DN Staff

August 3, 1998

5 Min Read
Powder metallurgy awards tap new markets

Las Vegas, NV--Add a pinch of ferrous metal, another of nonferrous metal, a smidgen of stainless steel, some metal-injection materials, and, for added flavor, some advanced particulate materials. Throw these ingredients into a mixing bowl, stir vigorously, and what do you get? In this case, the winning recipe for the grand prize awards in the 1998 Powder Metallurgy Design Competition, sponsored by the Metal Powder Industries Federation (Princeton, NJ).

High-strength auto transmission sprockets captured the Ferrous Grand Prize. The P/M alloy steel sprockets, made by Stackpole Ltd. (Mississauga, Ontario, Canada) for Borg-Warner Automotive Morse Tec Corp. (Ithaca, NY), feature two sets of phased teeth formed to AGMA Class 9 quality. Teeth and journal are selectively densified to a typical surface density of 7.8g/cm(super3). Endurance of the new P/M sprockets "exceed induction hardened malleable iron," the competitive material.

The award-winning parts' properties include a minimum ultimate tensile strength of 125,000 psi (860 Pa), a yield strength of 120,000 psi (826 MPa), a journal rolling contact fatigue of 580,000 psi (4,000 MPa), and a tooth/journal surface hardness of more than 60 HRC.

In action, the sprockets transmit power from the engine to the transmission via two silent chains, which reduce transmission noise. Three ratios are possible, depending on engine-transmission configuration. Each includes a drive and a driven, adding up to six parts per set. Secondary operations involve selective densification of teeth and journal surfaces, vacuum carburizing, machining and grinding, and polishing the journal.

ASCO Sintering Co. (Commerce, CA) walked off with the Nonferrous Grand Prize for a brass adjustment gear. The gear serves as a key component in commercial underground pop-up irrigation sprinklers. It has a typical density of 7.6 g/m(super3), a minimum yield strength of 13,000 psi (90 MPa), and a 14% elongation.

The gear consists of a serrated flange sintered to a hub with an 18-tooth gear to form a strong bond. Critical tolerances on the gear include: diametral pitch of 64, a 25-degree pressure angle, maximum total composite tolerance of 0.006 inch (0.1524 mm), and a maximum tooth-to-tooth composite tolerance of 0.0025 inch (0.635 mm). The design allows on-site adjustment to regulate the pattern and dispersion of water, as well as the rotation of the sprinkler head.

Secondary operations include deburring and resin impregnation for corrosion resistance and pressure tightness.

A latchbolt in a vertical rod panic/fire safety door unit won the Stainless Steel Grand Prize. Made by Ceromet (Anaheim, CA), for Dorma Door Controls (Steeleville, IL), the 304 stainless-steel part consists of two resistance-welded halves.

The complex part, formed to a 6.4 g/cm(super3) density, has an ultimate tensile strength of 43,000 psi (296 MPa), a compressive yield strength of 38,000 psi (262 MPa), and an unnotched Charpy impact energy of 4 ft-lb (5J). The bolt's two mating parts meet a pull strength load and shear load test of 500 lb. The part has passed the UL test for fire-exit safety door hardware in commercial buildings. Originally an investment casting, the P/M latchbolt "provided a superior surface finish and a 40% cost reduction."

Pivotal laproscopic surgical scissors with a cauterizing capability won the Metal Injection Molded Grand Prize. Produced by FloMet Inc. (DeLand, FL) for Imagyn Surgical (Richland, MI), the design encompasses a helical gear and two scissor blades.

Made from 17-4 PH stainless steel, the parts have a density of 7.5 g/cm(super3). The miniature helical gear has a minimum ultimate tensile strength of 115,000 psi (793 MPa), a minimum yield strength of 94,000 (648 MPa), and a minimum elongation of 4%. Solution-treated and aged, the blades have a minimum tensile strength of 155,000 psi (1,069 MPa), and a minimum yield strength of 140,000 psi (965 MPa).

The 20-tooth helical gear features a 20-degree pressure angle and a 14-degree, right-hand helix angle. FloMet coins the blades as pairs in a single strike to give them the correct interference, relief angle, and curvature, with Imagyn grinding a cutting edge to customer specifications. Use of metal-injection molding "provided a cost saving of more than 80% compared to machining the helical gear."

A steel P/M cylinder liner formed using cold isostatic pressing (CIP) by TecSyn PMP (Huntsville, AL) for Briggs & Stratton Corp. (Milwaukee, WI) won the Advanced Particulate Materials Grand Prize. The component lines new two-cylinder, four-stroke, air-cooled, 23-hp aluminum engines. The engines are designed for use on premium lawn and garden tractors and small construction equipment.

The liner measures 4.06 inches (103.2 mm) long and has an O.D. of 3.1 inches (78.7 mm). Inserted into the aluminum engine block during casting, it "maintains a cylindrical form of the bore better than conventional liners," reducing oil consumption, emissions, and wear. Featured properties include: tensile strength of 65,000 psi (448 MPa), yield strength of 48,000 psi (331 MPa), and a HRB apparent hardness of 85.

After CIP and sintering, the liners are machined on the ends and in the bore. The outer finish has a special texture that allows molten aluminum to penetrate during casting. This creates a very strong, uniform bond that improves thermal conductivity. P/M offered a 30% greater stiffness, which results in a higher resistance against plastic and elastic deformation.

An anode reactor powder core for high-voltage, dc transmission systems won the Overseas Grand Prize. Made by Hitachi Powdered Metals Co. Ltd. (Chiba-ken, Japan) for Hitachi Ltd. (Tokyo), the 41.6-lb (18.87 kg) part protects a thyristor valve from sudden power surges in transmission systems. It must provide reliable magnetic properties for more than 30 years.

The reactor consists of a set of powder cores and a molded coil. The thyristor valve changes electric power from ac to dc, dc to ac, or ac to ac.

A new, insulated iron powder composition provides high specific resistivity and low core loss. Assembled in six sections weighing about 6.9 lbs (3.1 kg) each, the cores are joined by epoxy-resin-impregnated sheets.

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