GB2142108A

GB2142108A - Fastener for securing roofing sheeting over soft insulating material to a fixed support

Info

Publication number: GB2142108A
Application number: GB08415501A
Authority: GB
Inventors: Gerhard Boegel
Original assignee: SFS Stadler AG
Current assignee: SFS Stadler AG
Priority date: 1983-06-22
Filing date: 1984-06-18
Publication date: 1985-01-09
Also published as: GB2142108B; DE3420863C2; NL193345C; NL193345B; ATA229683A; DE3420863A1; NL8401730A; AT380051B; DE3420863C3; GB8415501D0

Abstract

A fastener (1) for securing roofing sheeting over soft insulating material to a fixed support, comprises a screw (4) with a drilling tip (6) and a self-tapping screw-thread (7), and a plate washer (5) loosely received on a threadless shank portion (10) immediately adjacent the head (9) of the screw (4), so that the washer (5) can tilt. In the upper side of the washer, a recess (13) is formed for accommodating the screw head (9). An abutment in the form of a protruding collar or projection is arranged at a distance from the screw head (9) in or at the end of the thread-less shank portion (10); the abutment may be formed by the thread end. The fastener (1) is thus able to withstand being trodden upon. <IMAGE>

Description

SPECIFICATION Fastener for securing roofing courses on soft insulating material to a fixed support The invention relates to a fastener for securing roofing courses or sheeting on soft insulating material to a fixed support, comprising a self-drilling and self-tapping screw and a large area (plate) washer, wherein immediately adjacent the screw head the screw has a threadless shank portion whose diameter is the same as or less than the diameter of the opening in the washer to be fitted and wherein on the upper side of the washer, in the vicinity of its passage opening, a recess, countersinking or the like is provided for recessing the screw head.

Fasteners of this type are thus used to secure insulating materials on fixed supports, e.g. insulating panels on roofs. Insulating means of this type have paper or foil coverings which form a seal on their surface. For fastening there are used fasteners in the form of screws which have relatively large washers so as thereby to obtain a satisfactory mounting. A waterproof sealing is applied over this insulation.

When equipment has to be conveyed on a roof, it may happen that, for example, a worker steps on a washer or in the immediate vicinity thereof, or that vehicles or tools travel over the washer. Such locally concentrated forces result in the screw head being pushed through the applied sealing or in the washer piercing the roofing course applied on the insulating material. Damage of this type causes the roof to leak.

There are also insulations which sag in the course of time. Upon installation; sufficient resistance is offered when trodden on, but after two to three years the level of the insulation drops. The roof covering follows this sagging and the fastener recessed in the fixed support, e.g. a sheet-metal section, then protrudes with its head far above this level. The danger of damage as a result of wearing through is also evident. In the case of relatively hard insulations, a distance of the screw head from the aforementioned level of from 2 to 3 mm is sufficient. For soft insulations,e.g. for insulations consisting of mineral fibures, which sag in the course of time, it is necessary to stipulate a so-called tread-resisting construction. In this case it is important for the surface to be so raised that any treading through or wearing through is no longer possible.

Even if the washer is either firmly connected to the screw or is axially displaceable, it is not possible to eliminate all disadvantages. Fasteners of one known type are pressed at an angle when walked upon or travelled over. It is well known, when taking into account the admissible stress in the anchoring, that the most inclined position of the fastening is situated in the fixed support, namely in the sheet-metal section. The forces then occurring are so slight that folding over of a metal washer can no longer take place. The known development (DE OS 31 06 844) only deals with the fastening of the insulation. However, no sealing is necessary here. Even with regard to the fastening of the roofing sheets it does not involve the provision of a seal between these latter and the fastening means.

Instead, a seal is ensured by suitable design of the overiapping of the roofing sheets. This known development also concerns in particular the means for preventing rotation of the washer. For this purpose radially formed ribs are provided. Problems arise in washers of the type provided with ribs when they are being separated in automatic fitting devices. The fitting depth and thus the tightening condition cannot be accurately controlled. Normally, the counterpressure is produced by screwing in the screw until the disc is fully tightened and, in the case of soft insulation, the disc is fashion even recessed in cup-like. For this purpose no pressure must be exerted.

In order to remain operable over a long period, even with extremely soft insulating materials, it is necessary for the axially movable disc according to another known development (DE OS 31 37 836) to have a considerably greater range of axial play. Extremely deep cups have known for many years.

