Note: Descriptions are shown in the official language in which they were submitted.
~2i;~
The invention relates to improved techniques of treat-
ing certain stee]s with certain solid lubricants to mitigate
boundary friction and wear of those steels in sliding contacts
and to increase resistance to corrosion.
Molybdenum disulfide (MoS2), for instance, is a well
known, versatile solid lubricant having a lattice layer crystal
structure. Inherent basal cleavage occurring within its atomic
structure results in low lamellar shear strength and contributes
to its superior anti-friction or lubricious properties. There is
evidence to show that this property is caused by Van der IJaals
type bonding between two molecular unit cells on the basal plane
connecting the six-fold symmetry of the respective layers com-
prising the crystal structure as a whole. It is precisely these
chemical bonds, relatively long in physical length, which cause
low lamellar shear strength and therefore low dry friction
measurement on sliding and rotating contact. Conversely, the
chemical bonding occurring in the crystal plane located at right
angles to the basal plane is more typical o~ the mono-valent
type, shorter in physical length and therefore many times
stronger. Recent studies show the hardness for the basal plane
as measured on the Vickers Scale to be 32 Kg./mm2 and that for
the crystal plane to be 900 Kg./mm2, the latter thus being
harder by a multiple of nearly 29. Such a difference in physical
measurements within a single unit crystal causes anisotropy, a
condition which permits implantation of molybdenum disulfide into
metal surfaces to be practical and achievable.
In some motor spring applications an inorganic film
containing MoS2 and bonded to the spring material has been
utilized to improve the torque consistency of such springs.
Motor springs so treated have proved extremely useful in various
mechanical time fuzes and in horological mechanisms of the
--1--
classic escapement types. Indeed, clocks with such springs have
sometimes been operated 300% longer than those w:ithout coated
springs before rewinding is required. The increased performance
in these instances is a product of the reduction in the kinetic
coef~icient of frlction between the spring leaves during the
unwinding process, that is to say, a reduction ln the "stick-
slip" phenomenon historically associated with main spring
applications
Application of films of MoS2 to various metallic
substrat~s is usual:Ly by spraying or dipping methods and subse-
quent drying andJor baking, or even by electroplating the
molybdenum directly to the substrate and then heat treating in an
atmosphere containing sulfur or sulfide gases. ~hatever the
technique, however, it is performed after the material has been
processed to finaL or finished size. It has been suggested that
transfer oE the MoS2 film to a metallic substrate in these
instances is primarily a mechanical process resulting in
(a) direct embedding of the solid MoS2 into a softer surface,
- tb) deposition of the solid MoS2 into surface depressions
generated in the substrate by an "abrasivet' action of the solid
MoS2 itself during movement between the substrate and an
opposing surface, andlor tc) deposition of ~he solid ~foS2 into
the depressions indigenous of the original surface finish and
hardness of the substrate. But whatever the case may be, and
however satisfactory and lasting these techniques may be for
certain applications, the results are not sa~isfactory in the
case of items subject to high surface wear. The MoS2 film,
essentially still only a surface film, simply does not endure in
these environments but is rather quickly removed or destroyed by
abrasion. Such high wear items as piston rings, bearings,
journals, valve stems, shafts, and ~he like, for instance, are
~3~
composed of various grades of high carbon or stainless steels and
though obviously many of them could profit from the low friction
characteristics and protection afforded by ~1oS2, especially
when other lubrication is at a minimum, no feasible way, so far
as is known, has emerged for treating them with MoS2 such that
the latter becomes a much more enduring part of the steel itself.
Cold drawrl wire for use in stranded wire constructions,
such as wire rope for lifting mechanisms, ship board cable
systems, aircraft control cable and the like, and for use in coil
springs such as compression, extension and torsion types, is also
typically manufactured from various hlgh carbon steel alloysO
The inished wire is furnished to the spring manufacturer, for
example, and the springs themselves are ~ormed by various opera-
tions including coiling, grinding, secondary forming, stress
relieving, plating and, in many instances, special packing.
