Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/02—Compacting only
  • B22F2003/023—Lubricant mixed with the metal powder
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

• Powder metal composition comprising secondary amides as lubricant and/or binder.
• the present invention concerns a powder metal composition. Specifically the invention concerns a powder metal composition including a lubricant and/or binder comprising at least one secondary amide. The invention further concerns a method of producing a green body, a method of producing a bonded iron-based powder composition and use of the lubricant and/or binder.
• Metal powders are used in industry for the manufacture of metal products by compacting the metal powder in a die under high pressures, ejecting the compact from the die and optionally sintering the product.
• a lubricant is comprised in the powder in order to provide the necessary lubrication action between powder particles during compaction and between the die and the compact during ejection from the die.
• Lubrication achieved by a lubricant included in the metal powder is referred to as internal lubrication in contrast to external lubrication, which is achieved by applying a lubricant to the walls of the die, wherein the powder is compacted.
• Insufficient lubrication during ejection results in excessive friction between the compact and the die resulting in high ejection energies and damage of die surfaces and product surfaces .
• lubrication is achieved by using special lubricants. Normally these lubricants are admixed with the iron or iron-based powder in the form of a powder. Some lubricants may also be used for binding additives, such as e.g. alloying elements, to the iron or iron-based particles. In these cases the lubricants thus work as binding agents and reduce or eliminate segregation of the additives during shipping and handling. Commonly used lubricants for PM applications are metal soaps, such as lithium and zinc stearate.
• a disadvantage with this type of lubricant is that oxides of the metals in the lubricant contaminate the inside of the sintering furnace as a result of release of metals from the lubricant during sintering, another problem is that stains may be formed on the component after sintering.
• Another commonly used lubricant is ethylene bis stearamide (EBS) . Stains may also be formed on the component after sintering when using this lubricant, but to a lesser extent compared with using e.g. zinc stearate.
• EBS ethylene bis stearamide
• Stains may also be formed on the component after sintering when using this lubricant, but to a lesser extent compared with using e.g. zinc stearate.
• a powder metal composition comprising an iron based powder and a lubricant and/or binder comprising at least one secondary amide.
• the invention further concerns a method of producing a green body by subjecting the above mentioned composition to compaction.
• the method of producing a bonded powder metal composition comprises: mixing an iron-based powder with at least one secondary amide and heating the mixture to a temperature above the melting point of the at least one secondary amide.
• the invention concerns the use of the at least one secondary amide as a lubricating and/or binding agent for iron-based powders, and its use for die wall lubrication.
• the lubricant and/or binder in the powder metal composition according to the invention is at least one secondary amide that may be defined by the general formula:
• Ri- and R 2 ⁇ groups which may be the same or different, are straight or branched, saturated or unsaturated aliphatic hydrocarbon groups.
• Ri and R 2 independently include 10 to 24 carbon atoms .
• Ri and R 2 are selected from the group con ⁇ sisting of alkyl and alkenyl.
• the alkyl groups may be chosen from decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl.
• the alkenyl groups may be chosen from decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl, eicosenyl, heneicosenyl, docosenyl, tricosenyl, tetracosenyl.
• the amount of secondary amides may constitute 0.05- 2.0 % by weight of the powder metal composition, preferably 0.05-1.0% by weight.
• One embodiment of the invention concerns a powder metal composition
• a powder metal composition comprising a lubricant and/or binder further comprising at least one primary amide in addition to the at least one secondary amide.
• the at least one primary amide is preferably a saturated or unsaturated fatty acid amide having 12-24, preferably 14-22 C-atoms and most preferably 16-22 C-atoms.
• Especially preferred primary amides are stearic acid amide (stearamide) , behenic acid amide (behenamide) , eurcic acid amide (erucamide) , palmitic acid amide (palmitamide) and arachidic acid amide (arachidamide) .
• the primary and secondary amides according to the invention are either commercially obtainable or may be produced from commercially obtainable material by the use of processes well known in the art.
• the amount of primary and secondary amides may constitute a total of 0.05-2.0 % by weight of the powder metal composition, preferably 0.05-1.0% by weight.
