PULLEY

Abstract: A pulley composed of a composite material in which hard particles are dispersed in a matrix material, in which a part of the hard particles is exposed to the outside by removal of the matrix material at the pulley surface.

Description: The present invention relates to a driving device for use in small office equipment and the like, and in particular to a driving pulley for a steel belt. Office equipment requires a compact and light pulley, in consideration of the dimensions of the equipment. For this reason there have been employed pulleys made of light metals. Also for driving such a pulley there has been employed a steel belt for preventing elongation by fatigue, since a twisted wire belt or a rubber belt results in elongation after prolonged use, thus adversely affecting accuracy of the belt position. The surface of such a pulley should have a high hardness in order to increase its abrasion resistance. For this purpose, there has already been proposed a pulley having a thin film of a hard metal on the belt driving surface, as described in JP-U-47-29148. However such a pulley tends to exhibit only small friction resistance in engagement with a mirror-finished steel belt, thus eventually resulting in slippage. Also JP-A-58-162384 describes a process of mechanically finishing the surface of an aluminum pulley and depositing a suitable amount of an extremely hard material such as chromium oxide, alumina, tungsten or tungsten carbide on that surface by melt spraying, thereby obtaining a high hardness and a high friction on the surface. However such forced spraying of chromium oxide, and alumina, for example onto the surface of the pulley inevitably leads the pulley having a non-uniform external diameter, and such dimensional inaccuracy results in defective frictional drive of a steel belt. The present invention seeks to provide a pulley which is small in size, light in weight, has a high surface abrasion resistance and high friction on its belt driving surface, and additionally has a uniform external diameter and is adapted for mass production. According to the invention, there is now provided a pulley composed of a composite material in which hard particles are dispersed in a matrix material, characterised in that hard particles are partially exposed by removal of matrix material at the surface of the pulley. US-A-2976738 describes non-slip conveyor pulleys according to the preamble of claim 1 and having an outer surface comprising a mixture of rubber particles and a synthetic resin, the resin binding the particles to the pulley body and the rubber particles projecting from the resin. However, projection of the rubber particles is not achieved by removal of the synthetic resin from the pulley surface. Pulleys according to the invention are capable, even in combination with a mirror-finished steel belt with a low friction resistance, of generating a large friction resistance on the pulley surface by exposure of the hard materials having a high friction resistance, such exposure can be achieved by etching of the surface, thereby obtaining stable and reliable driving power. The invention will now be described in greater detail by way of example only with reference to the accompanying drawings, in which Fig. 1 is a front view of a pulley embodying the present invention; Fig. 2 is a schematic view showing a mixture of metal matrix and ceramic material; Fig. 3 is a schematic view similar to Fig. 2 but in which the ceramic material has been exposed by dissolving the surface of the metal matrix; Fig. 4 is a perspective view of a metal belt engaging with a pulley; Fig. 5 is a cross-sectional view of the second embodiment of the pulley of the present invention; Fig. 6 is a perspective view thereof; Fig. 7 is a schematic view of a cylindrical composite material in extrusion molding; Fig. 8A is a schematic view showing the cutting of the composite material into predetermined length; Fig. 8B is a schematic view showing the combination of the composite material with a bearing; and Fig. 8C is a view of a completed pulley. Referring first to Fig.1 of the drawings, ceramic particles 2 are mixed in a metal matrix 3, for example aluminum metal. In this operation the aluminum 3 is formed as granules of suitable size, and the ceramic particles 2 of a particle size of 50 to 300 µm are mixed in. The mixing ratio is about 30%. The above range of particle size provides an almost constant result in the measurement of friction coefficient, and is therefore most preferable for use and for manufacture. In practice, as shown in Fig.2, ceramic particles 2 of predetermined particle size are collected by passing a suitable filter, and are mixed in the metal matrix 3. The metal matrix 3 is preferably composed of a low-melting metal such as aluminum, but other metals such as magnesium, zinc or copper may also be employed in consideration of the ease of manufacture. The ceramic particles 2 are mixed, with a mixing ratio of about 30%, into the metal matrix 3, and the mixture is then fused by heating in a high-frequency electric furnace. By such heating, the metal matrix 3 is fused and turns to liquid mixed with the ceramic particles 2. Then the liquid metal matrix 3 is poured in a metal mold and cooled. The size of the pulley is determined by the metal mold. The pulley 1 has a smooth surface obtained by casting in the mold, and the metal matrix 3 at the surface is etched with a chemical agent to obtain friction resistance on the surface. For example, aluminum metal 3 in the present embodiment is dissolved, while partially exposing the ceramic particles 2 on