Here they were used only for extending the screws without forming a cold bridge. Discs with such deep cups cannot be delivered economically to an automatic fitting device.

The fastening elements also serve for direct fixing of the roof covering. The roofing sheet is secured at the seam, in which case the counterpressure of the insulation is of course desirable. If this counterpressure weakens, the sheet will, as it were, hang from the fastener. It is then possible for only slight tensile stresses to be taken up.

The invention is based on the object of obviating the disadvantages of the known fasteners and of enabling insulating material to be fastened in such a way that it can withstand being walked upon.

Accordingly it is proposed, in accordance with the invention, that an abutment, an optionally protruding collar, projection or the like, is formed or arranged at distance from the screw head in the threadless shank portion or at the end of the threadless shank portion, and that the washer abuts against the abutment, collar, projection or the like, with its area defining the passage opening and can be tilted relative to the screw axis.

As a result of these measures according to the invention there is devised a fastener for securing insulating material, which fastener can withstand being walked upon and which can be readily exposed to additional loads without causing damage to the applied sheets or loosening of the screw.

Users of mechanical fastenings of roofing sheets have considerable doubts regarding the anchoring reliability of screws in the thin supporting sheet metal, in particular under the expected repeated loading caused by drag forces. Moreover, the constant alternating loads and the deflection of the screw when the washer is trodden upon result in loosening of the screw connection. Because the washer can be tilted relative the screw axis, as a re sult of the measures according to the invention, the screw itself is not automatically placed under bending stress when a load is applied to the washer, but the washer can just move relative to the screw. The danger of the screw being "levered out" of the supporting metal sheet is thereby decreased.

Even if the insulating material is compacted in the course of time, the screw heads themselves do not protrude above the insulating material, and it is also brought about that the washers do not follow too deeply if the insulating material sags. The danger of the overlying roof covering being worn through is also excluded. With simple structural expedients applied to a screw and to a washer it is possible to provide a fastener having optimum operation precisely for this particular application.

The object set in accordance with the invention is achieved only by the measures according to the invention, namely the provision of an abutment or the like on a screw shank, against which the washer can bear, and by the possibility that the washer can move relative to the screw axis. Therefore, no bending stress is applied to the screw itself in the event of one sided loading of the washer, so that the screw cannot be loosened. The washer also cannot be pressed into the insulating material by the abutments or the like provided,but the screw head remains in practice always in the same recessed position in the washer, since this washer cannot in fact pass downwards over the abutment or the like on the screw.

Further inventive features and particular advantages will be explained in more detail in the fol lowing description with reference to the drawings; wherein: Figures 1 and 2 show a practical example of a rigid connection viewed normally and under load when using hitherto conventional fasteners; Figures 3 and 4 show a practical example of a fastener according to the invention in the normal condition and also in the condition under load; Figure 5 shows a view of screw, and Figure 6 shows a screw with fitted washer; Figure 7 shows a further screw embodiment, and Figure 8 shows this screw embodiment with fit ted washer; Figure 9 shows another embodiment of a screw; Figure 10 shows in section the washer illustrated in Figs. 6 and 8; Figures 11 and 12 show another washer in longitudinal section and in plan view;; Figures 13 to 16 show different views of another embodiment of a washer, wherein Fig. 13 shows a section along the line A-A, Fig. 5 shows a section along the line B-B and Fig. 16 shows a view in the direction C in Fig. 14; Figures 17 and 18 show two further embodi ments of a washer in an oblique view; Figure 19 shows a further embodiment of a screw; Figures 20 and 21 show two embodiments of a screw with specially shaped abutments for the washer; Figures 22 to 24 show further embodiments of screws, as well as support abutments for the washer, wherein Fig. 23 shows two screwed-in positions; Figures 25 and 26 show an embodiment with an additional insert to the washer; Figures 27 and 28 show two further embodiments of screws in conjunction with corresponding washers;; Figures 29 and 30 show a possibility for the arrangement of two washers situated in correspondence with one another; Figure 31 shows a possibility for the design of a screw and also of the associated washer, wherein two screwed-in positions are also illustrated; Figure 32 shows a special embodiment of a screw; Figure 33 shows a variant of a thread run-out in relation to Figure 19.

It is evident from Figs. 1 to 4 that a fastener 1 serves for securing insulating material 2 to a fixed support 3, e.g. a metal section. The fastener comprises here a screw 4 and a relatively large washer 5. In this case the screw is advantageously designed to be self-drilling and selftapping.

