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
  • 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
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/08—Metals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/01—Hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/05—Alcohols; Metal alcoholates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/07—Aldehydes; Ketones
• • 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

• the invention is based on a binder system according to the type of the main claim and a method for processing metal powders into sintered parts using the binder system according to the invention.
• MIM metal injection molding
• Binder systems based on waxes, such as paraffin wax, are known, e.g. B. from the lecture by Chan I. Chung: Binder-Assisted Injection Molding of Powders at the Rensselaer Symposium in Troy / New York from July 16 to 18, 1990.
• shortcomings of the wax-containing binder systems mentioned are already pointed out: low dimensional stability during thermal expulsion of the binder, long expulsion times, and a structural inhomogeneity of the green body after expulsion of the binder.
• New binder systems have therefore been developed which consist of a polymer component and a low molecular weight binder component which is solid at room temperature and which form solutions over a wide range of temperatures and mixtures, so-called solid polymer solutions (SPS). Compared to wax-containing SPS binder systems, they have the following advantages:
• the green bodies injection-molded therewith remain dimensionally stable while the binder is being driven out; after removal of the low-molecular component, a pore structure remains in the green compact, through which the gaseous crack products of the polymer component can escape; the low molecular weight component can be easily driven out and recovered below the melting point of the binder system.
• PLC binder systems are e.g. B. from the above-mentioned Vorschriftmanu ⁇ script by Chan I. Chung known, for example a system of 70% acetanilide, 20 ⁇ polymer and 10 " ⁇ stearic acid.
• the known SPS binder systems based on polystyrene or polyvinyl acetate and low molecular weight compounds such as acetanilide, diphenyl sulfone, diphenyl carbonate, antipyrine, naphthalene or decalin have the disadvantage that the low molecular weight components are harmful to health and therefore cannot be used everywhere for occupational safety reasons are.
• the known Binder systems wetting aids such. B. stearic acid. This is necessary for the fluidity of the compounds, but it is the cause of some difficulties in the process.
• binder systems according to the invention are based on non-toxic low molecular weight components and the polymer components are selected so that wetting aids such as, for. B. stearic acid are not necessary.
• wetting aids such as, for. B. stearic acid are not necessary.
• Cyclododecane, cyclododecanone, cyclododecanol or stearyl alcohol are suitable as low molecular weight components.
• cyclododecane is used as the low molecular weight component.
• Cyclododecane melts at 60 ° C, is largely physiologically harmless and can be removed very easily and quickly, by sublimation or by evaporation from the molding. It forms homogeneous melts with polyolefins below their solidification temperature.
• a relatively low viscosity polypropylene can e.g. B. can be obtained by oxidative degradation of most commercially available types of polypropylene.
• the binder system can easily be adapted for metal powders of different grain sizes and for different molded parts.
• Polypropylenes that are oxidatively degraded in air contain polar groups. They wet the metal powders coated with an oxide skin better than unmodified polypropylenes with the same flow index. This eliminates the need to add wetting aids.
• the binary binder system according to the invention is compounded with metal powders under protective gas in a kneader. The protective gas atmosphere during compounding prevents the oxidative dehydrogenation of the polymer component, which is catalyzed by many metal powders. When compounded in air, a partially dehydrated polypropylene would result. This results in inadmissibly high residual carbon contents when cracking under protective gas in the metal powder structure, which lead to structural defects during sintering, such as e.g. B. Carbide formation at the grain boundaries, voids and cracks due to methane formation.
• the residual carbon content in the sintered parts can be set in a wide range as desired and z. B. lower than 0.01% if desired.
• the pyrolysis time is therefore shorter than with the conventional temperature-time step functions.
• the additional preheating of the incoming protective gas makes the temperature in cracking and sintering furnaces more uniform. This reduces the time required for the thermal expulsion of the binder and the distortion of filigree molded parts during sintering.
• a commercially available type of polypropylene is oxidatively degraded by mastification at 200 ° C in air to a flow index 190 / 1.2 of 20 g per 10 minutes.
• low-boiling degradation products escape, which form during the oxidation of additives, such as stabilizers.
• the preparation takes place under protective gas, at 180 ° C. in a vacuum-tight SIGMA kneader, which was thoroughly rinsed with protective gas before heating.
• the compound granulates on its own during cooling while the kneader is running.
• the granules are processed into moldings in an extruder.
• Sintering takes place in several stages: first heating for three hours at 120 ° C in a gentle N stream to remove the cyclododecane, heating at 120 ° C / h under N stream to 260 ° C, heating at 20 ° C / h under N stream to 330 ° C, heating at 10 ° C / h under N flow to 430 ° C, rapid heating under H flow to 1280 ° C and 1.5 hours at 1280 ° C. Parts made in this way from 430 L steel powder had densities of 98.5% of the theoretically possible density.
• polystyrene resin In addition to polypropylenes, other polyolefins or copolymers of olefins with polar monomers in combination with cyclododecane are of course also suitable as binders for the MIM process.

Landscapes

• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)
• Compositions Of Macromolecular Compounds (AREA)

Applications Claiming Priority (2)

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• 1990
  • 1990-10-25 DE DE4033952A patent/DE4033952C1/de not_active Expired - Lifetime
• 1991
  • 1991-10-10 EP EP91917354A patent/EP0554272A1/de not_active Withdrawn
  • 1991-10-10 WO PCT/DE1991/000799 patent/WO1992007675A1/de not_active Application Discontinuation
  • 1991-10-10 JP JP3515730A patent/JPH06501985A/ja active Pending

Non-Patent Citations (1)

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