GB2447056A - Polymeric grommet with waist - Google Patents

Abstract

A generally annular grommet has a through hole 18 and a waist 14, and is made of a foamed polymer (such as foamed polyurethane) having a density between 0.1 and 1 g/cm<3>. The waist preferably defines surfaces above and below it. A slot 20 from the through hole to the outside allows the grommet to be fitted around a cable or conductor. Preferably the part above the waist forms a dome 12. The through hole may be tapered, towards one end or towards a point in the middle. The base 16 may be of a circular section, truncated by two chords, to form wide and narrow diameters which allow the grommet to act as a latch.

Description

Grom met

FIELD OF THE INVENTION S. * S

:..::: The present invention relates to a grommet. S...

BACKGROUND ART * . I * V

Grommets are devices to assist in conveying a cable or other elongate object through a hole in a bulkhead, wall, or other surface. Generally, they are provided in order to prevent the cable chafing against the edges of the hole * through which it passes, but may also provide a seal and/or prevent against undesired Ingress (such as of insects or other wildlife).

Specific problems arise in the context of low-voltage electrical distribution installations, where heavy-gauge cables are employed to conduct the required currents safely. These cables are typically of solid aluminium, solid copper, or stranded copper, and have cross-sectional areas of up to 185 or 300 mm2. They may also be asymmetrical, having a lozenge-or diamond-shaped section, and are thus difficult to bend and especially difficult to bend in the plane of the longer dimension.

Generally, the installation process for such systems involves bending the cable to the approximate shape required, positioning them in place such as against a pole, carrying out fine adjustment of the cable shape via a suitable lump hammer or other tool, and bolting them in place. Given that these connections can be dangerous; this is sometimes carried out at an elevated height to place the installation in a safe location, although they may also be at ground level where conditions permit. The cables are typically terminated via copper or aluminium connectors affixed to the cable end, having a flat lug drilled to receive an M16 or other bolt. Sliding a grommet over such a cable end, whilst for example, being on a ladder, and whilst seeking to adjust the cable shape to fit the installation, is therefore a difficult task involving some skill.

SUMMARY OF THE INVENTION

The present Invention therefore provides a grommet comprising a generally annular section having a through hole and a waisted outer profile, the section being of a closed cell foamed polymeric composition with a density : between 0.1 and 1 gcm3. A preferred polymer Is polyurethane * * S...

The waist preferably comprises a relatively narrower section bounded on * SS : * . at least one side by a surface extending radially outwardly in a direction away from and transverse to the through hole. It is preferably thereby bounded on both sides.

A slot extending from the through hole outwardly to the outer profile will assist in fitting the grommet around a cable or conductor.

It is also preferred that the outer profile includes a dome-shaped section extending from the waist to one end of the through hole. The dome shape is ideally rotationally symmetrical around the axis of the through hole.

The through hole can be tapered along all or part of its length, preferably with the wider end proximate the dome-shaped section.

The outer profile can also Include a latch section, extendIng from the waist to an end of the through hole, and comprising a profile with a diameter that varies from a minimum that is less than the minimum diameter of the remainder of the outer profile to a maximum that is greater than the maximum diameter of the remainder of the outer profile. This can be a generally circular section of the maximum diameter, truncated along one or more chords to produce the minimum diameter. Preferably the circular section is truncated by two chords, which are ideally parallel.

In this way, the present invention provides a grommet that can be fitted or retrofitted easily to a heavy gauge cable (via the slot) and which has the ability to accommodate greater variations In the cable position. This is very useful since, unlike normal cables, the precise position of electrical distribution cables is difficult to adjust. The foamed nature of the polymeric material combines the ability to accommodate variations in the cable position and size with the ability to maintain an adequate seal. The closed-cell nature of the foam prevents ingress of environmental contaminants such as rainwater.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; *. * * * * S

Figure 1 Is a perspective view of the grommet according to the present invention; S. * . Figure 2 is view of the grommet from one side; Figure 3 is a view of the grommet from beneath; Figure 4 is a view of the grommet from above; Figure 5 is a view of the grommet from one side, rotated 900 relative to figure 2; Figure 6 is a vertical section through the grommet in the plane of figure 5; Figure 7 is an enlarged view of the Intersection of the slot and the outer edge, viewed from below; Figure 8 Is a view of an alternative embodiment, from beneath; and Figure 9 is a cross-section of the alternative embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows the grommet 10 according to the present invention. It comprises a generally dome-shaped upper sectIon 12, beneath which is a waist 14 to accept the wall or bulkhead in which the grommet is to be fitted, and (beneath that) an enlarged section 16, acting as a latch for retaining the grommet 10 in place. A through-hole 18 is formed along the central vertical axis of the grommet, and a slot 20 extends radially from the through-hole 18 to the exterior of the grommet along a vertical plane.

