Note: Descriptions are shown in the official language in which they were submitted.
205260~
CARRIER--FREE METALWORKING LnBRIcANT
AND MET~OD OF MARING AND USING SAME
This invention relates to the field of
metalworking lubricants in general and, in one particular
respect, to forging lubricants. More particularly, it
relates in one aspect to a new forging lubricant
composition and a method of using that composition in the
hot forging of metal workpieces. Metal parts of a
multitude of sizes and shapes are manufactured by various
types of forging operations, and these parts are formed
from stock composed of a great many metals and metal
alloys. A great many parts are forged from such metals
and metal alloys as, for example, steel, aluminum,
titanium, and high nickel alloys, to name but a few.
The conditions under which metal parts are
forged, of course, are widely variable, depending upon not
only the nature of the metal, but upon the size and
complexity of configuration of the desired part. Small,
thin, simply shaped parts may obviously be forged from a
relatively flowable metal such as aluminum undor much less
rigorous conditions than are required to forge large more
complex shaped parts from a metal such as steel.
Each set of forging conditions requires a
specialized lubricant, and there is therefore a multitude
of aqueous-based, oil-based and organic solvent-baQed
lubricants currently in use in variou~ forging operations.
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Many such lubricant systems, particularly those used under
the most demanding forging conditions, by their nature
require the user to make compromises in order to achieve
the desired functional characteristics while avoiding as
much as possible any safety, occupational health or
environmental hazards involved in their use. Moreover, in
some instances, more restrictive health and environmental
guidelines are now in force which may make the use of
certain lubricant systems either extremely expensive or
simply unworkable. It is to these and related concerns
which the present invention is directed.
In a typical high performance forging operation,
such as one which might be devoted to the manufacture of
large, complex parts from aluminum alloy stock, an
effective lubricant is one which ordinarily contains a
variety of lubricity agents in a carrier comprising
mineral oil and/or volatile organic solvents. The dies
used in such forging operations are maintained at high
temperatures, in the range of 350F to 825F, in order to
permit proper metal flow during the forging operation.
The forging lubricant i8 typically applied to
the die and the workpiece by spraying, and, on account of
the temperatures involved, the mineral oil and volatile
organic compounds immediately flash off, leaving only a
relatively small amount of residue which actually
functions as the lubricant. As anyone who has observed
such a forge operation well knows, the flashing off of the
mineral oil and volatile organic compounds create~ a
significant amount of open flames, and the spray wand by
which the lubricant is applied takes on the appearance of
a flame thrower. Moreover, a large amount of smoke is
typically generated when the mineral oil and volatile
organic compounds flash off, since, at the same time, a
rather significant portion of the lubricity agents may
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burn off as well. In this context, it is well known thaè
any improvements in the performance of the forge lubricant
which are achieved by reformulation frequently come at the
cost of significantly higher smoke generation.
Similar difficulties are inherent when oil-based
paste type lubricant are utilized. While the paste
lubricants contain little or no volatile organic
compounds, their oil carriers partially or completely burn
at typical forging temperatures, resulting in significant
heavy smoke generation.
The hazards, expense and environmental problems
associated with such forging operations are of great
proportion and are quickly becoming even more so.
In a state such as California, where
environmental protection statues and regulations impose
rigid standards on industrial operations, and in other
states which have similar environmental protection
schemes, the smoke generated by a large forge operation
creates tremendous difficulties.
Since environmental agencies frequently monitor
smoke emissions by aerial surveillance, there is close
attention paid to reducing the smoke generated in the
forging operation. Unfortunately, this often limits the
efforts made to vent the smoke from the buildings in which
the forge operation is housed. The re~ult of this i9 a
significant degradation of the air quality within the
buildings.
An important economic consideration is that in
California, for example, a tax may be levied upon each
gallon of volatile organic compounds emitted into the air.
More importantly, as air quality standards are
progressively raised, there will soon come a time when a
forge operation will simply be prohibited from emitting
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large amounts of smoke. The choice then will be to find
an alternative lubricant which produces significantly
reduced amounts of smoke or to cease operations entirely.
Similar problems exist with respect to the use
of oil or solvent-based lubricants in smaller scale forge
and other metalworking operations, since waste lubricant
materials of this type are considered an environmental
hazard. Disposal is therefore tightly controlled and
increasingly expensive.
Other related concerns create a strong demand
for alternative meta}working lubricants.
As described above, open flame is generated when
conventional mineral oil and volatile organic compound-
based lubricants are applied to a heated die. One must
therefore have available fire prevention and fire control
equipment, such as fire extinguishers and sprinkler
systems, in the immediate area of the forge operation.
