Patent Publication Number: US-2022213916-A1

Title: Sealing plug

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application PCT/EP2020/072908 with an international filing date of Aug. 14, 2020 which claims priority from United Kingdom Patent Application No. GB1916187.6, filed Nov. 7, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to sealing plugs as used in blind installation environments and has particular, although not exclusive, relevance to such unthreaded plugs as may be used in hydraulic fluid sealing and flow control applications. The invention also relates to installation tools for use with these blind sealing plugs and methods of application of such plugs. Blind installation means that access to a hole in which the sealing plug is to be inserted (and provide fluid-tight sealing therefor) is only possible from one side. 
     BACKGROUND OF THE INVENTION 
     Blind sealing plugs generally operate on the principle of radial expansion of material within the blind hole. The radial expansion of the plug blocks the hole thereby to prevent fluid flow past the sealed plug. There are generally two types of expansion actuation: pushing and pulling. In each case, a relatively harder material than that which expands within the hole is used to cause the relatively soft, expanding material to flow radially outwards within the hole. With the pushing method, the pusher is sometimes removed from the hole after the plug has been set; whereas, with the pulling method, the puller is captive within the hole after setting. This usually means the puller has some form of structural weakness formed therein so that it fractures under a defined load thereby separating the puller from that which actuates it, thus leaving the plug within the hole. 
     An example of a known pulling type of sealing plug is disclosed in EP-A-1,440,272. This discloses a form of sealing plug constructed from a sleeve held around a stem. The stem has a head formed from material which is relatively harder than the material of the sleeve. The head carries an annular projection for penetration into the sleeve material on setting of the plug within a blind hole. The annular projection, once set within the sleeve, provides a fluid-tight seal between the head and the sleeve of the plug when set within the hole. 
     Whilst this type of sealing plug functions effectively, it has been found that its construction may be improved upon in order to provide a plug whose characteristics for setting within the blind hole are more controlled such that a progressive hole-filling action by the deforming sleeve is achieved and that the sleeve has no propensity to move axially within the hole during setting, as could be the case with known sealing plugs. This would also permit better containment of the sleeve material as it would be forced against the hole surface during setting and so be able to resist very high pressures, such as oil at over  1 , 600  bar, without the seal being ejected from the hole. 
     It is an object of the present invention to provide a sealing plug which overcomes these disadvantages and to provide a stem which is better retained within the sleeve both during the setting operation and thereafter. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides, in one of its aspects, a sealing plug for blind installation within a suitable hole, thereby to plug and seal the hole, the sealing plug comprising: a generally cylindrical hollow sleeve defining a first axis and having a given outer diameter; a stem comprising a proximal cylindrical projection, a distal head and a central portion located between the proximal cylindrical projection and the distal head, the stem head having an outer diameter which is greater than the outer diameter of the central portion, and wherein the outer diameter of the central portion is greater than the outer diameter of the stem proximal cylindrical projection, and wherein the stem defines a second axis; the stem head being formed of a material which is harder than the material of the sleeve; the stem central portion, when within the sleeve, is arranged to be held therewithin by frictional engagement between an outer part of the stem central portion and an inner part of the sleeve such that the first and second axes are co-axial; the sealing plug characterised in that the outer diameter of the stem central portion tapers in the direction from the stem proximal cylindrical projection to the stem distal head, with respect to the axis of the stem, to a minimum central portion diameter at the point where the stem central portion meets the stem head. 
     Preferably the stem head has an annular shoulder adjacent the stem central portion, which annular shoulder is inclined at an acute angle relative to a radius to the second axis. This aids control of radial flow of sleeve material during setting of the plug. 
     In a preferred embodiment the annular shoulder inclination forms a concave region facing the stem central portion. This again aids with material flow during setting of the sealing plug. 
     Preferably the shoulder angle of inclination relative to a radius to the second axis is between 5° and 25°, more preferably between 10° and 15° and even more preferably the shoulder angle of inclination is 14°. 
     Advantageously the stem head has formed thereon an annular protrusion facing the stem central portion. This annular protrusion, which may be in the form of a projecting ring, may be arranged to engage with the hollow sleeve. This provides a better fluid-tight seal between the stem head and the sleeve than if no such annular protrusion were present. 
     In another aspect, the present invention provides a method of setting a sealing plug, as defined above and in the appendant claims. 
