MAKING PULLEYS

Abstract: In the manufacture of poly-V belt pulleys from a flat disc-shaped blank which is formed into a cup-shaped can, after which external annular grooves are formed in the cylindrical portion of the can, the internal surface of this portion is provided with a limited number of ribs, e.g. four, forming a driving key co-operating with the mandrel on which the pulley is formed.

Description: MAKING PULLEYS This invention relates to the manufacture of poly-V belt pulleys. Since the replacement of a significant proportion of the old Vee-belts with so-called poly-V belts there has been a substantial amount of effort, as evinced by several existing published patent specifications, devoted to the manufacture of pulleys for such belts in a manner such as to make them as light and as strong as possible. Examples are (in approximate chronological order) U.S. Patent specifications 2,892,431 of Killian and 3, 366,376 of Previte, British 1 537 564 of Aspro Inc., French Utility Certificate 2,488,536 of Ducellier, British 2,087,270A of Drive Manufacturing Inc., European 0 083 684 of Goshi Kaisha, European 0 156 567 of Honda Giken, British 2,153,267A of Construcciones Radio Electro-Mechanicas S.A. and British 2, 135, 421A of Dyneer Corporation. In every one of the processes disclosed in these patent specifications a flat disc-shaped sheet metal blank of uniform thickness is formed by stamping or drawing into a cup-shaped or bell-shaped so-called can, and then the cylindrical portion of the can is in some way squeezed, deformed or thickened to reduce its axial length and to raise a series of ribs and grooves in its external surface to form the pulley. The initial formation of the can is performed in a press and then the subsequent deforming steps on the cylindrical portion are undertaken in various ways. Generally the can is mounted on a mandrel and then engaged by rollers or roll-forming dies which deform the cylindrical portion by axially compressing it to collapse it and other rollers or dies to impress the Vee grooves in its external surface. The side flanges of the pulley are formed at the same time or in a preliminary step. In some versions the cylindrical portion is engaged both from the outside and from the inside by ribbed rollers so as to impart an overall corrugated profile to the pulley. This makes for a light weight but it is a less easy process to put into practice than those in which the can is mounted on a solid cylindrical mandrel. The drawback, however, of using a solid mandrel, and accordingly only engaging the outside face of the can with profiled rollers, is that it is difficult to make this part of the pulley strong enough unless one starts with a blank of a thickness which is greater than is otherwise necessary for forming the radial part of the pulley, and thus one ends up with a pulley which is heavier than it need be. A process has been proposed in which the wall thickness of the grooved portion is initially stepped, so that it has three different internal diameters, the radial wall thickness being progressively less as one moves towards the free edge of the can (Dyneer GB-PS 2 135 421A) . In another (Honda EP-PS 0 156, 567) there is a series of closely spaced internal axially extending grooves. In a third process (Goshi Kaisha EP-PS 0 083 684) the outside surface is forced inwards by a groove-forming roller and the inside surface is supported by a mandrel having circumferential ribs, so that grooves are formed on the inside in alignment with the crests on the outside. The drawback of this is that the internal mandrel has to be smaller in diameter than the can, otherwise it could not be withdrawn after forming. The alternative of a collapsible mandrel is complicated and expensive. It is very desirable that the mandrel should be the full size of the inside of the can, so as to support it fully and ensure that there is no out-of-round distortion created during the forming process. Equally, those processes in which the inside of the can is smooth and cylindrical (e.g. GB-PS 2 087 270A of Drive Manufacturing Inc.) have the practical drawback that the can is difficult to hold against rotation on the mandrel during the groove-forming step, and in practice it may be necessary to clamp the can by means of the • mounting holes formed in its hub. The aim of the present invention is to provide a further development in the manufacture of poly-V pulley, avoiding the above-mentioned drawbacks of some of the known processes. According to the invention we achieve this by providing on the inside cylindrical surface of the can a limited number of axially extending ribs, preferably uniformly spaced apart. For example there may be four such ribs. The provision of these ribs is matched by the provision of corresponding grooves in the external surface of the mandrel onto which the can is fitted for the groove-rolling operation; the co-operation of the ribs and grooves forms a key which ensures that the can cannot inadvertently rotate. Alternatively, if the process is one in which the can is itself to be rotated, the ribs and grooves form driving dogs which have the effect of ensuring that there is no slip. The number of ribs is preferably small enough to make no significant difference to the weight of the final pulley.. Even a single rib would be sufficient. within the scope of the invention, to provide the necessary key, although four are preferred. As in the known proposals, a thickness of sheet metal can be selected for the blank only sufficient to give the hub and the radial portion of the pulley the required strength and rigidity. The axially extending portion, on which the grooves are subsequently formed, can be thickened, after formation of the can by drawing or stamping, and the thickening can be achieved by a known process, preferably by that forming the subject of European Patent Application No. 0 343 314 A2 of F Maschinenbau und Blechformtechnik GmbH & Co. KG. In that process the peripheral portion of a disc-shaped sheet metal blank is rolled over into a semi-circular profile and then that profile is squeezed radially inwards while restrained against axial expansion. Two examples of pulleys made by the process according to the invention are illustrated in the accompanying drawings. Figures 1 and 2 are respectively an axial view and a section on the line A-A in Fig 1 showing a first embodiment and Figure 3 and 4 are corresponding views of a second embodiment, the section of Figure 4 being on the line B-B in Figure 3. In the first version there are four ribs R, spaced 90° apart around the inside surface of the pulley. They are formed in the drawing of the initial blank or 'can' and serve to key the can to corresponding grooves in the mandrel (not shown) on which it is supported during the subsequent rolling operation in which the external V grooves are formed. In a typical example the starting material is 2 mm to 3 mm thick and in the finished pulley the radial distance between the base of each groove and the inside surface of the pulley is between 1.3 and 1.5 mm. The ribs themselves are of domed profile between 1.7 and 1.5 mm in radial depth and rather greater than this in circumferential extent. In the version shown in Figure 3 and 4 there are again four equally spaced ribs but in this case the ribs R 1 are of substantially greater circumferential extent, representing about 35% to 40% of the total internal surface of the pulley. With a starting material having a thickness of 2.2 mm, the thickness of metal between the bases of the belt grooves and the internal surface of the pulley is 1.1 mm on the regions between the ribs and 1.5 or 2.2 mm in the region of the ribs, that is to say, the ribs have a radial depth of 0.4 to 1.1 mm.

Claims: CLAIMS 1. A poly-V pulley formed from a sheet metal cup-shaped blank or can in which the inside cylindrical surface of the can is provided with a limited number of axially extending ribs (R) . 2. A pulley according to claims 1 in which the axially extending ribs are uniformly spaced apart. 3. A pulley according to claim 1 or claim 2 in which the number of axially extending ribs is limited to four. 4. A method of manufacturing a sheet metal poly-V pulley comprising the steps of forming a bell-shaped blank or can, and then mounting the can on a mandrel which is engaged by rollers which deform the cylindrical portion by axially compressing it to collapse it and then engaged by other rollers to impress the Vee grooves in its external surface, in which a limited number of axially extending ribs (R) are formed on the inside cylindrical surface of the can by the forming of the can. 5. A method according to claim 4 in which the external surface of the mandrel is provided with grooves which correspond to the ribs formed on the inside surface of the can.

Inventors: BAKER RONALD THOMAS, BAKER, RONALD, THOMAS
Applicants: BLOXWICH ENG, BLOXWICH ENGINEERING LIMITED
Application year: 1991
Main classification: B21D53
IPC codes: B21D53, F16H55