If fasteners are now used in which the washer 5 is connected relatively rigidly to the screw 4, the screw or the screw shank would have to follow any movement of the washer 5. In the hitherto known designs this would lead, as evident from Fig. 2, to bending stress on the screw shank, whereupon particularly with alternating loads this results in loosening of the screw and also damage to the thread.

However, as shown in the embodiment according to Figs. 3 and 4, if the washer 5 is designed to be tiltable relative to the screw axis, only the washer moves under a corresponding load, while the screw and thus the screw shank remains in a vertical normal position. As a result of this, firstly, the screw is not loosened and, secondly, any such movement does not cause damage to the roof covering or to insulating material 2.

A fastener as used in Figs. 3 and 4 will now be described in more detail with reference to Figs. 5 and 6. A fastener 1 thus comprises a screw 4 and a washer 5. The screw is designed to be self-drilling and self-tapping. Therefore, a drilling tip 6 and a screw shank 8 having a thread 7 are provided. Corresponding to the application, the washer 5 is designed to be large in area. Directly adjacent to the screw head 9 the screw 4 has a threadless shank portion 10, the diameter of which is the same as or less than the diameter of the opening 11 in the washer 5 (cf. Fig. 10). An abutment, collar, projection or the like is formed or arranged on the shank at a distance from the screw head 9. In the embodiment according to Figs. 5 and 6 this abutment 12 is formed by the end of one thread turn, in which case preferably a strengthened thread run-out according to Fig. 19 or Fig. 33 is provided.

On the upper side of the washer 5, in the vicinity of its passage opening 11, there is formed a recess 13, countersinking or the like for recessing the screw head 9. Because of this design and the threadless portion with the abutment 12, the washer 5 can be tilted relative to the screw axis 14 so as to enable insulating material to be secured in such a way that it can withstand being walked upon. Therefore, when such a washer 5 undergoes one sided loading, it is merely tipped relative to the screw axis 14 and practically no bending stress is exerted on the screw 4 nor on the screw connection between the screw 4 and the fixed support.

The washer 5 is here thus provided with an opening 11 whose diameter corresponds approximately to the core diameter of the thread of the screw used. The threadless portion also corresponds approximately to the core diameter of the threaded portion 8. The screw is screwed through the small opening 11 in the washer 5, whereupon the washer 5 is then situated freely rotatably on the threadless portion 10 below the screw head 9.

It is thus possible for the fitting position to be beyond the recessing of the screw. There is no de pendence upon pressing against the disc.

With relatively short fasteners, the amount of time required to screw the entire screw length through the washer can be tolerated. With greater lengths it is possible to provide after the threadless portion a short supporting thread 15 or 16 in accordance with Figs. 8 and 9.

Since the screws are produced by rolling without removing material, a transition zone of a shank with effective (flank) diameter is produced.

In the development according to Fig. 7, the threaded shank 8 is provided continuously with uniform thread but the threadless portion 10 is of smaller diameter than the core diameter of the threaded portion. A development of this type is also evident from Fig. 8. It is also shown in Fig. 8 that the supporting thread 15, which is disposed adjacent to the threadless portion 10, can be de signed as a two-start thread. Of course, it is also possible to provide multi-start threads. In the development according to Fig. 9, the supporting thread 16 is designed to be of larger effective di ameter than the thread 7 of the rest of the threaded shank portion 8. The anchoring thread may thus have the same external diameter as the supporting thread 15, 16 or else different diameters may be provided here.

It is remarkable that, despite the enlargement of the opening 11 in the washer 5 to the effective di ameter (that is if portions lying therebetween with effective diameter are provided), there are still sup porting forces of a magnitude of above 150 Pa with an external diameter of 4.8 mm and with metal sheet ST 37 provided as fixed support at a thick ness of 0.9 mm. This enables an extremely eco nomica! solution to be achieved.

In the development according to Fig. 8, in which the supporting thread 15 is of two-start design, the washer 5 reaches its free space more rapidly and is supported by two runout thread ribs. If a more slender thread rib is used than with the supporting thread, it would even be possible to extend it beyond the outer diameter thereof.

The development according to Fig. 9 is a somewhat more expensive embodiment in respect of production costs. However, greater supporting forces are provided here for the washer. The retaining thread 16 is intentionally designed to be larger than the anchoring thread 7.

