U.S. patent application number 08/952172 was filed with the patent office on 2002-02-14 for metalworking lubrication.
Invention is credited to BALLIETT, ROBERT W..
Application Number | 20020019321 08/952172 |
Document ID | / |
Family ID | 25492643 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019321 |
Kind Code |
A1 |
BALLIETT, ROBERT W. |
February 14, 2002 |
METALWORKING LUBRICATION
Abstract
Processes for working of refractory metals and other metals
employing a lubricant comprising perfluorocarbon compounds (PFCs),
including aliphatic perfluorocarbon compounds (.alpha.-PFCs) having
the general formula: C.sub.nF.sub.2n+2, perfluoromorpholines having
the general formula: C.sub.nF.sub.2n+1ON, perfluoroamines (PFAs)
and highly fluorinated amines (HFAs), and perfluoroethers (PFEs)
and highly fluorinated ethers (HFEs), and their polymerization
products.
Inventors: |
BALLIETT, ROBERT W.;
(WESTBOROUGH, MA) |
Correspondence
Address: |
PERKINS SMITH & COHEN
ONE BEACON STREET
BOSTON
MA
02108
|
Family ID: |
25492643 |
Appl. No.: |
08/952172 |
Filed: |
February 17, 1998 |
PCT Filed: |
May 8, 1996 |
PCT NO: |
PCT/US96/06445 |
Current U.S.
Class: |
508/246 ;
508/545; 508/582; 508/588; 508/590; 72/42 |
Current CPC
Class: |
C10N 2040/22 20130101;
B22F 1/10 20220101; C10N 2040/246 20200501; B21B 27/10 20130101;
C10M 105/70 20130101; C10N 2040/245 20200501; C10M 2215/04
20130101; C10M 2215/225 20130101; C10N 2040/24 20130101; C10M
2215/30 20130101; C10M 2211/042 20130101; C10M 2215/22 20130101;
B21B 3/00 20130101; C10M 2211/022 20130101; C10M 105/52 20130101;
C10M 2211/06 20130101; B21C 9/02 20130101; C10M 105/50 20130101;
C10N 2040/241 20200501; C10N 2040/242 20200501; C10M 2215/226
20130101; C10N 2040/243 20200501; C10N 2040/247 20200501; C10M
2215/221 20130101; B21B 45/0242 20130101; B21B 45/0248 20130101;
C10N 2040/244 20200501; C10M 2215/26 20130101; B21B 23/00 20130101;
C10M 105/58 20130101 |
Class at
Publication: |
508/246 ;
508/545; 508/582; 508/588; 508/590; 72/42 |
International
Class: |
C10M 15/50; C10M 15/52;
C10M 15/54; B21B 045/02 |
Claims
What is claimed is:
1. Process for metalworking comprising the lubrication of the metal
during the working process with a fluorinated, inert fluid selected
from the group consisting of aliphatic perfluoroalkanes having the
general formula C.sub.nF.sub.2n+2; perfluoromorpholines having the
general formula C.sub.nF.sub.2n+1ON, wherein n is at least 5, and a
boiling point of at least 50.degree. C.; perfluoroamines, having
the general formula C.sub.nF.sub.2n+3N, wherein n is at least 3,
and a boiling point of at least 155.degree. C.; highly fluorinated
amines; and their polymerization products; wherein said
fluorinated, inert fluids occur in substituted and unsubstituted
forms effective to enable the metalworking process to be performed
at high speeds, but in a way that lubricant-residue removal is not
required at the end of the process.
2. Process in accordance with claim 1 wherein said fluorinated,
inert fluid is provided in combination with at least one inert
carrying agent, such as in compositions selected from the group
consisting of greases, pastes, waxes, and polishes.
3. Process in accordance with claim 1 wherein, the material to be
worked is a refractory metal.
4. Process in accordance with claim 3 wherein the refractory metal
is tantalum.
5. Process in accordance with any of claims 1-4 wherein the
metalworking process is a wire-drawing process with multiple die
passes and the lubricant is perfluorocarbon liquid and the wire as
drawn has an average diameter between 5 mils (0.127 mm) and 20 mils
(508 mm).
6. Process in accordance with claim 1 wherein the fluorinated,
inert liquid compounds comprise fluoroaliphatic compounds having 5
to 18 carbon atoms.
7. Process in accordance with claim 1 wherein the fluorinated,
inert liquid compounds comprise at least one catenary heteroatom,
selected from the group consisting of divalent oxygen, hexavalent
sulfur, or trivalent nitrogen and have a H:F ratio under 1:1.
8. Process in accordance with claim 6 wherein the fluorinated,
inert liquid compounds have a hydrogen content of less than 5% by
weight.
9. Process in accordance with claim 7 wherein the fluorinated,
inert liquid compounds have a hydrogen content of less than 1% by
weight.
10. Process in accordance with claim 1 wherein the perfluorocarbon
fluid is selected from the group consisting of
perfluoroalkanes.
11. Process in accordance with claim 10 wherein the fluid is a
perfluoroalkane selected from the group consisting of
perfluoropentane, perfluorohexane, perfluoroheptane, and
perfluorooctane.
12. Process in accordance with claim 1 wherein the perfluorocarbon
fluid is a perfluoroamine.
13. Process in accordance with claim 12 wherein the perfluoroamine
is selected from the group consisting of perfluorotributylamines,
perflurotriethylamine, perfluorotriisopropylamines, and
perfluorotriamylamines.
14. Process in accordance with claim 1 wherein the perfluorocarbon
fluid is a perfluoromorpholine.
15. Process in accordance with claim 14 wherein the
perfluoromorpholine is selected from the group consisting of
perfluoro-N-methylmorpholines, perfluoro-N-ethylmorpholines, and
perfluoro-N-isopropylmorpholines.
16. Process in accordance with any of claims 1-4 wherein the metal
is drawn to a fine wire form and bonded as a lead wire to a porous
electrode mass.
17. A tantalum electrolytic capacitor anode and attached lead wire
as made by the process of claim 20.
18. Process in accordance with any of claims 1-4 wherein the
metalworking process is the rolling of seamless, metal tubes,
comprising the steps of pulling a large diameter tube or rod into a
tube-rolling machine having at least one set of reduction rolls;
lubricating the material during the rolling process with a fluid
selected from the group consisting of perfluoroalkanes having the
general formula C.sub.nF.sub.2n+2; rolling the tube or rod through
the at least one set of reduction rolls lubricated with a
perfluorocarbon fluid; and repeating the process until the
necessary tube size is obtained.
19. Process in accordance with claim 18 wherein the tube has an
average diameter between 10 mm and 50 mm and wall thickness between
0.5 mm and 10 mm.
