GB2305482A

GB2305482A - Split nut assembly

Info

Publication number: GB2305482A
Application number: GB9519384A
Authority: GB
Inventors: Richard Ian Johnston
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-09-22
Filing date: 1995-09-22
Publication date: 1997-04-09
Anticipated expiration: 2015-09-22
Also published as: GB9519384D0; GB2305482B

Abstract

To facilitate its removal when seized, the nut 1 is formed in two halves 2,3 which are clamped together by a retainer cap 10, so that the screwthread is continuous and the split nut assembly may be screwed onto a bolt or stud, and removed by pulling off the retainer cap 10. The nut halves 2,3 are formed as blanks cut from half hexagonal bar, and the cap 10 is press fitted onto the blanks which are then drilled and tapped. The cap 10 may have a flange, or only extend over part of the height of the nut halves 2,3 to provide a lip, engageable by a puller (not shown). Alternatively, the cap 10 has weakening grooves breakable by a spanner. The cap 10 may be welded to, or peened into holes 8 in, the nut 1. A spigot may project from one end of the nut 1 into engagement with a washer or a hole in a workpiece.

Description

IMPROVEMENTS IN OR RELATING TO NUTS This disclosure relates to the design of nuts which have to be removed after long periods in position on a bolt or stud and which consequently may have become seized in position.

The problem of removing nuts from bolts or studs where the threads have been corroded is well known and, in many cases, a nut splitter has to be used. The reason that corrosion occurs on the interengaging threads is because capillary action tends to draw moisture into the gaps and differential oxygen concentrations lead to the establishment of corrosion cells.

In another similar situation, nuts holding exhaust manifolds attached to the studs fitted to engine blocks also become seized in position. The mechanism here is one of'creep'; the heat from the cylinder head or manifold is conducted along the studs to the threads and over an extended period of time at a high temperature, local Hertzian stresses cause the metal to flow so that the two threads become tightly intermeshed. When removing such nuts, it is not unknown for the stud to shear off To replace a sheared stud means drilling and tapping the cylinder head or manifold. This operation usually requires the removal ofthe engine from its location. When the engine is in a car, this is inconvenient for the owner, but if it is in a train or boat, the knock-on effects of downtime can be costly.

With the increasing use of turbochargers, which are also located close to the engines and use the hot exhaust gas, similar problems may also occur.

There is thus a need for a design of nut which will facilitate easy removal in these situations and preferably without the need for the use of a nut splitter, which can also damage the threads on the studs.

According to the invention, there is disclosed a split nut assembly comprising two half nuts and a circumferential retaining member characterised in that; i. said two half nuts are cut along a diameter in the plane of the bore of the nut and said two half nuts are arranged so that the diametrical faces are contiguous; ii. the thread through the bore of said two half nuts is continuous; and iii. said circumferential retaining member is a tight fit around said two half nuts retaining them in position so that said split nut assembly may be fitted to a threaded member and tightened.

According to a first variation of the invention, said circumferential retaining member is provided with a means to remove it from said two half nuts by pulling in the axial direction of said bore in said split nut assembly.

According to a second variation of the invention, said two half nuts are machined from half hexagonal bar and said two halves are assembled with said diametrical faces contiguous with each other and held together while the axial hole is bored and tapped.

According to a third variation of the invention, said circumferential retaining ring is fitted round said two half nuts prior to boring and tapping.

According to a fourth variation of the invention, said half nuts are provided with a shoulder on the end of said half nuts adjacent to the article to be secured by said split nut assembly and an interengaging washer.

According to a fifth variation of the invention, said shoulder has a conical circumferential edge and said interengaging washer is a conically sided blind hole in said article to be secured by said split nut assembly According to a sixth variation of the invention, said circumferential retaining member is fast with each of said two half nuts.

According to a seventh variation of the invention, the leading radial edges of each half nut are chamfered.

According to a eighth variation ofthe invention, a washer is interposed between said split nut assembly and the item being secured by said split nut assembly.

