U.S. patent application number 11/768180 was filed with the patent office on 2007-10-25 for tribological materials and structures and methods for making the same.
This patent application is currently assigned to Tri-Mack Plastics Manufacturing Corp.. Invention is credited to Edward J. SR. Mack, James P. Mack, Thomas P. Mack.
Application Number | 20070249506 11/768180 |
Document ID | / |
Family ID | 27397037 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070249506 |
Kind Code |
A1 |
Mack; Edward J. SR. ; et
al. |
October 25, 2007 |
TRIBOLOGICAL MATERIALS AND STRUCTURES AND METHODS FOR MAKING THE
SAME
Abstract
An article having a bearing surface with improved wear
characteristics is provided. The article may be formed from a
composition that includes a polymeric material, a lubricious and
reinforcing additive, and a solid lubricant. Methods for forming
the compositions and structures are also provided.
Inventors: |
Mack; Edward J. SR.;
(Bristol, RI) ; Mack; James P.; (Bristol, RI)
; Mack; Thomas P.; (Warren, RI) |
Correspondence
Address: |
EDWARDS ANGELL PALMER & DODGE LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
Tri-Mack Plastics Manufacturing
Corp.
Bristol
RI
02809
|
Family ID: |
27397037 |
Appl. No.: |
11/768180 |
Filed: |
June 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
09833755 |
Apr 11, 2001 |
7235514 |
|
|
11768180 |
Jun 25, 2007 |
|
|
|
60222107 |
Jul 28, 2000 |
|
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|
60222108 |
Jul 28, 2000 |
|
|
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Current U.S.
Class: |
508/100 |
Current CPC
Class: |
C08K 7/06 20130101; F16C
33/201 20130101; C08K 3/38 20130101; C08K 7/00 20130101 |
Class at
Publication: |
508/100 |
International
Class: |
F16C 13/00 20060101
F16C013/00 |
Claims
1. A plastic article having a bearing surface, comprising: a
polymeric matrix material; and a first additive that is a
lubricious reinforcing fiber having a thermal conductivity of at
least about 50 W/m.degree. K.
2. The plastic article of claim 1, wherein the first additive has a
tensile strength of at least about 200 KSI.
3. The plastic article of claim 1, wherein the first additive has a
tensile modulus of at least about 100 MSI.
4. The plastic article of claim 1, wherein the first additive has a
coefficient of thermal expansion of about -1.4 parts per
million/.degree. C.
5. (canceled)
6. The plastic article of claim 1, wherein the first additive has a
thermal conductivity ranging from about 200 to about 1000
W/m.degree. K.
7. (canceled)
8. The plastic article of claim 1, wherein the article comprises
from about 5 percent to about 70 percent by weight of the first
additive based on the total weight of the article.
9. The plastic article of claim 1, wherein the article comprises
from about 30 percent to about 60 percent by weight of the first
additive, based on the total weight of the article.
10. The plastic article of claim 1, wherein the article comprises
from about 35 percent to about 55 percent by weight of the first
additive, based on the total weight of the article.
11.-17. (canceled)
18. The plastic article of claim 1, wherein the polymeric matrix
material is selected from the group consisting of polyamideimide,
polyetherimide, polyimide, polyetheretherketone, polyphenylene
sulfide, liquid crystal polymer, and combinations thereof.
19. The plastic article of claim 1, wherein the lubricious
reinforcing fiber is selected from the group consisting of
Thermalgraph DKD fibers, Thermalgraph DKA fibers, Dialead K223HG
fibers, and combinations thereof.
20. The plastic article of claim 1, further comprising a second
additive that is lubricious.
21.-27. (canceled)
28. The plastic article of claim 20, wherein the article comprises
from about 2 percent to about 75 percent by weight of the first
additive and about 2 percent to about 75 percent by weight of the
second additive, based on the total weight of the article.
29. The plastic article of claim 20, wherein the article comprises
from about 20 percent to about 60 percent by weight of the first
additive and about 20 percent to about 60 percent by weight of the
second additive, based on the total weight of the article.
30. The plastic article of claim 29, wherein the article comprises
from about 15 percent to about 40 percent by weight of the first
additive and about 15 percent to about 40 percent by weight of the
second additive, based on the total weight of the article.
31. The plastic article of claim 20, wherein the polymeric matrix
material is selected from the group consisting of polyamideimide,
polyetherimide, polyimide, polyetheretherketone, polyphenylene
sulfide; liquid crystal polymer, and combinations thereof.
32. The plastic article of claim 20, wherein the first additive is
selected from the group consisting of Thermalgraph DKD fibers,
Thermalgraph DKA fibers, Dialead K223HG fibers, and combinations
thereof.
33. The plastic article of claim 20, wherein the second additive is
selected from the group consisting of boron nitride, carbon,
graphite, molybdenum disulfide, talc, tetrafluoroethylene, and
combinations thereof.
34. The plastic article of claim 20, wherein the plastic article
comprises about 60 percent by weight of the first additive, and
about 10 percent by weight of the second additive, based on the
total weight of the article.
35. The plastic article of claim 34, wherein the first additive is
DKD, the second additive is boron nitride platelets, and the
polymeric matrix material is selected from the group consisting of
polyamideimide, polyetherimide, polyimide, polyetheretherketone,
polyphenylene sulfide, liquid crystal polymer, and combinations
thereof.
36. The plastic article of claim 34, wherein the first additive is
DKD, the second additive is tetrafluoroethylene, and the polymeric
matrix material is selected from the group consisting of
polyamideimide, polyetherimide, polyimide, polyetheretherketone,
polyphenylene sulfide, liquid crystal polymer, and combinations
thereof.
37. A plastic article having a bearing surface, comprising: a
polymeric matrix material; and about 5 percent to about 75 percent
by weight of a first additive having a density of at least about
2.0 gm/cm.sup.3; wherein the plastic article has a wear factor of
less than about 200 under a load of about 200 psi and a velocity of
about 50 feet per minute.
38. The plastic article of claim 37, wherein the polymeric matrix
material is selected from the group consisting of polyamideimide,
polyetherimide, polyimide, polyetheretherketone, polyphenylene
sulfide, liquid crystal polymer, and combinations thereof.
39. The plastic article of claim 38, wherein a first additive is
selected from the group consisting of Thermalgraph DKD fibers,
Thermalgraph DKA fibers, Dialead K223HG fibers, and combinations
thereof.
40. A plastic article having a bearing surface, comprising: a
polymeric matrix material selected from the group consisting of
polyamideimide, polyetherimide, polyimide, polyetheretherketone,
polyphenylene sulfide, liquid crystal polymer, and combinations
thereof; and about 5 percent to about 75 percent by weight of a
first additive selected from the group consisting of Thermalgraph
DKD fibers, Thermalgraph DKA fibers, Dialead K223HG fibers, and
combinations thereof; wherein the plastic article has a wear factor
of less than about 200 under a load of about 200 psi and a velocity
of about 50 feet per minute.
41. A plastic article having a bearing surface, comprising: a
polymeric matrix material; about 2 percent to about 75 percent by
weight of a first additive having a density of at least about 2.0
gm/cm.sup.3; and about 2 percent to about 75 percent by weight of a
second additive, wherein the plastic article has a wear factor of
less than about 200 under a load of about 200 psi and a velocity of
about 50 feet per minute.
