IES930464A2 - A lock nut - Google Patents

Abstract

A lock nut (1) comprising a body portion (15) having a substantially flat annular top surface (5), a substantially flat annular bottom surface (6), an outer edge between the top surface (5) and the bottom surface (6) and a central longitudinal axis (9) and a threaded central bore (3) coaxial with the longitudinal axis (9) extending through the body portion (15) characterized in that the body portion (15) further comprises at least one radial groove (7) extending at least partially between the bore (3) and the outer edge, the groove (7) defining at least one deformable segment (18) in the body portion (15) such that the bore (3) is inwardly deformable to define a tapered central bore when radially inwardly directed pressure is applied to the segment (18).

Description

Many applications require the use of lock nuts to produce a fixed positional relationship between a threaded rod and a workpiece. Typically, a lock nut is threaded or tightened along a threaded bolt or rod until a desired position is reached to secure or hold the workpiece in position. For example, lock nuts are used in conjunction with bolts in the fabrication of metal structures and in the assembly of machinery. However, conventional lock nuts, once tightened, are known to loosen, particularly when subjected to vibratory loads.

In an attempt to avoid loosening, various kinds of locking lock nuts have been developed. British Patent Specification No. 1 563 931 describes a self-locking nut having a plurality of projections for engaging a work piece on which the nut is mounted. European Patent Specification No. 0 243 463B describes a lock nut made up of first and second C-shaped nut members and having connection means between the nut members to enable relative displacement of the nut members to secure a tight fit between the nut and the workpiece. U.S. Patent Specificatioi No. 3841371 describes a lock nut having a number of grooves around the IE 930464 - 2 periphery of the central opening of the nut. The grooves define a number of land sections which engage with the work piece to ensure a tight fit.

It is an object of the invention to provide a substantially non-loosenable lock nut, which when fitted onto a thread will retain its operating tightness and will not loosen even when subjected to vibratory loads.

According to the invention there is provided a lock nut comprising a body portion having a substantially flat annualar top surface, a substantially flat annular bottom surface, an outer edge between the top surface and the bottom surface and a central longitudinal axis and a threaded central bore coaxial with the longitudinal axis extending through the body portion characterized in that the body portion further comprises at least one radial groove extending at least partially between the bore and the outer edge, the groove defining at least one deformable segment in the body portion such that the bore is inwardly deformable to define a tapered central bore when radially inwardly directed pressure is applied to the segment.

Preferably, the groove communicates between the bore and the outer edge.

More preferably, the grooves have a depth of between 35 and 45% of the nut height defined along the longitudinal axis.

In another aspect the invention provides a method for manufacturing a lock nut comprising forming a body portion having an outer edge and a central longitudinal axis, machining a threaded central bore co-axial with central longitudinal axis through the body portion, machining at least one groove in the body portion, the groove being a radial groove and extending at least partially between the bore IE 930464 - 3 and the outer edge to define at least one segment in the body portion, and pressing the segments radially inwards to inwardly taper the 5 central bore.

The invention will now be described with reference to the accompanying drawings in which Figure 1 is a top plan view of a first embodiment of a lock nut of the invention with the segments in the uncompressed state; Figure 2 is a side view of the lock nut of Figure 1 in the direction of the arrow A of Figure 1; Figure 3 is an alternative side view of the lock nut of Figure 1 in the direction of the arrow B of Figure 1; Figure 4 is a top plan view of a second embodiment of a lock nut 20 of the invention with the segments in the uncompressed state; Figure 5 is a side view of the lock nut of Figure 4 in the direction of the arrow C of Figure 4; Figure 6 is an alternative side view of the lock nut of Figure 4 in the direction of the arrow D of Figure 4; Figure 7 is a side view of the lock nut of Figures 4 to 6 with the segments in the compressed state to produce a tapered bore; Figure 8 is an alternative side view of the lock nut of Figure 7 showing the lock nut segments pressed together and the tapered bore in broken lines; Figure 9 is a cross-section through the lock nut of Figure 7 along the line IX - IX showing the tapered threaded side wall of the lock nut; Figure 10 is a schematic representation of the tapered threaded IE 930464 - 4 side wall of the lock nut and which defines the central bore of the lock nut; Figure 11 is a side view of the lock nut of Figures 7 to 10 in use mounted on a threaded bolt; Figure 12 is an end view of the lock nut and threaded rod of Figure 11; Figures 1 to 3 show a first embodiment of a lock nut 1 of the invention. As shown in Figure 1, the lock nut 1 is hexagonal and is made up of a body 15 having a central bore 3 therethrough concentric with the central longitudinal axis 9 of the body 15. The central bore 3 of the body 15 is defined by a threaded side wall 4. The body 15 has an annular flat top surface 5 and an annular flat bottom surface 6 (see Figures 2 and 3). The body 15 is formed with six equal axially disposed sides or faces 2 which are adapted for engagement with a suitable wrench or the like and also define six equally circumferentially spaced corners 8 between the faces 2.

