Patent ID: 12228155

DETAILED DESCRIPTION

Referring firstly toFIGS.1and2it can be seen that a stem200in accordance with the present invention comprises three main regions: a proximal cylindrical projection2, a central portion4and a distal head end6. The stem200may be formed as a single unit, or from several elements. In this example, the stem is formed as a single unit of heat-treated medium carbon steel. The three regions of the stem each have different outer diameters. The head6has a larger outer diameter than the central region4. The central region4has a larger outer diameter than the proximal cylindrical projection2. The reason for these different outer diameters will be explained below. The length of the stem200is not relevant to the present invention. Nor is the method by which the stem is gripped for placement of the sealing plug of the present invention.

The proximal cylindrical projection2terminates in an inwardly tapering end8so that the stem may be inserted more easily into a setting tool, as will be explained below. To further aid setting of the plug, the stem, in this example, carries a series of annular grooves10along its axial extent. The annular grooves enable the setting tool efficiently to grip and pull upon the projection2during installation of the plug.

As can be seen fromFIG.3, the stem200is arranged to sit within an outer sleeve12, formed of softer material than that of the stem200. In this example, the sleeve12is formed from annealed aluminium alloy 6061. The sleeve12defines an axis A-A. The stem200defines a second axis, B-B (seeFIG.2).

The sealing plug is formed from the union of the sleeve12and stem200, such that the stem200sits within the sleeve12and is co-axial therewith. InFIG.3, only axis A-A is shown for clarity, but those skilled in the art will appreciate that both axes A-A and B-B are coaxial; in this example, coincident.

Referring toFIG.2, the structure of the central region4can be seen. The central region includes a weakened zone14which, in known manner, provides the location for a stem200to break during its installation process once sufficient axial load is applied thereto. The force at which the stem will break at zone14is dictated predominantly by the radial depth of the zone14, as is apparent to those skilled in the art.

A maximum outer diameter of the central zone4occurs at16. The diameter here is chosen to be at least the same as the inner diameter of sleeve12so that, when the stem200is inserted into the sleeve12, an interference fit exists to hold the stem in place within the sleeve12. This interference fit ensures that the stem200and sleeve12are coaxial and that relative axial movement is avoided as the assembly is handled.

Situated between the zone14and maximum diameter16of the central zone4is tapered region15. This taper15assists with the assembly of the sleeve12onto the stem200. The taper15is radially inward from the maximum diameter16to the weakened region14, the purpose of which is to provide a lead-in to enable the assembly of the sleeve12onto the stem200. This is an assembly aid during formation of the plug (being the combination of the stem200and sleeve12) and plays no part during setting of the sealing plug in use.

Moving axially along B-B from the proximal cylindrical projection end2to the distal head6end of the stem (from the right to the left when viewingFIG.2), the outer diameter of the central region4tapers radially inwardly at 50 to a minimum diameter point18. The purpose of this taper along the central region4will also be explained below. An inner shoulder21is present between the minimum diameter point18and head6. Inner shoulder21is formed as part of the stem head6at its radially inner portion at the junction with the minimum diameter position18. Whilst the inner shoulder21is shown in this example, it is a preferable feature and need not employed. The present invention functions sufficiently even without such a shoulder21, as will be appreciated by those skilled in the art.

Referring now also toFIG.5it can be seen that the stem head6is formed with an annular shoulder20adjacent the central region4. In this example, the shoulder20abuts the inner shoulder21at the minimum diameter point18. The shoulder20sits along a surface22which is inclined at an acute angle, α, to a radius R-R to the axis B-B. The angle α is chosen to be in the range 5°-20°; preferably 10° and 15°. In this example, the angle is 14°. Whatever the angle α, it is chosen to ensure that the annular shoulder20inclination to the radius R-R forms a concave region facing the stem central portion4. In this example, the concave region extends to the outer rim of the shoulder at23. However, it need not extend completely radially from the central axis B-B to the circumferential periphery of the stem head6. This concave region may extend only partially between the axial centre and radial periphery and even in sections therebetween (as opposed to a single, unbroken length). Additionally, the surface20defining this concave region need not be straight. The purpose of this concave region will be explained below.