Figs. 20 and 21 show a special development of a screw in the vicinity of the threadless shank portion 10. Upon screwing in a screw of this type the washer 5 is intended to be tilted about the projecting cams 17. Its lower edge then rests on one projection 17. This is sufficient to provide adequate low-pressure protection against snow and from being accidentally stepped upon. The projecting cams 17 can also be formed by being stamped out, as is the case for example in Fig. 21. Such -stamped-out portions are known per se in thumbscrews or wing bolts. However, these cams 17 have a completely different purpose. In the embodiments illustrated, two cams 17 are provided lying opposed to one another in the longitudinal direction of the screw axis and turned through 1800.

Upon fitting the washer 5, therefore, a simple to and fro movement is necessary. However, it would be possible to provide a plurality of such cams on the periphery of the threadless shank portion 10, whereupon it would then be necessary to take appropriate measures to fit the washer. In order to ensure sufficient stability of the fitted washer 5, the cams 17 overlap in the longitudinal direction of the screw axis so that proper tilting by a given amount is necessary in order to enable fitting or removal of the washer 5 actually to be undertaken.

The washer 5 is provided with a funnel-shaped recess 13 both in the embodiment according to Fig. 10 and in the embodiments according to Figs.

11 to 16. This recess is large enough to be able to accommodate entirely the screw head 9 of a fitted screw.

In the embodiment according to Figs. 11 to 16, in plan view the washer is formed with parallel longitudinal boundaries 18 and with circularly rounded narrow ends 19. Because of its special shape, a design of this type is also particularly positively suited for being fed to automatic fitting devices for fastening the roofing sheet, roofing course,etc. In the special development according to Figs. 13 to 16, the opening 11 in the washer 5 for the passage of the screw shank has a radially outwardly extending notch or a corresponding slot or the like, in which case it is possible for the thread turn of the screw to pass through this notch 20. It is thereby readily possible for the screw to be screwed through, without impairing the supporting force of the washer 5.

The position of the radial notch 20, which allows the passage of the screw thread, is designed so as not to impede separation in an automatic fitting device. Incorrect positioning would result in a complete blockage of the fitting device. This notch provides a gaping opening in the plane B-B. At least after the passage of the reinforced thread run-out, this opening prevents any untwisting of the screw in the embodiment according to Fig. 19 or Fig. 33.

This effect could be reliably improved if the washer were to be made of resilient material. After the easy passage of the thread turn, the gap would be closed to an extent which totally excludes any passage through the gap in the event of reverse rota tion of the screw. A possibility is thereby provided of positively locking the rotation of the screw. As a result of the seam fastening of the roofing course,the washer is locked in a manner precluding rotation. Of course, different materials may be used here for such a washer, advantageously soft iron. Naturally it is also possible to provide a plastics disc for such a washer.

Figs. 17 and 18 show a possibility for the special development of the washer 5. It is evident here that with sufficient lowering of the centre of the washer it is likewise possible for such fasteners to withstand being walked upon to a certain extent. In the supply condition, namely whiie being fed to an automatic fitting device, the washer 5 has to be formed as flat as possible. As already stated, deep cups cannot be economically and efficiently stored in a magazine. The "deep cup" is achieved by lowering the disc centre. In the development according to Fig. 17, the washer 5 has slot portions 21 extending circularly coaxial to the central opening, the slot portions being disposed staggered relative to one another and with varying diameter encircling each other.In this way there is formed, as is it were, a "opened section" which offers a substantially satisfactory possibility of forming a depression. However, a development of this type is applicable only to square or circular washers 5.

In the development according to Fig. 18, the washer comprises two parts 22 and 23 movable relative to one another, wherein a central part 23 has the opening 11 and, optionally, a countersunk portion 24. The central part 23 is surrounded by the part 22, this central part 23 being suspended from the part 22 surrounding it and movable transversely to the support plane of the washer 5. In one advantageous embodiment, provision is made for the central part 23 to be suspended resiliently from the surrounding part 22. Accordingly, resilient connecting means 25 are provided which can be secured to the corresponding parts 22, 23, for ex ample, by respective turned-over flanges 26 and 27.

