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Tailored materials shape the future.

Tailored materials shape the future

Conventional ferrous and nonferrous metals often are bested by custom-made materials, including composites of boron, carbon, glass, and other fibers in metal or plastic matrixes. Many years ago, Alloy Technology International, West Nyack, NY, introduced a more familiar mix, a combination of 25 to 55 percent volume titanium carbide dispersed in an alloy binder. This Ferro-TiC metal-matrix composite originated long before its ingredients became buzzwords.

Today's formulations suit almost any tooling task, and many alloy composites serve as workpieces in highly engineered products. The right mix can solve wear problems, add strength, and match the material to the job. In its annealed state, the material is readily machinable on conventional equipment, but, when hardened, it performs like carbide. With compressive strengths up to 555,000 psi, Ferro-TiC can withstand heavy impact without deformation.

The Maytag experience

Another feature, transverse rupture strength to 450,000 psi, allows the composite material to take deflection under stress and transfer applied loads. For Maytag Company, Newton Iowa, it strengthens a core-rod backup member.

The appliance manufacturer employs the composite in tooling for compacting powdered stainless steel into gears for washing machines. In searching for an optimum material, the firm tried flame-plated tool steel and chrome-plated core rods with less than satisfactory results. Problems included peeling and chipping of coated material, early and frequent replacement, lengthy downtime, and low production rates.

Chipped coating flakes found their way into powdered stainless steel, where they caused pitting and scratches. Also, the chips were picked up randomly and compressed into the gears themselves, causing defects and slowing production speeds.

"By switching to Ferro-TiC metal-matrix composite, we increased times." production rates by five to ten says Senior Tool Engineer John Wickenkamp of Maytag. He adds, "The increase in production life results from the unusually high wear resistance and resistance to galling, chipping, and abrasion.

"And I like the in-house control I can exercise over on-site machining of the new material. It's supplied in blanks that we can easily fabricate into tips on steel shanks."

Maytag uses 3/8"-dia tool-steel core rods with Ferro-TiC tips. The rods are used in four lengths: 2 1/4", 6 1/2", 7", and 20". Wickenkamp reports current gear production figures of up to 500,000 parts per rod before replacement, a significant savings over other core-rod materials. Additional cost savings include reduced downtime for core-rod replacement, fewer defect-rejected gear parts, and more-efficient production of tooling.

Pelletizer knives

Increased performance requirements combined with more demanding designs have made proper material selection a critical factor in choosing pelletizer knife blades for production of plastics. Although there are many principles affecting knife performance, three main cause of premature blade failure stand out: adhesive wear, corrosion, and chipping of the knife edge.

Adhesive wear typically is observed as smeared metal on the cutting-edge surface, caused by excessive contact pressure between the knife and the die face. This contact leaves knives permanently softened - with low fatigue life.

Adhesion causes chips in the cutting edge that eventually form fatigue cracks. The cracks then propagate as a result of cantilever bending stresses applied to the knife while it's cutting. In some instances, aqueous corrosion can cause pitting on the cutting edge, thus further lowering fatigue resistance.

Generally, wear resistance increases with increased carbide content, decreased particle size, increased hardness of the matrix that cements the carbide particles in place, lower porosity, and better homogeneity of carbide distribution.

The mechanical properties that affect impact resistance, chipping, fracture toughness, and fatigue generally increase with decreased carbide content, increased particle size, and lower hardness of the matrix. Finally, corrosion resistance increases with the corresponding corrosion resistance of the matrix.

Alloy Technology International balanced all these factors to formulate a material that would optimize knife performance. The Ferro-TiC manufacturing process lends itself to individual tailoring of alloys for this or many other applications.

Matching grade to workpiece

A variety of Ferro-TiC grades are available to match usage. Polyethylene is less abrasive and less corrosive to the knife edge, and its processing is best handled by grade SK with 35-percent carbide content. This is a user-friendly material in a modified hot-work, chromium/tool-steel matrix for easy machinability.

Grade CM offers more resistance to wear and temper variances. It has a 45-percent TiC content, with the particles dispersed in a high-chromium, high-carbon, tool-steel matrix similar to D-2. This grade handles polyethylene production where wear life is a critical factor.

Polypropylene presents more severe operating conditions than polyethylene. Ferro-TiC PK, designed to solve abrasive and corrosive problems, is a special combination of 42 percent by volume TiC homogeneously dispersed in a modified stainless steel matrix. The PK grade also serves for compounding and granulating operations.

Major producers of polyethylene and polypropylene have replaced conventional D-2 and 440 stainless steel with the Ferro-TiC alloys in their pelletizer knives. The result is increased productivity and substantial reduction in downtime. The new composites often outperform conventional tool steels by 15 to 1. For more information, contact Alloy Technology International Inc, 169 Western Highway, West Nyack, NY 10994. One of the first custom-designed materials, Ferro-TiC is put together by cold isostatic (ISO) pressing, followed by sintering, hot ISO pressing (hipping), and machining. Most orders are for small lots, but the firm has the capacity to sinter large-volume orders to size.

The composite material and its processing compete with tool steels in many ways. In various formulations, the composites offer light weight, dimensional stability, high hardness, high lubricity, and high resistance to corrosion, abrasion, and temperature.

Because its titanium-carbide (TiC) particles are rounded, the material has a low coefficient of friction, making it easy to form before hardening. Also, it's available in nonmagnetic grades.

Users in the automotive, canning, steel, paper, and chemical industries report Ferro-TiC outperforms tool steels as much as 20 to 1 in wear applications. The material is available in near net shapes to match specifications and user applications.

Near net shapes can be produced from 75 - to 80-percent volume TiC dispersed in an alloy binder. As an example, the photo shows a lightweight, heavy-duty, Ferro-TiC sprocket for a chain saw, molded to near net shape. Other forms include easily machinable blanks.

PHOTO : Ferro-TiC revisited. New formulations produce materials tailor-made to user specifications. Photo shows array of wear-resistant metal-matrix tooling components.

PHOTO : Compression core rods made of Ferro-TiC composite material produce up to 500,000 gears before replacement.

PHOTO : Knives cut plastic into pellets. Plastic may be soft, but it cuts hard. Ferro-TiC tools survive much longer than conventional tools.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Title Annotation:custom-designed composites
Author:Miller, Paul C.
Publication:Tooling & Production
Date:Nov 1, 1989
Previous Article:MEs speak out on their changing role.
Next Article:Trends in laser measurement.

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