Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Reexamination Certificate
2000-07-31
2001-05-01
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
C264S122000, C264S126000, C264S331120, C264S331190, C264S109000, C264S101000, C427S213000, C427S214000, C427S216000, C427S221000, C427S410000
Reexamination Certificate
active
06224798
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to electromagnetic coils and more particularly to the fabrication of silicone-potted ignition coils and high temperature ignition coils.
2. Description of the Background Art
Conventionally, composite iron powders are coated with various polymeric binders, which insulate a plurality of iron powder particles from one another after the iron powder particles are pressed to form a part. An insulated core formed from iron powder particles may be utilized for AC electromagnetic applications because the magnetic characteristics are similar to a laminated sheet stack core. The binders may be thermoplastic polymeric materials, thermoset polymeric materials, inorganic materials, or a combination of all types of these materials. If a thermoset resin is used, the molded part can be cured (i.e., cross-linked) in an attempt to impart better molding properties. However, upon curing, undesirable results such as the formation of a hard insoluble film on the part's surface may occur. This unwanted film can cause inhibition problems with the potting materials, dimensional control problems, and performance difficulties. The film formation results in added expense for its removal, imposes additional processing time, and may degrade the dimensional control causing the need for machining the part.
Although various organic and inorganic materials have been used to coat the surface of a powdered metal, more frequently organic binders such as thermoplastics and thermosets are used. Thermoset resins are reactive materials, which cross-link or react upon exposure to various sources of energy such as heat, ultraviolet radiation, and pressure. When a powdered metal is coated with a thermoset binder, the binder is typically left unreacted (i.e. uncured) until the part is molded. Upon subsequent cross-linking, reaction by-products can be detrimental to the core or to the remainder of the system. These reaction by-products can include evolved gases, moisture, or a physical interaction with other organic materials (e.g. lubricants). If the thermoset coating on powdered metal (PM) is cross-linked when making static physical contact (i.e. at a stage prior to molding while still a free flowing powder), the powdered metal agglomerates or worse forms a large solid mass, taking the shape of its container.
BRIEF SUMMARY OF THE INVENTION
By way of example, and not of limitation, the present invention comprises a method of coating a powdered metal with a cross linking polymer and then curing the cross linking polymer after such polymer has been coated on the metal powder but before a part is molded, thereby forming a cured polymer matrix-powdered metal composite material. The pre-cured polymer coated powdered metal is preferably cured by retaining the pre-cured polymer coated metal in a fluidized bed contained within a fluidized bath (e.g. a fluid bed coater/drier apparatus) after the coating process has terminated. The polymer solution coated powdered metal is then dried in situ to remove the solvent. The temperature of the fluidized bed may then be raised by increasing the overall temperature of the fluidized bath, thereby curing the polymer onto the powdered metal in situ.
By keeping the polymer coated powdered metal in constant motion during the coating, the drying, and the curing process, the polymer coated powdered metal does not agglomerate or otherwise adhere to other polymer coated particles of powdered metal. Therefore, the need for post-curing, the inhibition problem, the lack of dimensional control, the lengthy tumbling process, the inability to use newer silicone impregnation materials, and other related problems are eliminated.
Additionally, the pre-cured polymer coated powdered metal maintains a surprisingly high green strength in the range of 2500 to 4000 psi as well as a high green density in the range of 7.10 to 7.30 g/cc for a typical 0.50% w/o phenolic polymer coated on a typical 100 micron particle size pure iron powder. Thus, a net-shaped part, which may be molded from such pre-cured polymer coated powdered metal, performs quite well.
By curing the thermoset polymer on the individual particles of powdered metal as a continuation of the coating process, rather than by curing the molded part in its entirety, the problems associated with curing by-products (such as silicone inhibition interaction or surface contamination) are circumvented. The cured polymer coated metal powder may then be molded (with optional warm pressing by uniaxial, isostatic, or dynamic magnetic compaction) into a net-shaped part, forming a polymer matrix-powdered metal composite material. The net-shape may comprise a core-shape for forming an electromagnetic coil core. This core may be configured in several shapes (e.g. cylinder, toroid, “E,” “EF,” “EM,” “U,” bus bar, bobbin, hollow, disk, or any combination thereof).
The cured polymer coated powdered metal may also be over-coated with one or more additional polymer or lubricant layers as needed. By layering with an additional coating, the powdered metal substrate can increase the strength, density, and moldability of a part, which may be further protected from detrimental diffusion of oxygen, moisture, and corrosive gases and vapors.
Multiple layers of polymer coating also provides a barrier form of protection for each particle against elemental magnetic degradation, which may occur, thereby lowering the irreversible losses. This is true especially in the case of neodymium-iron-boron (Nd—Fe—B) permanent magnetic materials when used as the substrate powdered metal, particularly when exposed to elevated temperatures. The use of multiple binders may also affect the electromagnetic properties of the molded part.
Traditional polymer coatings allow many gases to diffuse through the polymer layer. Such diffusion can allow a detrimental reaction between the diffused gasses and the metal substrate. A cured epoxy coating is particularly effective as a barrier to limit or prevent the diffusion of these gases. Another benefit conferred by the present invention is that the imidization of a polyimide resin binder provides very high temperature and corrosion resistance.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.
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patent: 5272008 (1993-12-01), Shain et al.
patent: 5591373 (1997-01-01), Ward et al.
patent: 5730922 (1998-03-01), Babb et al.
patent: 6046276 (2000-04-01), Ambrose et al.
patent: 6077608 (2000-06-01), Barkac et al.
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Theisen Mary Lynn
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