• the amount of the at least one primary amide may be 0.05-1.0% by weight and the amount of the at least one secondary amide may be 0.05-1.0% by weight for the embodiment of the invention comprising both types of amides .
• the lubricant and/or binder may be added to the powder metal composition in the form of solid particles of each amide.
• the average particle size may vary, but is preferably less than 150 ⁇ m.
• the lubricant and/or binder may be added to the powder metal composition as a molten and subsequently solidified particulate mixture of the amides. This may be accomplished by mixing the amides in a predetermined ratio, the mixture is then melted, cooled and subsequently milled to a lubricant powder.
• the at least one secondary amide according to the invention may be used as a binder for obtaining a bonded mixture, wherein optional alloying elements and the at least one secondary amide are bonded to the iron-based powder. This may be achieved by mixing an iron-based powder with at least one secondary amide according to the invention, and heating the mixture to a temperature above the melting point of the at least one secondary amide. At least one primary amide may further be mixed into the above mentioned mixture and the heating temperature may then be lower than the melting point of the primary amide.
• the powder metal composition according to the invention may, if so desired, contain other lubricants, such as zinc stearate, lithium stearate, EBS etc.
• bonding systems such as alkydes, cellulose ester resins, hydroxyalkyl cellulose resins having 1-4 carbon atoms in the alkyl group, or thermoplastic phenolic resins.
• iron-based powder encompasses powder essentially made up of pure iron, iron powder that has been pre-alloyed with other elements improving the strength, the hardening properties, the electromagnetic properties or other desirable properties of the end products and particles of iron mixed with particles of such alloying elements (diffusion annealed mixture or purely mechanical mixture) .
• alloying elements are copper, molybdenum, chromium, manganese, phosphorous, carbon in the form of graphite, nickel, silicon, boron, vanadium, titanium, aluminium, cobalt and tungsten, which are used either separately or in combination, e.g. in the form of compounds (Fe 3 P and FeMo) .
• the iron based powders may be used for the preparation of soft magnetic parts and may, for this application, be electrically insulated. Electrical insulation of the powder particles may be made of an inorganic material. Especially suitable are the type of insulation disclosed in the US 6348265, which concerns particles of a base powder consisting of essentially pure iron having an insulating oxygen- and phosphorus-contai ⁇ ning barrier. Insulated powder particles are available as SomaloyTM 500 and 550 from Hoganas AB, Sweden.
• the powder metal composition according to the invention may contain one or more additives selected from the group consisting of processing aids and hard phases.
• the processing aids used in the powder metal composition may consist of talc, forsterite, manganese sulphide, sulphur, molybdenum disulphide, boron nitride, tellurium, selenium, barium difluoride and calcium difluoride, which are used either separately or in combination.
• the hard phases used in the powder metal composition may consist of carbides of tungsten, vanadium, molyb ⁇ denum, chromium, AI 2 O 3 , B 4 C and various ceramic materials.
• the invention further concerns a method of producing a green body comprising: compacting the powder metal composition according to the invention to a compacted body, wherein the composition comprises an iron based powder and a lubricant and/or binder comprising at least one secondary amide having the general formula:
• Ri-NH-CO-R2 wherein Ri and R 2 are the same or different, straight or branched, saturated or unsaturated aliphatic hydrocarbon groups.
• the compacted body may be sintered or heat-treated. With the aid of conventional techniques, the iron- based powder, the lubricant and/or binder and optional additives may be mixed to a substantially homogeneous powder composition before the compaction step.
• the powder metal composition and/or the die may be preheated before the compaction.
• the invention further concerns the use of at least one secondary amide, defined as above, as a lubricating and/or binding agent for iron or iron based powders .
• a further embodiment of the invention concerns the use of at least one secondary amide, defined as above, as a die wall lubricant.
• FIG. 1 shows stain formation of components after sintering due to the use of different lubricants.
• EBS Ethylene bisstearamide
• This example demonstrates the lubrication properties of different secondary amides and different combinations of secondary and primary amides, which are added as a powder in iron-based powder mixes .