Fig. 19 shows another embodiment of the design of a screw, wherein it concerns particularly the threaded portion 8 adjoining the threadless shank portion 10. The thread turn 28 shown here is of reinforced or broadened design at the run-out end so as to form a substantially larger support surface, i.e. a corresponding abutment 12. In this con nection it is also advantageous if the ends of the thread turn or turns 28 associated with the thread less portion are cut off in a plane 29 extending transversely to the screw longitudinal axis. There is thereby formed a relatively large supporting surface extending over a corresponding peripheral zone, i.e. an abutment 12 extending correspond ingly over a large angle.

A special embodiment of a reinforced thread runout is evident from Fig. 33. Provision is made here for the thread section to undergo a transition from a triangular thread-rib cross-section to a tra pezium-shaped cross-section with approximately uniform base length. Relatively simple production of a rolling jaw is thereby possible. Therefore, particular importance is attached to the enlargement of the support surface for the washer and to the strengthing of the thread run-out, including satisfactory filling after the rolling operation. Of course, in the vicinity of the strengthened portion of the thread run-out, it is also possible for the base length to be greater in relation to the normal threaded portion so that, in certain circumstances, the thread flanks thus have the same angle of inclination both in the strengthened portion and in the normal threaded portion.

In the development according to Fig. 22, a circular abutment collar 30 is provided on the threadless shank portion at a distance from the screw head 9. A spring member 31 is inserted between the abutment collar 30 and the washer 5 fitted under the screw head 9. Therefore, a type of locking washer is fitted here beneath the screw head 9.

The spring member 31 provided here is thus helical and takes the form of a coiled plate spring, in which case it forms a type of thread which can pass through a slot 32 extending radially from the opening 11 in the washer 5. When trodden upon, this spring member 31 is correspondingly compressed and restored to its flat position, whereupon the washer is prevented from undergoing further downward movement.

In a development according to Fig. 23, a sleeve 33 is provided surrounding the screw shank 8, which sleeve in the screwed-up position abuts against the fixed support 3 and which at its upper end forms an abutment collar 34 for supporting the washer 5, The screw shank 8 and, here in particular, the threadless shank portion 10 have two zones 35 and 36 of different diameter, between which a likewise threadless portion 37 is provided the manner of a truncated cone. On the left-hand side in Fig. 23 there is shown the fitting position for the washer which, therefore, has to be fitted over the sleeve 33 and then encounters an abutment 34 above the sleeve. During further screwing-in or when the sleeve 33 encounters the portion 37, this upper end is widened and drawn over the zone 36 of the threadless shank portion 10.In this zone, therefore, the sleeve 33 is of greater diameter because of the widening, so that a more secure abutment 34 is created for the washer 5.

The sleeve 33 may be formed from a readily deformable aluminium or plastics tube. In order to ensure easier widening upon engaging over the zone 36, it is advantageous for the corresponding free end of the sleeve 33 to be provided with at least one longitudinal slot.

Instead of the aluminium or plastics tube, a helical spring could also be used which passes over the entire zone which is occupied by the insert 33 in the development according to Fig. 23. A helical spring of this type constitutes a sort of thread substitute but has the advantage of greater retention force when, at.the end of the fitting operation, turn abuts against turn.

The same applies to an embodiment according to Fig. 24, in which an additional neck 38 has to be provided which has to accommodate an equally short supporting spring 39. The abutment for pressing down the washer 5 is here also constituted by the uppermost coil of this supporting spring 39.

The direct support of the washer could also be effected by a stamped, resilient expanding sleeve which is either arranged below a washer 5 and bears against a circular collar of the screw or at the same time forms the washer itself by corresponding expanding of a conically widening zone. A development of this type could also be easily produced in the form of a mass-produced part, in which case high retaining forces could be guaranteed.

In the developments according to Figs. 25 and 26, an insert 40 corresponding to the shape of the recess 13 is provided on the underside of the washer 5, which insert abuts in form-locking manner against the washer 5 and can be securely connected thereto. On its upper rim this insert 40 has projecting, bendable tongues 41 which project into openings 42 in the washer 5 and which, after insertion, can be bent over so as thereby to effect mutual fastening. At the lower rim of this insert 40 there are likewise provided projecting tongues 43 which then serve as a support for the abutment, for example in the form of a circular collar 30, on the threadless portion 10 of the screw.The fitting of the washer 5 is thereby considerably facilitated, despite the presence of a circular collar 30, since the opening 11 in the washer can be made correspondingly large so that the washer 5 passes over the circular collar 30. The downwardly projecting tongues 43 of the insert 40 are deflected very slightly and spring back after the abutment collar 30 has passed.

