Polymer coating extends tool life.

A new polymer sealant for chrome-plated metal surfaces is getting good reviews from plastics processors in applications ranging from extruder screws and dies to injection molds and blow molding core rods. Called Micro Tuff, the sealant fills in microcracks and porosity in the chrome plate, adding lubricity and improving wear resistance. Micro Tuff is supplied to both processors and tool makers by Plating Resources Inc., Twinsburg, Ohio (see PT, Nov. '94, p. 10).

Though originally intended for use on chrome plating, Micro Tuff gets similar results when applied to nickel-plated tools and even unplated stainless or carbon steels. Tony Kupper, project manager at Plating Resources, says Micro Tuff has also been applied to arc-sprayed nickel-shell (or other metal) tooling, but he has no information on performance results. The company is at a loss to explain how Micro Tuff impregnates and bonds to surfaces that are much less porous than hard-chrome plate.

The lubricity imparted by the sealant translates into higher extrusion rates or easier mold release. It also reduces mold deposits and wear. Plating Resources says users may see a 14% rise in production rates, a 6% increase in machine uptime, and an 81% reduction in rechroming costs when Micro Tuff is applied to a new or reworked die.

Micro Tuff has been available in its present bar form for about two years but is just now catching on. The company now sells 10 times more bars in a week than it did in the entire first year. Plating Resources has over 100 customers that use or apply the sealant. Micro Tuff costs about $1200 for a package of three bars.

Several major extrusion die makers are now offering Micro Tuff treatment. But Micro Tuff can be applied by a processor in his own shop, saving the time and expense of shipping a mold, die, or screw out for treatment. Some users say they need only buffing tools, temperature-control equipment, and adequate ventilation to apply the sealant themselves.

HOW IT WORKS

Micro Tuff consists of a long-chain polymer combined with free chromium and an organic impregnating agent. The work-piece is heated to 275 to 300 F, and the sealant is brushed or rubbed on. A chemical reaction occurs, causing the polymer to crosslink and bond to the substrate.

Plating Resources recommends that Micro Tuff be applied to either a new tool or one that has been stripped of previous platings and then cleaned and replated. A highly polished mirror finish of 1 to 3 roughness average (RA) gives best results. If the sealant is applied over metal surfaces that are not perfectly clean, performance may be somewhat reduced.

Tests conducted by Plating Resources show that chrome plate sealed with Micro Tuff achieves 65 hr of corrosion resistance before failing vs. 1 hr for unprotected plating in the ASTM B-368 "Cass" test. And in the ASTM B-117 salt-spray test, plating with Micro Tuff lasted 530 hr vs. 5 hr without the sealant.

Users say Micro Tuff minimizes polymer build-up, plate-out, and burning and reduces the frequency of tool cleanings by at least 50% with such resins as PVC, CPVC, PS, acrylic, PTFE, and PE. One producer of coextruded vinyl siding was able to process 5 million lb of a troublesome powder formulation without shutting down because there was only minor polymer buildup on the die. The tool had been treated with Micro Tuff by the equipment supplier, Krauss-Maffei Corp., Florence, Ky. In the same siding plant, a similar line without the sealant experienced frequent shutdowns due to polymer burning.

In another case, a CPVC pipe maker cut its chrome-plating costs from $37,000/yr to $7000/yr after applying Micro Tuff to its pipe tooling and adapters, Kupper says.

SUCCESS IN THE FIELD

At least two flat-die makers - Cloeren Co., Orange, Texas, and Production Components/Chippewa Valley Die Inc., Eau Claire, Wis. - offer Micro Tuff coating as an option on their dies. (Extrusion Dies Inc., Chippewa Falls, Wis., offered Micro Tuff until it came up with its own coatings - see Technology Newsfocus.)

Production Components has applied Micro Tuff to nearly 60% of its dies in the last 18 months. Customers have reported a 50% reduction in plate out and die lines, says president Paul Peelman. Production Components typically charges $400 to $1500 to apply a Micro Tuff treatment to the die lips and flow passages. The company also offers to apply Micro Tuff on adapters, flanges, or "anywhere the polymer is in contact with tooling," Peelman says. He notes that Micro Tuff's lubricity acts as a "safety net" to protect tooling in the event of runaway extruder conditions.

Cloeren offers Micro Tuff treatment under the name Low Surface Energy (LSE) coating (PT, Jan. '95, p. 11).

PVC sheet extruder Rollex Corp. in Elk Grove Village, Ill., reports 20% greater lb/hr output with Micro Tuff treatment on the coathanger section of its chrome-plated dies. "Clean-up is easier, there's less burning, and die wear has been cut in half," says supervisor George Lang.

Another PVC sheet producer, Pure Plast Inc., Cambridge, Ont., applies Micro Tuff to the last five flights of an uncoated carbon-steel screw for better polymer release and reduced build-up of black specks.

A North American extruder of vinyl siding (which did not want to be mentioned by name) doubled the life of its extrusion tooling and increased productivity by 10% after applying Micro Tuff.

Whirley Industries Inc., Warren, Pa., a manufacturer of injection molded PP cups and PE lids, applies Micro Tuff in-house to the cores and cavities of its chrome-plated molds for better release. Whirley obtains at least a 5% improvement in cycle times, according to Ed Gowland, tooling manager. Micro Tuff cuts both machine downtime and frequency of tool cleaning and rechroming in half. Since rechroming a mold costs the firm $400 to $500, the savings are substantial.