Note: Descriptions are shown in the official language in which they were submitted.
:~3~
One ~ay of malclng gaslcet~ for aut.omoti.ve appli.cations,
for example, is by a lamination technique ln which a piece of
steel s~leet oO06 inch thick i5 clad on both sides wi~h graphite
Eoil made f rom expanded graphite O 'rhe foil is bonded to the
steel and then gaskets are punched from this laminatlon~ The
foil forms compressible sides for the gasketO Such a procedure
is wasteful of the graphite foil due to the punched-out portions
tha~ mus~ b~ scrapped. The process also requires the ~oil ~o
be ~abrlcated first and then glued to the metal surface O It has
been suggested that the process could be simplified ~ld the waste
eliminated if the graphite could be applied as a paint to a pre-
punched metal gasket substrateO Paint having a body of ordinary
unexpanded graphite or carbon is known but is unsatisfactory for
: gaskets and other seals because it is not compress~ble, On the
other hand, attempts to make a paint from expanded vermifonm
graphite have be n unsuccessful heretofore, due to the extremely
; low density of that form of graphlte, which is approximately
.06 g/cc. The lightness of the graphite caused it to float on
the surface of the paint vehicle and not mix intimately with
the v~hicle. Extended mixlng with a mechanical stirrer over a
period of several hours failed to solve the problem, as did also
the application of varuum to release en~rapped air ~rom the vermi-
form graphiteO It also was found that the addition o varlous
wettin" agents had lit~le effect. Mechanlcal attritiorl, as in
a ball j~r, was eliminated from consideration because the huge
volume of vermiform graphite th~t would be required fcr a few
milliliters of paint would require a battery of ball jarsO
..
Furthennore, graphite particles ill a ball. jar terld to ag~lomerate
rath2r than disilltegraLe, and ball milllng compacts the ~raphite
instead of allo~ing lt to remaLn compresslbleO Consequently, all
a~temps heretofore ~o rnake a graphi~e paint suitable for coating
the metal substrates of gaslcets and other articles needing com- ,
; pressible surfaces have proved to be unsuccessfulO
It is among the objects o~ this invention to provide a
simple and inexpenslve method of making a graphite paint that is
compressible and suitable for coating metal gasket substrates
and the like. Another object is to provide gaskets that are
~ forned from metal substrates with compressible graphite coatings
: tha-t have been applied by paintingO
In accordance with this invention a high speed el ectric
blender is partially filled with a solution of a binder and a
solvent to form the paint vehicle. When the blender is set in
operation, vermiform graphite is added to th~ solution or paint
~ehicle slowly ~nough to be drawn down into ito The addition can
be made continuously, or in increments to prevent the light
graphite fr~m piling up on top of ~he solutionO The blender is
; 20 operated long enough to vigorously agi~a~e the graphite worms in
the solution until they have been subdivided into particles small
enough to be completely wRtted by the paint vehicle so that they
will disperse in itl but not somall as to deprive the particles
of their compressibili~y. A satisfactory paint requires ~he
graphite particles forming the paint body to be in the range of
abou~ 40 to 500 micronsO ~enerally~ operation of thle blender until
five to ten minutes after the addition o the last of ~he graphite
is sufficient to produce the paintO Enough graphil:e is added to
~he solution during this process to form a slurry having ~he con-
sistency of thick SOUp.
~o~
The blendin~ operation just described is distinguishecl
herein from mechanical stirring) in that in stirring there is no
appreciable redu~tion in th~ size of ~he ~e~liform graphite,
while blending requires particle size reduction simultaneously
with th~ mixingn Unless there i5 suitable size reductlon of the :~
graphite, the desired graphite paint cannot be produced because
the particles will not be wetted suffic-Lerltl~ by the paint
vehicle0 The method described herein was carried out by using
Cc, ~fà Je~ k )
a No. 700A Waring~Blender of one liter capacityO Operating with
a spindle speed of 8~00 revolutions per minute~ the particle siæe
of the varmiform graphite was ~educed so that all of it wvuld pass
a 60 mesh Tyler screen~ At a lower spindle speed of 3700 rpm, the
graphite particles also will become small enough to produce a
satisfactory paint, although the paint film or coating will have
a much coarser grain. The ~raphite particles produced at this -:~
lower speed will all pass a 32 mesh Tyler scre0n, but only about
a third of them will pass the 60 mesh scrPenO At splndle speeds
appreciably below 3700 rpm, particle size attritlon is not
sufficient to produce a useable paintO
Various organic binders may be used, such as polyimides,
silicones, phenolics, or inorganic binders such as silicates,
borates and phosphatesO The solvent chosen, ~long which are
alcohols, ketones, aldehydes, amides, hydrocarbons, chlorohydro-
carbons and water, will depend upon the nature of the binder
selectedO The proper combination of solvent and binder is well
known to tho se skilled in the art O
As the inverltion disclosed herein ls presently practiced, a
phenolic resin is used as the binder, wi~h acetone as the solventO
~ o~
phenolic resin is preferred as the binder~ especiall~ if the
gaskets are to be used at a relatively high temperature becaus~
it fonms a char that stays in placeO Acetone ls preferred as
the solvent because of its high solvent power, and because it
evaporates rapidly at room temperature~ A typical paint formula~
tion in accor~ance with this invention would be the following:
9O0 g vermifonm graphite
25 ml.phenolic resin (60% solids in alcohol)
300 ml acetone
It is to be understood that the above composltio~ is
sub~ject to wide variations in content, but lt is one of general
utility and may be applied effectively to a variety of substrates
such as metal, paper, cloth, asbestos, ceramics and the like to
produce gasketing material~
Gasket forms or subs~rates of ~he desired shape are
punched from sheets. If metal substrates are used, they prefer-
ably are sand-blasted to roughen their surfacesO These gaske~
substrates then are dipped into the graphite paint, or the paint
is applied to them by brushing or otherwise spreading it over the
surfaces of the substrates, A drying period of about one-half
hour at room temperature will release the acetone by evaporation.
A subsequent drying of about one-half hour at 350F will cure or
set the binder in order to bind the graphite particles to one
another and to the rough surfaces of the substrate.
Ater ~he b~nder has been cured, the coated product has
good handling properties and can wi~hstand mechanical abuseO
;
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.
~ s~
The continuous coating fo~necl as just descri~ed wil:l have a
pOrO~lS matte finish and be very compressible. When the gasket
is put into use ~nd cla~ped in place betweell two memb~rs, between
which it is to fonn a seal, the graphite coating will undergo
more than a 50fO reductlon in thickness when subject~d to a
pressure o one-half ton per square inchO Such a gasket has such
properties as compressibility, lubricity and high temperature
capability, and is cheaper to make than comparable gaskets known
heretoforeO
If an impermeable smooth and shiny surface ls desired for
a product, the coating can be rolled or pressed to produce it.
However, care is taken to only partially compress the graphite
coating if it is to be compressed further in use,
. . . .
