NZ214341A - Self-tapping screw with space between the leading and trailing threads on the shank - Google Patents

Description

214341 Priority Date<s); .

Complete Specification Filed: cb«: ..*.1*625/001 Publication Dais: .

P.O. Journal, No: ... iaoa patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 > COMPLETE SPECIFICATION "FASTENING SCREW AND METHOD OF FIXING PROFILE SHEET" -3-/WE W.A. DEUTSHER PTY.LTD. incorporated under the laws y of the State of Victoria, Australia, of 600 South Road, Moorabbin, Victoria 3189 Australia, hereby declare the invention, for which -i/we pray that a patent may be granted to-me/us, and the method by which it is to be performed, to be particularly descri the following statement 3 214341 # This invention relates to a method of securing profiled sheet to an underlying support and is particularly although not exclusively concerned with securing profiled sheet metal.

One form of profiled sheet metal with which the invention can be used is corrugated sheet as used for roof coverings for example. An example sheet of that form is profiled so as to have a plurality of laterally spaced ribs, each of which has upwardly and inwardly sloping side surfaces and a substantially flat crown or crest surface. It will be 10 convenient to hereinafter describe the invention with reference to that particular form of metal sheet, but it is to be understood that the invention has wider application. For example, the sheet profile could be such that the ribs are square or rectangular in cross section or they may have a curved crown. 'vj Corrugated sheet of the foregoing kind is usually sfecured to an underlying support or purlin by fastening screws which extend through the crest of each rib and threadably engage within the purlin. Such screws are 20 generally of the self-drilling kind and have a non-threaded section between the head and the threaded section. A resilient washer or other sealing element is generally provided between the screw head and the rib crest so as to aid in achieving a water tight seal.

A problem with the foregoing method is that nothing holds the crest of the rib against downward movement or deflection away from the screw head. Such movement can occur as a result of pressure on the crest through wind loading or because of a person walking on the roof with the result that the seal between the screw head and crest is broken. Even apart from such separation under load the quality of the seal between the screw head and rib is not good because of the limited pressure which can be generated between the screw head and rib crest.

Another problem is that a downwardly sloping depression is formed around the hole through the crest. That depression is initiated by the screw thread during its passage through the crest and is subsequently increased by pressure appj^e^ '' " • 39 to the crest by the screw acting through the agency qjfy the {- \ sw -2- I 14JAW9B6r. o / 2: -341 #» washer located beneath that head. The absence of support beneath the crest allows such a depression to be created with the consequent disadvantage that it creates a moisture trap and therefore promotes leakage through the crest of the rib.

Although the foregoing problems are particularly evident in the case of profiled sheets, they may also occur in other situations. For example, the same problems of deflection and leakage may occur when a flat metal sheet extends between and engages two spaced supports and is secured to another 10 underlying member which is spaced from the sheet. That is, the fastening screws pass through the unsupported portion of the sheet to engage with the underlying member.

It is an object of the present invention to provide an improved screw for use in fastening sheet material and in particular profiled sheet material. It is another object of the invention to provide an improved method of securing a sheet, and particularly a profiled sheet, to a support which overcomes or minimizes the foregoing problems. Yet another object of the invention is to provide an improved assembly of 20 a sheet and a support which are fastened together by a screw of the foregoing kind.

According to one aspect of the present invention, there is provided a fastening screw including, an elongate shank, a head at one end of said shank, a leading thread formed on said shank adjacent the opposite end thereof, and a trailing thread formed on said shank adjacent said head and being spaced apart from said leading thread in the axial direction of said shank, the two said threads have a different helix angle, said trailing thread has a crest 10 diameter greater than that of said leading thread, and the section of said shank between said threads has a- diameter less than the crest diameter of said leading thread.

