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Patent Searching and Data


Title:
A FIXING
Document Type and Number:
WIPO Patent Application WO/2019/020695
Kind Code:
A1
Abstract:
A ratchet fixing (5) for connecting an insulation layer (4) to a precast concrete panel (2), a precast concrete panel system (1) comprising the fixing (5) and a method for (5) forming an insulated precast concrete panel system (1) comprising fixing an insulation layer (4) to a concrete panel (2) with fixings (5) in which the fixing (5) is made up of an insulation layer penetrating portion (18) and a concrete penetrating portion (19) contiguous with the insulating layer penetrating portion (18), the insulation layer penetrating portion (18) having a disc-like tension head (20) for abutting against the outer surface of the insulation layer (4) and a pawl (22) and ratchet (25) for securing the tension head (20) to the insulation layer penetrating portion (18).

Inventors:
WALSH, Conor (Waterford, IE)
Application Number:
EP2018/070181
Publication Date:
January 31, 2019
Filing Date:
July 25, 2018
Export Citation:
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Assignee:
WATERFORD INSTITUTE OF TECHNOLOGY (Cork Road, Waterford, IE)
International Classes:
E04B1/76; E04C2/288
Foreign References:
EP2660403A12013-11-06
US9010064B12015-04-21
US8555584B22013-10-15
Attorney, Agent or Firm:
LUCEY, Michael (PurdyLucey, Intellectual Property6-7 Harcourt Terrace, Dublin 2, 2, IE)
Download PDF:
Claims:
Claims

1 . A fixing for connecting an insulation layer to a precast concrete panel comprising:

an insulation layer penetrating portion and

a concrete penetrating portion contiguous with the insulation layer penetrating portion wherein the insulation layer penetrating portion comprises a flexible tie. 2. A fixing as claimed in Claim 1 wherein the insulation layer penetrating portion further comprises a tension head attachable to the flexible tie.

3. A fixing as claimed in Claim 2 wherein the flexible tie comprises a ratchet attachable to the tension head at a pawl.

4. A fixing as claimed in Claim 3 wherein the ratchet comprises through holes in the tie.

5. A fixing as claimed in Claim 3 or Claim 4 wherein the pawl comprises a slot in the tension head.

6. A fixing as claimed in Claim 5 wherein the tension head comprises a collar surrounding the slot. 7. A fixing as claimed in any of Claims 2 to 6 wherein the tension head comprises indents to define finger grips in the tension head.

8. A fixing as claimed in any of Claims 1 to 7 wherein the concrete penetrating portion comprises a wall plug.

9. A fixing as claimed in Claim 8 wherein the wall plug comprises a substantially cylindrical head.

10. A fixing as claimed in Claim 9 wherein the substantially cylindrical head comprises at least one laterally extending fin for maximizing grip of the wall plug on concrete. 1 1 . A fixing as claimed in Claim 9 or Claim 10 wherein the substantially cylindrical head comprises at least one notch for maximizing grip of the wall plug on concrete.

12. A fixing as claimed in Claim 8 wherein the wall plug comprises a substantially T-shaped head.

13. A fixing as claimed in any of Claims 1 to 12 wherein the concrete penetrating portion comprises a flange for stabilising the fixing in position during concrete pouring.

14. A fixing as claimed in Claim 13 wherein the flange extends laterally outwards from the concrete penetrating portion.

15. A fixing as claimed in any of Claims 1 to 14 further comprising at least one rib for strengthening the fixing.

16. A fixing as claimed in Claim 15 wherein the at least one rib is provided on the insulation layer penetrating portion. 17. A fixing as claimed in Claim 15 or 16 wherein the at least one rib is provided on the concrete penetrating portion.

18. A precast concrete panel system comprising a fixing as claimed in any of Claims 1 to 17.

19. A precast concrete panel system as claimed in Claim 18 wherein the system comprises a precast concrete panel reinforced with rebar and insulation fixed to the precast concrete panel by the fixing wherein the rebar and the fixing are spatially separate within the system.

20. A precast concrete panel system as claimed in Claim 18 or Claim 19 wherein the insulation layer comprises insulation board.

21 . A precast concrete panel system as claimed in Claim 20 wherein the insulation board comprises expanded polystyrene. 22. A method for forming an insulated precast concrete panel system comprising fixing an insulation layer to a concrete panel with fixings as claimed in any of Claims 1 to 17.

