BRIEF DESCRIPTION OF THE FIGURE(S)
To assist those of ordinary skill in the art in making and using the disclosed fabrication techniques and articles of manufacture, reference is made to the accompanying figures, wherein:
FIG. 1 is a schematic depiction of a conventional pressing step according to the present disclosure;
FIGS. 2A-2C are schematic diagrams showing an exemplary hot pressing technique for use in hot pressing an intermediate work piece according to the present disclosure;
FIG. 3 is a schematic illustration of three work pieces (brushes) that are distinguished by the orientation of the grains as they would be defined relative to a commutator;
FIG. 4 is a plan view of an exemplary brush with flex fabricated according to the advantageous method of the present disclosure;
FIG. 5 is a flow chart illustrating an exemplary fabrication technique according to the present disclosure;
FIG. 6 is a depiction of three individual conventionally pressed components in a side-by-side arrangement; and
FIGS. 7A and 7B are depictions of a multi-layered brush assemblies formed according to the present disclosure.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
Systems and methods for manufacture of electrical components, e.g., brushes, and advantageous electrical components, e.g., brushes/brush assemblies, are provided herein. The disclosed systems, methods and articles of manufacture advantageously control grain orientation in the manufacturing process such that advantageous physical and functional properties are imparted thereto. The disclosed systems and methods utilize hot pressing techniques to provide enhanced properties and/or functionalities to brushes and other electrical components, e.g., carbon and/or copper-containing systems, and find wide ranging applications, including the manufacture and/or fabrication of pressed-to-size brushes.
According to exemplary embodiments of the present disclosure, a powder mixture is initially pressed in a conventional manner to form an intermediate work product. With reference to FIG. 1, a conventional pressing step is schematically depicted. A substantially axial compression force, as represented by opposed arrows F1 and F2, is applied to a powder mixture 10 that is contained within a cavity or die (not pictured). As schematically depicted in FIG. 1, application of the compression force causes grains within the mixture to align in a substantially perpendicular orientation. Grain alignment is schematically depicted by a series of stacked planar regions 12a, 12b, etc. As is known in the art, conventional pressing of powder mixtures, e.g., carbon and/or copper-containing powder mixtures used in the fabrication of brushes/brush assemblies, necessarily establishes a grain orientation that is perpendicular to the force vectors applied thereto. Moreover, as is also known in the art, due to limitations associated with conventional pressing equipment, surface features can only be applied to or formed on the work piece during conventional pressing techniques on the top or bottom surface thereof. Attempts to apply/form surface features on side walls of the work piece are generally limited and/or foreclosed by the nature of the conventional pressing operation.
The operating conditions for the conventional pressing step may vary according to various process parameters, e.g., powder mixture, equipment capabilities, target geometry, and the like. The degree to which work piece density may be increased through conventional pressing techniques is generally restricted due to various processing limitations, e.g., the potential for cracked dies and/or parts sticking to tooling if the press tonnages are increased beyond certain limits.
According to the present disclosure, the intermediate work product formed through conventional pressing is further processed in an advantageous hot pressing step to enhance the properties thereof and, if desired, to provide beneficial surface features, combine ancillary components (e.g., a lead wire/flex), and/or form advantageous multi-layer articles, e.g., a multi-layer brush assembly. The intermediate work piece is thus positioned in a cavity/die that is adapted for hot pressing, as described herein. With reference to FIGS. 2A-2C, the interaction between an exemplary intermediate workpiece and an exemplary cavity/die in a hot pressing step is schematically depicted. Individual cavities/dies may be sized/configured so as to receive insets that provide desired geometric properties, surface features and/or accommodate positioning of ancillary component(s) that are to be joined to and/or captured by the work piece, e.g., a lead wire/flex.
Of note, the intermediate work piece may be introduced to the hot pressing cavity/die such that the grains formed in the previously completed, conventional pressing step are substantially aligned with the axis of the die, i.e., parallel to the force vector associated with the hot pressing step, or are substantially perpendicular to the force vector associated with the hot pressing step. In circumstances where the grains are positioned parallel to the hot pressing force vector, there are two degrees of freedom. Thus, with reference to FIGS. 2A-2C, intermediate work piece 20 is introduced to a hot pressing cavity/die 22 that includes a surface treatment geometry 24 formed on a lower face thereof. As clearly seen in FIG. 2A, the grains of the intermediate work piece 20 are advantageously aligned with force vectors F3 and F4 within die/cavity 22 (see force vectors in FIG. 2B). A hot pressing force is applied to intermediate work piece 20 (as shown in FIG. 2B), typically at an elevated hot pressing temperature, for a hot pressing treatment period sufficient to achieve the desired effect(s) on the intermediate work piece 20. A final work product 30 is formed with an advantageous surface effect 32 formed on the face that was in contact with surface treatment geometry 24. In the exemplary embodiment of FIGS. 2A-2C, the surface effect 32 takes the form of an arcuate, ridged surface, although the present disclosure is not limited to such exemplary surface effect, as will be readily apparent to persons skilled in the art. Indeed, surface effects may be achieved on the top, bottom and/or side surfaces of the intermediate work piece (and ancillary components may be introduced to the intermediate work piece, e.g., a lead wire) during the hot pressing step disclosed herein.
With reference to FIG. 3, three exemplary brushes are schematically depicted to illustrate potential grain orientations. In the left-most view, the grains are aligned having a circumferential grain orientation, i.e., a “G.C.” orientation. In the middle view, the grains are aligned with an axial grain orientation, i.e., a “G.A.” orientation. Finally, the right-most view illustrates an exemplary brush assembly wherein the grains form/define a tangential grain orientation, i.e., a “G.T.” orientation.
