Method of producing copper-base sintered bearing material

ABSTRACT

A method of producing a copper-base sintered bearing material is provided so that it is sintered with high thermal efficiency. As a heat source for a sintering furnace, an electric resistance heater which heats a furnace atmosphere and/or a high frequency induction heater, is provided, and also a microwave oscillating device which irradiates microwaves to copper alloy powder to be sintered is provided therewith. A steel sheet, which is a steel backing metal, can be heated by an electric resistance heater and/or a high frequency induction heater, and the copper alloy powder can be heated directly by microwaves.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a sintering system in accordance with an embodiment of the present invention; and

FIG. 2 is a sectional view of a sintering furnace in the system shown in FIG. .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 schematically shows the whole of a sintering system. This sintering system is mainly composed of a sintering furnace . On the inlet side of this sintering furnace , a hopper is provided to scatter copper or copper alloy powder on a steel sheet when a copper-base sintered bearing material with a steel backing metal is produced. Also, a high frequency induction heater is provided on the inlet side of the sintering furnace , and a cooling chamber is continuously formed on the outlet side thereof. A material to be sintered is put on a belt of a belt conveyor as a carrier device, and is carried successively to the high frequency induction heater , the sintering furnace , and the cooling chamber . The internal surface of the sintering furnace is lined with refractories , which is a dielectric substance as shown in FIG. . In the sintering furnace , an electric resistance heater wire is provided along a furnace wall constructed by the refractories , and this electric resistance heater wire constitutes an electric resistance heater . Also, in the upper central portion of the sintering furnace , a microwave oscillating device is provided. This microwave oscillating device generates microwaves with a frequency of, for example, 2.45 GHz in the high frequency induction heater and the sintering furnace .

The copper-base sintered bearing material with a steel backing metal is produced by using the above-described sintering system in a way as described below. First, a steel sheet is placed on the belt and is conveyed, and copper or copper alloy powder is scattered on the steel sheet by using the hopper . Subsequently, the steel sheet on which the powder has been scattered is carried into the high frequency induction heater having a reducing atmosphere or an inert gas atmosphere. The steel sheet having been carried into the high frequency induction heater causes self heat generation by means of induction heating, so that the copper alloy powder is heated by microwaves.

Subsequently, the steel sheet is carried into the sintering furnace , and therein is further heated by radiation from the electric resistance heater wire or by a furnace gas heated by the electric resistance heater wire . Also, although the copper or copper alloy powder is heated by the electric resistance heater wire in the same way as described above, it is heated mainly by microwaves and is sintered. Then, the steel sheet mounted with a sintered layer is carried into the cooling chamber , and therein is cooled, by which it is completed as the copper-base sintered bearing material with a steel backing metal. The copper-base sintered bearing material may subsequently be rolled to densify the sintered layer or may be subjected to sintering and rolling operations repeatedly.

The present inventor conducted an experiment to compare the producing method in accordance with the present invention with the conventional producing method in which the material is heated only by the conventional electric resistance heater.

The material to be sintered was a material in which copper alloy powder (−60 mesh) containing 10 mass % Sn, the balance being Cu, was scattered on a steel sheet 150 mm in width and 1.5 mm in thickness to a thickness of 1 mm.

The conventional sintering furnace using electric resistance heating is divided into four zones. The size of each zone was equal to each other, measuring 160 mm wide by 100 mm high by 750 mm long. The maximum output of the electric resistance heater wire of each zone was set at 20 KW.

The sintering furnace of the present invention is basically the same as the conventional sintering furnace using electric resistance heating, and differs from the conventional sintering furnace in that there is provided a microwave oscillating device consisting of a microwave generator of a frequency of 2.45 GHz and an output of 10 KW. The microwave oscillating device was provided between the second zone and the third zone from the inlet side. The position, frequency, and output of the microwave oscillating device are not limited those described above.

Further, the sintering furnace of the present invention also differs from the conventional sintering furnace in that a high frequency induction heater is provided at the inlet of sintering furnace. The position of the high frequency induction heater is not limited to the inlet. Also, sometimes, the electric resistance heater is not needed.

In the case of this embodiment, heating was performed with a frequency of 10 KHz and an output of 60 KW when the electric resistance heating is applied, and with a frequency of 10 KHz and an output of 30 KW when the electric resistance heating is not applied. The frequency and output are not limited to these values.