An isometric view of the stem200can be seen atFIG.4.

Reference now to the series ofFIGS.6-11illustrates how the sealing plug ofFIGS.1-5is set within a blind hole34. In the example shown, the hole34is formed in a workpiece36(such as an hydraulic valve block).

The illustration ofFIG.6shows the complete sealing plug formed from the stem200held within the sleeve12. As discussed above, the stem200is held inside the sleeve12because of the interference fit therebetween, resulting from the choice of outer diameter16of the stem central region4and the inner diameter of the sleeve12.

It can be seen that a radius drawn to the outer diameter of the stem head6, R6, is greater than a radius to the outer diameter, R12, of the sleeve12. This is chosen because, when the plug is inserted into the blind hole34to be sealed, the sleeve12(being made, in this example, from a, relatively, softer aluminium material than the steel of the stem) may be damaged by the material in which the hole is formed during the process of inserting the plug into the hole. This is especially so if the material in which the hole is formed is, say, steel. By ensuring that R6is greater than R12, this risk of sleeve damage is obviated. In the present example, the difference between R6and R12, shown as reference numeral26, is 0.1 mm, but any suitable difference may be employed. As can be seen from the left-hand side ofFIG.6, to aid insertion of the stem head6into the hole (not shown), the end of the head6may be rounded28, or chamfered, so that the head6readily passes into and centralises within, the hole34on insertion thereinto.

Reference now toFIG.7shows the proximal cylindrical projection2being inserted into a nosepiece400of a setting tool600. The setting tool600will not be further described here, as those skilled in the art understand and appreciate how such tools operate in order to set blind sealing plugs. It is sufficient to say that the purpose of the tool600is to grip and then apply an axial force to the projection2, whilst holding the sleeve12against an axial movement, so that movement of the head6relative to and towards the sleeve12occurs. The front face30of nosepiece400is tapered and shown in this example as a convex conical form, as will be explained below.

FIG.8shows the position where the projection2is drawn fully into the tool600via nosepiece400such that the tapered face30abuts the sleeve12. Typically, a vacuum advance mechanism pulls projection2into the tool and holds sleeve12against the face30. The reason for this abutment between the face30and sleeve12is to prevent axial movement of this end of the sleeve12towards the tool600during setting of the plug. The tapered face30of the nosepiece400is arranged to provide a convex conical surface towards the sleeve12. The angle, β, made by the taper relative to the radius, R, of the stem200is between 10°-20°; preferably 14°-16°. In this example, the angle is 15°. This means there is a tapered gap32formed between the face30and sleeve12, the purpose of which will be explained below.

Reference now toFIG.9shows that a front member38of the tool600is formed as an annular shoulder on the nosepiece400and engages with (and contacts) the face of the workpiece36in addition to the tapered face30being in engagement with the sleeve12within the hole34.

In order to set the plug, the tool600applies an axial force to the projection2(towards the right-hand side ofFIG.9), in known manner.

Reference now toFIGS.10(a)-(d)illustrate the consequences of this operation. InFIG.10(a), the slight, commencing, axial force applied by the tool to the stem200is insufficient to move the stem relative to the sleeve12.

Once the force applied by the tool600to the stem200is sufficient to cause relative movement between the stem and the sleeve12, then because the front member38of the nosepiece400of the tool600abuts and is held positively against the workpiece36, relative movement between the tool600and workpiece36is prevented. The only movement permitted, therefore, is that of the stem200within the hole34(towards the right of the figure, as shown by arrow M).