42. The plastic article of claim 41, wherein the polymeric matrix
material is selected from the group consisting of polyamideimide,
polyetherimide, polyimide, polyetheretherketone, polyphenylene
sulfide--liquid crystal polymer, and combinations thereof.
43. The plastic article of claim 42, wherein the first additive is
selected from the group consisting of Thermalgraph DKD fibers,
Thermalgraph DKA fibers, Dialead K223HG fibers, and combinations
thereof.
44. The plastic article of claim 43, wherein the second additive is
selected from the group consisting of boron nitride, carbon,
graphite, molybdenum disulfide, talc, tetrafluoroethylene, and
combinations thereof.
45.-82. (canceled)
83. A plastic article having a bearing surface, comprising: a
polymeric matrix material; and a first additive that is a
lubricious carbon fiber having a thermal conductivity of at least
about 50 W/m.degree. K.
84.-85. (canceled)
Description
RELATED CASES
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/833,755, filed Apr. 11, 2001, pending,
which claims the befit of priority under 35 U.S.C. .sctn.119(e) to
U.S. Provisional Patent Application Nos. 60/222,107 and 60/222,108,
both filed on Jul. 28, 2000. The contents of each of these
applications are incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The present application is related to tribological materials
and structures, and methods of making the same and in particular,
to plastic bearings and methods of making the same.
BACKGROUND AND RELATED ART
[0003] The field of tribology deals with the science of interacting
surfaces in relative motion. Tribology generally involves the study
of friction, wear, and lubrication in relation to such surfaces.
Tribological materials are generally characterized by a variety of
parameters including, inter alia, wear, load and velocity carrying
capacity, coefficient of friction, coefficient of expansion,
stiffness, and dimensional stability.
[0004] Early tribological materials used in applications where wear
resistance and low faction was desired in sliding interfaces were
generally metal such as brass, bronze, and other metal alloys, and
woods, especially hard woods. The limitations of these materials
for friction and wear applications are well known and include the
need for constant lubrication, heavy weight, rapid wear, high
expense of fabrication, and other problems. These problems drove
the development of plastic tribological materials for bearing
applications, which to a certain extent addressed some of these
limitations.
[0005] Plastic bearings are generally made by incorporating
additives such as fillers, reinforcement materials, and/or solid
lubricants to a polymeric material. The tribological and other
properties of such materials depend on the particular polymeric
matrix utilized as well as the particular fillers, reinforcements
and lubricants compounded with the polymeric matrix material.
[0006] Plastic bearings have replaced other materials in many
applications because they have high weight to strength ratios and
can be made self-lubricating, among other desirable
characteristics. Although plastic bearings are important in many
applications, their use has been limited in some instances. For
example, the use of plastic bearings in high performance
applications involving high loads or high velocities has been
limited because under such extreme conditions of load or velocity,
plastic bearings are generally prone to failure due to the high
frictional heat generated. The high frictional heat generated
causes softening and melting of the polymeric matrix material. In
addition, there are many applications in which plastic bearings
generate an unpleasant squeal, as well as excessive heat.
[0007] The "wear" of a material generally refers to the amount of
material removed from a bearing surface as a result of the relative
motion of the bearing surface against a surface with which the
bearing surface interacts. The wear of a material is generally
reported as a "wear factor" or "K-factor." As a relative measure of
the performance of materials under the same operating conditions,
K-factors have proven to be highly reliable.
[0008] The load and velocity bearing capability of a material is
generally considered that combination of load and speed at which
the coefficient of friction or the temperature of a bearing surface
fails to stabilize. As used herein, the term "PV limit" will be
used to denote the pressure-velocity relationship determined by the
combination of load and speed at which the coefficient of friction
or the temperature of a bearing surface fails to stabilize,
expressed by the product of the unit pressure P (psi) based upon
the projected bearing area and the linear shaft velocity V
(FPM).
[0009] Any improvement in the tribological properties of plastic
bearing is desirable.
SUMMARY
[0010] The compositions and articles of the present invention have
substantially and unexpectedly improved tribological
characteristics in comparison to other commercially available
plastic materials, including improved wear characteristics, reduced
coefficient of expansion, low temperature generation, reduced
K-factors, increased stiffness, and improved dimensional stability.
Moreover, it is possible to mold thicker shapes and to hold closer
molding tolerances using the compositions of the present invention,
in comparison to other plastic compositions.
[0011] One embodiment is directed to a plastic article having a
bearing surface. The article includes a polymeric matrix material
and a first additive that is a lubricious reinforcing fiber having
a thermal conductivity of at least about 50 W/m.degree. K. In some
embodiments, the article includes a second additive that is
preferably lubricious.
[0012] In another embodiment the article includes a polymeric
matrix material, and about 5 percent to about 75 percent by weight
of a first additive having a density of at least about 2.0
gm/cm.sup.3. In this embodiment, the plastic article has a wear
factor of less than about 200 under a load of about 200 psi and a
velocity of about 50 feet per minute.
[0013] In another embodiment the article includes a polymeric
matrix material selected from the group consisting of
polyamideimide, polyetherimide, polyimide, polyetheretherketone,
polyphenylene sulfide, liquid crystal polymer, and combinations
thereof and about 5 percent to about 75 percent by weight of a
first additive selected from the group consisting of Thermalgraph
DKD fibers, Thermalgraph DKA fibers, Dialead K223HG fibers, and
combinations thereof. In this embodiment, the plastic article has a
wear factor of less than about 200 under a load of about 200 psi
and a velocity of about 50 feet per minute.
[0014] In another embodiment the article includes a polymeric
matrix material, and about 2 percent to about 75 percent by weight
of a first additive having a density of at least about 2.0
gm/cm.sup.3, and about 2 percent to about 75 percent by weight of a
second additive. In this embodiment, the plastic article has a wear
factor of less than about 200 under a load of about 200 psi and a
velocity of about 50 feet per minute.
[0015] In another embodiment the article includes a polymeric
matrix material selected from the group consisting of
polyamideimide, polyetherimide, polyimide, polyetheretherketone,
polyphenylene sulfide, liquid crystal polymer, and combinations
thereof about 2 percent to about 75 percent by weight of a first
additive selected from the group consisting of Thermalgraph DKD
fibers, Thermalgraph DKA fibers, Dialead K223HG fibers, and
combinations thereof, about 2 percent to about 75 percent by weight
of a second additive selected from the group consisting of boron
nitride, carbon, graphite, molybdenum disulfide, talc,
tetrafluoroethylene, and combinations thereof. In this embodiment,
the plastic article has a wear factor of less than about 200 under
a load of about 200 psi and a velocity of about 50 feet per
minute.
[0016] In yet another embodiment the article includes a polymeric
matrix material, a lubricious reinforcing first additive, and a
lubricious second additive. In this embodiment, the article has a
wear factor of less than about 25 under a load of about 200 psi and
a velocity of about 50 feet per minute.
[0017] Another aspect is directed to a method of forming a bearing
composition. The method involves forming a solution of a polymeric
matrix material and a first additive, and evaporating the
solvent.
[0018] Another aspect is directed to an additive for a polymeric
matrix material containing a lubricious reinforcing first additive
and a lubricious second additive.