20. Process in accordance with any of claims 1-4 wherein the
metalworking process is the drawing of seamless metal tubes using
multiple die passes and the lubricant is perfluorocarbon liquid and
the tubes drawn have an average diameter between 0.005" (0.127 mm)
and 2.0" (50.8 mm) and wall thickness between 0.001" and 0.050"
(0.025 to 1.27 mm).
21. A process of providing lubrication wherein the lubricant is a
fluorinated, inert fluid selected from the group consisting of
aliphatic perfluoroalkanes having the general formula
C.sub.nF.sub.2n+2, perfluoromorpholines having the general formula
C.sub.nF.sub.2n+1ON, perfluoroamines, and highly fluorinated
amines; wherein said perfluoroamines and highly fluorinated amines
occur in substituted and unsubstituted forms.
22. Process in accordance with claim 21 wherein said fluorinated,
inert fluid is provided in combination with at least one inert
carrying agent, such as in compositions selected from the group
consisting of greases, pastes, waxes, and polishes.
23. Process in accordance with any of claims 1-4, 21 or 22 wherein
the fluorinated inert fluid is mixed with a solid lubricant and
provided in solid form therewith as a paste, gel or other solid
form.
24. Process in accordance with claim 23 wherein the solid lubricant
is selected from the class consisting of graphite, TEFLON.TM.,
fused fluorides, MoS.sub.2, WS.sub.2, MoSe.sub.2, MoTe.sub.2 and
similar solid lubricants.
29. Process in accordance with any of claims 1-4, 25 or 26 wherein
the metalworking process is a powder metallurgy compaction of metal
particles coated with said inert fluid.
30. Process in accordance with either or claims 27 or 28 wherein
the metalworking process is a powder metallurgy compaction of metal
particles coated with said inert fluid and co-lubricant
Description
FIELD OF THE INVENTION
[0001] The present application relates to lubrication, especially
as it relates to various metalworking processes, including
non-cutting forming processes and cutting/machining processes. The
forming processes include drawing metal wire, tube forming in
seamless and seamed modes, tube rolling, forging (including
upsetting, swaging, and thread rolling), rolling (including flat
product and shape rolling), extrusion, sheet fabrication processes,
including blanking, coining, deep drawing, punching, shearing,
spinning, stamping, and stretch forming, metal cutting and
machining operations, including cutting, boring, broaching,
drilling, facing, milling, planing, reaming, sawing, tapping,
trepanning, and turning, and abrasive cutting, grinding, sanding,
polishing, and lapping. These various operations are performed on
mill products and/or fabricated parts (workpieces).
BACKGROUND OF THE INVENTION
[0002] Many forming and cutting processes of metalworking utilize
lubricants for cooling the work and the tool, flushing removed
metal in cutting processes, lowering friction between the tool and
the work, and as a barrier layer to prevent binding or galling. The
extent of these various lubrication needs differs among the various
metalworking processes and as to a particular such process as
applied to different metals. This is illustrated by the situations
of lubrication requirements for drawing wires of refractory metals
(Ta, Nb, Mo, W, Ti, Zr, Hf and alloys) and steel and common ferrous
and non-ferrous metals (Fe, Cu, Al, Ni, and alloys, such as
INCONEL.TM. and steels) and precious metals (Au, Pt, Pd, Rh, Re).
The term "metal" as used herein includes those ceramics as cermets
that are workable in substantially the same manner as metals and
wherein lubrication is employed to reduce tool wear and/or
otherwise enhance the metalworking process.
[0003] Because of the severe sliding contact between the workpiece
and the tool, lubricants are used in all metalworking operations to
reduce friction between the workpiece and the tool, to flush the
tool to prevent the buildup of fines and dirt on the tool surface,
to reduce wear and galling between the workpiece and the tool, to
remove heat generated during plastic deformation, and to protect
the surface characteristics of the finished workpiece.
[0004] The lubricants used today to work the common metals are a
complex blend of various esters; soaps; solid lubricants, such as
graphite, TEFLON.TM., fused fluorides, MoS.sub.2, WS.sub.2,
MoSe.sub.2, MoTe.sub.2, and similar solid lubricants; and other
extreme-pressure lubricants. Oil- or polyglycol-based lubricants
are often used in the form of emulsions in water at concentrations
on the order of 10%, sometimes with additives to give the emulsions
the necessary detergency to keep both the workpiece and the tool
clean. Ease of cleaning is a fundamental parameter in the selection
of metalworking lubricants. In the state-of-the-art, these classes
of lubricants have been found to be inadequate, e.g., in the
production of refractory metal wire. This is particularly
troublesome with the solid lubricants.
[0005] It is well known that wire and tube drawing, particularly of
refractory metals, present the most extreme metalworking conditions
in terms of frictional forces between tool and workpiece, tool
wear, and stresses experienced by the workpieces. Accordingly, for
purposes of illustration only, the following discussion will
concern refractory metal wire and tube drawing, with the
understanding that the discussion applies equally to other
metalworking operations and workpieces of other metallurgy.
[0006] Various chlorinated oils have been used over phosphate
precoats, as well as mixtures of various graphite and molybdenum
disulfide lubricants, with limited success to draw refractory metal
wire. More recently, chlorotrifluoroethylene (CTFE)-based oils have
become the lubricant of choice in the production of refractory
metal wire, generally in a viscosity range of 20 to 150
centistokes. While CTFE lubricants are now used almost exclusively
in the production of electronic-grade tantalum wire, they present a
number of serious operating limitations. Because of the poor heat
transfer characteristics of the CTFE lubricants, drawing speeds
must be very slow, generally in the range of 100 to 300 FPM.
Typical wire-drawing speeds for the common metals are in the range
of 5000 to 20,000 FPM. As a result, drawing costs for refractory
metals are very high by comparison.
[0007] In addition, the CTFE lubricants are only marginally
effective in reducing wear and galling between the wire and the die
and in flushing the wear products away from the die entrance, These
problems are very evident in the short die life (<20 pounds per
set) obtained when using carbide dies to draw tantalum wire and in
continuing problems with surface roughness and dimensional control
(including both diameter and roundness). All of these limitations
associated with CTFE lubricants make refractory metal wire drawing
an inherently high-cost process with less than desired quality of
product.
[0008] A more serious limitation of the CTFE lubricants is found
when attempting to remove them from the surface of the finished
wire. The removal of these lubricants is typically accomplished
using solvents, typically 1,1,1-trichloroethane. With the
increasing restrictions placed on solvent use because of
flammability, toxicology, ozone depletion, and global warming, it
is almost completely impossible to remove the CTFE lubricants from
wire products. A number of hot, aqueous degreasing systems, with
and without ultrasonics, have been used to attempt to remove these
lubricants with limited success. CTFE lubricant residues on
electronic-grade wire surfaces continue to be a cause of electronic
component failure.
