GB2225833A - Shaft couplings - Google Patents

Abstract

A sleeve coupling for a pair of aligned drive shafts 1, 2 comprises an inner sleeve 4 and an outer sleeve 3, the abutting common surfaces of which are machined to a shallow taper so that relative axial movement of the sleeves causes radially inwardly directed forces to be applied to the ends of the drive shafts. At least the inner sleeve 4 of the sleeve coupling is made from grey cast iron, preferably a perlitic cast iron which is essentially ferrite free. <IMAGE>

Description

Improvements in and relating to shaft couplings This invention is concerned with the shaft couplings of the kind in which a pair of drive shafts are coupled end-to-end without bolts and/or flanges, using a metal sleeve which encloses the gap between the abutted ends of the shafts.

One such coupling is extremely well-known, having been in use for at least forty years. It comprises an outer sleeve and an inner sleeve, the latter being a sliding fit on the shafts. The outer surface of the inner sleeve and the abutting inner surface of the outer sleeve are accurately machined to a common, matching shallow taper, typically 1 in 30. The outer sleeve is recessed at one end to receive an annular nut engaged on a threaded end portion of the inner sleeve. This nut together with the adjacent regions of both sleeves and the recess together define an annular space which can be pressurised hydraulically to displace one sleeve relative to the other along the taper in a direction which causes the inner sleeve to contract radially onto the shafts, thereby locking them together in a friction grip.

The tapered conical interface between the sleeves is provided with at least one oilway through which oil is injected to facilitate relative movement of the sleeves with minimal jack-up force, as well as to enable essentially zero force reverse movement to free the coupling, should that be necessary for inspection/ maintenance purposes.

With this known type of coupling between the ends of shafts transmitting high mean and vibratory torques, any frettage can give rise to oil leaks which make removal of the coupling difficult if not impossible by normal means.

The resultant damage may even require the replacement of both shafts.

It is an object of this invention to provide an improved coupling of the kind just described, herein referred to lv generally as a "sleeve coupling".

According to this invention, at least the inner sleeve of a sleeve coupling is made from grey cast iron.

The cast iron is preferably a perlitic cast and more preferably, a perlitic cast iron which is essentially ferrite-free.

According to a further feature of the invention, a coupling comprising a grey perlitic cast iron inner sleeve portion is fitted essentially dry. "Dry" in this present context means oil/grease free; it achieves a higher coefficient of friction between the sleeves resulting in increased compression forces betwwen the inner sleeve onto the ends of the shafts to be joined by the coupling. This reduces the risk of frettage. Also, cast iron is a bearing material; it does not "scuff" when used in contact with steel, so that the lubrication requirement imperative with steel-to-steel contact is not neccessary.

A further advantage of the increased frictional grip achieved is that couplings may be made smaller and lighter for a given torque rating. This is particularly important where access to the shafting is limited.

Whilst the invention enables a sleeve coupling to be installed dry, it will be appreciated that removal for inspection/maintenance purposes must be carried out by injecting oil into the interface. It is therefore preferred to provide the outer sleeve with conventional oil injection ports towards each end of the coupling, with a further port intermediate said ends. Each port communicates with an annular groove or series of grooves in the inner surface of the sleeve to ensure accessibility of oil all round the interface.

However, for reasons which will shortly be discussed, it is also preferred to provide inflatable O-ring seals between the oil injection ports and the respective ends of the sleeves, so as to ensure that as far as possible, oil injected to remove the coupling travels along the interface and does not leak out axially of the coupling.

This feature is equally applicable to conventional, oil-fitted sleeve couplings and accordingly the invention includes a conventional, steel-to-steel contact, oil-fitted sleeve coupling provided with inflatable annular seals adjacent each end of the coupling to enclose/seal the oil-fitted interface.

A coupling with this feature has also certain safety advantages. Should there be seizure and/or frettage which causes severe oil leakage during an attempt to disassemble the coupling, oil can be injected through separate ports directly into the inflatable seals to pressurise the latter, whilst oil continues to be injected at the other ports to release the sleeve. In this way, it may be possible to separate a damaged coupling without inflicting further damage, e.g. by cutting it off.

In order that the invention be better understood, a preferred embodiment of it will now be described by way of example with reference to the accompanying drawing in which the sole figure is a side cross-section through a coupling in accordance with the invention.