[0019] Another embodiment is directed to a plastic article having a
bearing surface. The article includes a polymeric matrix material
and a first additive that is a lubricious carbon fiber having a
thermal conductivity of at least about 50 W/m.degree. K.
[0020] Another embodiment is directed to a plastic article having a
bearing surface. The article includes a polymeric matrix material,
a first additive that is a lubricious carbon fiber having a thermal
conductivity of at least about 50 W/m.degree. K, and a lubricious
second additive.
[0021] Another embodiment is directed to a plastic article having a
bearing surface. The article includes a polymeric matrix material,
a first additive that is a lubricious carbon fiber having a thermal
conductivity of at least about 50 W/m.degree. K, and a lubricious
second additive selected from the group consisting of boron
nitride, carbon, graphite, molybdenum disulfide, talc,
tetrafluoroethylene, and combinations thereof.
[0022] The industries in which the articles of the present
invention may be used include aircraft, automotive, textiles,
computers, military, chemical, appliances, etc. Specific
applications include vane bushings in jet engines; valve seats in
high pressure chemical valves; picker finger in copiers and
printers; piston rings and valve guides in non lubricating air
compressors; compressor vanes in rotary compressors and vacuum
pumps; seals in automotive transmissions, especially trucks and
tractors; piston and seals in refrigeration equipment; components
in aviation flight control actuators; bearings in watt-hour meters;
components in missiles; bushings in textile weaving equipment;
chemical pumps; windshield wiper bushings; power steering units;
air break piston rings; splines; and components in small internal
combustion engines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] It should be understood that the drawings are provided for
the purpose of illustration only and are not intended to define the
limits of the invention. The foregoing and other objects and
advantages of the embodiments described herein will become apparent
with reference to the following detailed description when taken in
conjunction with the accompanying drawings in which:
[0024] FIG. 1A is a top view of a bearing test apparatus;
[0025] FIG. 1B is a cross-section through line 1B-1B of the test
apparatus shown in FIG. 1A;
[0026] FIG. 2 is a table (Table 1) listing the Limiting PV of
various plastic compositions under typical test conditions for
plastic bearings;
[0027] FIG. 3 is a table (Table 2) listing the wear properties of
various plastic compositions under typical test conditions for
plastic bearings;
[0028] FIG. 4 is a table (Table 3) listing the wear properties of
various plastic compositions at high PVs;
[0029] FIG. 5 is a table (Table 4) showing the comparative wear,
shaft temperature, and coefficient of friction of various plastic
compositions under extreme test conditions of high loads and low
speeds;
[0030] FIG. 6 is a table (Table 5) showing the relative thermal
conductivity of certain additives;
[0031] FIG. 7 is a table (Table 6) showing the wear, shaft
temperature, and coefficient of friction of compositions containing
the additives;
[0032] FIG. 8 is a table (Table 7) showing the characteristics of
various carbon fibers;
[0033] FIG. 9 is a table (Table 8) showing the wear, shaft
temperature, and friction of various compositions that include the
carbon fibers shown in Table 8; and
[0034] FIG. 10 is a table (Table 9) showing the comparative thermal
conductivities of a variety of compositions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The present invention involves the discovery that plastic
structures formed from compositions that include certain types of
additives provide substantially and unexpectedly improved
tribological properties such as low wear, low friction, low
temperature generation and high limiting PVs in comparison to other
plastic structures. Such structures provide exceptionally high
limiting PVs at extreme conditions of low pressure and high
velocity, as well as high pressure and low velocity. Preferably,
the present compositions and structures also provide a negative
coefficient of expansion, improved dimensional stability, and
greatly improved noise characteristics in comparison to other
plastic structures.
[0036] The present compositions are useful for producing plastic
structures such as, for example, bearings or articles with a
bearing surface that are subjected to relatively high loads,
relatively high speeds, or both. "Bearing," and "bearings," as used
herein, refers to any article(s) having a surface that interacts
with a surface in relative motion, for example, by sliding,
pivoting, oscillating, reciprocating, rotating, or the like.
Examples of such articles include, but are not limited to, sleeve
bearings, journal bearings, thrust washers, rub strips, bearing
pads, ball bearings, including the balls, valve seats, piston
rings, valve guides, compressor vanes, and seals, both stationary
and dynamic.
[0037] As discussed previously, a variety of materials may be added
to the polymeric matrix materials to provide or enhance the
tribological properties of the polymeric matrix material. The
selection of additives to improve tribological properties has been
and continues to be difficult, as an additive that provides or
enhances one desirable tribological property, such as lubricity,
may degrade another desirable characteristic, such as wear.
Although not wishing to be bound by any theory, it is theorized
that an additive that provides both lubricity and structural
reinforcement may contribute to the improved tribological
properties evident in the present compositions and structures.
[0038] According to one embodiment, the present structures and
compositions preferably include a continuous phase of at least one
polymeric material and a dispersed phase including a first additive
that provides both lubricity and structural reinforcement when
added to a polymeric material. "Continuous phase," as used herein,
refers to the major component of the composition and "dispersed
phase," as used herein, refers to the minor component of the
composition, which may or may not be uniformly dispersed in the
continuous phase. Generally, the major component is the polymeric
matrix material and the minor component is the additive(s).
[0039] For purposes of the present compositions and structures, any
material that provides both structural reinforcement and lubricity
to a polymeric matrix material to which it is added may be included
within the definition of "first additive." Generally, polymeric
matrix materials may be reinforced structurally by including
reinforcing agents in the polymeric matrix material and may be made
more lubricious by including certain lubricious materials, such as
solid lubricants, thermal insulators, or highly electronegative
polymeric materials such as tetrafluoroethylene. As used herein,
the term "thermal insulator" will refer to a material having a
thermal conductivity of less than about 0.5 W/m.degree. K.
Reinforcing agents are well known to those of ordinary skill in the
art, and may have a variety of shapes and sizes, including fibers.
For purposes of the present compositions and structures, as used
herein, a "lubricious" material means any material that when added
to a polymeric matrix material will improve the tribological
properties of the resulting plastic material by, for example,
decreasing the coefficient of friction, increasing the wear
resistance, generating less heat under high loads, and any
combination thereof.
[0040] Those of ordinary skill in the art will recognize that it is
not necessary for the lubricious component and the reinforcing
component of the additive to be a unitary structure. For example,
any reinforcing agent that has been coated with a lubricious
material may be considered useful as the first additive for the
present compositions and structures provided it improves the
tribological characteristics of the polymeric matrix material.
[0041] In preferred embodiments, the first additive may be a
lubricious reinforcing fiber. "Fiber," and "fibrous material," as
used herein, means a fundamental form of solid (often crystalline)
characterized by relatively high tenacity and an extremely high
ratio of length to diameter. Although preferred, the first
additives are not limited to fibrous materials.