[0009] The first step in the production of seamless metal tubes is
often accomplished by rolling cast or previously rolled round
billets. The heavy walled tube produced is drawn as a tube shell. A
number of different methods of manufacture are used, depending on
the tube diameter and wall thickness required. The oldest method of
making seamless tubes is the Mannesmann piercing process, which
employs the principle of helical rolling. The machine comprises two
steel rolls whose axes are inclined in relation to each other. They
both rotate in the same direction. The space between rolls
converges to a minimum width called the gorge. Just beyond the
gorge is a piercing mandrel. A solid round bar of metal, revolving
in the opposite direction to the rolls, is introduced between the
rolls. When the leading end of the bar has advanced to the gorge,
it encounters the mandrel, which thus forms a central cavity in the
bar as the latter continues to move through the rolls.
[0010] The thick-walled tube produced by the Mannesmann process can
subsequently be reduced to thin-walled tube by passing it through
special rolls in a so-called Pilger mill. These rolls vary in
cross-sectional shape around their circumference. The tube, fixed
to a mandrel, is first gripped by the narrow portions of the rolls.
Rotation of the special rolls, so that progressively thicker
portions of the rolls contact the tube and generate increasingly
larger compressive forces on the tube wall, reduces the tube's wall
thickness until each roll has rotated to such an extent that the
widest part of its cross-section is reached and the tube is thus no
longer gripped. The tube is then pulled back some distance so that
again a thick-walled portion of the tube is gripped by the rolls.
The mandrel is rotated at the same time in order to ensure uniform
application of the roll pressure around the entire circumference of
the tube.
[0011] A second common method of manufacturing seamless metal tubes
is the Stiefel piercing process, wherein a round bar is first
pierced on a rotary piercing mill and the heavy-walled shell
obtained in this way is then reduced in a second piercing
operation, on a two-high rolling stand, to form a thinner-walled
tube.
[0012] A third common method of manufacturing seamless metal tubes
is the rotary forge process, wherein a square ingot, heated to
rolling temperature, is shaped to a shell closed at one end. This
shell is then reduced and stretched on a rotary piercing mill and
finally passed through sets of four rolls, disposed about the
circumference of the tube at 90.degree. intervals, whereby the
diameter is progressively reduced.
[0013] A fourth common method of manufacturing seamless metal tube
shells is extrusion, wherein a billet is forced between a die and a
mandrel (to maintain the tube's central cavity). The extruded tube
shells are then reduced to final diameter and wall thickness by
using one of the processes described above.
[0014] Extrusion is a metalworking process used to produce long,
straight metal products including bars, tubes, hollow sections,
rods, wires, and strips. In this process, a billet, disposed within
a closed container under high load, is forced through a die to
produce an extrusion having the desired cross-section. Extrusion
can be carried our at room temperature or at elevated temperatures,
depending on the metal or alloy being processed.
[0015] The cold extrusion process is used extensively for the
extrusion of low-melting metals, including lead, tin, aluminum,
brass, and copper. In this process, the billets are placed in a
chamber and are axially compressed. The metal flows through a die
having one or more openings to form the cross-section of the
product being extruded.
[0016] The most widely used method for producing extruded shapes is
the direct, hot extrusion process. In this process, a heated solid
metal billet or a metal can containing metal or ceramic powder or a
preform or the like is placed in a chamber and then axially
compressed by a ram. The end of the cylinder opposite the ram
contains a die having an orifice of the desired shape or a
multiplicity of orifices.
[0017] Like the direct, hot extrusion process, the hydrostatic
extrusion process involves the forcing of a solid metal billet or a
metal can containing metal or ceramic powder or a preform through a
suitably shaped orifice under compressive forces. In both
processes, the workpiece or the like is placed in a chamber, one
end of which contains a die having an orifice of the desired shape
or a multiplicity of stepped orifices. Unlike the direct, hot
extrusion process, where the compressive forces operating on the
workpiece are generated by direct contact between the workpiece and
a ram, the compressive forces in the hydrostatic extrusion process
are translated to the workpiece indirectly through a thrust medium
(fluid or powder mass) that surrounds the workpiece. In this way,
all compressive forces operate equally on the workpiece. The
hydrostatic extrusion has been applied to almost all materials,
including aluminum, copper, steel, and ceramics.
[0018] In addition, extrusion of metal is variously termed heading,
pressing, forging, extrusion forging, extrusion pressing, and
impact extrusion. The cold heading process has become popular in
both steel and nonferrous metalworking fields. The original process
consists of a punch (generally moving at high velocity) striking a
blank (or slug) of the metal to be extruded, which has been placed
in the cavity of a die. Clearance is left between the punch and the
die walls. As the punch comes in contact with the blank, the metal
has nowhere to go except through the annular opening between the
punch and the die. The punch moves a distance that is controlled by
a press setting. This distance determines the base thickness of the
finished part. The advantages of cold extrusion are higher strength
of the extrusion because of severe strain-hardening, good finish,
dimensional accuracy, and minimum of machining required. However,
the increased friction between the blank and the die requires a
highly efficient lubricant to ensure that the extrusion conforms
with the desired technical specifications and that the blank does
not jam in the die.
[0019] Hollow cylinders or tubes that are manufactured by these
processes above are often cold-finished by drawing. Cold-drawing is
used to obtain closer dimensional tolerances, to produce better
surface finishes, to increase the mechanical properties of the tube
material by strain hardening, to produce tubes with thinner walls
or smaller diameters than can be obtained with hot-forming methods,
and to produce tubes of irregular shapes.
[0020] Tube drawing is similar to wire drawing. Tubes are produced
on a drawbench or bull block and with dies similar to those
employed in wire drawing. However, in order to reduce the wall
thickness and accurately control the inside diameter, the inside
surface of the tube must be supported while it passes through the
die. This is usually accomplished by inserting a mandrel inside the
tube. The mandrel is often fastened to the end of a stationary rod
attached to one end of the drawbench and is positioned so that the
mandrel is located in the throat of the die. The mandrel may have
either a cylindrical or a tapered cross-section.
[0021] Tubes also may be drawn using a moving mandrel, either by
pulling a long rod through the die with the tube or by pushing a
deep-drawn shell through the die with a punch. Because of
difficulties in using long rods for mandrels, tube drawing with a
rod usually is limited to the production of large diameter tubing.
For small diameter tubes, the rod supporting the stationary mandrel
would be too thin to have adequate strength.