Indeed, fire extinguishers see regular use in many forge
operations, and the cost of their maintenance is
significant. In general, fire prevention, fire control
and fire detection systems of all types are regular and
significant capital and maintenance cost items for hot
forge operations.
A related problem associated with the use of
conventional volatile organic compound-based lubricants is
the need for speclal storage facilities on account of
their high flammability. This too imposes a significant
cost associated with the use of conventional lubricants.
Transportation of these flammable lubricants in
special containers and special vehicles is yet another
source of additional cost, hazard, and inconvenience
associated with their use.
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A still further disadvantage of conventional
lubricant systems which results from the flashing off of
oil and solvent carriers is that the smoke generated forms
tar-like deposits on machinery, finished parts, floors,
windows, and nearly everything else housed in the same
building with the forge operation. Quite apart from the
aesthetic undesirability of such deposits, there are
economic and health concerns as well. Many large forge
operations maintain permanent steam-cleaning facilities at
a significant cost.
Various types of dry lubricants and methods for
applying them to metal surfaces have been proposed for use
in diverse environments, but none has been widely adopted
on account of certain inherent disadvantages in either the
lubricant itself or the method of its application.
For example, in titanium forging operations, it
has been proposed to utilize a powdered lubricant composed
of glass and ceramic components, with the optional use of
steel shot, in a process in which the lubricant is
imbedded in the forge tool surface by a high pressure
spray. This process is described in terms of sandblasting
the lubricant onto the tool surface, and is intended to
effect a cold working and smoothing of the tool surface.
Of course, such a high pressure spray process involves the
use of rather expensive spray equipment, and it also
presents the risk of worker injury due to misdlrected
gpray.
Others have proposed to spray dry reactant
materials onto hot metal surfaces in order to form a
reaction product lubricant in situ. Still others have
proposed various combinations of dry lubricant components
for use in a wide range of applications. Many of these
lubricant compositions, however, have drawbacks, as well.
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After forging, whether with a conventional or
dry lubricant, aluminum parts are subjected to a caustic
etch for the purpose of removing lubricant residues. In a
preferred procedure which is well known in the art, the
S caustic etch may be used in combination with an acid wash.
In many aluminum forge operations, the acid wash
advantageously precedes the caustic etch.
As is well known in the art, the conditions of
these wash and etch procedures are quite harsh.
Typically, the caustic etch bath is 5% to 15% by weight
alkali metal hydroxide in water. Typical acid baths are
similarly strong, often containing a high concentration of
nitric acid. In forge operations using conventional
solvent or oil based lubricants, the wash and etch
procedure works quite well to remove essentially all
lubricant residues from the forged parts.
Notwithstanding the harsh conditions of the wash
and etch, however, it has been found that residues of
powdered lubricants may still adhere to the parts with
such tenacity that even subjecting the parts to physical
removal procedures, such as brushing and scraping, after
the etch will not adequately clean them.
It has also been found, in working with multi-
component powdered lubricants, that obtaining a consistent
spray pattern using conventional powder coating equipment
is extremely difficult. Overspray, underspray, puffing,
and sputtering have been found to be serious drawbacks,
both from the standpoint of obtaining a functional
lubricant coating on the workpiece And from tho standpoint
of efficient use of powder lubricant material. Overall,
the spray process has heretofore been found too erratic to
be acceptable commercially. Moreover, it has been
unexpectedly found that the spray was particularly
unpredictable when utilizing powder coating equipment
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which, as is quite common, utilizes a fluidized bed as a
reservoir from which the powder was sprayed. Even
utilizing powder coating equipment which has a gravity-fed
reservoir has typically provided only a marginal
improvement in consistency.
While the particular problems encountered in an
aluminum forge operation have been described in detail,
many of the same and other related concerns exist in other
metal working environments. These include not only other
hot forge operations, such as the manufacture of forged
steel and titanium parts, but also a wide variety of other
metalworking and metal forming operations. Examples
include extrusion, drawing, stamping, and other hot and
cold forming operations, many of which employ lubricants
in agueous or solvent based carriers. Thus, many of the
same technical and economic benefits could be realized in
~uch operation~ by adopting an improved dry lubricant
composition.
It is therefore an object of the
present invention to provide a novel forge lubricant and a
method of its use .
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In its mos~ basic form, the composition of the
present invention i9 a carrier-free pulverulent
metalworking }ubricant, i.e., one which i~ entirely free
of the oils and voiatile organic compounds commonly
employ-d aa carriers for forge lubricant compo~i~ions.
