GB2341655A

GB2341655A - Locking threaded fasteners

Info

Publication number: GB2341655A
Application number: GB9924065A
Authority: GB
Inventors: Barry Littlewood
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-15
Filing date: 1998-09-15
Publication date: 2000-03-22
Anticipated expiration: 2018-09-15
Also published as: GB2341655B; GB9819939D0; GB9924065D0; GB2341654A; GB2341654B

Abstract

A locking device to prevent loosening of a bolt 30 comprises a tapered insert 26 received in a complementary recess 27 in a slotted end of the bolt, the insert having an inner threaded bore 46 which receives the end of a secondary, locking, bolt 47. Rotation of the secondary bolt 47 pulls the insert 26 into the recess 27, which has a smaller angle of taper than the insert, to expand the slotted end of the bolt and so lock the bolt in a nut or bore in which it is engaged. The insert 26 is held in the recess 27 against rotation by a non-circular end 42 (e.g. square, polygonal or splined) engaging in a similarly-shaped base 35 of the recess. A stud having a screw thread at each end may have a recess and insert at each end interconnected by a central threaded locking member (Fig. 3).

Description

2341655 FURTHER IMPROVEM-ENTS RELATING-T-O-TH-READT-Q-S-E-C-U-RING DEVICES

This invention relates to threaded securing devices.

Z.

When sections of engineering assemblies, that are subject to vibration and impact during operation, are clamped together, using male threaded fasteners that are 1 1 1 screwed into tapped holes in assemblies it is important that there is resistance to self loosening and a capability of maintaining the mathematically calculated bolt pre-load at the sections interface. The pre-load is generated by applying a pre-determined amount C1 - 0 of torque to the male threaded fastener so that as it is rotated into the tapped hole of the assembly an elastic extension of the male fastener is produced and the joint becomes tighter. In many instances, however, it is also important for the threaded 1 fasteners to be easily disassembled in a planned manner so that clamped joints can be separated in order to facilitate such activities as maintenance of the assemblies.

The whole process of resisting self loosening whilst maintaining the preload is based 17 1 C-1) on ensuring a high ffictional load exists between the threads of the male threaded fastener, the tapped hole in the assembly and the parent materials. Basically, the clamping load at the sections interface must be at least equal to any external load if the joint is to remain rigid.

During tightening of the male threaded fastener into the tapped hole the male fastener C extends and narrows resulting in increases in thread spacings at the thread interfaces.

1.

Under dynamic loading conditions, which are apparent during the operation of 0 engineering assemblies, external loads induce movement of the fasteners relative to each other and to the members being clamped. Radial sliding movements created at the fastener thread interfaces can be of the magnitude of the maximum allowed tolerances and occur more often in practice than is admitted. As a result there is a loss of effective tension in the fasteners and a reduction in clamping load. The fasteners eventually become &ee of friction in a circumferential direction which results in the rotational loosening of the male threaded fastener.

Objects of the invention, therefore, are to provide increases in resistance to self loosening for male threaded fasteners to be used in tapped holes, by ensuring:

(a) the maximum pre-load is induced and maintained during the operation of the assembly, (b) there is a reduction in lateral thread spacings and an increase in frictional force at the threads interface, (c) there is an increase in resistance to rotational loosening (d) there is a simple and quick installation and disassembly procedure when required, (c) the procedure is universally implementable, (f) the fasteners are reusable.

2 According to the present invention there is provided a device for assembling and 1-7 1-:1 disassembling sections of engineering assemblies that have threaded fasteners screwed Z. I into tapped holes that are subject to viabration and impact that resists self loosening and maintains the pre-determined load at the sections interface.

A male threaded fastener is selected and into the threaded end is introduced a slotted recess of basic frusto conical shape. Along the axis of the male threaded fastener is a I plain cylindrical bore extending from the recess to the other extreme end. Into this fi-usto conical recess is positioned an insert having a tapped hole through its axis that is 4 In threadedly engaged by a secondary male threaded fastener that fits through the axial bore of the primary male threaded fastener with its head at the same end as the head of the primary male threaded fastener. This secondary male threaded fastener is then loosely screwed into the insert and this unit is then screwed into the tapped hole of the assembly section to a pre-determined torque value and the secondary male threaded fastener is then screwed into the insert to another pre-determined torque value causing I the insert to be drawn into the recess allowing the segments in the end of the primary I male threaded fastener created by the slots to expand and be forced into the threads of the tapped hole.

