GB2132729A

GB2132729A - Torque indicating means for nuts on screw-threaded shanks

Info

Publication number: GB2132729A
Application number: GB08332628A
Authority: GB
Inventors: Heinrich Sohnius
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-12-22
Filing date: 1983-12-07
Publication date: 1984-07-11
Also published as: AU2185883A; GB8332628D0

Abstract

Torque indicating means are provided on a nut which is to be threaded on a shank wherein the nut is to rotate in unison with the shank until a predetermined torque is reached, at which stage a closure or stop 2 welded to the nut 1 at one end thereof fractures either along preformed zones of weakness 4 or at one or more welds 7, thereby enabling the bore through the nut to be opened by the shank so that the nut can rotate freely relative to the shank. The invention finds particular application as a means for indicating the extent of setting of a resin or like setting mixture during the installation of a resin or like bonded rock bolt. A dimple 8 is provided to provide an axial abutment for the bolt 10 to avoid sharp edges coming into contact with the closure 2 and severing it prematurely. <IMAGE>

Description

SPECIFICATION Torque indicating means for nuts on screwthreaded shanks THIS INVENTION relates to torque indicating means for nuts on screw threaded shanks wherein the nut is to rotate in unison with the shank until a predetermined torque is reached at which stage the nut is to rotate relative to the shank. One such application is in means for indicating the extent of setting of resin or like setting mixture during installation of a resin or like bonded rock bolt.

Generally in the case of resin bonded rock bolts, the resins or setting mixtures are contained in capsules, the mixture components being separated either in frangible compartments in a capsule or in separate capsules.

In the installation process, a selected number of capsules are placed in a pre-drilled hole and a rotating rock bolt is then driven into the hole, bursting the capsules and mixing the components of the resin.

On mixing, the resin begins to set, the setting time being dependent on the type of resin used. Difficulty can be experienced in knowing when to cease rotating the bolt to allow the mixture to set and thus accept the necessary tension to be applied to the bolt to render it effective for rock bolting.

In an effort to alleviate this problem a nut has been proposed which has deformed regions of the thread to prevent it from rotating past a predetermined position relation to a roof bolt shank until the desired torque is applied to such nut. The arrangement is set forth in South African Patent No. 77/4905.

It is the object of the present invetion to provide nut means for indicating when a predetermined torque is applied to such a nut, and thus in the abovedescribed application to indicate when the required state of setting of resin or the like setting mixture for a rock bolt is reached.

In accordance with the invention, there is provided a nut having a stop welded to the nut and at least partly bridging the base at one end thereof wherein predetermined zones are adapted to be severed when a predetermined torque is applied between the nut and a threaded shank on which the nut is to be used to enable the stop to be moved by the shank end from the position in which it at least partly bridges the bore.

Further features of the invention provide for the stop to be a disc or strip; for the stop to be a disc having a central region adapted to be fractured from the surrounding region when said predetermined torque is applied; and for said central region to be attached to the said surrounding region by angularly spaced integral zones in between which the disc is substantially severed from the surrounding region in a substantially circular path.

A still further feature of the invention pro -vides for the stop to hve an inwardly directed formation on the axis of the nut to contact a shank roughly axially in use, and, in the case where the stop is made of metal plate, for the stop to be inwardly dimpled to achieve such axial contact with the end of a shank.

As an alternative to the fracture of a central zone of a disc or strip from the surrounding or outer regions, the welds may be made such that they fracture when the predetermined torque is applied.

The welds could be any type but it is envisaged that spot welds will be most conve nient. Furthermore, the stop could be de signed simply to be severed by the bolt shank when said predetermined torque is applied.

Two examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is an isometric view of a nut according to the invention; Figure 2 is a sectional view taken along line Il-Il in Fig. 1; Figure 3 is a sectional view of a rock bolt according to the invention in position in a section of rock; and Figure 4 is an isometric view of an alterna tive form of nut.

Figs. 1 and 2 show an ordinary hexagonal nut 1 having a metal disc 2 at one end of the threaded bore. The disc 2 has a central por tion 3 which is defined by discontinuous cut lines 4 of weakening of circular shape and between which angularly spaced integral zones 5 connect it to the outer annular portion 6 of the closure. The integral zones 5 are convenienly three in number and are equally angularly spaced about the disc. The cut lines preferably sever the central portion from the outer annular portion between said integral zones.