In a preferred design, the two half nuts are machined from half hexagonal bar so that they have a common diametrical face and are of a length to give appropriately sized blanks for the half nuts. The hexagonal circumferential retaining member is fitted round the two half nuts before placing in ajig with their diametrical faces in contact and held tightly together. The circumferential retaining member is a tight fit over the half nuts and is pressed into place. An hole is bored through the centre ofthe two half nuts, i.e. through a point lying on both diameters of the two half nuts and in the plane of the diametrical faces. The split nut is then tapped so that the screw threads in the two half nuts are continuous from one half nut to the other.

In one preferred arrangement, the circumferential retaining member is pressed from metal strip to give the form ofan hexagonal tube bent over at the top to form a rounded cap with an axial hole, to permit the threaded shaft onto which the split nut is screwed, to pass through. In this arrangement, the skirt of the retaining member may be shorter than the axial length ofthe bolt, so that a puller may be inserted and used to draw the retaining circumferential member axially off the split nut. In an alternative arrangement, hexagonally shaped tube is used.

In another preferred arrangement, the hexagonal circumferential retaining member is provided with an outwardly tacking circumferential lip to engage with the puller. In both the alternatives disclosed, the split nut may be fitted with conventional spanners and removed in the same way. If,however, the threads of the nut and stud, to which it is fitted, have become seized together, a puller may be used to remove the circumferential retaining member and thus allow the two half nuts to be removed from the threaded member using a smaller size conventional open-ended spanner.

It will be noted that the retaining member is a tight fit around the two half nuts, this is essential in order that the split nut is retained as a single unit when subject to the torque of tightening, etc. There are various levels of interference fit known and an appropriate one would be chosen to give the required mechanical properties. The retaining member itself would be of a material to give an adequate inwardly radial force for the retention of the half nuts in juxtaposition up to at least the required tightening torque.

In addition to the interference fit, the strength ofthe fit between the circumferential retaining member and half nuts can be increased by, for example, spot welding or peening. In the case of peening, small depressions may be drilled in opposite faces of the half nuts and the retaining member pressed into the depressions using a centre punch.

In use, the split nut assembly is fitted, e.g. to a stud, using a normal spanner and tightened to a given torque. To remove the nut, the same size spanner may be used to unscrew the whole assembly. However, the nut may be seized in position. In this case, a puller is used to draw the circumferential retaining member axially off the split nut.

To do this, the lip(s) of the puller are engaged underneath the edge of the retaining ring and the nut of the puller tightened axially onto the end of the stud. A new split nut is used for reassembly.

For a clearer understanding of the invention and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying Figures in which: Figure 1 is a plan view of two half nuts according to the invention; Figure 2 is a plan view of the two half nuts of Figure 1 assembled into a 'split nut'; Figure 3 is a sectional plan view along line AA of Figure 4 showing one design of circumferential retaining member to fit over the split nut of Figure 2; Figure 4 is a sectional elevation of the circumferential retaining member shown in Figure 3; Figure 5 is a side elevation of the half nuts shown in Figure 2; Figure 6 is a side elevation of another design of circumferential retaining member for the split nut of Figure 1;; Figure 7 shows the fitting of the circumferential retaining member in Figures 3 and 4 onto the split nut shown in Figure 2; Figure 8 is a sectional elevation ofthe split nut assembly fitted to a stud.

Figure 9 is a side elevation of a split nut assembly according to the invention with a conical shoulder and the mating blind hole.

Figure 10 is a side elevation of a split nut assembly according to the invention with a shoulder and a matching washer.

Figure 11 is a sectional plan view of an open-ended spanner fitting the circumferential retaining member.

Figure 12 is a side elevation of a circumferential retaining member with a removal groove.

In this specification the same reference numeral is used for the same component or different components fulfilling identical functions.

Referring to Figure 1, two half nuts 2, 3, are shown. These have been machined from half hexagonal bar. The centres of the half nuts are shown by the two crosses 4.

