Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Electro-static or inductive field
Reexamination Certificate
2000-02-07
2001-03-20
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Electro-static or inductive field
C156S379700, C219S601000, C219S633000, C264S487000, C264S496000
Reexamination Certificate
active
06203306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vulcanized rubber-metal plate composite which comprises a plurality of rubber layers and metal plates overlaid alternately, a method and an apparatus for heating an unvulcanized rubber-metal plate composite which is the original state of the vulcanized rubber-metal plate composite, and a method and apparatus for manufacturing the vulcanized rubber-metal plate composite.
2. Description of the Related Art
Vulcanized rubber-metal plate composites have been used in, for example, anti-seismic dampers or rubber bearings. The anti-seismic dampers are placed on the foundations of structures, e.g. buildings, bridges and machines to reduce response acceleration to excitation force due to earthquakes and thus to reduce damage to the structures. A typical anti-seismic damper for buildings has a large size, i.e., a design load over 500 tons and a diameter of approximately 1 meter.
Such a rubber-metal plate composite is manufactured by bonding a plurality of vulcanized rubber layers and metal plates alternately or by heating an unvulcanized rubber-metal plate composite to a vulcanization temperature while compressing it. A method for bonding the vulcanized rubber layers and the metal plates is disclosed in Japanese Patent Publication No. 59-19018, in which bonding layers are primarily heated by induction heating of the metal plates. Since this method requires a step for vulcanizing unvulcanized rubber layers one by one and a step for applying a bonding agent on the metal plates and overlaying the vulcanized sheets and the metal plates alternately, it is not desirable for large size composites such as anti-seismic dampers.
It is therefore preferred that a composite comprising unvulcanized rubber layers and metal plates is heated while being compressed to vulcanize the rubber layers. General methods for heating unvulcanized rubber include hot-plate pressing and hot pressing. Also, heating unvulcanized rubber due to heat transfer from a mold heated by electromagnetic induction is proposed in Japanese Patent Laid-Open No.
57-193340.
Since unvulcanized rubber is a heat-insulating material, the heating of rubber articles by means of an external heat source, e.g. a hot plate or a mold, needs a long time before the interior of the rubber is sufficiently heated, resulting in decreased productivity. Such a trend is noticeable in large size anti-seismic dampers. For example, a large anti-seismic damper for buildings having a design load of approximately 500 tons and a diameter of approximately 1 meter requires a vulcanization time of 10 to 20 hours. Heating while compressing such a large composite for a long time also consumes much energy resulting in increased production costs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for rapidly heating an unvulcanized rubber-metal plate composite.
It is another object of the present invention to provide a method for heating an unvulcanized rubber-metal plate composite so as not to cause temperature differences in the composite during heating.
In accordance with the present invention, a vulcanized rubber-metal plate composite is obtained by overlaying a plurality of unvulcanized rubber layers and metal plates alternately and heating thereof by magnetic induction heating.
Since the metal plate which is a conductive material can be heated by eddy currents, magnetic induction heating can be used in the heating process of the composite.
Examples of metal plates include steel plates, stainless steel plates, aluminum plates, aluminum alloy plates, copper plates and copper alloy plates. A composite using metal plates other than steel plates barely causes a decrease in design load due to corrosion compared with a composite using steel plates.
A second aspect of the present invention is a method for heating an unvulcanized rubber-metal plate composite comprising the steps of: placing the composite comprising a plurality of unvulcanized rubber layers and metal plates, each being overlaid alternately, into a place affected by an induction coil; heating the metal plates due to eddy currents formed in the metal plates by applying an alternating current to the induction coil; and vulcanizing the unvulcanized rubber layers due to heat conduction from the heated metal plates.
In the metal plate which is a conductive material, eddy currents are generated due to change in magnetic flux. The magnetic flux density formed by the induction coil increases with the magnetic characteristics of the metal plate. The magnetic material enhances the magnetic field and the eddy currents and thus generate a large amount of heat. Other heat sources may be used to supply heat. Preferably, the metal plate is a steel sheet in view of strength and material costs.
Both the top and bottom layers of the composite are metal plates. These metal plates have a larger diameter than that of other metal plates in the composite, because the protruded section of each end metal layer is used as a flange and provided with holes for fixing the composite product to the foundations. In general, the composite is a solid cylindrical column or a cylindrical column having a central cavity. The composite may also be a polygonal column, such as a triangular prism with or without an inner cavity.
Preferably, the induction coil is arranged so as to generate eddy currents in the metal plates sandwiched between the vulcanized rubber layers along the direction perpendicular to the longitudinal direction of the composite in view of heating efficiency.
A preferable method for generating eddy currents in the metal plates along the direction perpendicular to the longitudinal direction of the composite or along the transverse direction of the composite is to place the composite inside the induction coil. Arrangement of a plurality of induction coils on the periphery of the composite may also be used. The heat applied to the periphery of the plate rapidly transfers to the entire metal plate having high thermal conductivity, and the unvulcanized rubber layers are heated by the metal plate heated on the whole. Herein, the word “periphery” represents the outer periphery of a solid column or the outer and inner peripheries of a column having a central cavity. One of or both of the outer and inner peripheries may be heated. The inner periphery can be heated by an induction coil inserted into the central cavity.
In the second aspect, the alternating current applied to the induction coil may have a frequency in a range from 1 Hz to 1 kHz.
Heating efficiency decreases as the frequency decreases. An optimum frequency is determined so that uniform heating and heating efficiency are compatible. A frequency of less than 1 Hz needs a long time before the composite reaches a given temperature.
On the other hand, a frequency of not greater than 1 kHz does not cause temperature differences between the center and the top or bottom end of the composite. The higher the frequency, the more the top and bottom ends of the composite are intensively heated. Application of an alternating current with a low frequency can generate a uniform magnetic field over all the metal plates of the composite and thus uniformly heat these metal plates in a short time.
In the second aspect, the frequency of the alternating current applied to the induction coil may be varied during heating.
Varying the frequency controls heat generation at the periphery and the inside of each metal plate and thus reduces the temperature differences between them.
In the second aspect, the method may be applied to a preliminary step for heating the unvulcanized rubber in the composite to a predetermined temperature.
The vulcanization of the unvulcanized rubber requires a preliminary heating step and a vulcanizing step of the preheated rubber at a given temperature while compressing the preheated rubber. After the preheating step is performed by induction heating, the rubber may be vulcanized by a conventional method, such as hot-plate pressing or hot pressing,
Adachi Shigeto
Fukumoto Hirohiko
Inoue Yoichi
Kurokawa Yoshinori
Sakiyama Kazuhiko
Davis Robert
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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