Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Thread or shank structure
Reexamination Certificate
2000-04-03
2001-11-27
Saether, Flemming (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Thread or shank structure
C411S423000
Reexamination Certificate
active
06322307
ABSTRACT:
This invention relates to improvements in fixing anchors, in particular threaded fasteners for fixing into brick, blocks, masonry or the like.
BACKGROUND OF THE INVENTION
It is well known that with the exception of resin anchors, fixing anchors for use by the construction industry or hobbyists are generally designed to work in specific substrates such as concrete or masonry. One well known method for fixing to relatively hard and/or brittle substrates such as concrete or brick or stone, is to first drill a hole in the substrate and then insert an anchor which includes an expansion mechanism. A standard screw may then be inserted within the anchor which causes the anchor to expand as it is tightened. The expansion of the anchor exerts a radially directed compressive force on the walls of the pre-drilled hole which holds the anchor in place.
SUMMARY OF THE INVENTION
An alternative method of fixing into concrete is to employ a self tapping screw. However, such a fixing is suitable where only light loads are to be carried by the fixing, and is not well suited to soft substrates.
According to a first aspect of the invention, a threaded fastener for anchoring into a substrate comprises a core portion having at least one helical continuous thread provided along a substantial portion of the length of the core, in which the helical thread has a substantially V-shaped cross section defining two flanks which subtend an angle of between 60° and 90°, and the thread has a helix angle of between approximately 20° and 45°, and characterised in that the two flanks meet at a crest which is rounded.
The helix angle between 20° and 45° allows the fastener to be inserted into the substrate with a small number of turns compared to a small helix angle of, say, 5° to 10°. The choice of 60° to 90° for the thread ensures that tensile forces applied along the axis of the fastener are directed into the substrate at an angle well away from the axis providing good tensile performance in soft substrates and indeed across a wide range of substrates.
The threaded fastener is suitable for use with any substrate, but is most preferably used for fastening in relatively soft substrates such as brick or blockwork, sand stone or lime stone.
Most preferably, the helix angle of the thread is 25°.
A flat/radius for the crest of 0.01-0.015 inches is preferred.
An advantage of the provision of only a single helical thread is that it provides a reduced insertion torque when compared to the provision of a dual thread. Also, a dual thread offers a reduced distance between the threads for any given helix angle which is disadvantageous.
Preferably, the ratio of the outside diameter of the thread to the pitch of the thread is substantially within the range 0.5 to 0.9. This ensures good levels of performance in soft substrates.
Preferably, the ratio of the outside diameter of the thread to the inside diameter of the thread (i.e. the outside diameter of the core) is substantially in the range 1.25 to 1.5. Thus, the diameter of the thread is quite large compared to the diameter of the core, which ensures that the fastener remains fast within the substrate under large tensile loads.
The threaded fastener may further include a secondary balancing thread which may be located in between the turns of the first helical thread. This thread can help guide the fastener when inserting into a pre-drilled hole, and may be chosen to have a diameter approximately equal to the hole diameter whilst the core is slightly smaller in diameter than the hole. The crest of the secondary thread may be flattened or rounded.
Preferably, the core portion is substantially smooth and cylindrical over a substantial portion of its length other than the provision of the first (and optional second) helical threads. Thus, no grooves are provided at the join between the sides of the thread and the shank which could clog with loose debris during installation.
The two flanks of the first and/or second threads may subtend equal angles with the core. Alternatively, the angle between one thread flank and the core and the other thread flank and the core may be different provided the angle subtended by the two flanks is in the range 60° to 90°.
A bolt head or other head form (such as a stud, hook or eye) may be provided on one end of the core which has a hexagonal outline for engagement with a suitably shaped insertion tool.
The other end of the core may finish at a point or taper, and may be provided with one or more axially extending grooves spaced around the circumference of the core. The first and/or second threads may extend to a point or taper at the tip of the core to facilitate self-tapping of the fastener into the substrates. These notches help to facilitate ease of thread cutting in harder substrates.
A method of inserting the fastener according to the first aspect into a substrate may comprise pre-drilling a hole having a diameter greater than the core of the fastener but smaller than the outside diameter of the main thread and inserting the fastener into the hole. When a secondary thread is also provided, the diameter of the pre-drilled hole may be slightly smaller than or substantially equal to the outside diameter of the secondary thread. This allows the second threads to act as a guide in the hole or possibly bite into the substrate.
The fastener may be fabricated from a material, i.e. steel which is then hardened. This is particularly suitable for use of the fastener in relatively hard and/or abrasive substrates such as concrete. Alternatively, the fastener may be made from a plastics material, e.g. for use with aercrete substrates.
The fastener may be made by rolling to produce the thread or by turning or casting. The fastener may be hardened after it is produced.
REFERENCES:
patent: Re. 34969 (1995-06-01), Dixon
patent: 3495494 (1970-02-01), Scott
patent: 3865006 (1975-02-01), Massoney
patent: 3942405 (1976-03-01), Wagner
patent: 4439077 (1984-03-01), Godsted
patent: 4572720 (1986-02-01), Rockenfeller
patent: 4673323 (1987-06-01), Russo
patent: 5190426 (1993-03-01), Wieder
patent: 5674035 (1997-10-01), Hettich
patent: 5800107 (1998-09-01), Giannuzzi
patent: 5957646 (1999-09-01), Giannuzzi
patent: 4227272 (1994-02-01), None
patent: 1343865 (1963-11-01), None
patent: 2688689 (1993-09-01), None
patent: 1580356 (1980-12-01), None
Laff, Whitesel & Saret, Ltd.
Saether Flemming
Unifix Limited
Whitesel J. Warren
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