CA1056660A - Metal substrate with compressible graphite coating and method of making it - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A paint formed from a slurry of resin and solvent and solvent-wetted particles of vermiform graphite is applied to a substrate to form a coating thereon, which is then dried to release the solvent, followed by curing the resin to bind the graphite particles to one another and to the substrate, whereby a compressible coating is formed.

Description

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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

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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.

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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

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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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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, . . . .

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of forming a compressible coating on a substrate, comprising applying to a substrate a coating formed from a slurry of resin and solvent and solvent-wetted particles subdivided from vermiform graphite, drying the coating to re-lease the solvent, and curing the resin to bind said particles to one another and the substrate to form a coating with a matte finish.

2. The method recited in claim 1, including first forming said slurry by feeding vermiform graphite to a solution of thermosetting resin and solvent and simultaneously vigorously agitating the solution to reduce the vermiform graphite to parti-cles small enough to be completely wetted by the solvent.

3. The method recited in claim 1, including the addi-tional step of compressing the coating sufficiently to provide it with a smooth and shiny surface but not enough to fully compress the coating.

4. The method recited in claim 1, including forming the substrate into the shape of a gasket before applying said coating.

5. The method recited in claim 4, in which said sub-strate is metal, and including the step of sand-blasting the metal substrate to roughen its coating-receiving surface before the coating is applied.