GB2041139A

GB2041139A - Locking of nuts

Info

Publication number: GB2041139A
Application number: GB8003778A
Authority: GB
Original assignee: HALILOVOC E
Current assignee: HALILOVOC E
Priority date: 1979-02-07
Filing date: 1980-02-05
Publication date: 1980-09-03
Also published as: ATA59080A; BR8000773A; FR2448655A1; SE8000968L; RO85066A; AT367876B; DD149106A5; YU41612B; PL221871A1; YU27279A; DE3004021A1; JPS55109816A; IT8067177A0; NL8000703A

Abstract

An assembly of a nut 1 and a ring 2 having a tapering hole therethrough. The nut has a tapered, e.g. hemi-spherical, portion extending within the ring 2. Preferably, the nut has a longitudinal slot. The preferred embodiment as illustrated produces self-tightening of the nut 1 about a bolt since the ring 2 bears on the nut to contract it radially. Also, the nut 1 is able to rock slightly in ring 2 to compensate for misalignment of nut axis and bolt axis as a result e.g. of manufacturing errors. <IMAGE>

Description

SPECIFICATION Nut assemblies The present invention relates to nut assemblies.

The problem of maintaining bolted joints in a tightened condition is of concern in many machines, especially in those where high dynamic forces occur. The problem particularly appears in vibrators, where strong alternating forces tend to reduce the friction between the inner and the outer threaded portions, thereby loosening the connection. Consequently, the connection may unscrew or its elements may break owing to damage occuring in the loose connection. As a result, the operation of the machine as a whole may be severely affected and it may even break down completely. In many cases a tightened connection is additionally loaded with forces resulting from geometrical errors in the contact surfaces of the fastening elements.For example, a small deviation from a right angle between the thread axis and the contact surface of the nut can cause higher stresses in the materials of the threaded elements than the tightening process itself produces normally. Hence quite small additional dynamic forces may suffice to cause overstressing of the material or even fracture of the elements, Known locking elements of screw fastenings, e.g. spring lock washers of various shapes, safety tab washers, cotter pins, friction elements in the nut, self-locking frictional threads, the use of check nuts and check screws, are insufficient for machines operating with large impact forces and vibrations. In such cases, the fastenings have previously been reinforced or the elements locked several times.On the other hand, by such solutions the dimensions of the fastening increase, the assembly and disassembly becomes more complicated (which is important e.g. at quickrelease couplings and anchors) and the complete fastening assembly becomes relatively expensive.

According to the invention, there is provided a screw-threaded nut assembly comprising: a nut member having a through-going screw-threaded hole; and a ring member having a tapering through-going hole, the nut member being tapered adjacent one end of the screw-threaded hole to fit within the tapering hole and to abut the wall thereof.

Preferably, a portion of the nut member adjacent the other end of the screw-threaded hole protrudes from the ring member.

Preferably, said portion is shaped for engagement by a wrench.

Said portion may be at least partially included in the tapered part of the nut.

Preferably, said tapering through-going hole is frusto-conical.

Preferably, the tapered part of the nut member is of rounded shape.

Preferably, said rounded shape is part of a spherical surface.

Preferably, a line of contact between the nut member and the ring member makes an angle a with planes perpendicular to the axis of the nut member, a being in the range of from 20 to 25 , with the nut member and ring member coaxial.

Preferably, the wall of said screw-threaded hole is slotted longitudinally.

Preferably, said wall of said screw-threaded hole is slotted for the entire length of said nut member.

The axis of the slot preferably extends parallel to the axis of said screw-threaded hole.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 shows a longitudinal sectional view of a screw-threaded nut; Figure 2 is a plan view of the nut of Fig. 1; Figure 3 is a longitudinal sectional view of a support ring; and Figure 4 is a longitudinal sectional view of the nut and ring member assembled together.

The figures show a self-locking and selfaligning lock nut assembly.

Fig. 1 shows an axial sectional view of a nut 1 and Fig. 2 shows a plan view thereof in the direction A of Fig. 1.

The nut 1 is provided with a longitudinal slot 1 a, a hemispherical part 1 b and a hexagonal head 1c for engagement by a wrench.

The hemispherical part 1 b has a radius R, and through the centre of curvature there passes a plane x-x, which is perpendicular to the axis of the thread of the nut 1 and delimits the hemispherical part I b of the nut.

Fig. 3 shows an axial section of a support ring 2, which has a funnel-shaped recess 2a.

Fig. 4 shows the nut 1 and the support ring 2 as a functional assembly. It is evident therefrom that the hemispherical part 1 b extends slightly from the ring 2. An important constructional feature of this fastening is that angle a between the plane x-x and the radius R of the hemispherical part 1 b of the nut when the radius passes through a point of contact between the nut 1 and the supporting ring 2 and both elements are coaxial. This angle is preferably in the range of from 20 to 25'.

