Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-05-24
2003-03-18
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06534564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for making metal-based compacted components and metal-based powder compositions suitable for cold compaction. More particularly, the present invention is directed to a method of compacting certain metal-based powder compositions at cold compaction temperatures to form metal-based components. The method is particularly useful for making magnetic core components.
BACKGROUND OF THE INVENTION
Iron-based particles have long been used in the manufacture of metal-based components by powder metallurgical methods. The iron-based particles are first molded in a die under pressure in order to produce the desired shape. After the molding step, the metal-based component (e.g., a “green” part) usually undergoes a sintering step (i.e., temperatures greater than about 490° C.) to impart the necessary strength to the component.
The powder metallurgy art generally uses four standard temperature regimes for compacting a metal powder to form a metal component. These include chill-pressing (pressing below ambient temperatures), cold-pressing (pressing at ambient temperatures), hot-pressing (pressing at temperatures above those at which the metal powder is capable of retaining work-hardening), and warm-pressing (pressing at temperatures between cold-pressing and hot-pressing).
Iron-based powder compositions that are generally warm pressed include iron particles that are either admixed or coated with a thermoplastic material. Examples of such iron-based powder compositions are disclosed in for example U.S. Pat. Nos. 5,063,011, 5,198,137, 5,225,459, 5,268,140, 5,767,426, and 6,039,784. These types of iron-based powder compositions have typically been compressed at die temperatures above the glass transition temperature of the thermoplastic material. For example, the aforementioned U.S. Pat. No. 5,268,140 discloses a method of compacting iron-based particles coated or admixed with a thermoplastic material that includes compacting the powder in a die at a temperature above the glass transition temperature of the thermoplastic material and separately heating the component to a temperature that is at least as high as the compaction temperature. Such compaction temperatures are used because it was believed that compaction temperatures below the glass transition temperature of the thermoplastic material would yield components having poor strength and density properties.
Moreover, as iron-based powders admixed or coated with a thermoplastic material are often used to form magnetic core components, it was believed that compacting such powders below the glass transition powder of the temperature would yield components having poor magnetic performance. Important magnetic characteristics of a core component are its magnetic permeability and core loss characteristics. The magnetic permeability of a material is an indication of its ability to become magnetized, or its ability to carry a magnetic flux. Permeability is defined as the ratio of the induced magnetic flux to the magnetizing force or field intensity. Core loss, which is an energy loss, occurs when a magnetic material is exposed to a rapidly varying field. The core losses are commonly divided into two categories: hysteresis and eddy-current losses. The hysteresis loss is brought about by the necessary expenditure of energy to overcome the retained magnetic forces within the metal-based core component. The eddy-current loss is brought about by the production of electric currents in the metal based core component due to the changing flux caused by alternating current (AC) conditions.
Despite the advantages of warm compaction methods as described above, heating the die to above the glass transition temperature of the thermoplastic material can be time consuming and can cause excessive wear on the die. Moreover, often it is desired to heat the iron-based powder prior to introduction in the die. Heating the iron-based powder can also be time consuming as well. Thus, it is desirable to provide a method for compacting iron-based powders that does require the die to be heated or the iron-based powder to achieve acceptable properties such as strength, density, and magnetic performance.
U.S. Pat. No. 5,754,936 to Jansson (“Jansson”), discloses a process where iron particles are first treated with phosphoric acid to form an iron phosphate layer and the resulting phosphate coated particles are admixed with a thermoplastic resin and lubricant, and compacted at a temperature below the glass transition temperature of the thermoplastic resin. The compacted component is then heated to the curing temperature of the thermoplastic resin. Although the compaction in Jansson can be carried out at ambient temperature, Jansson requires coating the iron first with phosphoric acid to form an iron phosphate layer. This extra processing step can be time consuming as the solvent (e.g., water) carrying the phosphoric acid must be removed and the particles must then be heat treated to form the iron phosphate layer.
Thus, it is desired to provide an efficient method of making metal-based components that does not require heating of the die and/or the metal-based powder for compaction, and provides metal-based components having acceptable properties.
SUMMARY OF THE INVENTION
The present invention provides a method of making a metal-based component that includes providing a metal-based powder composition containing metal-based particles having an outer coating of at least one thermoplastic material, the thermoplastic material constituting from about 0.001% to about 15% by weight of the metal-based particles as coated, wherein the metal-based particles are free of an iron phosphate layer; and compacting the composition in a die at a temperature below 55° C. to form a component.
In another embodiment, the present invention provides a method of making a metal-based component that includes providing a metal-based/thermoplastic powder composition containing metal-based particles that are free of an iron phosphate layer and that are admixed with a thermoplastic material in particulate form, the thermoplastic material constituting from about 0.001% to about 15% by weight of the composition. The metal-based/thermoplastic powder composition is then compacted in a die at a temperature below about 55° C.
The metal-based components thus formed surprisingly have comparable properties of strength, density, and magnetic performance to metal-based components compacted at temperatures above the glass transition temperature of the thermoplastic material. Thus, the present invention is also useful for making magnetic components by providing a metal-based composition containing metal-based particles and a thermoplastic material and compacting the composition in a die at a temperature below about 55° C.
In another embodiment, the present invention provides a metal-based powder composition suitable for cold compaction containing from about 80.0 weight percent to about 99.8 weight percent of a metal-based powder, containing metal-based particles, where the metal-based particles are free of an iron phosphate layer; from about 0.001 weight percent to about 15 weight percent, of a thermoplastic material selected from polyetherimides, polyphenylene ethers, polyethersulfones, polycarbonates, polyethylene glycol, polyvinyl acetate, polyvinyl alcohol or combinations thereof; and from about 0.1 weight percent to about 2.0 weight percent of an oligomer of a polyamide.
DETAILED DESCRIPTION
The present invention provides a method for compacting metal-based powder compositions at cold compacting temperatures to form metal-based components, thus eliminating the need to use a heated die to produce the compacted components. The present invention also provides certain metal-based powder compositions suitable for cold compaction. By “cold compaction” as used herein, it is meant compacting a metal-based powder composition, where the die or metal-based powder composition is at a temperature ranging preferably from ambient temperature to about 65° C., more preferably
Hanejko Francis G.
Luk Sydney
Narasimhan Kalathur S. V. L.
Cain Edward J.
Hoeganaes Corporation
Woodcock & Washburn LLP
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