The recess comprises a plain cylindrical bore adjacent the wide end of the frusto cone and a plain square bore adjacent the narrow end of the frusto cone the recess extending axially from the wide end at the extreme threaded end of the primary male threaded fastener inwardly to the narrow end ftom where the plain cylindrical bore extends along the full length of the axis to the other extreme end of the primary male threaded fastener. The head of the primary male threaded fastener is counterbored at its axis to accept the head of the secondary male threaded fastener which is of smaller diameter than the primary male threaded fastener. The bores at either end of the frusto conical part of the recess ensure alignment of the insert and concentricity of expansion of the I segments but the square bore prevents the insert from rotating in the recess when the C zl., secondary male threaded fastener is tightened into it during assembly and released from it during disassembly. Axially directed slots radiused at the forward end to relieve any C) stresses raised during expansion of the segments positioned circumferentially around I the recess extend forwardly to the most forward position of the plain square bore. Into this recess is positioned an insert of substantially the same basic fruso conical form as the recess. At the wide end of the frusto cone and leading from it forwardly is a plain cylinder that fits into the corresponding plain cylindrical bore in the recess aiding alignment and concentricity of expansion of the segments. Leading rearwardly from and adjacent the large diameter cylinder is an abutment whose outer diameter is smaller than the inner diameter of the threads of the primary male threaded fastener andprevents the insert being overtightened during assembly. Adjacrnt the narrow end 1:1 C, C of the frusto cone is a plain square extension that fits into the corresponding square bore in the recess aiding alignment of the insert and concentricity of expansion of the segments and preventing rotation of the insert during assembly and disassembly. Along the axis of the insert is an internally threaded bore that accepts the secondary male threaded fastener that is screwed into it ftom the head end of the primary male threaded fastener opposite the recess. After this unit has been loosely screwed into the tapped hole of the assembly section and torqued to its pre-determined value by rotating the head of the primary male threaded fastener using a driviho, instrument such as a In In torque wrench the secondary male threaded fasteneris then torqued to its 3 predetermined torque value using a suitable driving instrument and because the frusto conical angle of the insert is greater than that of the frusto conical part of the recess C) there is face to face contact of the firusto conical parts of the insert and recess. During C, this tightening process the threads on the outside of the se0ments are expanded and forced into the counterparts of the tapped hole in the assembly section increasinor the 1=1 frictional force between the enaaaed threads eliminatino, the lateral interencracement C) I=> C) I=) _n spacings at the extreme threaded end of the primary male threaded fastener preventing V It) rotational looseninc, C', The volume of the recess is related to the bending resistance of the material from which the primary male threaded fastener is manufactured at the position of the flexure hinges at the most forward end of the slots. For example if the material is very hard the thickness of the flexure hinge is required to be less than for a softer material in order to allow the threads of the segments to expand into their female counterparts of the tapped hole.

t4- DESCRIPTION OF DRAWINGS

Figure 1 is a section of the male threaded fastener and insert in an exploded view as would be utilised in a tapped hole situation or nut and bolt situation where the nut is difficult to access and apply torque.

Figure 2 is a section of the primary male threaded fastener and insert fully engaged in a 0 0 tapped hole situation.

Figure 3 is a section of a fully engaged engineers' stud and insert showing zy 1 In W modifications to both ends of the stud.

Figures 4A to 4F show sections and plans of various types of insert to be used with secondary male threaded fasteners showing some anti-rotational devices, Figures 5G - 5K show sections of various inserts and recesses used in tapped hole situations.

DESCRIPTION OF EMBODINIENTS

30) to be modified is screwed Figure 1 applies to a fastening system where the MTI into a tapped blind hole. Such depictions are shown in Figure 1 and 2. The principle is that the crests of the threads of the MT17 (30) are forced into the roots of the threads of the FT17 (34) whereby the thread clearances are eliminated and lateral movement is prevented, but the introduction of the insert (26) into the recess (27) is carried out in a different manner using a secondary 1M (47), see Figure 2. This system can also be

1 It) used in a situation where the nut is difficult to access. In this case the tightening cl operation takes place from the head end of the primary MTF. The secondary MTF is then tightened as described later.