23. A method as claimed in Claim 22 comprising fitting the fixings to the insulation layer via the insulation layer penetrating portion, laying the insulation layer in a deck and pouring concrete into the deck to encapsulate the concrete penetrating portion of the fixings.

24. A method as claimed in Claim 23 further comprising the step of constructing a rebar in the deck before pouring the concrete.

25. A method as claimed in Claim 24 wherein the rebar is spatially separated from the fixings to prevent thermal bridging.

Description:
Title

A Fixing Introduction

This invention relates to a fixing for connecting an insulation layer to a precast concrete panel and to a precast concrete panel system made up of the concrete panel and the fixing. The invention also relates to a method for forming an insulated precast concrete panel. Background

Precast concrete panels for walls, floors, ceilings and the like are increasingly used in the construction of industrial, commercial and residential buildings. Most commonly, the precast concrete panel is formed off-site and then delivered to a construction site for assembly.

Precast concrete wall panels are generally manufactured on the flat in wooden concrete decks or forms sized to define the perimeter of the concrete panel.

A grid of steel rebar can be constructed and tied in-place within the form to reinforce the panel. Embeds for attaching the structural panel to footings, other panels, columns, slabs, roof systems, or for receiving building accessories and inserts which serve as attachment points for lifting hardware and temporary braces can also be provided in the form. Anchor-like fixings can also be employed to secure insulation to the concrete.

Concrete is then poured into the form in the same manner as floor slabs and is then finished as required e.g. a trowel finish or other types of architectural finishes and patterns. Precast concrete panels offer a number benefits for construction. Whilst enjoying the benefits of being formed from concrete, the panels can be manufactured consistently and reproducibly with the high degree of accuracy required in modern construction. The pre-cast panels can then be rapidly assembled at building sites facilitating rapid builds.

Generally, precast concrete wall panels fall into three basic categories: sandwich, thin-shell and solid while the wall panels can be designed as non- loadbearing or loadbearing, carrying floor and roof loads, as well as lateral loads.

As indicated above, precast concrete panels are typically manufactured off-site, although the panels can be manufactured on-site, and the necessary external finishes, such as plaster boarding and plastering, and services, such as electrics and plumbing, fitted following installation of the panels on-site.

The precast panels must also be insulated when used for domestic, institutional and commercial buildings. In sandwich panels, rigid insulation is sandwiched between two layers of concrete. The insulation thickness can vary to create the desired thermal insulating property ("U" value, or known as 'R' value in the United States) for the wall. However, sandwich panels are relatively expensive and more time consuming to manufacture due to the multiple layers of concrete required. Moreover, as the insulation is placed between two layers of concrete, a significant risk exists that undesirable levels of thermal bridging can occur across the pre-cast panel.

Thin-shell wall panels consist of a thin outer-layer of concrete connected to a back-up system typically constructed of steel framing or concrete which connects the wall panel to the building structure. A layer of rigid insulation is generally placed between the exterior layer of concrete and the back-up system. However, thin-shell wall panels can also be expensive and slow to produce due to the relatively complex nature of the required back-up system and multiple layers required.

Solid precast concrete wall panels are typically formed from a single solid concrete layer and as such are quicker and less expensive to produce than sandwich or thin shell precast panels. Insulation can be fixed to the pre-cast panel wall insulation anchors following removal of the precast panel from its form. However, the manual fixing of insulation to the precast panel following removal from the form introduces another step to the manufacturing process can slow down manufacture and increase the risk of thermal bridging. Alternatively, as described in US Patent Specification No. 8,555,584, an insulation layer provided with rigid anchors which also serve to support the steel rebar can be included in the form during casting of the panel. However, due to the rigid nature of the anchor, the anchor can fail during expansion/contraction of the concrete during curing while contact of the anchor with the steel rebar can result in thermal bridging across the panel. European Patent Specification No. 3,106,579, German Patent Specification No. 101 18 678, US Patent Specification No. 5,660,015 and PCT Patent Specification No. WO 2017/1 16237 all describe similar fixing methods in which fixings can be retrofitted to existing concrete substrates in a manner requiring the use of labour-intensive pre-drilling steps, nail guns, fastening guns and the like.