Figure 2 shows the two half nuts assembled into a 'split nut' 1. The two half nuts are manufactured by cutting off lengths from an hexagonal bar with diametrical faces 5, 6.

The two halves are then assembled so that the two diametrical faces 5 and 6 mate exactly, a circumferential retaining member is fitted and, with two halves held rigidly together, the centre hole 21 is drilled and tapped 7.

It is an important feature of the disclosure that the two half nuts 2, 3 are drilled and tapped as an entity so that the threads of the two half nuts 2, 3 will match to form a single continuous thread to fit a bolt or stud. It will be noted that this result cannot be achieved by taking two normal nuts and cutting them to give diametrical faces 5 and 6 as, when the two halves are assembled (Fig. 2) the threads would not align. Similarly, it is not possible to achieve the same results by taking a single nut and cutting along a diameter as this would leave a gap between the two faces 5 and 6 equal to the width of the saw blade.

In the Figures, a nut template has been used, but it will be appreciated that when such nuts are machined from solid half hexagonal bar, they may not look exactly like conventional machine made nuts (see Figs. 9 and 10). The template has been used to give a better representation ofthe nuts than might be possible without its use.

In order to hold the two half nuts fast together, a circumferential retaining member, shown as cap 10, is provided. Preferably, the cap is pressed and/or drawn from metal strip to give an hexagonal form of a diameter to be a press fit over split nut 1. As shown (Figs. 3 and 4), cap 10 consists of a parallel sided section 11 with a formed top 12. The curves 12A represent the effect of the forming and show how the inside of cap 10 will fit split nut 1.

Figure 7 shows the assembly of cap 10 over split nut 1 by pressing 22. There are various types of interference fit known in engineering and the method preferred here would be an adequate interference fit to give a sufficient inward radial retaining force to hold two half nuts 2 and 3 together against the torque applied when tightening the split nut onto a stud 23. The inward radial retaining compressive force is provided by the combination of the interference fit and the mechanical properties of the material of cap 10. A normal design level for the inward radial retaining force would be that required to resist one and a half times the reaction to the maximum torque to be applied to the split nut assembly.

Figure 8 shows in sectional view the assembled split nut 1 and cap 10 on a stud 23 set into the surface 20 of a member 24. The centre line of split nut 1 is shown as reference number 4A, passing through the centres 4 of each half nut 2, 3. The centre line 14A of cap 10 is also shown passing through centre 14 (Fig 3). As shown in Figures 7 and 8, the two centre lines 4A and 14A coincide when the split nut 1 and cap 10 are assembled. A hole 13 is provided in cap 10 to allow for the end of stud 23 to pass through when the split nut is tightened.

It is advantageous that the leading edges of each half nut 2,3 are chamfered 9 so that, when the split nut 1 is being torqued into position, the leading edges of each half nut do not cut into the surface 20 of cylinder head or manifold 24 or into the surface of a washer (not shown) between the two. If the leading edge is not so chamfered 9, the effect ofthe bolt cutting into surface 20 will be to strain cap 10 and result in an inadequate stress being applied to the threads 7. The trailing edges may also be chamfered (not shown), if required, but this is not essential.

When assembled the cap 10 may be secured to split nut 1. Various methods are possible, for example, peening 17 into holes 8, or spot welding, etc.

The dimensions of split nut 1 and cap 10 are chosen to fit the standard range of spanners available. In a typical example, if the size of split nut 1 fitted a particular size of spanner, a spanner one or two sizes larger would be required when cap 10 was fitted.

In a mass production environment, the raw material may be extruded bright metal half hexagonal bar, possibly with half of the bore also formed in position, having the required diametrical faces 5,6. Bright metal bar can be extruded to give the required dimensional accuracy but if this was not the case, the diametrical faces 5,6 would be milled accordingly. Two half hexagonal bars are assembled in a lathe with a feeding head and machined as a single unit; this would include drilling bore 21 if the bars were not provided with half holes. Cap 10 would then be pressed over the two half nuts 2,3 (Fig. 2) and the half nuts cut from the bars. The half nut assemblies would fall into a bin to be tapped subsequently.As a part of the manufacturing process, anti-corrosion treatments are applied, for example, caps 10 may be dipped in zinc to galvanise, in particular, the inner faces to facilitate subsequent removal 22 from half nut 1.