The consequence of this stem200movement is that the stem head6is pulled into engagement with the left-hand side of sleeve12. The initial contact between the stem head6and the sleeve12is that of the inner shoulder21. Because inner shoulder21is formed from the stem head6material (here steel) and due to the material of the sleeve12being softer than this (in this example, the sleeve material being aluminium), then the protruding outer edge of shoulder21penetrates into the end of sleeve12. This sleeve penetration is part of the sealing effect. This is the situation shown inFIG.10(b).

The next contact, shown inFIG.10(c), as the movement of the stem head6continues due to the axial pull force of the setting tool600, is between the stem head6annular outer rim23and the radially outer part of the sleeve12. This again, causes penetration of the stem head6into the sleeve12, as can be seen at reference numeral42. This penetration is also part of the sealing effect.

Concomitant with the above contact between the stem head6and sleeve12, is contact between the other side (right-hand side ofFIG.10) of the sleeve12and tapered face30of nose piece400. Again, because the material of the nose piece400is harder (in this example, hardened steel) than that of the sleeve12, deformation of the right-hand side of the sleeve12occurs. Due to the convex shape of the tapered face30(as seen by the sleeve12), the deformation of the sleeve here causes material flow of the sleeve12to commence from its radially inner portion44(which first contacts the tapered face30) and this sleeve material flow (which is plastic flow) is in a radially outward direction away from the axis B-B. This is shown inFIG.10(d).

It should be understood that the first flow of sleeve material occasioned by movement of the stem200is that caused by the shape of the nose piece taper30. In other words, the radially outward plastic flow of sleeve12material (at the right-hand side of sleeve12) is the first flow. The effect of this is to push the sleeve12material flowing radially outwardly into contact with the inner surface of the hole34, thereby preventing any axial movement of the sleeve12within the hole34at a region labelled35. Any axial slipping of the sleeve12within hole34during the setting process (which has been known to occur in prior art sealing plug setting operations where deformation of the sleeve occurs firstly from the distal end of the sleeve) is to be avoided, as this can compromise the integrity of the finished sealing surface provided at the interface of the sleeve12and the hole34surface.

Continued movement of the stem200toward the setting tool600induces continued flow of sleeve material (which flow has commenced from the right-hand side of sleeve12and progresses from there towards the left-hand side). This hole-filling action is due to the sleeve12contacting the inside surface of hole34progressively from right to left, as the stem head6moves from left to right. The next flow is that of radial expansion (radially outward) due to the sleeve12being squeezed within the hole34between the tapered face30and the stem head6. As axial movement of the sleeve12is not possible at its right-hand end (due to contact with the setting tool nose piece front face30), the material of the sleeve12expands radially to fill the hole34as the sleeve material reaches and contacts the inner surface of hole34at position48.

The final radial movement of the sleeve12is at the left-hand side thereof where it is in contact with the stem head6. The radial movement here, due to the taper50formed on the stem central region4from its maximum diameter to its minimum diameter18, is inwardly towards the axis B-B. It will be appreciated that, as the outer part of the sleeve12is already in contact with the inner part of hole34at both regions35and48, the sleeve material flow at this stage is into the gap52formed between the taper50and inside of sleeve12. This is because of both the taper50and also the angle α of the stem head shoulder20. The combined effect of these two features is to force plastic flow of sleeve material radially inward into gap52and the recess between the surface22and the left-hand end of sleeve12.

The inward radial movement here completes the sealing of the hole34by the sleeve12and continued axial force applied to the stem projection2by the nose piece400causes the strain limit (appreciated by those skilled in the art) to be reached at the breakneck14, at which point the stem projection2snaps, leaving the set plug sealed within the hole34, as shown inFIG.11.

It will be appreciated that the optional addition of an annular projection24, in this example an annular ring formed with an acute peak profile, as shown inFIG.12, may further serve, during the setting operation, to displace sleeve12material both radially outward to seal hole34and radially inwards to seal upon inner shoulder21and taper50. Additionally, the annular projection24may provide an extended sealing surface between the stem head6and the sleeve12end (abutting the stem head6) for enhanced fluid leak resistance.

