GB2040104A

GB2040104A - Disc rotor for an electrical machine

Info

Publication number: GB2040104A
Application number: GB7939997A
Authority: GB
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri France SA
Priority date: 1978-11-22
Filing date: 1979-11-20
Publication date: 1980-08-20
Also published as: FR2442530A1; ES486151A1; CH633391A5; SE7909540L; JPS5574327A; FR2442530B1; GB2040104B; DE2852979A1

Abstract

A disc rotor for an electrical machine comprises a rotor body (1) of a temperature resistant polycrystalline sintered ceramic material which is insensitive to heat shock and a winding of bare metal conductors (2) applied to adhere firmly to both sides of the body (1) by direct eutectic bonding. The ceramic may be Al2O3, BeO or Si3N4, and the conductors may be copper or aluminium, in the latter case bonded by an Al/Si eutectic. <IMAGE>

Description

SPECIFICATION Disc rotor for an electrical machine This invention relates to a disc rotor for an electrical machine, having a rotor body which comprises a thin insulating disc of polycrystalline sintered ceramic material.

Disc rotors for electrical machines are known in various forms. They are distinguished by a very low moment of inertia and great adaptability in operation. The rotor body, generally composed of a glassfibre-reinforced plastics disc serves at the same time as a carrying memberforthewinding and as its insulating member. The electrical conductors, which generally consist of flat copper wires, can be applied to the rotor body by various methods. A current mode of securing consists of "casting in" or "sticking in" as part of the polymerisation process of the plastics material reinforced with glass-fibre fabric (polyester or epoxy resin).In orderto increase the thermal loading capacity, it has already been proposed to produce the rotor body from ceramic material and to apply the winding by screen printing, vapour deposition under high vacuum, application of metallizing pastes etc. (for example German published patent application 1 808 763).

Furthermore the direct connection of metals to ceramic materials by the so-called eutectic process is known from the metal coating art, such as is used above all in electronics in print production. In this case, a bonding mechanism, which is effective in the sub-microscopic atomic range, is utilized by the production of a metal/metallic oxide eutectic, the melting point of which is only just below that of the pure metal. This bonding mechanism which is effective at the boundary surfaces metal/ceramic directly and without intermediate layers permits a bond which adheres extremely firmly between the two different components (see, for example, J. F. Burgess and C.

A. Neugebauer, "The Direct Bonding of Metals to Ceramics by the Gas-Metal Eutectic Method", J.

Electrochem. Soc. May 1975, Vol. 122, No. 5; J. F.

Burgess, C. A. Neugebauer, G. Flanagan, R. E.

Moore, "The Direct Bonding of Metals to Ceramics and Applications in Electronics", General Electric Report No. 75CRD105, May 1974; U.S. Patent 2766 634; U.S. Patent 3 911 553).

Disc rotors with plastics carrier members have only a limited operating temperature and should not be overloaded thermally, even for a short time, because of the risk of "warping". The metallizing processes mentioned above produce only thin layers of high resistance or windings which are satisfactorily connected to the ceramic disc but which are generally not compact and ductile.

In accordance with this invention, there is provided a disc rotor for an electrical machine, without active iron parts for the magnetic flux, having a rotor body which comprises a thin insulating disc of polycrystalline sintered ceramic material, and bare metal conductors, forming a winding, applied to the rotor body on both sides and forming a eutectic direct mechanical bond thereto. A disc rotor is thus obtained having a compact body of stable shape and high strength, which can be highly loaded thermally and be briefly overloaded. The rotor, whilst having a simplified production method, also has, thanks to its so-to-speak monolithic construction and the extraordinarily strong metal/ceramic adhesion, a high stability of shape and a low sensitivity to heat shock under all operating conditions.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa side view of a disc rotor, showing the rotor body in section; Figure 2 is a plan view of the rotor body, showing part of the winding of the disc rotor; and Figure 3 is an enlarged section through a detail of the rotor body and the winding.

Referring to the drawings, a disc rotor has a rotor body 1 constructed in the form of a thin ceramic disc of Awl203, and a copper winding 2 produced from flat wire or foil. The remaining construction of the rotor results in conventional manner. The ceramic disc is secured to a shaft 6 by means of an attachment flange 5 and a hub 4.

Figure 3 shows in section a detail of the securing of the winding to the outer periphery of the rotor body 1. Thanks to a eutectic bond 3 present at the boundary surface, the copper winding 2 adheres firmly and is secure against heat shock to the rotor body 1.

The invention is not restricted to the shapes and pairs of materials mentioned in relation to the Figures. In particular, other ceramic compositions can be used as a rotor body such as BeO or Si3N4. Likewise, the rotor winding may also consist of silver, a metal of the iron group or of aluminium.

Example A flat disc of densely sintered fine crystalline alumina (Al203) with an external diameter of 114 mm and an internal diameter of 60 mm and 0.5 mm thick was degreased by means of trichloroethylene, cleaned in aqua regia, etched in concentrated sul phuric acid at 1000C and annealed at 1100 Cfori hour. A flat copper wire of 0.4 x 3 mm cross-section was degreased by means of trichloroethylene, cleaned in 10% hydrochloric acid, etched in 1 mol of ammonium persulphate, dried and oxidized over one side for 1 minute at 9500C in a weakly oxidizing atmosphere consisting of the purest nitrogen with the addition of 0.03% by volume of oxygen.After this treatment, the thickness of the oxide layer amounted to about 500 . The copper conductor was then laid with the oxidized surface against the surface of the ceramic disc and the whole heated to 10720C, as a result of which the eutectic copper/cuprous oxide (Cu/Cu2O) was formed with a melting point of 1065"C. The latter displays a satisfactory wetting capacity both of the metal and of the ceramic and flows easily into their pores. After cooling, an extremely firm adhesion between the copper conductor and the alumina disc is achieved by the formation of this very thin solidified eutectic intermediate layer.

In this manner, flat wires and stamped foils of other metals can be applied to the ceramic discs serving as rotor bodies and can be rigidly connected to these.

In the case of aluminium as the electric conductor material, instead of the metallmetallic oxide eutectic, the Al/Si eutectic may be used as a bonding mechanism. The preoxidizing of the copper is replaced by the vapour deposition of a thin silicon layer (for example 0.1 to 1 thick). Bearing in mind the eutectic temperature of 577"C for the system Al/Si, the working temperature for the connection of the conductor to the substrate would amount to about 585"C to 600"C.

Claims

1. A disc rotor for an electrical machine, without active iron partsforthe magnetic flux, having a rotor body which comprises a thin insulating disc of polycrystalline sintered ceramic material, and bare metal conductors, forming a winding, applied to the rotor body on both sides and forming a eutectic direct mechanical bond thereto.

2. A disc rotor as claimed in claim 1, wherein the rotor body consists of sintered fine crystalline Awl203.

3. A disc rotor as claimed in claim 1, wherein the rotor body consists of sintered fine crystalline BeO.

4. A disc rotor as claimed in claim 1, wherein the rotor body consists of sintered fine crystalline Si3N4.

5. A disc rotor as claimed in any preceding claim, wherein the electrical conductors forming the winding consist of copper.

6. A disc rotor as claimed in any one of claims 1 to 4, wherein the electrical conductors forming the winding consist of aluminium which is bonded to the rotor body by means of an Al/Si eutectic.

7. A disc rotor substantially as herein described with reference to the accompanying drawings.