METHOD OF MAKING MULTI-CHAIN SPROCKETS

Abstract: A multi-chain sprocket is manufactured by moulding a central hub (10) from a powder of a metal or metal alloy, and moulding a plurality of sprocket rings (11) from a powder of the same or a different metal or metal alloy. The moulded sprocket rings (11) are mounted on the hub (10) in required locations, then the rings are bonded to the hub (preferably by sintering). The product multi-chain sprocket is usually hardened or steam treated before the bore of the hub and the location face of the sprocket are finish ground.

Description: - 1 - Title; "METHOD OF MAKING MULTI-CHAIN SPROCKETS" Technical field This invention concerns multi-chain sprockets. More particularly, it concerns a method of making multi-chain sprockets using moulded components which are bonded together to form the multi-chain sprocket,. Background Art The conventional method of manufacturing multi-chain " sprockets involves fully machining the sprockets from metal bar stock, or partially machining a blank formed by a pressure moulding process. When bar stock has to be machined, the steps involved are as follows: (a) the bar is turned on a lathe until its diameter is the maximum diameter of the sprocket; (b) the turned bar is bored, and then faced off to the required length (thickness) of the sprocket; (c) the keyway is then broached; (d) the individual sprocket teeth are machined into the blank, using a process that is similar to gear cutting; (e) the groove (or grooves) required to separate the sets of sprocket teeth is (are) then cut; (f) the workpiece is then hardened; and (g) finally, the bore and the location face of- the multi-chain sprocket are ground. If the multi-chain sprocket is formed by the pressure moulding technique, the required steps are as follows: (a) the sprocket wheel is pressed from a metal or metal alloy powder as a single-sprocket arrangement, with the sprocket form on the outside and the keyway in the bore; (b) the pressure moulded single sprocket is sintered (usually at a temperature of about 1120 C in a protective atmosphere); (c) the groove (or grooves) is (are) machined into the sprocket form; (d) the workpiece is then hardened; and (e) the bore and location face of the multi-chain sprocket are ground. Whichever of these manufacturing processes is adopted, there is considerable machining of the workpiece. The multiple machining operations represent a significant proportion of the total cost of the product. It has been recognised for a long time that a reduction of the number of machining steps, and a consequential reduction in the manufacturing costs, is most desirable. Disclosure of the present invention It is an object of the present invention to produce multi-chain sprockets without the current number of machining steps. This objective is achieved by moulding a hub and a series of sprocket "rings" from a metal powder or a metal alloy powder, then mounting the rings on the hub and bonding them to the hub in their required positions. Normally the assembled multi-chain sprocket will then be hardened or steam treated and its bore and location face will be finish ground. Thus, according to the present invention, there is provided a method of manufacturing a multi-chain sprocket comprising the steps of: (a) pressure moulding a cylindrical hub from a powder of a metal or a metal alloy; (b) pressure moulding a plurality of sprocket rings from the same or from a different powder of a metal or metal alloy, each sprocket ring having an internal bore such that the sprocket ring is a precise fit on the hub; (c) mounting the sprocket rings on the hub in required locations; and (d) bonding the sprocket rings to the hub. Any suitable bonding technique may be used for step (d). The bonding is preferably effected by sintering the components so that there is a diffusion of the elements in the sprocket rings into the hub material and vice versa. The metal or metal alloy powder from .which the multi-chain sprocket is formed may be any suitable metal or metal alloy powder. Preferably the hub is pressure moulded from a copper-iron powder and the sprocket rings are formed from a powder of a nickel alloy steel. After manufacture in accordance with the above-noted steps, the multi-chain sprocket will normally be hardened - by known techniques - or steam treated to increase the density and wear resistance of the sprocket rings. The final step in its manufacture will usually be a finish grinding of the bore of the hub and the location face. The present invention also encompasses a multi-chain sprocket manufactured by the technique outlined above. By way of example, embodiments of the present invention will now be described with reference to the accompanying drawings. Brief description of the drawings Figure 1 is an exploded perspective sketch of the moulded components of a multi-chain sprocket having two rings of sprocket teeth. Figure 2 is a transverse sectional view of a 3-piece multi-chain sprocket constructed in accordance with the present invention. Figures 3, 4, 5 and 6 are transverse sectional views of alternative multi-chain sprocket constructions. Detailed description of the illustrated embodiments As shown in Figure 1, a multi-chain sprocket consists of a hub member 10 on to which a plurality of sprocket "rings" 11 are mounted. Two sprocket rings are included in the multi-chain sprockets illustrated in Figures 1, 2 and 4, but any required number of sprocket rings can be mounted on a single hub 10. Three sprocket rings 11, for example, are shown in the construction illustrated in Figure 3. To ensure that the sprocket rings 11 are correctly assembled on the hub 10, at least one locking key 14 (and usually three keys 14, as shown in Figure 1) is formed on the hub and a corresponding locking key receiving groove 15 (or grooves 15) is (or are) formed on the internal surface of the sprocket rings. As shown in Figures 4 and 6, it is not necessary for the number or size of the teeth of each of the sprocket rings to be identical. There are more sprocket teeth on ring 11A in the embodiment of Figure 4 than on the ring 11B. If required, sprocket rings of different internal diameter can be mounted on a single hub if, as shown in Figures 5 and 6, the hub 50 is moulded to have a stepped region 52 onto which a sprocket ring 51 is mounted. As already noted above, the individual components of the multi-chain sprocket are pressure moulded from metallic powders. Standard powder moulding techniques are used for this purpose. The internal diameter d (see Figure 1) of the sprocket rings 11 must be substantially the same as the external diameter p_ of the hub 10, but such that the sprocket rings are a precise fit on the hub, so that when the preferred sinter bonding of the components is effected after the multi-chain sprocket has been assembled, there is a migration of molecules from the ring to the hub and vice versa to perform the bonding. Subsequently the bonded multi-chain sprocket will usually be hardened (using conventional hardening practice) or steam treated and the bore of the hub 10 and the end faces of the sprocket will be finish ground. The main benefits of the present invention are reduced production costs for multi-chain sprockets and the ability to produce a multi-chain sprocket having individual sprocket rings with differing diameters and timing characteristics. The reduced production costs are achieved by avoiding the machining steps in the conventional production of multi-chain sprockets, and by using less raw material to produce the sprockets. Industrial application Multi-chain sprockets manufactured by the method of the present invention may be used in any situation where a multi-chain sprocket is required. Examples of such situations are in motor vehicle engines and in the wheel hubs of multi-speed bicycles.

