Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Patent
1996-01-04
1997-10-07
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
411411, 411418, F16B 2500, F16B 3504
Patent
active
056740352
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
A known screw of this kind (CH-A-651 115) has a thread having a ratio of the external diameter to the lead of about 2.5 and a profile angle in the range between 50.degree. and 65.degree.. In an embodiment, a ratio of approximately 1.3 is realized between the external diameter and the core diameter.
It is the object of the invention to devise a thread forming screw of the kind indicated in the preamble of claim 1 such that simple and reliable fixing of structural components to concrete or masonry will be possible without the use of dowels or other aids.
With the thread forming screw according to the invention the dimensioning parameters of the thread are selected such that material, such as concrete will not be excessive; account the property of concrete of being able essentially to transmit thrust and only small tensile forces.
According to a further development of the invention, the shank of the screw has depressions at either side of the thread base to receive the concrete or rock flour which has broken away, something which is known per se for a different purpose in connection with a wood screw, namely to improve the retention.
Further dimensioning specifications are given regarding the lead p, the core diameter d.sub.k, and the external diameter d.sub.a of the thread with respect to the diameter d.sub.b of the bore which is to be predrilled in the concrete or masonry. Claims 3 to 5 specify ranges of the parameters indicated within which the screw will provide optimum results as regards the screw-in torque and retention.
EP 89 123 699.4 discloses a thread forming screw, the thread burr of which has bow-shaped cutting teeth. The known screw has been devised to be screwed into wood or chipboard material. Surprisingly, using such cutting teeth also in case of the screw according to the invention results in much easier introduction of the screw into the brittle concrete which breaks away easily, and also into masonry or rock. An embodiment according to claim 7 is preferred in this respect.
Modifying the known screw according to EP 89 123 699.4, it is preferred with the screw of the invention for the recesses which define the cutting teeth to have a depth corresponding to from 5/7 to 7/7 of the thread height.
Concrete is a material with a tendency to form cracks. Now, in order to warrant sufficient load accommodating capacity of the screw also in case of cracks forming, e.g. due to local tensile stress under load of the screw, the features recited in claim 12 are provided in a preferred modification of the invention. The small angle of attack claimed, which provides an asymmetric shape of the thread cross section, prevents abrasive wear of the concrete in the zone of the crack due to relative movements between the thread flank at the side facing the screw head and the concrete.
The screw according to the invention also may be designed as a tool for forming a tapped hole in concrete, rock, masonry, or the like, as defined in claim 13. Then it is easy to introduce a screw having a thread according to claim 1 into the tapped hole formed with such a tool; in this event the screw may do without cutting teeth as claimed in claim 6 or 7.
Further modifications of the invention are indicated in the other subclaims .
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail below with reference to diagrammatic drawings of embodiments, in which:
FIG. 1 is a side elevation of a screw according to the invention;
FIG. 2 shows a modified screw according to the invention;
FIG. 3 is a part sectional view in the direction of the arrows III--III in FIG. 4;
FIG. 4 is a part sectional view in a plane including the thread burr of a partial area of the thread;
FIG. 5 is a partial view in the direction of the arrow V in FIG. 4 in a rolled out representation;
FIG. 6 is a part sectional view in a plane including the thread burr of a partial area of the thread of a modified screw according to the invention;
FIG. 7 is a view in the direction of the arrow VII in FIG. 6 in a rolle
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patent: 5531553 (1996-07-01), Bickford
Hettich Stefan
Hettich Ulrich
Ludwig Hettich Schraubenfabrik GmbH & Co.
Wilson Neill R.
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