In short, conventional block on flat construction methods are slow while known precast panels suffer from a number of disadvantages - e.g. structural insulated panels (SIP's) require a cavity and outer layer of blockwork and insulated structural panels (ISP's) require an inner layer of concrete coupled with an outer layer of concrete and insulated core. Moreover, all of the above construction methods are labour intensive and require skilled on-site construction while all suffer from excessive thermal bridging. Summary

According to the invention there is provided a fixing, as set out in the appended claims, for connecting an insulation layer to a precast concrete panel comprising: an insulation layer penetrating portion and

a concrete penetrating portion contiguous with the insulation layer penetrating portion wherein the insulation layer penetrating portion comprises a flexible tie. Suitably, the insulation layer penetrating portion further comprises a tension head attachable to the flexible tie. The tension head can have one or two pawls depending on pull off requirements and wind loads on larger residential buildings. Preferably, the flexible tie comprises a ratchet attachable to the tension head at a pawl. Advantageously, the ratchet comprises through holes in the tie.

Preferably, the pawl comprises a slot in the tension head. Suitably, the tension head comprises a collar surrounding the slot.

Preferably, the tension head comprises indents to define finger grips in the tension head.

Suitably, the concrete penetrating portion comprises a wall plug.

Preferably, the wall plug comprises a substantially cylindrical head. More preferably, the substantially cylindrical head comprises at least one laterally extending fin for maximizing grip of the wall plug on concrete. Advantageously, the substantially cylindrical head comprises at least one notch for maximizing grip of the wall plug on concrete. Alternatively, the wall plug comprises a substantially T-shaped head.

Preferably, the concrete penetrating portion comprises a flange for stabilising the fixing in position during concrete pouring. More preferably, the flange extends laterally outwards from the concrete penetrating portion.

In one embodiment, the fixing comprises at least one rib for strengthening the fixing. Preferably, the at least one rib is provided on the insulation layer penetrating portion. Alternatively or in addition, the at least one rib is provided on the concrete penetrating portion.

The invention also extends to a precast concrete panel system comprising a fixing as hereinbefore defined. Preferably, the precast concrete panel system comprises a precast concrete panel reinforced with rebar and insulation fixed to the precast concrete panel by the fixing wherein the rebar and the fixing are spatially separate within the system.

More preferably, the insulation layer comprises insulation board. Most preferably, the insulation board comprises expanded polystyrene. In a further embodiment, the invention also extends to a method for forming an insulated precast concrete panel system comprising fixing an insulation layer to a concrete panel with fixings as hereinbefore defined.

Preferably, the method comprises fitting the fixings to the insulation layer via the insulation layer penetrating portion, laying the insulation layer in a deck and pouring concrete into the deck to encapsulate the concrete penetrating portion of the fixings.

Suitably, the method further comprises the step of constructing a rebar in the deck before pouring the concrete.

Preferably, the rebar is spatially separated from the fixings to prevent thermal bridging. The invention meets and exceeds modern building regulation requirements for both domestic and commercial projects by enabling a fast, energy efficient/thermal bridge free construction. The fixing and associated precast panel system of the invention eliminate the need for the majority of skilled on-site labour thus providing a faster construction method.

The fixing and precast concrete panel system of the invention formed with the fixing exhibit minimal thermal bridging as compared with the fixings and insulated precast concrete panels of the prior art. In particular, the flexibility of the tie of the insulation penetrating portion of the ratchet fixing of the invention offers room for expansion and contraction during concrete curing thereby preserving the structural integrity of the system and eliminating the risk of thermal bridging caused by damage to ties and/or insulation during curing. Moreover, as the ratchet tie is structurally and spatially separated from and independent of any steel rebar employed in the precast concrete panel, the method for forming a precast concrete panel system eliminates the likelihood of thermal bridging through fixings and rebars. The ratcheting action of the ratchet tie also allows the tie to adapt to insulation of varying thicknesses whilst also enabling secure attachment of the insulation to the solid concrete panel.

Moreover, the solid precast concrete panel system and associated method for forming the system of the invention do not require the use of sandwiched layers of insulation resulting in an insulated concrete panel that is easier to form and manufacture to a high degree of accuracy with optimal thermal characteristics. The solid precast concrete panel of the invention is also relatively inexpensive to manufacture compared with sandwich and thin shell concrete panels.

