GB2159745A

GB2159745A - A drill screw

Info

Publication number: GB2159745A
Application number: GB08512465A
Authority: GB
Inventors: Frei Markus
Original assignee: SFS Stadler AG
Current assignee: SFS Stadler AG
Priority date: 1984-05-25
Filing date: 1985-05-16
Publication date: 1985-12-11
Also published as: ATA174884A; DE3515531C2; DE3515531A1; GB2159745B; FR2564916B1; FR2564916A1; GB8512465D0; AT380545B; DE8512712U1

Abstract

In the case of a special screw for securing profiled plates (1) to a fixed substructure a screw (3) is provided which has a drilling tip (4), a threaded portion (5), wing- like boring projections (8), a threadless shank portion (6) and also a screw head (7). The length (L) between the start of the threaded portion (5) in the vicinity of the drilling tip (4) and the boring projections (8) corresponds approximately to the distance (A) resulting from the height (H) of the profile elevation (2) of the profiled sheets (1) less the thickness (D) of the sheets (1). In practice, the boring operation by the boring projections (8) is thereby complicated before the threaded portion (5) penetrates into the solid substructure (9). A tapered widening (12) is provided at the end of the screw shank (6) the largest diameter of which corresponds approximately to the bore diameter (C) of the boring projections (8) and to the hole diameter of a sealing washer (13) inserted beneath the screw head (7). <IMAGE>

Description

SPECIFICATION A screw The invention relates to a screw having a drilling tip, a screw shank with a self-tapping threaded portion adjoining the drilling tip, a threadless shank portion following the threaded portion and a screw head, wherein at the transition between the threaded portion and the threadless shank portion there are provided radially protruding wing-like, threadlike or rib-like boring projections for securing profiled panels or sheets of metal, plastics, fibre cement or the like to a solid substructure, in each case in the vicinity of a profile elevation.

Screws with the aforementioned structural features are known in various different embodiments.

In a known screw the possibility is also provided of securing profiled sheets to a solid substructure in each case in the vicinity of a profile elevation. In fact, in the case of sheets of porous material, for example of plastics or fibre cement, particular difficulties arise in producing the relatively large hole in the profiled sheets by means of radially protruding boring projections, because even prior to the application of these boring projections the thread of the threaded portion is driven into the solid substructure so that the advance of this screw upon being screwed in is dependent upon the thread pitch.As a result of the relatively high speed of rotation upon screwing in screws of this type, an excessively rapid advance for the drilling operation by means of the boring projections takes place, which leads to a break through in the vicinity of the through-hole in the profiled sheets. Subsequently, this may result in leakage, since profiled sheets of this type are mainly used for roofing. In this known development there is also the disadvantage that between the drilling tip and the threaded portion further radially protruding boring projections are provided so that, after the passage of these boring projections in the vicinity of the profiled sheets, the screw can drop freely downwards until the drilling tip comes into contact with the solid substructure.This leads to defects in screwing in and, generally, the screwing-in takes place at an angle since guidance is no longer provided in the vicinity of the screw shank.

The present invention is based on the object of devising a screw which is specially suited for use in securing profiled sheets or panels, in which during the screwing-in operation the screw is afforded constant guidance and in which, when the boring projections are in use, the boring advance is independent of the thread pitch.

According to the invention, with a screw of the initially described type this is achieved in that the length between the start of the threaded portion in the vicinity of the drilling tip of the screw and the boring projections corresponds approximately to the distance resulting from the height of the profile elevation of the profiled sheets less the thickness of the sheets. As a result of these practical measures according to the invention it is achieved that, until the drilling tip is applied against the solid substructure, the screw is guided in the profiled sheet, namely by the threaded portion which has been screwed therethrough. Furthermore, as a result of this special design it is achieved that, when the boring projections are in use, the boring advance is determined solely by the pressure on the screw and not, depending on the speed of rotation, by the thread pitch provided.Therefore, as soon as the threaded portion penetrates into the solid substructure, the boring operation of the boring projections is already completed or is immediately prior to completion. It thus cannot result in a break through or unintentional breaking off of these boring projections. Moreover, it is thereby ensured that until the threaded portion penetrates into the solid substructure a double guidance is afforded both by the drilling tip and by the boring projections rotating in the widened bore in the profiled sheet.