Figure 2 shows a view from the side of the grommet 10, along the line of arrow II shown on figure 1. It can be seen that the dome-shaped upper section 12 is symmetrical around the central vertical axis 21 of the grommet 10. In this example, the dome is, In total 70mm wide, formed by a continuous 20mm radius.

: around the circumference. Thus, a narrow flat central region 22 is formed around the opening of the through-hole 18, which (at this end of the grommet 10) has a diameter of 27.7mm.

Behind the dome-shaped upper section 12 is the waist 14, defined by a narrowing of the grommet to 54mm behind a flat horizontal radial surface 24.

The waist is relatively thin, 3mm, to accept a wall of corresponding thickness.

* Clearly, this dimension could be adjusted to fit the thickness of a wall with which the grommet 10 was to be used.

Behind the waist, defined by a further flat horizontal radial surface 26, the enlarged section 16 is shown. This varies In width, figure 2 illustrating the narrowest section at 54mm. Thus, at this point it is slightly wider than the waist 14 but narrower than the dome-shaped upper section 12.

FIgure 3 illustrates the grommet 10 from below, and shows the overall shape of the enlarged sectIon 16. ThIs Is oval in section, with an shape defined by two 36mm radIus arcs set at centres spaced at 6mm apart symmetrically either side of the central axis 21, the semicircies being joined by parallel straIght edges 28, 30 54mm apart. Thus, the width across the central axis 21 varies between a minimum of 54mm and a maximum of 78mm, the maximum being greater than the 70mm diameter of the dome-shaped upper section 12. The slot extends from the through-hole 18, radially outwardly and parallel to the straight edges 28, 30.

Figure 4 shows the grommet 10 from above. The dome-shaped upper section 12 is symmetrical around the central axis 21 and the through-hole 18.

This can be seen to be tapered, having a wider upper opening 32 (27.7mm) at the upper end and a narrower tower opening 34 (12.4mm) at the lower end where it intersects with the lower face of the enlarged section 16.

Figure 5 shows the grommet 10 from the side, along the direction of arrow V In figure 1. This Illustrates the larger width of the enlarged section 16, wider than the diameter of the dome-shaped upper sectIon 12. Comparison of figures 2 and 5 shows that the waist 14 is uniformly narrower than the enlarged :... section 16, showing that the profile of the waist section 14 is the same as that of .... the enlarged section 16, albeit smaller. S. *S

* .. FIgure 6 is a section through the grommet, illustrating the tapered nature of the through-hole 18, narrowing from a maximum diameter at its opening 32 on the dome-shaped upper section 12 to a minimum diameter at its opening 34 on the enlarged section 16.

In some specific applications, It may be advantageous to locate the through-hole at an offset location, i.e. not centred on the central axis 21 of the grommet 10. ThIs will lead to an asymmetrical grommet, which may offer better performance where the cable to be protected exits the hole through the wall or bulkhead In an asymmetrical manner, such as slightly offset or slightly non-perpendicular. This applies particularly to electrical distribution cabling which tends to be rigid in nature and unable to bend locally so as to accommodate the needs of a grommet.

Where the through-hole 18 is offset in this way, it is preferable for it to be offset in the direction of the slot 20, i.e. be offset along the line of the slot 20 or directly away from the line of the slot 20. This will ensure that the tool used for producing the grommet will remain symmetrical, without becoming "handed".

Figure 7 shows an enlarged view of the region VII on figure 3. The slot 20 is visible as a small clearance between opposing faces 16a and 16b of the enlarged section 16.

Figures 8 and 9 show an alternative embodiment. In this version, the grommet 50 is identical to the grommet 10 of the first embodiment, except that the through-hole 52 is redesigned to assist in coping with heavy-gauge cables that are not oriented perpendicularly to the bulkhead. Otherwise, the grommet is that same, and thus has a dome-shaped upper section 54 and an enlarged lower section 56 eIther side of a waIst 57, and a slot 58 extending from the through-hole 52 to the outer edge of the grommet 50.