The axis of the nut 1 and the axis of the ring 2 need not be coaxial. As a result the effect of geometrical errors in the elements upon the stresses in the materials of the fastening when tightened is reduced. The following example will show the grave consequences which result if compensation for such errors is not effected. An M20 bolt having a length to the nut of 40mm with a geometrical error between the supporting areas of only 0.5' is to be tightened. At tightening, a torsional stress of about 80 kp/cm2 will be caused in the bolt owing to said error. Thus, great stresses result from a "small" geometrical error, i.e. if the supporting surface of the nut with respect to the supporting plane of the nut is only inclined by 0.5".

To the above-mentioned torsional stresses caused by geometrical deviations there have to be added tensile stresses which result from the normal tightening force. Normally used engineering materials cannot withstand all these stresses.

At greater geometrical deviations, which are possible in practice, the consequences are even more serious.

The relative self-alignment between the nut 1 and supporting ring 2 as proposed by the illustrated self-locking and self-aligning nut lock reduces deficiencies which can result from geometrical errors in the elements of the bolt connection.

The self-locking feature of the illustrated nut assembly results from its constructional, geometrical and mechanical characteristics.

At tightening the nut 1 is resiliently contracted by narrowing of its slot as a result of penetrating into the funnel-shaped recess of the supporting ring 2, thereby tightening the thread and increasing the friction at all contact surfaces by elastic deformation therein. The elastically deformed material zones, which occur in the areas between the supporting ring 2 and the nut 1 as well as between the threads of the nut 1 and of the bolt, maintain the bolt connection under strong impacts and vibrations, whereby self-locking of the bolt connection is achieved.

The above-mentioned advantages of the self-locking and self-aligning lock nut, the simplicity and the low price of its manufacture and application make possible a wide technical application thereof.

It will be apparent that the self-locking feature is dependent upon the tapering fit between the nut 1 and the ring 2 and upon the ability of nut 1 to contract radially to grip the bolt, e.g. by the provision of the slot 1 a.

It does not, for example, depend upon the fact that the nut is of rounded, e.g.

hemispherical, shape at one end thereof.

Thus, both the tapered surface of the nut 1 could be frusto-conical in the same manner as ring 2 to achieve self-locking. On the other hand, the feature of compensation for misal ignment of contact surfaces is dependent upon the rounded shape of the nut 1 which allows a certain amount of rocking motion of the nut 1 to occur by slight rotation of the nut 1 relative to ring 2. Thus, the presence of slot 1 a is not essential for such compensation to take place.

Claims

1. A screw-threaded nut assembly comprising: a nut member having a through going screw-threaded hole; and a ring member having a tapering through-going hole, the nut member being tapered adjacent one end of the screw-threaded hole to fit within the tapering hole and to abut the wall thereof.

2. An assembly according to claim 1 wherein a portion of the nut member adjacent the other end of the screw-threaded hole protrudes from the ring member.

3. An assembly according to claim 2 wherein said portion is shaped for engagement by a wrench.

4. An assembly according to claim 2 or 3 wherein said portion is at least partially included in the tapered part of the nut.

5. An assembly according to any one of the preceding claims wherein said tapering through-going hole is frusto-conical.

6. An assembly according to any one of the preceding claims wherein the tapered part of the nut member is of rounded shape.

7. An assembly according to claim 6 wherein said rounded shape is part of a spherical surface.

8. An assembly according to claim 7 wherein a line passing through the centre of curvature of said spherical surface and intersecting a line of contact between the nut member and the ring member makes an angle a with planes perpendicular to the axis of the nut member, a being in the range of from 20 to 25 , with the nut member and ring member coaxial.

9. An assembly according to any one of the preceding claims wherein the wall of said screw-threaded hole is slotted longitudinally.

10. An assembly according to claim 9 wherein said wall of said screw-threaded hole is slotted for the entire length of said nut member.

11. An assembly according to claim 9 or 10 wherein the axis of the slot extends parallel to the axis of said screw-threaded hole.

1 2. A nut assembly substantially as hereinbefore described with reference to the accompanying drawing.

1 3. A self-locking and self-aligning nut assembly comprising: an axially slotted nut; and a support ring having a funnel-shaped recess, in which rests a hemispherical part of the nut, which part extends slightly from the funnel-shaped recess and is integral with a head for a wrench.

14. An assembly according to claim 13, wherein the hemispherical part of the nut is supported by the funnel-shaped recess in such a way that the angle (a) between the plane which is perpendicular to the nut axis and passes through the centre of curvature of the hemispherical part, and the radius where it passes through a point of contact between the nut and the ring amounts to between 20 and 25 , with the nut and ring coaxial.

1 5. First and second parts joined together by a nut assembly according to any one of the preceding claims in combination with a screwthreaded bolt.