GB2112488A

GB2112488A - Improvements in or relating to threaded fastener and nut assemblies and mounting tools therefor

Info

Publication number: GB2112488A
Application number: GB08232005A
Authority: GB
Inventors: Ingvar Algot Eklund
Original assignee: BULTEN AB
Current assignee: BULTEN AB
Priority date: 1981-11-09
Filing date: 1982-11-09
Publication date: 1983-07-20
Also published as: DK495282A; GB2112488B; IT8224142A0; DE3241389A1; NL8204326A; FI823820L; IT1154539B; FI823820A0; NO153701B; NO823713L; SE8106626L; FR2537225A1; FR2537225B1; NO153701C

Abstract

A screw and nut assembly comprises a nut 20 and a screw 11 having a screw shank 12 which has a head 13 at one end thereof and a pin 14 at the other end thereof for engagement with a holding sleeve e.g. 35 (Figure 3, not shown). With the nut 20 applied loosely, the pin 14 protrudes outwardly of the nut 20 and is accessible for the holding sleeve as the nut 20 is being tightened by means of a driving sleeve (33, Figure 3 not shown). The nut may be self- locking (e.g. by having a non-circular hole) and may have a circumferential flange 25 the inner diameter of which is such that there is formed a space 26 for the thread exit 12B. <IMAGE>

Description

SPECIFICATION Improvements in or relating to threaded fastener and nut assemblies and mounting tools therefor The present invention relates to a threaded fastener and nut assembly of the type comprising a threaded fastener having a shank with a head at one end and a key or hold-up pin at the other end, the shank having a threaded portion adjacent the key or hold-up pin and an unthreaded portion adjacent the head. The invention also relates to a mounting tool for such assemblies. The term "threaded fastener" is used herein includes screws and bolts.

One of the oldest proposals for a screw and nut assembly of the type described is disclosed in US Patent No. 3394623 which relates to a tool for mounting of such screw and nut assemblies. In this case the screw end is provided with a square recess, into which a square pin may be inserted in order to hold the screw against rotation, from the screw end, while the nut is screwed on the screw from the same side.

A somewhat similar system is disclosed in a pamphlet from Lamson & Sessions, Cleveland, OHIO, printed in the US in 1975, which pamphlet discloses the so called Una-Drive-tool. Also US-PS 3 789705 discloses a similar system, but in this case the recess is hexagonal.

A comparatively similar system is marketed by Nippon Steel Bolt Company Ltd., which markets so called High Strength T.C. bolts, where the letters T.C.

are used to denote "tension control". In this case the screw end has been provided with a key pin by means of which the screw is held as the nut is screwed on. The pin is broken when the desired torque has been achieved, or at least that is the intention.

Each one of the above mentioned systems has its inherent special problems. Thus, one of the problems of the screw and nut assemblies where the screw end is provided with a recess is that the recess in the screw end cannot be obtained directly with present cold heading techniques but has to be made in an additional step in a second machine. Another problem during the manufacture is the very common hot zinc coating step, during which the recesses in the screw ends are often clogged by zinc.

A further problem with screw and nut assemblies wherein the screw has an engagement recess in the end is noticed by mounting during winter-time, in as much as the screw and nut assembly is first mounted manually, and the final mounting is carried out subsequently, sometimes after several days.

Alternating weather conditions with snow, thaw and rain, followed by cold weather may result in the recesses being clogged by ice, which may be difficult to remove and in any case requires some kind of action before the mounting tool may be applied.

In the case of screw nut assemblies having a pin at the screw end, mounting is first carried out manually whereupon the tightening tool is applied and tightening to the predetermined torque is carried out.

Often, the tightening tool is designed in such a manner that an innermost sleeve grips the pin while an outermost driving sleeve tightens the nut until the correct torque has been attained, whereupon the pin is twisted off. Thus, a surface of fracture is formed, which leads to corrosion if it is not painted. Further, it is very difficult to dimension the fracture kerf in the key in such a manner that variations in strength of the screw do not jeopardize tightening.

According to one aspect of the invention, there is provided a threaded fastener and nut assembly comprising a threaded fastener having a shank with a head at one end and a key or hold-up pin at the other end for engagement with a key or hold-up sleeve, the shank having a threaded portion adjacent the key or hold-up pin and an unthreaded portion adjacent the head, the axial length of the unthreaded portion of the shank corresponding to or slightly exceeding the combined thickness of the work pieces which are to be joined together, the axial length of the threaded shank portion being such that, with the nut applied loosely, optionally with a washer, at least a portion of the key or hold-up pin protrudes outwardly of the nut so as to be accessible to a key or hold-up sleeve when the nut is being tightened by means of a drive sleeve.