Likewise, the wire for stranded wire constructions is also
shipped to a separate place for manufacture of the rope itself.
The wire for both springs and rope is produced by a combination
of cold working, annealing and final tempering operations to a
predetermined diameter and shipped on spools, reels or loose
wound coils.
Significant improvement in the performance o~ stranded
wire cables ought also to be achieved by a solid lubricant such
as MoS2 applied to the wire strands in view of earlier work
done by the Polymer Corporation of Reading, Pennsylvania, where
crane sheaves macle of nylon containing a fine dispersion of
MoS2 were manufactured and tested. The lifetime of wire cable
passing over the special sheaves was increased, in comparison to
that when using standard sheaves. Eventual failure was caused by
friction between individual strands in the wire cable.
~21:~8~5
Aircraft carrier arresting cables represent another
area of utility for a solid lubricant such as MoS2. Current
practice is to reduce friction and corrosion of such cables by
repeated applications of a barrier film, such as grease ~ut _he
grease is gradually removed from the cable during use. and causes
the flight deck to become slippery in critical places~ In adfll~
tion, the grease, being flammable, is a fire hazard, and ~ts
elimination would thus provide safer operating condi~ions.
Another carrier-related problem is corrosion of internal aircra~t
con~rol cables by sal~ air, and those too ought to ~e i~ipro-~red
both in longevity and corrosion resistance by such a lubric1nt.
In short, a wide range of products formed from medium
to high carbon and stainless steels ought to benefit greatly from
treatment by a solid lubricant such as MoS2 if only the endur-
ance of the treatment could be increased by making the lubricant
more a part of the steel itself. Not only would friction be
reduced but corrosion resistance increased as well in those
applications where corrosion is a problem that must be reckoned
with. These are thus the chief objects of the present invention.
The invention takes advantage of certain properties of
medium to high carbon and stainless steels when they are cold
worked in ordcr to bring them down to a predetermined finished
size. Here and in the appended claims by "cold working" is meant
operations such as drawing, forging, rolling and other standard
methods of cold working metal, and by "medium to high carbon and
stainless steels" are meant carbon steels, such as AISI-SAE Nos.
1035 to 1095 and AISI-SAE stainless Types 301, 302, 304, 316,
316L, 416, and the like, all of which ar~ "interstitial" in
nature or structure and typically used for high surface wear
applications. I~hen such steels are cold worked they tend, as is
well known, to "work hardened", whereupon they must be annealed
~%~
in order to relieve the dislocation of their crystal lattice
which the cold working has produced, the annealing being done at
each metal's "recrystallization" temperature. After annealing
the metal is then suitable for further cold working. Hence, in
many appllcations the cold working process involves a succession
of cold workings interspersed by a succession of annealings, the
number of each and their arrangement depending upon the extent to
which the metal must be reduced in cross sectional size, some-
times re~erred to as "breaking down" of the metal to ~inished
si2e.
A byproduct of the annealing operation is a phenomenon
called "carbide precipitation" owing to the interstitial nature
of the metals concerned. During cold working the metal substrate
forms macro~molecu]ar carbon clusters between asperities on the
metal's surface from which the heat of the annealing process
removes the carbon and thereby creates decarbonized voids on the
surface of the metal. These voids, not surprisingly, are more
pronounced in siæe at -the end of an annealing operation than they
are at the end of a subsequent cold working operation.
The essence of the invention, therefore, is the appli-
cation of a solid lubricant such as MoS2, for instance/ to the
metal after the final annealing operation but before the final
cold working operation, the final annealing operation in this
case in effect constituting a preparation of the metal for
deposit of the MoS2. At that time the surface hardness of the
metal is less than it is after final cold working and tempering.
Hence the final cold working, owing to the extreme pressure under
which it occurs, will effectively embed the MoS2 into the
micro-structure of the metal substrate. Furthermore, the
anisotrophlc properties of the MoS2 allow the latter better to
penetrate the voids than is possible when the MoS~ is applied
to the metal substrate after final cold working when the sub-
strate possesses a higher superficial hardness.
