Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to the field
of solid lubricants.
Solid lubricants are being used more and more `
in modern lubricating technology in order to overcome
the increasing demands for improved properties, for
example, to avoid or minimize specific conditions at
friction points. Such solid lubricants are not only
being used in the common method of applying them in
powder form to a surface, but they are also being used
in oil-based lubricants and greases and as bonded coatings.
There have beeff instances when such solid
lubricants have been incorporated in plastics or metals
in order to maXe self-lubricating surfaces.
In addition to the now amiliar solid -
lubricants, molybdenum disulfide and graphite, a whole ;
series of wideIy varying chemical compounds consisting
of hydroxides, oxides, sulfides, fluorides and phosphates '
has been studied and utilized in the solid lubricant
technology.
Such known lubricants can be found, for instance, ;~
in U.S. Patent No. 3,377,279. Such solid lubricants are
described as graphite, sulfides of metals from Group II
of the periodic system of elements~ particularly zinc
sulfide and cadmium sulfide and inorganic fluorides such
as calcium fluoride and cryolite. Those solid lubricants
are then treated with lnorganic anions, the whole purpose `
of the treatment being to give enhanced adhesion of the
.
lubricant to the surface.
Essentially the same solid lubricants are
` 30 referred to again in U.S. Patent No. 3,453,209 as being
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useful lubricating materials for use with metal-forming
dies such as presses, forges and drop hammers. It is
noted that the composition consists of a solid lubricant
and a material which evolves gas under those operating ~`
conditions.
Finally, in U.S. Patent No. 3,808,130, essentially
the same solid lubricants are again set forth as part of
compositions including perfluoroalkylene polymers and -~
epoxy resins, which are useful in preparing self-lubricating
bearings and other machine elements. The object of that
,
invention is to produce large numbers of self-lubricating
parts with` excellent precision and low dimensional change. - -
In order to accomplisll this object, the U.S.
Patent No. 3,808,130 speaks of using compositions
which contain "... inorganic solid materials... of at ~
least one and preferably two solid lubricants." Thus, ~' `
it is known from such patent that solid lubricants !'~':"' ' ' ` ` ;''
can be used in conjunction with the perfluoroalkylene
polymer and epoxy resin in preparing self-lubricating
materials.
l~hat the 3,808,130 patent does not teach or ~ ~`
make obvious, however, is that certain combinations of ` -
solid lubricants in specific ratios, without the aid
of the perfluoroalkylene polymers, have synergistic ; :
lubricating effects which give high load carrying ~ -
capacities and reduced wear and friction.
It is, therefore, an object of this invention
to provide lubricant compositions which consist of certain ~ -
solid lubricants in specific ratios to give enhanced -~
lubricating properties which allow high load carrying
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capacities and reduced wear and friction on metal-to-metal
interfaces,
In connection with achieving such an object,
it has now been found that a combination of graphite,
zinc sulfides, calcium fluoride and optionally molybdenum
sulfide in specific weight ratios results in a surprising .
synergism in lubrication properties whereby exceptional
properties are obtained.
The solid lubricant composition of the instant : -
invention consists therefore of 20 to 70 percent by
weight of graphite, lS to 50 percent by weight of zinc
sulfide, 3 to 30 percent by weight of calcium fluoride
and 0 to S0 percent by weight of MoS2. Preferably, :~
the composition consists of 35 to 50 percent by weight ~-
of graphite, 20 to 40 percent by weight of zinc sulfide,
7 to 25 percent by weight of calcium fluoride and
10 to 30 percent by weight of molybdenum disulfide :: -
and, the components graphite, zinc sulfide and calcium :
fluoride, are present primarily in a weight ratio of
5 to 4 to 1. :~
: All of the materials employed in this composition . .
are standard articles of commerce and their methods of .
preparation are not considered material to this invention.
The compositions of this invention can be :~
prepared by any conventional means such as simply blending
the materials in a mixer or milling on a roll mill.
The compositions can be further treated to
render them useful for specific applications such as ~ ;
embedding the solid lubricants in curable binders such
as epoxy resins, silicone resins or phenolic resins :~
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in order to prepare bonded coatings and composites such :~
as brake linings and the like. Further, such combinations
can be carried in solvents and used as lacquers which
can be used as dips or sprays or can be brushed in place
which upon curing give lubricating films.
