WO2012116085A1

WO2012116085A1 - Connection

Info

Publication number: WO2012116085A1
Application number: PCT/US2012/026151
Authority: WO
Inventors: John Mallet; David Collinson
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2011-02-23
Filing date: 2012-02-22
Publication date: 2012-08-30
Anticipated expiration: 2013-08-23
Also published as: TW201235575A; AU2011200765A1; AU2011200765B2

Abstract

A connection between metal members (2, 4) assembled together to form a building component, wherein each of the members is formed with a hole (8) of generally star- shaped profile providing a series of inwardly- directed angularly- spaced teeth (12) to receive a screw fastener (6) passing through the holes of the two members to connect the members. The teeth of the two members are in face -to -face engagement and each tooth has a tip (12a) with a concave curvature of a diameter approximately the same as the root diameter of the thread of the screw. The configuration provides a reduced torque requirement for installation of the screw while achieving a high strip torque.

Description

CONNECTION

The present invention relates to a connection between metal members assembled into a building component such as a frame, truss, or post.

In domestic building construction, steel framing is now commonly used for wall frames, roofing trusses and flooring trusses, and steel sections are used as footing posts or columns. The frames or trusses (herein referred to for simplicity as "frames") are assembled from frame members of rolled steel section fastened together and the posts or columns are also assembled from lengths of rolled steel section fastened together. Common methods for fastening the members together are welding, riveting, crimping, and screwing. Welding is only applicable for use with thicker steel sections, requires a high skill level and suffers from the disadvantage that a frame made from the sections cannot easily be disassembled. Riveting, although requiring a lower skill level than welding, likewise suffers from the disadvantage that disassembly is difficult and also requires the use of accurate alignment in pre-punched holes in the frame members for receiving the rivets. Crimping likewise makes disassembly difficult and also suffers from the possibility of loosening of the connection during transportation to the building site. Screwed connections involving the use of screws driven into pre-punched holes in the frame members, although permitting easier disassembly than the methods discussed above, nevertheless are not without their problems when using current techniques and these mainly arise from the fact that a high installation torque is required. The high installation torque is a consequence of ensuring that the thread formed by deformation of the steel surrounding the hole does not strip in the final stages of driving the screw. The high assembly torque required using current techniques contributes to operator fatigue, frequent breakage of screwdriving bits and, in most cases, necessitates the use of impact screwdrivers which tend to be very noisy in operation.

The present invention in its preferred embodiments provides a specially shaped hole punched into each of the sections to be connected to provide for reduced installation torque of a screw into the holes, while also providing a high strip torque. According to the present invention there is provided a connection between metal members assembled together to form a building component, wherein each of the members is formed with a hole of generally star-shaped profile providing a series of inwardly-directed angularly- spaced teeth to receive a screw fastener passing through the holes of the two members to connect the members, the teeth of the two members being in face-to-face engagement and each tooth having a tip having a concave curvature of a diameter approximately the same as the root diameter of the thread of the screw. According to another aspect of the invention there is provided a tool for punching a hole into a metal member to receive a screw threaded fastener, the tool comprising a punch pin shaped to form a hole of generally star-shape as specified above, and a die of complimentary shape to the punch pin. An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows schematically a screwed connection between steel frame members of a building frame;

Figure 2 shows an enlarged detail A of Figure 1 ;

Figure 3 shows in enlarged detail a hole of generally star- shape punched into each of the frame members;

Figure 4 shows an enlarged detail B of Figure 3;

Figure 5 shows an enlarged detail C of Figure 4;

Figure 6 is a fragmentary view showing a connecting screw driven through the holes in the two frame members;

Figure 7 is a section on line A- A of Figure 6;

Figure 8 shows an enlarged detail B of Figure 7;

Figures 9 and 10 show enlarged details C and D of Figure 8;

Figure 11 is a perspective view showing a punch and die assembly for producing the hole;

Figures 12 and 13 are views of the punch pin; and Figure 14 shows the die.

In accordance with the preferred embodiment of the invention a screwed connection between the frame members of a building frame is achieved using a specially shaped hole punched into each of the frame members, the special shape of the hole enabling a significantly reduced installation torque for the screw while still achieving a structurally sound connection between the two members. Figures 1 and 2 show steel frame members 2, 4 (usually termed in the industry as "steel sections") interconnected by screws 6 driven into punched holes 8 in accordance with the preferred embodiments of the invention.

In common with existing techniques, the hole 8 is punched at the plane base of a dimpled recess 10 pressed into the steel section so that when the screw is driven to its seated position, the head of the screw will not project beyond the surface of the section or at least will not have substantial projection beyond the surface. The shape of the hole 8 is shown in detail in Figures 3 to 5. It will be seen to be approximately star-shaped with a series of projecting teeth 12 spaced uniformly in a circumferential direction. In the embodiment shown, there are eight such teeth although there may be more than or less than eight teeth depending on the thickness of the steel section and diameter of the hole; however it is envisaged that the number of teeth would be unlikely to exceed about 12 or to be less than about four. Each tooth 12 is of approximately v-shaped configuration having a tip 12a having a concave curvature R which is centered on the axis O of the hole 8 and which is of a diameter of approximately the same as that of the root of the thread of the screw 6.