[0022] Another tube forming method is tube sinking, in which no
mandrel is used to support the inside surface of the tube as it is
drawn through the die. Since the inside of the tube is not
supported in tube sinking, the wall thickness will either increase
or decrease, depending on the conditions imposed in the process. On
a commercial basis, tube sinking is used only to produce small
tubes. However, tube sinking represents an important problem in
plastic-forming theory because it occurs as the first step in tube
drawing with a mandrel. In order that the tube dimensions can be
controlled by the dimensions of the mandrel, it is necessary that
the inside diameter of the tube be reduced to a value a little
smaller than the diameter of the mandrel by a tube-sinking process
during the early stages of its passage through the die.
[0023] Tubes have been produced from all of the common metals,
including steel, copper, aluminum, gold, silver, etc., as well as
from the refractory metals, including tantalum, niobium,
molybdenum, tungsten, titanium, zirconium, and their alloys and the
like. Because of the severe sliding contact between the tube and
the die, and between the tube and the mandrel, lubricants are used
in tube-forming operations to reduce friction between the tube and
the forming tools, to flush the tools to prevent the buildup of
fines and dirt on the tool surface, to reduce wear and galling
between the tools and the tube, to remove heat generated during
plastic deformation, and to protect the surface character-istics of
the finished tube.
[0024] As with wire-drawing, ease of cleaning is a fundamental
parameter in the selection of tube-rolling lubricants.
State-of-the-art lubricants have been found to be inadequate in the
production of refractory metal tubing.
[0025] The poor heat transfer characteristics of the CTFE
lubricants greatly limits drawing speeds, generally in the range of
50 to 100 FPM. Typical tube-drawing speeds for the common metals
are in the range of 1,000 to 4,000 FPM. As a result, drawing costs
for refractory metals are very high by comparison. In addition, the
CTFE lubricants are only marginally effective in reducing wear and
galling between the tube and the die and in flushing the wear
products away from the die entrance, These problems can lead to
short die life and problems with surface roughness and dimensional
control (including both diameter and roundness). Also, as in wire
drawing, the CTFE lubricants can leave difficult residues (on the
exterior and interior surfaces of the finished tube).
[0026] A further problem occurs with tubes that cannot be coiled.
These are drawn in straight lengths on draw benches, which use
speeds typically up to 1000 FPM. Therefore, the tendency to form a
partially hydrodynamic film is greatly reduced, even at the outside
surface of the tube. Conditions are even more severe at the
internal surface; good coverage cannot be guaranteed with drawing
pastes or solid soaps, even when applied by dipping, and lubricant
breakdown will frequently lead to galling at dry spots.
[0027] Liquid lubricants can be applied more easily to the inner
surface of the tube, but few liquids are efficient enough boundary
lubricants to prevent some metal-to-metal contact, and those that
do suffice frequently promote corrosive wear of the mandrel (e.g.,
the chlorinated oils). Wear problems are doubled in any event,
since ringing wear is evident on the plugs as well as on dies.
These difficulties are greatly magnified when less reactive
materials, such as stainless steels or titanium alloys, are to be
drawn.
[0028] It is an object of this invention to provide improved
metalworking processes using a lubricant that provides superior
lubricity, as compared with conventional lubricants.
[0029] Another object is to improve the process of working metals
in a way avoiding the foregoing problems.
[0030] A further object of the invention is to use in a
conventional metalworking process a nonflammable and nontoxic
lubricant.
[0031] It is another object of the invention to use in a
conventional metalworking process a lubricant having zero ozone
depletion potential (ODP).
[0032] It is a still further object of the invention to use in a
conventional metalworking process a lubricant that is
photochemically nonreactive in the atmosphere, is not a precursor
to photochemical smog, and is exempt from volatile organic compound
(VOC) definitions of various countries and international
organizations.
[0033] Similarly, it is an object of this invention to provide an
improved process of providing lubricity, avoiding the foregoing
problems.
[0034] It is a further object of the invention to reduce wear of
metals and associated components in processes that involve
lubrication, but are not generally considered as metalworking
processes, e.g., operation of gears, chain drives, and
transmissions in lubricated casings or in open mode; and shafts
moving rotationally or axially on bearings, journals, or
bushings.
SUMMARY OF THE INVENTION
[0035] The present invention, as applied to processes and equipment
(machines) for drawing wire, for drawing, sinking, or rolling
tubes, strip rolling, upsetting, coining, forming seamless metal
tubes, forging, swaging, and extrusion, preferrably using fully and
highly fluorinated lubricants and more particularly are preferrably
applied to making refractory metal mill products and fabricated
parts. The preferred processes and machines employ a lubricant
comprising one or more of: (a) perfluorocarbon compounds (PFCs),
including aliphatic perfluoroalkanes (.alpha.-PFCs) having the
general formula C.sub.nF.sub.2n+2, (b) perfluoromorpholines (PFMs)
having the general formula C.sub.nF.sub.2n+1ON, (c) perfluoroamines
(PFAs), (d) highly fluorinated amines (HFAs), and their respective
polymerization products. Such fully and highly fluorinated carbon
compounds exhibit a very high degree of thermal and chemical
stability due to the strength of the carbon-fluorine bond. PFCs are
also characterized by extremely low surface tension, low viscosity,
and high fluid density. They are clear, odorless, colorless fluids
with boiling points from approximately 30.degree. C. to
approximately 300.degree. C. These fluids may be used alone or in
combination with inert carrying agents, such as in greases, pastes,
waxes, polishes, and the like.
[0036] Fluorinated, inert liquids usable in accordance with the
present invention can be one or a mixture of .alpha.-PFC, PFM, PFA,
and HFA compounds having 5 to 18 carbon atoms or more, optionally
containing one or more catenary heteroatoms, such as divalent
oxygen, hexavalent sulfur, or trivalent nitrogen and having a H:F
ratio under 1:1, preferably having a hydrogen content of less than
5% by weight, most preferably less than 1% by weight. These
materials can be used in liquid phase alone, mixed or emulsified
with other functional or carrier liquids and/or mixed with
particulate solids as pastes (e.g., mixed with known particulate
form solid lubricants such as neodynium fluoride, molybdenum
sulfide, tungsten sulfide, molybdenum selenide, molybdenum
telluride, graphite, TEFLOW.TM., fused fluorides and similar solid
lubricants). Carrying agents for the fluorinated liquids and in
accordance with the process of the invention can be provided, e.g.,
greases, pastes, wax and polish.
