Abstract:
A plug for use in sealing a hole and surrounding surfaces of a substrate while a coating is being applied to that substrate. The plug comprises a shank provided with a head and a blind bore extending through its centre. The head includes a gripping portion for restraining the plug during installation and a sealing portion configured to bear against the substrate. The shank can be temporarily elongated so as to reduce its diameter enabling installation in the hole. Once the shank is in the hole of the substrate, the plug can be returned to its pre-elongated shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from European Patent Application No. 14306483.0, filed on Sep. 25, 2014, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a plug for temporarily sealing a hole and the surrounding area of a substrate. More particularly, the invention relates to a plug for maintaining the electrically conductive surface of the substrate while said substrate is being finished. 
         [0003]    In many industries, electrical components and cables must be electrically and mechanically connected to large substrates. For instance, sensors must be connected to fuselages of aircraft, earthing cables must be connected to the rails of railroads, and so forth. Elaborate connecting devices are available for suitably connecting components and cables to such large substrates, and which typically comprise an electrically conductive body mechanically fastened to a hole within the substrate and defining a threaded bore to which the component or cable can be fastened. However, the integrity of electrical connections is reliant on the clean contact surface of the substrate, the connecting devices and the components themselves. Many substrates are finished with paint or alternative coatings which have poor electrical conductivity and thus affect the integrity of the electrical connection between the substrate and the connecting device, or the connecting device and the components depending on whether the paint is applied before or after the fitting of the connecting device. It is therefore necessary to ensure that the critical contact surfaces of the substrate and connecting device (if fitted before painting) are free from paint. 
         [0004]    Some plugs have been proposed previously for this particular application, but they have proven to be ineffective at preserving the integrity of the electrically conductive surface. Plugs have also been proposed for other applications, but they too have lacked the characteristics required of a plug that must provide a good seal and must be suitable for temporary installation. 
         [0005]    The present invention seeks to solve the shortcomings associated with existing plugs. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the invention, there is provided a plug for temporary location in a hole formed in an electrically conductive body so as to conceal the hole and surrounding surfaces when applying a coating to said body, the plug comprising: 
         [0007]    a shank having front and rear ends and made from an elastically deformable material; 
         [0008]    a head provided on the rear end of the shank and defining an opening; 
         [0009]    a bore extending axially from the opening in the head towards the front end of the shank, 
         [0010]    characterised in that the head comprises a sealing portion proximal to the shank and a gripping portion distal to the shank. 
         [0011]    In a preferred arrangement, the sealing portion may comprise a flange extending radially from the shank. Advantageously, the flange may be circular, but may also be polygonal or even an irregular shape. The flange may define a forward facing contact area at least partway around the shank and which may occupy the whole area of the flange or perhaps an area of the flange distal from the shank. The purpose of the forward facing contacting area is to provide a suitable seal between the plug and the electrically conductive body in the vicinity of the hole. 
         [0012]    Typically, the flange may have front and rear faces, which may be arranged generally opposite each other. The front face may be concaved and or the rear face may be convex. The concave and convex front and rear faces may be domed or conical. The concaved front face results in the portion of the flange distal from the shank being the most forward portion of the flange, which is a required characteristic of the forward facing contact area. Furthermore, the flange may include a peripheral face extending at least partway therearound and preferably the full way therearound. In this manner, the peripheral face may interface the front and rear faces of the flange. 
         [0013]    In one embodiment, the contact area comprises an annular edge defined between the front face and the peripheral face. A contact area of that nature may be rather narrow and may require the surface against which it bears to be smooth in order to create an effective seal. 
         [0014]    In an alternative embodiment, the peripheral face is rounded and defines the forward facing contact area. This contact area may be preferable as the rounded face may deform slightly to create a wider contact area and thus a potentially better seal. 
