WOOSTER, Ohio—If there's any single distinguishing characteristic to a Michelin Retread Technologies Inc. (MRTI) plant, it's attention paid to detail. That's the message Ken Smetzer, owner of Smetzer's Tire Center Inc. in Wooster, is trying to relay to his commercial customers. Mr. Smetzer recently converted his retreading plant from Oliver Rubber Co.'s process to the MRTI system.
From casing inspection to final inspection, the personnel at MRTI plants have undergone extensive training and are supported by the latest technology, Mr. Smetzer told customers attending an open house at his MRTI plant in Wooster.
An MRTI precure plant starts and ends with U.S.-made equipment, but in between the shop floor is a showcase of European engineering.
Starting with German-engineered Steinbichler shearography machines, casings are buffed on Danish-built SIO buffers, followed by cushion gum application from German-manufactured A-Z roller die extruders and treads applied by automated SIO tread applicators, and finally secured in envelopes with the aid of Italian-sourced TRM envelope spreaders.
The process starts off, however, with visual inspection aided by Hawkinson NDT II nail hole testers. Curing takes place in chambers by Cure Tech Inc.
After the visual/nail hole examination—where the casing inspector also checks for possible body-ply problems by scanning the sidewall with a fluorescent light—each casing goes through shearography. When coupled with computerized imaging, it becomes the ``Michelin Casing Integrity Analyzer.''
Michelin has developed its own computerized imaging software—called Automatic Casing Evaluation—to help the operator identify belt-edge separations by flagging irregularities as yellow (needs further inspection) or red (reject) highlight boxes on screen.
Depending on the results of the visual and shearography inspections, casings then may be X-rayed (Fluoroscan X-ray equipment) to check possible damage to the steel body and tread plies as well as to inspect the integrity of existing section repairs.
Buffing begins with an automated undertread sensor measuring residual tread rubber, a value that the buffer's computer program uses to set the buffing parameters.
The buffing wheels on the SIO machine cut perpendicular to tire rotation, creating a ``crepe-like'' buffing texture running across the tread surface radially. While this type of buffing is not widespread now among retreaders, it earlier was commonplace when the industry was still predominantly bias-ply, according to Marvin Bozarth, executive director of the International Tire and Rubber Association.
Michelin seeks to assure repair integrity by thorough training of a franchisee's personnel and by follow-up audits. As part of its retread/casing guarantee, MRTI requires that section repairs in casings not done originally by an MRTI franchisee be removed and redone for over-the-road haulers.
The A-Z extruder used in the ``Cushion to Casing'' extrusion system is designed to recognize skives and buzzouts and adjust the flow of rubber automatically to fill these indentations. This frees up the repair department from having to do these manually and yields a precise bonding layer, according to Michelin literature.
Michelin promotes heavily to the end user that the rubber and tread patterns used for its precured treads are the same as that go into its new tires. For the time being, Oliver Rubber Co. is molding the treads for Michelin using Michelin-specified compounds and parameters.
The built-up casings are double vacuum enveloped ``to assure uniform curing and complete integration of repairs,'' Michelin literature states. The curing cycle runs no more than two hours, and averages about 90 minutes for shallow tread retreads. The chambers hold 25 tires at a time.
Michelin franchisees agree to refrain from ``sleeper cures''—starting the final batch of the day at closing time and allowing the next day's first shift to remove them—to preclude the possibility of overcuring tires.
The extra attention to casing inspections allows Michelin to offer a limited warranty on MRTI franchisee products that includes covering the casing—regardless of whether it's a customer's casing for an MRTI franchisee-procured one—for up to 34 weeks after retreading, or through the first 25 percent of tread life.