[0037] Suitable fluorinated, inert liquids useful in this invention
may include more particularly, for example, perfluoroalkanes, such
as perfluoropentane, perfluorohexane, perfluoroheptane, and
perfluorooctane; perfluoroamines, such as perfluorotributylamine,
perflurotriethylamine, perfluorotriisopropylamine,
perfluorotriamylamine; perfluoromorpholines, such as
perfluoro-N-methylmorpholine, perfluoro-N-ethylmorpholine, and
perfluoro-N-isopropylmorpholine; and the polymerization products of
these classes.
[0038] The prefix "perfluoro" as used herein means that all, or
essentially all, of the hydrogen atoms are replaced by fluorine
atoms. Perfluorocarbon fluids originally were developed for use as
heat-transfer fluids. They are currently used in heat-transfer,
vapor phase soldering, and electronic testing applications and as
solvents and cleaning agents. The term "highly fluorinated" as used
herein means having a H:F ratio under 1:1.
[0039] Commercially available fluorinated, inert liquids useful in
this invention include FC-40, FC-72, FC-75, FC-5311, FC-5312
(available from 3M Company under the tradename designation of
"Fluorinert," 3M Product Bulletin 98-02110534707(101.5)NP1 (1990));
LS-190, LS-215, LS-260 (available from Montefluos Inc., Italy); and
Hostinert.TM. 175, 216, 272 (available from Hoechst-Celanese).
[0040] Importantly, because PFCs are highly or fully fluorinated,
and therefore do not contain chlorine or bromine, they have zero
ozone depletion potential (ODP). The foregoing fluids are
nonflammable and nontoxic Further, because they are photochemically
nonreactive in the atmosphere, they are not precursors to
photochemical smog and are exempt from the federal volatile organic
compound (VOC) definition.
[0041] In addition, the PFC fluids cost significantly less than the
chlorotrifluoroethylene oils currently in use. Accordingly, these
fluorinated, inert fluids are advantageous for processes described
herein and PFCs are presently the preferred lubricants in
high-speed fine wire drawing of refractory metals.
[0042] In the wire drawing process, the perfluorocarbon fluids have
greatly extended the ranges of the major wire drawing variable
available to the process engineer. While using the CTFE lubricants,
the reduction per die was limited to approximately 15%. The use of
PFC lubricants allows reductions as large as 26% per die. This will
allow the next generation of wire drawing equipment to be much more
productive. In addition, operating speeds can be increased by more
than ten fold, greatly reducing the number of wire drawing machines
required at a given production level. The CTFE lubricants were
limited to approximately 200 FPM while the PFC lubricants have been
used at speeds of over 2,000 FPM with no signs of having reached an
upper limit. In addition, die wear is minimized to the point that
wire can be drawn without annealing from 0.103" (2.5 mm) to a final
diameter of 0.005" (0.127 mm) with a die life of more than 200 lbs
of finished, hard drawn wire.
[0043] In the tube drawing process, the perfluorocarbon fluids
greatly extend the ranges of the major drawing variables available
to the process engineer. While using conventional lubricants, the
reduction per pass is limited to approximately 10-15%. The use of
PFC lubricants allows reductions as large as 30%. This enables new
and modified tube drawing processes and equipment that are much
more productive. Operating speeds can be increased by more than
tenfold, greatly enhancing the throughput at a given production
facility. The conventional lubricants were limited to approximately
100 FPM while the PFC lubricants can be used at speeds of over
2,000 FPM. The PFC lubricants of the present invention enhance the
production of smaller diameter tubes, particularly hypodermic
needles and capillary tubing 0.005 to 0.125" (0.127 to 3.17 mm) in
diameter having wall thicknesses in the range of 0.001" to 0.050"
(0.025 to 1.27 mm).
[0044] Tantalum wire- and tube-drawing create in the metalworking
field among the most severe operating conditions requiring
lubrication. The results shown herein establish feasibility for
less severe metalworking processes and with other, more ductile and
malleable materials.
[0045] All grades of the perfluorocarbon fluids evaluated to date
have been used to produce high-quality tantalum wire and tubes. PFC
fluids ranging from 3M's PF-5050 (C.sub.5F.sub.12) having a boiling
point of only 30.degree. C. and a viscosity of 0.4 centistokes to
perfluoroamines having the general formula C.sub.nF2.sub.n+3N, such
as 3M's FC-70 (a blend of perfluorotripropylamine (C.sub.3F.sub.9N)
and perfluorotributylamine (C.sub.4F.sub.11N)) having a boiling
point of 215.degree. C. and a viscosity of 14 centistokes, to other
PFCs (e.g., perfluorotributylamine, perfluorotriamylamine, and
perfluorotripropylamine) having boiling points up to 240.degree. C.
and a viscosity of 40 centistokes at ambient temperature have all
been used to produce high-quality wire at high drawing speeds and
high-quality tubes at high rolling and/or drawing speeds. 3M
Company's FC-40 (perfluorotripropylamine (C.sub.3F.sub.9N)) has
been extensively evaluated because of its combination of low price
and high boiling point (155.degree. C.). This fluid has a viscosity
of only 2 centistokes and a vapor pressure at room temperature of 3
torr. All of the data suggest that there are many other PFC fluids
that are good metalworking lubricants.
[0046] The fact that lubricating characteristics are not dependent
upon PFC fluid viscosity is unique to this class of fluids and is
not yet understood in terms of current metalworking lubrication
theory. In fact, the use of a metalworking lubricant having a
viscosity of less than 1 centistoke is contrary to most lubrication
theories.
[0047] In addition, a major reduction in the amount of submicron
tantalum fine particle debris produced during the above drawing
processes has been observed. While using the conventional
lubricants, the lubricant becomes black and "tarry" due to high
concentrations of tantalum fines within a few hours. When using PFC
fluids, the fluids can be maintained crystal clear using a simple
filter. In contrast with conventional lubricants, PFCs vaporize off
the surface of the tube as it exits the machine. Thus, not only
does the use of these lubricants result in a smoother, cleaner, and
better-performing product than is possible with conventional
lubricants, but a subsequent cleaning step is not required, as with
conventional lubricants.
[0048] A variety of metalworking tasks can be enhanced through the
above process. Particular benefits are realized in the context of
making fine tantalum wire to be used as anode lead wires in
tantalum electrolytic capacitors. The tantalum wire (typically 5
mils to 20 mils (0.127 mm to 0.508 mm in diameter) is buttwelded to
a porous, sintered powder anode, or is embedded therein prior to
sintering and bonded thereto in sintering. Minimizing leakage of
the capacitor using such an anode depends in part on the
cleanliness of the lead wire, which is directly affected by
lubricant selection.