Similarly, in on- form, the method of the invention i~ a
method of forming a workpiece in a metal-forming apparatus
which includes the steps of applying to at least one of
the metal-orming apparatus and the workpiece a coating of
an effective amount of a carrier-free pulverulent
~0 lubricant composition, and forming the workpiece in the
apparatu~
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The carrier-free pulverulent metalworking
lubricant of the invention may, in general, include any
material which will provide lubricating properties at the
temperatures typically encountered in a forging process
and which can be put into a physical form which permits it
to be applied to the die and/or the workpiece by
conventional powder-coating equipment.
In accordance with the present invention, the
need to incorporate a mineral oil and/or a volatile
organic compound-based carrier is completely eliminated,
with the result that the smoke generated by conventional
lubricants is significantly reduced.
In one form, the invention is a carrier-free
pulverulent metalworking lubricant composition including
at least one resin having a highly polar functional group,
which may be solubilized under strong acid or basic
conditions, and which is a solid at room temperature.
In another aspect, the invention is a carrier-
free metalworking lubricant composition having a
substantially uniform particle size.
Yet another aspect of the invention is a method
of forming a carrier-free pulverulent metalworking
lubricant composition, which includes the steps of forming
a dry admixture of lubricant components, heating the
admixture to a temperature sufficient to melt at least one
component of the admixture, agitating the heated admixture
to form a substantially homogenous melt, cooling the
substantially homogenous melt to form a substantially
solidified mass, and comminuting the substantially
solidified mass to a desired particle size. In an
alternative aspect, the invention is a method of forming a
homogeneous melt of lubricant components and then spray --
drying the melt to a desired particle size.
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A still further aspect of the invention is a
method of forging a workpiece in a die which includes the
steps of applying to at least one of said die and said
workpiece a coating of an effective amount of a carrier-
free pulverulent lubricant composition having at least oneresin having a highly polar functional group, which may be
solubilized under strong acid or basic conditions, and
which i9 a solid at room temperature, and forging the
workpiece in the die.
The advantages inherent in the composition and
method of the invention are numerous.
The elimination of much of the smoke previously
generated by the flashing off of a mineral oil and
volatile organic compound carrier permits a forging
lS operation to continue in business in full compliance with
environmental statutes and regulations. Moreover, the
business may continue without the economic burden of tax
payment~ based on the emission of volatile organic
compounds. In many instances, the use of the composition
and method of the present invention will permit a forge
operation to continue in existence under a stringently
regulated environmental scheme which would otherwise cause
it to be shut down entirely.
Other economic advantages of the composition and
method of the invention are of equally great importance.
The reduction in weight and volume which occurs
when the carriers of conventional lubricants are
eliminated leads to savings in the cost of shipmqnt and
storage. Even further savings are realized in
transportation and storage costs because the carrier-free
composition of the invention is neither flammable nor
hazardous, and it can be shipped and stored in the same
manner as any other nonhazardous material. Moreover,
packaging costs are significantly reduced, since a five-
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gallon plastic pail of the carrier-free pulverulent
metalworking lubricant of the present invention will be
the functional replacement for a fifty-five gallon steel
drum of a conventional lubricant.
In the forg~ operation itself, the composition
and method of the invention result in significant
reductions in the cost of installing and maintaining fire
prevention and fire control sys~ems, and in general permit
the maintenance of a much safer environment for personnel
at a much lower cost.
Still further savings resulting from the use of
the composition and method of the invention may be
realized in reduced premiums for fire, workmen'~
compensation, and liability insurance.
The elimination of the carrier material
significantly reduces raw material cost, since, on a
weight and volume basis, the carrier in conventional
lubricants accounts for well over 90% of the composition.
The need to maintain expensive and space-
consuming cleaning facilities for plant and finished parts
is also reduced by the use of the composition and method
of the invention, since significantly less combustion
residues will be produced in the absence of the flashing
off of mineral oil and volatile organic compound carriers.
Additional functional advantages are also
achieved by the present invention.
The incorporation of a res~n which i9
solubilized in an alkali and/or acid bath provides the
advantage of a cleanable forged part, even with the use of
a dry powder lubricant.
Further, maintaining the particle size of thelubricant powder within a narrow range permits a uniform
coating of lubricant powder to be applied with
conventional powder coating equipment, even when utilizing
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equipment which employs a fluidized bed as a powder
reservoir. And, controlling the particle size of the
lubricant powder by its novel method of manufacture not
only provides spray consistency, but improves lubricant
s properties and cleanability as well.
As stated above, the composition of the present
invention, in its most basic form, is a carrier-free
pulverulent metalworking lubricant. It may include any
material which will provide lubricating properties at the
temperatures typically encountered in a metal-forming
process and which can be put into a physical form which
permits it to be applied to the die and/or the workpiece
by conventional powder-coating equipment.
