Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Metal and nonmetal in final product
Patent
1997-01-21
1998-05-19
Jordan, Charles T.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Metal and nonmetal in final product
419 29, 419 35, 419 37, B22F 100
Patent
active
057549362
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process of heat treating compacted iron-based powder compositions. More particularly, the invention relates to a process, in which iron compositions are mixed with thermoplastic resins, compacted and heated. The process is particularly useful for making magnetic core components having good soft magnetic properties and high strength.
U.S. Pat. No. 5,268,140 discloses a method for producing a high-strength iron-based component by powder-metallurgical techniques. According to this method a powder composition of iron-based particles, which are coated or admixed with a thermoplastic material in the presence of an organic solvent, is compacted in a die at a temperature above the glass-transition temperature of the thermoplastic material and the obtained component is separately heated at a temperature that is at least as high as the compacting temperature up to about 800.degree. F. (427.degree. C.). The resulting component has increased strength and can be used as a structural component or as a magnetic core component. Furthermore, this patent discloses that, according to the most preferred embodiment, the thermoplastic material is present as a coating on the surfaces of the individual iron particles. In variations of this embodiment the iron particles can be double-coated such as where, in addition to an outer layer of the thermoplastic material, the particles have a first inner coating of an insulative material such as iron phosphate.
In brief, the present invention concerns a process, according to which powder compositions of iron-based particles are admixed with a thermoplastic material. The obtained mixture is compacted at a temperatue below the glass-transition temperature or melting point of the thermoplastic material and the compacted product is heated in order to cure the thermoplastic resin. Subsequently the obtained compacted component is optionally annealed to a temperature above the curing temperature.
Specifically, the invention concerns a process for powder-metallurgical preparation of products having high strength and improved soft-magnetic properties comprising the following steps acid at a temperature and for a time sufficient to form an iron phosphate layer material, selected from the group consisting of polyphenylene ethers and polyetherimides and oligomers of amide type, and with a low-melting lubricant to form a substantially homogeneous particle mixture, the glass-transition temperature or melting point of the thermoplastic resin thermoplastic resin, and f) optionally annealing the obtained component to a temperature above the curing temperature of the thermoplastic resin.
In step a) of the process, particles of an atomised or sponge iron powder are preferably treated with an aqueous phosphoric acid solution to form an iron phosphate layer at the surface of the iron particles. The phosphoric acid treatment is carried out at room temperature and for a period of about 0.5 to about 2 hours. The water is then evaporated at a temperature of about 90.degree. C. to about 100.degree. C. in order to form a dry powder. According to another embodiment of the invention the iron powder is treated with phosphoric acid dissolved in an organic solvent.
The phosphorous layer should be as thin as possible and at the same time coating the separate particle as completely as possible. Thus the amount of phosphorus is higher for powders with a larger specific surface area. As sponge powders have a higher specific surface area than atomised powders the amount of P should generally be higher for sponge powders than for atomised powders. In the first case the P amount may vary between about 0.02 and 0.06, preferably between 0.03 and 0.05 whereas in latter case the P amount might vary between 0.005 and 0.04, preferably between 0.008 and 0.03% by weight of the powder.
The thermoplastic materials used in the process of the invention may be polymers having a weight average molecular weight in the range of about 10 000 to 50 000 and a level of crystallinity that allows them to be dissolved in
REFERENCES:
patent: 5211896 (1993-05-01), Ward et al.
patent: 5268140 (1993-12-01), Rutz et al.
patent: 5563001 (1996-10-01), Gay
Chi Anthony R.
Hoganas AB
Jordan Charles T.
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