According to a further aspect of the present invention there is provided a method of fixing a sheet to an underlying member by means of a fastening screw having an elongate shank, a head at one end of said shank and a drilling configuration at the other, and a leading thread and a trailing thread formed on said shank in axially spaced 39 relationship and being respectively remote from and adjac SW -3- 214341 to said head, said trailing thread having a crest diameter greater than that of said leading thread; said method including the steps of, engaging the drilling configuration end of said screw against a portion of said sheet, rotating said screw to drill through said sheet portion and to cause said leading thread to form a substantially complementary thread in the hole so formed in said portion, advancing said screw through said sheet portion to bring said drilling configuration end into engagement with said member, causing Pk said screw to drill into said member and form therein a w>- w thread substantially complementary to said leading thread, and advancing said trailing thread through said sheet portion hole so as to form a substantially complementary thread in said hole, whereby said trailing thread supports said sheet portion against deflection towards said member.

The essential features of the invention, and further optional features, are described in detail in the following passages of the specification which refer to the accompanying drawings. The drawings however, are merely illustrative of 20 how the invention might be put into effect, so that the specific form and arrangement of the features (whether they be essential or optional features) shown is not to be understood as limiting on the invention.

In the drawings: Figure 1 is an elevation view of one form of screw to which an embodiment of the invention has been applied; Figure 2 is an enlarged view of portions of the screw shown in figure 1; Figure 3 is a view similar to figure 1 but showing an 3fcr alternative form of screw; Figures 4 to 6 show a method of attaching a profiled sheet to a timber purlin by means of a screw as shown in figure 1; and Figure 7 shows the sheet rib as in figure 6 but with the screw omitted for convenience of illustration.

Figure 1 shows an example form of screw 1 to which an embodiment of the invention has been applied, and that screw 1 is of the self-drilling kind. That is, the screw 1 has a At i.. 39 drilling configuration 2 at the terminal end of the sfe&ftk 3 ' . sw ~4" I 14 JAN 1986 £ 2; >341 # and a threaded section 4 (hereinafter called the leading threaded section) is located adjacent that drilling configuration 2. Another threaded section 5 is located adjacent the screw head 6 and will be referred to as the | trailing threaded section. A relatively small non-threaded | section 7 is provided between the screw head 6 and the j trailing threaded section 5 to provide a recess for location of a sealing washer.

The trailing threaded section 5 has an outside diameter , 10 "D" (figure 2) which is greater than the outside diameter "d" ^ of the leading threaded section 4, and the outside diameters "D" and "d" of both threaded sections 5 and 4 is greater than the diameter "a" of the intervening non-threaded or plain i section 8. That plain section 8 will be hereinafter referred j to as the intermediate plain section so as to be j distinguishable over the short non-threaded section 7 I adjacent the screw head 6/ and the diameter "a" of that section 8 is preferably greater that the root diameter "b" of 5 the leading threaded section 4. In order to optimise the ? 20 desired result as hereinafter described, tests suggest that the outside diameter "D" of the trailing threaded section 5 • should be at least 15% greater than the outside diameter "d" jj of the leading threaded section 4 and an upper limit of 1 approximately 20% is preferred. It may be that success can | be achieved outside the range specified, but it seems that the stated relationship leads to more consistent results.

Figure 2 shows a preferred arrangement in which the root diameter of the trailing threaded section 5 is equal to the diamter "a" of the intermediate plain section 8. 30 Satisfactory results can be achieved if the aforementioned root diameter is less than "a", but in that event it is preferred that the root " diameter is . no more than 5% less than the diameter "a". The significance of the relationship between the aforementioned diameters will become apparent from the following description.

It is preferred that the respective threads of the two threaded sections 4 and 5 have the same pitch "p" and in view of the different outside diameter of those threads results in each having a different helix angle ~5" 19 juN1987£Ij / , / 214341 i respectively (see figure 2). In addition, the different depth of each thread causes the respective thread forms to be different and in particular have a different included angle os and-^-respectively as shown in figure 2. By way of example, if the larger and smaller threads are fourteen guage and twelve guage respectively and each has fourteen threads per inch, the included angle oc. of the larger thread may be 40° whereas the included angle of the smaller thread may be 60°. . ■>-- A laterally projecting flange 9 may be formed integral ^ with the screw head 6 as shown in figure 1 so as to provide a relatively broad bearing surface and a recess 10 is preferably formed in the underside of that flange 9. In the example shown in figure 1, the underside surface of the _ flange 9 slopes radially inwardly and axially away from the N ! — drill end 2 to form the recess 10. A neoprene or other resilient washer may be provided on the screw so as to bear , against the recessed undersurface of the flange 9.