Many materials which will perform the function
of lubricating the die and maintaining a physical
separation between the die and the workpiece are well
known, and, of these materials, many are in the physical
form necessary to the practice of the preæent invention;
namely, a solid at room temperature. It i3 not necessary
that the materials employed in the compoqition of the
invention remain either solid or pulverulent at the
temperatures typically encountered during a hot forging
operation, e.g., about 600F up to 1000F for alumlnum,
and about 1500F up to 2500F for steel or titanium. It
is enough that they may be made to exist in a particulate
form at a~bient temperature~. In that form, they can be
applied by conventional powder-coating eguipment, even
though they may partially or completely melt or burn when
in contact with the heated die or workpiece. Indeed, it
is preferred that at least one compqnent of the carrier-
free pulverulent metalworking lubricant become~ sticky
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upon being heated so as to assist in adhering the dry
metalworking lubricant composition to the workpiece and
die surfaces.
Typical materials which are capable of
maintaining a physical barrier between the die and the
workpiece and which function as solid lubricants are
contemplated for use in the composition of the invention.
They include, by way of example only, metal soaps, fatty
acids, graphite, ceramics, high melting polymer resins,
natural and synthetic waxes, gilsonite, glasses, and
mixtures of these materials.
Useful metal soaps are those which are solids at
room temperature, including many sulfonates, nap~thenates,
and carboxylates. Of these, fatty acid soaps such as zinc
stearate and sodium stearate are preferred on account of
their known properties, their ready availability and low
cost. However, other metal soaps known for their
lubricant properties, including, by way of example only,
tin, copper, titanium, lithium, calcium, and other alkali
and alkaline earth metal soaps of fatty acids, may be
advantageously included.
Fatty acids themselves which are solids at room
temperature may also be included, and their relatively low
cost, ready availability, and their contribution to the
overall lubricity of the composition makes them attractive
for such use. One example is stearic acid, which i9
advantageou~ly used since it has good lubricating
propertieg~ i9 nontoxic, inexpensive, and readily
available.
Materials such as graphite and certain ceramic
materials such as boron nitride are useful for maintaining
a phy3ical separation between the die and the workpiece.
While the precise mechanism of the physical separation is
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not known, this characteristic is believed to be
attributable to the relatively planar crystalline
structure of these materials.
Useful high melting polymer resins include, by
way of example, poly(tetrafluoroethylene) (PTFE), high
den~ity polyethylene ( HDPE~ t poly(vin~lchloride) (pvc)~
polyesters, polyethylene glycols, polyacrylates,
polymethacrylates, and polyamides. Indeed, almost any
thermoplastic material may be used.
Of the natural and synthetic waxes which may be
advantageously employed, polyethylene waxes of relatively
high molecular weights are in general preferred on account
of the lubricity which they impart.
Glass materials useful in the present invention
are preferably the low melting glasses, includinq alumina,
aluminatsilica, silica, and borax. Optionally, these
glass materials may be used in chopped fiber form.
In one basic form of the method of the
invention, a coating of an effective amount of a carrier-
free pulverulent lubricant composition is applied to atleast one of the die and the workpiece, and the workpiece
is then formed into the desired finished part. In
general, the application of the lubricant in accordance
with the invention may be accomplished by any conventional
powder-coating equipment.
In one alternative method falling within the
scope of the present invention, the carrier-free
pulverulent metalworking lubricant 1g applied by means of
an electrostatic spray apparatus, inasmuch as there is
little loss of material on account of the electrostatic
attraction of the particles to the die and/or workpiece,
and, since electrostatic spray is known to produce a
uniform coating on even complex-shaped parts.
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In high temperature environments, such as
aluminum, steel, and titanium forging operations,
maintaining sufficient charge on the lubricant particles
is quite difficult when the powder spray is directed to
S the die or workpiece in the vicinity of the press, and the
electrostatic powder coating apparatus provides little
advantage over non-electrostatic equipment. However, an
electrostatic apparatus provides a significant benefit for
pre-coating aluminum, steel, or titanium workpieces at
ambient temperature, after which the workpiece is heated
in an oven prior to insertion into the press. Similarly,
in cold forming operations, such as stamping and the like,
which are carried out at much lower temperatures, the
advantages of electrostatic spray are maintained.
The lubricant of the invention may be applied to
a heated or heating die in a manner analogous to the
application of conventional lubricants. Alternatively,
the lubricant composition may be sprayed onto a cold
unforged workpiece, after which the workpiece is heated to
achieve a partial melt of the composition and subsequently
placed into a heated die for forging. In cold-forming
operationR, the workpiece may be spray-coated, and the
conventional step of heating the workpiece to flash off or
evaporate an aqueous, solvent or oil carrier may be
eliminated.
