GB2093148A - Toothed rotary drive- transmitting members with replaceable teeth - Google Patents

Abstract

In a toothed rotary drive- transmitting member such as a sprocket for a chain conveyor, the teeth 14 are removably mounted on the body 10 of the drive member either individually or in groups in such a manner that when the drive member is entrained by a chain or the like the individual teeth or a group of teeth may be removed from the body without disengaging the chain from the drive member. <IMAGE>

Description

SPECIFICATION Toothed rotary drive-transmifting members with replaceable teeth This invention relates to toothed rotary drivetransmitting members, for example drive sprockets for chain conveyors and other types of drive transmitting sprockets.

Hitherto, in overhead chain conveyors as used in for example motor manufacturing plants, renewal of worn drive sprockets has been an expensive and labour intensive procedure resulting in the conveyor being out of service for a considerable period of time and scrapping of the worn sprockets.

The object of the present invention is to provide an improved form of toothed rotary drivetransmitting member which, especially in the case of overhead conveyor systems, significantly reduces costs and maintenance time.

According to the present invention I provide a toothed rotary drive-transmitting member comprising a body on which the teeth are provided characterised in that at least some of the teeth are removably fastened to said body so as to enable them to be replaced either individually or in groups.

In the following, the invention will be discussed in terms of sprockets; however, it is to be understood that the invention is applicable to other forms of toothed rotary drive members such as spur gears for example.

Conveniently said removable teeth or groups of teeth are fastened to said body by fastening elements in such a way that radial and tangential forces acting on the teeth are transmitted to the body via said fastening elements rather than by direct contact between those parts which carry the teeth and the body. Such an arrangement eliminates the need for close tolerance fitting between the parts which carry the teeth and the body and also affords the possibility of introducing a torque-limiting facility by designing the fastening elements so as to prevent overloading.

Preferably each tooth or group of teeth is provided on a base which is adapted to interengage with the body of the sprocket. For example, each base may be formed with a groove or channel into which the peripheral edge of the sprocket engages so that the base straddles said peripheral edge in the manner of a saddle.

Alternatively, the peripheral edge of the sprocket body may be formed with a groove or channel into which a projection or tongue on each base projects.

The periphery of said body may be polygonal and those surfaces of the bases which confront the edges of the sprocket body may be generally planar. However, where the fastening elements are arranged to transmit the loading as aforesaid, the peripheral shape of the sprocket body is not critical and it may be for example circular in which case the confronting surfaces of said bases may be planar or curved so as to conform generally with the periphery of the sprocket body.

As well as the teeth per se being replaceable, it is envisaged in some applications that the parts which bound the intertooth gaps may be replaceable independently of the teeth. This is particularly advantageous for conveyor chain drives where the rate of wear of the toothed areas may differ from that of the intertoothed areas.

As mentioned above, in some instances it may be desirable for each tooth to be replaceable as an individual unit (possibly in conjunction with at least part of the circumferentially adjacent nontoothed areas). In other cases, the teeth are conveniently divided into groups each carried on a segment so that when the segments are assembled to the sprocket body they collectively provide a continuous set of teeth around the sprocket The circumferential extent of each segment or base is such that, when used in conjunction with a chain or the like which entrains part of the sprocket periphery (e.g. 1800 of the periphery) at least one segment can be removed without disengaging the chain or the like from the sprocket.

In a typical embodiment of transmission sprocket, there may be four such segments identical with one another and each carrying the same number of teeth; however, it is not essential for each segment to carry the same number of teeth or to be identical to the others. The important requirements to be satisfied are that when assembled to the sprocket body, the teeth are evenly spaced and sized around the entire circumference of the sprocket and are readily removable without disengaging the component driving or drive by the sprocket.To promote further understanding of the invention, several embodiments will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a fragmentary view of a conveyor chain drive sprocket; Figure 2 is a cross sectional view taken in the direction 2-2 in Figure 1; Figure 3 is a cross sectional view taken in the direction 3-3 in Figure 1; Figure 4 is a diagrammatic perspective view of a transmission sprocket with only one tooth carrying segment shown; Figure 5 is an enlarged view showing the shape of the segment in Figure 4; Figures 6 and 7 are similar views to those of Figures 4 and 5 but of a different embodiment; Figure 8 is a side view of another form of transmission sprocket shown partly in axial.

section; and Figure 9 is a front view of the sprocket of Figure 8 partly sectioned on the line 9-9 in Figure 8 and being shown with one of the segments omitted.

As shown, a drive sprocket for an overhead endless conveyor chain of the well known 458 type comprises a body in the form of a plate 10 of annular form which in use is mounted on a hub (not shown) and whose outer periphery is of regular polygonal configuration. On alternate edges of its polygonal periphery, the plate 10 carries a set of saddle-shaped bases 12 provided with teeth 14 and flanges 1 6 which support the more widely spaced pairs of links of the 458 chain on each side of the teeth 14. Between each pair of adjacent tooth carrying bases 12, the plate 10 carries a plain untoothed saddle-shaped base 1 8 which supports the less widely spaced pairs of links of the 458 chain.In transverse section, each base 12, 1 8 is substantially symmetrically shaped with respect to a medial plane through the plate 10 so as to distribute load uniformly about the sprocket.