         [0015]    Turning now to the gripping portion, that may comprise an abutment surface, which is at least partially forward facing and engageable by a tool for urging the plug rearwardly. An advantageous feature of the invention is to enable the plug to be restrained as the shank is being urged forward; the abutment surface lends itself well to that purpose. The gripping portion may comprise a narrow first part adjacent the sealing portion and a wider second part distal from the sealing portion, the abutment surface being defined between the first and second parts. The abutment surface may comprise a step such that it is mostly forward facing or a taper such that it is less forward facing. 
         [0016]    The forward facing abutment surface can be achieved in various ways. The abutment surface may comprise one facet or multiple facets spaced around the head. The abutment surface may be a continuous surface extending around the head. Most important is that the abutment surface can be suitably gripped to enable the plug to be restrained. 
         [0017]    In a second aspect of the invention there is provided a tool for installing a plug, such as that described above. The tool comprises: 
         [0018]    a body having front and rear ends and a chamber extending therealong; 
         [0019]    a receiver provided on the front end of the body and configured to engage the gripping portion of the plug; 
         [0020]    a plunger disposed in the chamber and moveable therealong; and 
         [0021]    a needle provided on the plunger and extending through an aperture in the body. 
         [0022]    Advantageously, a spring acts between the plunger and the body to urge the plunger and thus the needle rearwardly. This assists the operator in withdrawing the needle who need only release the plunger and allow it assume its normal position under the bias of the coil spring. 
         [0023]    The tool may also include handles that are suitably positioned and shaped to facilitate use by the operator. The handles may be provided on the body and, depending on the size of the tool, may be configured to be gripped by two fingers. For instance, the handles may extend outwardly from opposed sides of the body. 
         [0024]    The receiver should be shaped and sized to accommodate the gripping portion of the plug for which the tool is intended. The main purpose of the receiver is to hold the plug steady and to restrict axial movement of the plug, particularly in the forward direction. 
         [0025]    According to a further aspect of the invention, there is provided a method of inserting the above described plug into a hole of a substrate or a connecting device, the method comprising the steps of: 
         [0026]    selecting a plug having a shank with a diameter larger than that of the hole; 
         [0027]    inserting a needle in to the bore of the plug; 
         [0028]    elongating the shank by driving the needle forwards and urging the gripping portion rearwards; 
         [0029]    locating the elongated shank of the plug in the hole and arranging the sealing portion against the substrate or the connecting device; and 
         [0030]    withdrawing the needle from the hole so as to enable the shank to attempt to return to its pre-elongated shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    By way of example only, one embodiment of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
           [0032]      FIG. 1  is a cross-sectional view of a prior art connecting device suitable for connecting an electrical terminal to a substrate; 
           [0033]      FIG. 2  is a side plan with partial cross section view corresponding to  FIG. 1 , but showing the prior art connecting device and a prior art electrical conductor and a screw in a preassembled arrangement; 
           [0034]      FIG. 3  is a perspective view of the plug according to the invention, which is configured for insertion into the connecting device of  FIGS. 1 and 2 . 
           [0035]      FIG. 4  is a vertical cross-sectional view of the plug shown in  FIG. 3 ; 
           [0036]      FIG. 5  is a vertical cross-sectional view of an alternative plug 
           [0037]      FIG. 6  shows a perspective view of a tool for inserting the plug into the connecting device; 
           [0038]      FIG. 7  shows a longitudinal cross-sectional view of the tool shown in  FIG. 6 ; and 
           [0039]      FIGS. 8A to 8G  show the plug of  FIGS. 3 to 5  being inserted into a connection device of  FIGS. 1 and 2  using the tool of  FIGS. 6 and 7 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    With reference to  FIGS. 1 and 2 , there is shown a prior art connecting device  1  adapted for mechanically and electrically connecting an electrical conductor  5  to a substrate  3  having a hole  2  formed therethrough. For instance, the electrical conductor  5  may comprise an earthing terminal, a sensor or the like and the substrate may include an aircraft fuselage, the rail of a railroad or the like. 
