The present invention relates to an alarm system suitable for use with rollers and other rotary mechanisms having relatively rotatable parts with a bearing therebetween.

The invention relates particularly to a device which gives an indication that a bearing is overheating and thereby gives an early indication of possible bearing failure. When a bearing is contaminated by dirt or moisture and/or is rotated with insufficient lubricant or an excess or lubricant and/or is overloaded, the bearing temperature generally increases progressively until eventually it is well above the normal working temperature of the bearing. Such increases in temperature are generally a symptom of impending bearing collapse or seizure which may cause damage to other components in a machine. Furthermore as a bearing overheats it may reach a temperature whereby it ignites surrounding material and it is therefore highly desirable to obtain early warning of such problems.

Conventional monitoring of rollers bearings by maintenance personnel or by instrumentation has generally been found to be either impractical or prohibitively expensive.

It has previously been proposed (GB-A-2 155 678) to utilize a thermal release device which trips when the temperature exceeds a control temperature, and whose position is sensed by a sensing means which transmits a signal to a central monitoring unit. In this case though the thermal release device is mounted radially of the bearing. This presents considerable practical difficulties in relation to installation in many

situations such as in conveyor rollers and further substantial difficulties in relation to monitoring of the tripping of the device since the annular zone around the bearing and thermal release device is often obstructed in one way or another in such situations e.g. by the outer roller casing, conveyor belt supported thereby, bulk material carried on the belt etc. It is an object of the present invention to avoid or minimise one or more of the above disadvantages.

The present invention provides an alarm system suitable for use in warning of overheating in a rotatable bearing comprising first and second bearing portions, said alarm system comprising an alarm signal generator means having a thermally activated engagement element provided on a first bearing portion or on a body connected thereto so as to be in thermal connection with said bearing portion and formed and arranged so as to be driven upon reaching a predetermined elevated temperature from a first primed retracted position into a second deployed extended alarm position for contacting with an engaging portion provided on a second bearing portion or body connected thereto during relative rotation between said first and second bearing portions and formed and arranged so as to produce together therewith a distinctive alarm signal, indicating that said bearing has exceeded said predetermined temperature, when said engagement element is brought into contact therewith, wherein said engagement element is mounted for displacement between its retracted and extended positions, generally axially of the rotatable bearing.

Preferably at least one of said engagement element and engaging portion has an acoustic element formed and arranged at a substantially external portion of the bearing portions and any said bodies connected thereto

so as to transmit to the exterior of said bearing portions and any bodies connected thereto, upon contacting of the engaging portion by the engagement element, a substantial acoustic distinctive alarm signal.

Thus the engagement element is mounted for displacement between its retracted and extended positions in a direction which is generally parallel to the rotational axis of the bearing, conveniently more or less substantially offset from said rotational axis.

it will be appreciated that various forms of alarm signal generator means may be used in accordance with the present invention. Thus there may be used a signal generator means having an engaging portion in the form of one or more generally axially extending projections on said second bearing portion or body connected thereto which is (are) periodically struck by the deployed engagement element as the bearing portions rotate relative to one another, so as to generate a form of more or less audible "clicking" sound, at least one of the engagement element and the projection(s) preferably being resiliently deflectable so as to permit continued alarm signal generation over an extended period of time without damage to the parts.

In another alternative form of the invention there could be used an engaging portion in the form of an at least partially angularly extending surface for providing an extended period or periods of frictional interengage ent, said engagement element and engaging portion being formed and arranged so that said frictional interengagement directly generates an acoustic signal e.g. a screech.

As used herein the expression "acoustic element" indicates any element which upon contacting of the engaging portion by the engagement element is conducive to a greater or lesser extent to the conversion of the energy dissipated by said contacting into an acoustic signal. Thus, for example, in the case of a periodic striking contact the acoustic element could be in the form of a generally bell-shaped member with one or more axially extending projections constituting said engaging portion(s) .