Also, as a gas in the sintering furnace, hydrogen gas was used in a reducing atmosphere, and nitrogen gas was used in an inert gas atmosphere.

When the copper alloy powder used in this experiment was sintered by the conventional producing method, the time when a powder layer to be sintered was shrunk by 13% in thickness was taken as the finish of sintering. Therefore, in this experiment as well, the time when the powder layer was shrunk by 13% was taken as the finish of sintering.

The results of this experiment are given in Tables 1 and 2.

As seen from Table 2, according to comparative examples 1 and 2, when sintering was performed with an output of electric resistance heater of 65 KW, sintering was finished by heating for 30 minutes in a reduced atmosphere. However, in an inert gas atmosphere, sintering could not be finished by heating for 30 minutes.

On the other hand, according to the producing method in accordance with the present invention, in embodiment 1, when sintering was performed with an output of microwave oscillating device of 60 KW, sintering finished in 28.5 minutes even in an inert gas atmosphere.

In the comparative examples 1 and 2, about three hours were required as preheating time for making the interior of sintering furnace in a constant temperature state. However, in the embodiment 1, sintering could be finished by starting the sintering operation from the state in which the temperature in the sintering furnace was room temperature.

Also, in the embodiments 2 and 3, when sintering was performed with an output of microwave oscillating device of 10 KW and an output of electric resistance heater of 65 KW, sintering finished in a shorter time than that in the comparative example 1. In embodiment 4, if control was carried out so that sintering finished in the same time as that in comparative example 1 in a reducing atmosphere, only an output of electric resistance heater of 38 KW was needed, and sintering finished with a lower output than that of comparative example 1 even considering the addition of the output of microwave oscillating device of 10 KW.

Also, in embodiments 5 and 6, when sintering was performed with an output of microwave oscillating device of 10 KW and an output of high frequency induction heater of 30 KW, sintering sill finished with a lower output in a shorter time than in comparative example 1.

Also, in embodiments 7 and 8, when sintering was performed with an output of microwave oscillating device of 10 KW, an output of electric resistance heater of 30 KW, and an output of high frequency induction heater of 10 KW, sintering finished in a far shorter time.

Thus, according to the producing method in accordance with the present invention, sintering can be performed in a shorter time with a lower output than in the conventional manufacturing method. Further, sintering can be performed in an inert gas atmosphere in which sintering is difficult to perform by the conventional producing method.

The present invention is not limited to the embodiment described above and shown in the drawings, and can be expanded or modified as described below.

Sintering may be performed continuously by scattering copper or copper alloy powder on a steel strip and by causing the steel strip to pass through the sintering furnace continuously.

After sintering has been performed, rolling may be performed to densify the sintered layer.

Sintering and rolling operations may be performed repeatedly.

As described above, according to the present invention, the following effects can be achieved.

In the inventions according to a first aspect, the copper or copper alloy powder can be heated directly by microwaves, so that the thermal efficiency is high.

In the invention according to a second aspect, the copper or copper alloy powder can also be heated by the electric resistance heater and/or the high frequency induction heater, so that sintering can be performed in a shorter time with a lower output.

By using microwave heating, as in the invention according to a third aspect, sintering can be performed in either a reducing atmosphere or an inert gas atmosphere.

CLAIMS

1. A method of producing a copper-base sintered bearing material with a backing metal in which copper or copper alloy powder is scattered on a steel sheet, and subsequently said copper or copper alloy powder on said steel sheet is sintered by a sintering furnace, wherein a microwave oscillating device is used as heating means provided in said sintering furnace, and said copper or copper alloy powder is heated and sintered by said microwave oscillating device.

2. The method of producing a copper-base sintered bearing material according to claim 1, wherein said sintering furnace is provided with an electric resistance heater and/or a high frequency induction heater as heating means in addition to said microwave oscillating device.

3. The method of producing a copper-base sintered bearing material according to claims 1, wherein the interior of said sintering furnace is in a reducing atmosphere or an inert gas atmosphere.

4. The method of producing a copper-base sintered bearing material according to claims 1, wherein the interior of said sintering furnace is in a reducing atmosphere or an inert gas atmosphere.

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