[0042] Those of ordinary skill in the art will recognize that
lubricity has been and remains a material characteristic that is
difficult to quantify and/or qualify. Examples of suitable
lubricious materials include, but are not limited to, solid
lubricants, thermal insulators, or highly electronegative polymeric
materials such as tetrafluoroethylene. Examples of lubricious
materials include tetrafluoroethylene (TFE), molybdenum disulfide,
carbon, graphite, talc, and boron nitride, in any shape and in any
combination thereof, "Solid lubricant," as used herein, and as
generally used, means a material having a characteristic
crystalline habit which causes it to shear into thin, flat plates,
which readily slide over one another and thus produce an
antifriction or lubricating effect, for example, mica, graphite,
molybdenum disulfide, talc, and boron nitride. Such solid
lubricants may be useful as the lubricous component of the first
additives in some instances, but those of ordinary skill in the art
will recognize that when used alone, they generally do not provide
the greatly improved wear performance of the present compositions
and structures, nor do they always provide structural
reinforcement. Moreover, the first additives are not limited to
those that obtain their lubricity from solid lubricants.
[0043] Examples of materials that have been found suitable for use
as the first additive in the present compositions and structures
include, but are not limited to, materials having tensile strength
of greater than about 200 KSI, a tensile modulus of greater than
about 100 MSI, and a density of greater than about 2.0 gm/cm.sup.3.
In preferred embodiments, the first additives also have a thermal
conductivity (T.sub.c) of greater than about 400 W/m.degree. K in
the axial direction, and a coefficient of thermal expansion (CET)
of about -1.4 ppm/.degree. C.
[0044] One preferred material for use as the first additive may be
a graphitized pitch-based carbon fiber. The fibers may be
continuous, discontinuous, milled, chopped, and combinations
thereof. Generally, as the degree of graphitization of a carbon
fiber increases, so does the density and the thermal conductivity
of the carbon fiber. Pitch-based carbon fibers are preferred as the
first additive because they generally have a relatively higher
graphite content than polyacrylonitrile (PAN) carbon fibers and are
consequently more highly lubricious than PAN carbon fibers.
Pitch-based carbon fibers and methods of production are disclosed,
inter alia, in U.S. Pat. Nos. 5,552,098; 5,601,794; 5,612,015;
5,620,674; 5,631,086; 5,643,546; 5,654,059; 5,705,008; 5,721,308;
and 5,750,058. Examples of graph tined pitch-based carbon fibers
that have been found suitable in the present structures and
compositions include Dialead K 223HG and Dialead K 223HG LG
(hereinafter "HG" and "LG," respectively, both available from
Mitsubishi Chemical America) and Thermalgraph.RTM. DKD and DKA
(hereinafter "DKD" and "DKA," respectively, both available from
BPAmoco). These fibers are generally characterized by a relatively
high concentration of graphite crystals which are oriented axially
in the fibers.
[0045] The DKD fibers have a tensile strength of greater than about
200 KSI, a tensile modulus ranging from about 100 to about 135 MSI,
a density ranging from about 2.15 to about 2.25 gm/cm.sup.3, a
T.sub.c ranging from about 400 to about 700 W/m.degree. K, a carbon
assay of 99+ percent, and a CET of about -1.445 ppm/.degree. C. The
DKD fibers also have a diameter of about 10 microns and a length
distribution in which less than 20 percent of the fibers are less
than 100 microns and less than 20 percent of the fibers are greater
than 300 microns.
[0046] The DKA fibers have a tensile strength of greater than about
350 KSI, a tensile modulus ranging from about 130 to about 145 MSI,
a density ranging from about 2.15 to about 2.25 gm/cm.sup.3, a
T.sub.c ranging from about 700 to about 1100 W/m.degree. K, a
carbon assay of 99+ percent, and a CET of about -1.45 ppm/.degree.
C. The DKA fibers also have an average diameter of about 10 microns
and an average length of about 200 microns.
[0047] The HG and LG fibers have a tensile strength of greater than
about 450 KSI, a tensile modulus of greater than about 130 MSI, a
density of about 2.2 gm/cm.sup.3, a T.sub.c of about 540
W/m.degree. K, and an average diameter of about 7 microns. In
addition to the foregoing, the HG fibers have an average length of
about 300 microns; the LG fibers have an average length of about
6000 microns.
[0048] As shown above, the graphitized pitch-based carbon fibers
typically have relatively high T.sub.c in comparison to other
carbon fibers, including PAN carbon fibers, as a result of the
increased graphite content. The increased graphite content also
increases the T.sub.c of the plastic structures formed from
compositions including such fibers, which may be desirable in any
application in which the transfer of heat is important, as is the
case in many bearing applications. Thus, for applications in which
the dissipation of heat is important, the first additives
preferably have a T.sub.c of at least about 50 to about 1500
W/m.degree. K, more preferably about 200 to about 1000 W/m.degree.
K, and more preferably still about 400 to about 800 W/m.degree. K,
in the axial direction. Additives having a higher T.sub.c may be
used, but they typically become more expensive as the T.sub.c
increases due to processing costs. Moreover, additives having a
higher T.sub.c do not necessarily provide corresponding increases
in the wear performance of the present compositions and structures.
Examples of materials that may have relatively high lubricity and
relatively high T.sub.c include, but are not limited to, the
foregoing pitch-based carbon fibers, pitch-based graphitized carbon
fibers, boron nitride flakes and fibers, and any combinations
thereof.
[0049] There are no constraints on the type of polymeric material
that may be used in the present structures and compositions, other
than those related to practical considerations such as the
processing methods used for the compositions and/or the application
in which the plastic structure may be used. The polymeric matrix
materials suitable for use in the present compositions may be in
any form such as granules, pellets, and the like. Thus, any
polymeric matrix material may be used for the present compositions
and structures, whether thermoplastic or thermosetting. The
thermoplastic polymeric materials may be amorphous, crystalline,
semi-crystalline, and any combination thereof. Examples of
polymeric matrix materials that may be used in the present
structures and compositions include, but are not limited to,
acetals, acrylics, flouropolymers, ketone-based polymers, liquid
crystal polymers (LCP), phenolics, polyamides (nylons) (PA),
polyamideimide (PAI), polyarylate, polybutylene terephthalate
(PBT), polycarbonate (PC), polyetherimide (PEI), polyethylene (PE),
polyethylene naphthalate (PEN), polyethylene terephthalate (PET),
thermoplastic polyimide (TPI), polyphenylene sulfide (PPS),
polypropylene (PP), silicones, sulfone-based polymers, and
combinations thereof. As stated previously, the polymeric matrix
material may be a blend of at least two polymeric matrix
materials.
[0050] Many "commodity" polymeric materials that are generally not
suited for bearing applications may be improved when combined with
the foregoing additives. In addition, polymeric materials that may
be used for less critical bearing applications may be improved when
combined with the foregoing additives such that they would be
suitable for more critical bearing applications. Some polymeric
materials that have improved tribological properties when combined
with the foregoing additives include PAI, polysulfones, and
combinations of PEEK, PEI, PPS, TPI, and LCP.
[0051] For high performance bearing applications, it is preferred
that the polymeric matrix material may be selected from the group
of "engineering" polymers, which are generally relatively high
flow, thermoplastic polymers and combinations of polymers. Examples
of high flow, polymeric matrix materials include, but are not
limited to, nylons, acetals, polycarbonate, ABS, PPO/styrene,
polybutylene terephthalate, and combinations thereof.
