AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant: BLUESCOPE STEEL LIMITED Invention Title: A CLIP The following statement is a full description of this invention, including the best method for performing it known to me/us: - 2 A CLIP The present invention relates to a clip for fixing a roof or other cladding sheet to an underlying 5 support structure. The present invention relates particularly, although by no means exclusively, to a clip for fixing a roof cladding sheet to an underlying roof support 10 structure. Typically, roof cladding sheets are roll-formed from painted or unpainted steel strip and include one or more parallel ribs with opposed sides, pan sections, and 15 side edge formations that enable the sheets to be positioned side by side in overlapping relationship. It is known to secure cladding sheets to an underlying roof support structure, such as roof purlins, 20 by fastening the sheets directly to the underlying structure using fasteners, such as roofing nails and screws, that pierce the sheets and penetrate the underlying structure. 25 It is also known to secure cladding sheets to an underlying structure by using clips that are secured to the structure by fasteners and are formed to extend into the ribs and include retaining members or tabs that can engage re-entrant portions of the ribs and thereby retain 30 the sheets to the clips. These clip assemblies are often preferred over nails because they enable concealed fixing of cladding sheets to an underlying structure. In use, the concealed fixing retaining clips are 35 secured to an underlying structure at spaced intervals related to the spacing between the ribs of the cladding sheets. Thereafter, cladding sheets are positioned on the 2343198_1 (GHMatters) 16/07/10 - 3 clips in overlapping relationship by successively pressing the sheets down onto the clips so that the sides of the ribs are initially forced outwardly to allow the re entrant portions of the ribs to pass over the retaining 5 members and then snap inwardly into engagement with the retaining members. There are a number of known concealed fixing retaining clips. The clips include a series of clips 10 disclosed in International application PCT/GB91/00450 (WO 91/12392) in the name of Stramit Industries Limited, a clip disclosed in Australian patent 685102 and other Australian patents and patent applications in the name of Stramit Corporation, and a clip disclosed in International 15 application PCT/AU01/00818 (WO 01/02666) in the name of the applicant. The clip disclosed in International application PCT/AU01/00818 is marketed in Australia under the trade mark KLIPLOK. 20 An object of the present invention is to provide an alternative concealed fixing retaining clip to the above-mentioned clips that has advantages over one or more of these clips. 25 The applicant has developed a new form of concealed fixing retaining clip that is a relatively straightforward construction compared to the above mentioned clips and has at least comparable performance to one or more of these known clips. 30 The present invention provides a concealed fixing retaining clip for fixing a roof or other cladding sheet to an underlying support structure of the general type that includes: (a) a base; 2343198_1 (GHMatters) 16/07/10 - 4 (b) a pair of side walls that extend from the base and converge towards each other; and (c) a pair of flanges that define retaining members 5 for engaging re-entrant portions in the sides of ribs of cladding sheets, with one flange extending from an upper end of one side wall and the other flange extending from an upper end of the other side wall. 10 The clip of the present invention has a number of features that are described below that contribute to the performance of the clip in a number of important areas. 15 One area is resistance to uplift forces acting on a cladding sheet. Uplift forces acting on an installed cladding sheet can cause the sheet to be released from concealed 20 fixing retaining clips. Depending on the circumstances, the uplift forces may cause: (a) the sides of the ribs of the sheet to rotate outwardly and thereby disengage from the flanges 25 of the clips; and/or (b) the flanges of the clips to fold upwardly and thereby release the sheet from the clips. 30 Another area is damage to a cladding sheet that can occur when cladding sheets are positioned on concealed fixing retaining clips. Specifically, it has been found that cladding 35 sheets that are used with known clips, particularly clips that have relatively short and stiff retaining members, are susceptible to a problem of denting when cladding 2343198_1 (GHMatters) 16/07/10 - 5 sheets are forced onto the sheets. The dents form in the sections of the sheets that contact and slide over the clips as the sheets are forced onto the clips. The dents do not affect the mechanical performance of the sheets. 