tongues.

8. A device as claimed in claim 1, and for supporting a rod-shaped body which is always advanced in one direction only, wherein the slotted end of the inner sleeve is located at the rear end of the device as viewed in the direction of advance.

Claims (8)

1. A device for guiding and supporting a rod-shaped body having a nominally circular cross-section and which is advanced in its longitudinal direction through the device, said device comprising a stationary outer sleeve and an inner sleeve axially displaceable within said outer sleeve, which inner and outer sleeves over a part of their length have opposed cylindrical mating surfaces engaging with a tight sliding fit, said inner sleeve having at one end thereof an internal, cylindrical or substantially cylindrical contact surface for engagement with the outer surface of said rod-shaped body and an external contact surface inclined with respect to the longitudinal axis of the device, said inner sleeve being formed at said end with a plurality of tongues separated by axially extending slits, said outer sleeve having an inclined internal contact surface for engagement with said inclined external contact surface on said inner sleeve, and spring means between said inner and outer sleeves for urging said inclined external and internal contact surfaces on said sleeves into mutual axial engagement.

2. A device as claimed in claim 1, wherein said inclined internal and external contact surfaces are conical and the vertical angle of the internal surface is greater than the vertical angle of the external contact surface.

3. A device as claimed in claim 2, wherein the vertical angle of the internal surface is approximately 24* and the vertical angle of the external surface is approximately 18*.

4. A device as claimed in claim 1, wherein said cylindrical mating surfaces of said inner and outer sleeves extend from the end remote from said slitted end of the inner sleeve and, at least, to the root ends of the tongues.

5. A device as claimed in claim 1, wherein the inner sleeve is formed with an odd number of tongues.

6. A device as claimed in claim 5, wherein the number of tongues is an odd multiple of three, preferably nine.

7. A device as claimed in claim 1, wherein said outer sleeve is made of metal and said inner sleeve is made of a plastics material such as polytetrafluoroethylene.

8. A device as claimed in claim 1, and for supporting a rod-shaped body which is always advanced in one direction only, wherein the slotted end of the inner sleeve is located at the rear end of the device as viewed in the direction of advance.

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