U.S. patent number 3,723,165 [Application Number 05/186,492] was granted by the patent office on 1973-03-27 for mixed metal and high-temperature plastic flame spray powder and method of flame spraying same.
This patent grant is currently assigned to Metco, Inc.. Invention is credited to George J. Durmann, Frank N. Longo.
United States Patent |
3,723,165 |
Longo , et al. |
March 27, 1973 |
MIXED METAL AND HIGH-TEMPERATURE PLASTIC FLAME SPRAY POWDER AND
METHOD OF FLAME SPRAYING SAME
Abstract
The flame spraying of high temperature plastic powder as for
example polyimides, polyamide-polyimides, polyester imides, or
aromatic polyester high temperature plastics in admixture with a
flame spray metal powder as for example aluminum alloy, nickel,
copper, bronze, babbitt or stainless steel flame spray powder.
Inventors: |
Longo; Frank N. (East
Northport, L.I., NY), Durmann; George J. (Farmingdale, L.I.,
NY) |
Assignee: |
Metco, Inc. (Westbury, L.I.,
NY)
|
Family
ID: |
22685170 |
Appl.
No.: |
05/186,492 |
Filed: |
October 4, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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16247 |
Mar 3, 1970 |
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Current U.S.
Class: |
427/447; 75/252;
427/427; 427/452; 427/456; 277/922; 277/946 |
Current CPC
Class: |
B05D
1/10 (20130101); C23C 4/04 (20130101); B05D
2508/00 (20130101); B05D 2401/32 (20130101); B05D
2505/50 (20130101); B05D 2505/00 (20130101); Y10S
277/922 (20130101); Y10S 277/946 (20130101); B05D
2601/20 (20130101) |
Current International
Class: |
C23C
4/04 (20060101); B05D 1/08 (20060101); B05D
1/10 (20060101); B44d 001/097 (); B05b
007/22 () |
Field of
Search: |
;117/93.1PF,105,105.1,105.2 ;106/1 ;260/47C,841,65 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leavitt; Alfred L.
Assistant Examiner: Newsome; John H.
Parent Case Text
This application is a continuation-in-part of copending application
Ser. No. 16,247 filed Mar. 3, 1970 now abandoned.
Claims
What is claimed is:
1. A process for flame spraying high temperature plastic powder
which comprises heating a mixture of the plastic powder and at
least about 5 - 99 percent by weight of a flame spray metal powder
to a temperature sufficient to substantially melt the metal powder
and surface heat soften the high temperature plastic, said plastic
powder having a particle size between about -170 and +325 mesh and
said metal powder having a particle size between about -325 mesh
and +10 microns, the particle sizes of said plastic and metal
powders being selected relative to each other such that the metal
is melted but the plastic is only surface softened and propelling
the thus heated particles onto a surface, forming a coating.
2. Process according to claim 1, in which the particles are heated
in a plasma flame.
3. Process according to claim 1, in which said high temperature
plastic is an aromatic polyester.
4. Process according to claim 3, in which said high temperature
plastic is a poly (paraoxybenzoyl) ester.
5. Process according to claim 4, in which said metal powder is an
aluminum powder.
6. Process according to claim 5, in which said aluminum powder is
an aluminum silicon alloy containing about 5 to 30 percent
silicon.
7. Process according to claim 1, in which said metal powder is
present in an amount of about 40 to 80 percent by weight.
8. Process according to claim 7, in which said metal powder is
present in an amount of about 60 percent by weight.
9. Process according to claim 1, in which said mixture is formed of
individual composite particles containing both said plastic and
metal.
10. A flame spray powder for use in the process according to Claim
1, comprising a mixture of a high temperature poly (paraoxybenzoyl)
ester plastic having a particle size between about 100 mesh and 0.5
microns and 5 to 99 percent by weight of a flame spray metal powder
having a melting point below about 3,000.degree.F and a particle
size between 100 mesh and 0.5 microns.
11. A flame spray powder according to claim 10, in which said
mixture is a simple blend of said plastic having a particle size
between about 100 mesh and 5 microns and said metal having a
particle size between about 100 mesh and 5 microns.
