From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Extracts from a paper on the properties and performance of carbon brushes.
| Identifier | ExFiles\Box 50\5\ Scan141 | |
| Date | 2nd December 1922 | |
| X.4333 Typed 2.12.22. X.4333 - EXTRACTS FROM PAPER ON "CARBON-BRUSHES" - (HUNTER BROWN) (I.E.E.Journal Feb.1919.). Spec. resistance various from .003 to .0003w/cu." Loss due resistance, only 10-15% total brush loss, (or drop and friction loss.) Remainder due contact drop. Small addition Cu increases resis. Contact may be better. More Cu reduces to 5 x 10^-6 still lubricating. Low friction important. Especially high speed. Friction independent of ordinary temperatures. Current alters friction. Pressure alters it greatly. Vacuum effects - sticking. Air effects drop of friction. Contact drop 1.6 - 2.0 volts. Pressure lowers contact drop. [Graph 1 showing Air effects drop: Volts vs {J. Vickers} Amps, with axes labelled up to 2.5 volts and 80 amps respectively.] [Graph 2 showing Pressure lowering contact drop: Volts vs {J. Vickers} Pressure, with axes labelled up to 2.0 Volts and 10 lbs/sq" respectively.] Thermal conductivity. Large in graphite, less in Cu-graphite, down to carbon very small. Capping better if of insulation. Lighter, wear electrical, prevents current through spring. Copper plating causes currents direct from holder - wear. Mechanical arrangements must be good. Boxes should have 4 unbroken sides. Clearance .2 mm. circumferential and .3 axial or 1/4 of these amounts. | ||