Typically, Mo is in micro-powder form which is sul-
onatecl to obtaln MoS2, also a powder. That is then sometimes
mixed with graphite in a liquid carrier such as perchlorethylene,
the graphite being added to improve lubricity at lower loads.
I~hen one form o~ the invention is practiced the MoS2 in the
foregoing state is further mixed ~ith an inorganic binding agent
such as sodium silicate. After the final annealing operation the
steel is coated, ln the manner hereafter described, with the
Eoregoing mixture and the perchlorethylene "flash evaporated"
before the final cold working operation. Where corrosion is not
a problem this manner o~ practicing the invention is satis-
factory. But in environments where the steel is open to corro-
sion when employec7 in various finished products, the graphite
tends to accelerate corrosion rather than to decrease it even
though the surface of the steel is somewhat decarburized by the
final annealing. In order to avoid that effect the invention is
practiced in another form in which graphite is omitted and an
organic based synthetic resin system is used as the binding agent
in place of sodium silicate. The system includes a corrosion
inhibiter in the form of a "redox" resin.
The latter are synthetic polymers having a highly
cross-linked hydro-carbon matrix with inherent reversible func-
tional groups attached, such as quinone-hydro-quinone, which are
al~ernately oxidi7.ed and reduced. In terms of corrosion inhibit-
ing these resins can be referred to as "election exchangers",
"redox ion exchangers" or simply redox resins. In fact rapidly
reacting MoS2 bonded films containing organic based binding
systems including redox resins have only comparatively re-
cently become commercially available. The corrosion inhibiting
--6--
principle is based UpOIl the slowing of the reaction rate in which
corrosion occurs. In the oxidation phase, as metallic components
ionize they attract anions and form a soluble salt or oxides,
causing erosion o~ ~he base metal. In the reduction phase
metallic cations are attracted toward cathodic cells that are
created or become present owing to the ambient environment. The
latter type of corrosion is typically termed galvanic corrosion.
I~hen redox resins are present and in intimate contact within the
surface interface, they act as solid electrolytes facilitating an
electrical balance, chemically speaking, and cause the rate at
which the various reactions occur to be slowed. Corrosion pro-
tection is af~orded the base alloy even in the absence of a
sacrificial ad~ition of anodic protection.
Since tungsten disulfide (WS2) and graphite (C) are
also solid lubricants, having lattice layer crystal structures
similar to ~loS2, it is believed and forecast that they too
could advantageously be included using the process of the in-
vention though to date no tests have yet been conducted to that
end. Furthermore, it is contemplated that antimony thioanti-
monate (Sb-SbS4) might be added to the MoS2, WS2 or C.
This is because recent studies have shown that certain complex
chalcogenides used in combination with solid lubricants, such as
~foS2, WS2 and C, have improved the wear properties of steel
in counter-conformal sliding contact under partial hydrodynamic
conditions in the presence of certain greases having those
lubricants as addi~ives. Among these chalcogenides are arsenic
thioantimonate and antimony thioantimonate. The first 9 unlike
the second, is suspected of being toxic and is therefore not
deemed suitable.
30Hence in its broad aspect the invention contemplates a
process of providing a lubricious sur~ace for medium to high
carbon and stainless steels for high wear applications wherein
a length of the steel is reduced from an initlal larger to
a final smaller cross-sectional size by one or more cold
working operations. A process of providiny a lubricious
surface for medium to high carbon and stainless steels for
hi~h wear applications wherein a length of the steel is reduced
from an initial larger to a final smaller cross-sectional
size by one or more cold workings. The process is carried
out by preparing the surface of the steel including annealing
the steel in order to form voids on the surface thereof, then
covering the surface of the steel by coating the same with
micrometer sized particles of at least one inorganic solid
lubricant, and then subsequently cold working the steel after
the coating to reduce the same to the final cross-sectional
size, the temperatures during -the coating and subsequent cold
working being below the oxidation temperature of the lubricant.
