METALWORKING LUBRICATION

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™ 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™, fused fluorides, MoS2, WS2, MoSe2, MoTe2, 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° 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 (α-PFCs) having the general formula CnF2n+2, (b) perfluoromorpholines (PFMs) having the general formula CnF2n+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° C. to approximately 300° 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 α-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™, 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™ 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 (C5F12) having a boiling point of only 30° C. and a viscosity of 0.4 centistokes to perfluoroamines having the general formula CnF2n+3N, such as 3M's FC-70 (a blend of perfluorotripropylamine (C3F9N) and perfluorotributylamine (C4F11N)) having a boiling point of 215° C. and a viscosity of 14 centistokes, to other PFCs (e.g., perfluorotributylamine, perfluorotriamylamine, and perfluorotripropylamine) having boiling points up to 240° 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 (C3F9N)) has been extensively evaluated because of its combination of low price and high boiling point (155° 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° 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× and 1000× 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× and 1000× 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× and 1000× 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× 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× of a 50μ2 area of the surface of TPX wire drawn with CTFE lubricant.

[0059]
FIG. 6 shows an SPM micrograph at 2500× of a 50μ2 area of the surface of TPX wire drawn with FC-40 PFC fluid.

[0060]
FIG. 7 shows an SPM micrograph at 2500× of a 50μ2 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 μA/cm2 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× and 4500× 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 μm) with the average roundness at the end of each coil averaging 18 millionths of an inch (45.7 μm). 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 μm) with the average roundness at the end of each coil averaging 11 millionths of an inch (27.3 μm). 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 μm) with the average roundness at the end of each coil averaging 16 millionths of an inch (40.6 μm). 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 μm) with the average roundness at the end of each coil averaging 17 millionths of an inch (43.2 μm). 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 μm). 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× and 1000× 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× 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×. 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 μamps/cm3. They certainly compare favorably with recent production and compare very favorably with the specification maximum of 10 μamps/cm3 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× and 4500×, 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×. FIG. 15B shows the surface of a 0.500″ diameter tube drawn using a CTFE oil at a magnification of 319×. 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×. 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× 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 (Ra) was consistently measured at better than 32 microinches. An SEM image of the threads at 31× is shown in FIG. 18B showing the excellent thread form obtained and showing no evidence of tearing. An SEM split image at 25× and 250× 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) q_{\max} = \frac{1 - 1 + 0.133 B^{'}}{1 + B^{'}} - 1 / B

where B^{'} = \frac{2 f}{\tan α}

[0094] and where f is the coefficient of friction between the die and the workpiece for a particular lubricant and α is one half the apex angle of the die, in this case held constant at 12°.

[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,

{(B^{'})}_{conventional} = \frac{2 (0.10)}{\tan α} = 1.903 and

{B^{'}}_{PFC} = \frac{2 (0.005)}{\tan α} = 0.095

[0096] Therefore, qmax(conventional)=35% and qmax(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.

METALWORKING LUBRICATION

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