In the figure, two drive shaft ends 1 and 2 respectively are shown as connected end to end by a sleeve coupling constituted by an outer sleeve 3 and an inner sleeve 4, the latter being of perlitic grey cast iron, substantially free from ferrite.

The interface between the two sleeves is a conical tapered surface 5, the degree of taper being 1 in 30. The small diameter end 6 of the inner sleeve 4 is screw-threaded to receive an annular nut 7, the inner bore of the outer sleeve 3 being recessed to define between the respective components an annular cylinder 8. A port 9 is provided in the sleeve 3 to enable hydraulic fluid to be injected into this cylinder 8, an annular seal 10 being provided in the base of the against the face of the nut 7 to minimise the risk of loss of fluid therefrom. Adjacent each end of the coupling, the outer sleeve 3 is provided with oil injection ports 15,16, a further oil injection port 17 being provided towards the centre of the coupling. Each port communicates with an annular groove machined into the inner surface of the outer sleeve 3, the grooves being numbered 21, 22, and 23 respectively.

It will be seen that these ports communicate directly with the interface 5 between the two sleeves. Oil dispersal is assisted by a number of small, subsidiary grooves (not shown) which extend between the main grooves. Axially outwardly of each of the ports 15, 16 there are inflatable O-ring seals 18, 19 respectively, contained in annular recesses machined into the inner surface of the outer sleeve 3. These seals are connected through moulded teats (not shown) to ports (also not shown) on the outer surface of the sleeve.

To install the coupling, the inner sleeve 4 is approximately centred over the ends of the shafts 1, 2.

The outer sleeve 3 is then slid onto the inner sleeve and the annular nut 7 is screwed down the threaded end 6 of the inner sleeve until it is firmly engaged inside the outer sleeve 3. Both sleeves and the shaft ends are thoroughly degreased before hand; the assembly is completely dry.

Hydraulic fluid is then applied to the chamber 8 through the port 9. The nut 7 and the outer sleeve 3 act as a piston and cylinder respectively; they slide axially with respect to one another, forcing the outer sleeve along the taper, (to the right in the drawing).

This causes radially-inwardly directed pressure to be applied to the inner sleeve portion 4 which contracts inwardly to grip the ends of the shafts 1, 2. The relative axial movement is monitored, until a prechosen axial movement has been achieved, corresponding to a target value of contraction/gripping force on the shaft ends.

The hydraulic pressure may then be removed, the coupling being locked in place by friction.

Removal of the coupling is effected by injecting oil under pressure into the ports 15, 16 and 17, the pressure being increased until the frictional forces are sufficiently reduced to enable the two sleeves to be slid apart. Should there be leakage for any reason, such as damage (from either or both ends of the sleeves) oil can be forced in to inflate the O-ring seals to temporarily seal th-e leak, whilst continuing to force in oil at the ports 15, 16 and 17, to separate the sleeves.

It will be appreciated that although the foregoing description is especially applicable to the preferred coupling in which at least the inner sleeve 4 is made of perlitic grey cast iron, the use of the inflatable O-ring seals with extra ports to enable the latter to be pressurised to reduce leakage is particularly useful in a conventional, all-steel, oil-fitted coupling.

Claims (10)

CLAIMS:

1. A sleeve coupling as hereinbefore defined wherein at least the inner sleeve is made from grey cast iron.

2. A sleeve coupling according to claim 1 wherein the cast iron is a perlitic cast iron.

3. A sleeve coupling according to claim 1 or claim 2 wherein the cast iron is essentially ferrite-free.

4. A sleeve coupling according to any preceding claim wherein the outer sleeve is provided with an annular oil seal adjacent each end thereof.

5. A sleeve coupling according to claim 4 wherein each of said seals is located in a recess provided with a port through which a pressurising fluid can be injected.

6. A method of installing the sleeve coupling of any preceding claim, including the step of degreasing the parts of said coupling prior to assembly on the abutting ends of shafts which are to be coupled together.

7. The method of claim 6 further including the step of degreasing said shaft ends.

8. The method of claim 6 or claim 7 wherein said sleeve coupling is installed dry, without lubrication.

9. A sleeve coupling as hereinbefore defined wherein an inflatable annular oil seal is provided between the sleeves of said coupling towards the respective ends thereof, each of said seals being housed in a recess provided with a port whereby fluid can be injected to pressurise said seal.

10. A sleeve coupling and method of installing the same subtantially as hereinbefore described and as illustrated by the accompanying drawing.