The invention will first be set forth in terms of
a partially predicted application of a solid lubricant to
the manufac-ture of piston ring material for internal combustion
en~ines.
Piston rings for that purpose are typically
fabricated from various high carbon steel alloys.
Vsually the material is furnished the ring manufacturer in
the form of flat strips of cross-sectional dimensions, for
example, of .61 mm by 2.70 mm in the case of material for
oil control rings, produced by a combination of cold working,
annealing and final tempering operations. The invention,
of course, would be practiced by the manufacturer of the strips
before the latter are shipped to the ring maker. Assume,
for example, a strip of the above dimensions in finished size
whose cross sectional area is thus 1.665 mm2. Assume further
that the interim cross-sectional area of the strip after
the penultimate cold working operation and the ultimate
--8--
annealing operation but before the final or ultimate cold working
operation is 4.645 mm2 whereby the latter operation accom-
plishes about a 65~ reduction in cross-sectional area.
Essentia]ly the invention may be practic~d in this
instance by coiling an interim size strip, after preparation by
final annealing, on a take-off drum providing a low back tension
on the strip and then recoiled on a suitable take-up drum spaced
from the former drum in a sometimes called "coil-to-coil" opera-
tion. Between the two drums i5 disposed a tank, which may be
open to the atmosphere, of perhaps 84 litre capacity and equipped
with a suitable stiring device. Into the tank is placed a mix-
ture of solid, micro-meter sized particles of the lubricant,
e.~, MoS2, graphite, a liquid carrier such as perchlorethylene
and an inorganic bonding agent such as sodium silicate, all more
or less at room temperature. Between the tank and the take-~lp
drum is placed a thermostatically controlled oven or furnace
capable of maintaining a temperature of about 260 C over a
distance of 2 linear metres. The strip from the take-off drum is
then led by suitable well known means through the mixture in the
tank~ which is agitated by the stirring device in order to keep
the MoS2 in suspension, from which i~ emerges "we~", and then
through the oven where the perchlorethylene is "flash evaporated"
in order to produce a dry bonded film of MoS2 on the strip, the
latter being finally recoiled on the takeup drum, all at the rate
of about 3.65 linear metres per minute. A 34 litre mi~ture con-
taining 3275 cc of solid MoS2, sodium silicate, and graphi~e in
the proportions of 71, 22 and 8, respectively, the balance being
perchlorethylene should result in ~ dry bonded film of MoS2 on
the strip of between .0025 and .005 mm thickness. The strip from
the take-up drum is next finally cold worked to its finished
cross-sectional dimension in the us~al manner and then tempered
12131~S
at about 200 C. The temperatures of the strip during the
deposit of the MoS2, the riddance of the carrier liquid and the
final cold working and tempering operations, should be kept below
the oxidation temperature of the MoS2 which is about 425-480
C Even so, the oxidation rate of MoS2 to MoO3 is quite slow
and studies have shown that MoS2 does not lose its lubricity at
those temperatures until 30% or so has been oxidized.
As a result the MoS2 is mechanically embedded or
"included" in the working surfaces of the piston ring material to
a greater extent than would be the case were the MoS2 applied
in the usual manner as a film after cold working to finished
size. This is borne out by a quantity of piston ring high carbon
compression ring steel, AlSl-SAE-C1075, in the form of cold
rolled strip 1.78 mm thick and sub-critically annealed for 5
hours at 649C in an argon atmosphere. The material was divided
into three specimens: the first was left without treatment; the
second had a .0051 mm thick film of MoS2 applied to it using
sodium silicate as a bonding agent; the third was given a brief
anneal in air at 649C and then a bonded film of MoS2 as in the
second specimen. The extra annealing or decarburization of the
third specimen before treatment was done in order to determine
what effect that would have on depth penetration with respect to
implantation of MoS2 into the micro-9tructure of the substrate.