12. A flame spray powder according to claim 11, in which said metal
powder is an aluminum powder.
13. A flame spray powder according to claim 12, in which said
aluminum powder is an aluminum silicon alloy powder containing 5 to
30 percent silicon.
14. A flame spray powder according to claim 10, in which said
mixture is formed of individual composite particles containing both
said plastic and metal.
Description
This invention relates to the flame spraying of high temperature
plastics.
Various plastic materials which remain stable at elevated
temperatures are known. These plastics are generally known and
referred to as high temperature plastics and remain stable at
temperatures above 500.degree. F and often will not melt even at
temperatures as high as 1,000.degree. F. These high temperature
plastics may often be formed and worked in accordance with metal
working technology as, for example, formed into shaped articles by
hot sintering of the powder.
It has also been proposed to form coatings with the high
temperature plastics utilizing the well known flame spraying
techniques that are conventionally utilized for applying metal
coatings. Due to the thermal stability of a high temperature
plastic, however, it is often necessary to effect the spraying with
a higher temperature plasma flame. While the sprayed coatings thus
formed by the flame spraying of these high temperature plastics
have many desirable characteristics, particularly with respect to
their temperature stability, dielectric strength and the like,
their usefulness and desirability could be greatly enhanced if
their strength, hardness and erosion resistance could be increased.
Furthermore, a reduction in the coefficient of friction of the
sprayed surfaces would greatly increase their desirability as
bearing surfaces, particularly of the self-lubricating type.
Another problem with flame sprayed coatings of the high temperature
plastic is a tendency to fail upon thermal cycling to high
temperature, and it would be desirable to improve on this thermal
shock resistance. Thus in spite of the basic ability to remain
chemically stable at high temperature, the high temperature
plastics have mechanical shortcomings in thermal environments.
It is an object of this invention to enhance the characteristics of
flame sprayed coatings formed of high temperature plastics in the
above indicated manners. This and still further objects will become
apparent from the following description:
In accordance with the invention a high temperature plastic powder
is flame sprayed in admixture with about 5 - 99 weight percent, and
preferably about 40 - 80 weight percent, of a flame spray metal
powder by heating the mixture to a temperature sufficient to
substantially melt the metal powder and surface heat-soften the
high temperature plastic, and propelling the thus heated particles
onto a surface, forming a coating.
The high temperature plastic powder which may be flame sprayed in
accordance with the invention may be any of the known or
conventional high temperature plastic powders which remain
thermally stable at temperatures up to 500.degree. F and preferably
do not melt even at higher temperatures as for example temperatures
up to 1,00.degree. F.
Examples of these high temperature plastics include the well known
polyimide plastics, polyamide-polyimide plastics, the polyester
imide plastics and the aromatic polyester plastics.
High temperature plastics of the above mentioned types are, for
example, described in U.S. Pat. No. 3,238,181; U.S. Pat. No.
3,426,098, U.S. Pat. No. 3,382,203 and British Pat. No.
570,858.
Particularly suitable are high temperature aromatic polyester
plastics of the type formed from phenyl acetate as for example the
poly(para-oxybenzoly) ester or poly(para-oxybenzoylmethyl)
ester.
The starting high temperature plastics should be in powder from
having a particle size between about -100 mesh and 3 microns, and
preferably between -140 and 5 microns.
As is conventional in flame spray techniques the particle size
distribution range should be as narrow as possible, as for example
one desirable size distribution is -170 - + 325 mesh, and another
desirable size distribution is -325 - +5 microns.
The high temperature plastic powder is admixed with about 5 - 99
weight percent, preferably 40 - 80 weight percent of a conventional
flame spray metal powder having a melting point below about
3,000.degree. F and preferably below 2,000.degree. F.
Typical metal powders for mixing with the plastic are aluminum
alloys, nickel alloys, copper, bronze, babbit and stainless
steels.
Since the density of a metal is many times greater than the density
of a plastic, the percentages by weight as given herein actually
reflect lower volume percentages.