     Other features of the invention are also set out in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A specific embodiment of the present invention will now be described, by way of example only and with reference to the accompanying drawings, of which: 
         FIG. 1  shows an axial section through a stem of a sealing plug in accordance with the present invention. 
         FIG. 2  shows a detailed view, at enlarged portion A, of  FIG. 1 . 
         FIG. 3  shows a section through an unset sealing plug in accordance with the present invention therein. 
         FIG. 4  shows an isometric view of the stem of  FIG. 1 . 
         FIG. 5  shows a detailed section, at enlarged portion D, of the stem head  FIG. 1 . 
         FIG. 6  illustrates schematically a complete sealing plug before installation. 
         FIG. 7  illustrates schematically the sealing plug of  FIG. 6  when starting to be introduced into a setting tool. 
         FIG. 8  shows the commencement of installation of the sealing plug by the setting tool. 
         FIG. 9  shows the illustration of  FIG. 8  in sectional detail. 
         FIGS. 10( a )-( d )  illustrate schematically the sequential stages of installing of a sealing plug in accordance with the present invention. 
         FIG. 11  shows the installed sealing plug. 
         FIG. 12  shows an alternative stem head in accordance with the present invention including an annular projecting ring. 
     
    
    
     DETAILED DESCRIPTION 
     Referring firstly to  FIGS. 1 and 2  it can be seen that a stem  200  in accordance with the present invention comprises three main regions: a proximal cylindrical projection  2 , a central portion  4  and a distal head end  6 . The stem  200  may 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 head  6  has a larger outer diameter than the central region  4 . The central region  4  has a larger outer diameter than the proximal cylindrical projection  2 . The reason for these different outer diameters will be explained below. The length of the stem  200  is 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 projection  2  terminates in an inwardly tapering end  8  so 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 grooves  10  along its axial extent. The annular grooves enable the setting tool efficiently to grip and pull upon the projection  2  during installation of the plug. 
     As can be seen from  FIG. 3 , the stem  200  is arranged to sit within an outer sleeve  12 , formed of softer material than that of the stem  200 . In this example, the sleeve  12  is formed from annealed aluminium alloy 6061. The sleeve  12  defines an axis A-A. The stem  200  defines a second axis, B-B (see  FIG. 2 ). 
     The sealing plug is formed from the union of the sleeve  12  and stem  200 , such that the stem  200  sits within the sleeve  12  and is co-axial therewith. In  FIG. 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 to  FIG. 2 , the structure of the central region  4  can be seen. The central region includes a weakened zone  14  which, in known manner, provides the location for a stem  200  to break during its installation process once sufficient axial load is applied thereto. The force at which the stem will break at zone  14  is dictated predominantly by the radial depth of the zone  14 , as is apparent to those skilled in the art. 
     A maximum outer diameter of the central zone  4  occurs at  16 . The diameter here is chosen to be at least the same as the inner diameter of sleeve  12  so that, when the stem  200  is inserted into the sleeve  12 , an interference fit exists to hold the stem in place within the sleeve  12 . This interference fit ensures that the stem  200  and sleeve  12  are coaxial and that relative axial movement is avoided as the assembly is handled. 
     Situated between the zone  14  and maximum diameter  16  of the central zone  4  is tapered region  15 . This taper  15  assists with the assembly of the sleeve  12  onto the stem  200 . The taper  15  is radially inward from the maximum diameter  16  to the weakened region  14 , the purpose of which is to provide a lead-in to enable the assembly of the sleeve  12  onto the stem  200 . This is an assembly aid during formation of the plug (being the combination of the stem  200  and sleeve  12 ) and plays no part during setting of the sealing plug in use. 
     Moving axially along B-B from the proximal cylindrical projection end  2  to the distal head  6  end of the stem (from the right to the left when viewing  FIG. 2 ), the outer diameter of the central region  4  tapers radially inwardly at 50 to a minimum diameter point  18 . The purpose of this taper along the central region  4  will also be explained below. An inner shoulder  21  is present between the minimum diameter point  18  and head  6 . Inner shoulder  21  is formed as part of the stem head  6  at its radially inner portion at the junction with the minimum diameter position  18 . Whilst the inner shoulder  21  is shown in this example, it is a preferable feature and need not employed. The present invention functions sufficiently even without such a shoulder  21 , as will be appreciated by those skilled in the art. 