1 From the threaded end face (29) of the primary MTF (30) in Figure 1 the recess (27) 1 begins with a chamfer (3 1) leading into a plain cylinder (3 M which continues into the 0 C) largest diameter of the frusto conical portion (3)33). The included angle and length of this frusto cone (335) depend upon the amount of thread engagement between the primary MTF (30) and the tapped blind hole (34) and the radial movement necessary between the primary MTF (30) and the recess end of the tapped blind hole (34) to eliminate any clearance at the thread interfaces and prevent any, lateral movement between them when the male and female threads are forced into each other to ensure security and resistance to loosening. Although a frusto conical recess has been 0 described there are other forms of recess which can be utilised which are shown in Figures 5G to 5K and which will be described later. Continuing from the smaller diameter end of the frusto conical recess is a square recess which acts as an anti rotational device for the inseri which will be described later. Continuing from this recess and blendina into it is a central bore that exits at the other extreme end of the primary MTF (3 0). The extreme threaded end (29) of the MT17 (3) 0) has A ots 8) as previously described with the slots terminating at the start of the central bore (22). Into this bore (22) along the axis of the primary XITF (30) fits a secondary MTF (47) see Fig.2. If the primary NITF (30) is, for example, a hex head bolt or set screw then the secondary MTF (47) is introduced into the axial bore (22) of the primary '.\4TF (30) from the head end (37) until the head (28) of the secondary MTF (47) rests against the head (37) of the primary MT17 (30). The head (28) of the secondary MT17 (47) could be hexagon or any other external polygonal form or could be a socket cap screw or any other internal polygon drive form. The heads (37) of the primary MWs (30) are counterbored to accept the heads (28) of the secondary IMWs (47) If the primary MTF (30) was a socket cap screw or similar the secondary MT17 (47) would usually be a socket cap screw or similar, of smaller diameter, and fitted into a counterbore within the socket head, or similar, of the principal MTF (30) However, those skilled in the arl could apply any form of combination between the primary (30) and secondary MWs (47).

Into the recess (27) in the extreme threaded end (29) of the primary MTF (30) is placed an insert (26). The end of the insert (26) that enters the recess (27) initially has a square register (42) that fits into the corresponding recess (35) within the primary 0 c MTF (30). Leading from this register (42) is the narrow end of the frusto conical form Z=.

of the insert (26), the included angle of which is greater than that of its counterpart =5 =P 1 1 (27) in the primary MTF (30) by an amount that allows the extreme threaded end (29) of the primary MTF (30) to be forced into the female threads of the tapped blind hole when the insert (26) is drawn into the recess (27) by the secondary MTF (47). When this is accomplished and the lateral movement between the threads of the primary MTF (330) and the tapped blind hole (34) has been eliminated, the flusto conical faces of the insert (26) and recess (27) are touching along their length- Leading on from the wide end of the frusto conical section (26) is a plain cylindrical register (44). This is an aid to concentricity. Continuing from this register is an abutment (45) which prevents overtightening W C Along the axis of this insert (26) is a threaded bore (46) of the same diameter and form as the threaded part of the secondary MTF (47). Slots (38) in the end (29) of the primary NM (.3) 0) placed as in the earlier description allow the extreme threaded ends (29) of the primary MTF (30) to expand radially when the secondary MTF (47) is screwed into the insert (26). The square register (42) at the narrow end of the insert (26) when placed in the corresponding part of the recess 5) at the end of the through bore (22) prevents the insert (26) from rotating when the secondary MTF (47) is screwed into it. As screwing progresses the insert (26) is drawn into the recess (27) ly It> but the square register (42) of the insert (26) never touches the end of the corresponding part (35) of the recess (27) furthest away from the extreme threaded end (29) of the 1\4TF (30) such that the radial expansion of the extreme threaded end (29) of the primary MTF (30) is fully effected- As already mentioned the ability of the insert not to be rotated by the screwing action of the secondary 1MF in the tapped blind hole and the difficult nut access situation is vital to the assembly and disassembly of the components.

Besides the method described of preventing rotation of the insert there are other 0 methods of performing this technique and some are described later and relate to Figures 4A to 4F.

Besides the nut and bolt and tapped hole situations this invention can also be applied to engineers' studs where either or both ends are required to be secured in position. If c the end of the stud screwed into a tapped hole only requires to be secured then the "tapped hole" arrangement can be used. If the end of the stud protruding from the assembly only requires to be secured then the "nut and bolC method can be used. However, if both ends of the stud are required to be secured then the embodiment is as shown in Figure 3.

