Continuous metal fiber brushes

Abstract

A conductive fiber brush including a brush stock composed of plural conductive fibers or strands of fibers at least some of which may have plural bends along the length of the fibers or strands. The fibers may have a diameter less than 0.2 mm and are arranged in contacting engagement with each other with the touching points among the fibers or strands maintaining elastic tension between the fibers or strands and thereby maintaining voids between the fibers or strands to produce a packing fraction between 1 and 50% and in extreme cases up to 70% but generally between 10-20% depending on the various factors, including the materials used, the current densities to be conducted, and the sliding speeds under operation. The plural bends are implemented by producing fibers or strands having a regular or irregular spiral, wavy, saw-tooth, triangular, and / or rectangular pattern, or other undulating pattern. Optionally, the voids in brush stock may be partially filled with a strengthening, lubricating, abrasive, and / or polishing material, and may be wrapped in an outer sheath, slid into a casing, or provided with an other covering of all or part of the area of the brush stock, be infiltrated or sprayed at the surface with some material, have an increased packing fraction at the surface and / or have some or all of the touching points between the fibers or strands soldered, welded or otherwise thermally joined. Optionally also, the friction among the fibers may be reduced through light lubrication applied by rinsing the brush or brush stock in a lubricant. In one embodiment, the fiber brush is employed in a brush loading device having a hydrostatically controlled brush holder wherein the force exerted on the brush is controlled by a metallic or other conductive hydrostatic fluid which at the same time conducts the current to the brush.

Description

DESCRIPTION[0002] 1. Technical Field[0003] This invention relates to fiber brushes, and in particular, the improvements in the design and manufacture of fiber brushes of the type disclosed in commonly owned U.S. Pat. Nos. 4,358,699 and 4,415,635, the disclosures of which are incorporated by reference herein.[0004] 2. Background Art[0005] Although graphite and metal-graphite brushes have for nearly 100 years dominated the field of electrical brushes, for many applications there now exists a superior form of sliding electrical conduction; high performance fiber brushes wherein typically the fibers are made of metal for which reason they are called metal fiber brushes. Prime candidates for this new technology include sliding electrical systems which require high current densities, high sliding speeds, low electrical noise, high efficiency (low brush losses), compact size, or long brush lifetimes.[0006] In particular, low voltage electric motors and generators can be made smaller, more ...

AI Technical Summary

Benefits of technology

[0044] The inventors realized that a rod-like, tube-like or strip-like fiber assembly as discussed would perhaps not necessarily need, but would mostly benefit from, some "surface treatment" to counteract the tendency for unraveling of the fibers about the circumference and at the rotor surface. "Surface treatments" include any and all treatments which will join the peripheral fibers more firmly together than interior fibers or to provide some kind of strengthening "skin". The effect of such surface treatments is to protect the macroscopic brush shape against splaying apart under the applied lengthwise force, preventing fibers at the surface to fluff out or unravel, and to increase the resistance of the brush stock against imposed forces, e.g. bending on account of friction against the tangentially moving rotor surface.

[0050] U.S. Pat. No. 4,415,635 envisaged metal fiber brushes composed of hair-like metal fibers protruding from a matrix material and conducting current to an electrically conducting surface (typically in relative motion to the brushes) against which the fiber ends were lightly, mechanically pressed. U.S. Pat. No. 4,358,699, greatly elaborated on different possible configurations of the concept of using hair-fine wires in electrical brushes, including the fibers contacting the conductor along their long surfaces, being felted or woven together, and strengthened in various manners, including by the incorporation of "support fibers", being fibers which are substantially more rigid and of a length a little shorter than the average fibers so as to protect these from accidental damage. The drawback of other than end-on contact between fibers and opposing conducting surface is too short a wear-life. Namely, wear by one fiber diameter shortens a fiber little if it occurs end-on but cuts off a whole length of fiber if it occurs on a lengthwise surface.

[0052] A further object of this invention is to provide a new and improved electrical fiber brush stock from which electrical brushes can be cut having low electrical contact resistance, and associated therewith low interfacial heat generation and a low sliding wear rate.

[0055] Yet another object of this invention is to provide a fiber brush that has a long wear life and does not change its characteristics through wear.

[0056] Another object of this invention is to provide a fiber brush which is compact in size.

[0062] Still another aspect of the present invention, there is provided a brush holder which uses the elasticity of the brush stock to guide the brush stock forward against the contacting surface.

Problems solved by technology

This translates to extremely long brush life and greatly lengthened service intervals.

Because they operate at low loads and have very low resistance, metal fiber brushes dissipate much less heat than typical brushes in high-current or high-sliding-speed applications.

Unlike graphite-based brushes, metal fiber brushes do not generate fine carbon dust, which can cause problems not only with appearance and clean-up but also with long-term fouling and shorting.

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