When it is required to remove split nut 1, the larger size of spanner may be fitted to see if the nut will release. If this is not the case, a puller (not shown) may be used to remove 22 cap 10. As shown in Figure 8, the height 15 of the parallel section 11 of cap 10 is less than the height of split nut 1. There is thus a gap 16 for the puller (not shown) to engage with edge 11A ofcap 10 and pull it off22. Once cap 10 has been removed, the smaller size of spanner may be used to turn split nut 2. It is recommended that an open-ended spanner is used as this will enable the two halves 2, 3 to separate from stud 23 more easily than if a ring or box spanner were to be used. A new cap 10 could be fitted if the existing half nuts 2, 3 were to be reused, but it is preferable to fit a complete new split nut and cap assembly.

The purpose of the disclosure is to remove the nut from stud 23 without damaging the stud itself so that, under most conditions, it would be expected that a new split nut and cap would be fitted. It should be noted that the split nuts 1 and caps 10 would be factory assembled units. The arrows 17 (Fig. 8) are shown only to indicate the peening of cap 10 into depressions 8 on nut 1; this would be a factory manufacturing operation and the presence of arrows 17 (Fig. 8) does not indicate that this process takes place after the nut and cap have been fitted to stud 23. Fig. 8 is the most convenient one to teach the use of this operation.

Figure 6 shows an alternative form of cap 18, in which the hexagonal upstand 11 is the same as in Figure 4, but the upper part has been pressed down to form a flange 19 for use with a puller (not shown).

The nuts of the disclosure would be manufactured from half hexagonal mild steel, high tensile steel, aluminium or any other suitable metal bar. Caps 10, 18 would be pressed or fabricated from mild steel strip, hexagonal tubing or an equivalent metal. The thickness of the tubing would be chosen to provide adequate radial compression on half nuts 2 and 3 during the torquing process and to fit a standard size of spanner.

Reference to Fig. 8 shows that the parallel sided section 11 of cap 10 does not extend to the bottom part 16 ofthe split nut 1 and so the circumferential retaining force will be less over this part of split nut 1. Provision of a conical edged shoulder, or spigot, 25 (Fig. 9) to mate in a conically-sided blind hole 26 in cylinder head or manifold 24 gives a radially inward force to overcome this problem. Fig. 10 shows another arrangement in which shoulder 27 does not have a conical edge; instead a mating washer 28 with a neatly-fitting 30 hole 29 is provided to give the radial retention. Washers 28 may be provided with conical holes 29 for use where blind conically-sided holes 26 are not provided.

Half nut 2,3 are shown of greater axial length in Figs. 9 and 10 than in the other Figures to indicate that this may be a design requirement in some applications.

The preferred method of removing seized split nut assemblies is by pulling off 22 the cap 10. In some applications, there may not be room to use a puller. An alternative means of removal is shown in Figs. 11 and 12 in which opposite faces of cap 10 are scored to provide weakening grooves 32. In use Fig 11, the tightening action 33 of spanner 31 acts on unscored parts of parallel section 11 and the forces adjacent to scores 32 are mainly tensional. The removing action applies forces 34 to the areas of scoring 32 generating a shearing action which propagates the scoring 32 through the metal of section 11 thus tearing cap 10 and allowing easy removal. In a typical example, the required tightening torque may be, say, 40 Nm and the design stress level based on 1.5 times this figure, i.e. 60 Nm. However, an unscrewing torque of 70 Nm would rupture the metal in way of groove 32 so that a torque of this level would tear the metal of retaining ring 11.