The exact relationship between the diameter of the tip 12a and the thread root diameter is such that in practice the tip 12a can either be an interference fit with the thread root or a clearance fit. However in either case the interference is not substantial and the clearance is not substantial. If the interference is too great the required installation torque of the screw will be raised without any practical benefit. Accordingly, if the tip 12a is sized to provide an interference fit the degree of interference will be sufficiently small to still enable installation of the screw with a low torque. On the other hand if the tip 12a is sized to provide a clearance fit with the thread root, if the clearance is too great there is a risk that the screw will strip during installation and will not achieve the required pull-out retention strength. The necessary balance to be achieved is that of a low installation torque but a high strip torque. The small extent of interference or clearance needed to achieve this balance can readily be determined empirically taking into account also standard tolerances inherent in the manufacture of the punch tooling used to form the holes and of the screws which will be used to form the connection.

The space 14 defined between each adjacent pair of teeth 12 is substantially v- shaped, with its base 14a being of radiused form as is clearly shown in the drawings. It will be noted that the transition between the tip 12a of the tooth and the adjacent flank 12b of the tooth is formed by a substantial radiused zone 12c. These radiused zones are present primarily so as to prolong the working life of the punch tool which is itself of a shape complimentary to that of the hole. The curved base 14a of the space 14 and which merges smoothly with the flanks 12b of the adjacent teeth has a similar effect in prolonging the working life of the punch tool.

Figures 6 to 10 in detail the screwed connection between the two sections 2, 4 and in particular the interaction between the tips of the teeth and the thread of the screw (see Figures 9 and 10 which shows the tip/thread engagement in greatly enlarged detail). The action which occurs is that the tip zones of the teeth are deformed rather than being flexed to follow the helix of the thread. Effectively, the screw forms a thread within the thickness of the steel sections. The required effect does impose a relationship between the thickness of the steel sections and the thread pitch to ensure that each of the steel sections has threaded engagement with the screw. As a generality it may be stated that the thread pitch is less than the combined thickness of the two steel sections. In a practical example, a combined steel section thickness of 1.5mm would result in thread engagement of at least one full thread with a thread pitch of 1.0mm.

The use of the punched hole shape as described significantly reduces the torque required for installation while still providing a sufficiently high strip torque. In one practical example, for rolled steel sections each of 1.0mm thickness and using an M6 screw, the installation torque is approximately 2 to 3Nm, so low that hand application could be undertaken if required. On the other hand, the strip torque in the same thickness of material is above 1 INm thereby providing a ratio of installation torque to strip torque of 1 to 3.6 or higher. Although the use of the star-shaped hole in the sections reduces the required installation torque to such an extent that installation could be effected by hand, in practice of course, powered drivers will be used. However the low installation torque reduces the wear on the driver bit and also reduces fatigue of the operator. Moreover it permits the use of non-impact drivers which can be adjusted to a peak torque below the strip torque to provide effective tightening of the screw.

Figures 11 to 14 show a punch and die assembly for producing the star-shaped hole 8. The assembly comprises a punch pin 20 and die 22 configured to fit into a standard press tool. The punch pin is profiled to produce the hole shape described above and the corresponding aperture in the die is of complimentary shape to that as will be well understood by those skilled in the art.

Although the invention has been described with reference to the construction of a building frame (such as a wall frame, or a roof or floor truss), it is also applicable to the construction of other building components such as footing posts or columns formed from lengths of rolled steel section connected to form a tubular configuration.

The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A connection between metal members assembled together to form a building component, wherein each of the members is formed with a hole of generally star-shaped profile providing a series of inwardly-directed angularly- spaced teeth to receive a screw fastener passing through the holes of the two members to connect the members, the teeth of the two members being in face-to-face engagement and each tooth having a tip having a concave curvature of a diameter approximately the same as the root diameter of the thread of the screw.

2. A connection according to claim 1, wherein the diameter of the tips of the teeth is such as to provide an interference fit with the root of the screw thread.

3. A connection according to claim 1, wherein the diameter of the tips of the teeth is such as to provide a clearance with the root of the screw thread.

4. A connection according to any one of claims 1 to 3, wherein the thread pitch is less than the combined thickness of the two frame members.

5. A connection according to any one of claims 1 to 4, wherein each tooth is defined by radially inclined flanks which are convergent towards the tip.

6. A connection according to claim 5, wherein in each tooth its tip merges with the inclined flanks via convexly curved edges.

7. A connection according to claim 5 or claim 6, wherein a space between each pair of adjacent teeth is bordered at each side by the inclined flanks of the teeth and at its base by an arcuately curved edge which merges smoothly with the flanks of the teeth.

8. A connection according to any one of claims 1 to 7, wherein the members are rolled steel sections assembled to form a frame or post for use in building construction.

9. A tool for punching a hole into a metal member to receive a screw threaded fastener, the tool comprising a punch pin shaped to form a hole of generally star-shape as specified in any one of claims 1, 5 or 6, and a die of complimentary shape to the punch pin.