Each base 12,18 is fastened to the plate 10 by a pair of nut and bolt fasteners 20 engaging in aligned apertures in the plate 10 and the limbs 22 of the saddles, the arrangement being such that the underside of each saddle is spaced from the associated polygonal edge of the plate by a gap 24. In this manner, the tangential and radial loading exerted by the chain (not shown) is transmitted to the plate 10 via the nut and bolt fasteners 20 rather than by contact between the periphery of the plate and the underside of the saddles. Such an arrangement avoids the need for accurate matching of the bases 12, 1 8 to the plate 10.Further the fact that the loading is transmitted via the fasteners enables the fasteners to be designed so as to prevent overloading, e.g. by arranging for them to shear in the event of the loading exceeding a preselected value. Thus for instance the bolts may be formed with reduced section necks so as to shear at those points in the event of an overload.

In use, the 458 chain will span substantially 1 800 of the periphery of the sprockets so that a number of the teeth of the sprocket are completely disengaged from the chain. Thus, when a tooth breaks or becomes worn, the associated saddleshaped base can be renewed together with the tooth simply by incrementing the chain and sprocket until that base is freed from the chain thus allowing its removal by releasing the bolts and nuts 20 and repiacement by a fresh toothed saddle-shaped base 12.Likewise the untoothed bases may be renewed in similar fashion. in this manner, maintenance of the chain is greatly simplified and the conveyor need only be out of service for a relatively short interval of time compared with conventional sprocket drives where, in the past, the sprocket as a whole has been renewed necessitating breaking the chain to allow its removal. As well as being a time consuming task, replacement of the entire sprocket is obviously much more costly than replacing individual teeth thereof.

Referring now to Figures 4 and 5, the embodiments shown comprises a transmission sprocket having a disc 40 rotatably fast with a hub 42 and provided with removable segments 44 carrying a set of teeth. In Figure 4, only one such segment 44 is shown but it will be understood that in practice a further three segments will be assembled to the disc 40 so as to provide a continuous set of teeth. In this embodiment, each segment 44 is formed with a groove at its internal periphery so as to enable it to seat on the edge of the disc 40 and pins 46 or other fasteners are inserted into registering holes in the segment 44 and the disc 40 so as to locate each segment.

Figures 6 and 7 show an alternative form of transmission sprocket in which the disc 50 is mounted on a hub 52 and is formed at its outer periphery with a continuous groove for reception of a tongue provided on the internal periphery of each segment 54. Again, pins 56 or like fasteners are used to locate the segments 54 on the disc 50, the pins 56 being inserted into registering holes 58 in the disc and in the tongue provided on each segment.

Referring now to Figures 8 and 9 this form of transmission sprocket comprises a generally tubular body 70 formed with a keyway slot 84 to enable it to be mounted for rotation with a shaft.

The teeth are provided on segments 72 which are removably mounted on the body 10. In this embodiment, instead of providing the body of the sprocket with a groove of circular configuration, the groove is of non-circular configuration, in the form of a square as illustrated. The square configuration may be achieved by milling slots into the outer periphery of the body 70.

Each segment 72 is provided at its inner periphery with tongues 76 for engagement in the slots formed in the body 70 so as to contact the square portion at the corner thereof. At the opposite ends of the segment, the tongues 76 are formed with part circular recesses which, when the segment is assembled to the non-circular portion of the body 70 register with axial holes drilled into the body. These holes are conveniently tapped for reception of bolts 80 in the manner shown in Figure 8 so that each bolt 80, in effect, engages in the part circular recesses 77 in adjacent segments. This arrangement facilitates removal of the segments for the purposes of renewal; in particular, it will be understood that all four segments can be renewed simply by removing only two of the bolts.

Claims (10)

1. A toothed rotary drive-transmitting member comprising a body on which the teeth are provided characterised in that at least some of the teeth are removably fastened to said body so as to enable them to be repiaced either individually or in groups.

2. A drive-transmitting member as claimed in Claim 1 in which said removable teeth or groups of teeth are fastened to said body by fastening elements in such a way that radial and tangential forces acting on the teeth are transmitted to the body via said fastening elements rather than by direct contact between the teeth and the body.

3. A drive-transmitting member as claimed in Claim 2 in which the fastening elements are adapted to shear in response to the application of torque exceeding a preselected value.

4. A drive-transmitting member as claimed in any one of Claims 1 to 3 in which each tooth or group of teeth is provided on a base which is adapted to interengage with said body.

5. A drive-transmitting member as claimed in Claim 4 in which the periphery of said body is polygonal and those surfaces of the base which confront the edges of the body are generally planar.

6. A drive-transmitting member as claimed in any one of Claims 1 to 5 in which the parts which bound the intertooth gaps are replaceable independently of the teeth.

7. A drive-transmitting member as claimed in any one of Claims 1 to 6 in which the teeth are divided into groups each carried on a segment so that when the segments are assembled to said body they collectively provide a continuous set of teeth around the body.

8. A drive-transmitting member as claimed in any one of Claims 1 to 7 in which the circumferential extent of each part carrying a tooth or group of teeth is such that, when used in conjunction with a chain or the like which entrains part of the periphery of the body, at least such part can be removed without disengaging the chain or the like from the body.

9. A drive-transmitting member as claimed in any one of Claims 1 to 8 in which said body includes a non-circular portion and in which those parts which carry the teeth or groups of teeth include surfaces which conform generally to said non-circular portion of the body.

10. A drive-transmitting member as claimed in Claim 9 in which said non-circular portion of the body is of square configuration.

1 A toothed rotary drive-transmitting member substantially as hereinbefore described with reference to, and as shown in, any of the embodiments illustrated in the accompanying drawings.