Whilst the alarm system is preferably formed and arranged for direct generation of an acoustic alarm signal, there may be used instead sensor means for detecting the contacting of the engagement element and engaging portions by other means e.g. there may be used a piezoelectric sensor for detecting periodic striking contact, said sensor being formed and arranged for transmitting electrical signals generated therein to a suitable circuit for directly or indirectly driving a suitable audible and/or visual alarm device such as a warning bell, siren etc. and/or a flashing light. In general though alarm systems of the invention with direct acoustic alarm signal generation are preferred since these are on the one hand of simpler and more economical construction, and on the other hand are more reliable in operation and facilitate more or less ready localisation of an individual overheating bearing from amongst a group, without the need for extensive communication links to a central control system.

Thus with an alarm system of the present invention a distinctive alarm signal may be generated in a particularly simple, effective, and economic manner upon overheating of a bearing in use of the system so that said overheating bearing may be readily detected and

replaced thereby minimising the risk of fire etc. from continued overheating. Moreover by using a generally axially operating configuration of the alarm, the acoustic element may be more or less readily disposed at a substantially external portion of the rotary bearing installation thereby maximising transmission of the acoustic alarm signal to the surrounding area and thereby maximising the ease and speed of detection thereof. Nevertheless if desired additional audio transmission, modulation, amplification and/or relay means may be used in order, still further to enhance the attention - attracting guality of the acoustic alarm signal generated directly by said contact. A further significant advantage of the axially operating configuration and substantially external mounting it permits, is that this considerably facilitates the application of the present invention to existing rotary bearing installations i.e. so-called retro-fitting as will be further explained hereinbelow.

Thus in a further aspect the present invention provides an alarm signal generator means suitable for use in an alarm system of the invention, which alarm signal generator means comprises a thermally activated engagement element formed and arranged so as to be driven upon reaching a predetermined elevated temperature from a first primed retracted position into a second deployed extended alarm position, and having an engagement element support means formed and arranged for mounting of said element to said first bearing portion or body connected thereto in use of the signal generator means so that said engagement element is displaceable from its retracted to its extended position, generally axially of the rotatable bearing, and said support means therefor is restrained against displacement in the opposite direction, said alarm signal generator means

also including an engaging portion having an engaging portion support means formed and arranged for supporting said engaging portion on a said second bearing portion or body connected thereto in use of the signal generator means, for positive contacting by the engagement element in its extended position.

One especially useful application of the present invention is to the rollers of* belt conveyors, including both idler and driving rollers, particularly for use in potentially hazardous environs such as underground coal mines and the like. The alarm system of the present invention has many other applications, though, in rotary bearings in machinery used in the petrochemical industry, automobiles, elevators, lifts, machine tools, strips, docks, sugar and grain processing, manufacturing, printing, the gas industry etc.

It will be appreciated that various forms and methods of activating and driving said thermally activated engagement element may be employed. Thus for example a bi-metallic strip, a bi-metallic spring or other combinations of at least two elements of materials having different coefficients of expansion may be used as well as a memory metal, a memory strip or spring or other material having shape memory characteristics, may be used wherein the activation and the driving of said engagement element are integrated into a single component. In another form, the activation and the driving functions of said engagement element may be performed by separate means, for example the driving of the engagement element may be by a pre-stressed resilient biasing means e.g. an helical coil spring, which is retained in place by a low melting point alloy plug, wherein the melting point of said alloy plug corresponds to said predetermined elevated temperature.

so that when said plug melts it releases the resilient biasing means so as to drive said engagement member into a deployed alarm position.

The engagement element thermal activation means may be formed and arranged for activation at any suitable temperature, conveniently a temperature in the range from 60° to 130 ^β C, for example at a temperature of about 70°C.

By using a distinctive acoustic alarm signal, an overheating bearing may be more or less readily heard by any passing operative without the need for any special procedures thereby substantially simplifying and speeding up the monitoring of conveyor systems for overheating bearings and indeed substantially increasing the likelihood of detection by any passing operative including those engaged in other tasks. Nevertheless, if desired, there may also be provided suitable acoustic signal monitoring eguipment for activation of (conveniently remotely situated) suitable alarm means such as warning bells, sirens, klaxons etc. and/or warning lights such as flashing lamps, l.e.d.s etc.