The end of the primary engineers' stud (50) that fits into the tapped blind hole (56) has 1 a fi-usto conical recess (57), the extreme end of which there is an optional chamfer (58) and an optional plain cylinder (59). This plain cylinder (59) leads into the widest end of the frusto conical section (57). The narrow end of this frusto conical section (57) then leads into a square recess (61) and from here running along the full length of the stud 1 c axis is a plain bore (62). The end (63)) of this plain bore (62) leads into a square recess (64) which then leads into the narrow end of a frusto conical recess (54), the wide end of which leads into a plain bore (75) which exits the end of the stud via a chamfer (76). Circumferentially placed narrow slits (52,53) are cut into the extreme threaded 7 ends of the engineers' stud (50), extending to the plain bore (62) at either end of the stud. These slits are radiused at the closed ends furthest away from the extreme threaded ends of the studs.

Into the frusto conical recess (57) at the end of the stud (50) that screws into the tapped blind hole (56) fits a similarly shaped insert (55). At the widest end of the insert (55) there is an abutment (65) and cylindrical register (66) which fits into the widest end of the frusto conical insert (55). The narrow end of this fi-usto conical insert then leads into a square register (67) which then blends into a cylindrical secondary male threaded fastener (68) that fits through the axial plain bore (62) and exits the stud (50) through the other recess (54) for a predetermined distance. Into this recess (54) at the end of the stud (50) carrying the hexagon nut or similar (5 1) fits another insert (69) of essentially a frusto conical section. At the widest end of the insert (69) is an abutment (70) and cylindrical register (71) which lead into the widest end of the frusto conical insert (69). The narrow end of this frusto conical insert (69) leads into a square register (72). Alone, the axis of this insert (69) is a plain bore (73) of the same diameter as the axial bore (62) through the stud (50).

The preferred method of installation and assembly is to firstly locate the insert (55) into the end of the primary stud (50) that screws into the tapped blind hole (56). The insert (69) that fits into the recess (54) at the other end of the stud (50) is placed in position and the threaded end (74) of the secondary male threaded fastener (68) has screwed loosely onto it a secondary hexagon nut (77) or other open female threaded fastener when both inserts fit snugly into their respective recesses (57,54). Rotation of c the inserts (55,69) Is unable to take place because of the square registers (67,72) that fit into their counterpart recesses (61,64). The primary stud (50) is then screwed into the tapped hole (56) of the component (48) to the recommended torque. The other component (47) to be clamped is then placed into position and the primary female fastener (51) is also tightened to the recommended torque.The secondary female threaded fastener (77) is then tightened to its recommended torque causing both extreme ends of the enaineers' Stud (50) to be forced into the threads of their female counterparts (56,51) ensuring security and prevention of lateral movement during operation.

Figures 4A to 4F show various forms of insert that can be used in the tapped hole situation. They are by no means exhaustive and those skilled in the art could produce many more variations. However, the principle of the insert is to prevent its rotation during assembly and disassembly of the insert when used in the "tapped hole" situation.

Diagram A shows a pin or dowel (80) inserted or welded to the insert (81) that fits 1 into one of the axial slots in the recess of the primary fastener. During assembly the pin or dowel (80) prevents the insert (81) from rotating. As many pins or dowels as deemed necessary are used. This method of anti- rotation is useful if the parts of the insert at either end of the flusto conical portions are cylindrical. Along the axis of the 0 insert runs a tapped bore (86) into which is screwed the secondary MTE Diagram B is similar to Diagram A except that instead of a pin or dowel a fin (82) C5 is utilised. The method of operation is the same as described in Diagram A.

Diagrams C and D show a square section (83) of the narrow end of the fruso conical C> section. This square section could be any polygonal shape but the object is to fit into its counterpart in the primary MTF to prevent rotation during assembly and 1-P disassembly.

Diagrams E and F show the tapered section of the insert (84) to be pyramidal with the W section at the narrow end of the pyramid being square (85), although any polygonal C1 1 I= section could be utilised. A similar arrangement is shown in Figure 5H.

