Patent ID: 12186808

It should be understood that various aspects of the invention are presented inFIGS.1-3which may not be drawn to scale and which are not intended to be limiting with respect to the scope of the invention now being claimed. In most cases like components which are illustrated in the drawings are numbered using like reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in terms of the method which it employs in manufacturing high strength, durable toroidal parts, such a gears, bearing races, and one-way clutches. It should be understood thatFIGS.1-3and the descriptions of the present invention provided herein have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements and/or descriptions that are well-known to those skilled in the art. Those of ordinary skill in the art will recognize that other elements may be desirable in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein.

The toroidal parts of this invention are comprised of an external component (an external layer) and an internal component (an internal layer).FIG.1is an illustration of a gear1which was manufactured in accordance with this invention. As can be seen, this gear includes such an external component2and an internal component3. As can be seen, the external component2includes an external gear face5which is situated on the outer radial surface of the gear1. The external component2is comprised of a double press double sinter powder metal or forged powder metal or a wrought metal and is manufactured utilizing conventional techniques. A “wrought metal” is traditionally cast into a solid form which can be subsequently worked, such as by machining, forging, stamping, pressing, or another metal working technique, into a final form. The term “wrought metal” as used herein characterizes a full density metal that is cast from a molten (liquid) state rather than coming from a powder metal and being of a lower density. Accordingly, wrought metal internal components of the toroidal parts of this invention are comprised of a full density metal and are made by casting and optionally subsequent metal working steps. Such wrought metal internal components are not made with powder metals.

The internal component3of the gear1is comprised of a powder metal which has been formed within the confines of the external component2under pressure and sintered. Under optimum material combinations, during sintering, the internal component may3expands and by virtue of compressive forces against the external component2is thereby provided with higher strength of the internal component. This results in an increase in torsional and radial strength due to compressive load. In any case, the internal component3can be molded so as to have an internal profile of any desired shape, such as a gear face or a hexagon shaped hole, or in the case of the gear illustrated inFIG.1a circular shaped hole4.

In the first step of the process of this invention the outer component of the toroidal part is manufactured employing conventional equipment and techniques. In one scenario the outer component is made with double press double sinter powder metal or forged powder metal and in yet another scenario the outer component of the part is made with a wrought metal. In one embodiment of this invention grooves can be included on inner surface of the outer component to facilitate strong bonding between the inner component and the outer component of the toroidal part. Such grooves6are shown on the outer component a gear as illustrated inFIG.3.

The inner component of the part is molded in the outer component by placing a metal powder composition into a mold with the outer component of the part defining the outer periphery of the inner component. The powder metal is then compacted in the mold under a high pressure which is typically within the range of 20 tsi to 70 tsi (tons per square inch) and is preferably within the range of 40 tsi to 60 tsi. This results in the formation of an uncured or green inner component of the part which is contained radially within the outer component of the part. The part having the green inner component is then cured or sintered by heating the entire part in a sintering furnace, such as an electric or gas-fired belt or batch sintering furnace, for a predetermined time at high temperature in a protective atmosphere, such as under nitrogen, hydrogen, or argon. In any case the metal powders can be sintered in the solid state with bonding by diffusion rather than melting and re-solidification.

The metal powders that can be utilized in manufacturing high strength toroidal parts of this invention are typically a substantially homogenous powder including a single alloyed or unalloyed metal powder or a blend of one or more such powders and, optionally, other metallurgical and non-metallurgical additives such as, for example, lubricants. Thus, “metallurgical powder” may refer to a single powder or to a powder blend. There are three common types of powders used to make powder metal mixes and parts. The most common are homogeneous elemental powders such as iron, copper, nickel and molybdenum. These are blended together with other additives as desired to attain needed results, such as lubricants and graphite, and molded as a mixture. A second possibility is to use various alloyed powders, such as an iron-nickel-molybdenum-copper steel or iron-chromium-molybdenum-copper steel. In this case, the alloy is formed in the melt prior to atomization and each powder particle is a small ingot having the same composition as the melt. Again, additives of graphite, lubricant and elemental powders may be added to make the mix. A third type is known as “diffusion bonded” powders. In this case, an elemental powder, such as iron, is mixed with a second elemental powder, including copper, and is subsequently sintered at low temperatures so partial diffusion of the powders occurs. This yields a powder with fairly good compressibility which shows little tendency to separate during processing. While iron is the most common metal powder, powders of other metals such as aluminum, copper, tungsten, molybdenum and the like may also be used as long metal composition expands during sintering to a greater degree than does the metal utilized in the outer component of the part. Also, as used herein, an “iron metal powder” is a powder in which the total weight of iron and iron alloy powder is at least 50 percent of the powder's total weight. While more than 50% of the part's composition is iron, the powder may include other elements such as carbon, sulfur, phosphorus, manganese, molybdenum, nickel, silicon, chromium, and, of course, copper.