In the development according to Fig. 27, the threadless shank portion 10 is provided with circu lar grooves and projections 45 which together form an approximately sawtooth-like cross-section in the direction of the screw axis. In the vicinity of the opening the washer is punched out to such an extent that a type of movable shim washer 46 forms the base of the funnel-shaped recess 13. This shim washer 46 pivots under compressive load and thus self-locking occurs.

In the development according to Fig. 28, an an nular tongue 47 is provided axially spaced from the opening 11 at the base of the funnel-shaped recess 13 in the washer 5, which tongue is provided with a second opening 11'. The centre axes of the two openings 11,11' are disposed offset relative to one another. When fitting the washer 5, the opening 11 and then the opening 11' are thus guided over the circular collar 30 one after the other, whereupon snap-fitting occurs so that subsequent loosening is no longer possible in practice. However, sufficient space is provided for tilting of the washer 5 relative to the screw axis.

With the development according to Fig. 29 it is possible to solve, as it were, a major problem in securing roof coverings on soft insulation. Hitherto it was not taken into consideration that with soft insulation the counter pressure necessary for satisfactory fastening of the sheets at the seam was lacking. After the sagging of the insulation, the sheet sticks in the shanks of the fastener.

It is evident that the intensity of the hole-loading stresses of the roofing sheets 48 does not allow any excessive over tightening. Logically this phenomenon should be considered in the case of a mechanical fastening able to withstand being walked upon. A washer 5 is placed under the sheet seam to be fastened and, at the same time, a second washer 5 is fitted thereover. After this, screws of the types of construction already described are screwed in. The lower washer 5 fixed in the thread now works as a clamp. Positive securing of the roofing sheet can thus be ensured. The recess 13 of both washers 5 acting as a centering funnel provides, as a reinforcement, additional resistance to simple withdrawal of the sheet seam.Admittedly this doublewasher arrangement is not possible with existing apparatus for automatic fitting however, it would not be difficult to develop suitable solutions therefor in respect of apparatus.

A special possibility in the design according to Fig. 29 is thus provided if the two approximately similarly "shaped" washers 5 have mutually corresponding, claw-like punched-out portions or openings. It is thereby possible to effect a substantial improvement in the seam fastening. Of course, an arrangement of this type is only advantageous if positive manual fitting takes place. The projecting claws would obstruct an automatic feed.

For manual installation, both washers 5 could be joined together by a web 49 provided at one edge boundary so that, after fitting a sheet 48 on the seam, the two interconnected washers 5 can be compressed, whereupon the edge zone of the sheet 48 is retained accordingly.

With regard to the embodiment according to Figs. 29 and 30, a saving in material could be achieved by not making the two washers the same size so that, in addition to a correspondingly large washer, in the form of the second part there is provided merely a second clamping element having a cone with a small collar.

In the development according to Fig. 31, an insert sleeve 50 is provided in the vicinity of the opening 11 in the washer 5, the edge of the opening 11 engaging in a circular groove 51 in the insert sleeve 50. The diameter of the opening 11 in the washer 5 is here substantially larger than the diameter at the groove base of the insert sleeve 50, so that the washer 5 can thus be moved laterally and also tilted. The insert sleeve 50 is provided with a continuous longitudinal slot so that, when passing over the abutment collar 30, this insert sleeve 50 can be forced outwards, which is in fact also possible as a result of the correspondingly large opening 11. After passing over the abutment collar 30, the insert sleeve 50 snaps in above the abutment collar and thus the washer 5 is held in its position in which it is of course correspondingly movable.

It is of course possible for the washer 5 to be made from different materials. As a result of the special design it can also be satisfactorily made of metal, which has considerable influence in roofs particularly with regard to inflammability. Con struction in plastics material is also possible.

In the design according to Fig. 32, the threaded portion 8 of the screw 1 is designed to taper towards the screw tip. It is thereby possible to achieve a considerable improvement in the anchoring reliability of screws in the thin supporting parts of the fixed support in roof structures. Therefore, in contrast to hitherto conventional screw designs, the threaded portion 8 is designed to be slightly conical. It is thereby ensured, irrespective of the screwed-in depth, that a radial stress is always present in the metal sheet. Once a hole has been widened, cylindrical screws spread it out to an increasing extent when screwed in further. Therefore adhesives are suitable only to a limited extent.