CLAMS A threaded device for assembling and disassembling sections of engineering assemblies, 0 I-D In that are subject to vibration and impact, that resists self loosening and maintains the pre-determined load at the sections interface, whereby the primary male threaded fastener has introduced into its threaded end a slotted recess, whose basic form is frusto conical, into which is positioned an insert, having a tapped hole through its axis, that is threadedly engaged by a secondary male threaded fastener that fits throu- h an axial bore of the primary male threaded fastener from the head end and is loosely screwed into the insert forming a unit which is then screwed by the driving means at the head of the primary male threaded fastener into the tapped hole of the assembly section to a pre-determined torque value, followed by the male secondary fastener being tightened to its pre-determined torque value by the driving means at its head, 0 In 0 causin- the seaments in the threaded end of the primary male threaded fastener, created by the slots, to expand radially and be forced into the threads of the tapped hole as the insert is drawn into the recess, which comprises a plain cylindrical bore adjacent the wide end of the frusto cone, and a plain square bore adjacent the narrow end of the frusto cone, the recess extending axially from the wide end at the extreme D I threaded end of the primary male threaded fastener inwardly to the narrow end from where a plain cylindrical bore extends along, the full length of the axis to the other extreme end of the primary male threaded fastener where the head is counterbored to accept the head of the secondary male threaded fastener, which is of smaller diameter than the primary male threaded fastener, the bores at either end of the frusto cone part of the recess ensuring alignment of the insert and concentricity of expansion of the segments which occur due to the presence of axially directed slots, radiused at the forward end to relieve any stresses raised by the expansion of the segments, positioned circumferentially around the recess, that extend forwardly to the most forward position of the square bore, that accepts the square extension of the insert preventing the insert from rotating in the recess when the secondary male threaded fastener is tightened into it during assembly and disassembly, the insert being further characterised by a rearward extending frusto cone of the same basic shape as the recess with the wide end extending rearwardly to a plain cylinder that fits into the plain cylindrical bore of the recess, aiding all-nment of the insert and concentricity of radial expansion of the segments, and having an adjacent abutment whose outer diameter is smaller than the inner diameter of the threads on the primary male threaded fastener preventing the insert bein- overti-htened during assembly into the tapped hole, as the secondary male t) In 1-1) threaded fastener is screwed into the threaded axis of the insert by an appropriate driving instrument, resulting in the insert, whose fi-usto conical angle is greater than that of the frusto conical part of the recess, being drawn into the recess until there is face to face contact of the frusto conical parts of the insert and recess such that during this tightening process the threads on the outside of the segments are expanded radially 1 0 and forced into the counterparts of the tapped hole in the assembly section increasing the frictional force between the engaged threads, eliminating the lateral interengagement spacings at the extreme threaded end of the primary male threaded I I I fastener, preventing its rotational loosening, 1. 1 1 ro 2/ A securing method according to claim 1 characterised by the primary male threaded It> 0 fastener having two threaded ends and both ends being engaged with female threaded 0 _n CI 5 C: > counterparts one of which is a tapped hole the other of which is an open nut, with the primary male threaded fastener having a bore along its axis from one recess to the W c) other through which runs a secondary male threaded fastener having an insert attached to the end which fits into the tapered hole and a threaded portion at the opposite end, which fits through another insert, onto which is screwed a secondary female threaded fastener which causes both inserts to be activated resulting in the thread clearances between both ends of the primary male threaded fasteners and their counterparts to be eliminated.

A securing method according to claim 1 whereby the shapes of insert and recess could be pyramidal, splined, knurled or other polygonal form but being of taper form whereby the included angle of the insert is greater than that of the recess to allow the threads of the split end of the male threaded fastener to expand outwards into the threads of the female threaded fastener and to prevent rotation of the insert during assembly and disassembly.

4/ A securino, method whereby all the cylinders and registers in the recesses and inserts 0 could be of square, splined, knurled or other polvCFonal shapes to prevent rotation of 1 Z the insert during assembly and disassembly in the tapped hole situation.

5/ A securing method according to claim 1 whereby a pin could be introduced into the 1 frusto conical face of the insert and slide into one of the slots on the recess and prevent the insert from rotating in the tapped hole situation.

1, 61 A securing method as in claim 5 whereby the pin could be substituted by a fin or fins that are attached to the insert and which fit into the slots in the end of the recess to prevent rotation of the insert during assembly and disassembly.

1 7/ A securing method according to claim 1 whereby the insert comprises two parts, 1 C one part being of fi-usto conical shape having an anti-rotational polygonal or splined 1:1 0 register at the narrow end of the frusto cone and a second part being a male threaded 1 1 fastener that fits through an axial bore of the insert and screws into its counterpart in the primart male threaded fastener.