Tests have shown that even with profiled sheets of fibre cement the screw according to the invention offers the possibility of direct fastening. Previously, with such profiled sheets of fibre cement, it was always necessary for the entry bores to be provided in the sheets by predrilling, after which the screws could only then be inserted.

Further features and special advantages of the invention will be explained in more detail, by way of example, in the following description with reference to the drawings, wherein Figure 1 shows a cross-section through a profiled sheet; Figure 2 shows a screw according to the invention for use in a solid substructure of metal; Figure 3 shows an example of a screw of the type according to Figure 2 in use; Figure 4 shows a screw for use in a solid substructure of wood, and Figure 5 shows an example thereof in use; Figure 6 shows a section through two profiled sheets overlapping one another; Figures 7 and 8 show two cross-sectional shapes of the screw in the vicinity of the boring projections.

The profiled sheets are standardized in certain dimensions. In the case of the corrugated sheet illustrated in Figure 1, the height H of a profile elevation 2 and the thickness D and thus the distance A are predetermined in accordance with standards. Therefore, the sheets 1 available on the market from a wide variety of manufacturers always have the same dimensions.

The screw 3 according to Figure 2 comprises a drilling tip 4, a screw shank with a self-tapping threaded portion 5 adjoining the drilling tip 4, a threadless portion 6 and a screw head 7. Radially protruding boring projections 8 are provided at the transition between the threaded portion 5 and the threadless shank portion 6.

To enable optimum drilling, screwing in, thread cutting and optimum guidance to be carried out during the screwing-in operation, the dimensions of the screw 3 are dependent upon a sheet 1 and are determined as follows.

The length L between the start of the threaded portion 5 in the vicinity of the drilling tip 4 and the boring projections 8 corresponds here to the distance A which corresponds precisely to the height H of the profile elevation 2 less the thickness D of the sheets 1.

In the case of the screw in Figure 2 a machine thread is provided in the vicinity of the threaded portion 5 and the drilling tip 4 is designed as a metal-drilling tip so that a screw 3 of this type is suitable for use with a solid,metal substructure 9. In an embodiment of this type it is also advantageous if the sum of the length L from the start of the threaded portion 5 up to the boring projections 8 and the length B of the drilling tip 4 corresponds approximately to the height H of the profile elevation 2 of the profiled sheets 1, the length B of the drilling tip 4 being equal to or greater than the thickness D of the profiled sheets 1.

Referring now to Figure 3, it is evident that when screwing in a screw 3 firstly the drilling tip 4 passes through the sheet 1, whereupon the thread of the threaded portion 5 engaging in the bore wall ensures guidance and thus alignment of the screw 3. Subsequently, when the boring projections 8 come into use, in an embodiment of this type at most one thread is still applied at the lower edge of the sheet 1, in which case this single thread cannot entail any increase in advance. Therefore, the boring procedure with the boring projections 8 then commences, so that a larger through-hole 10 is provided in the sheet 1. During this boring operation by means of the boring projections 8 the drilling tip 4 has already penetrated into the solid substructure 9, e.g. consisting of a metal sectional bar.As a result of the special dimensions in the vicinity of the screw shank it is now achieved that, prior to the penetration of the threaded portion 5 into the bore in the solid substructure 9, the boring operation by the boring projections 8 in the sheet 1 is completed or the completion of the boring operation is immediately imminent. It is thereby achieved that the boring operation can take place at a rate of advance which is in fact advantageous for boring. The screwing-in of the thread then takes place at a substantially higher rate of advance, since this advance is determined by the speed of rotation when screwing in the screw and by the thread pitch.

The measures according to the invention enable a clean bore to be provided in the profiled sheet 1, without tearing the bore walls and without accidentally breaking,off the boring projections 8. This is of particular importance precisely when applying delicate profiled sheets, for example fibre cement boards.

The embodiment according to Figure 4 relates to a screw 3 with a wood-screw thread in the region of the threaded portion 5 and a drilling tip 4 adapted thereto, in which a milled cutting slot 11 is provided. The cutting slot also extends into the threaded portion 5.