At least four types of metallic iron powders are available. Electrolytic iron, sponge iron, carbonyl iron and nanoparticle sized iron are made by a number of processes. Electrolytic iron is made via the electrolysis of iron oxide, and is available in annealed and unannealed form from, for example, OM Group, Inc., which is now owned by North American Höganäs, Inc. Sponge iron is also available from North American Höganäs, Inc. There are at least two types of sponge iron: hydrogen-reduced sponge iron and carbon monoxide-reduced sponge iron. Carbonyl iron powder is commercially available from Reade Advanced Materials. It is manufactured using a carbonyl decomposition process.

Depending upon the type of iron selected, the particles may vary widely in purity, surface area, and particle shape. The following non-limiting examples of typical characteristics are included herein to exemplify the variation that may be encountered. Electrolytic iron is known for its high purity and high surface area. The particles are dendritic. Carbonyl iron particles are substantially uniform spheres, and may have a purity of up to about 99.5 percent. Carbon monoxide-reduced sponge iron typically has a surface area of about 95 square meters per kilogram (m2/kg), while hydrogen-reduced sponge iron typically has a surface area of about 200 m2/kg. Sponge iron may contain small amounts of other elements, for example, carbon, sulfur, phosphorus, silicon, magnesium, aluminum, titanium, vanadium, manganese, calcium, zinc, nickel, cobalt, chromium, and copper. Additional additives may also be used in molding the preform for the inner component of the toroidal part being manufactured.

A more detailed description of metal powder compositions that can be used in the practice of this invention is given in U.S. patent application Ser. No. 14/974,498, filed on Dec. 18, 2015. The teachings of U.S. patent application Ser. No. 14/974,498 are incorporated herein by reference in their entirety. In any case, the metal powder composition used will normally include at least 2.5 weight percent to 5 weight percent copper and will frequently contain from 3 weight percent to 4 weight percent copper. In many cases, the metal powder composition will also contain from 0.2 weight percent to 1.5 weight percent molybdenum and from 0.2 weight percent to 4 weight percent nickel. In some cases it is advantageous for the metal powder composition to include from 0.1 weight percent to 2 weight percent graphite in addition to the copper.

The powder metal preform is then sintered. After being removed from the preform die, the toroidal part is typically placed in a sintering furnace where it is sintered at a temperature which is about 60% to about 90% of the melting point of the metal composition being employed. The sintering temperature will normally be in the range of 1700° F. (927° C.) to 2450° F. (1343° C.). The sintering temperature for the iron based compacts normally utilized in the practice of this invention will more typically be within the range of 2000° F. (1093° C.) to about 2400° F. (1316° C.). In any case, the appropriate sintering temperature and time-at-temperature will depend on several factors, including the chemistry of the metallurgical powder, the size and geometry of the compact, and the heating equipment used. Those of ordinary skill in the art may readily determine appropriate parameters for the molding steps to provide a green preform of suitable density and geometry which is then placed into a furnace at 2000° F. to 2450° F. for approximately 20 minutes under a protective atmosphere to sinter the metal. In any case, the sintering step with be conducted for a time and under conditions which allow for a metallurgical bonds to form between the external component and the internal component of the part.

As previously noted, the sintering temperature will typically be within the range of 2000° F. (1093° C.) to 2400° F. (1316° C.) and may be, for example, within the range of 2050° F. (1121° C.) to 2100° F. (1149° C.) for many iron-based preforms. Depending on, for example, the type of powder metal and the desired article, the sintering temperature can vary. After being sintered in the furnace the toroidal part is normally cooled to room temperature.

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.