It will be understood that bearings in normal use will cause a certain amount of background noise (which may be acoustic in nature and/or in the form of periodic mechanical strain) , however, in accordance with the present invention a failed bearing will produce a distinctive warning signal in a generally stepwise increment above any background noise and which thus may be readily detected.

It should also be understood that the present invention may be employed with any form of rotary bearing from integrally formed bearing means which simply comprise

complementary male and female cylindrical surface portions of two relatively rotating bodies such as a cylindrical shaft and a plain annular wheel or roller mounted directly thereon, to discrete rotary bearing systems formed and arranged for mounting between two bodies which are required to be relatively rotatable. Accordingly each of the alarm components may be mounted on a said body or on a respective discrete bearing component mounted thereto.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings in which:- Fig. 1 is a cross section through one end of a conveyor idler roller showing a first embodiment of the bearing alarm system of the invention;

Fig. 1A is a detail view of the thermally actuated ngagement element of Fig. 1 and part of its mounting, on an enlarged scale;

Fig. 2 is an end elevation of the roller of Fig. 1; and Fig. 3 is a view similar to Fig. 1 of a conveyor drum with a second embodiment of the invention.

Fig. 1 shows a rotary mechanism in the form of a driveless idler roller generally indicated by reference number 1 such as is used to support the moving belt (not shown) of a belt conveyor. The roller 1 comprises a tubular member 2 having a stepped annular end support 3 rotatably mounted via rotary bearings 4 on a fixed shaft 5. At an axially and radially outer portion 7 of the support 3 is mounted a thermally activated engagement element 8 in the form of a pin having a short generally cylindrical body 8a with an elongate spindle 8b at one end 8c and a generally hemispherical head portion 8d at

its other end 8e which end portion 8d is disposed outwardly of a tubular casing 8f_. Axially inwardly of the hemispherical head portion 8d is the cylindrical body 8a which is separated from the head portion 8d by an annular groove 8h so as to form a shoulder 8i. on said cylindrical body 8a for engagement with a lip 8j at the mouth of said casing 8f so as to yieldably retain the cylindrical portion 83 within said casing 8f_ in the primed condition of the element 8. The engagement element 8 is mounted so as to be in relatively good thermal connection with the bearing 4 through the support 3. In more detail it may be seen that the element 8 is secured with the end of a unit 8k in a small metal cup 7a which is a push fit inside an aperture 7b in the axially outer portion 7 of the support 3.

Immediately axially outwardly of the bearing 4 is mounted an annular seal 9 of a suitable natural or synthetic polymer (e.g-. a rubber or polyalkene) for protecting the bearing 4 against the ingress of contaminants. Axially beyond the seal 9 is mounted on the shaft 5 an acoustic element in the form of an annular, partly dished or belled, plate 10 which has an axially inwardly extending dimple projection 11.

Under the normal operating conditions of the roller 1, the engagement element 8 is retained in its primed retracted position with the cylindrical portion 8g inside the casing 8f_.The spindle 8b of the pin 8 has disposed concentrically therearound a memory coil spring 16 having one end 16a engaging the base 81_ of the casing 8f_, and its other end 16b against said one end 8c of the pin body 8a. Should the bearing 4 start to fail heat is generated which is transferred through the support 3 to the cup 7a and thence to the engagement element 8

mounted inside it. The memory spring 16 is formed and arranged so as to extend to its original size when an elevated temperature indicative of likely bearing failure and/or a likely fire hazard in the immediate environment, is reached. As the spring 16 extends and drives the engagement element cylindrical body shoulder 8i against the lig 82 of the casing 8f splaying it open and pushing the element head portion 8d out of the cup 7a into contact with the protrusion 12, to strike it once each revolution thereby causing a distinct acoustic signal which may be readily heard by any operating personnel in the vicinity. As may be seen in Fig. 1, the cup 7a has an outwardly turned lip 7c which engages the support portion 7 around the aperture 7b at its axially outer side 7d thereby to restrain the cup 7a against being forced through the aperture 7b when the head 8 of the engagement element 8 strikes the dimple projection 11 on the acoustic plate 10.

