Glass Banded Commutators
Glass band commutators are named for the glass bands that are used to retain the copper bars and mica segments. The bands are applied in two or more grooves that have been machined into outer diameter of the copper bars. The glass bands consist of an electrical grade tape comprised of high tensile strength parallel glass yarns bonded with thermosetting resins. The tape is applied under tension and cured in an oven.
One of the advantages to this type of commutator is that it can be retained in multiple locations over the entire length of the commutator bar. This results in greater stability for units with longer bars. A comparable v-bound commutator is only retained by the V’s on each end of the bar so it may not be adequate to provide stability in the middle of a long bar. A glass bound unit with long bars typically has bands spaced every four inches so it provides a more uniform method of retaining the copper bars and mica.
Glass band commutators can also be lighter than a comparable v-bound unit due to the fact that less steel is required. The steel on a glass band commutator generally consists of a barrel that is wrapped with insulation. The inner diameter of the copper bar and mica segment pack is machined so there is sufficient interference when it is mounted over the insulated steel barrel.
Depending on the design of the steel barrel, a glass band commutator can generally fit into a smaller profile than a v-bound commutator. This means the distance from the outer diameter of the shaft to the brush diameter of a glass band commutator can be smaller than that of a v-bound commutator.
Another advantage to glass band commutators is the copper bars are less likely to be moved or damaged from a bump. The inner diameter of the copper bar is supported by the barrel and barrel insulation and therefore makes it less likely that the copper bars will be deflected if the brush diameter is bumped.