[0052] Examples of polymeric matrix materials that have been found
suitable for the present compositions when used to form high
performance bearing structures include, but are not limited to,
polyetheretherketone (PEEK), polyetherimide (PEI), polyphenylene
sulfide (PPS), TPI, and LCP. Blends of TPI and LCP with other
polymeric materials have been found suitable as well.
[0053] The compositions and structures of the present embodiment
preferably include a sufficient amount of at least one of the first
additives, by weight, to provide, the desired tribological
properties for the application in which the structure may be used.
In theory, the upper limit of the first additive that may be
included in the composition is limited only by practical
considerations, such as the amount of polymeric matrix material
required to bind the material together, or the method of blending
the materials. Throughout this document, all percentages indicated
are by weight based on the total weight of the composition or
structure. Generally, compositions and structure containing at
least about 5 percent, by weight, of the first additive, have been
found to provide an improvement in at least one of the foregoing
characteristics in comparison to that of the polymer matrix without
the first additive. Preferably, the present compositions and
structures contain from at least about 5 percent to about 75
percent of the first additive, more preferably from at least about
30 percent to about 60 percent, and most preferably about 35
percent to about 55 of the first additive, by weight, based on the
total weight of the composition. Obtaining concentrations of the
first additive in percentages greater than about 40 to about 50
percent by weight has sometimes been problematic, as is well-known
to those of ordinary skill in the art. Suitable methods for
obtaining desired concentration levels, including concentrations
levels greater than about 40 percent to about 50 percent by weight,
are discussed in further detail below.
[0054] Thus, one embodiment is the provision of a plastic structure
that includes a polymeric matrix material and a lubricious
reinforcing additive, and a composition from which the plastic
structure may be formed.
[0055] The tribological properties of the present compositions and
structures may be further improved by the addition of a second
additive. The polymeric materials and first additives suitable for
use in the present embodiment are the same as those described
above. The second additive provides the compositions and structures
of the present embodiment with substantial improvements in a
variety of tribological properties including, but not limited to,
wear, friction resistance, temperature generation, and PV limits.
The substantial improvements achieved with the preferred
embodiments of the present invention have been surprising and
unexpected. Suitable materials for the second additive include, but
are not limited to, solid lubricants, thermal insulators, and
electronegative fluorinated polymeric materials such as Kevlar and
Teflon. Examples of the foregoing include tetrafluoroethylene
(TFE), molybdenum disulfide, carbon, graphite, talc, and boron
nitride, in any shape and in any combination thereof. Preferred
second additives include TFE powder and TFE fiber (both available
from DuPont Corporation), boron nitride (BN) powder (available from
Carborundum), BN platelets, BN flakes, graphite powder, graphite
flakes, and combinations thereof. Again, those of ordinary skill in
the art will recognize that some of the second additives may be
considered solid lubricants, but the second additives include any
lubricious material, in any shape or size.
[0056] In the present embodiment, the compositions and structures
preferably contain at least one polymeric material, from at least
about 2 percent to about 75 percent of the previously described
first additive, and from at least about 2 percent to about 75
percent of the second additive. The compositions and structures
more preferably contain about 20 percent to about 60 percent of the
first additive and about 20 percent to about 60 percent of the
second additive; and most preferably contain about 15 percent to
about 40 percent of the first additive and about 15 percent to
about 40 percent of the second additive.
[0057] For exemplary bearing applications, it has been found that a
composition or structure containing about 30 percent of at least
one polymeric matrix material, about 60 percent of a first
additive, and about 10 percent of a second additive, by weight,
based on the total weight of the composition, provides the most
desirable characteristics for use in, for example, high performance
bearing structures. A particularly preferred embodiment includes
about 30 percent PEEK, about 60 percent DKD, and about 10 percent
boron nitride platelets, by weight, based on the total weight of
the composition.
[0058] According to either embodiment, compositions containing the
preferred ranges for the additives provide bearing compositions and
structures with substantial improvements in all or most
tribological properties. Again, it is possible to tailor the
compositions and structures to maximize, for example, a specific
desired tribological property by selecting an additive(s) and
concentration range for the additive(s), which may not necessarily
fall within the foregoing preferred ranges. Tailoring the
compositions as desired may involve routine experimentation known
to those of ordinary skill in the art.
[0059] According to either embodiment, additional materials may
also be added during the blending stage to impart whatever
properties such materials normally would be expected to impart to
plastic materials. However, the amount of additional material that
may be added to the composition may be limited due to the
exceptionally high loading already achieved in the present
compositions in order to achieve the desired wear performance.
Examples of additional materials include flow rate enhancers,
reinforcing fibers, colorants, and the like.
[0060] Thus, one embodiment is the provision of a plastic structure
that includes a polymeric matrix material, a lubricious reinforcing
additive, a lubricious second additive, and a composition from
which the plastic structure may be formed.
[0061] In general, suitable blending techniques should be employed
to maintain the integrity of the additives while ensuring
homogeneity of the composition. Some fibrous materials,
particularly the DKA and DKD fibers, are unusually sensitive to
fiber break-down and present special problems in blending and
molding. Moreover, the wear of a composition increases with the
number of fiber ends contained in a composition and structure.
Thus, it may be important to minimize breakage of fibers to
minimize the number of fiber ends that are contained in a
composition. Minimizing fiber breakage may also contribute to
increased thermal conductivity, when the fibers are thermally
conductive. Therefore several blending methods have been used to
form the present compositions.
[0062] In addition to maintaining the integrity of the additives,
the present blending methods provide concentrations of additive
material(s) in a polymeric material that are substantially higher
than obtained using other methods. For example, it has been
generally difficult or impossible to make, using an extrusion
method, moldable compounds having concentrations of additive
material of greater than about 50 percent without adversely
affecting the characteristics of the final polymeric material. Most
likely this is because the wettability and dispersability of an
additive material in the melt stage of a polymeric material is less
than when the polymeric material is dissolved in a solvent. The
wettability and dispersability of the additive material depends on
the ability of the polymeric material to encapsulate and separate
individual particles of additive material. As the wettability and
dispersability of an additive material is increased, so is the
effectiveness of the additive material, especially when attempting
to increase the thermal conductivity of a polymeric material.
[0063] There are several methods which may be used to form useful
compositions of the polymeric material and the additive
material(s). One method may be particularly useful for polymeric
materials that may be obtained in fine grinds. The fine grinds may
be mixed in dry form at room temperature and tumbled to obtain a
fairly uniform mixture. Thereafter, it is generally desirable to
add the mixture to a pulverizing machine such as a hammer mill to
grind and further mix the resinous components to ensure
homogeneity. In practice, it has been found desirable to pass the
mixture through a hammer mill pulverizer having a screen with
apertures of about 1/8 inch diameter. The best results are
typically achieved when the mixture is passed through the hammer
mill at least once. Thereafter, the resulting dried polymeric
material may be injection molded in tubular sections for testing,
as described in further detail below.
[0064] Another method involves dissolving the polymeric material in
a suitable solvent and then adding the additive(s) to the solution.
The solution may be stirred, preferably very gently, until the
additive(s) are completely wetted out, and continued until the
solvent substantially evaporates. Evaporation of the solvent
results in a relatively thick suspension of the additive(s) in the
dissolved polymeric material. The suspension may be allowed to dry,
for example, overnight in an oven at a temperature greater than
ambient, for example, about 350 degrees Fahrenheit. Thereafter, the
resulting dried polymeric material may be granulated and processed
as desired.