All specimens were then returned to the mill and cold rolled to
.60 mm thickness, a reduction in cross-sectional area of about
65%.
Upon their return from the mill the second and third
specimens were then cut lengthwise at right angles to the direc-
tion of rolling or grain elongation to determine the amount of
MoS2 inclusion within the micro-structure of the substrate.
Observation of the cut specimens showed partial and total
-10-
mechanical inclusion of MoS2 in unusually large deposits. The
depth of the inclusion in the case of the second specimen was .02
mm while that of the third or decarburized specimen was .02~ mm.
Tlence it appeare(i that the clepth of the inclusion is ~ f~lnc~ion
o ~he depth oi lhe respective decarbur{zed zone9; that is to
say, the clegree of inclusion appears constant at about 55-60% of
the starting dep~h of the zones concerned for a given amount of
cold working. It was also concluded that annealing of the steel
before treatment produces a relatively soft ferritic transforma-
tion near the surface compared with the underlying pearlite and
therefore that ferritic layer Oll the surface of the substrate
lends itself to substrate embodiment by the implantation process
of the invention.
Friction tests performed on the first and third speci-
mens showed a reduction in friction by approximately 25~ in the
case of the third specimen compared with the first. This was
determined, briefly speaking, by mounting each specimen and two
strain gauges intermediate the ends of a lever pivoted at one end
and loaded by a weight at the other. Each specimen pressed upon
the peripheral surface of a disk of AlSl 4340 steel 73 mm in
diameter and 7.2 mm thick revolving at a constant 100 rpm. No
fluid lubrication was used between the specimens and the disc.
Output of the strain gauges were led through an amplifier to a
Brush Mark 220 strip chart recorder.
Wear tests were also conducted on the second and third
specimens using the above test apparatus by weighing the speci-
mens before and after in order to determine the loss of welght of
the specimens during the tests. The following results were
obtained, the weight loss values being averages of three to five
tests:
-11-
3~
Reduction of wear
Weight on specimen Average weight loss (mg) of specimen 3 vs.
(kg) Specimen 2 Specimen 3 specimen 2 (%~
2.5 2.1 1.5 29
~:lO m.irl. )
2.0 1.1 1.05 5
(10 min.)
1.25 1.15 0.77 33
(20 min.)
1.0 0.85 0.7~ $
(20 min.)
The data shows that the third specimen (that having the e~tra
ann~aling and hence decarb~lrization and thus a deeper implanta-
tion of MoS2) compar~d with the second specimen (that having
only the initial annealing) had 'less material loss for each of
the applied loads. The cumulative average material loss for the
third specimen was 19~ less than that for the second.
In another test, two plain carbon steel strips,
AlSl-1078, were annealed in air. One was then coated with a mix-
ture f M~2 and a bonding agent, sodium silicate in a liquidcarrier, dried, and reduced by cold working to.3.28 mm width and
.61 mm thickness. The other strip was cold worked to the same
dimension before being coated with the foregoing mixture. Both
strips were then mounted in epoxy so that their cross-sections
were visible and ground and polished using .05 micron alumina
powder. Precautions were taken to minimize edge rounding during
the polishing. Both samples were then viewed with incident light
in a metallurgical microscope at magnifications up to l,000x.
The first sample showed numerous inclusions of dark material into
the surface to typical depths of .0025 mm, while the second
sample showed no such inclusions.
Further wear tests were conducted using C1075 steel
specimens to compare untreated steel (I~plain steel"), steel
-12-
~L2~3~
coated with MoS2 hy spraying as in the prior art ("sprayed
steel"), ancl steel treated by the process of the invention in-
clllding the extra anneallng ("Badger steel"). Each specimen had
undergone a Einal cold working whlch reduced its cross-sectional
area by 65~, the cold worki.ng of the sprayed steel having been
done beEore app]:icat:ion of the MoS2 and that of the Badger
steel after the two annealings and the application of the MoS2.