5 However, the dents affect the aesthetic appeal of the cladding sheets and this has been found to be a significant issue. Another area is damage to cladding sheets that 10 can occur when it is necessary to remove cladding sheets from concealed fixing retaining clips. Specifically, it has been found that it is difficult to remove cladding sheets from known clips, 15 particularly clips that have relatively short and stiff retaining members, without damaging the sheets. This is a significant issue because there are often situations, for example when installing an air conditioner onto a roof, when it is necessary to be able to remove cladding sheets 20 to allow access to the roof cavity and thereafter replace the removed sheets. With regard to the above, the concealed fixing retaining clip of the present invention includes: 25 (a) a base; (b) a pair of side walls that extend from the base, with the side walls being formed so that they do 30 not contact each other in the as-manufactured form of the clip and are forced inwardly towards each other or into contact with each other when, in use, a cladding sheet is positioned on the clip, and wherein each side wall includes one or 35 more than one reinforcing rib to improve the stiffness of the side wall; and 2343198_1 (GHMatters) 16/07/10 - 6 (c) a pair of flanges that define retaining members for engaging re-entrant portions in the sides of ribs of cladding sheets, with one flange extending from an upper end of one side wall and 5 the other flange extending from an upper end of the other side wall. The above feature of the side walls of the clip being formed so that they do not contact each other in the 10 as-manufactured form of the clip and are forced inwardly towards each other or into contact with each other when, in use, a cladding sheet is positioned on the clip is an important feature. This feature makes it easier to install the clip to an underlying structure because there 15 is a gap between the clip side walls for inserting a screw-driver to facilitate securing the clip to the underlying structure. The above feature that each side wall includes 20 one or more than one reinforcing rib to improve the strength and stiffness of the side wall is another important feature. Preferably the clip is formed from a resilient 25 material so that each side wall of the clip applies an outwardly directed force in response to the side walls being forced together when, in use, a cladding sheet is positioned on the clip. This feature contributes to ensuring engagement of the flanges and the re-entrant 30 portions of the ribs of the cladding sheet. Specifically, the resultant outward force forces the flanges against the cladding sheet. Preferably the flanges are a mirror image of each 35 other about a centre-line plane that passes perpendicularly through the base of the clip. 2343198_1 (GHMatters) 16/07/10 - 7 Preferably the side walls and the base are straight sides so that the side walls and the base define a triangular structure when viewed from a side of the clip. This feature contributes to the overall strength 5 and stiffness of the clip. More particularly, the triangular structure contributes to the capacity of the clip to withstand downward loading of the clip, for example when a person presses down on a rib of a cladding sheet to force the rib over the clip. In addition, the 10 triangular structure can accommodate off-centre downward loading that may be applied to the clip when a cladding sheet is forced down onto the clip. Specifically, the side walls of the clip can slide relative to each other in response to off-centre downward loading and return to the 15 original profile. In addition, the triangular structure contributes to the resistance of the side walls to outward movement of the side walls beyond the as-manufactured positions of the side walls and therefore is a factor in the clip being able to resist uplift forces on a cladding 20 sheet. Preferably at least one edge of each side wall includes an inwardly turned flange to improve the strength and stiffness of the side wall. 25 Preferably the flanges define at least part of an arch when, in use, a cladding sheet is positioned on the clip with the side walls forced together. This feature contributes to the capacity of the clip to resist uplift 30 forces acting on the cladding sheet. Specifically, this feature takes advantage of a characteristic of an arch that it is a structure that can translate uplift forces to outward forces. 