As with the conventional pressing step discussed above, the processing parameters associated with the hot press step may be varied without departing from the spirit or scope of the present disclosure. Processing conditions will depend on such variables as the composition of the intermediate work piece, the desired geometric properties of such work piece at the conclusion of the hot pressing step, and the desired physical/functional properties thereof.
With further reference to FIG. 3, it is noted that surface properties may be advantageously established through the disclosed hot pressing technique on the top and/or bottom faces of the G.C. and G.A. brushes that could not be effectively achieved with conventional pressing techniques. While it is possible to machine surface features onto the end faces of a work piece after conventional pressing, it is not possible to form detailed and/or non-planar surface features on the faces of the work piece that are perpendicular to the grain orientation. Moreover, the advantageous fabrication techniques of the present disclosure facilitate the formation of detailed and/or non-planar surface features in the hot pressing step, thereby greatly enhancing the effectiveness, flexibility and utility of electrical component fabrication, e.g., brush fabrication.
With reference to FIG. 4, an exemplary brush 40 is depicted that includes an intricate and non-planar surface geometry 42 on a face that is perpendicular to the grain orientation thereof. Such non-planar surface geometry 42—which may be termed a “press-to-fit” geometry—is advantageously defined during the hot pressing step by forcing the intermediate work piece (with grains aligned with the force vector) into a mold having the desired geometry. In addition, a lead wire/flex 44 is advantageously introduced to and captured by brush 40 in an orientation that is perpendicular to the grain orientation of the brush 40. As with non-planar surface geometry 42, introduction of a lead wire 44 in a perpendicular orientation as shown in FIG. 4 cannot be achieved with conventional pressing techniques.
With reference to FIG. 5, an exemplary flow chart for the disclosed fabrication technique is provided. As shown therein, the process generally involves:
- 1. Providing a powder mixture having desired blend characteristics, e.g., a carbon and/or copper-based powder mixture;
- 2. Conventionally pressing the powder mixture to form an intermediate work product; and
- 3. Hot pressing the intermediate work product to form a final work product.
Operating conditions associated with the hot pressing step will vary depending on a host of factors, e.g., the powder constituents and relative percentages thereof, size and geometry of the intermediate work product, etc. Generally, the hot pressing step is conducted at temperatures that range from about 125° to 1000° F., at pressures that range from about 4000 to 50,000 psi, and for processing times sufficient to achieve the desired work product design/functionality.
Through the hot pressing step, the density of the work piece is further increased relative to the density achieved by way of a conventional pressing step, thereby enhancing the durability of the work piece, e.g., when employed as a brush/brush assembly. Superior functional properties such as specific resistivity/lower resistance and strength are also imparted to the work piece through the disclosed hot pressing technique. The final work piece may also demonstrate increased oxidation resistance, longer life and, as noted previously, may feature complicated/advantageous shapes/surface features. Exemplary advantageous results achieved through the fabrication process of the present disclosure are set forth in TABLE 1 herein below. The “control” results are reflected at the left for each physical property, and the results according to the present disclosure are set forth at the right.
As shown above, the disclosed fabrication method that involves hot pressing a conventionally-pressed intermediate work product yields a work piece with superior properties, with testing showed excellent improvements in all relevant properties. The disclosed fabrication method yielded products with reduced resistance, greater strength, and higher density (which translates to enhanced durability). The superior properties imparted through the disclosed fabrication technique are effective across a variety of powder mixtures, and the contents and percentage composition of the such powder mixtures, e.g., carbon and/or copper-containing mixtures, are not significant to the superior results achieved thereby. Indeed, the disclosed fabrication technique may be applied to any carbon and/or copper-containing powder mixture/blend.
With reference to FIGS. 6 and 7A, the advantageous utility of the disclosed fabrication technique in forming a multi-layer brush assembly is illustrated. In FIG. 6, three distinct conventionally-pressed intermediate work products 50, 52, 54 are shown in a side-by-side position. Each of the intermediate work products is characterized by a grain orientation that is independent of the potential line of contact with an adjacent work product. Indeed, one or more of the elements that are positioned in a side-by-side relationship may be devoid of grain orientations. By positioning the intermediate work pieces in a cavity/die for hot pressing, as disclosed herein, a multi-layered brush assembly 60 as shown in FIG. 7A is fabricated. An adhesive material may be placed between adjacent intermediate work products, if desired.
Of note, in exemplary embodiments of the present disclosure, one or more of the layers need not take the form of a pressed work product. For example, as shown in FIG. 7B, outer layers 72, 76 may surround an intermediate layer 74 that takes the form of a tape, powder and/or wafer of a completely different material, to form an advantageous multi-layer assembly 70. The multi-layer brush assemblies of FIGS. 7A and 7B benefit from the attributes of the individual intermediate work products and are particularly useful in high intensity applications, e.g., washing machine motors or the like.
Thus, the present disclosure provides advantageous systems and methods for fabrication of carbon-based members, e.g., brushes, and advantageous articles of manufacture fabricated thereby. Although the disclosed systems, methods and articles of manufacture have been described with reference to exemplary embodiments thereof, the present disclosure is not limited by such exemplary embodiments. Rather, the disclosed systems, methods and articles of manufacture are susceptible to modifications, enhancements and/or variations without departing from the spirit or scope of the present disclosure. Such modifications, enhancements and/or variations are expressly encompassed within the scope of the present invention.
Patent Application
20080054753
