SANDRIN GIANNINO (IT)
| EP0709596A2 | 1996-05-01 | |||
| US4497766A | 1985-02-05 | |||
| US5931755A | 1999-08-03 | |||
| EP1484152A1 | 2004-12-08 | |||
| US4793659A | 1988-12-27 | |||
| US4668209A | 1987-05-26 |
PATENT ABSTRACTS OF JAPAN vol. 1996, no. 05 31 May 1996 (1996-05-31)
CLAIMS
1. Method for producing a pulley, in particular intended for use in drive systems provided to rotatably drive the drum of clothes washing machines, by injection-moulding a plastic material filled with glass fibres for reinforcement, said pulley (10) being comprised of a central hub (12) connected through a plurality of radially extending spokes (16) with a peripheral rim (18), around which there is capable of being wrapped a driving belt or the like, characterized in that the molten plastic material is injected into the mould through a hot runner (20) a plurality of nozzles (24) arranged close to the central hub (12), so that the joining or welding spots of the plastic material are caused to occur and lie along the peripheral rim of the pulley at the melting temperature of the same plastic material, Le. approx. 250 0 C.
2. Method according to claim 1, characterized in that the plastic material used is an engineering-type thermoplastic material, such as polypropylene, polyamide, or the like, and that the pulley (10) is entirely and solely made of such material.
3. Method according to claim 1 or 2, characterized in that the reinforcement glass-fibre filling in said plastic material is in the range between 40% and 70%.
4. Method according to any of the preceding claims, characterized in that the glass-reinforced plastic material has a modulus of elasticity of at least 15,000 MPa and a surface hardness of at least 100 R.
5. Method according to any of the preceding claims, characterized in that the pulley (10) is moulded in an injection-moulding machine using multiple-cavity interchangeable moulds.
6. Pulley used in the drive system of a clothes washing machine to rotatably drive the drum thereof, produced with the method according to any of the preceding claims, characterized in that the sprue gates for the injection of the material are provided close to the central hub (12) and the joining spots of the molten material occur solely along the peripheral rim (18) of the pulley.
7. Pulley according to claim 4, characterized in that it is entirely and solely made of an engineering-type thermoplastic material, such as polypropylene, polyamide, or the like, which is filled with glass fibres to a percentage ranging from 40% to 70% for reinforcement, and has a modulus of elasticity of at least 15,000 MPa and a surface hardness of at least 100 R. |
MANUFACTURING METHOD FOR PRODUCING A PULLEY OF PLASTIC MATERIAL AND PULLEY PRODUCED WITH SUCH
METHOD
DESCRIPTION
The present invention refers to an improved manufacturing method for producing a pulley of plastic material, as well as to a pulley produced using this method, as intended in particular for use in drive systems provided in clothes washing machines to rotatably drive the drum thereof.
Pulleys used in such kind of applications are generally known to be usually made of some aluminium-based metal alloy, in view of ensuring the necessary properties in terms of mechanical strength, chemical and heat resistance that such pulleys are required to possess in order to withstand the corresponding stresses, which they usually undergo under normal operating conditions.
In the course of the last few years, however, there have been developed also pulleys made of plastic material, which is widely known in the art to be much more lightweight and resistant to corrosion than metal alloys. However, serious problems soon arose in this case, when such plastic pulleys had to be coupled with a drive shaft made of metal.
The disclosure in US patent No. 5,720,685 suggested that such problems be solved by providing a plastic pulley integrally with the drive shaft, as referred in particular to the application in connection with the pump of a clothes washing machine. Unfortunately, the proposed solution failed to prove really satisfactory, owing to both the complexity involved in moulding the related part and the poor resistance of the same part under the actual operating conditions encountered in the machine.
The US patent publication No. 5,931,755 describes a pulley, which is particularly suitable for use in motor-vehicles and is made of such thermoplastic materials as PPS (polyphenylsulfide), generally reinforced with glass fibres. However, in order to prevent the plastic body from breaking off owing to mechanical stresses, the need arises in this case for a metal bush, as made in particular of P-20 aluminium, to be press fitted into the hub thereof, with the result that the pulley itself cannot be readily recycled. Furthermore, the method used to mould the pulley calls for the plastic material to be injected through a single central runner, without therefore ensuring any certain, reliable and even distribution of the injected material.