The body 15 is also provided with six grooves or slots 7 which extend axially partially through the thickness of the body and project radially inwardly from each circumferentially spaced corner 8 and communicate with the central bore 3. The slots 7 are arranged radially about the nut 1 so that the centre line of each slot 7 intersects the central longitudinal axis 9 of the lock nut 1 to divide the lock nut 1 into six segments 18. Therefore, the slots 7 are arranged such that their central lines extend between opposed circumferentially spaced corners 8.

Figures 2 and 3 more clearly illustrate the manner in which the slots 7 extend only partially axially through the thickness of the body 15 to form the segments 18. Typically, the slots 7 extend to a depth of between 35% and 45% of the nut height along the central longitudinal axis 9. The width of the slots 7 is determined by the taper of the tapered portion 16. Where the taper is 3°, the slots are about l/16th inch in width, and of a depth corresponding to 35% to 45% of the nut height.

IE 930464 - 5 As illustrated in Figures 2 and 3 the circumferentially spaced corners 8 are champfered to define inwardly champfered edges 10.

Figures 4 to 6 show an alternative embodiment of the lock nut 1 of the invention in which the lock nut body 15 is square in plan view having four faces 2 and four slots 7 extending radially inwardly from four circumferentially spaced corners 8 to define four partial segments 18. As previously described, the body 15 has a central bore 3 with which each slot 7 communicates and the slots extend to a depth of between 35% and 45% of the nut height along the central longitudinal axis 9.

Figure 7 shows a side view of the lock nut 1 of Figures 4 to 6 with the segments in the compressed state with the threads of the threaded wall 4 indicated in broken lines. In the compressed state, a portion of the threaded side wall 4 corresponding to the depth of the slots 7 (indicated by the line referenced by the numeral 17) is inwardly radially tapered about the threaded rod 19. The inwardly tapered portion shall be designated by the reference numeral 16.

Tapering of the threaded side wall 4 is achieved by rotating the lock nut 1 into the desired position on the rod 19 in the usual fashion (e.g. using a wrench) and subsequently applying radially inwardly directed pressure to the faces 2 of the segments. The application of pressure to the side faces 2 causes the segments 18 to be urged towards one another at the slots 7 so that the inwardly tapered threaded side wall portion 16 is produced. Therefore, the threads of the threaded wall portion 4 and the threaded rod 19 in the vicinity of the tapered wall portion 16 are locked together and the nut cannot be loosened as the internal diameter of the central bore 3 at the tapered portion 16 is reduced such that the lock nut 1 firmly grips the thread of the threaded rod 19 and prevents relative movement between the lock nut 1 and the threaded rod 19.

Figure 8 shows an alternative side view of the lock nut 1 of Figure 7 in which the segments 18 of the lock nut 1 are deformed and converge and meet across the slot 7 to produce the tapered central bore 3.

JF 930464 - 6 Figure 9 shows an enlarged longitudinal cross-section along the line IX - IX of Figure 7 and clearly illustrates the inwardly tapered portion 16 of the threaded wall 4. As shown in the drawing, the threaded wall 4 is inwardly tapered in the region of the slots 7 as indicated by the broken line 17 to ensure the non-loosenable grip about the threaded rod 19. The tapered nature of the threaded wall 4 is further illustrated in exaggerated form in Figure 10.