[0049] Significant reduction in wire DC leakage has been achieved
with wires produced in accordance with the present invention. The
leakage current is directly related to the surface topography of
the wire, as well as the amount of lubricant that remains trapped
in the cracks and crevices on the surface of the wire. DC leakage
currents can be reduced by producing a smoother wire surface and
eliminating residual lubricant from the wire surface. The DC
leakage is measured by anodizing a length of wire to completely
cover the surface with a tantalum oxide dielectric film. This
anodized wire is placed in an electrolyte and a DC voltage is
applied to the tantalum lead itself. The DC current "leaking"
through the dielectric film is measured at a fixed voltage. This
leakage current is a measure of the integrity of the dielectric
film. The dielectric film integrity itself is a measure of the
overall surface roughness and cleanliness of the wire surface. By
producing a smooth surface free from residual lubricants, improved
dielectric films are produced, thus improving the DC leakage
characteristics of the wire and of the anode that has the wire
attached to it.
[0050] In addition, significant benefits are realized in the
context of making tantalum tubes to be used as tubes in heat
exchangers. The tantalum tube (typically 10 to 40 mm in diameter)
is used in heat exchange applications in the chemical process
industry where no other metallic material will survive. These
benefits are also realizable under other, less severe operating
conditions, including other metalworking processes and with other,
more ductile and malleable materials or materials (i.e., metals, as
defined herein, that present a metalworking task of similar or
greater severity). The present invention is also applicable to
general lubrication applications, such as case lubrication, bearing
lubrication, and the like.
[0051] The invention is generally not applicable to elevated
temperature metalworking processes conducted at temperatures above
the decomposition temperature of the fluorinated liquids
(>600.degree. C.). The temperatures to be considered are the
result of external heating applied to the metalworking machine's
forming or cutting surfaces and/or the workpiece (e.g., a billet
heated prior to extrusion) and through the mechanical contact
between tool surface and workpiece. Boiling can occur at the end of
the lubricated metalworking process and often does in cold and warm
processes (and even in normal hot processes) that are enhanced
through the present invention. The vapors from the fluorinated
liquid can be recovered by condensation with use of chilled
surfaces. The condensed liquid can be re-used without
reconditioning.
[0052] The invention also includes compression powder metallurgy
usage in that the fluorinated inert materials in liquid or solid
form are usable as coatings of metal particles, e.g. powder and/or
flakes of primary or secondary (pre-agglomerated) form when the
particles are to be pressed in a mold or isostatically. The
particles can be tumhled with the liquid in a mixer until
completely coated, in a manner similar to customary coating with
customary lubricant/binders such as stearic acid. Initial pressing
produces a coherent compact usually of a porous form with point to
point welding among particles. Then the compact is heated to above
the boiling point of the fluorinated coating to drive it off
through the porous mass leaving essentially no residue of the
fluorinated compound. Depending on the end use application, the
compact can be used as such or further consolidated and
strengthened by pressing and/or hearing in cold pressing, hot
pressing, sintering or other known process steps.
[0053] The fluorinated inert liquid can be used alone or with
co-lubricants in powder metalurgy compaction. Its usage can be
limited to coating the metal particles or (in combination with
suitablesolid materials including co-lubricants) forming a matrix
within the compact and/or binding the compact together before
pressing. In such cases the matrix as a whole including the
fluorinated inert material is removed via conventional debindering
techniques after initial compaction of the metal. Boiling off of
the fluorinated inert material and co-lubricant(s) is
preferred.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 shows scanning electron micrographs at 300.times. and
1000.times. of the surface of wire drawn using FC-40
perfluorocarbon fluid at 200 ft/min (61 m/min).
[0055] FIG. 2 shows scanning electron micrographs at 300.times. and
1000.times. of the surface of wire drawn using FC-40 PFC fluid at
500 ft/min (152.4 m/min).
[0056] FIG. 3 shows scanning electron micrographs at 300.times. and
1000.times. of the surface of wire drawn using FC-40 PFC fluid at
1,000 ft/min (304.8 m/min).
[0057] FIG. 4 shows scanning electron micrographs at 1000.times. of
the surface of two wire samples drawn using a CTFE lubricant at 200
ft/min (61 m/min).
[0058] FIG. 5 shows an SPM micrograph at 2500.times. of a
50.mu..sup.2 area of the surface of TPX wire drawn with CTFE
lubricant.
[0059] FIG. 6 shows an SPM micrograph at 2500.times. of a
50.mu..sup.2 area of the surface of TPX wire drawn with FC-40 PFC
fluid.
[0060] FIG. 7 shows an SPM micrograph at 2500.times. of a
50.mu..sup.2 area of the surface of capacitor-grade tantalum wire
drawn with CTFE lubricant.
[0061] FIG. 8 shows the reference micro-FTIR spectrum of the 3M
FC-40 PFC fluid.
[0062] FIG. 9 shows the micro-FTIR spectrum of the extract from a
sample of capacitor-grade tantalum wire together with the reference
spectrum of the FC-40 PFC fluid.
[0063] FIG. 10 shows the micro-FTIR spectrum of the extract removed
from a sample of capacitor-grade tantalum wire after cleaning in an
ultrasonic strand cleaning system used to draw capacitor-grade
tantalum wire on a production basis.
[0064] FIG. 11 shows the as-cleaned micro-FTIR spectrum
superimposed on the reference spectra of a CTFE oil and an
ester-based rod-rolling oil.
[0065] FIG. 12 shows as-received leakage in .mu.A/cm.sup.2 of TPX
wire as drawn with FC-40 PFC fluid.
[0066] FIG. 13 shows a schematic of a PFC fluid recapture and
recycling apparatus for use in wire-drawing.
[0067] FIGS. 14 A-D show scanning electron microscope images at
300.times. and 4500.times. of ETP copper wire drawn with FC40 and a
hydrocarbon based copper drawing lubricant.
[0068] FIGS. 15 A-B show scanning electron microscope images of
tantalum tubes drawn with FC40 and CTFE lubricants.
[0069] FIGS. 16 A-B show scanning probe microscope images of the
surfaces of tantalum tubes drawn with FC40 and CTFE lubricants.
[0070] FIG. 17 shows a scanning electron microscope image of the
surface of 0.0993" 302 stainless steel wire with with L13557
perfluorocarbon fluid.
[0071] FIGS. 18 A-C show the surfaces of 4 mm tantalum nuts
machined using L13557 perfluorocarbon fluid.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0072] The practice of the invention according to preferred
embodiments thereof is indicated by the following non-limiting
examples:
EXAMPLE 1
[0073] 169.5 lbs (77.1 kg) of 0.0098" (0.0249 cm) half-hard temper
tantalum wire was drawn through a Heinrich wire-drawing machine
(MODEL #21W21) using FC-40 perfluorocarbon fluid (3M Company) as
the lubricant. Wire speed ranged from 200 ft/min (61 m/min) to 1386
ft/min (424.5 m/min). The average roundness measured using a laser
micrometer at the beginning of each of the coils of wire was 16
millionths of an inch (40.6 .mu.m) with the average roundness at
the end of each coil averaging 18 millionths of an inch (45.7
.mu.m). An average of 42.4 lbs of wire was produced per set of
dies.