The respective lengths of the two threaded sections 4 I 20 an<* 5 and the intermediate plain section 8 are selected to . suit requirements. In particular, those lengths may be related to the depth of the profile or corrugated rib of a ' sheet with which the screw 1 is intended to be used. j i Preferably, each screw 1 can be used with a range of profile | depths.

| Figure 3 illustrates an alternative form of fastening ! screw 11 and parts of that screw 11 which correspond to previously described parts of the screw 1 are identified by ^ the same reference numerals. ^ 30 Figures 4 to 6 illustrate how a screw 1 as shown in figure 1 can be used to fasten one form of profiled sheet 12 to an underlying member 13, which in the example illustrated is a metal purlin. In figure 4, the drill end 2 of the screw 1 has been engaged with the crest 14 of a rib 15 of the sheet 12 and the screw 1 has been rotated so as to drill through that crest 14. The leading threaded section 4 moves into the hole so formed and proceeds to form a corresponding thread in the sheet 12 so that the screw 1 is progressively advanced 39 through the sheet 12 towards the underlying purlin 13. y.?'Jtffteri SW -6- ' the leading threaded section 4 completes its passage through the sheet crest 14 the intermediate plain section 8 enters the threaded hole and reforms that hole to a larger size. Preferably, that occurs before the drill end 2 of the screw 1 reaches the purlin 13.

Continued penetration of the screw 1 then causes the drill end 2 to form a hole in the purlin 13 and the leading threaded section 4 self forms a thread in that hole so that the screw 1 is progressively drawn downwards (figure 5). During this part of the operation the trailing threaded section 5 engages within the hole in the sheet crest 14 and begins to form a corresponding thread in that hole. The neoprene washer 16 is subsequently brought into contact with the upper surface of the sheet crest 14 and is compressed by continuing rotation and consequent downward movement of the screw 1.

Since the root diameter of the trailing threaded section 5 is substantially equal to the diameter "a" of the plain section 8, the thread of the threaded section 5 will have maximum contact with the crest 14 during its passage through the crest 14. That is, the surface to surface engagement between the thread and the crest 14 will be over substantially the full depth of the thread. Such a high degree of engagement optimizes the ability of the screw 1 to support the crest 14 against downward deflection and also optimizes another aspect as described below.

It is preferred that the trailing threaded section 5 runs out when the screw 1 has completed approximately one full turn beyond the position at which the neoprene washer 15 begins to compress. That is, at that position the sheet crest 14 moves into the short non-threaded section 7 adjacent the screw head 6. As that run out of the trailing threaded section 5 occurs there is interaction between the last thread of that section 5 and the sheet which causes the portion of the sheet around the hole to be extruded upwards. The result is that an upwardly projecting lip 17 (figure 7) is formed around the hole and that provides an effective moisture barrier. The size of that lip 17 and conseque moisture barrier effectiveness is determined by the SW contact between the thread of the threaded section 5 and the crest 14. Optimum results are therefore achieved if that contact is over the full depth of the thread.

In the final position of the fastening screw 1 the neoprene washer 16 is compressed between the screw head 6 and the sheet crest 14 and the crest 14 is firmly held against downward movement of deflection by the trailing threaded section 5. That is, the crest 14 is supported by interference between it and the trailing threaded section 5. 10 The screw 1 therefore serves the dual functions of holding the sheet 12 to the purlin 13 and supporting the rib crest 14 against downward deflection. As a result, the seal between the screw head 6 and the crest 14 remains undisturbed by wind loading and any other loading on the sheet 12. Furthermore, the security of the seal is enhanced by the backward extrusion of the sheet 12 as referred to above.

It will be apparent from the foregoing that the present invention provides a substantial improvement over the prior art and that is achieved without adding to the operations 20 necessary to fasten the profiled sheet to a support.

Various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention as defined by the appended claims.

O 30 39 SW I 1 4 JANlvSo,.

V* / 21 ;341 G

Claims (24)

WHAT WE CLAIM IS-.

