Patent Application
20120216479
This invention relates to a means by which fittings can be rigidly connected to extruded beams so as to maximise the attachment clamping force and slip resistance.
Framework systems require beam members to be rigidly coupled. Beams are typically extruded in aluminium and include features like “T” slots that enable external fittings to be attached.
Whereas “T” slots and their insert counterparts are a simple solution, they rely on the tensile capabilities of fasteners to effect their clamping power. This may be inadequate when the attachment point has to be able to resist axial slip, as the effective co-efficient of friction limits slip resistance to a small factor of the clamping force. Also as all the load is on the thread, a thread failure could be catastrophic when employed on large structures.
It is an object of this invention to be able to attach fittings to extruded features with very high clamping forces.
It is a further object of this invention that such fittings can be attached with minimum preparation to the extruded beam feature.
It is a further object of this invention that the system can be retro-fitted to work with conventional “T” slot provisions.
It is a further object of this invention that the system is easy to prepare and easy to operate. It is a further object of this invention that the retaining force is not solely dependent on the thread of the employed fasteners but rather once attached becomes supported by the mating sections themselves and is thereby failsafe.
The adoption of the “T” slot for linking accessories to extruded beam sections is almost universal. However it is far from ideal. The only simple way of clamping to a “T” slot is to insert an element that will be trapped by it and screw a fastener in. But then the coupling will be load limited by the thread of the fastener and the resistance of the slot overhang lips to peeling open.
The invention is defined in the appended claims.
This invention proposes an anchor shape attached to the beam member, with a conforming two part clamp as shown in
The fastener in this case is being used to establish the wedge preload. Once set, the coefficient of friction between the clamp wedge and anchor holds most of the load, taking the unreliable fastener out of the critical force loop.
This design also confers considerable cost advantages in being able to make high load fittings from low cost extruded sections. Loads into the beam can be taken straight down the shaft of the anchor and webbed into the supporting extrusion.
Where it is desirable to employ such high load fittings on existing structures with more conventional “T” slot provision, an anchor adaptor fitting can be provided to locate in the “T” slot as shown in
Providing a clamping system that is so capable of resisting axial slip and offering equally high tensile loading enables new possibilities for effecting high load support frameworks, whether for automation systems or multi story structures.
A further benefit is that it is easy to operate in the field as clamp parts come pre-assembled and only need tightening.
And of equal importance is the inherently low cost of manufacture as features will principally be extruded in aluminium and will then require a minimum of preparation to become the final part.
With safety attracting an ever greater premium, an attachment system that is significantly immune to fastener thread failure is greatly preferred, particularly as thread forms in aluminium are notoriously unreliable.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings of which:
The two parts of the attached clamp 1 and 2 grip the anchor from both sides and are pre-loaded together by the fastener 5.
The clamp has a tapered face 7 and a flat face 8 which together act as a wedge, jamming under the anchor overhang when the fastener is tightened. Face 7 may also advantageously include a concave form such that the wedge jamming angle reduces the further the wedge inserts under the anchor overhang.
The two parts 1 and 2 also lock together about the further wedge 9, whose faces may be curved such that part 2 can settle at a small range of angles with respect to part 1.
The resulting assembly is not over-constrained so that it locks without slack or ambiguity. If the fastener which in this embodiment is M6 can achieve a tensile loading of about 24 kN with a steel thread insert, this is approximately halved by the reduced leverage resulting from the fastener being mid way between the pivot wedge 9 and the anchor wedge 7.
However the load on the anchor faces is then increased by a factor of about ten resulting from the small wedge angle. With a co-efficient of friction estimated at 0.2 between the anchor and the wedge, the axial slip resistance will be about 24,000*0.5*10*0.2 N, totalling 24 kN. This would reduce to about 10 kN without the steel thread insert.
On an extended say 100 mm length of extrusion, for the anchor to fail under tensile loading it would have to snap off about 8 cm2 of aluminium which at an average extrusion grade would require a force of >80 kN. This is similar to the >70 kN of axial slip resistance achieved from 3 fasteners.