The diameter of the central portion 3 is fractionally larger than the inner diameter of the nut.

The outer annular portion of the closure is secured to the end of the nut in the position illustrated and as above described. Such se curing is effected by welding (as indicated by numeral 7 in Fig. 1). This welding can be of any type but arc welding and spot welding are preferred.

It will be understood that where a cropped end of a roof bolt shank is to be contacted it may be sharp and cut the closure to pass therethrough prematurely. To prevent this from happening the central region is inwardly dimpled as indicated by numeral 8 so that a cropped end 9 of a roof bolt shank 10 is contacted substantially axially as indicated by numeral 11.

In use the zones of weakening defined by the cut lines and interposed integral webs are designed to give way when the nut is screwed onto a bolt with a torque in excess of a predetermined value. Clearly the outer portion of the disc will be secured to the nut so asto be capable of withstanding more stress than the zones of weakening.

Installation of a resin bonded roof bolt may thus take place as follows: The nut is screwed onto the end of the roof bolt until the end contacts the disc 2.

The bolt is then rotated via the nut and drive in a predrilled hole 12 in a rock bed 13.

The hole contains resin 14 which is mixed by the rotating bolt 10.

As the resin hardens, the torque required to rotate the bolt increases. When the desired consistency of setting resin is reached, this torque exceeds the breaking limit of the integral zones and the central part of the closure gives way, allowing the nut to be moved along the screwthread on the bolt.

Thus the desired state of resin setting is indicated and rotation of the bolt can cease.

It will be appreciated that the predetermined torque required to break the zones of weakness, or in this case integral webs of material, may vary accoridng to the resin used, and its particular setting time and hardening characteristics.

In particular, if the resin is slow setting, the torque at which fracture occurs can be increased to allow for additional stress as a result of the longer rotational time required to mix and set the resin.

One alternative form of the invention is illustrated in Fig. 4 of the drawings. In this case a flat metal strip 1 5 is spot welded (as indicated by numeral 16) at each end to the nut so as to extend diametrically over one end of the bore 1 7 of a conventional hexagonal nut 18. The strip may be adapted to be simply cut by a cropped end of a roof bolt when the torque turning the nut exceeds a predetermined value. However, the spot weld can alternatively be "tailored" to fracture when a predetermined force is exerted on the strip by an end of a shank.

The dimple, or other axially extending formation may again be present but may, as illustrated, be omitted if a satisfactory reslt can be achieved without it.

Clealy many variations may be made to the above described embodiment without departing from the scope of the invention. The nut need not be hexagonal, and the stop need not be a disc or strip. All that is required is that a stop on the nut be physically fractured or servered after the nut is rotated with a predetermined torque applied to the bolt via the nut to subsequently allow the nut to be moved axially along the shank.

Claims

1. A nut having a stop welded to the nut and at least partly bridging the bore at one end thereof wherein Dredetermined zones are adapted to be severed when a predetermined torque is applied between the nut and a threaded shank on which the nut is to be used to enable the stop be be moved by the shank end from the position in which it at least partly bridges the bore.

2. A nut according to Claim 1 wherein the stop bridges the bore completely at said one end of the nut.

3. A nut as claimed in either of Claims 1 or 2 in which said predetermined zones are zones of weakness.

4. A nut according to any one of Claims 1 to 3 wherein the stop is in the form of a disc having a central region adapted to be fractured from the surrounding region which is welded to the nut when said predetermined torque is applied.

5. A nut according to Claim 4 wherein the central region of the disc is attached to the surrounding region by angularly spaced integral zones in between which the disc is substantially severed from the surrounding region in a substantially circular path.

6. A nut according to either of Claims 4 or 5 wherein the central region of the disc is fractionally larger than the inner diameter of the nut.

7. A nut according to any one of claims 1 to 5 in which at least one of the welds is adapted to fracture when said predetermined torque is achieved to enable the shank to pass the stop, the weld thus constituting said predetermined zones.

8, A nut according to any one of the preceding claims wherein the stop has an inwardly directed formation on the axis of the nut.

9. A nut according to Claim 8 wherein the stop is of metal plate and is inwardly dimpled on the axis of the nut to define said inwardly directed formation.

10. A nut substantially as described in the accompanying description with reference to any one of the accompanying drawings.