When simply admixed or blended with the high temperature plastic
powder the metal powder should have a size and form that is
conventionally used in flame spraying as for example a particle
size between about -100 mesh, U.S. standard screen size, and 3
microns, and preferably between 140 mesh and 5 microns. The
particle size distribution should also be as is conventional in
flame spray powder.
It is preferable to use a finer size metal powder than the plastic
powder, for example -170 +325 mesh plastic and -325 mesh +10 micron
metal powders. Generally the higher the melting point of the metal
the finer the powder should be in relation to the size of the
plastic.
In addition to simple blends or mixtures of the high temperature
plastic powder and flame spray metal powder, composite particles
containing the metal and the high temperature plastic may be used.
Thus for example, plastic particles of the above mentioned type,
but coated with finer particles of the metal, may be used. For this
purpose, the metal may be in the form of a very fine powder or dust
as for example having a particle size between about 25 and 0.5, and
preferably between 10 and 1 microns, which is bonded to the surface
of a plastic as for example with a binding agent such as a phenolic
resin binding agent or any other organic binding agent or is simply
thermally bonded or bonded in any other manner to the plastic.
Alternately, the individual particles may be metal particles of
size suitable for flame spraying, but coated with finer particles
of the plastic. In this case the plastic is in the form of a very
fine powder or dust such as between about 25 and 0.5 and preferably
between 10 and 1 microns. Similar binding means as described above
may be used.
The powder may also comprise individual composite grains containing
sub-particles of both the metal and plastic. Both the metal and
plastic sub-particles may be in the form of a very fine powder or
dust as for example having a particle size between 25 and 0.5 and
preferably between 10 and 1 microns. The aggregate particles may be
formed or briquetted or tableted from the finer particles by
conventional powder metallurgy techniques with or without a bonder,
or by spray drying, as for example described in co-pending
application Ser. No. 671,880 filed Sept. 29, 1967 now U.S. Pat. No.
3,617,358.
The spraying of the powder mixture in accordance with the invention
is effected in the conventional well-known manner for flame
spraying, utilizing conventional flame spray equipment, i.e.
conventional flame spray guns. The spraying must be effected under
conditions, however, which will cause the metal powder to
substantially completely melt while at the same time surface heat
softening the high temperature plastic. Factors of flame
temperature and residence time determine the temperature to which
the particles are actually heated. In this connection it must be
noted that due to the greater thermal conductivity of the metal
particles the same will be much more rapidly heated and thus may
reach their melting temperature of for example between
2,000.degree. and 3,000.degree. F in the same environment and under
the same conditions that the high temperature plastic powder
particles are only surface heat softened.
The term "surface heat softened" as used herein is intended to
describe a thermal conditioning of the plastic particles in which
their surface is heated to a temperature at which the same will
deform and flow under pressure or impact without complete melting
of the particles and without heating the entire particle to a
detrimental or degrading temperature. Such surface heat softening
may include a superficial chemical or physical modification of the
plastic surface of each particle.
The spraying may be effected, for example, using a conventional
powder type plasma flame spray gun as for example a Metco Type 3MB
plasma flame spray gun using a GP nozzle, No. 2powder port, argon
plasma forming gas at 100 psi and 200 standard cubic feet per hour
(SCFH) with hydrogen added at 50 psi and 5 SCFH, 70 to 80 volts and
500 amperes. Powder is fed to the gun with a Metco Type 3 MP powder
feeder using the S powder conveying wheel at a speed adjusted to
feed the powder at about 3 pounds per hour into 10 SCFH argon
carrier gas.
Spraying may be effected on any surface or substrate such as carbon
steel, stainless steel, aluminum, copper or copper alloys, nickel
alloys, cobalt alloys and titanium. Although metals are generally
used for substrates, other substrate materials may include oxide
ceramics, plastics, fiberglass-plastic composites, or even cloth or
wood. The surface must be cleaned and roughened to achieve bonding
of the plastic mixture. To roughen the surface, grit blasting is
used such as with SAE G25-40 steel grit or -16 +20 mesh aluminum
oxide propelled by high pressure air.
A substrate surface roughness of at least 75 microinches RMS should
be achieved for this coating, and preferably about 200 RMS.
