LOUISVILLE, Ky.-The industry task force investigating ``zipper'' failures in steel-radial truck tires wants dealers and retreaders to furnish it with details of the ruptures when they occur. The 13-member task force, which met for the first time July 19 at the American Retreaders' Association's headquarters in Louisville, Ky., is particularly interested in what happened to the tires before they failed, according to ARA Executive Director Marvin Bozarth, who is serving as the group's chairman.
The task force, made up of representatives from the major tire manufacturing companies, independent retreaders, ARA Technical Director Bob Majewski and others, was organized after an April forum on zipper ruptures.
It was the consensus at that gathering that more needs to be known about zipper ruptures, which reportedly have ``exploded'' with a force that has hurled victims several feet.
Mr. Bozarth said when furnishing the task force with information on zipper failures, dealers should include as much information as possible about the service history of the failed tires, including whether they were overloaded or run underinflated or flat.
Dealers also should provide information concerning the circumstances under which the failure occurred and details about the tire's brand, size and type.
Mr. Bozarth said data obtained through laboratory wheel tests may help determine whether, as some have suggested, overloading and underinflation are primary causes of zipper ruptures-and, if so, how long this process of casing degradation takes.
The task force already has assembled a number of tires for examination, he said. Some of the tires already have zippered while others in the group are expected to do so once inflated.
Some of these zippers-in-the-making were detected through visual inspection by inflating the tires to 20 psi and directing a light on the sidewalls to create shadows that reveal surface irregularities, indicative of broken cords under the rubber surface. Others turned up through X-ray and ultrasonic tests.
Inflating such tires to 20 psi and then letting the air escape often causes them to emit a ``clicking'' sound, as if someone were tapping on the sidewall with a metal ballpoint pen, Mr. Bozarth said.
He theorized that the tapping sounds are caused when inflation-stressed steel body cords are allowed to slip back into place.
In a letter mailed to task force members prior to the July meeting, Mr. Bozarth said the three primary objectives for the group were to search for methods of safely handling and servicing tires that could zipper; to develop better methods of detecting the presence of damage that may cause tires to zipper; and to encourage developments in tire technology that will reduce or eliminate zippering.
To report zipper failures, contact Mr. Bozarth at the ARA, P.O. Box 37203, Louisville, Ky. 40233-7203; (800) 426-8835 or (502) 968-8900. Fax: (502) 964-7859.