the surface, by immersion in aqueous solution of sodium hydroxide. Thus the exposed amount of the ceramic particles 2 is determined by the mixed amount thereof, and the members providing the friction resistance are formed in this manner. Fig.4 shows a state in which a metal belt 5 is wound around the pulley 1 thus formed. The mirror-finished surface of the metal belt 5 and the surface of the pulley 1, maintained in contact during rotation, do not cause mutual slippage but can achieve stable driving due to the friction resistance of the surface 4 of the pulley. The surface 4 of the pulley 1 is made coarse by the presence of the ceramic particles 2 and generates a friction resistance in contact with the surface of the belt 5 by means of the irregular coarse surface, thus obtaining stable driving capability. Since the pulley 1 is formed by molding with molten metal, the exposed ceramic particles 2 have a uniform exposed height over the entire surface, and the exposed height is small, so that the metal belt 5 is not damaged by the particles. Consequently there can be constantly obtained stable driving performance. Though the foregoing explanation has been limited to aluminum metal, similar results can be obtained with other soft metals or resin materials. Also the ceramic material may be replaced by similar hard materials. In the following there will be explained a second embodiment of the present invention. As shown in a cross-sectional view in Fig.5 and a perspective view in Fig.6, a pulley 11 of the second embodiment is composed of a cylindrical composite member 12 of a predetermined width L composed of a light metal or a resinous material incorporating powdered hard material 14 in a similar manner as in the foregoing embodiment, and a bearing portion 13 consisting of a core member inserted in a penetrating hole 15 of the cylindrical composite member 12. More specifically, the cylindrical composite member 12 is obtained by fusing light metal or resin chips in which the powdered hard material 14 such as alumina or tungsten carbide is mixed, and extruding the fused material in a long form as shown in Fig.7 from an extrusion molding machine. Such integral molding of a long cylindrical member allows to obtain pulleys with uniform internal and external diameters in mass production. Among the above-mentioned powdered hard materials, either one can be selected, according to the molding conditions to be employed. The bearing portion 13 is molded with a resin material, by means of a mold of a width corresponding to that of the pulley 1, in such a manner that the external diameter becomes equal to the internal diameter of the cylindrical composite member 12 and that a penetrating hole 16 is formed in the center. The hole 16 at the center of the bearing portion 13 serves for accepting a shaft when the completed pulley 11 is rotated. For mutually combining the molded parts 12 and 13, the composite member 12 is cut to pieces of a predetermined width L as shown in Fig.8A. The cutting may be achieved with a diamond cutter since the mixed powdered hard material 14 has a high hardness. Then, as shown in Fig.8B, the bearing portion 3 is pressed into the penetrating hole 5 of the composite member 2 which is already cut as explained above. The width of the bearing portion 3 is selected equal to or slightly smaller than the width L of the composite member 2. Through these steps an independent pulley 11 as shown in Fig.8C can be obtained. Also in this embodiment powdered hard particles are exposed to increase the friction resistance, by etching the matrix material on the surface of the pulley with a chemical agent or the like, as already explained in the first embodiment. As explained in the foregoing, the pulley of the present embodiment can be mass produced inexpensively with uniform performance, as it is composed of a composite member and a bearing portion, both of which can be obtained by mass production by means of molding operation. Also the presence of powdered material mixed in the composite member constituting the pulley provides a high hardness and ensures a high abrasion resistance, thereby significantly extending the service life of the pulley. On the other hand, the resin core member inserted into the pulley allows to reduce the weight thereof and to economize the matrix material and the powdered hard material. Furthermore, in contact with a metal belt, there is generated a friction resistance between the pulley and the belt, and said resistance prevents the slippage and always ensures stable driving performance. This fact is important in the use of the office equipment and in the protection of the belt.

Claims: A pulley (1,11) composed of a composite material in which hard particles (2,14) are dispersed in a matrix material (3), characterised in that hard particles (2,14) are partially exposed by removal of matrix material (3) at the surface (4) of the pulley. A pulley according to Claim 1, wherein the matrix material (3) is composed of a light metal or a resinous material, and the hard particles (2,14) are composed of a ceramic material or a metal alloy. A pulley according to Claim 1 or Claim 2, wherein the matrix material (3) at the pulley surface (4) is removed by chemical etching. A pulley according to any one of Claims 1 to 3, wherein the pulley (11) is composed of a cylinder (12) of the composite material and a bearing member (13) inserted as a core into a penetrating hole (15) of the cylinder.

Inventors: OHKATA, ICHIZO, TAKAHASHI, HIROSHI
Applicants: KATO HATSUJYO CO., LTD.
Application year: 1987
Main classification: F16H55
IPC codes: F16H55