The insulated precast panel systems of the invention can be formed off-site regardless of weather conditions and can then be rapidly assembled on site with significantly reduced skilled labour requirements. Accordingly, construction projects can be completed sooner and faster than with conventional construction methods. In summary, the fixing of the invention can be installed, pre-pouring of concrete with minimal effort. Moreover, as insulation can be provided with suitable perforations to receive the fixings, no drilling or steel nail fastening is required when employing the fixing. Accordingly, the fixing of the invention dramatically reduces the need for onsite labour and allows for the delivery of a factory made fully structural insulated concrete panel that is of monolithic construction. The flexible plastics fixings of the invention, being separate from the structural steel and the like, minimise the risk of thermal bridging compared with the fixings and methods of the prior art. The fixing of the invention is also suitable for use with all concrete types.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a cross-sectional view through a precast concrete panel system of the invention made up of a precast panel adapted to define a window opening for receiving a window in which the precast panel is laid on the flat and has an upper concrete layer over a lower insulation layer and the insulation layer is anchored to the concrete panel by a two-part ratchet fixing/anchor extending between the insulation layer and the concrete panel;

Figure 2 is an external plan view of the precast panel system of Figure 1 from the insulation layer side of the precast concrete panel with the render finish omitted to reveal the tension heads of the multiple ratchet fixings visible on the insulation layer;

Figure 3 is a partially cutaway view of the precast concrete panel of Figure 2 showing the wall plug of the ratchet fixings embedded in the concrete layer;

Figure 4 is an enlarged perspective view from above and one side and from the concrete penetrating portion of the ratchet fixing;

Figure 5 is a perspective view from above and one side of the two-part ratchet fixing of Figure 4 with the tension head of the ratchet fixing removed i.e. before use of the ratchet fixing;

Figure 6 is a perspective view from above and one side and from the insulating penetrating portion of the ratchet fixing; Figure 7 is a perspective view from above and one side and from the insulating penetrating portion of the two-part ratchet fixing with the tension head removed i.e. before use of the ratchet fixing; Figure 8 is a plan view of the ratchet fixing;

Figure 9 is a perspective view from above and one side of a second embodiment of a fixing of the invention, with the tension head omitted, in which the wall plug of the concrete penetrating portion is substantially T-shaped and the fixing is provided with stabilising and strengthening ribs to reinforce the fixing;

Figure 10 is an enlarged perspective view from above and one side of the tension head of the fixing of Figure 9; Figure 1 1 is a side elevation of the tension head of Figure 10;

Figure 12 is a cross-sectional view through the tension head of Figure 1 1 , and Figure 13 is an enlarged side elevation of the T-shaped wall plug of the concrete penetrating portion of the fixing of Figure 9 with strengthening ribs provided adjacent the stabilising flange of the wall plug on the insulation penetrating portion. Detailed Description of the Invention

As shown in the drawings, a precast concrete panel system of the invention is generally indicated by the reference numeral 1 and (when viewed on the flat as shown in Figure 1 ) is made up of a precast panel 2 having an upper concrete layer 3 and a lower insulation layer 4 typically of expanded polystyrene or similar secured to the concrete layer 3 by a first embodiment of a two-part ratchet anchor or fixing 5 of the invention. The concrete layer 3 is also provided with a grid of steel rebar (not shown) to reinforce the precast panel 2 while an external render finish 6 is provided on the outer surface of the insulation layer 4 and plasterboard 7 is mounted over a cavity 8 defined by timber stud 9 at the outer face of the concrete layer 3. The cavity 8 contains internal insulation material 10.

As shall be explained more fully below, the ratchet fixing 5 securely attaches the insulation layer 4 to the concrete layer 3 and is independent of the grid of steel rebar i.e. does not contact the grid of steel rebar thereby minimising thermal bridging across the panel system of the invention whilst, being flexible, the ratchet fixing 5 offers room for expansion and contraction of concrete during curing.

The precast panel 2 is shaped to define scarf joints 1 1 for interconnecting individual precast panels 2 during the construction of a building.