1. A fastening screw including, an elongate shank, a head at one end of said shank, a leading thread formed on said shank adjacent the opposite end thereof, and a trailing thread formed on said shank adjacent said head and being spaced apart from said leading thread in the axial direction of said shank, the two said threads have a different helix angle, said trailing thread has a crest diameter greater than that of said leading thread, and the section of said shank between said threads has a diameter less than the crest diameter of said leading thread.

2. A fastening screw according to claim 1, wherein a drilling configuration is provided at said opposite end of the shank.

3. A fastening screw according to claim 1 or 2, wherein the crest diameter of said trailing thread is 15% to 20% greater than the crest diameter of said leading thread.

4. A fastening screw according to any preceding claim, wherein the diameter of said shank section is greater than the root diameter of said leading thread.

5. A fastening screw according to any preceding claim, wherein the thread form of said leading thread is different to the thread form of said trailing end.

6. A fastening screw according to claim 5, wherein the thread form of said leading thread has an included angle of substantially 60° and the thread form of said trailing thread has an included angle of substantially 40°.

7. A fastening screw according to any preceding claim, wherein an annular recess is formed in the undersurface of said head to receive a resilient sealing ring or washer.

8. A fastening screw according to any preceding claim, wherein the root diameter of the trailing threaded section is substantially equal to the diameter of said shank section.

9. A fastening screw according to any one of claims 1 to 7, wherein the root diameter of the trailing threaded section is no more than 5% less than the diameter of said shank section.

10. A method of fixing a sheet to an underlying member by •^Jvmeans of a fastening screw having an elongate shank, a head t one end of said shank and a drilling configuration at the ther, and a leading thread and a trailing thread formed on - 9 - / 21 :34l said shank in axially spaced relationship and being respectively remote from and adjacent to said head, said trailing thread having a crest diameter greater than that of said leading thread; said method including the steps of, engaging the drilling configuration end of said screw against a portion of said sheet, rotating said screw to drill through said sheet portion and to cause said leading thread to form a substantially complementary thread in the hole so formed in said portion, advancing said screw through said sheet portion to bring said drilling configuration end into engagement with said member, causing said screw to drill into said member and form therein a thread substantially complementary to said leading thread, and advancing said trailing thread through said sheet portion hole so as to form a substantially complementary thread in said hole, whereby said trailing thread supports said sheet portion against deflection towards said member.

11 A method according to claim 10, wherein said leading and trailing threads have the same pitch and a different helix angle.

12. A method according to claim 10 or 11, wherein said trailing thread is passed completely through said sheet portion to locate beneath that portion.

13. A method according to any one of claims 10 to 12, wherein as said trailing thread passes through said sheet portion it causes the part of said portion which surrounds the hole therein to be extruded away from said member and thereby form an outwardly projecting lip.

14. A method according to any one of claims 10 to 13, wherein sheet is profiled and said portion thereof is the crest of a rib of the profiled sheet.

.15. A method according to any one of claims 10 to 14, wherein said fastening screw is a screw according to any one of claims 1 to 9.

16. An assembly including a sheet, a member underlying said sheet, and at least one fastening screw extending through a hole in a portion of said sheet and threadably engaging within SW -10- 2• *341 said member, wherein said fastening screw is a screw according to any one of claims 1 to 9, said leading thread engages within said member, said trailing thread is located within or below said sheet portion so as to support that portion against deflection towards said member, and said head overlies said sheet portion.

17. An assembly according to claim 16, wherein said sheet is profiled and said portion thereof is the crest of a rib of the profiled sheet.

18. An assembly according to claim 16 or 17, wherein a resilient sealing ring or washer is clamped between said head and said sheet portion.

19. An assembly according to any one of claims 16 to 18, wherein a portion of said sheet portion surrounding the hole therein is extruded away from said member to form an outwardly projecting lip.

20. An assembly according to any one of claims 16 to 19, when formed by the method of any one of claims 10 to 15.

21. A fastening screw according to any one of claims 1 to 9, wherein said two threads each have the same pitch.

22. A fastening screw substantially as herein particularly described with reference to either one of the embodiments shown in the accompanying drawings.

23. A method of fixing a sheet to an underlying member substantially as herein particularly described with reference to what is shown in the accompanying drawings.

24. An assembly including a sheet and an underlying member substantially as herein particularly described with reference to what is shown in the accompanying drawings.