[0065] Suitable solvents for use in the present method include
methylene chloride (available from Dow Chemical Corporation) and
N-methyl pyrrolidone (available from by BASF Corp). Both methylene
chloride and N-methyl pyrrolidone have excellent wetting
characteristics. Therefore, polymeric solutions of methylene
chloride and N-methylene pyrrolidone effectively disperse,
encapsulate, and separate individual particles of additive(s). In
this manner, the present blending method provides polymeric
materials with substantially higher additive concentrations than
other methods. The present solvent blending method may be used to
form compositions containing up to about 90 percent of the
additive(s) by weight, based on the total weight of the
composition.
[0066] Another method is a variation of the afore-mentioned solvent
method, and is useful for polymeric matrix materials that are not
soluble in ordinary solvents or may not be available in, for
example, fine grinds. Generally, it has been difficult or
impossible to blend large amounts of additive(s), especially
fibrous material, with dry blended granules. Therefore, the present
method solves the problem by forming a first solvent blend having a
high concentration of additive(s) (typically about 60 percent to
about 90 percent) from a polymeric matrix material that is
compatible with the desired polymeric matrix material and adding
the desired polymeric matrix material to the first solvent blend.
For example, PEI is soluble in methylene chloride and is compatible
with PI, LCP, PEEK, and PPS. Therefore, PEI may be selected as the
polymeric matrix material to make the concentrated solvent blend.
As described above, high concentrations of additive(s) may be
dispersed in the solution of the polymeric matrix and solvent. The
mixture then may be dried out and granulated. The granules can then
be blended with, for example, PI, PEEK, LCP, and/or PPS, or any
other desired polymeric matrix material. These blends of granules
can be easily fed into, for example, an injection molding machine,
which results in blending to the final compound.
[0067] Preferably, the concentration of additive(s) in the
concentrates may be at least about 80 percent, more preferably at
least about 85 percent, and more preferably still at least about 90
percent by weight. Preferred embodiments of the method provide
concentrates having about 90% by weight of the foregoing preferred
additive(s) materials.
[0068] An alternate blending method involves blending the polymeric
material with the additive(s) using a twin screw extruder, which is
well known to those of skill in the art. However, high sheer
stresses in the twin screw extruder, which are good for mixing, may
break down the length of the fibers. Therefore, in some instances,
one of the previously described methods may be desired for blending
the compositions. After extrusion, the solid polymeric material may
be broken and granulated for further downstream processing such as
injection molding processes. Thereafter, the resulting dried
polymeric material may be processed as desired according to the
intended application of the part.
[0069] The compositions, however obtained, are very useful and have
exceptional properties, including wear, when molded to form an
article having a bearing surface. This utility is substantially
greater than the utility of the polymeric matrix material alone and
substantially greater than other commercially available preblended
plastic materials.
Test Methods
[0070] Standard test methods are known for testing bearing
performance (see ASTM-3702, Thrust Washer Test). However, it has
been found that the industry standard test methods are generally
not stringent enough to predict the performance of bearing
materials under many actual operating conditions. Therefore, the
following test apparatus and methods were developed and were used
to evaluate the present structures and compositions.
[0071] A representative technique for preparing test bearings
involves preparing blanks by injection molding, followed by
machining the test bearings from the injection molded blanks. The
injection molding machine was a 28-ton Engle. The cavity molded a
blank that had an O.D. of 23/32 inches, an I.D. of 16/32, and a
length of 17/32. The molding cycles were varied based on the
polymeric matrix material and the amount of the additive(s).
Typical molding cycles used for the present compositions were
similar to those that would be used for each respective matrix
material. The only significant difference was that very high inject
and hold pressures were used to successfully mold parts from these
highly filled compounds. Injection pressures as high as about
20,000 psi were used, whereas injection pressures of about 10,000
are typical. Hold pressures were also as high as about 20,000 psi,
whereas about 8,000 psi is typical. All other parameters--barrel
zone, nozzle, mold temperatures, and injection speeds were as one
would expect for the polymeric matrix material. No back pressure
was used, and gates and runners were larger than normal to allow
the viscous compound to flow into the molds.
[0072] Using the foregoing technique, test bearings having the
following dimensions were formed from a variety of compositions, as
shown in the Examples below. O.D.=0.689(+0.002-0.000)inches
I.D.=0.504(+0.002-0.000)inches Length=0.500(+0.010-0.000)inches
Test Apparatus
[0073] FIGS. 1A and 1B, taken together, illustrate an exemplary
test apparatus 10 that was used to evaluate the present
compositions and structures as well as those that are commercially
available. Test apparatus 10 includes a cylindrical inner aluminum
housing 12 and a cylindrical outer aluminum housing 14, with a
cylindrical ball bearing assembly 16 disposed therebetween. A key
18 is connected to the inner housing 12 to prevent test bearings
from rotating in inner housing 12. The ball bearing assembly 16
includes two spaced apart inner and outer races 16a, 16b between
which a plurality of ball bearings 20 may be disposed for rotation
therein. Inner housing 12 has the following dimensions:
O.D.=2.000''(+0.002-0.000) I.D.=0.687(+0.001-0.000)
Length=0.500(+0.010-0.000)
[0074] A shaft 22 extends coaxially through inner housing 12 and is
supported by a motor (not illustrated). Shaft 22 includes a central
bore 24 into which a thermocouple (not illustrated) may be received
for measuring the temperature of shaft 22. Shaft 22 was a 1/2 inch
diameter mild steel shaft that was polished to a 16 finish and made
adjustably rotatable by means of pulleys (not illustrated)
connected to the motor. Shaft 22 may be attached to the motor in
any suitable manner. A drive mechanism (not illustrated), such as a
drive belt and pulleys, must be provided to accurately rotate shaft
22 at selected rotation rates in order to obtain the proper V
(ft/min) for the particular test being run.
[0075] Inner housing 12, ball bearing assembly 16, and outer
housing 14 are maintained in adjacent relation by a torque arm 26,
through which the frictional force generated by the test bearing
may be measured, as described below. Torque arm 26 includes an
upper arm 26a and a lower arm 26b. Two bores 28 extend through
upper arm 26a, inner housing 12, and lower arm 26b. Upper and lower
arms 26a,b of torque arm 26 are connected and maintained in
assembled relation by fasteners (not illustrated) that extend
through bores 28.
[0076] Test set-up involves inserting a test bearing 30 into inner
housing 12 as illustrated in FIGS. 1A and 1B, and mounting inner
housing 12 onto shaft 22, which is fixed to the motor. Key 18 is
then locked into inner housing 12 to prevent test bearing 30 from
rotating in inner housing 12. Inner housing 12 and test bearing 30
are then inserted into ball bearing assembly 16 within outer
housing 14. Upper and lower torque arms 26a,b are then fastened to
the assembly with fasteners extending through bores 28.
[0077] During operation, a load is applied to test bearing 30 at
"L" in the direction of the arrow "1" as shown in FIG. 1A. The load
may be applied pneumatically or with dead weights (not shown), or
any suitable method. The motor can now be started and the test
begun.