However, instead of or in addition to roughening, a suitable
bonding coating material, and preferably a self-bonding material
may be flame sprayed onto a surface which has merely been cleaned
such as by machining, etching or by light grit blasting.
Self-bonding coating materials are well known in the flame spray
art and, for example, include molybdenum or composite
nickel-aluminum powders or wires for plasma or combustion flame
spraying such as described in U.S. Pats. Nos. 3,222,515 and
3,436,248. These self-bond to most metal substrates. Suitable known
coating materials for bonding to other substrates may be used, such
as copper or glass to ceramic substrates, or zinc to low melting
substrates including plastics. In each case the bond coat is
applied in the known manner to a thickness of approximately 0.005
inches. The plastic metal powder is sprayed directly onto the bond
coating. The mixture is sprayed to any thickness from about 0.001
inches to 1/4 inch or more depending on the application. The
coatings may be used in their as-sprayed condition, or may be
easily machined to suitable dimension or to provide a smooth
surface.
Coatings sprayed with the plastic powder mixture are excellent for
use in seal areas such as on engine or pump shafts, or as low
friction bearing surfaces especially where no further lubrication
is used, or as abradable coatings as in gas compressor or pump
housings.
Very surprisingly, the coatings formed in accordance with the
invention show marked increase in hardness and strength as compared
with coatings of pure plastic. Furthermore in many instances there
is a dramatic drop in the coefficient of friction, as for example
with coatings formed from poly(paraoxybenzoyl) esters and
aluminum-silicon alloys containing for example 5 to 30 and
preferably about 12 percent silicon by weight of the aluminum
alloy. With for example 60 percent by weight of the 12 percent
silicon-aluminum alloy, the coefficient of friction drops manyfold,
while at the same time the hardness and strength shows a manyfold
increase over that of the pure plastic. Another surprising result
is a major improvement in resistance to cracking and spalling from
thermal cycling between about 600.degree. F and room temperature.
Whereas sprayed coatings of pure plastic failed, the coatings
combining plastic and aluminum alloy performed well.
The following examples are given by way of illustration and not
limitation.
EXAMPLE 1
A blend of 60 percent by weight (73 percent by volume) of a high
temperature aromatic polyester plastic, poly(paraoxybenzoyl) ester,
sold under the trade name of EKONOL by the Carborundum Company,
having a size of -170, +325 mesh, U.S. standard screen size, is
blended with 40 percent by weight (27 percent by volume) of a
silicon - aluminum alloy containing 12 percent silicon and of a
size of -325, +10 microns.
This blend is sprayed with a Metco 3 MB plasma flame spray gun and
3 MP powder feeder. Additional heavy air vibrator is mounted on the
meter block and operated at 15 lbs. of air pressure to produce a
more uniform flow of powder. An "S" powder feed wheel at 28 RPM and
an argon carrier gas flow of about 10 SCFH results in a feed rate
of approximately 3 1/2 lbs. per hour. Parameters are GP nozzle; No.
2 feed port; Argon gas 100 psi and 200 SCFH; secondary gas Hydrogen
50 psi and 5 SCFH; 500 amperes and 70 volts. A standard Metco Type
PSA air cooler is also used at 75 lbs. air pressure and the cooling
air streams are parallel to the flame. Nozzle to work distance is 3
1/2 inches. The substrate is 1 inch .times. 3 inch .times. 1/8 inch
mild steel. Steel grit G 25-40 with suction feed at 90 psi air in a
3/8 inch diameter nozzle is the method of blast separation. Coating
thickness is 0.100 inch.
EXAMPLE 1-A
Example 1 is repeated exactly, except with a blend of 40 percent by
weight (55 percent by volume) of the high temperature plastic
powder and 60 percent by weight (45 percent by volume) of the
silicon aluminum alloy powder.
EXAMPLE 1-B
Example 1 is repeated exactly, except using pure high temperature
plastic powder.