EXAMPLE 2
[0074] 70.2 lbs (31.9 kg) of 0.0079" (0.0201 cm) extra-hard temper
tantalum wire was drawn through a Heinrich wire-drawing machine, as
in Example 1, using 3M's FC40 perfluorocarbon fluid as the
lubricant. Wire speed ranged from 500 ft/min (152.4 m/min) to 1000
ft/min (304.8 m/min). The average roundness at the beginning of
each of the coils of wire was 11 millionths of an inch (27.9 .mu.m)
with the average roundness at the end of each coil averaging 11
millionths of an inch (27.3 .mu.m). An average of 35.1 lbs of wire
was produced per set of dies.
EXAMPLE 3
[0075] 231.8 lbs. (105.4 kg) of 00079" (0.0201 cm) hard temper
tantalum wire was drawn through a Heinrich wire-drawing machine, as
in Example 1, using 3M's FC-40 perfluorocarbon fluid as the
lubricant. Wire speed ranged from 800 ft/min (243.8 m/min) to 1480
ft/min (451.1 m/min). The average roundness at the beginning of
each of the coils of wire was 12 millionths of an inch (30.5 .mu.m)
with the average roundness at the end of each coil averaging 16
millionths of an inch (40.6 .mu.m). An average of 46.4 lbs of wire
was produced per set of dies.
EXAMPLE 4
[0076] 49.4 lbs (22.5 kg) of 0.0075" (0.0191 cm) hard temper
tantalum wire was drawn through a Heinrich wire-drawing machine, as
in Example 1, using 3M's FC-40 perfluorocarbon fluid as the
lubricant. Wire speed ranged from 1480 ft/min (451.1 m/min) to 1600
ft/min (487.7 m/min). The average roundness at the beginning of
each of the coils of wire was 15 millionths of an inch (38.1 .mu.m)
with the average roundness at the end of each coil averaging 17
millionths of an inch (43.2 .mu.m). An average of 24.7 lbs of wire
was produced per set of dies.
EXAMPLE 5
[0077] 71.6 lbs (32.6 kg) of 0.091" (0.0231 cm) annealed temper
tantalum wire was drawn through a Heinrich wire-drawing machine, as
in Example 1, using 3M' 6 FC-40 perfluorocarbon fluid as the
lubricant. Wire speed was 1200 ft/min (365.8 m/min). The average
roundness at the beginning and the end of each of the coils of wire
was 20 millionths of an inch (50.8 .mu.m). An average of 71.6 lbs
of wire was produced per set of dies.
EXAMPLE 6
[0078] In addition to the normal dimensional, visual, and
mechanical property evaluation performed on the wire as it is
produced, the wire drawn using the perfluorocarbon lubricants was
evaluated using scanning electron microscopy (SEM).
[0079] Scanning electron micrographs taken at 300.times. and
1000.times. of capacitor-grade tantalum wire drawn using FC-40 at
200 ft/min (61 m/min), 500 ft/min (152.4 m/min), and 1000 ft/min
(304.8 m/min) are shown in FIGS. 1-3, respectively. The 300.times.
pictures show that wire surface quality actually improves with
increasing drawing speed. Overall, the frequency and depths of the
cracks and crevices on the surface of the wire drawn using
perfluorocarbon fluid lubricant diminish with increasing
wire-drawing speed.
EXAMPLE 7
[0080] The surface of a capacitor grade tantalum wire drawn using a
CTFE lubricant at 200 ft/min (61 m/min) is shown in FIG. 4 at
1000.times.. This picture shows the typical structure seen on wire
drawn using a conventional chlorotrifluoroethylene lubricant. As
can be seen, this wire shows a great deal of surface damage,
particularly in the form of relatively thin platelets of material
torn from the surface of the wire. This appears to be the mechanism
by which most of the "fines" observed in the fine wiredrawing
process are generated. The fact that fines are not observed in wire
drawn using the perfluorocarbon fluid lubricant indicates that
surface damage due to this flaking caused by galling and seizing
(as a result of lubricant breakdown) has been eliminated.
EXAMPLE 8
[0081] In order to evaluate the overall degree of cleanliness of
the as-drawn wire produced using a perfluorocarbon lubricant,
samples were submitted to micro-FTIR infrared analysis. The
reference spectrum of the 3M FC-40 lubricant is shown in FIG. 8.
The spectrum of the methylene chloride extract from a sample of TPX
501G wire drawn using the perfluorocarbon lubricant, together with
the reference spectrum of the FC-40, are shown in FIG. 9. It is
important to note that essentially no lubricant residue of any kind
is found on the wire, and that whatever residue that is present is
definitely not FC-40. The overall absorbence values can be compared
to the data shown in FIG. 10, which shows the FTIR spectrum of the
extract removed from a sample of TPX 501G after cleaning in an
ultrasonic strand cleaning system used to remove CTFE lubricants.
Total absorbence values on the order of 0.1 absorbence units are
typical of wire cleaned in the unit. In general, these absorbency
values represent less than one monolayer of residual lubricant on
the surface of the wire. The perfluorocarbon wire as drawn has less
than 20% of this amount of surface contamination and is truly an
electronically clean material.
[0082] FIG. 11 shows the as-cleaned spectrum superimposed on the
reference spectra of CTFE oil and an ester-based rod-rolling oil
used in earlier stages of the wire production process. These two
materials account for essentially 100% of the residue found on the
surface of our uncleaned capacitor-grade wire. No indication of any
residual FC-40 was found. As a result of this analysis, it appears
that wire drawn using the perfluorocarbon lubricant can be used as
drawn. Subsequent ultrasonic cleaning will only serve to
contaminate the surface of the wire.
EXAMPLE 9
[0083] In order to further verify this finding experimentally,
samples of both 0.0079" (0.0201 cm) and 0.0098" (0.0249 cm)
diameter wire were submitted for as-received leakage tests. The DC
leakage is measured by anodizing a length of wire to completely
cover the surface with a tantalum oxide dielectric film. This
anodized wire is placed in an electrolyte and a DC voltage is
applied to the tantalum lead itself. The DC current "leaking"
through the dielectric film is measured at a fixed voltage. This
leakage current is a measure of the integrity of the dielectric
film. The dielectric film integrity itself is a measure of the
overall surface roughness and cleanliness of the wire surface. By
producing a smooth surface free from residual lubricants, improved
dielectric films are produced; thus improving DC leakage
characteristics of the wire. These data are shown in FIG. 12 and
indicate that the as-received leakage values for as-drawn wire fall
in the range of 1 to 3 .mu.amps/cm.sup.3. They certainly compare
favorably with recent production and compare very favorably with
the specification maximum of 10 .mu.amps/cm.sup.3 commonly seen in
the industry.