It has been found that on account of their very
powdery, even dust-like, nature, such materials as
graphite and amorphous boron nitride are, unless they have
an electrostatic charge, less easily retained on the
surfaces of the die and workpiece than are some of the
other materials enumerated above. Drafts or currents of
air may therefore undesirably remove the pulverulent
forging lubricant from the die and/or the workpiece prior
to the forging operation. Thus, when including one or
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more of these materials in a lubricant of the invention
formed as a dry admixture which is to be delivered by a
non-electrostatic powder coating apparatus, it is
preferred to also include at least one component having
S adhesive properties at typical forging temperatures, such
as a glass, gilsonite, or high melting polymer resin for
the purpose of retaining the lubricant on the die and the
workpiece.
Some examples of the lubricant composition and
metalworking method of the invention are set forth below.
EYamP1eS 1 and 2
The following compositions were used to forge a box
channel with high walls, approximately 0.125 inches thick,
in a wrap die from aluminum alloy stock. The press was of
the hydraulic type, with the workpiece temperature being
700F and the die temperature 375F:
EYample 1
Component Weight%
gilsonite 5
20 zinc stearate 34
sodium stearate 10
graphite 17
polyethylene 3~
100
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Example 2
Component Weight~
gilsonite 5
zinc stearate34
5 sodium stearate 10
graphite 17
amide wax 34
100
Only seven parts were forged; thus, optimization
of spray techniques could not be achieved. However,
examination of the forged parts showed excellent metal
movement, with a complete die fill of the walls of the
channel. There was excellent downsize of the critical
part dimension, and the parts released easily from the
die, with no sticking. The dies had some tendency to
stick together; however, this is normally experienced with
this configuration of parts. Smoke levels were noticeably
lower than those produced when a conventional salvent, oil
and graphite lubricant was used. Based on this rather
limited trial, the composition of Example 1 outperformed
the composition of Example 2 in each of the observed
respects, though both were effective as forging
lubricants.
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Example 3
In a comparative trial, the composition of
Example 1 was evaluated using a conventional solvent-based
zinc stearate forging lubricant as a standard. The press
was of the mechanical type, with the workpiece temperature
being 700F and the die temperature 400F.
Forty parts were forged from each composition.
Examination of the forged parts showed excellent metal
movement with no drag. There was excellent downsize of
the critical part dimension. The parts released easily
from the die, with no sticking, and there was no buildup
of lubricant residue on the parts. Smoke levels when
using the composition of Example 1 were significantly
lower than those produced during the trials reported in
Examples 1 and 2.
Examples 4 and 5
Each of the following compositions was evaluated
under the same conditions as those of Example 3, and each
was found to perform satisfactorily with ~ignificantly
lower smoke generation than conventional solvent-based
lubricants.
Esample 4
Component Weight~
graphite 33.0
25 zinc stearate 34.5
gilsonite 10.9
polyethylene wax 21.1
99.5
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Example S
Component Weight%
graphite 23.8
sodium stearate33.4
5 gilsonite 23.8
polyethylene wax 9.5
zinc stearate 9.5
100.0
The composition of Example 5 was also evaluated
in the high-temperature environments of steel and titanium
forging, and it was found to perform satisfactorily in the
forging of both metals.
Esamplea 6-8
The following carrier-free pulverulent lubricant
compositions have also been found useful for the forging
of aluminum and aluminum alloy workpieces:
EYample 6
Component Weight %
20 graphite 23.8
gilsonite 23.0
sodium stearate 33.4
polyamide 9.5
zinc stearate 9.5
100 . O
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Example 7
Component Weight %
graphite 23.8
gilsonite 23.8
5 sodium stearate 33.4
polyacrylate 9.5
dibutyl tin
carboxylate 9.5
100.O
Example 8
Component Weight %
graphite 75
gilsonite 25
100
Example 9
Component Weight%
graphite 50
20 gilsonite 25
zinc stearate 15
poly(tetrafluoroethylene) 10
100
Examplea 10-15
Other carrier-free pulverulent lubricant
compositions have been found useful for high temperature
forging of titanium and steel, and they include the
following:
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Example 10
Component Weight%
graphite 20.0
gilsonite 20.0
S sodium stearate 30.0
stearic acid 20.0
polyethylene wax 10.0
100.O
Example 11
Component Weight%
graphite 15.0
gilsonite 20.0
sodium stearate 30.0
15 stearic acid 20.0
polyethylene wax 10.0
boron nitr.ide S.0
100.O
E~ample 12
Component Weight%
graphite 40.0
gilsonite 20.0
sodium stearate 20.0
25 stearic acid 20.0
100.O
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Example 13
Component Weight%
aluminatsilica
glass 40
5 graphite 60
100
Example 14
Component Weight~
10 boron nitride 25
borax 75
100
EYample 15
15 Component Weight%
graphite 35
borax 65
100
It i9 possible to achieve a limited improvement
in cleanability of aluminum and aluminum alloy parts by
reducing or eliminating gilsonite from the composition,
since it tends to contribute to the formation of tar-like
residues on the forged parts. But eliminating this
component improve~ cleanability only marginally, and at
the price of reduced performance, since the gilsonite
provides good lubricity, while at the same time its tacky
character at forging temperatures tends to help a
lubricant formed as a dry admixture to adhere to the
workpiece and the die.