Essentially the same test apparatus described above was used and
the surEaces of the specimens were loaded onto the steel disc
sufficiently to guarantee that boundary lubrication conditions
were present, producing a value of PV of equal to aro~md 80,000
lb-in. 2 ft min 1 This quantity represents a measure of how
much energy per urlit time (or power) is being absorbed by the
spccimen surfaces ln a counter-conforming mode of sliding contact
with the disc. The quantity P is the load per projected area,
and the quantity V is the relative velocity of the two surfaces.
This value of PV has been found to cause significant wear of un-
treated surfaces under boundary lubrication conditions. For each
test five examples of eac'n of the three specimens were fabricated
and were each weighed on a chemical balance capable of discrimi-
nation to four places of decimals of a gram. The test apparatus
was then run in each case at 100 rev/min, a direct load of 2.5 kg
was applied together with the requisite number of oil drops per
hour. The following table gives the weight of material removed
by wear as well as the rate of lubrication of the contacting
surfaces:
Type of Final Weight
Surface Initial After After After After
And Oi.l ~eight 1 hr 2 hr 3 hr 4 hr
Rate gms gms gms gms gms
___ __ ___ ___ __ _
l'lain _teel
8 drops/hr 0.46~5 0.~670 0.4585 0.4584
Sprayed Steel
60 drops/hr 0.4824 0.4757
8 drops/hr 0.4735 0.4714 0.4668 0.4507
Badger Steel
6n drops/hr 0.4799 0.4793
8 drops/hr 0.4917 0.4915 0.4914 0.49150.4915
Rate of Revolution = lOO rev/min
Surace Direct Load = 24.5 newton
Approximate Value of PV = 80,000 lb-in 2 ft min 1
No of Samples for Each Test = 5
It is clear from the table that under conditions of
boundary lubrication the wear rate of the Badger steel is sub-
stantially zero after the first hour's run, and its actual wear
rate is only one-tenth that of the sprayed steel. In addition,
in the case of the sprayed steel, wear appears to continue after
the first hour and its rate is approximately 50% greater than
that of the plain steel after 1 hour's run. After two hours run-
ning, the rate of wear increases and thence the sprayed steel has
approximately twice the wear rate of the plain steel~ Another
remarkable aspect is that the at the beginning of the runs the
width of the contact area between the specimens and the steel
L3~
disc of the test apparatus was .254 mm while at the conclusion of
the runs that widt~h in the case of the plain steel was 1.52l~ mm
but only .762 mm in the case of the Badger steel. ~lence the
con~.act area of the plain steel was twice that of the Badger
steel so that tlle pressure upon the latter was twice that upon
the former. There~ole the greatly improved wear rate of the
Bad~er steel was obtained even though the pressure upon it rose
to twice that upon the plain steel.
No essential change in the steel itsel~, from the
standpoints of hardness, strength, and the like, seems to occur
when treated by the process of the invention. The steel can
thereafter be fashioned into piston rings, for instance, in the
conventional manner but the typical operation of chrome plating
of the finished ring would be omitted. The customary differen-
tial is superficial hardness between the chrome plated ring and
the cylinder wall is thus reduced and thereby wear on the wall
itself is also diminished. At the same time wear on the ring is
reduced because its inherent lubrication supplements normal
liquid or hydrodynamic lubrication between the ring and the
cylinder wall. The lubricated ring better withstands high
operating loads, better operates for short periods with boundary
lubrication, better distributes local loads, and betters the wear
characteristics of the mating surfaces. This is especially
important adjacent top and bottom dead centers since the greatest
wear of a cylinder wall in an internal combustion engine has been
found to occur where piston direction changes and where the oil
film is unable to accumulate sufficient thickness to separate the
two opposing surfaces. This is because the zero velocity of the
piston at those two points means that the hydrodynamic require-
ment of relative velocity between opposing surfaces is not met atthese precise locations. The lubricated rings, on the other
-15-
~2~L3~
hand 9 provides supplemental lubrication at these points at these
crucial times, somethlng a chrome plated ring cannot do, as well
as over the ent:lre cylincler wall during the critical breakin
period of a new engitle.