35 Preferably the side walls contact each other or are in close proximity to each other at or in the vicinity of the upper ends of the clip when, in use, a cladding 2343198_1 (GHMatters) 16/07/10 - 8 sheet is positioned on the clip and forces the side walls together. This feature ensures that there is clip material as close as possible to the apex of the arch and thereby contributes to concentrating as much clip material 5 as possible in the upper section of the clip and thereby optimising the strength of the clip in this section of the clip. Preferably the flanges extend outwardly and 10 downwardly relative to each other as viewed when the clip is positioned with the clip base on a horizontal surface. The flanges may describe a relatively steep approach angle relative to a rib of a cladding sheet so 15 that there is gradual rather than sudden outward deflection of the sides of the rib of the cladding sheet when, in use, the cladding sheet is forced downwardly onto the clip to position the sheet on the clip. This feature contributes to minimising denting of the sheet. 20 With this arrangement, preferably the flanges are relatively long, preferably at least 25% of the height of the clip. 25 Preferably the approach angle, described by each flange and the base of the clip, is between 40* and 750. Alternatively, the flanges may describe a relatively gentle approach angle relative to a rib of a 30 cladding sheet so that there is sudden rather than a gradual outward deflection of the sides of the rib of the cladding sheet when, in use, the cladding sheet is forced downwardly onto the clip to position the sheet on the clip. 35 With this arrangement, preferably the flanges are relatively short, preferably less than 25% of the height 23431981 (GHMatters) 16/07/10 -9 of the clip. Preferably the approach angle, described by each flange and the base of the clip, is less than 400. 5 Preferably each flange has a sharp outer end that contacts and thereby engages securely the re-entrant portion of one of the ribs of a cladding sheet when, in use, the cladding sheet is positioned on the clip. 10 Preferably the outer end of each flange is outwardly directed. In other words, preferably the outer end of each flange is not inwardly turned towards the side walls of the clip. 15 Preferably each flange includes the two corner sections that are folded inwardly and form surfaces that extend transversely to the outer end of the flange and contact and thereby engage a re-entrant portion of one of 20 the ribs of a cladding sheet when, in use, the cladding sheet is positioned on the clip. This feature increases the surface area of contact between the flanges and the re-entrant portions and thereby makes it possible to minimise damage to the sheet when it is necessary to 25 remove the sheet from the clip. Preferably the transitions between the side walls and the flanges are tight radius curves in order to concentrate as much clip material as possible in the upper 30 section of the clip to optimise the strength and stiffness of this section of the clip. Preferably the upper ends of the side walls are shaped to define a generally circular opening in the as 35 manufactured clip to facilitate insertion of a screw driver to secure the clip to an underlying structure. 2343198_1 (GHMatters) 16/07/10 - 10 According to the present invention there is also provided a clip assembly which includes: (a) an elongate strap; and 5 (b) a plurality of the concealed fixing retaining clips described above mounted to an upper surface of the strap. 10 The present invention is described further by way of example with reference to the accompanying drawings, of which: Figure 1 is a perspective view of one embodiment 15 of a clip in accordance with the present invention in an as-manufactured form; Figure 2 is a side elevation of the clip shown in Figure 1 in the direction of the arrow "A" in Figure 1; 20 Figure 3 is a side elevation of the clip shown in Figure 1 in the direction of the arrow "B" in Figure 1; Figure 4 is a top view of the clip shown in 25 Figure 1; Figure 5 is a bottom view of the clip shown in Figure 1; 30 Figures 6a, 6b, and 6c are sketches that illustrate engagement of a cladding sheet with the clip shown in Figure 1; Figure 7a and 7b are sketches that illustrate 35 release of a cladding sheet from the clip shown in Figure 1; 2343198 _1 (GHlatters) 16/07/10 - 11 Figure 8 is a perspective view of one embodiment of a clip assembly in accordance with the present invention which includes a strap and two clips similar to the clip shown in Figures 1 to 7 in an as-manufactured 5 form mounted to the strap; Figure 9 is a top view of the clip shown in Figure 8; 10 Figure 10 is a side elevation of the clip shown in Figure 8; Figure 11 is a bottom view of the clip shown in Figure 8; 15 Figure 12 is an end view from the right hand end of the clip shown in Figure 8 as viewed in Figure 8; and Figure 13 is an end view from the left hand end 20 of the clip shown in Figure 8 as viewed in Figure 8. Figures 1 to 5 illustrate one embodiment of a clip 3 formed in accordance with the present invention. Figure 6 illustrates the interaction between the clip and 25 a cladding