It will be appreciated by those skilled in the art that the presence of annular projection24is preferable, but not essential, for utility of the present invention. It can be seen that, where present on the shoulder20, annular projection24is for the same purpose as that disclosed in EP-A-1,440,272, namely, so that the annular projection24penetrates into the material of the sleeve12during setting of the sealing plug, thereby to create an additional and effective fluid-tight seal between the head6and sleeve12in the blind hole. Penetration of the annular projection24into the material of the sleeve12is possible due to the material of the head6being harder than that of the sleeve12, as explained above.

During setting of the sealing plug in the example described above, it will be understood that the high axial force (in this example 17.5 kN to seal an 8 mm diameter hole34) applied to the sleeve12by the stem head6results in effective axial containment of the sleeve material within the hole34and the static tapered nose piece30, due to high (radial pressure may peak at 200 MPa and after fracture of the breakneck14, residual stress is of the order 100 MPa) resultant radial stresses. These stresses serve to provide an effective seal between the hole34and the sleeve12and also between the sleeve12and the stem200surfaces (6,50and46) so as to provide a leak-proof plug.

The close fit of the stem head6within the hole34additionally serves to minimise the escape of sleeve12material around the outer rim of the shoulder23. Annular projections, such as24, formed on the inner shoulder21or outer rim23, serve to embed and provide separate sealing features of the stem head6against the sleeve12and thereby prevent leakage through the installed sleeve12bore. Equally the close fit of the nosepiece conical front face30within the hole34limits the escape of sleeve12material around this nosepiece front face30and towards the setting tool600.

Fracture of the breakneck14results in a recoil force acting to urge the remaining stem200portion within the sleeve12towards the left, as indicated by arrow “N” inFIG.12in a manner that is well-known to those skilled in the art. However, the intimate contact formed between the taper50on the stem200and the radially inner compressed sleeve12material which has flowed into gap52ensures that there is no relative axial movement which may serve to reduce the effectiveness of the seal formed between the outer surface of the sleeve12and the hole34. This taper50also serves to preserve the integrity of the seal if the end of the stem200is later subject to accidental impact by an external object or by deliberate tampering.

Whilst in the above examples, the stem200has been shown to carry a series of annular grooves10along its axial extent, there are alternatives available to those skilled in the art. For example, the external surface of the stem200could be formed with a spiral groove. In this case, the nosepiece400of the setting tool600would also carry a complimentary spiral groove for rotational engagement with the external spiral groove of the stem, thereby to enable the tool600to move the stem200relative to the sleeve12, to effect installation of the plug in known manner. Indeed, it will be appreciated that the stem could carry, for example, a female screw thread and the setting tool600a complimentary male one. However, there is also no requirement for the outer surface of the stem to carry any profile at all.

Those skilled in the art will appreciate that the breakneck14is not necessary for the present invention. As an example of an alternative, the tool600may exert a predetermined pull force on the stem200and then be simply detached from the stem. Such is possible by, for example, a spin-pull tool engaging with a spiral groove outer surface formed on the outer surface2.

LIST OF FEATURES

200stem400nosepiece600setting tool2proximal cylindrical projection4central region6distal head end8tapering end of stem10stem annular grooves12sleeve13front tapered region14weakened zone for breakstem15rear tapered region16maximum diameter of central region418minimum diameter of central region20annular shoulder21inner shoulder22surface of shoulder2023outer rim of shoulder24annular projection26diameter difference between head and sleeve28stem head rounding30nosepiece front face32gap between nosepiece and sleeve34blind hole35region of first sleeve material flow36workpiece in which hole34is formed38front member of nosepiece42penetration of head6into sleeve1244sleeve radially inner portion46radially inner part of sleeve1248contact point between hole34and sleeve50internal stem taper52gap between inner of sleeve12and stem taper50