Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Torque responsive nut or bolt driving connection – Frangible connection
Reexamination Certificate
2000-06-16
2001-10-02
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Torque responsive nut or bolt driving connection
Frangible connection
C411S003000, C411S429000, C411S432000
Reexamination Certificate
active
06296429
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to devices employed in reinforcement and support of rock structures, and more specifically to nuts having frangible portions for applying tension to threaded rods or bolts which are anchored in blind drill holes in rock formations such as mine roofs, and the like.
Among the means for effecting rock structure support and reinforcement are those wherein an elongated rod or bolt is installed in a blind drill hole bored in the formation. A breakable cartridge containing mutually isolated components of a resin grouting material is inserted into the hole, followed by one end of the rod. The cartridge is fractured against the end of the hole by advance of the rod, and the released resin components are mixed by rotation of the rod. A short time, e.g., a few seconds, after mixing the components harden to provide a secure anchor for the end of the rod within the drill hole.
In the usual situation, it is desirable to place the rod in tension in order to compress and reinforce the rock structure surrounding the drill hole. This may be done by threading a nut on the end of the rod outside the drill hole and rotating nut against a metal support or bearing plate. In order to permit mixing of the resin components and tensioning of the rod in a single operation, nuts have been provided with frangible portions so that the rod will rotate to mix the components in response to rotation of the nut, and the frangible portion will break upon application of excess torque to the nut after sufficient hardening of the grouting mix to apply the desired degree of tension to the rod.
Examples of so-called tension nuts which have been used in the past are shown and described later herein. The frangible portion of some nuts of this type is located in the threaded portion of the nut, raising the possibility that the threads may become fouled or damaged, resulting in malfunction or at least inconsistent operation of such nuts. In other types of tension nuts, the frangible portion may break before the resin components are thoroughly mixed, resulting in poor anchoring of the rod.
It is a principal object of the present invention to provide a novel and improved tension nut for use with a threaded rod in rock support and reinforcement applications.
Another object is to provide a mine roof bolt tension nut which ensures complete and thorough mixing of relatively large amounts of resin grouting components by rotation of an elongated rod upon which the nut is mounted.
A further object is to provide a nut having a frangible portion for fracture by a rod upon which the nut is threadedly secured by application of relatively high torque to the nut, and wherein the fracturing torque is relatively consistent from one nut to the next.
Other objects will in part be obvious and will in part appear hereinafter.
SUMMARY OF THE INVENTION
One of the most widely used tension nuts for mine roof support applications over the past 20-odd years is that made and sold by the Frazer and Jones Division of applicant's assignee under the trademark “Domenut.” This tension nut is shown and described in U.S. Pat. No. 4,662,795 and includes the usual body portion having an internally threaded bore for engagement with the threaded end of a length of reinforcing bar, and an additional, dome-shaped wall surrounding one end of the threaded bore. An opening in the top of the dome-shaped wall is coaxial with, and of smaller diameter than the threaded bore in the nut. Thus, as the end of the bar is threaded into the nut, threaded advance is limited by contact of the end of the bar with the inside of the dome-shaped wall. After the resin mix has hardened sufficiently to prevent rotation of the rod by a torque sufficient to fracture the dome, continued rotation of the nut causes such fracture and permits further rotation to apply tension to the rod.
It has been found that in some anchoring applications, such as those requiring a relatively large amount of resin, the dome portion of the nut is fractured before the resin components have been mixed to the desired extent. That is, the components sometimes begin to harden before mixing is complete and this initial hardening is sufficient to retard rotation of the rod to an extent that the dome portion of the nut fractures. The nut may then be further rotated to apply tension to the rod, but anchoring of the rod is inadequate due to the incomplete mixing. Attempts to overcome the problem by thickening or otherwise reinforcing the dome section, as conventional wisdom would dictate, were largely unsuccessful.
The tension nut of the present invention adds to the prior art Domenut tension nut a metal disc or washer, inserted into the area above the threads and surrounded by the cylindrical portion which is later deformed by a die into the dome-shaped configuration. The disc is of smaller diameter than the inside diameter of the cylindrical portion, but greater than that of the opening in the dome. As the nut is threaded onto the rod, the end of the rod contacts the disc, causing the latter to contact the interior of the domed portion above the thread zone about the entire periphery of the disc. The rod will then be rotated together with the nut as the resin components are mixed. When mixing is complete, rotation is halted for a few seconds as the mixture hardens sufficiently to resist rotation of the rod against a torque great enough to cause the rod to distort the disc toward a dome shape and to fracture the dome portion of the nut and expel the disc. The nut is then torqued to the degree necessary to produce the desired tension in the rod.
The foregoing and other features of structure and operation of the tension nut of the invention will be more readily understood and fully appreciated from the following detailed disclosure, taken in conjunction with the accompanying drawings.
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patent: 5873689 (1999-02-01), Mensour et al.
Hancock & Estabrook, LLP
McGuire George R.
The Eastern Company
Wilson Neill
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