It therefore is an object of the present invention to provide an improved method for producing a pulley that is entirely and solely made of glass- reinforced plastic material, and that is both lightweight and satisfactorily resistant to the various stresses, in particular of a mechanical nature, which ϋ is due to undergo under operating conditions. As a result, such pulley is fully and readily recyclable, without any need for it to be submitted to any preliminary operation to separate dissimilar materials. Moreover, the pulley according to the present invention must be such as to allow for the greatest possible flexibility in producing pulleys of different models, types and size, so as to reduce production times and the related costs.
According to the present invention, these aims, along with further ones
that will become apparent from the following disclosure, are reached in a pulley that is made in accordance with the method as defined and recited in the appended claims.
Features and advantages of the pulley according to the present invention will anyway be more readily understood from the description that is given below way of non-limiting example with reference to the accompanying drawings, in which:
- Figure 1 is an overall, perspective view of a pulley according to the present invention;
- Figure 2 is a cross-sectional view of the pulley shown in Figure 1 , as viewed along the axis A-A;
- Figure 3 is a partially cross-sectional, schematic view of the injection mould used to produce the pulley shown in Figure 1; and
- Figure 4 is an enlarged view of the central portion of the injection mould shown in Figure 3.
A pulley 10, as produced with the method according to the present invention and illustrated in Figures 1 and 2, is provided with a central hub 12 that is in turn provided with a hole 14 for press-fitting onto a rotatably driving shaft (not shown). The hub 12 is connected by a plurality of radially extending spokes 16 to a peripheral crown or rim 18, around which a driving belt or similar strap (not shown) is capable of being wrapped.
According to the present invention, the pulley 10 is produced by injection moulding using a plastic material reinforced with glass fibres. The preferred plastic material in this application is an engineering-type thermoplastic material, such as polypropylene, polyamide, or the like,
which is filled with glass fibres to a percentage ranging from 40% to 70%, and has a modulus of elasticity of at least 15,000 MPa and a surface hardness of at least 100 R.
A basic feature of the structure of the pulley according to the present invention is represented by the fact that the kind of material used to produce it enables a pulley to be obtained that is entirely and solely made of plastic material, i.e. is free of any metal insert or other metal element that might be used - in particular in the hub portion - in view of enhancing the strength thereof. This feature is further accompanied by a number of other advantageous properties, such as a high resistance to heat (200-300 J/m 2 ), an excellent shape and dimensional stability and, above all, full recyclability.
These features are such as to allow the pulley according to the present invention to be suitable for use in a number of industry sectors, such as for instance the motor industry and the appliance industry. In particular, a pulley of this kind is found to be quite suitable for application in drive systems used to rotatably drive the drum of clothes washing machines.
For producing a pulley as the one described above, an improved injection-moulding method has been developed. The newly devised method calls for the molten plastic material to be injected into the mould through a hot runner 20 in the moving part 22 of the same mould and a plurality of nozzles 24 arranged close to the central hub 12 of the pulley (Figures 3 and 4), so that the joining or welding spots of the plastic material are caused to occur and lie along the peripheral rim of the pulley at the melting temperature of the same plastic material, i.e. approx. 250 0 C.
In particular, the joining spots of the plastic material come to lie along the peripheral rim 18 of the pulleys at points that are located in an intermediate position between the end portions of the spokes 16 joining
with the same rim.
The moulding method according to the present invention calls for the use of a dual press with multiple-cavity interchangeable moulds, preferably two moulds provided with four cavities each. These moulds should be interchangeable in view of allowing for a maximum extent of production flexibility regardless of the different sizes and shapes of the pulleys to be moulded.
The moulds themselves must of course undergo the whole set of necessary treatments as largely known as such in the art, since the plastic material to be moulded is filled with a quite significant amount of reinforcing glass fibres.