Wheel substitutes for land vehicles – Endless belt having nonmetallic track or tread – Track formed of endless flexible belt
Reexamination Certificate
2002-07-22
2004-10-05
Thomas, Alexander S. (Department: 1772)
Wheel substitutes for land vehicles
Endless belt having nonmetallic track or tread
Track formed of endless flexible belt
C305S178000, C524S492000, C525S098000
Reexamination Certificate
active
06799815
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an endless vehicular rubber track designed for extreme cold temperature working environment. The invention particularly relates to such track having a combination of tread, supporting carcass and guide lug components of rubber compositions intended for such purpose.
BACKGROUND OF THE INVENTION
Endless rubber tractor tracks are increasingly being used for propelling various vehicles over the ground such as, for example, various tractors and other agricultural vehicles including, for example, combines and spreaders, as well as various earth moving machines.
Such tracks are conventionally designed for operation over a wide temperature range such as, for example, from −20° F. to 70° F., (−28° C. to 21° C.).
However, sometimes it is desired for such tracks to be used under rather extreme cold (e.g. arctic) conditions of temperatures lower than −50° F., (−45° C.), yet over a wide atmospheric service range of about −55° F. to about 90° F., (−48° C. to about 32° C.).
Accordingly, it is desired to provide a vehicular track with components comprised of alternate rubber compositions.
Endless rubber tracks, in general, are conventionally positioned over at least two wheels, normally a drive wheel for engaging an inner surface of the track, often guide lugs as a part of the carcass of the track and driving the track and at least one driven wheel to control the path of the track as it moves to propel the associated vehicle. The outer surface of the peripheral tread component of the track typically contains a plurality of spaced apart raised lugs designed for engaging the ground and assisting the propelling of the associated vehicle such as, for example, a tractor over the ground.
Such tread, in turn, is integral with and supported by a rubber carcass which, for said track, is intended to travel around said drive and driven wheels of an associated vehicle. Rubber guide lugs (which may also serve as drive lugs) are integral with and of a unitary rubber composition with the inner surface of such track carcass.
In practice, the tread of such rubber tracks provide a considerably wider footprint than conventional pneumatic tires and are, thereby, more adaptable to travel over various irregular surfaces such as, in that they offer better flotation over many and varied ground conditions than rubber tires. In addition, use of rubber tracks instead of pneumatic tires may be more useful for traveling over complex ground conditions under relatively extreme cold temperature conditions as compared to vehicles equipped with conventional pneumatic rubber tires.
Historically, the vehicular rubber track carcass component contains continuous steel cables molded into the rubber composition itself to add dimensional stability for the track.
As the rubber track is driven around the aforesaid wheels, it is subject to extensive contortional flexing and, thus, may be subject to tread crack initiation and propagation over time which may be of significant concern when operating the vehicle under very cold conditions.
Accordingly, it is desired that the rubber composition for the tread component and associated carcass and guide lug components of the track have appropriate resistance to flex fatigue, resistance to abrasion and durability under low temperature conditions.
For this description, the term “phr” relates to parts by weight of a material or ingredient per 100 parts by weight rubber.
For this description, the terms “elastomer” and “rubber” may be used interchangeably unless otherwise indicated, and the terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.
For this description, a glass transition temperature, or Tg, of a material, particularly an elastomer, may be determined by DSC technique, for which ASTM D3418 may be referred to.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, an endless rubber track designed to encompass at least one drive wheel and at least one driven wheel wherein said track is comprised of:
(A) an outer rubber tread component comprised of a plurality of spaced apart, raised lugs designed to be ground-contacting,
(B) a unitary
(1) rubber carcass component integral with, underlying and supporting said tread component, and
(2) a guide lug component comprised of a plurality of spaced apart rubber guide lugs positioned on and integral with the outer exposed surface of said carcass component, wherein said guide lugs are and designed to be engaged and/or guided by one or more of said drive and driven wheels, wherein
(a) said tread component is of a rubber composition comprised of, exclusive of elastomers having a Tg higher than −50° C. which comprises, based upon 100 parts by weight elastomers (phr),
(1) about 15 to about 40 phr of cis 1,4-polybutadiene elastomer having a Tg within a range of about −90° C. to about −115° C., and
(2) about 85 to about 60 phr of cis 1,4-polyisoprene rubber having a Tg within a range of about −70° C. to about 80° C.,
(3) about 38 to about 80 phr of reinforcing filler comprised of about 35 to about 65 phr of rubber reinforcing carbon black and about 3 to about 15 phr of aggregates of precipitated silica, and exclusive of a coupling agent having a moiety reactive with silanol groups on the surface of said silica and another moiety interactive with said elastomer(s),
(4) sulfur curative in a range of about 0.75 to about 1.75 phr and a sulfenamide sulfur cure accelerator,
(5) zero to about 10 phr, and preferably exclusive of, rubber processing oil selected from at least one of aromatic, naphthenic and paraffinic rubber processing oil and their mixtures, and wherein
(b) said unitary carcass and said guide lug components are of a unitary rubber composition, exclusive of elastomers having a Tg higher than −50° C., comprised of, based on parts by weight per 100 parts by weight rubber (phr):
(1) about 80 to about 100 phr, alternately about 85 to about 90 phr, of cis 1,4-polyisoprene natural rubber having a Tg within a range of about −70° C. to about −80° C., and
(2) zero to about 20 phr, alternately about 15 to about 10 phr of synthetic cis 1,4-polyisoprene rubber having a Tg within a range of about −70° C. to about −80° C.,
(3) about 38 to about 75 phr of reinforcing filler comprised of about 35 to about 60 phr of rubber reinforcing carbon black and about 3 to about 15 phr of aggregates of precipitated silica, and a coupling agent having a moiety reactive with silanol groups on the surface of said silica and another moiety interactive with said elastomer(s),
(4) sulfur curative in a range of about 0.75 to about 1.75 phr and a sulfenamide sulfur cure accelerator
(5) zero to about 10 phr, and preferably exclusive of, rubber processing oil selected from at least one of aromatic, naphthenic and paraffinic rubber processing oil and their mixtures,
(6) about 5 to about 10 phr of rubber plasticizer, other than an oil, and preferably a monomeric, synthetic rubber processor, having a freeze (melt) point (ASTM D1519) of lower than −45° C.
A significance of limiting the tread rubber composition of the tread component of said track to the cis 1,4-polybutadiene rubber and cis 1,4-polyisoprene rubber (natural rubber) to the exclusion of other elastomers having a Tg of higher than −50° C.
A significance of limiting the unitary carcass component and guide lug component rubber composition the natural cis 1,4-polyisoprene rubber and, optionally said synthetic cis 1,4-polyisoprene rubber to the exclusion of other elastomers having a Tg of higher than −50° C. is to promote very low temperature flexibility for the rubber composition.
It is to be appreciated that styrene/butadiene copolymer rubbers (SBR) may often typically have a Tg above −50° C., depending somewhat upon whether the SBR is derived from an organic solvent-based polymerization of the styrene and 1,3-butadiene monomers (S-SBR) or an aqueous emulsion polymerization thereof (E-SBR). It is also appreciated that such
Beery Ray Eugene
Krishnan Ram Murthy
Lukich Lewis Timothy
Rabatin Glenn Charles
Rodgers Michael Brendan
The Goodyear Tire & Rubber Company
Thomas Alexander S.
Young, Jr. Henry C.
LandOfFree
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