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April 1, 2002

4 Min Read
Changing the ties that bind

Mathson used agar-based binder technology to mold this exhaust gas recirculation valve shaft out of a 316-L stainless steel feedstock. The valve shaft was molded in a 30-second cycle and weighs 75.4g. Originally, the part was made from five separate machined components that were welded into a single piece that weighed 174.5g.

By: Tony Deligio

As General Electric maneuvered to acquire Honeywell last year—Jack Welch's bid for a final jewel in his acquisition crown—the European Union's subsequent blocking of the deal commandeered the headlines. Far removed from the front page, Honeywell jostled its units and shed noncore business in an attempt to appease EU regulators and GE. One such divestiture garnered little attention, but its technology (see "Technical Developments Drive PIM Industry Growth," December 1999 IMMC, p. 21) represented a momentous advance for PIM. Now one molder is attempting to apply this technology to a broader range of automotive applications.

The agar-based aqueous binder system relinquished by Honeywell changes debinding as it's currently known to metal and ceramic injection molders using feedstocks bound with polyacetals. Rutgers University was granted Honeywell's patent for the technology during that company's move to trim operations. Prior to this, Mathson Industries Inc. had teamed with Honeywell in July 2000 to help market the process to PIM businesses. Mathson now has acquired a license from Honeywell to continue its work. Recently, Latitude Mfg. Technology (see related news story, p. 2) obtained the full rights from Honeywell to make and sell the agar feedstocks known as PowderFlo.

Boney Mathews, president and ceo of Mathson, is using his company's license to apply the technology to a variety of automotive parts. In fact, Mathson has already filed for patents involving exhaust manifolds created by the process, and now it is working to gain wider acceptance for parts created using the process from automotive OEMs.

"In automotive, you have to validate everything," Mathews explains, "so typically we work three years in advance. So right now I'm working on 2004, 2005, and 2006 applications."

From Polyacetals to Polysaccharides

The process marks a dramatic shift from the polyacetal-based binders used in some PIM feedstocks. Debinding these feedstocks requires the catalyst nitric acid, a potentially noxious and environmentally unfriendly substance. Molded parts, depending on their size, sit in the acid for anywhere from 8 to 15 hours. The parts are then sintered, which can release further toxins.

With agar-based binding systems, the molded part simply rests in the ambient air for approximately 1 hour before it's ready to move on to sintering. Nitric acid is replaced with regular air and 8 to 15 hours of debinding becomes 1 hour of drying. During sintering only water and environmentally benign agar—a water-soluble polysaccharide derived from seaweed—are released.

To produce feedstocks using the agar technology, metal or ceramic powder is mixed with water, agar, and a borate compound in gel form. The gel reduces the amount of binder needed to 2 to 3 percent in terms of total feedstock weight and imparts high strength and deformation resistance. Water constitutes 55 percent of the mixture by volume and acts as a solvent and carrier for the agar. Dispersants or biocides can also be added.

PIM Redefined

The viscosity of feedstocks that use agar-based binders is roughly equivalent to that of unfilled nylon 6. This allows for molding at reduced pressures and temperatures.



Eliminating the need for harmful catalysts like nitric acid is not the only benefit of this technology. The agar-based system also allows molders to create large parts in soft tools while running at significantly lower pressures and temperatures.

Heavier parts, ranging in size from 1 to 2 kg, are possible since feedstocks using the agar binder are roughly equivalent to nylon 6 in terms of rheology and viscosity vs. shear (see chart, right). Typical molding pressures for agar parts range from 450 to 900 psi with temperatures usually staying below 100C.

"The viscosity vs. shear is very low," Mathews says. "That is the reason you can have very long flow without much pressure drop, so you'll have a consistent part and consistent density."

Such low pressures can present cost savings by allowing the use of softer tooling. For production runs of less than 10,000 parts, aluminum or other soft tooling materials are a viable option. In some cases, agar feedstocks can even be molded in SLA molds, speeding product development.

Contact information
Mathson Industries Inc.
Troy, MI
Boney A. Mathew
(248) 269-7696
www.mathson.com

 

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