According to another aspect of the invention, there is provided a tool for mounting a threaded fastener and nut assembly of the kind comprising a nut and a screw having a head and a shank which has, at an outermost end thereof, a hold-up means, the tool comprising a drive sleeve for tightening the nut a hold-up tool for engaging the hold-up means as the nut is tightened by means of the drive sleeve, and spring means arranged to act axially between the hold-up tool and the drive sleeve to bias the hold-up tool and the drive sleeve axially apart from each other in such a manner that, as the hold-up tool is applied to the hold-up means, the drive sleeve is automatically maintained in engagement with the nut.

It is thus possible to provide a screw and nut assembly whereby the above mentioned drawbacks are reduced or avoided. It is further possible to provide a mounting tool for a screw and nut assembly of the above-described type which tool is comparatively simple and inexpensive but which is safe and reliable in operation.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a screw and nut assembly constituting a preferred embodiment of the invention formed of steel; Figure 2 is an end-view of the screw and nut assembly of Figure 1, Figure 3 shows a mounting tool constituting a first embodiment of the invention in side view and partly in section; Figure 4 is an end view from above of the tool of Figure 3; Figure 5shows a mounting tool constituting a second embodiment of the invention in side view and partly in axial section; Figure 6 is a plan view of the tool of Figure 5 as seen from above; Figure 7shows a mounting tool constituting a third embodiment of the invention in side view and partly in axial section; and Figure 8 is a plan view of the tool of Figure 7 as seen from above.

A screw and nut assembly, generally denoted 10, as shown in Figure 1 comprises a screw 11 with a shank 12 which has at one end thereof a head, in the present case in the shape of a hexagonal head 13, and which as at the other end thereof a key pin 14 for engagement with a suitable key sleeve. The screw shank has a threaded portion 15 and an unthreaded portion 12A of the screw shank is of such an axial length that the so called thread exit, i.e. the transition between the unthreaded portion 1 2A and the thread 15 may be situated just outside the two elements 16, 17 which are joined together by means of the screw and nut assembly. The thread exit has been denoted 12B in Figure 1.

The screw end which is formed with the key pin 14 is simply embodied by a portion of reduced diameter of the screw shank, which portion has been flattened from two opposite sides to form two key engagement surfaces 18, 19. The screw end may also be formed with other key grips, such as hexagonal grips.

The nut 20 is a steel construction nut of the self-locking type, in the present case self-locking in that a throat 21 on the nut has been formed with three radially inwardly directed impressions 22, 23, 24 which result in the nut hole being initially slightly triangular. In this way there is obtained within the thread on one hand a locking portion, essentially within the nut throat 21, and on the other hand a free-spinning portion between the locking portion and a space 26. It is essential that the free-spinning portion is long enough to permit easy mounting of the nut on the screw unto a position where the screw pin 18 is accessible to the tightening tool. Of course, the locking function may be achieved in other ways than the one as described above either by a corresponding design of the nut or of the screw.The nut has, at its side facing the work pieces 16, 17, a circumferential flange 25 which forms the space 26, wherein the thread exit 1 2B is housed. Due to the just-described design with a circumferntial flange 25, it is possible to avoid the otherwise usual need for a washer between the nut and the most adjacent work piece 17.

The embodiment of the mounting tool as shown in Figures 3 and 4 comprises a latch or ratchet wrench 30 which is known per se and which therefore does not need any detailed description. The wrench may be caused to operate in a tightening direction or releasing direction by actuating a control handle 31.

The latch wrench 30 comprises a gear wheel 32 the lowermost portion of which is, for example, square and carries a drive sleeve 33. Through the gear wheel 32 there extends an inner sleeve 34, of round cross-section in the present case, which sleeve has, at the lowermost end thereof, a sleeve 35 which is arranged to engage drivingly the key grip portion 14 of the screw. The uppermost end of the innermost sleeve protrudes above the gear wheel 32 and is provided with a handle 36. The innermost sleeve 34 is axially biased by a spring 37 in such a manner that the lowermost end of the innermost sleeve 34 and the lowermost end of the sleeve 33 are normally situated comparatively close to each other.

The tool is utilized in the following manner.

First, the screw and nut assembly is positioned within the workpieces 16, 17 and then the nut is manually tightened on the screw as much as possible. Thus, the key pin 14 will protrude at least slightly from the end surface of the nut. Then, the wrench is applied to the screw and nut asembly whereby the end of the sleeve 33 is positioned on the nut, simultaneously as the sleeve end 35 is placed on the key pin 14. Then, while holding the screw against rotation by holding the handle, the nut is screwed on the screw by swinging the handle of the wrench 30 back and forth the required number of times until the bolt joint has been established with the predetermined torque.

The embodiment shown in Figures 5 and 6 is similar to the above described embodiment in that it comprises a latch wrench 30 with a gear wheel 32 which carries a drive sleeve 33 and through which there extends an axially displaceable and rotary inner sleeve 34 with a key sleeve 35.