sheet 29 as the cladding sheet is being positioned onto the clip. Figure 7 illustrates the interaction between the clip and a cladding sheet as the cladding sheet is being removed from the clip. 30 The clip 3 is formed by folding a flat metal, preferably steel (but not necessarily spring steel), blank into the configuration shown the figures. The clip 3 includes: 35 (a) a base 5; 2343198_1 (GHMatters) 16/07/10 - 12 (b) a pair of side walls 7 that extend from the base; and (c) a pair of flanges 9 that define retaining 5 members for engaging re-entrant portions of ribs of cladding sheets, with one flange 9 extending from an upper end of one side wall 7 and the other flange 9 extending from an upper end of the other side wall 7. 10 The base 5 includes a pair of outwardly extending tabs 15 to facilitate locating a plurality of the clips 3 onto a strap (see Figure 8 embodiment). 15 With reference to Figure 1, in addition, each side wall 7 includes a relatively narrow strap section 7a that extends upwardly from the base 5 and a relatively wider upper section 7b that extends from the strap section 7a. The upper section 7b is symmetrically positioned with 20 respect to the strap section 7a so that the side wall 7 has 2 downwardly facing shoulders 73. These shoulders 73 further facilitate locating the clip 3 onto a strap (see Figure 8 embodiment). 25 The base 5 includes an opening 63 to facilitate securing the clip 3 to an underlying roof structure, such as a roof purlin (not shown). The side walls 7 and the base 5 are straight 30 walls and define a substantially triangular structure in side view shown in Figure 2. In the as-manufactured form shown in Figures 1 to 5 the side walls 7, whilst converging towards each other, 35 do not actually contact each other and there is a gap G between the side walls 7 at the upper end of the side walls. However, as is shown in Figure 6c, in use, the 2343198_1 (GHMatters) 16/07/10 - 13 side walls 7 are forced into contact with each other at the upper ends of the side walls when a cladding sheet is positioned on the sides walls. 5 Each side wall 7 includes a reinforcing rib 11 to improve the stiffness of the side wall 7. The upper ends of the side walls 7 are shaped to define a generally circular opening 13 that facilitates 10 insertion of a screw-driver (not shown) to install the clip to an underlying structure. The flanges 9 are shaped to form at least part of an arch. 15 The transitions between the side walls 7 and the flanges 9 are tight radius curves in order to concentrate as much clip material as possible in the upper section of the clip 3 to optimise the strength and stiffness of this 20 section of the clip. Each flange 9 has a relatively steep approach angle of the order of between 40* and 75* described by the flange and the base 5. With reference to Figure 2, the 25 approach angle is described by the 2 dotted lines in the Figure and the angle between the lines is indicated to be 40*. Each flange 9 terminates in a sharp lower 30 outwardly facing (as opposed to inwardly turned) end that forms a contact surface 25 for engaging a re-entrant portion of one of the ribs of a cladding sheet. Each flange 9 includes in-turned sections 17 at 35 the two corners at the lower ends of the flange 9. The corner sections 17 form contact surfaces 21 that extend transversely to the contact surface 25 of the outer end of 23431981 (GHMatters} 16/07/10 - 14 the flange. With reference to Figures 6 and 7, each cladding sheet 29 is roll-formed from sheet steel and includes a 5 leading edge (not shown), a trailing edge (not shown), a central lengthwise extending rib, generally identified by the numeral 31, and pair of lengthwise extending pans 51 on opposite sides of the rib 31. 10 The cladding sheet 29 may be of any suitable length and width and may include any suitable number of ribs separated by pans. The rib 31 of the cladding sheet 29 includes two 15 sides, generally identified by the numeral 35, that are separated by a flat upper section 33. Each side 35 includes a section 41 that extends outwardly and downwardly from the upper section 33, a section 43 that extends downwardly and inwardly from the lower edge of the 20 section 41, and a section 45 that extends downwardly and outwardly from the section 43, and a downwardly and outwardly shoulder 45 that merges with a pan 51. The sections 43 of each upper retaining clip 25 section 15 define opposed re-entrant portions of the rib 13 and are hereinafter referred to as "re-entrant portions 43". The leading and trailing edges (not shown) of the 30 cladding sheet 29 are formed as partially-completed ribs in order to facilitate interlocking of successive cladding sheets. These partially-completed ribs are hereinafter referred to as "leading edge formations" and "trailing edge formations". 