The grip achieved between the lock nut 1 of the invention and the threaded rod 13 provides a lock nut in which the lock nut is first tightened in the usual fashion onto the threaded rod 19 and is then re-tightened to engage the threads of the threaded rod 19 and the threads of the tapered wall 4 so that a non-loosenable grip is produced between the lock nut 1 and the threaded rod 19. Therefore, the lock nut 1 fitted on to for example a medium fit thread will retain its operating tightness and will not loosen when subjected to vibratory loads.

Figure 11 shows a side view of the square lock nut 1 of Figures 4 to 6 in use mounted on a threaded bolt 13. The bolt 13 is made up of a threaded rod 19 and a head 20 at one end. The rod 19 is provided with threads 14 which are of a suitable pitch to engage the threaded side wall 4 of the central bore 3 of the lock nut 1. The lock nut 1 is rotated or tightened to the desired position on the threaded rod 19 in the usual manner to ensure a non-loosening fit as will be described more fully below.

Figure 12 shows an end view of the lock nut 1 mounted on the threaded rod 19 of Figure 7. As shown in the drawing, the lock nut 1 has a square configuration as illustrated in Figures 4 to 6 and the threaded rod 19 extends through the central bore 3 of the lock nut 1. The threaded wall 4 of the lock nut 1 engages the thread 14 of the threaded rod 19 so that the lock nut 1 may be tightened onto the threaded rod 19. The tapered central bore 3 ensures that the threads of the threaded rod 19 and of the side wall 4 are tightly engaged to ensure a substantially non-loosenable fit.

Preferably, the tapered central bore is produced using a hydraulic IE 930464 - 7 press applied to the side faces 2. The preferred depth of the slots 7 is a depth between 35% and 45% of the nut height. This depth achieves a preferred internal taper of the central bore of approximately 3° in the tapered portion 16.

Typically the lock nut is produced from material having a minimum tensile strength of 34 to 40 tonnes per square inch tensile strength or grade 8 as specified by BS3693 for nuts. The thread form tolerance is produced in accordance with BS84 specification for medium class fit nuts. The nut is therefore produced according to standard procedures and a further operation follows in which the slots are formed in the lock nut. The slots are cut to a depth of between 35% and 45% of the nut height and the width of each slot is preferably selected such that when pressed closed under pressure an internally tapered thread is formed with a radially inwardly extending taper of approximately 3 degrees.

The tensile strength for Grade 8 in accordance with BS3692 is 80 2 kgf/mm follows and (all a typical nut specification in dimensions are in inches): accordance with BS84 is as 2 3 4 5 6 7 8 9 1 BSW thread 8 1.00 0.9268 0.0068 0.9200 0.8720 0.0320 0.84 1 BSF thread 10 1.00 0.9426 0.0066 0.9360 0.8990 0.0270 0.827 KEY: Column threads per inch major diameter minimum effective diameter maximum effective diameter tolerance effective diameter minimum minor diameter maximum minor diameter tolerance minor diameter minimum IE 930464

Claims (5)

1. A lock nut comprising a body portion having a substantially flat annular top surface, a substantially flat annular bottom surface, an 5 outer edge between the top surface and the bottom surface and a central longitudinal axis and a threaded central bore coaxial with the longitudinal axis extending through the body portion characterized in that the body portion further comprises at least one radial groove extending at least partially between the bore and the outer edge, the 10 groove defining at least one deformable segment in the body portion such that the bore is inwardly deformable to define a tapered central bore when radially inwardly directed pressure is applied to the segment. 15

2. A lock nut as claimed in claim 1 characterized in that the groove communicates between the bore and the outer edge.

3. A lock nut as claimed in claim 2 characterized in that the grooves have a depth of between 35 and 45% of the nut height defined along the 20 longitudinal axis.

4. A method for manufacturing a lock nut comprising forming a body portion having an outer edge and a central 25 longitudinal axis, machining a threaded central bore co-axial with central longitudinal axis through the body portion to form a substantially flat annular top surface and a substantially flat annular bottom surface, machining at least one groove in the body portion, the groove being a radial groove and extending at least partially between the bore and the outer edge to define at least one segment in the body portion, and pressing the segments radially inwards to inwardly taper the central bore. IE 930464 - 9

5. A lock nut substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.