[0078] Torque arm 18 may then be used to measure frictional force,
as will be discussed below. A means of measuring the frictional
force at the torque arm, such as a strain gage type load cell, or a
force gauge is also needed but not illustrated in the drawing. A
force gauge or load cell (not illustrated) may be attached to
torque arm 26 at "F." Naturally, to resist the torque generated by
the test sample bearing friction, and to effectively measure this
frictional force, one end of the force gauge or load cell must be
connected to the torque arm, and the other end must be somehow
attached to solid ground, such as the lab bench. Of course, this
also has the effect of preventing the test sample bearing, inner
housing, and torque arm assembly from spinning freely. Thus, the
load cell or force gage measures the frictional force generated
through the torque arm.
[0079] During operation, the test bearing, inner housing, and
torque arm are free to rotate with the inner race of the ball
bearing assembly. The load is applied through the outer housing
which is pressed to the outer race of the ball bearing assembly.
The application of this load prevents the outer race of the ball
bearing assembly and the outer housing from rotating. Thus, the
inner race is free to rotate, along with the test bearing, inner
housing, and torque arm assembly. Consequently, all the frictional
force generated between the test bearing and the rotating shaft
during the test is transmitted through the torque arm, and is
resisted by the load cell or force gauge that is attached to the
torque arm at "F" in FIG. 1A as shown.
Bearing Wear
[0080] The test procedure for determining wear involved weighing
the test bearings and the inner aluminum housing before testing to
the nearest milligram, and determining the weight loss of the
bearing by weighing the bearing and the inner aluminum housing
after testing. The weight loss of the test bearing assembly was
then converted to volumetric units by relating it to the specific
gravity of the polymeric material from which it was formed. The
volume was then converted to 0.001'' of wear by dividing by the
projected area of 1/4 in.sup.2. The K-factor at 10,000 PV was
determined by the formula: K = Wear PVT ##EQU1##
Coefficient of Friction
[0081] The coefficient of friction was determined after the
frictional force was measured at the point where it was measured on
the torque arm. A correction factor was first applied to correct
for the multiplication of the frictional force through the torque
arm. The radial distance from the center of the shaft to the
outside surface of the shaft (the surface where the frictional
force is generated) is 0.250 inch. The length of the lever arm from
the center of the shaft to the point where the frictional force is
measured on the torque arm (as shown in FIG. 1) is 2.500 inches.
Therefore, the force measured at the point indicated on the torque
arm has to be multiplied by 10 to find the frictional force, where
it is generated between the shaft and the test sample bearing. Once
the frictional force generated by the test bearing is known, the
coefficient of friction can be calculated by dividing this
frictional force by the force (or load) that is applied to the
bearing.
Limiting Pressure-Velocity (LPV)
[0082] The load and velocity bearing capability of a material may
be expressed by the product of the unit pressure P (psi) based upon
projected bearing area and the linear shaft velocity V. (ft./min.).
The symbol PV will be used to denote this pressure-velocity
relationship. The limiting PV (LPV) of a composite is that
combination of load and speed when either the coefficient of
friction or the temperature at the bearing surface does not
stabilize. This increase in torque or temperature results in
bearing failure and/or excessive wear. It should be noted that this
test is a short-term test independent of wear rate. It is important
to note that the addition of fibrous reinforcement is required to
develop minimum wear at elevated temperatures.
LPV Based on Increasing Speed,
[0083] The PV limit based on speed of test bearings formed from
various compositions were measured using the device shown in FIG.
1. The load was set at 100 Psi, and the speed was increased in
increments of 100 feet/minute until the bearing failed, either by a
rapid increase in friction or by a rapid increase in temperature.
The test bearings were run at each PV level for about 1/2 hour
before the speed was increased to the next increment of 100 FPM.
Thermoplastic polymeric materials are generally prone to failure at
these conditions because the high frictional heat generated causes
softening and melting.
LPV Based on Increasing Pressure
[0084] The PV limit based on increasing pressure of test bearings
formed from various compositions were measured using the device
shown in FIG. 1. The pressure was increased pneumatically through
the air cylinder, or dead weights were added, until the bearing
failed, either by a rapid increase in temperature or by a rapid
increase in friction. The test bearings were run at each PV level
for about 1/2 hour before the speed was increased to the next
increment.
Temperature Generation
[0085] The shaft temperature was measured by inserting a
thermocouple, which was held in a separate adjustable device
directly into a hole in the shaft, and which extended immediately
below the bearing. The thermocouple did not actually touch the
walls of the shaft.
[0086] The present invention will be further illustrated by the
following examples, which are intended to be illustrative in nature
and are not to be considered as limiting the scope of the
invention.
WORKING EXAMPLES
Example 1
[0087] A variety of plastic compositions were formed from a variety
of polymeric matrix materials, including high performance bearing
polymeric matrix materials. Test bearings were formed from the
compositions, according to the previously described method. The
ratios of materials in the compositions, as well as the blending
methods by which the compositions were formed, where applicable,
are shown in the Tables (FIGS. 2-9).
[0088] Test bearings were also formed from a variety of
commercially available plastic materials, which are also shown in
the Tables. The commercially available materials are listed as
"Commercially Available Cometetive Materials (PreBlended)." The
types and concentration of any additives in the commercial
materials are also shown in the tables for comparative purposes.
All information concerning the commercial compounds was obtained
from the manufacturer of the material.
[0089] Several tests were performed on the test bearings, including
the limiting PV based on speed; the limiting PV based on increasing
pressure; wear; temperature generation; and coefficient of
friction. The test bearings were tested under typical industry
standards as well as under extreme conditions for bearing
applications. The test type, test conditions, and test results are
also shown in the Tables. Those tests that exceeded the capacity of
the tester are indicated by a plus (+) sign.
Table 1
[0090] Table 1 (FIG. 2) shows the results of testing the limiting
PV based on increasing velocity at 100 psi and the limiting PV
based on increasing pressure at 25 feet/minute.
[0091] Test bearings formed from compositions having a PEI matrix
polymer, DKD, and Teflon fiber generally provided higher PV limits
than test bearings formed from compositions having a PEI matrix
polymer, DKD, and Teflon powder.
[0092] Compositions of polymeric matrix material in combination
with only DKD or DKA typically required higher concentrations than
compositions containing DKD or DKA in combination with Teflon or
boron nitride in order to achieve comparable PV limits.
[0093] Compositions formed using the solvent blending method
generally provided higher limiting PVs than compositions formed
using the dry blending method.
[0094] Adding a second additive to compositions containing DKA or
DKD provided the highest limiting PVs. Test bearings containing DKD
in combination with a second additive, such as Teflon.RTM. fiber or
boron nitride, had the highest limiting PVs.
[0095] Overall, the test results show that all of the present
compositions had substantially higher limiting PVs than other
commercially available plastic materials.
Table 2
[0096] Table 2 (FIG. 3) shows the results of testing the wear (K),
shaft temperature, and coefficient of friction of test bearings at
10,000 PV and at three variations of pressure and velocity: 10,000
PV at 200 psi.times.50 feet/minute; 100 psi.times.100 feet/minute;
and 50 psi.times.200 feet/minute. These are standard wear
conditions for high performance materials. The test results are
shown in Table 2.
[0097] The test results show that the present compositions and
structures provided substantially improved wear, temperature, and
friction resistance than other commercially available materials.