         [0041]    Connecting devices  1  may take many forms depending on their particular application, though generally they include a main body  4  having a first outer portion  4   b  arranged to be securely located in the hole  2  of the substrate  3  and a second inner portion  4   a  defining a threaded hole. The main body  4  of the exemplary connecting device  1  is provided with a flange  9  extending radially from one end of the main body and configured to bear against a face of the substrate  3 . The connecting device  1  cooperates with a screw  6  having a radially enlarged head  6   a  and a threaded shank  6   b  arranged to engage the threaded hole  4   a.  The electrical conductor  5  includes a generally planar portion  5   b  provided with a through hole  5   a  sized to enable the threaded shank  6   b  of the bolt  6  to pass therethrough. The planar portion  5   b  may be clamped between the flange  9  of the main body  4  and the head  6   a  of the screw  6 , the main body and screw being formed from an electrically conductive material so as to promote the flow of electrical current between the electrical conductor  5  and the substrate  3 . 
         [0042]    Referring now to  FIGS. 3 and 4 , there is provided a novel plug, generally indicated  10 , which comprises a shank  11  having a front end  12  defining a tip  13  and a rear end  14  provided with a head  15 . The shank  11  is generally cylindrical and the tip  13  may be domed or conical. The shank  11  is made from an elastically deformable material operable to permit the shank to axial stretch while radially narrowing. The head includes a sealing portion  16  proximal to the tip  13  and a gripping portion  17  distal to the tip  13 . 
         [0043]    The sealing portion  16  comprises a circular disc extending radially from the shank  11  and having a front face  20 , a rear face  21  and a circumferential periphery  22 . In one arrangement ( FIGS. 3 and 4 ), the front face  20  is generally concaved, the rear face  21  is generally convex and the circumferential periphery  22  is rounded. The rounded circumferential periphery  22  defines an annular contact surface  23  which is the most forward part of the sealing portion  16 . In an alternative arrangement ( FIG. 5 ), the front and rear faces  20 ,  21  are slightly conical so as to extend forward from the shank  11 . The circumferential periphery  22  is angled relative to the shank  11  and defines in combination with the front face  20  an annular contact edge  24  which is the most forward part of the sealing portion. In both arrangements, the front face  20  is profiled so as to form a cavity. 
         [0044]    The gripping portion  17  includes a narrow part  26  proximal to the sealing portion  16  and a wide part  27  distal to the sealing portion  16 , between those parts there being defined a shoulder  28  which may be stepped, tapered or otherwise formed. The narrow part  26  and the wide part  27  both have circular cross-sections. 
         [0045]    The plug  10  includes a bore  30  formed axially therein, the bore extending from an opening  31  in the centre of the rear end  14  towards a point near the centre of the front end  12 . The length of the bore  30  extends through a large proportion of the shank  11  and terminates a small distance from the front end  12 . The bore  30  may have a circular cross-section with a generally uniform diameter. Most of the shank  11  is generally tubular and as such has an annular wall, which may have a substantially uniform thickness along its length. 
         [0046]    Referring now to  FIGS. 6 and 7 , there is shown a tool  40  for manipulating the plug  10 . The tool  40  comprises a body portion  41  having two arms  42  extending outwardly from a pair of opposed side walls  43 . The arms  42  are arcuate such that their end portions extend forward and define in combination with the side walls  43  of the body portion  41  a pair of curved forward facing finger pads  44  to be gripped by the operator. The body portion  41  includes a rear most portion  45  extending rearward of the arms  42  and which is adapted to support a coil spring  46 , to be discussed further below. The body portion  41  also includes a front most part  48  extending forward of the arms  42  and provided with a receiver  50  for holding a single plug  10 . The receiver  50  comprises a circumferential wall  52  enclosing a receiving space  51  and having a free edge provided with an inwardly turned lip. A portion of the circumferential wall  52  is removed so as to provide lateral access to the receiving space  51 . An elongate chamber  55  is formed in the body portion  41  and extends from an opening  56  in the end face of the rear most part  45  towards an aperture  57  in the front most part  48 . 