Greater screw-in depths of the same fastener are unavoidable for practical reasons because of variations in the thickness of the insulating material, in particular when refitting old buildings. The taper may be so designed that in a proposed metal-sheet penetration zone an optimum ratio to tightening and loosening torque can be achieved over the entire screw-in range. This embodiment according to Fig. 32 is intended only for relatively thin sheet metal (e.g. up to 1 mm). Of course, the taper is so slight that in practice it is hardly visible. A tapered construction of this type can only be noticed in action.

The threaded portions of the screw may be of widely varying design. Not only can the thread forms be varied according to the application but the provision of two-start or multi-start threads is possible. Optionally, two threaded portions spaced apart from one another can have similar or different thread forms; both threaded portions can be of single or multi-start design and also combinations of these forms of embodiment are possible in both threaded portions. In the case of thread forms for special applications, a saw-tooth thread, for example, is provided.

The shape of the screw head is not limited to the illustrated embodiments. Widely varying head designs can be used here, the spanner engagement faces (flats) and shapes also being variable according to the particular application. It would also be possible for the screw head to be sheathed so as thereby to achieve additional corrosion protection.

In this case "sheathing" is also intended to include a coating or cap of plastics material, as well as a corresponding metallic covering.

Tests have shown that the so-called "raising" of the screws under drag forces or under special loads can be prevented by the measures according to the invention. The raising of the screws is not as a rule caused by loosening via a rotational movement. On the contrary, the screw is thoroughly levered out by drag loads and will thus slide higher turn by turn. This spring effect can be clearly observed in tearing-out tests. Although the screw springs out by one thread rib creating a loud noise, it still exhibits considerable residual extraction force. This is also demonstrated by the protrusion of certain screws observed in practice. Only after a very long time would these screws be torn out together with the roof covering under strong drag loads.

It may thus be assumed that the fastener is loaded on one side and irregularly via the roofing sheet. If one proceeds from the known embodiments, which provide a rigid connection between the washer and screw, all these one sided applied drag loads will be directed via bending loads of the screw into the anchoring point. However, if a supported washer according to the present invention is considered, which is angularly movable, it will be apparent that oblique loads will not be transmitted to the screw in the same proportion as bending loads. The danger of the screw being levered out of the supporting metal sheet is thereby considerably decreased. This has also been confirmed by tests.

The measures according to the invention thus provide a possibility for securing insulation on a fixed support, whereby important advantages over the known embodiments are achieved.

Claims

1. A fastener for securing roofing courses on soft insulating material to a fixed support, comprising a self5 drilling and self-tapping screw and a plate washer, wherein immediately adjacent the screw head the screw has a threadless shank portion whose diameter is the same as or less than the diameter of the opening in the washer to be fitted and wherein on the upper side of the washer, in the vicinity of its passage opening, a recess, countersinking or the like is provided for recessing the screw head, characterised in that an abutment, an optionally protruding collar, projection or the like, is formed or arranged at distance from the screw head in the threadless shank portion or at the end of the threadless shank portion, and in that the washer abuts against the abutment, collar, projection or the like, with its area defining the passage opening and can be tilted relative to the screw axis.

2. A fastener according to Claim 1, characterised in that the abutment is formed by the end of the threaded portion next to the threadless portion.

3. A fastener according to Claim 1, characterised in that the ends of the thread turns associated with the threadless portion are of reinforced design.

4. A fastener according to Claims 1 to 3, characterised in that the diameter of the threadless portion of the screw corresponds to the core diameter of the threaded portion.

5. A fastener according to Claims 1 to 3, characterised in that the diameter of the threadless portion of the screw is less than the core diameter of the threaded portion.

6. A fastener according to Claims 1 to 5, characterised in that at least one sub-portion of the threaded portion, which sub-portion is situated next to the threadless shank portion, is designed with two-start or multi-start thread.

7. A fastener according to Claims 1 to 5, characterised in that a sub-portion of the threaded portion, which sub-portion adjoins the threadless portion, is of greater diameter than the threaded portion at the screw-in tip of the screw.

8. A fastener according to Claims 1 to 7, characterised in that the ends of the thread turn or turns associated with the threadless portion are cut off in a plane extending transversely to the screw longitudinal plane.

9. A fastener according to Claim 1, characterised in that on the threadless portion of the screw there are formed one or more cams projecting beyond the diameter of this portion.