Greases can also be formulated from the basic ;~
solid lubricant combinations. Ordinary oil-based greases
such as lithium soap greases are an example~ -
It is within the scope of this invention to
include as optional ingredients those materials commonly
known and used in the lubricating industry such as ~;
viscosity regulators, corrosion inhibitors~ detergents,
emulsifiers and the like.
The invention will be described in greater
detail by way of the following examples which are not
to be considered as limiting the scope of the invention. ~;
Example 1 `~; -
'.. - :. .
An epoxy resin (prepared from bis(para-hydroxyphenyl)-
dimethylmethane and epichlorohydrin, epoxy equivalent
weight ca. 500) is filled with 80 percent by weight of
. . .
a solid lubricant combination of 50 percent by weight
graphite and 50 percent by weight of a varying mixture -
of zinc sulfide and calcium fluoride and is made into
cylindrical cans with an inside diameter of 25 mm., an
outside diameter of 30 mm. and a length of 25 mm. in a
known manner. The cans thus obtained are then subjected
to a wear test, the A. A. ~artel Lubrimeter (Schmiertechnik ~;
3, 184 ~1956)). The solid materials and solid lubricant `-
combinations used here and the test data obtained therefrom
are given in Table I. It can be seen that the
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three-component system of 50 percent graphite with the :~
remainder of varying quantities of zinc sulfide and .`
calcium fluoride acts synergistically, whereby the
best wear is obtained from a solid lubricant combination
of 50 percent by weight graphite, 40 percent by weight
zinc sulfide and 10 percent by weight calcium fluoride.
TABLE I .
% Graphite % ZnS % CaF2 % MoS2 Wear
0 0 11 .
0 6
0 8
~0 30 0 10
0Greater than 18 .:
0 50 0Greater than 18
Example 2 . .
The solid lubricant combinations were prepared
as shown in Table II
The above combinations and their pure individual
components are made into pastes each con~aining 60 percent
by weight solid lubricant combinations or individual solid
lubricant and 40 percent by weight oil having lubricating
oil viscosity, the pastes being given a uniform viscosity ;~ :
by adding 1 percent by weight of a thickener ~based on ~::
the silicon dioxide). The friction values of these pastes
are then determined on the LFW-4 testing machine ~see .
U.S. Patent No. 3,028,746) and the frictional force
an Almen-Wieland machine (Schmiertechnik 7, page 284 ~1970))
under a final load of 2000 kp. The solid lubricants used
for this example and the results obtained are noted on
~ Teble III which follows:
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TABLE III
~lid Lubricant Friction Friction Force in kp
Molybdenum `.`
Disulfide 0.05 243
Graphite 0.14 > 350
Zinc Sulfide 0.20 > 350 :. .
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Calcium Fluoride 0.18 > 350 : : :
Combination A ~ :~
(Example 2) 0.13 242 `
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Combination B i~
t~xample 2)0.13 262 ~ `~
Combination C
(Example 2)0,04 228
Combination D .`:
Example 2) 0.05 180 ~
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Example 3 . ~
Lithium soap greases (lithium-12-hydroxy stearate) .- : . :
are prepared using the solid lubricants and solid lubricant ..
combinations designated in Table IV in the percentages : :
given. The lubricity of these greases is then established - .
by evaluating the so-called load allowance in a four-ball
apparatus (DIN 51350) (ASTM D-2596-67T). The load .
allowance values can be seen in Table IV. ::~
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TABLE IV
Loads in the 4-Ball Apparatus
in kp at the Given Percentages
o Solid Lubricants in the
Grease
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Solid Lubricant 3 Wt. % 5 Wt. % 7 Wt, % `
Molybdenum ,~
Disulfide 210 220 190
Graphite 200 260 300
Zinc Sulfide 200 240 280
Calcium Fluoride 190 240 240
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Combination A
tExample 2) 260 360 420
Combination B
~Example 2) 260 340 440
Combination C
(Example 2) 280 360 420
Combination D
(Example 2) 260 320 340
ample 4 , `
Lubricant lacquers were prepared with the use
:.. ~ . . .
of the solid lubricants and solid lubricant combinations -
specifled ln Table V in a solvent dispersion which also ;
contained some curable organic resin. 20 percent solld
lubricant or solid lubricant combination was used.
The data obtained while determining the friction values "
by the Press Fit Method on the LFW-4 tes~ing machine as i `
:. -
described in Example 2 and the evaluation of the life
of the gliding lacquer film on the LFW-l testing machine
(ASTM D-2714) may be taken rom Table V.
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