Therefore, if the solid substructure 9 consists of wood, it is necessary to provide a threaded portion 5 in the manner of a wood-screw thread. A wood-screw thread of this type has greater thread pitch than a machine thread, so that precisely in such an embodiment the dimensions according to the invention are also of considerable importance. In this development the length L is also matched approximately to the distance A in the profiled sheets 1. However, in this embodiment the drilling tip 4 is made substantially shorter, since with a wood screw the thread must adjoin the drilling tip as closely as possible.Therefore, in this special development, in addition to the conditions of the particular length L, the further advantageous specification may be required according to which the sum of the length L from the start of the threaded portion 5 up to the boring projections 8 and the length B of the thread less drilling tip 4 is equal to or less than the height H of the profile elevation 2 of the profiled sheets 1, the length B of the threadless drilling tip 4 being the equal to or less than the thickness D of the sheets 1. Figure 5 illustrates a practical example of such a screw 3 according to Figure 4. Here too it is shown that when the drilling tip 4 penetrates into the solid substructure 9 of wood the boring operation by the boring projections 8 is already completed or completion is immediately imminent. More over, here too corresponding guidance is provided during screwing in until the thread penetrates into the solid substructure 9.

Figure 6 shows a cross-section through a sheet joint, namely where two profiled sheets 1 are placed one on top of the other at their adjoining ends. At such a sheet joint, for guidance reasons, the dimensions of the screw are of course matched to the underlying profiled sheets 1, especially as in the material of the profiled sheet 1, which is relatively softer with respect to the substructure, the region of the threaded portion immediately adjacent the boring projections 8 turns freely so that in practice the guidance is afforded by the thread outer diameter and the advance of the boring operation of the boring projections 8 is not determined by the thread pitch.In an embodiment with a wood-screw thread it is normally not possible to speak of a drilling tip and a threaded portion following the drilling tip, since for the best possible engagement in the solid substructure the threaded portion extends immediately up to the drilling tip at the free end of the screw. In such an embodiment the length L from the free end of the screw up to the boring projections 8 then corresponds approximately to the distance A of the profiled sheets 1 explained in detail above.

Precisely when using a threaded portion 5 in the form of a wood-screw thread and when using such screws in fibre cement boards, difficulties arise in drilling into and boring through the fibre cement boards. According to the present invention, in the screw embodiment according to Figure 4, the drilling tip 4 is provided with a point angle of approximately 90 , so that it is possible to prevent any splintering and splitting of the profiled sheets in the drilling zone.

The boring projections 8 can in known manner be arranged in pairs opposite one another. However, it would also be entirely possible to provide a plurality of boring projections spaced apart multiply on the periphery of the screw shank. Figures 7 and 8 show two possibilities for the design of such boring projections. The difference merely lies in the slightly different radii at the transition of the boring projections 8 into the shank portion 6. A slight variation between these two Figures is also to be found in the thickness of the boring projections 8. As is evident here, stamping out the boring projections 8 in this way offers the possibility of weakening the screw shank 6 as little as possible, since the latter has to transmit the torque during the screwing-in of the threaded portion 5 and during the drilling by the drilling tip 4.The boring projections 8 may be of very simple shape when they are rounded on their outer side, in which case for most applications no additional cutting edge is required in practice.

Instead of the boring projections 8 shaped in the form of wings, it is also of course possible to provide radially protruding ribs aligned concentric to the screw axis. Ribs of this type could, if necessary, also extend helically on the screw shank 6.

The bore diameter C of the boring projections 8 is preferably in the region of 2 to 4 mm greater than the diameter E of the threadless screw shank 6. It is thereby possible to achieve adequate mobility of the profiled sheets 1 to be secured, relative to the substructure 9.

Another advantageous development of the screw according to the invention lies in that a tapered widening 1 2 is provided at the end of the screw shank 6 on the screw head side, in which case the diameter of the base of this widening 1 2 on the screw head side corresponds approximately to the bore diameter C of the boring projections 8. Moreover, this diameter corresponds approximately to the hole diameter of a sealing washer 1 3 which can be inserted under the screw head 7. The sealing washer 1 3 can thereby be fitted very simply over the screw and thus also over the boring projections 8 under the screw head 7.