The invention will next be set forth in terms of a pre-
dicted application o~ a solid lubricant to the manufacture of
cold drawn wire for use in springs and stranded wire con-
structions.
~ ssume, for example, wire having a finished diameter of
.71 mm or a cross-sectional area of .40 mm2, and that the
in~erim diameter of the wire after the penultimate cold working
operation and the ultimate annealing but `before the ultimate cold
working operation is about 1.90 mm or a cros~-sectional area of
2.84 mm2, whereby the latter operation accomplishes about an
85% reduction in cross- sectional area. Also assume that the
foregoing annealing was accomplished in the usual mamler in a
non-oxidizing atmosphere to achieve recrystalization and that a
subsequent anneallng operation is performed in a strand type
annealer at about 650 C for a flash type decarburiæation of
between 40 and 60 seconds duration, the latter operation broaden-
ing the decarburlzed zone to about .045 mm and thus optimizing
the surface for mechanical inclusion pursuant to the invention.
As before, the wire a~ter the latter annealing opera-
tion, may be coiled on a pay-off reel with which is appropriately
associated a take-up reel for a coil to-coil coating operation.
Between the two reels is disposed a refrigerated tank of perhaps
70 to 80 litre capacity into which is placed a mixture of solid,
micro-meter sized lubricant, e.g., MoS2, organic based binding
agents, such as phenolic-vinyl-resin or epoxy-vinyl-resin,
together with redox resins to act as corrosion inhibiting agents,
and a guick drying composite solvent or liquid carrier consisting
-16-
of 60% cellulose acetate, 30% xylene, and 10% methyl ethyl
ketone. The refrigeration of the tank is regulated to keep the
mixture at a tempcrature between 0 and 5 C owing to the vola-
tili~y of the solvent. Between the tank and the take-up reel is
also disposed a thermostatically controlled oven or Eurnace
capable of maintailling a temperature of 260 C over a distance of
2 linear metres. The wire from the pay-off reel is then led by
well known means through the mixture in the tank which is agi-
tflted by a suitable stirring device in order to keep the MoS2
in suspension. The wire then emerges from the tank "wet" and
into the oven where the solvent is "flash evaporated" in order to
leave a dry bonded film of MoS2 on the wire. The latter is
recoiled on the take-up reel at the rate of 3 to 3-1/2 linear
metres per minute, the rapid rate of reaction of the resins con-
cerned being essentlal because of the relatively immediate
recoiling of the wire after it has passed through the tank.
Finally, the wire is transferred to a suitable wire drawing in-
stallation and reduced in cross-sectional area, that is to say,
cold worked, to its previously mentioned finished diameter. Such
cold working in this case should be kept at temperatures below
about 315 C because the resins involved tend to decompose above
that point.
Wire so treated would have several advantages. For
instance, when used to manufacture coil springs, expensive post-
plating for corro.sion protection would become unnecessary, thus
eliminating the inherent problems of hydrogen embrittlement,
tangling of springs, and the absence of pla~ing between the
close-wound coils of extension springs. Furthermore, the wire
would retain improved duc~ility and toughness compared to hot
dipped galvanized wire because the brittle alloy between the zinc
and the steel interface would be eliminated. The same or similar
-17-
~3~
advantages would also accrue to such wire when employed in
various stranded wire construction, as previously mentioned. To
the extent the fi.nal cold working diminishes some of the corro-
si.on inhibiting ploperties achievecl by the invention, for added
protecti.on the w:i.re can be recoated with MoS2 by the previously
described prior art methocls after final colcl working.
The invention is also believed applicable to other high
wear components previously mentioned, such as bearings, journals,
shafts and so forth, on which it would be practiced in manners
analogous to those described in the cases of piston rings and
wire.
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