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What has been discovered to be extremely
effective, however, is to replace the gilsonite with a
component which unexpectedly provides the combination of
the same desirable performance attributes contributed by
gilsonite and other similar tacky substances, together
with a level of cleanability which is the equal of a
conventional solvent and/or oil based forging lubricant.
Specifically, the use of a resin component
having certain physical and chemical attributes can
provide the combination of good performance and far
superior cleanability required for successful industrial
use.
In general, any resin which has good lubricity
properties at forqing temperatures, is a solid at ambient
temperatures, and contains a highly polar functional group
which enables the resin to be solubilized in the caustic
etch and/or acid bath will provide this combination of
properties. In general, halogenated resins are preferably
avoided in hot forging operations on account of their
tendency to form hazardous combustion products.
Particular resins which have been found useful
in the practice of the invention include the polyethylene
glycol resins, polyester resins having terminal hydroxyl
or carboxyl functional groups, polyacrylate,
polymethacrylate,`and polyamide resins and mixtures of
these resins. Presently preferred are the polyester and
polyethylene glycol resins on account of their good
lubricity properties, superior cleanability, and lack of
objectionable burn characteristics. Some examples of such
resins are the polyethyleneglycol resin~ sold under the
tradename Pluracol by BASF, such as E4000 and E8000, the
hydroxyl functional polyester resins sold by Cargill, such
as 30-3016, and the carboxyl functional polyester resins
sold by Cargill, such as 30-3065. These materials are
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generally dry solids at room or ambient temperature, so
that they are readily applied to the workpiece and die by
conventional powder coating equipment.
These resins provide the desired combination of
lubricity and cleanability characteristics when utilized
in the composition of the invention in amounts of from
about 5% to about 50~ by weight of the composition, with a
preferred range of from about 10% to about 30~ by weight
of the composition. Most preferably, the amount of resin
is maintained as low as possible while still providing the
desired performance characteristics, since these resins
tend to be more expensive on a weight unit basis than many
of the other components of the composition. While, in
general, an observable improvement in cleanability is
achieved when at least about 5% by weight of the
composition is a high-melting resin having a highly polar
functional group, the upper concentration limit is more an
economic than a functional one.
It is important to note in this regard (and with
respect to the determination of the optimum concentration
of any of the other components of the composition) that
small variations in the amount of resin used do not
manifest themselves in readily observable variation~ in
per~ormance or cleanability. Indeed, the evaluation of
performance and cleanability is highly subjective and not
susceptible to quantification to any meaningful degree.
Thus, the weight percentage of resin or any other
component in the lubricant composition i9 not narrowly
critical to the practice of the present invention and may
vary considerably without an adverse effect on
performance.
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Example 16
A lubricant powder composition was formulated in
accordance with the invention as follows:
Component Weight%
5 graphite 15
stearic acid 15
zinc stearate 30
sodium stearate 10
polyethylene glycol 20
10 carboxyl functional
polyester 10
100
The lubricant so formulated was successfully
utilized in a high performance aluminum forge operation
for the purpose of forging a number of aircraft parts.
The lubricant of Example 16 was further found to perform
successfully in typical steel lengine valves) and titanium
(turbine blades) forging operations.
Example 17
The forging of a first group of aluminum parts
using the composition of Example 16 was carried out
together with the forging of a second group of aluminum
parts using the composition of Example 5, and a series of
three comparative cleaning tests was conducted~ The
cleaning procedure~ and the results obtained are
summari2ed below:
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Cleaning Tests Detail
Test A - Process (Standard Etch)
Step 1 - Caustic soda, 8 oz/gal, 175-180 F, 120 sec
Step 2 - Rinse, cold
Step 3 - Rinse, cold
Step 4 - Desmut, nitric acid 25%, 60 sec
Step 5 - Rinse, cold
Step 6 - Rinse, cold
Step 7 - Rinse, hot
Results:
Removing Example 5 lubricant: poor cleaning
Removing Example 16 lubricant: marginally acceptable
cleaning
Test 8 - Process:
5tep 1 - 24% sulfuric acid, 6% nitric acid, 180 F, 10 min.