• Base powder ASC 100.29 (available from Hoganas AB, Sweden) was mixed with 0.5% by weight of graphite (uf-4 from Kropfmuhl) and 0.8% by weight of lubricants, according to Table 3 and 4, in a L ⁇ dige mixer for 2 minutes.
• Ethylene bisstearamide (EBS, available as Licowax TM from Clariant, Germany) was used as a reference.
• the lubricants had a particle size less than 150 ⁇ m.
• Compositions comprising both a secondary and a primary amide contained 50% of each amide (0.8% by weight of the total composition) .
• the base powder ASC 100.29 was mixed with 2% by weight of Copper (-lOO ⁇ m) , 0.8% by weight graphite and 0.8% by weight of lubricants (a) EBS or b) oleyl palmitamide) in a L ⁇ dige mixer for 2 minutes .
• the lubricants had a particle size less than 150 ⁇ m.
• cylindrical components with a diameter of 64 mm and a height of 32 mm were compacted to a green density of 7.1 g/cm 3 at ambient temperature.
• the weight of one cylinder was 700 g.
• the components were sintered in an atmosphere containing 90/10 N 2 /H 2 at 1120 0 C for 15 minutes.
• This example demonstrates the lubrication properties of different combinations of secondary and primary amides, which have been melted together, cooled and milled before being mixed with iron-based powder mixes .
• the lubricant combinations were made according to following method: The mixed lubricants, 50% primary and
• the base powder ASClOO.29 was mixed with 0.5 % by weight of graphite and 0.8 % by weight of lubricant combination (see Table 5), in a L ⁇ dige mixer for 2 minutes.
• rings with inner diameter of 45 mm, outer diameter 55 mm and a height 10 mm were compacted at three different compaction pressures, 400, 600 and 800 MPa at ambient temperature.
• the resulting ejection energies and densities are shown in Table 5.
• Table 5 Densities and ejection energies (secondary + primary amides and reference) .
• This example demonstrates the lubricating and binding properties of different combinations of amides in powder metal compositions.
• the lubricants had a particle size less than 150 ⁇ m.
• the base powder ASClOO.29 was mixed with 2% by weight Cu-100, 0.8 % by weight of graphite and 0,8 % by weight of lubricant/binder combination according to Table 6, in a Lodige mixer for 2 minutes.
• the mixture with EBS was kept as reference while the mixtures comprising amides were heated to a temperature above the melting point of the secondary amide but below the melting point of the primary amide during mixing in another mixer followed by cooling to accomplish bonding of the additives to the iron powder.
• the secondary amide will thus act as a binder and the primary amide will act as a lubricant.
• the melting temperatures of the amides are disclosed in Table 7.
• the ejection energy was measured on rings having an outer diameter of 55 mm and an inner diameter of 45 mm and a height of 10 mm compacted at three different compaction pressures, 400, 600 and 800 MPa at ambient temperature.
• the resulting ejection energies and green densities are shown in Table 8.
• Samples produced with the aid of the lubricant/binder according to the invention show lower ejection energies compared to samples produced with the lubricant used as reference, i.e. EBS.
• Use of the powder composition comprising the lubricant/binder according to the invention resulted in compacted sintered parts (sintered in 90/10 N 2 /H 2 at 112O 0 C for 30 minutes) with excellent surface finishes, i.e. essentially without scratches and no stain formation.
• Example 5 A coarse soft magnetic iron-based powder, wherein the particles are surrounded by an inorganic insulation was mixed with secondary amide lubricant according to Table 9.
• secondary amide lubricant As reference lubricants the known substances Zinc- stearate and EBS were used.
• the particle size distribution of the used iron-based powder is disclosed in Table 10.
• the obtained mixes were transferred to a die and compacted into cylindrical test samples (50 g) having a diameter of 25 mm, in an uniaxial press movement at a compaction pressure of 1100 MPa.
• the die material used was conventional tool steel. During ejection of the com ⁇ pacted samples the ejection force was recorded. The total ejection energy/enveloping area needed in order to eject the samples from the die was calculated.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Lubricants (AREA)
• Powder Metallurgy (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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• 2005
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