The fitting can be attached to other extruded beams or plates, in this embodiment extending tongues 6 can be bonded into a conforming beam profile.
This adaptor need not compromise the strength and slip resistance of the assembly compared with the formed in anchor as the clamping load between the adaptor and beam will be the same as the clamping between adaptor and fitting.
The lower component set is exploded to better see the individual elements.
The two back to back adaptor extrusions 10 and 11 are shown partially extracted from the section 12 that would otherwise be part of a more substantial beam. Similarly 13 shows an equivalent slot feature that would be part of a beam.
The anchor clamp parts 1 and 2 are shown connected by fasteners 5a and 5b, with part 2 shown pulled aside such that they could be fitted around the adaptor anchor.
Part 1 shows the extruded tongues 6 that provide a large bonding surface area to beam 6. As a further safety precaution, pins 8a and 8b could be inserted through holes drilled through 7 and 1.
Part 20 is a representative beam featuring several anchor elements e.g. 14. The beam will be attached to a further beam whose “T” slot features are shown by 15 with dual back to back adaptors fitted as shown by 16.
The two bracket parts are constructed from tongue and a groove extrusions, which can then be mitred and bonded together as shown by 17 and 18. The brackets can then be bolted together around the anchor features 14 and 16 by fasteners e.g. 21a and 21b.
This style of bracket can also be produced with different length extrusions on either side, where for example additional fasteners need to be accommodated to increase the slip resistance.
The bracket could also be produced from simple plates which have the conforming anchor form machined in on orthogonal sides. Two such plates can then be bolted together in a similar style to produce a bracket of virtually any size or aspect ratio.
In this embodiment tags 17 and 18 and tags 19 and 20 are bolted together around extruded anchor feature 14 and anchor adaptors 16 such as to retain plate 21.
Similar constructions could be employed to facilitate a wide range of attachments.
Anchor bracket part 26 is attached to part 25 with a suitable fastener. It is then bonded into post 22 which is brought into orthogonal face contact with beam surface 23 that has anchor adaptors 24 inserted into it's “T” slot.
A hole 27 in the post enables a hex key to be inserted to tighten the trapped fastener such that it clamps around the anchor adaptors.
Beams e.g. 28 and 29 are separated and stiffened into a truss matrix by diagonal cross brace members e.g. 30 using anchor extrusion based fittings e.g. 31.
Features of the invention are as following:
1. An attachment system comprising an anchor shaped external feature on the one part, and a two part conforming clamp on the other, such that as the clamp parts are brought together around the anchor feature by fastening means, the lips of the clamps act as wedges in jamming underneath the anchor overhang thereby exerting enhanced clamping pressure.
2. An attachment system as in feature 1 where the anchor feature comprises of an adaptor fitting that can be inserted into a conventional “T” slot.
3. An attachment system as in feature 2 where the adaptor is comprised of two identical parts, separately inserted through the narrow “T” slot opening and then brought together back to back.
4. A means of making a brace for a construction system whereby the attachment system described in any of the preceding features is attached to either end of a beam mitred such that the orthogonal clamps can be bolted to orthogonal beams.
5.A bracket fabricated from two plates machined with orthogonal conforming grooves on its edges leaving a wedge form along the edges that will jam under anchor features as described in features 1, 2 and 3 when brought together tightly by fasteners.
6. A bracket as in feature 5 where the plates are fabricated from two extrusions each featuring the orthogonal wedge form that conforms with the anchor as described in features 1, 2 and 3, that can be bonded together orthogonally by overlapping features such as tongue and groove.
7. A concealed framework attachment system utilising the connection system as described in features 1, 2 and 3 where one clamp part is bonded into the end of a beam extrusion fully recessed, with accommodation for the loosely fitted second clamp part attached to the first part by a fastener, and access means, typically a hole, through the beam such that a tool can be inserted to tighten the captured fastener.
8. A framework construction system where brace elements can be variously attached utilising the clamping system described in any of the preceding features.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2009/001926 | 8/5/2009 | WO | 00 | 5/15/2012 |