Step 2 - Rinse, cold
Step 3 - Rinse, cold
Step 4 - Caustic soda, 8 oz/gal, 175-180 F, 120 sec
Step 5 - Rinse, cold
Step 6 - Rinse, cold
Step 7 - Desmut, nitric acid 25%, 60 sec
Step 8 - Rlnse, cold
Step 9 - Rinse, cold
Step 10 - Rinse, hot
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Results:
Removing Example 16 lubricant: essentially clean;
equivalent to cleaning liquid lubricant with standard
etch process.
~est C - Process:
Step 1 - Nitric acid 50%, 120 sec
Step 2 - Rinse, cold
Step 3 - Caustic soda, 8 oz/gal, 140 F, 30-180 sec
Step 4 - Rinse, cold
Step 5 - Desmut, nitric acid 50%, 120 sec
Step 6 - Rinse, cold
Step 7 - Rinse, hot
Results:
Removing Example 16 lubricant: essentially clean;
lS equivalent to cleaning liquid lubricant with the same
etch process.
Following a number of such comparative cleaning
tests, a still further advantage of the lubricant of
Example 16 over a conventional zinc-containing lubricant
was discovered; namely, a 95~ reduction in the amount of
zinc present in the etch solutions. Reduction of the
metal content of indu~trial wastes i9~ of course, a
valuable environmental and economic benefit.
Example 18-21
Lubricant powder compositions also formulated in
accordance with the present invention are:
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Example 18 EYample 20
Component Weight% Component Weight~
graphite 15 graphite 40
stearic acid 20 hydroxyl functional
5 dibutyl tin polyester 20
carboxylate 20 zinc stearate 20
sodium stearate 25 stearic acid 20
polyamide 10
hydroxyl functional 100
polyester 10
100
Example 19 Example 21
Component Weight~ Component Weight%
15 graphite 15 alumina/silica glass 40
carboxyl functional graphite 55
polyester 20 polyethylene glycol 5
sodium stearate 20
stearic acid 20 100
20 polyethylene
glycol 10
boron nitride 5
100
In another aspect of the invention, maintaining a
narrow particle size range provides greatly improved spray
efficiency and consistency, such that a substantially
uniform coating of powder lubricant could be applied to the
workpiece. The best results are obtained, of course, when
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the particles of lubricant powder are of essentially uniform
size. For the purpose of the invention, "substantially
uniform size" means that there are relatively few or no
particles more than 15% larger or smaller than the average.
Most preferably, there are relatively few or no particles
more than 10~ larger or smaller than the average.
In general, a particle size of from 10 microns to
300 microns produces acceptable results, though a size of 40
microns or greater is preferred to minimize the extent to
which lubricant particles remain airborne in the form of
dust. There are two objectives in minimizing dusting;
namely, to provide an environmentally safer environment for
the worker, and to reduce lubricant material loss by
increasing the efficiency and accuracy of the powder spray.
The upper limit on particle size is essentially a
function of the capability of the spray equipment and of the
ability of the particles to adhere to the surface of the
workpiece in a substantially uniform coating. Most
preferably, a particle size of about 50 microns to about 100
micron~ is utilized, since commercially available powder
coating equipment functions best in this range.
One manner of controlling both particle size and
the range of particle sizes is to utilize as starting
materials lubricant components which have been ground or
sieved to a sub~tantially uniform size. The components may
then be readily admixed by conventional dry mixing
techniques, ~uch as by use of a ribbon blender, a tumbling
blender, or a twin shell blender. An obvious drawback of
this procedure is the time, effort, and expense involved in
either purchasing or processing each of the components to
the desired size and size range. Moreover, the dry blending
proce~s itself causes the particles to abrade one another,
thereby creating a multitude of small particles, and
therefore once again broadening the particle size range.