Figure 9 shows the cross-section of the through-hole 52, which adopts a profile In approximating to a venture-section. A minimum diameter 60 lies at : . the lower end of the through-hole 52, roughly proximate the middle of the S...

enlarged section 56. The through-hole widens linearly either side, to a primary maximum 62 at the top of the dome-shaped upper section 54 and a secondary * maximum 64 at the base of the enlarged section 56. *.

Figure 8 illustrates that the through-hole is not rotationally symmetric.

Thus, the secondary maximum 64 is oval-shaped; the widening of the through- * hole 52 only takes place In the plane of figure 9, parallel to the slot 58. In the transverse plane, the through-hole remains the same width, thus leading to the oval nature of the secondary maximum 64.

The primary maximum 62 is, in this embodiment, circular. Thus, the through-hole 52 widens uniformly in all planes above the minimum 60. This is not essential, however, and other arrangements could be adopted.

The material for the grommets is a visco-elastic polyurethane closed cell foam with a density specificatIon of 0.4 gcm3 0.5. Generally, we prefer that the density is in the range 0.1 to 1 gcm3 as this offers the appropriate degree of resilience. Within that range, the area from 0. 2 to 0.6 gcm3 offers partIcularly suitable compromIse between usability and longevity. Such a composition is able to compress to approximately 25% of its original size and spring back to its original shape on release, thereby allowing for variation in cable position and size.

The material could of course vary within the grommet, with coatings or inserts of an alternative material having the potential to offer advantages of their own. For example, a coating or skin of a solid (i.e. unfoamed) composition offers distinct advantages in terms of weather resistance and longevity, especially under UV exposure such as sunlight. Nevertheless, provided the annular section that defines the grommet Is principally of the above-specified material, the necessary grommet properties should be obtained. Other potentially suitable materials include foamed silicone rubber.

In the above description, dimensions have been provided for the various aspects of the grommet 10. These are of course subject to normal engineering ::.. tolerances, given the low-density nature of the material, and can be adjusted to .. take account of the intended use such as of different gauge cables or bulkheads of differing thickness.

Likewise, reference has been made In the above to upwards and downwards directions for descriptive purposes. Where used, such terms are based on a convention that the grommet Is fitted to a horizontally-disposed * bulkhead with the dome-shaped upper section uppermost. Where the grommet is fitted In a different disposition, the descriptive terms will need to be adapted accordingly.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present Invention.

Claims (15)

1. A grommet, comprising a generally annular section having a through hole and a waisted outer profile, the section being of a closed cell foamed polymeric composition with a density between 0.1 and 1 gcm3.

2. A grommet according to claim 1 In which the polymer Is polyurethane.

3. A grommet according to claim 1 in which the waist comprises a relatively narrower section bounded on at least one side by a surface extending radially outwardly in a direction away from and transverse to the through hole.

4. A grommet according to claim 3 in which the waist is bounded on both sides by a surface extending radially outwardly In a direction away from and transverse to the through hole. S... * . ****

5. A grommet according to any one of the preceding claims In which a slot * extends from the through hole outwardly to the outer profile. *.

6. A grommet according to any one of the preceding claims In which the outer profile Includes a dome-shaped section extendIng from the waist to one end of the through hole.

7. A grommet according to claim 6 in which the dome shape is substantially rotationally symmetrical around the axis of the through hole.

8. A grommet according to any one of the preceding claims in which the through hole Is tapered along all or part of Its length.

9. A grommet according to claim 8 as dependent on claim 6 or claim 7, in which the wider end of the through hole is proximate the dome-shaped section.

10. A grommet according to claim 8 or claim 9 in which the through hole tapers from both openings thereof toward a minimum within the grommet.

11. A grommet according to any one of the preceding claims in which the outer profile includes a latch section, extending from the waist to an end of the through hole, and comprising a profile with a diameter that varies from a minimum that is less than the minimum diameter of the remainder of the outer profile to a maximum that is greater than the maximum diameter of the remainder of the outer profile.

12. A grommet according to claim 11 In which the latch section Is a generally circular section of the maximum diameter, truncated along one or more chords to produce the minimum diameter.

13. A grommet according to claim 12 In which the circular section is truncated by two chords.

14. A grommet according to claim 13 in which the two chords are parallel.

15. A grommet substantially as herein described with reference to and/or as illustrated in the accompanying figures.

I * S S IS. S. S * * S * S.