35 In use, a plurality of the clips 3 are fastened to purlins at spaced intervals along the length of the 2343198 1 (GHMatters) 16/07/10 - 15 purlins using screws. Thereafter, cladding sheets 29 are successively placed over the purlins in overlapping relationship. 5 The cladding sheets 29 are then progressively engaged with the clips 3 as the sheets are successively placed over the purlins. 10 This is achieved by successively pressing the leading edge formations, the ribs 31, and the trailing edge formations of the sheets 29 onto the clips 3 so that the leading edge formations, the ribs 31, and the trailing edge formations deflect outwardly and the flanges 9 of the 15 clips 3 deflect inwardly. This movement allows the leading edge formations 8, the ribs 11, and the trailing edge formations 10 to be positioned on the clips 3 with the surfaces 25 at the 20 lower ends of the flanges 9 and the surfaces 21 of the in turned corner sections 17 of the flanges 9 engaging the re-entrant portions 43 of the ribs 31 so that the cladding sheets 29 are secured to the clips 3. 25 This movement is illustrated in Figure 6 in relation to locating the rib 31 of one cladding sheet 29 onto one clip 3. It is noted that the steep approach angle of the flanges 9 and the inward movement of the side walls 7 illustrated in the Figures minimises the 30 possibility of denting of the sections of the cladding sheet that contact and slide over the flanges 9. It is also noted that in the installed position shown in Figure 6c the upper ends of the side walls 7 are in contact with each other. 35 Figure 7 illustrates the interaction between the clip 3 and the cladding sheet 29 as the cladding sheet is 2343198_1 (GHMatters) 16/07/10 - 16 being removed from the clip - as may be necessary in order to gain access to the roof cavity. With reference to Figure 7a, the first step of 5 removing the cladding sheet 29 from the clip 3 involves lifting the right hand side of the cladding sheet 29, as viewed in the figure, outwardly so that the cladding sheet is moved clear of the flange 9 on that side of the clip 3 and the section 45 of that side of the rib 31 is brought 10 into contact with and rests on the outer surface of the flange 9 on that side of the clip - as shown in Figure 7b. With reference to Figure 7b, the second step of removing the cladding sheet 29 from the clip 3 involves 15 moving the left hand side of the cladding sheet 29, as viewed in the figure, outwardly so that the cladding sheet is moved clear of the flange 9 on that side of the clip 3. It can be appreciated that the contact surfaces 21 of the in-turned corner sections 17 of the flanges 9 on that side 20 of the clip prevent the contact surfaces 25 formed on the lower end of the flange 9 digging into and damaging the rear-entrant portion 43 of the cladding sheet on that side of the cladding sheet. 25 Figure 8 is a perspective view of one embodiment of a clip assembly in accordance with the present invention which includes a strap 81 and two clips 83 that are similar to the clip 3 shown in Figures 1 to 7 in an as-manufactured form mounted to the strap 81. 30 Figures 9 to 13 are further views of the assembly shown in Figure 8 and one of the clips 83. As is indicated above and is apparent from the 35 drawings, the clips 3 and 83 are similar and the same reference numerals are used to describe the same structural features. 2343198_1 (GHMatters) 16/07/10 - 17 The strap 81 is a convenient means of fastening a plurality of the clips 83 to purlins (not shown) at required spaced intervals along the length of the purlins. 5 The strap 81 includes a flat base 87 and raised lengthwise extending sides 89. The sides 89 are in the form of downwardly opening channels. The inwardly facing walls (see Figure 8) of the sides 89 have spaced apart 10 slots (not shown) for receiving the outwardly extending tabs 15 of the base 5 of each clip 83. In addition, the width of the flat base 87 and the height of the sides 89 of the strap 81 are selected so that the clips 83 fit snugly on the flat base 87 and the downwardly facing 15 shoulders 73 of the clips 81 (see the shoulders 73 of the Figure 1 embodiment) rest on the top walls 93 of the sides 89 of the strap 81. The main differences between the clips 3 and 83 20 are as follows. 1. The flanges 9 of the clip 83 have a relatively gentle angle of approach and the length of the flanges is relatively short compared to the angle of approach and 25 length of the flanges of the clip 3. 2. The clip 83 does not have inwardly turned corners on the flanges 9. 30 3. The clip 83 has inwardly turned flanges 97 along the edges of the side walls 7 to improve the stiffness of the side walls. Many modifications may be made to the preferred 35 embodiment of the roofing system described above without departing from the spirit and scope of the present invention. 2343198_1 (GHMatters) 16/07/10