As shown particularly in Figure 2, the precast panel 2 is substantially rectangular in shape and has a bottom edge 12, a top edge 13 and first and second side edges 14,15 connecting the bottom and top edges 12,13. A window opening 16 is defined in the precast panel 2 for receiving a window 17.

Figures 4 to 8 show enlarged views of the first embodiment of the ratchet fixing 5. As shown in the drawings, the ratchet fixing 5 is made up of an insulation layer penetrating portion 18 and a concrete penetrating portion 19 contiguous with the insulation layer penetrating portion 18. The insulation layer penetrating portion 18 has a disc-like tension head 20 for abutting against the outer surface of the insulation layer 4 as shown in Figures 2 and 3 and for urging the insulation layer 4 against the concrete layer 3 in use. The tension head 20 has a rectangular central slot 21 which defines a pawl 22 while a series of circular openings 23 are arranged circumferentially around the central slot 21 .

The insulation layer penetrating portion 18 is also made up of a substantially rectangular elongate flexible tie 24 which extends between the tension head 20 and the concrete penetrating portion 19. More particularly, the flexible tie 24 is insertable in the central slot 21 of the tension head 20 and is securely attachable to the pawl 22 in the central slot 21 via a ratchet 25 formed in the flexible tie 24. In the present embodiment, the ratchet 25 is defined by through holes or notches 26 in the flexible tie 24. However, as will be appreciated by those skilled in the art, the ratchet 25 can be defined by teeth or similar structures on the tie 24 if desired.

The concrete penetrating portion 19 is made up of a circular stabilising flange 27 extending laterally outwards from the concrete penetrating portion 19 for stabilising the ratchet fixing 5 in position during concrete pouring. The circular stabilising flange 27 has a diameter smaller than that of the tension head 20. A wall plug 28 is mounted on the stabilising flange 27 for anchoring and embedding the concrete penetrating portion 19 in the concrete layer 3 of the precast panel 2. As shall be explained more fully below, the concrete penetrating portion 19, and in particular the wall plug 28, is encapsulated in the concrete layer 3 during manufacture of the precast panel system 1 of the invention.

In order to provide a highly effective anchor in the concrete layer 3, the wall plug 28 is made up of a substantially cylindrical head 29 having a pointed tip 30 and first and second pairs of laterally extending fins 31 , 32 respectively for maximising grip in the concrete layer 3. The cylindrical head 29 is also provided with a first and second pair of notches 33, 34 respectively between the fins 31 , 32 to further enhance the grip of the wall plug 24 in the concrete layer 3.

Figures 9 to 13 show a second embodiment of a ratchet fixing 5 of the invention similar to the ratchet fixing of Figures 1 to 8 and like numerals indicate like parts. However, in the present embodiment, the wall plug 28 of the concrete penetrating portion 19 is substantially T-shaped and the ratchet fixing 5 is provided with stabilising and strengthening ribs 36 to reinforce the ratchet fixing 5. As shown in the drawings, in the present embodiment, three strengthening ribs 36 are provided on the insulation penetrating portion 18, and more particularly the elongate tie 24, adjacent the stabilising flange 27. The strengthening ribs 36 extend laterally outwards from the longitudinal axis defined by the elongate tie 24 to strengthen engagement between the ratchet fixing 5 and insulation layers 4 in use i.e. the laterally extending ribs 36 increase surface contact between the ratchet fixing 5 and the insulation layer 4 to assist in stabilising the ratchet fixing 5 in the insulation layer 4 whilst still allowing the elongate tie 24 to flex in the insulating layer 4. If desired, additional or alternatively positioned strengthening ribs 36 can be provided on the insulation penetrating portion 18.

In the present embodiment, the circular tension head 20 of the ratchet fixing 5 is provided with peripheral indents 37 to define finger grips 38 for gripping and positioning the tension head 20 in use. The tension head 20 is also provided with a central collar 39 surrounding the central slot 21 . The central collar 39 serves to assist in supporting the elongate tie 24 in the toothed pawl 22 of the rectangular central slot 21 in use. As shown particularly in Figure 13, the wall plug 28 is formed as a substantially T-shaped head 40 to assist in anchoring the concrete penetrating portion 19 in concrete. The T-shaped head 40 has an upright portion 41 and an arcuate "cross" or transverse portion 42. The arcuate transverse portion 42 is curved towards the upright portion 41 and the flange 27 to assist in strengthening the anchoring relationship between the ratchet fixing 5 and the concrete layer 3 in use. The upright portion 41 and the arcuate transverse portion 42 of the T- shaped head 40 are further provided with head ribs 43 to further enhance surface contact with the concrete layer 3 and acts to maintain rigidity of the fixing 5. The ratchet fixing 5 of the present embodiment can be easily and simply manufactured using injection moulding techniques.

