Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-02-28
2004-06-29
Kiliman, Ieszek B (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S404000, C427S212000, C427S215000, C427S216000, C427S219000
Reexamination Certificate
active
06756118
ABSTRACT:
FIELD OF THE INVENTION
The present method relates to a powdered metal composite material having a high specific electrical resistance, and to a starting material and a method for producing such a composite material.
BACKGROUND INFORMATION
Powdered metal composite materials having high specific electrical resistance can be applied technically, for instance, as high-ohmic steels and as magnetically soft components in high-speed magnetic valves. Special powdered metal/plastic composites have been developed for the latter application. They are made by using the techniques of powdered metallurgy, by compression molding of powdered metal particles coated with electrically insulating plastic. The pressure-molded powdered metal particles are bonded to one another by the plastic. These powdered metal/plastic composites have a very high electrical resistance compared to pure iron. But the situation is that, as opposed the classical sintering materials, they show a reduction in strength, permeability, magnetic saturation and temperature and fuel resistance.
In powdered metallurgy (PM), the metal powders are laced with small proportions of antitack or lubricating agents. This addition has the effect of making the molded article denser, since it promotes gliding on one another of the powdered metal particles during the compression, reduces the releasing forces and increases the service life of the press tool by lubricating the press die and female die.
The antitack or lubricating agents are usually added to the powdered metals in quantities between 0.1 and 1.5% by weight. Apart from just mixing finely pulverized antitack agents with powdered metals, it is also possible to coat the powdered metal particles with antitack agents. This can be done by using a solution of the antitack agents in a suitable solvent, as described, for example, in European Published Patent Application No. 0 673 284, or by wetting the metal particles with the fused mass of the antitack agent. Molding by axial pressing is usually followed by heat treatment. During that process, the added processing materials undergo pyrolysis at temperatures between 150 and 500° C., which is far below the sintering temperature of the powdered metal (sintering temperature of iron 1120° C. to 1280° C.).
Whereas antitack agents, organic based, such as waxes and fatty acids, pyrolyze largely free of any residue under a protective gas, metal soaps, for example, leave metal oxides in the powder union. These, such as ZnO, weaken the structure to the extent that they cannot be reduced to their metals in a reducing atmosphere in the subsequent sintering process, as can, for example the oxides of iron, cobalt, nickel, copper, molybdenum or manganese. Thus, European Published Patent Application No. 0 673 284 describes how, by combination of different metal soaps as antitack agent, by the reduction of the oxides generated by the pyrolysis in a hydrogen atmosphere and by sintering, targeted metallic alloys among one another or with the molded powdered metals are created.
Soft magnetic composite materials for magnetic valves can also be manufactured in this manner. However, in order to achieve good switching dynamics, the sintered, axially molded soft magnetic powdered metals would have to have a substantially higher electrical resistance (by a factor of 100, or so).
SUMMARY OF THE INVENTION
It is the object of the present invention to state a powdered metal composite material having a high specific electrical resistance along with good mechanical strength, a very good temperature and fuel resistance and a starting material and a method for the efficient production of such a composite material.
This object is attained by a powdered metal composite material a starting material and a method for producing the composite material, all of which are according to the present invention.
Whereas oxides, in composite materials consisting mainly of powdered metal, have a partially negative influence on the properties, such as the mechanical and possibly the magnetic properties, the inventors have determined that several oxides, which form at least one common phase, can impart to the composite materials a very good mechanical, thermal and chemical stability.
According to the present invention, the starting material for manufacturing a powdered metal composite material having a high specific electrical resistance can be made up without a problem in such a way that the composite material made of it has a satisfactory compressed density in addition to the high resistance. To the extent that the amount of antitack agent, required for high resistance in the composite material, is too great for simultaneously obtaining optimal compressed density, in such cases, oxidic fine powder can be added to the at least one antitack agent, which can form at least one common phase with the pyrolysis product created from the at least one antitack agent, during further processing. In this connection, one must not accept any deterioration of the composite material properties.
The method according to the present invention is therefore especially advantageous, because the oxides created by the pyrolysis of the antitack agents used in powdered metallurgy can be used to produce the common phase.
In an advantageous manner, according to the present invention, the high-ohmic composite materials, in their embodiment as soft magnetic composite materials, can also be used particularly for magnetic valves having good switching dynamics, on account of their high magnetic saturation and their high permeability. In this connection, it is especially favorable if the powdered metal is made substantially of iron materials, such as iron, iron-silicon, iron-cobalt and iron-nickel or mixtures of the materials named, iron being especially preferred. The phrase “is made substantially of” means, in this connection, that further materials can be present only in such quantities that the soft magnetic properties do not deteriorate noticeably.
It is advantageous if, as the at least one common phase, a glass is used, such as a silicate or boron-containing glass, or a specific compound selected from the group of mixed oxides having a spinel structure, of metal phosphates and of metal silicates.
It is favorable if, as antitack agent, at least one metal soap and/or at least one material from the group of mono, di or triesters of phosphoric acid, boric acid and silicic acid with long-chain alcohols and/or polydimethyldisiloxane is(are) contained in the starting material.
In the starting material according to the present invention, in the case of the combination of an antitack agent with oxidic fine powder, preferably at least one metal oxide and/or silicic acid is(are) used.
In order to ensure a high reactivity of the fine powder with the pyrolysis residues of the antitack agents, it is particularly advantageous if the particle diameter (initial grain size) of the fine powder is ≦ approximately 100 nm.
A satisfactory compressed density of the molded article, combined with a sufficiently high electrical resistance of the powdered metal composite material, is achieved in advantageous fashion if the proportion of the antitack agents in relation to the weight of the powdered metal 2.0 lies between approximately 0.1 and approximately 1.5% by weight, or the sum of the proportions of antitack agent and fine powder lies between approximately 0.2 and approximately 3% by weight.
It is advantageous if the relationship of the added amounts of antitack agents, or antitack agents and fine powder, as the case may be, is approximately stoichiometric with respect to the at least one specific compound to be formed in response to the reaction of the oxides, possibly in consideration of the quantities of the metal from the surface of the powdered metal entering into the reaction.
It is of advantage if, during pyrolysis and reaction, heating is carried on to a temperature distinctly below sintering temperature of the powdered metal, and it is particularly preferred, as long as the metal is iron, if heating is performed to a temper
Aichele Wilfried
Harzer Andreas
Koch Hans-Peter
Kenyon & Kenyon
Kiliman Ieszek B
Robert & Bosch GmbH
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