Samples of the sprayed coatings of Examples 1, 1-A, and 1-B are
measured for hardness, elastic limit, rupture strength, modulus of
elasticity, coefficient of friction, density and blast erosion
resistance, and the results are set forth in Table I. ##SPC1##
EXAMPLE 2
The following mixtures of the aromatic polyester plastic powder
described in Example 1 with aluminum powders are prepared and
sprayed: Blends comprising 10 and 50 weight percent pure aluminum
powder in the size range -170 +325 mesh; blends comprising 20, 30,
40, 50 and 60 weight percent of an aluminum alloy powder containing
24 percent silicon (based on the alloy). Coatings similar to those
described in Examples 1 and 1-A are obtained. These coatings are
for lightweight abradable sealing surfaces for aircraft engines.
The different proportions of aluminum provide different degrees of
abradability and erosion resistance for different applications for
abradable coatings. The coatings with 60 percent aluminum are also
useful for low friction bearing type of applications.
EXAMPLE 3
Aluminum flake powder of substantially -5 micron size is used to
clad the same plastic powder of Example 1 using a phenolic resin
binding agent. The plastic powder is clad with 20 wt-percent
aluminum powder whose average particle size was 3.5-4.5 microns.
Cladding procedure is as follows: 80 gms of plastic, essentially
-170 +325, is mixed with 12 gms of phenolic binder (15 wt-percent
of the plastic). To 20 gms of the -5 micron aluminum powder, is
added enough phenolic thinner (5 gms) to dampen the aluminum flake.
This combination is then introduced to the plastic mixture and
blended in an electric mixer until completely dry. Halfway through
the mixing period of 20 - 30 minutes, heat is applied to the mixing
container to speed up the drying process. Final product is screened
through a 100 mesh screen and the material retained on the screen
discarded.
Other powders are made using 5 and 10 wt-percent of the aluminum
flake. Coatings similar to those of Examples 1 and 2 are obtained
by plasma flame spraying these composite powders.
EXAMPLE 4
The plastic powder of Example 1 is blended with an aluminum-bronz
alloy powder, i.e., a copper alloy containing about 9 percent
aluminum, of size -270 mesh +10 microns. Different mixtures contain
20, 30, 40, 60 and 95 wt-percent bronze. The 95 wt-percent bronze
corresponds to about 80 volume percent metal and 20 percent
plastic. Coatings of this type offer a hard but permanently
lubricated surface for sliding contacts such as in bridge plates
and airplane flaps.
EXAMPLE 5
Mixtures of 20 and 50 wt-percent pure copper powder -325 mesh are
prepared with the same plastic of Example 1. Another blend is
prepared containing 42 wt-percent -170 +325 mesh of copper. Other
powders are prepared by cladding 20 and 35 wt-percent -5 micron
copper flake onto the same type of plastic particles using a
phenolic binding agent. 20 wt-percent copper flake corresponds to
four percent by volume of the composite powder. All these powders
are plasma flame sprayed in the same manner as Example 1, producing
bearing surfaces of good thermal conductivity, low friction and
self-lubrication.
EXAMPLE 6
A mixture of 35 percent -325 mesh pure nickel powder is blended
with the same plastic of Example 1. Another powder is prepared with
97 wt-percent +200 -325 mesh nickel. A composite powder is prepared
using 20 wt-percent -5 micron nickel flake coated on the plastic
articles using a phenolic binding agent. Excellent flame sprayed
coatings are produced.
EXAMPLE 7
Similar blends of powder are prepared with SAE type 316 stainless
steel +270 mesh +10 microns size. Powders with 20, 40 and 60
wt-percent stainless steel powder are made. Plasma flame sprayed
coatings are produced which were hard and corrosion resistant
bearing surfaces.
EXAMPLE 8
Poly(paraoxybenzoyl) ester powder of size -325 mesh was blended
with -325 mesh aluminum - 24 percent silicon alloy and plasma flame
sprayed to produce a fine textured coating.
While the invention has been described in detail with reference to
certain specific embodiments, various changes and modifications
will become apparent to the skilled artisan. The invention is
therefore only intended to be limited by the appended claims or
their equivalents, wherein we have endeavored to claim all inherent
novelty.
* * * * *