     Referring now also to  FIG. 5  it can be seen that the stem head  6  is formed with an annular shoulder  20  adjacent the central region  4 . In this example, the shoulder  20  abuts the inner shoulder  21  at the minimum diameter point  18 . The shoulder  20  sits along a surface  22  which 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 shoulder  20  inclination to the radius R-R forms a concave region facing the stem central portion  4 . In this example, the concave region extends to the outer rim of the shoulder at  23 . However, it need not extend completely radially from the central axis B-B to the circumferential periphery of the stem head  6 . 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 surface  20  defining this concave region need not be straight. The purpose of this concave region will be explained below. 
     An isometric view of the stem  200  can be seen at  FIG. 4 . 
     Reference now to the series of  FIGS. 6-11  illustrates how the sealing plug of  FIGS. 1-5  is set within a blind hole  34 . In the example shown, the hole  34  is formed in a workpiece  36  (such as an hydraulic valve block). 
     The illustration of  FIG. 6  shows the complete sealing plug formed from the stem  200  held within the sleeve  12 . As discussed above, the stem  200  is held inside the sleeve  12  because of the interference fit therebetween, resulting from the choice of outer diameter  16  of the stem central region  4  and the inner diameter of the sleeve  12 . 
     It can be seen that a radius drawn to the outer diameter of the stem head  6 , R 6 , is greater than a radius to the outer diameter, R 12 , of the sleeve  12 . This is chosen because, when the plug is inserted into the blind hole  34  to be sealed, the sleeve  12  (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 R 6  is greater than R 12 , this risk of sleeve damage is obviated. In the present example, the difference between R 6  and R 12 , shown as reference numeral  26 , is 0.1 mm, but any suitable difference may be employed. As can be seen from the left-hand side of  FIG. 6 , to aid insertion of the stem head  6  into the hole (not shown), the end of the head  6  may be rounded  28 , or chamfered, so that the head  6  readily passes into and centralises within, the hole  34  on insertion thereinto. 
     Reference now to  FIG. 7  shows the proximal cylindrical projection  2  being inserted into a nosepiece  400  of a setting tool  600 . The setting tool  600  will 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 tool  600  is to grip and then apply an axial force to the projection  2 , whilst holding the sleeve  12  against an axial movement, so that movement of the head  6  relative to and towards the sleeve  12  occurs. The front face  30  of nosepiece  400  is tapered and shown in this example as a convex conical form, as will be explained below. 
       FIG. 8  shows the position where the projection  2  is drawn fully into the tool  600  via nosepiece  400  such that the tapered face  30  abuts the sleeve  12 . Typically, a vacuum advance mechanism pulls projection  2  into the tool and holds sleeve  12  against the face  30 . The reason for this abutment between the face  30  and sleeve  12  is to prevent axial movement of this end of the sleeve  12  towards the tool  600  during setting of the plug. The tapered face  30  of the nosepiece  400  is arranged to provide a convex conical surface towards the sleeve  12 . The angle, β, made by the taper relative to the radius, R, of the stem  200  is between 10°-20°; preferably 14°-16°. In this example, the angle is 15°. This means there is a tapered gap  32  formed between the face  30  and sleeve  12 , the purpose of which will be explained below. 
     Reference now to  FIG. 9  shows that a front member  38  of the tool  600  is formed as an annular shoulder on the nosepiece  400  and engages with (and contacts) the face of the workpiece  36  in addition to the tapered face  30  being in engagement with the sleeve  12  within the hole  34 . 
     In order to set the plug, the tool  600  applies an axial force to the projection  2  (towards the right-hand side of  FIG. 9 ), in known manner. 
     Reference now to  FIGS. 10( a )-( d )  illustrate the consequences of this operation. In  FIG. 10( a ) , the slight, commencing, axial force applied by the tool to the stem  200  is insufficient to move the stem relative to the sleeve  12 . 
     Once the force applied by the tool  600  to the stem  200  is sufficient to cause relative movement between the stem and the sleeve  12 , then because the front member  38  of the nosepiece  400  of the tool  600  abuts and is held positively against the workpiece  36 , relative movement between the tool  600  and workpiece  36  is prevented. The only movement permitted, therefore, is that of the stem  200  within the hole  34  (towards the right of the figure, as shown by arrow M). 