The test results also show that the method of blending the
compositions significantly affected the properties tested.
Table 3
[0098] Table 3 (FIG. 4) show the results of testing the wear (K),
shaft temperature, and coefficient of friction of test bearings
under extreme PV conditions (i.e. at high PV values). These tests
were not run in the manner of PV limit where the bearing is run by
increasing velocity in thirty-minute intervals. Rather, PV was
increased in separate 24 hour tests (with the exception of the
10,000 PV test) by holding pressure constant at 200 psi while
increasing the velocity. Thus, the 10,000 PV test was run for one
hundred (100) hours, after which the test bearing was removed from
the test apparatus, cleaned and weighed, and a new test bearing
installed. Thereafter, the 20,000 PV was then run for twenty-four
hours (24), after which the test bearing was removed from the test
apparatus, cleaned and weighed, and another new test bearing
installed, which was run at 30,000 PV for twenty-four hours (24).
This sequence was repeated up to the 100,000 PV test, with each of
the remaining tests being run for run for twenty-four hours
(24).
[0099] Compositions having the best wear properties using PEI as
the matrix material were PEEK/DKD/UMHW polysiloxane (28/70/2) and
PEI/DKD/BN (30/60/10).
[0100] Compositions having the best wear properties using PEEK as
the matrix material were PEEK/DKD/CAPOW L38/H (29/70/1) and
PEEK/DKD/BN (50/25/25). Adding siloxane improved the composition,
as shown by a comparison of the PEEK compositions including 25% DKD
and 25% Boron Nitride.
[0101] Compositions having the best wear properties using PPS as
the matrix material were PPS/DKD/POLYSILOXANE (28/70/2) and
PPS/DKD/graphite (30/10/60). Overall, the test results show that
all of the present compositions provided significantly improved
wear properties in comparison to other commercially available
materials.
Table 4
[0102] Table 4 (FIG. 5) shows the comparative results of the wear
(K), shaft temperature, and coefficient of friction of test
bearings under extreme conditions of high loads and low speeds. The
tests were performed at a pressure of 2,000 Psi and a velocity of
25 feet/minute. As in the previous table, the failure point was
measured by the melting of the plastic, and extremely high wear was
indicated by debris, extremely high temperature, or extremely high
friction. The tests were run for twenty-four (24) hours.
[0103] The test results showed that all of the commercially
available preblended compositions failed under these extreme
conditions, whereas all of the present compositions survived. The
best PEI matrix composition was the PEI/DKD/DC4-7105 (28/70/2).
There was not any significant difference between any of the present
compositions using the PEEK matrix. Compositions using a PPS matrix
and DKD showed a significant improvement as the concentration of
DKD increased.
[0104] Overall, the test results shown in Table 4 again showed that
all of the present compositions provided significantly improved
wear properties in comparison to other commercially available
materials.
Comparative Example A
[0105] A variety of additives may be added to a polymeric matrix
material to enhance various characteristics of the plastic material
formed from the polymeric matrix material. The thermal conductivity
of a variety of some well-known additives is shown in Table 5 (FIG.
6).
[0106] To illustrate some of the difficulty in selecting an
additive to provide improved wear characteristics in a polymeric
matrix material, a variety of compositions were formed using
various thermally conductive additives. The ratios of materials in
the compositions are shown in Table 6 (FIG. 7). The compositions
were blended using one of the previously described methods, which
is also indicated in Table 6. Test bearings were formed from the
compositions, using the previously described method. The wear,
temperature generation, and coefficient of friction of the test
bearings were tested according to the foregoing methods.
[0107] The data clearly show that the addition of a thermally
conductive filler or a solid lubricant to a polymeric matrix does
not necessarily result in good wear properties. The data also shows
that the addition of a thermally conductive filler and a solid
lubricant to a polymeric matrix material does not necessarily
result in good wear properties.
[0108] Thus, the results of the tests show that the wear properties
of a composition cannot be predicted solely on the basis of the
thermal conductivity of a material added to a polymeric matrix
material. This confirms the unexpected and surprising nature of the
results provided by the present compositions and structures.
Comparative Example B
[0109] A variety of compositions were formed using various PAN and
Pitch carbon fiber materials. The characteristics of the fibers are
shown in Table 7 (FIG. 8). The ratios of materials used in the
compositions are shown in Table 8 (FIG. 9). The compositions were
blended using one of the previously described methods, which is
also indicated in Table 8.
[0110] The tests results show that the DKD and Dialead fibers
provided superior wear characteristics in comparison to other PAN
and Pitch carbon fibers, and that the wear properties of the DKD
and Dialead fibers are maintained over a wide variation in
concentration and in many different types of plastic
compositions.
[0111] The data also show that the DKD fibers, at identical
concentrations, provided greatly improved wear performance in
comparison to PAN fibers.
[0112] Pitch-based carbon fibers having thermal conductivities in
the same range, such as the Dialead, provided similar results to
the DKD fibers. Pitch-based carbon fibers with lower thermal
conductivities, such as the VMX-24 fibers, did not provide the
degree of improvement in wear characteristics as the DKD and
Dialead fibers. Because the thermal conductivity generally
indicates the degree of graphitization of the carbon fiber, and
consequently the degree of lubricity of the fiber, this confirms
that structural fibers having relatively high lubricity provide the
unexpected wear performance observed in the present compositions
and structures.
[0113] The results show that there is not a direct correlation
between wear and thermal conductivity. Without wishing to be bound
by any theory, it is believed that the most important contributing
factor to the wear improvements of the present compositions is due
to the degree of graphitization and consequently increased
lubricity of the fibers, rather than the thermal conductivity of
the fibers. The DKA fibers have slightly higher density and
significantly higher thermal conductivity than either the DKD or
Dialead fibers, and the VMX-24, but they do not provide
significantly higher wear characteristics than the DKD fibers. This
may be confirmed by comparing the wear performance of compositions
containing DKA, DKD, Dialead K 223HG, and VMX-24 fibers.
[0114] The results of the tests show that the K-factor of a
composition cannot necessarily be predicted on the sole basis of
the thermal conductivity of a material added to a polymeric matrix
material. The excellent wear results provided by the DKD and
Dialead K 223HG carbon fibers, especially at high speeds and high
loads, may be due to a combination of thermal conductivity, the
fibrous nature of the filler, the graphite content of the filler,
the low coefficient of expansion of the filler, and the
compatibility with the matrix material.
Comparative Example C
[0115] The Coefficient of Thermal Conductivity of a variety of
compositions was tested using ASTM E-1461-92 "Thermal Diffusivity
of Solids by Flash Method." The ratios of materials used in the
compositions is shown in Table 9 (FIG. 10), along with the test
results.
[0116] The results of the tests show that the thermal conductivity
of the present compositions and structures generally fall within
the range of less than about 10 W/m.degree. K.
[0117] Although particular embodiments of the invention have been
described in detail for purposes of illustration, various changes
and modifications may be made without departing from the scope and
spirit of the invention. All combinations and permutations of the
compositions and methods are available for practice in various
applications as the need arises. For example, the compositions and
methods of the invention may be applied to processes that are
presently not practically feasible. Accordingly, the invention is
not to be limited except as by the appended claims.
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