The tapered widening 1 2 ensures that, even in the event of possible angled screwing in of the screw 3, the sealing washer 1 3 is nevertheless centred relative to the screw head so that no sealing problems can arise.

Precisely with such an application of a screw 3 the action is very important with a sealing washer 1 3 of this type. The sealing washer 1 3 used here consists of a disc-like metal washer 14 and one or more resilient sealing rings 1 5 thereunder, provided facing away from the screw head 7. Preferably, these sealing rings have a thickness of up to 6 mm, so that adequate sealing is provided even in the case of a screw which, nevertheless, has been inserted at an angle.

The measures according to the invention have been described on the basis of a corrugated profiled sheet. Of course, the measures according to the invention are likewise applicable to differently profiled sheets, in which case adaptation to the standardized sheet dimensions is of course always necessary.

The indicated dimensional comparisons may of course vary within the normal tolerances; however, it is necessary to retain the basic feature that, prior to the necessary penetration of the thread into the solid substructure. the boring operation by the boring projections 8 must be completed or the termination of this operation must be immediately imminent.

Claims

1. A screw having a drilling tip, a screw shank with a self-tapping threaded portion adjoining the drilling tip, a threadless shank portion following the threaded portion and a screw head, wherein at the transition between the threaded portion and the thread less shank portion there are provided radially protruding wing-like, thread-like or rib-like boring projections for securing profiled panels or sheets of metal, plastics, fibre cement or the like to a solid substructure, in each case in the vicinity of a profile elevation, characterised in that the length between the start of the threaded portion in the vicinity of the drilling tip of the screw and the boring projections corresponds approximately to the distance resulting from the height of the profile elevation of the profiled sheets less the thickness of the sheets.

2. A screw according to Claim 1, with a machine thread in the vicinity of the threaded portion and a metal drilling tip, characterised in that the sum of the length of the start of the threaded portion up to the boring projections and the length of the drilling tip corresponds approximately to the height of the profile elevation of the profiled sheets, the length of the drilling tip being equal to or greater than the thickness of the profiled sheets

3.A screw according to Claim 1, with a wood-screw thread in the vicinity of the threaded portion and a drilling tip with a milled cutting slot, characterised in that the sum of the length of the start of the threaded portion up to the boring projections and the length of the threadless drilling tip is equal to or less than the height of the profile elevation of the profiled sheets, the length of the threadless drilling tip being equal to or less than the thickness of the sheets.

4. A screw according to Claim 1, with a wood-screw thread in the vicinity of the threaded portion and a drilling tip with a milled cutting slot, characterised in that the threaded portion extends as far as immediately up to the drilling tip at the free end of the screw.

5. A screw according to Claim 3 or Claim 4, characterised in that the drilling tip has a point angle of approximately 90 .

6. A screw according to Claims 1 to 4, characterised in that the boring projections are arranged in pairs opposite one another or multiply spaced apart on the periphery of the shank.

7. A screw according to Claims 1 to 4 and 6, characterised in that in per se known manner the boring projections are in the form of wings, ribs or the like projecting over the screw shank and aligned concentric to the screw axis.

8. A screw according to Claims 1 to 4, 6 and 7, characterised in that bore diameter of the boring projections is from 2 to 4 mm greater than the diameter of the screw shank.

9. A screw according to Claim 1 and any of the preceding Claims, characterised in that a tapered widening is provided at the end of the screw shank on the screw head side, in which case the diameter of the base of the widening on the screw head side corresponds approxi mately to the bore diameter of the boring projections and also to the hole diameter of a sealing washer which can be inserted beneath the screw head.

10. A screw according to Claim 9, characterised in that the sealing washer consists of a disc-like metal washer and one or more resilient sealing rings thereunder, provided facing away from the screw head.

11. A screw substantially as hereinbefore described with reference to and as shown in Figure 2 or in Figure 4, or in Figures 2 or 4 as modified by Figure 7 or Figure 8 of the accompanying drawings.