     The consequence of this stem  200  movement is that the stem head  6  is pulled into engagement with the left-hand side of sleeve  12 . The initial contact between the stem head  6  and the sleeve  12  is that of the inner shoulder  21 . Because inner shoulder  21  is formed from the stem head  6  material (here steel) and due to the material of the sleeve  12  being softer than this (in this example, the sleeve material being aluminium), then the protruding outer edge of shoulder  21  penetrates into the end of sleeve  12 . This sleeve penetration is part of the sealing effect. This is the situation shown in  FIG. 10( b ) . 
     The next contact, shown in  FIG. 10( c ) , as the movement of the stem head  6  continues due to the axial pull force of the setting tool  600 , is between the stem head  6  annular outer rim  23  and the radially outer part of the sleeve  12 . This again, causes penetration of the stem head  6  into the sleeve  12 , as can be seen at reference numeral  42 . This penetration is also part of the sealing effect. 
     Concomitant with the above contact between the stem head  6  and sleeve  12 , is contact between the other side (right-hand side of  FIG. 10 ) of the sleeve  12  and tapered face  30  of nose piece  400 . Again, because the material of the nose piece  400  is harder (in this example, hardened steel) than that of the sleeve  12 , deformation of the right-hand side of the sleeve  12  occurs. Due to the convex shape of the tapered face  30  (as seen by the sleeve  12 ), the deformation of the sleeve here causes material flow of the sleeve  12  to commence from its radially inner portion  44  (which first contacts the tapered face  30 ) and this sleeve material flow (which is plastic flow) is in a radially outward direction away from the axis B-B. This is shown in  FIG. 10( d ) . 
     It should be understood that the first flow of sleeve material occasioned by movement of the stem  200  is that caused by the shape of the nose piece taper  30 . In other words, the radially outward plastic flow of sleeve  12  material (at the right-hand side of sleeve  12 ) is the first flow. The effect of this is to push the sleeve  12  material flowing radially outwardly into contact with the inner surface of the hole  34 , thereby preventing any axial movement of the sleeve  12  within the hole  34  at a region labelled  35 . Any axial slipping of the sleeve  12  within hole  34  during 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 sleeve  12  and the hole  34  surface. 
     Continued movement of the stem  200  toward the setting tool  600  induces continued flow of sleeve material (which flow has commenced from the right-hand side of sleeve  12  and progresses from there towards the left-hand side). This hole-filling action is due to the sleeve  12  contacting the inside surface of hole  34  progressively from right to left, as the stem head  6  moves from left to right. The next flow is that of radial expansion (radially outward) due to the sleeve  12  being squeezed within the hole  34  between the tapered face  30  and the stem head  6 . As axial movement of the sleeve  12  is not possible at its right-hand end (due to contact with the setting tool nose piece front face  30 ), the material of the sleeve  12  expands radially to fill the hole  34  as the sleeve material reaches and contacts the inner surface of hole  34  at position  48 . 
     The final radial movement of the sleeve  12  is at the left-hand side thereof where it is in contact with the stem head  6 . The radial movement here, due to the taper  50  formed on the stem central region  4  from its maximum diameter to its minimum diameter  18 , is inwardly towards the axis B-B. It will be appreciated that, as the outer part of the sleeve  12  is already in contact with the inner part of hole  34  at both regions  35  and  48 , the sleeve material flow at this stage is into the gap  52  formed between the taper  50  and inside of sleeve  12 . This is because of both the taper  50  and also the angle α of the stem head shoulder  20 . The combined effect of these two features is to force plastic flow of sleeve material radially inward into gap  52  and the recess between the surface  22  and the left-hand end of sleeve  12 . 
     The inward radial movement here completes the sealing of the hole  34  by the sleeve  12  and continued axial force applied to the stem projection  2  by the nose piece  400  causes the strain limit (appreciated by those skilled in the art) to be reached at the breakneck  14 , at which point the stem projection  2  snaps, leaving the set plug sealed within the hole  34 , as shown in  FIG. 11 . 