Claims: Claims 1. A method of manufacturing a multi-chain sprocket comprising the steps of: (a) pressure moulding a cylindrical hub (10) from a powder of a metal or a metal alloy; (b) pressure moulding a plurality of sprocket rings (11) from the same or from a different powder of a metal or metal alloy, each sprocket ring (11) having an internal bore (d) such that the sprocket ring is a precise fit on the hub (10); (c) mounting the sprocket rings on the hub in required locations; and (d) bonding the sprocket rings to the hub. 2. A method as defined in claim 1, in which the bonding is effected by sintering the assembled hub and sprocket rings. 3. A method as defined in claim 1 or claim 2, including the additional steps of (i) hardening or steam treating the product multi-chain sprocket; and (ii) finish grinding the bore of the multi-chain sprocket and its location face. 4. A method as defined in claim 1, claim 2 or claim 3, in which the hub (10) is moulded from a copper-iron powder and the sprocket rings (11) are moulded from powder of nickel alloy steel. 5. A multi-chain sprocket formed by the method of any preceding claim. 6. A multi-chain sprocket as defined in claim 5, in which the hub (10) is provided with at least one key (14) extending from its outer cylindrical surface and each sprocket ring (11) is provided with an equal number of key-receiving grooves (15) in its surface which is adjacent to the outer cylindrical surface of the hub when the multi-chain sprocket is assembled. 7. A multi-chain sprocket as defined in claim 5 or claim 6, in which the hub (50) has a portion (52) of greater diameter, on which is mounted at least one respective sprocket ring (51). 8. A method of making a multi-chain sprocket, substantially as hereinbefore described with reference to the accompanying drawings. 9. A multi-chain sprocket as defined in claim 5, substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: RIDSDALE ALAN, SERVENT DAVID IAN, TURNEY NORMAN JAMES, RIDSDALE, ALAN, SERVENT, DAVID, IAN, TURNEY, NORMAN, JAMES
Applicants: NILSEN SINTERED PRODUCTS AUSTR, NILSEN SINTERED PRODUCTS (AUSTRALIA) PTY LTD
Application year: 1987
Main classification: B22F5
IPC codes: B22F5, B22F7, F16H55