In the present case the upper end of the innermost sleeve 34 carries a pivotallyjournalled hold-up arm, which is arranged to be locked against rotation in relation to the innermost sleeve by means of a roller 38 which may enter into an axial slot 39 at the uppermost end of the inner sleeve. The roller is held in locking position by means of a locking cylinder 40 which is turnable by means of a handle 42, biased into locking position by means of a spring 41. As the handle 42 is pivoted anticlock-wise as seen in Figure 6, against the action of the spring 46, a flat surface on the locking cylinder 40 is positioned opposite the roller 38 which may move slightly out of the way and thus release the hold-up arm 43 for pivotal movement around the innermost sleeve 34.At its outer end the hold-up arm 43 has one or more bores, the axis or axes of which is or are parallel to the axis of the innermost sleeve. In these bores a hold-up pin 44 may be inserted at a desired distance from the axis of the innermost sleeve, and the hold-up pin is lockable in any desired axial position by means of a set screw 45 which acts radially against the hold-up pin.

The hold-up assembly comprising the arm 43, the pin 44 etc is axially biased by the spring 46 in a direction such that the outermost end of the drive sleeve 33 and the key 35 of the innermost sleeve should be disposed axially as far as possible from each other. The reason for the spring-biasing is that it may be desired during mounting to press the drive sleeve 33 from below upon the nut, and then to press the key 35 on to the key end 14 of the screw, and then simply press the hold-up assembly upwardly, in which case one relies on the spring 46 for the task of holding the latch wrench and the other parts in their upper position with the drive sleeve 33 gripping around the nut. Then, it is sufficient merely to swing the handle of the latch wrench back and forth to establish in the bolt joint a predetermined torque.

Figure 6 shows that the handle of the latch wrench has marks M12, M14 and M16 which are intended to lead up to a correct gripping around the handle in order to attain the predetermined torque for each application. Thus, on application of a screw and nut assembly of the M12 size the hand should be placed closer the axis of the drive sleeve than would be the case on application of a screw and nut assembly of the M14 and M16 size. These marks may, of course, also take other shapes, e.g. in that the handle is provided with three spaced serrated fields.

With the embodiment of Figure 5 and 6, the hold-up pin 44 of the hold-up arm 43 would normally be placed against a fixed structural detail to be held stationary as the nut is tightened or loosened.

Sometimes this would not be possible and for such circumstances the end of the hold-up pin may be provided with a thread which is screwed into the end of the hold-up arm, axially thereof, i.e. from the left to the right as seen in Figure 5. In such a case it may possibly be necessary to design the outer end of the hold-up arm 43 with some kind of a thickening so as to permit boring therein to form a bore of a sufficient size in the outermost end of the hold-up arm 43.

The structural details of the embodiment shown in Figures 7 and 8 correspond essentially to those of Figures 5 and 6, and thus will not be described in detail. The various parts of the embodiment shown in Figures 7 and 8 to facilitate a comparison with the embodiment of Figures 5 and 6, have been provided with the same reference characters with an addition of a suffix A. Various modifications may be made within the scope of the invention. For instance, the tightening force may be achieved by using hydraulic, pneumatic or electric drive tools.

Claims

1. Athreadedfastenerand nutassemblycomprising a threaded fastener having a shank with a head at one end and a key or hold-up pin at the other end for engagement with a key or hold-up sleeve, the shank having a threaded portion adjacent the key or hold-up pin and an unthreaded portion adjacent the head, the axial length of the unthreaded portion of the shank corresponding to or slightly exceeding the combined thickness of the work pieces which are to be joined together, the axial length of the threaded shank portion being such that, with the nut applied loosely, optionally with a washer, at least a portion of the key or hold-up pin protrudes outwardly of the nut so as to be accessible to a key or hold-up sleeve when the nut is being tightened by means of a drive sleeve.

2. A threaded fastener and nut assembly as claimed in claim 1, in which the nut is a self-locking nut having a circumferential flange of internal diameter sufficient to form a space for the thread exit.

3. A threaded fastener and nut assem bly sub- stantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

4. A tool for mounting a threaded fastener and nut assembly of the kind comprising a nut and a screw having a head and a shank which has, at an outermost end thereof, a hold-up means, the tool comprising a drive sleeve for tightening the nut a hold-up tool for engaging the hold-up means as the nut is tightened by means of the drive sleeve, and spring means arranged to act axially between the hold-up tool and the drive sleeve to bias the hold-up tool and the drive sleeve axially apart from each other in such a manner that, as the hold-up tool is applied to the hold-up means, the drive sleeve is automatically maintained in engagement with the nut.

5. A tool for mounting a threaded fastener and nut, substantially as hereinbefore described with reference to and as illustrated in Figures 3 to 8 of the accompanying drawings.