10. A fastener according to Claim 9, character ised in that two cams are provided lying opposed to one another in the longitudinal direction of the screw axis and turned through 180 .

11. A fastener according to Claims 9 and 10, characterised in that the cams extend in the longitudinal direction of the screw axis and overlap one another in the direction of the screw axis.

12. A fastener according to Claim 1 and any of the preceding Claims, characterised in that a circular abutment collar is provided on the threadless shank portion spaced apart from the screw head.

13. A fastener according to Claim 12, character ised in that a spring member is inserted between the abutment collar and the washer fitted under the screw head.

14. A fastener according to Claim 13, characterised in that the spring member takes the form of a helically coiled plate spring.

15. A fastener according to Claim 13, characterised in that the spring member takes the form of a helical spring.

16. A fastener according to Claim 1 and any of the preceding Claims, characterised in that the threadless shank portion has two zones of different diameters.

17. A fastener according to Claim 16, characterised in that the transition zone between the two diametral zones of the threadless shank portion (10) is of frustoconical shape.

18. A fastener according to Claim 1 and any of the preceding Claims, characterised in that a sleeve surrounding the screw shank and bearing against the fixed support in the screwed-in condition is designed as an abutment, arranged at a distance from the screw head, for the washer.

19. A fastener according to Claim 18, characterised in that at its free end facing the screw head the sleeve has at least one longitudinal slot.

20. A fastener according to Claim 1, characterised in that the threadless shank portion is provided with circular grooves, projections or the like.

21. A fastener according to Claim 20, characterised in that the successive grooves and projection constitute a sawtooth-like cross-section in the direction of the screw axis.

22. A fastener according to Claim 1, characterised in that the washer has a funnel-like recess for accommodating the height of the entire screw head.

23. A fastener according to Claim 1 and any of the preceding Claims, characterised in that the opening in the washer has a radially extending notch, slot or the like for the passage of the screw shank.

24. A fastener according to Claim 1, character ised in that the washer has circularly extending slot portions coaxial to the central opening, the slot portions being disposed staggered relative to one another and with varying diameter encircling each other.

25. A fastener according to Claim 24, characterised in that the circularly extending slot portions each extend over an angle of just less than 180 .

26. A fastener according to Claim 1, character ised in that the washer comprises two parts mova ble relative to one another, wherein a central part has the opening and, optionally, a countersunk portion, and this central part is suspended from a part surrounding it and is movable transversely to the support plane of the washer.

27. A fastener according to Claim 26, characterised in that the central part is suspended resiliently from the surrounding part of the washer.

28. A fastener according to Claim 1, characterised in that a funnel-shaped insert corresponding to the shape of the recess can be secured in formlocking manner to the underside of the washer.

29. A fastener according to Claim 28, characterised in that on its upper and/or lower rim the insert has projecting, bendable tongues which for connection, on the one hand, engage in openings in the washer and, on the other hand, bear against an abutment, e.g. an abutment collar, of the screw.

30. A fastener according to Claim 1 and any of the preceding Claims, characterised in that at an axial distance from the opening at the base of the funnel-shaped recess an annular tongue adjoins a second opening, the oentre axes of the two openings being disposed offset relative to one another.

31. A fastener according to Claim 1 and any of the preceding Claims, characterised in that two approximately similarly shaped washers are provided, which have mutually corresponding, clawlike stamped-out portions or openings for securing a roofing-course seam inserted between the two washers.

32. A fastener according to Claim 1 and any of the preceding Claims, characterised in that two approximately similarly shaped washers are joined together via a web disposed at an edge boundary, the two mutually corresponding funnel-shaped recesses engaging in one another.

33. A fastener according to Claim 1 and any of the preceding Claims, characterised in that an insert sleeve, preferably of plastics material, is provided in the vicinity of the opening in the washer, the edge of the opening engaging in a circular groove in the insert sleeve.

34. A fastener according to Claim 33, characterised in that the diameter of the opening in the washer is substantially larger than the diameter at the groove base of the insert sleeve, but smaller than the outer diameter of the insert sleeve and in that the insert sleeve is provided with a continuous longitudinal slot.

35. A fastener according to Claim 1 and any of the preceding Claims, characterised in that the threaded portion is designed to taper towards the screw tip.

36. A fastener as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in any one of Figures 3 to 33 of the accompanying drawings.

37. A roof having roofing courses secured thereon by means of at least one fastener as claimed in any one of the preceding claims.