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Metal Reinforced Plastic Pinion Gear

IP.com Disclosure Number: IPCOM000110482D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 55K

Publishing Venue

IBM

Related People

Hu, PY: AUTHOR [+2]

Abstract

A metallic pinion gear was fabricated utilizing the classical gear design criteria such as the involute profile, pitch diameter, etc., for proper gear to gear engagement. The metallic gear tooth profile, however, is altered and undersized so that a plastic coating can be applied over the gear tooth profile. The substrate gear tooth conforms to this criteria except in the tooth tip area, where an ice-cream cone-like shape was formed. It was found that the tip region is most likely to fail due to high stress concentration and much lesser material support. The ice-cream cone-shape profile, as shown, provides not only additional material support, but also prevents plastic flow and material breakaway at the tip.

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Metal Reinforced Plastic Pinion Gear

      A metallic pinion gear was fabricated utilizing the classical
gear design criteria such as the involute profile, pitch diameter,
etc., for proper gear to gear engagement.  The metallic gear tooth
profile, however, is altered and undersized so that a plastic coating
can be applied over the gear tooth profile.  The substrate gear tooth
conforms to this criteria except in the tooth tip area, where an
ice-cream cone-like shape was formed.  It was found that the tip
region is most likely to fail due to high stress concentration and
much lesser material support.  The ice-cream cone-shape profile, as
shown, provides not only additional material support, but also
prevents plastic flow and material breakaway at the tip.  While the
substrate tooth profile is being modified to be non-involute shape,
the external plastic overmold continues to have involute profile to
insure proper action.  The process to achieve this composite gear is
first to produce an undersized gear blank.  This gear blank is then
selectively cut in several places as shown in Figure 1 to insure that
the plastic material flows into these cavities to provide better
mechanical anchoring.  The metallic gear blank is then inserted into
an injection plastic mold.  This plastic mold has the involute
profile necessary for gearing action and engagement.  The most
effective plastic overmold material is polyurethane, although other
plastic material can be used as well w...