Claims

What I claim is:

1. A split nut assembly comprising two half nuts and a circumferential retaining member characterised in that; i. said two half nuts are cut along a diameter in the plane of the bore of the nut and said two half nuts are arranged so that the diametrical faces are contiguous; ii. the thread through the bore of said two half nuts is continuous; and iii. said circumferential retaining member is a tight fit around said two half nuts retaining them in position so that said split nut assembly may be fitted to a threaded member and tightened.

2. A split nut assembly, as claimed in claim 1, in which said circumferential retaining member is provided with means to remove it from said two half nuts by pulling in the axial direction of said bore of said split nut assembly.

3. A split nut assembly, as claimed in claim 2, wherein said means to remove it from said half nut is a circumferential edge.

4. A split nut assembly, as claimed in claim 2, wherein said means to remove it from said half nut is an outwardly facing circumferential lip.

5. A split nut assembly, as claimed in claims 2,3 or 4, in which the means of removing said circumferential retaining member is a puller.

6. A split nut assembly, as claimed in any preceding claim, wherein said two half nuts are machined from half hexagonal bar.

7. A split nut assembly, as claimed in claim 6, wherein said half hexagonal bar has a diametrical face.

9. A split nut assembly, as claimed in claim 7, wherein said half hexagonal bar has a half bore in said diametrical face.

10. A split nut assembly, as claimed in claim 9, wherein said two half nuts are held together with their machined diametrical faces in contact and bored and/or tapped as a single unit.

11. A split nut assembly, as claimed in claim 10, wherein said axis of said axial hole is coincident with said diametrical faces of each half nut and normal to the diameter of said half nuts.

12. A split nut assembly, as claimed in claim 11, wherein said circumferential retaining member is fitted prior to boring and/or tapping.

13. A split nut assembly, as claimed in claims 11 or 12, wherein said two half nuts are placed in a jig prior to drilling and/or tapping.

14. A split nut assembly, as claimed in any preceding claim, wherein a shoulder or spigot is provided on the ends of said two half nuts.

15. A split nut assembly, as claimed in claim 14, wherein a washer is provided to fit over said shoulder or spigot.

16. A split nut assembly, as claimed in claim 14, wherein the edge of said shoulder or spigot is conical.

17. A split nut assembly, as claimed in claim 16, wherein a conically-sided blind hole is provided on the article to be secured by said split nut assembly.

18. A split nut assembly, as claimed in any preceding claim, wherein said circumferential retaining member is fast with each of said two half nuts.

19. A split nut assembly, as claimed in claim 18, wherein said circumferential retaining member is peened onto each of said two half nuts.

20. A split nut assembly, as claimed in claim 18, wherein said circumferential retaining member is spot welded to each of said two half nuts.

21. A split nut assembly, as claimed in any preceding claim, wherein a groove is scored into a face of said circumferential retaining member.

22. A split nut assembly, as claimed in claim 21, wherein said groove is scored into the trailing edge of said face of said circumferential member so that the action of a spanner undoing said split nut assembly bears on said groove.

23. A split nut assembly, as claimed in any preceding claim, wherein the leading radial edges of each half nut are chamfered..

24. A split nut assembly, as claimed in any preceding claim, which may be fitted using standard sizes of spanners.

25. A split nut assembly, as claimed in any preceding claim, wherein said circumferential retaining member is an interference fit over said two half nuts so that the inwardly acting radial compressive force provided by the combination of said interference fit and the mechanical properties of the material of said circumferential retaining member is adequate to retain the integrity of said split nut assembly up to at least the maximum tightening torque to be applied when fitting said split nut assembly.

26. A method of fitting and removing a nut comprising:i. providing two half nuts with contiguous diametrical faces and a single continuous axial thread; it. providing a circumferential retaining member to locate and hold said two half nuts tightly together; in. fitting said circumferential retaining member around said two half nuts iv. fitting said split nut assembly to a stud or bolt; and v. removing said circumferential retaining member by pulling it axially off said two half nuts, so that said two half nuts may be removed from said stud or bolt.

27. A split nut assembly, as claimed in any preceding claim, as described in the text hereinbefore and with reference to the attached drawings.