GB2058987A - Locking of screw threaded connections - Google Patents

Abstract

As a threaded plug 10 is screwed into a threaded sleeve 16, the plug surface 34 abuts a spacer 24 and the diameter of the inner end of the plug 10 is increased so as to lock the screw-threads 12, 20 together. The inner end of the plug 10 is slotted, and frusto-conical surfaces 34, 30 are provided on the plug 10 and the spacer 24. The edge 26 of the spacer 24 furthest from the frusto-conical surfaces 30 and 34 abuts against a projection 28 on the inner surface of the sleeve 16 which prevents movement of the spacer 24. The use of such apparatus in connectors for optical fibres is described. In a further embodiment, the sleeve 16 is formed in two parts, the spacer 24 screwing into one part and being locked as described above. <IMAGE>

Description

SPECIFICATION Improvements in or relating to screw threaded connections The present invention relates to screw threaded connections, and more particularly, to connections where it is required to secure one part of the connection into place when it is screwed into the other part of the connection.

If a screw, or other threaded member, is screwed into a connection, it will turn freely at first then, as it reaches the limits of its thread, it will become more difficult to turn. This is known as being "hand tight". The screw can be further tightened by use of a tool. This stage involves a deformation of the material forming the screw and the surrounding thread so that the screw is secure against further movement.

In such a position, however, the stresses on the thread are such that it will tend to deform to reduce the forces, making the screw loose again. It would therefore require further tightening to secure the screw.

In connections where the position of the connector or screw is important, such as where items attached to the screw and the connector are to be separated by a small fixed distance, the further tightening of the screw would alter the positions. Hence it is difficult to ensure that the screw connection is secure when in position, with no possibility that the screw can "work loose".

According to a first aspect of the present invention there is provided an apparatus for securing a screw thread comprising a first member with a screw thread on an outer cylindrical surface and a second member with a screw thread on an inner cylindrical surface, said first member screwing into said second member and abutting against an abutment part of the second member, thereby to increase the diameter of the first member adjacent said abutment part.

Preferably, the first member is provided with at least one slot in the region of its screw thread, the slot allowing the first member to deform in the region of the slot, thereby increasing the diameter of the first member.

In a preferred form, four slots are provided, spaced equi-distantly around the circumference of the outer cylindrical surface of the first part.

To facilitate the part of the screwing operation when abutment occurs, the first member is provided with a frusto-conical surface which abuts against the abutment part of the second member.

According to a second aspect of the present invention there is provided a method of securing a screw thread comprising the steps of screwing a first member carrying the screw thread into a second member until it contacts an abutment part of said second member and further screwing the first member onto the abutment part thereby to increase the diameter of the first member adjacent said abutment part.

An apparatus according to the present invention may be used, for example, in couplers for optical fibres and especially those disclosed in British Patent Application Nos.

79.17,999, 79.18,000 and 79.18,001 (Publications Nos. , and , respectively). The use of such an apparatus allows accurate connections to be made between parts of an optical fibre coupler, to permit accurate spacing of various parts of the coupler, the screw thread being unable to "work free" thereby altering the spacing and reducing the efficiency of the optical connection.

The present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a section through a first coupler for an optical fibre having an apparatus for securing a screw thread according to the present invention; Figure 2 shows a part of the coupler in greater detail; Figure 3 shows a view of an end of the part of the coupler shown in Fig. 2 which carries the screw thread; Figure 4 shows a section through a second coupler for an optical fibre having apparatus for securing screw threads according to the present invention.

Referring first to Fig. 1, the coupler for an optical fibre has a first member in the form of a plug 10 with a screw thread 12 on part of its outer surface. The plug 10 has a central bore 14 which may receive a clamp or other support for an optical fibre. The plug 10 screws into a second member 16, which has a central bore 18, a part 20 of which is threaded to receive the plug 10.

The second member 16 shown in Fig. 1 has latches 22 which connect with further parts (not shown) of the coupler for an optical fibre. The latching part of the coupler may be formed in accordance with the apparatus disclosed in British Patent Application No.

79.18,000 (Publication No. ) or British Patent Application No. 79.18,001 (Publication No.

A spacer 14 fits within the bore of the second member 16 and the end surface 26 of the spacer 24 remote from the plug 10 abuts against a projection 28 inside the bore 18.

This prevents movement of the spacer 24 away from the plug 10.

The opposite end 30 of the spacer 24 adjacent the plug 10 is formed in the shape of the frustum of a cone, decreasing in diameter with increasing distance from the end surface 26 of the spacer 24. The spacer 24 has a bore 32 coaxial with, and of the same diameter as the bore 14 in the plug 10.

The end 34 of the plug 10 adjacent the spacer 24 is also in the shape of the frustum of a cone, the sides of which subtend a smaller angle at the apex of the cone than the sides of the frustum of a cone formed on the spacer 24. Hence the frustum in the plug 10 decreases in diameter with increasing distance from the spacer 24. Hence the plug 10 and the spacer 24 abut only at the outer edge of the plug adjacent the screw thread 12.