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It has been discovered that one may overcome the
shortcomings of the method of controlling particle size just
described, and may also achieve other si~nificant
improvements, by forming the lubricant powder in an entirely
different manner. Specifically, it has been discovered that
a high performance powdered lubricant having a well-
controlled particle size range may be formed by the
following method: Pirst, the lubricant components, which
may be in any conveniently available comminuted form, such
ac powders, flakes, small pellets, and the like, essentially
regardless of their particle size, are admixed in the
desired proportions to form a dry lubricant premix. The dry
lubricant premix is then heated with agitation to form an
essentially homogenous melt. A temperature of from about
100 C to about 200 C is usually sufficient to provide a
consistency which permits melt mixing. The homogenous melt
is then cooled to form a solid mass. The solid mass is then
ground at low temperature to the desired particle size by
conventional cold-grinding techniques. Equipment capable of
performing this operation is commercially available. In one
such process, the homogenous lubricant melt is discharged
onto a rotating metal plate which is chilled to about 40 F
(10 C) to solidify the mass in sheet form. The sheets are
then broken into shards which are in the range of 1 to 3
centimeters across. The shards are then, in turn, hammer-
milled to the desired particle size in an air-conditioned
room. Other similar processes solidify the melt into ribbon
form, after which it is broken into chips and milled to the
desired particle size under suitable conditions.
Typically, the milling equipment is rather
massive, and is constructed of steel or other metal. It
therefore become~ conditioned to the ambient room
temperature of on the order of about 60F to 70F, and
provides a highly efficient heat sink for the lubricant
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composition as it is milled. If necessary, the apparatus
can be further chilled by, for example, circulating liquid
nitrogen through a network of internal channels provided for
that purpose. This temperature control permits optimization
of the process in terms of controlling particle size, since
many of the lubricant components would become tacky or
semi-solid upon being subjected to the heat generated in
conventional grinding or milling processes, but remain dry
solids at lower temperatures.
Alternatively, the lubricant of the invention may
be produced by forming a homogenous melt of the components
as described above, and then spray-drying the melt in a
conventional manner to the desired particle size.
Not only do these processes of producing the
lubricant of the invention greatly facilitate controlling
the particle size of the composition, thus optimizing the
process of applying it to the die and workpiece, but they
produce improvements in the performance of the lubricant
composition. Since the lubricant particles are ground or
spray-dried from an essentially homogenous ma~s, the
lubricant components are far more evenly distributed in the
composition than could be accomplished using conventional
dry mixing techniques. Indeed, the process described can
produce individual particles of heterogeneous composition,
and having much more uniform dielectric properties than a
strictly dry-mixed composition.
The result is that, when sprayed onto the die and
workpiece at elevated temperatures, the particles melt and
fuse to form a lubricant film which is substantially
uniform. Not only are the lubricant components more evenly
distributed on the die and workpiece surfaces when the
particles are manu~actured in this fashion, thus providing
improved resistance to sticking and more uniform metal flow
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along surfaces, but the cleanability of the composition is
improved on account of the more uniform distribution of the
resins which are included for that purpose.
The process of applying the lubricant of the
invention is carried out at essentially ambient pressure by
the use of con~entional powder coating equipment. For
example, it is well known that, in a conventional
electrostatic powder coating apparatus, a fluidized bed of
powder feeds a spray wand having an electrode at its tip.
While the apparatus injects air into the powder at rather
low pressure to form the fluidized bed, by the time the
powder reaches the applicator wand tip (typically a distance
of about 20 feet), the air carrying the powder (and
therefore the powder stream) is at quite low, essentially
ambient pressure. The charge imparted to the powder by the
electrode provides the acceleration necessary to carry the
powder to the die (maintained at ground). Once on the die
surface, the lubricant powder may be retained there by the
adhesive properties of at least one component included for
that purpose.
Alternatively, a conventional powder coating
apparatus, whether electrostatic or non-electrostatic, may
utilize a gravity-fed conical hopper as a powder source,
rather than a fluidized bed. Such an apparatus has been
found particularly useful when utilizing lubricant powders
of widely varying particle size or relatively heavy
lubricant blends, which do not readily orm fluidized bed~.
When such a gravity-fed apparatus i9 utilized, it has been
further found that optimal results in feeding the powder to
the spray wand are obtained when the lubricant particles are
either ub~tantially spherical in shape or have
substantially smooth surfaces, or, most preferably, both.
These characteristics permit the lubricant particles to flow
more easily, since they will have less tendency to fuse on
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account of impact or to wedge aqainst one another, ~hereby
blocking flow of material. From the standpoint of
optimizing both shape and surface characteristics, the
method of manufacture described above which employs spray-
drying is the preferred one, since spray-drying inherently
produces substantially spherical, substantially smooth
particles.
In the process of the invention, a coating of the
lubricant powder is applied to the workpiece and the die in
a fashion much like painting. The lubricant is not worked
onto or into the die or workpiece surface. Rather, the
process i9 more akin to painting the lubricant onto the die
than to hammering it into the surface.
From the foregoing description and examples, it is
apparent that the object of the present invention have been
achieved. While only certain embodiments have been set
forth, alternative embodiments and various modifications
will be apparent to those skilled in the art. These and
other alternatives and modifications are considered
equivalents and within the spirit and scope of the present
invention.
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