The precast concrete panel system 1 of the invention can be manufactured by first constructing a form or deck on the flat in accordance with the shape and size of precast panel 2 required. The deck is made up of supporting sides having a depth greater than the final depth required in the precast concrete panel 2. By way of example for a precast panel system 1 as shown in Figure 2 having a height of 2400mm, a width of 2200mm and a thickness of 150mm. The total thickness can be 370mm, comprising 4mm Hard wall Internal Finish, 12.5mm Plaster boarding, 44mm Timber Battens, 150mm Reinforced Concrete, 150mm EPS Insulation, 9mm External Rendering with Reinforced Fiberglass Mesh cloth and Finished using a Silicone Topcoat. An insulation layer 4 in the form of pre- formed perforated insulation boards 4 (e.g. expanded polystyrene), suitable for use with the ratchet fixing 5 are then fitted with the desired number and layout of ratchet fixings 5.

In particular, elongate ties 24 of the ratchet fixing 5 with the tension head 20 removed as shown in Figures 5 and 7 are inserted through the insulation boards 4 so that the free end 35 of each elongate tie 24 is at the outer surface of the insulation layer 4 as shown in the drawings and the stabilising flange 27 of each concrete penetrating portion 19 abuts the opposite internal face of the insulation layer 4. The tension heads 20 are then engaged with the free end 35 of each elongate tie 24 by inserting the free ends 35 of the elongate ties 24 in the central slots 21 of the tension heads 20 so that the pawls 22 in the central slots 21 irreversibly engage the ratchets 25 on the elongate ties 24. The engagement of each pawl 22 and ratchet 25 can be tightened as needed to increase grip or tension across the insulation layer 4 as required.

The insulation boards 4 are then laid face down in the deck i.e. with the tension heads 20 disposed downwards and the wall plugs 28 disposed upwards in the deck. Upon completion of the above steps, concrete is then poured into the deck to encapsulate the wall plugs 28 of the ratchet fixings 5 and the steel rebar structural support. The resultant precast concrete panel system 1 is a structurally sound, highly insulated structure which exhibits minimal thermal bridging characteristics of about 0.002 W/m 2 K or greater and which is suitable for delivery to a construction site for building construction. If desired, a rebar can be constructed in the deck before pouring concrete e.g. in the present example a grid of steel rebar made up 50 x 6mm iron ribs placed around the edges of the deck and at centres that do not interfere with the ratchet fixings 5 during manufacturing can be incorporated into the deck. The ratchet fixing 5 can be formed from any suitable material such as plastics, nylon and the like and can be sized as required. For example, for the precast concrete panel system described above in Figures 1 to 8, a ratchet fixing 5 having an overall length of about 203mm is suitable with the tension head having a thickness of about 3mm, the elongate tie 24 having a length of about 150mm, the stabilising flange 27 having a thickness of about 5mm and the concrete penetrating portion 19 and in particular the wall-plug 28 having a length of about 50mm for embedding in the concrete layer 3 and a maximum width of about 30mm. Such a ratchet fixing 5 exhibits thermal bridging of less than half that of known fixings which, at best, exhibit thermal bridging of about 0.02 W/m 2 k. It is envisaged various lengths ranging from 250mm up to 400mm can be embodied depending on U-value requirements and insulation options. For example, the ratchet fixing of Figures 9 to 13 can have an insulation layer penetrating portion 3 length of about 310mm, a wall plug length of about 30mm, a T-shaped head 39 width of about 35mm and thickness of about 13mm, a flange 27 diameter of about 28mm, a tension head 20 diameter of about 60mm and thickness of about 1 1 mm.

In an embodiment there is provided a conical flange positioned near the inside of the tension head, whose function is to hold a second or a stronger pawl depending on kN/mm required.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiments herein described which may be varied in construction and detail without departing from the scope of the invention.