It will be appreciated that the somewhat bell-shaped form of the acoustic plate helps to maximise the amplitude of the sound generated by the striking thereof with the engagement element head portion 8d. Furthermore the position of the acoustic plate 10 at the axially outer end 5a of the shaft 5 and outside the enclosed interior of the roller 1 helps to avoid loss of the sound through its being muffled inside the roller and any belt supported thereby in use of the roller, and thus helps to maximise the sound transmitted to the surrounding area and hence the ease and speed of detection of an alarm condition by any passing personnel.

Fig. 3 shows a generally similar form of the alarm system of the invention applied to a return roller or drum 20 for an endless conveyor belt installation and like parts corresponding to those in Figs. 1 and 2 are

indicated by like reference numbers. It will be noted that in this case the support 3 between the tubular member 2 of the drum 20 and the radially outer bearing portion 4a, has secured thereto a sealing collar 21 for mounting of flexible annular seals 9 around the shaft 5 so as to prevent ingress of foreign matter to the bearing 4. The sealing collar 21 is secured to the support 3 by means of a plurality of bolts 22 one of which is conveniently replaced by a thermally actuated element 8 whose head is driven axially outwardly towards an acoustic plate 10 (not dished in this case) upon thermal actuation for periodic contacting with an opposed boss projection 11.

Fig. 4 is a detail sectional view corresponding to that of Fig. 1A of another form of thermally activated. element in which like parts corresponding generally to those of Fig. 1A are indicated by like reference indicia. In this case the outside face 7c of the cup member 7a has a plurality of frusto-conical ring formations 7d forming a serrated surface which facilitates force fitting of the cup 7a in the aperture 7b in the end support 3 of the roller 1 whilst resisting withdrawal therefrom. The distal end 8m of the elongate spindle 8b has an annular groove 8n which is engaged by a retaining circlip 8o which abuts one end 23 of an annular spacer 24 whose other end 25 abuts the outside 7e of the cup base 7f_, which has a central aperture 7g through which extends the pin spindle 8b. A compression spring 26 is disposed around the pin spindle 8b for acting between the one end 8c of the main body 8a of the pin and the base 7f_ of the cup 7a, so as to tend to urge the head 8c of the main pin body 8a outwardly of the cup 7a.

The annular spacer 24 is made,of a low melting point (e.g. 80°C) alloy so that when the bearing overheats the spacer 24 melts and is displaced from between the refraining circlip 8o and the cup base 7f allowing the former to approach the latter as the pin body 8a is driven away from the cup base 7f by the expanding compression spring 26.

It will of course be appreciated that various different forms of thermally activated engagement element may also be used in the various embodiments. Moreover in the case of critical and/or larger components especially such as an end drum for a conveyor run, two or more engagement elements formed and arranged for activation at different, progressively higher, temperatures may be employed in order to signal different levels of overheating e.g. corresponding to early warning and imminent danger conditions.

As indicated above, the thermally activated engagement element may be provided at or on either a fixed or moving bearing portion, the engaging portion being mounted at or on the other bearing portion i.e. the moving or fixed bearing portion, respectively. Figs 5 and 6 show a pedestal bearing provided with an overheat system of the present invention.

In more detail Fig.5. shows a drum 27 fixedly mounted on a. shaft 28 which is rotatably supported via pedestal bearings 29 (only one shown) . Also fixedly mounted on the shaft 28 externally of the drum 27, is an annular acoustic plate 30 constituting an engagement portion of the alarm system. The main fixed body 31 of the pedestal bearing 29 has fixedly mounted therein an elongate thermally activated engagement element 32 (somewhat similar to that of Fig.4) which projects

axially outwardly of the pedestal bearing body 31 towards the acoustic plate 30. The engagement element 32 is formed and arranged to be supported clear of the plate in its primed retracted position and then to engage with a with a dimple projection 11 on the plate 30 in the tripped deployed condition of the engagement element 32.