     It will be appreciated that the optional addition of an annular projection  24 , in this example an annular ring formed with an acute peak profile, as shown in  FIG. 12 , may further serve, during the setting operation, to displace sleeve  12  material both radially outward to seal hole  34  and radially inwards to seal upon inner shoulder  21  and taper  50 . Additionally, the annular projection  24  may provide an extended sealing surface between the stem head  6  and the sleeve  12  end (abutting the stem head  6 ) for enhanced fluid leak resistance. 
     It will be appreciated by those skilled in the art that the presence of annular projection  24  is preferable, but not essential, for utility of the present invention. It can be seen that, where present on the shoulder  20 , annular projection  24  is for the same purpose as that disclosed in EP-A-1,440,272, namely, so that the annular projection  24  penetrates into the material of the sleeve  12  during setting of the sealing plug, thereby to create an additional and effective fluid-tight seal between the head  6  and sleeve  12  in the blind hole. Penetration of the annular projection  24  into the material of the sleeve  12  is possible due to the material of the head  6  being harder than that of the sleeve  12 , 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 hole  34 ) applied to the sleeve  12  by the stem head  6  results in effective axial containment of the sleeve material within the hole  34  and the static tapered nose piece  30 , due to high (radial pressure may peak at 200 MPa and after fracture of the breakneck  14 , residual stress is of the order 100 MPa) resultant radial stresses. These stresses serve to provide an effective seal between the hole  34  and the sleeve  12  and also between the sleeve  12  and the stem  200  surfaces ( 6 ,  50  and  46 ) so as to provide a leak-proof plug. 
     The close fit of the stem head  6  within the hole  34  additionally serves to minimise the escape of sleeve  12  material around the outer rim of the shoulder  23 . Annular projections, such as  24 , formed on the inner shoulder  21  or outer rim  23 , serve to embed and provide separate sealing features of the stem head  6  against the sleeve  12  and thereby prevent leakage through the installed sleeve  12  bore. Equally the close fit of the nosepiece conical front face  30  within the hole  34  limits the escape of sleeve  12  material around this nosepiece front face  30  and towards the setting tool  600 . 
     Fracture of the breakneck  14  results in a recoil force acting to urge the remaining stem  200  portion within the sleeve  12  towards the left, as indicated by arrow “N” in  FIG. 12  in a manner that is well-known to those skilled in the art. However, the intimate contact formed between the taper  50  on the stem  200  and the radially inner compressed sleeve  12  material which has flowed into gap  52  ensures that there is no relative axial movement which may serve to reduce the effectiveness of the seal formed between the outer surface of the sleeve  12  and the hole  34 . This taper  50  also serves to preserve the integrity of the seal if the end of the stem  200  is later subject to accidental impact by an external object or by deliberate tampering. 
     Whilst in the above examples, the stem  200  has been shown to carry a series of annular grooves  10  along its axial extent, there are alternatives available to those skilled in the art. For example, the external surface of the stem  200  could be formed with a spiral groove. In this case, the nosepiece  400  of the setting tool  600  would also carry a complimentary spiral groove for rotational engagement with the external spiral groove of the stem, thereby to enable the tool  600  to move the stem  200  relative to the sleeve  12 , 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 tool  600  a 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 breakneck  14  is not necessary for the present invention. As an example of an alternative, the tool  600  may exert a predetermined pull force on the stem  200  and 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 surface  2 . 
     LIST OF FEATURES 
     
         
           200  stem 
           400  nosepiece 
           600  setting tool 
           2  proximal cylindrical projection 
           4  central region 
           6  distal head end 
           8  tapering end of stem 
           10  stem annular grooves 
           12  sleeve 
           13  front tapered region 
           14  weakened zone for breakstem 
           15  rear tapered region 
           16  maximum diameter of central region  4   
           18  minimum diameter of central region 
           20  annular shoulder 
           21  inner shoulder 
           22  surface of shoulder  20   
           23  outer rim of shoulder 
           24  annular projection 
           26  diameter difference between head and sleeve 
           28  stem head rounding 
           30  nosepiece front face 
           32  gap between nosepiece and sleeve 
           34  blind hole 
           35  region of first sleeve material flow 
           36  workpiece in which hole  34  is formed 
           38  front member of nosepiece 
           42  penetration of head  6  into sleeve  12   
           44  sleeve radially inner portion 
           46  radially inner part of sleeve  12   
           48  contact point between hole  34  and sleeve 
           50  internal stem taper 
           52  gap between inner of sleeve  12  and stem taper  50