The part of the plug 10 carrying the screw thread 12 is also provided with slots 36. As shown in Fig. 2, the slots 36 extend from the end of the plug 10 adjacent the spacer 24, parallel to the axis of the bore 14 to a length slightly less than the depth of the frustoconical part of the plug 10 and to a depth so that they provide a passage from the bore 14 to the screw threaded surface 12.

Four such slots 36 are formed in the plug 10 and, as shown in Fig. 3, are spaced equidistantly around the end surface 30 of the plug 10.

When the plug 10 is screwed into the second member 16, its leading edge abuts the spacer 24. The frusto-conical surfaces 30 and 34 cooperate so as to deform the end of the plug by widening the slots 36 and hence increasing the diameter of the screw thread 12 adjacent the spacer. This forces the screw thread 12 into the thread 20 in the second member 16, thereby securing it.

The depth that the plug 10 can be screwed into the second member 16 is accurately controlled by the length of the spacer 24 and hence parts of the coupler, attached via the latches 22 and a crimp spigot 38 on the plug 10, can be positioned accurately relative to each other with no possibility that the connection would "work loose".

Fig. 4 shows a second coupler having two screw threads secured by apparatus according to the present invention. The coupler has a first part having a connector 39, a clamping sleeve 40 and a plug 42 which screws onto the connector 38, and a second part having a crimping spigot 44 and an outer retainer (not' shown) which secures to the connector 39 and which receives the crimping spigot 44.

The connector 39 and clamping sleeve 40 shown in Fig. 4 are designed according to British Patent Application No. 79.17,999 (Publication No.

The connector 39 has a central bore 46 which has a region sufficiently wide to receive the sleeve 40. The sleeve also has a central bore 48, coaxial with the bore 46 which receives an optical fibre. One end of the connector has a screw thread 50 on the surface of the bore 48 which receives a corresponding thread 52 on the plug 42.

The plug 42 is provided with a frustoconical surface 54 which, when the plug 42 is screwed into the connector 39, abuts against one end of the sleeve 40. This clamps the sleeve 40 in position and, if the end of the sleeve 40 furthest from the plug 42 is designed similarly to the sleeve disclosed in British Patent Application No. 79.17,999 (Publication No. ), this also has the effect of clamping the optical fibre.

The end of the plug 42 carrying the screw thread 52 is provided with slots, in a similar way to the plug 10 shown in Figs. 2 and 3.

Hence, when the plug 42 is screwed into the connector 39, the surface 54 abuts against the sleeve 40 and its diameter is increased.

Hence the plug 42 is secured in position.

The end 56 of the plug 42 furthest from the screw thread 52 is also shaped in the form of the frustum of a cone, decreasing in diameter with increasing distance from the thread 52. The crimping spigot 44 also has a frusto-conical surface 58 which cooperates with the end 56 of the plug 42. The outer surface of the spigot 44 has a screw thread 60 and is provided with slots (not shown) in the end adjacent the plug 42. The spigot 44 screws into the outer retainer and the frustoconical surfaces widen the spigot 44 at the end adjacent the plug thereby securing the spigot in place.

Claims (11)

1. An apparatus for securing a screw thread comprising a first member with a screw thread on an outer cylindrical surface and a second member with a screw thread on an inner cylindrical surface, said first member screwing into said second member and abutting against an abutment part of the second member, thereby to increase the diameter of the first member adjacent said abutment part.

2. An apparatus according to claim 1, wherein said first member is provided with at least one slot in the region of its screw thread, said at least one slot allowing the first member to deform in the region of said at least one slot, thereby increasing the diameter of the first member.

3. An apparatus according to claim 2, wherein four slots are provided, said four slots being spaced equi-distantly around the circumference of said outer cylindrical surface of the first part.

4. An apparatus according to any one of the preceding claims, wherein said first member has a surface in the form of the frustum of a cone which abuts against the abutment part of the second member.

5. An apparatus according to claim 4, wherein said abutment part has a surface in the form of the frustum of a cone which fits within the frusto-conical surface of the first member, the abutment occurring only at the outer edges of the frusto-conical surfaces.

6. An apparatus according to any one of the preceding claims, wherein said second member has a first part and a second part, said two parts fitting one inside the other, the inner of said two parts carrying said abutment part and also bearing against an abutment surface inside the outer part.

7. A method of securing a screw thread comprising the steps of screwing a first member carrying the screw thread into a second member until it contacts an abutment part of said second member and further screwing the first member onto the abutment part thereby to increase the diameter of the first member adjacent said abutment part.

8. A method of securing a screw thread according to claim 7, further including the step of providing the first member with slots in the region of its screw thread, thereby to facilitate the further screwing step.

9. An apparatus for securing a screw thread substantially as herein described with reference to, and as illustrated in the accompanying drawings.

10. A coupler for an optical fibre having an apparatus for securing a screw thread according to any one of claims 1 to 6 or claim 9.

11. A method of securing a screw thread substantially as herein described with reference to and as illustrated in the accompanying drawings.