EXAMPLE 10
[0084] To evaluate the effectiveness of the perfluorocarbon fluids
for use in copper wire drawing operations, 0.0120" diameter ETP
copper wire was produced using an instrumented laboratory wire
drawing machine using FC40 and a hydrocarbon based copper drawing
oil having a viscosity of approximately 20 centistokes as the
drawing lubricants. The drawing force was measured when drawing
0.0128" diameter wire through the last die to produce 0.0120"
diameter wire, a reduction of 12.1%. The force observed when using
FC40 was 560 grams compared to the observed force of 720 grams when
using a hydrocarbon based copper drawing lubricant.
[0085] Scanning electron micrographs, taken at magnifications of
285.times. and 4500.times., of the ETP copper wire drawn using both
lubricants are shown in FIG. 14. While the surfaces of wires drawn
with both lubricants are similar at low magnification, high
magnification examination reveals many chevron shaped cracks on the
hydrocarbon lubricant drawn sample indicative of grain boundary
separation that may result in wire breakage if additional drawing
were to be attempted.
EXAMPLE 11
[0086] The surface of tantalum tubes drawn using both FC40 and CTFE
lubricants were examined using the scanning electron microscope.
FIG. 15A shows the surface of a 0.250" diameter tube having a
0.010" wall thickness drawn using FC 40 at a magnification of
315.times.. FIG. 15B shows the surface of a 0.500" diameter tube
drawn using a CTFE oil at a magnification of 319.times.. These
micrographs clearly show extensive metal loss from the surface of
the tube drawn using the CTFE oil.
[0087] To quantify the difference in surface roughness between
these tubes, samples of both were examined using a scanning probe
microscope. FIG. 16A shows the three dimensional image of the
surface of the tube drawn using FC40 having an average surface
roughness (Ra) of 93.15 nm. FIG. 16B shows the three dimensional
image of the surface of the tube drawn using a CTFE oil having an
average surface roughness of 294.92 nm. These data show that the
tube drawn using the CTFE oil had a surface roughness value three
times that of the tube drawn using FC40, a perfluorocarbon
fluid.
EXAMPLE 12
[0088] To evaluate the effectiveness of the perfluorocarbon fluids
for use in stainless steel wire drawing operations, 0.139" diameter
302 stainless steel wire was obtained from Carpenter Technology and
drawn through four successive reductions using L13557
perfluorocarbon fluid as a lubricant to product 0.0993" diameter
wire. Using normal stainless steel drawing practices, only three
18% reductions are possible without annealing the wire and
recoating with a phosphate lubricant carrier.
[0089] An SEM image of the surface of the 0.0993" wire drawn using
the perfluorocarbon lubricant is shown in FIG. 17 at 255.times..
This image clearly shows the presence of the phosphate lubricant
carrier over most of the wire surface after four 18%
reductions.
EXAMPLE 13
[0090] To evaluate perfluorocarbon fluids in tantalum machining
operations, an experimental perfluoroamine fluid was substituted
for the CTFE oil normally used in a sequential machining operation
to produce 4 mm tantalum nuts. These nuts were produced from
punched blanks in a series of machining operations including
drilling, tapping, turning and facing operations. The introduction
of L13557 resulted in a more than four fold increase in machining
speed from 200 surface feet per minute to >850 surface feet per
minute while increasing tool life by at least a factor of 10. When
using CTFE oils, the facing tool bit is resharpened every 50 to 100
pieces. Usen using L13557, tool resharpening occurs at intervals of
more than 2000 pieces. Similar increases in tool life were observed
for drills and taps as well.
[0091] An SEM image at 25.times. of a section of one of the 4 mm
nuts is shown in FIG. 18A. This image shows the high quality
surface finish obtained on the outermost thread surface as well as
the faced surface. The average surface finish (R.sub.a) was
consistently measured at better than 32 microinches. An SEM image
of the threads at 31.times. is shown in FIG. 18B showing the
excellent thread form obtained and showing no evidence of tearing.
An SEM split image at 25.times. and 250.times. of the surface of
one of the 4 mm tantalum nuts machined using L13557 is shown at
FIG. 18C showing the overall freedom from tears and gouges
typically found on machined tantalum surfaces at this
magnification.
END OF NUMBERED EXAMPLES
[0092] In actual production trials employing the 3M Company's FC-40
perfluorocarbon fluid, the most significant advantages observed
include a greater than five-fold increase in die life, a greater
than ten-fold increase in wire-drawing speed, "electronically
clean" as-drawn wire, and a five-fold reduction in lubricant cost
per pound of wire drawn. In addition, a major reduction in the
amount of submicron tantalum fine particle debris produced has been
observed. While using the CTFE lubricants, the filters on the
wire-drawing machines are changed at the end of every production
shift. When using PFC fluids, these filters are changed every one
to two months. And, as shown in FIG. 13, the PFC fluids used may be
recaptured from the wire-drawing machine and recycled, thereby
reducing operating expenses and even further enhancing the
environmental benefits that are possible.
[0093] When drawing tubes of any metallurgy, the maximum
theoretical reduction per pass (over a fixed, cylindrical mandrel)
is calculated as: 1 ( 1 ) q max = 1 - 1 + 0.133 B ' 1 + B ' - 1 / B
where B ' = 2 f tan
[0094] and where f is the coefficient of friction between the die
and the workpiece for a particular lubricant and .alpha. is one
half the apex angle of the die, in this case held constant at
12.degree..
[0095] For normal lubricants, f normally varies between 0.05 and
0.15. For PFC fluid lubricants, f has been estimated at 0.003 to
0.005. Thus, 2 ( B ' ) conventional = 2 ( 0.10 ) tan = 1.903 and B
' PFC = 2 ( 0.005 ) tan = 0.095
[0096] Therefore, q.sub.max(conventional)=35% and
q.sub.max(PFC)=56%, a sixty percent increase in the maximum
theoretical reduction per pass possible when using a PFC lubricant,
as compared with a conventional lubricant.
[0097] It will now be apparent to those skilled in the art that
other embodiments, improvements, details, and uses can be made
consistent with the letter and spirit of the foregoing disclosure
and within the scope of this patent, which is limited only by the
following claims, construed in accordance with the patent law,
including the doctrine of equivalents.
* * * * *