         [0047]    A plunger  60  is disposed in the chamber  55  and arranged for sliding movement therealong. The rear end of the plunger  60  has an end plate  61  which extends outwardly beyond the body portion  41  and terminates in a small forward facing rim  62 . The plunger  60 , the end plate  61  and the rim  62  collectively define a shallow annular recess in which a free end of the coil spring  46  locates. The front end of the plunger  60  is furnished with a needle  65  which extends through the aperture  57  formed in the front most part of the body portion  41 . 
         [0048]    Use of the tool  40  to insert a plug  10  into a connecting device  4  will now be described with reference to  FIGS. 8A to 8G . 
         [0049]      FIG. 8A  shows the tool  40  arranged to receive a plug  10 . It should be noted that at this point the shank  11  of the plug  10  is too wide to be located in the connecting device  1 . 
         [0050]      FIG. 8B  shows the plug  10  located in the receiver  50  of the tool  40 . In particular, the gripping portion  17  of the plug  10  is accommodated in the receiving space  51  such that the shoulder  28  of the head  15  bears against the lip of the circumferential wall  52 . Since the plug  10  and the tool  40  are arranged coaxially, the needle  65  of the tool is aligned with the opening  31  of the bore  30 . 
         [0051]    Referring now to  FIG. 8C , the plunger  60  is then pressed into the chamber  55  so as to cause the needle  65  to extend into the bore  30  of the plug  10 . The operator may achieve this by positioning the end plate  61  in the palm of his hand, placing two fingers on the two finger pads  44  and gently closing his hand so as to urge the plunger  60 , against the bias of the coil spring  46 , further into the chamber  55 . As the plunger  60  sinks further into the chamber  55 , the needle  65  engages the bottom of the bore  30  and continued extension of the needle  65  begins to elongate the shank  11 . As the shank  11  elongates, its width begins to reduce to the extent that it then becomes smaller than the width of the bore  30  of connecting device  1 . 
         [0052]      FIG. 8D  shows the tool  40  and plug  10  presented to the connecting device  1 . 
         [0053]      FIG. 8E  shows the plug  10  inserted into the connecting device  1 , such that the shank  11  extends fully through the hole and the contact surface of the sealing portion  16  engages the flange  1   b  of the connecting device  1 . The plug  10  can be urged firmly against the connecting device  1  such that the rounded peripheral face  22  may flatten to increase the width of the contact surface  23  and thus create an improve seal. This will further restrict the flow of paint into the critical area and help maintain the integrity of the connecting device  1 . 
         [0054]    In  FIG. 8F , the pressure on the end plate  61  has been removed and the plunger  60  extends upwardly from the chamber  55  under the bias of the coil spring  46 . Withdrawal of the needle  65  allows the elasticity of the plug  10  material to attempt to return the shank  11  to its normal shape. In so doing, the diameter of the front most portion of the shank  11  which extends beyond the connecting device  1  becomes greater than the diameter of the bore of the connecting device  1 . This prevents removal of the plug  10  from the connecting device  1  while also sealing the hole and the flange  1   b  of the connecting device  1 . The remainder of the shank  11  located in the hole of the connecting device  1  will also widen, but to a lesser extent since it is limited by the width of the hole. Nevertheless, as the remainder of the shank widens it bears firmly against the surface of the hole so as to prevent paint flowing therealong. 
         [0055]    Finally, as shown in  FIG. 8G , the tool  40  may be removed from the plug  10 . This may be achieved by moving the tool  40  laterally to enable the receiver  50  to move clear of the gripping portion  17 . 
         [0056]    In the event that the connecting device  1  is to be fitted after the substrate  3  has been painted, it will instead be necessary to protect the substrate  3  rather than the connecting device  1 . The plug  10  may be used to protect the substrate  3  in the same way as has been described above for protecting the connecting device  1 , the only difference being that a suitably sized plug must be selected for the larger hole  2  in the substrate. 
         [0057]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.