Launch Slideshow

From inspection to curing: the tire retread process

Retreading truck tires involves a series of precise steps — including inspection, preparation, and repair — to return them to perfect operating condition.

From inspection to curing: the tire retread process

Retreading truck tires involves a series of precise steps — including inspection, preparation, and repair — to return them to perfect operating condition.

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    Photos: Bridgestone Bandag Tire Solutions

    Visual inspection: A visual, hands-on inspection from bead to bead, inside and out, is done to find and mark all visible defects.
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    Secondary inspection: Electronic inspection is designed to find all “through-the-tire” penetrations in the crown and sidewall areas.
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    Shearography: Determines conditions within the casing by subjecting casing to a vacuum while lasers measure surface anomalies (ie: expanding pockets of air). An animated visual of the anomalies aids in determining the casing’s condition. At the end of the initial inspection, information such as casing condition, casing age, and fleet specifications are considered to determine if the tire can be retreaded.

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    Buffing: The casing is inflated to operational pressure. This process removes the worn tread surface, trues up the roundness, and prepares the surface for a new tread.

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    Repair: Removing all injuries identified during initial inspection and replacing the material with structurally sound materials to return the casing to a useful life.

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    Applying cushion: In a one-step process, an uncured bonding layer is extruded onto the prepared casing surface, all skives are filled, and the shoulders are stripped. The casing is now ready for its new tread.
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    Building: The 5400 OSM Builder automatically applies a new tread so it is straight, centered on the casing, and the end splices match.
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    Enveloping: Encases the uncured, built tire in an elastic envelope in preparation for curing.

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    Curing: An autoclave-type device applies heat and pressure, and over time causes the bonding layer in the built tire to cure. This permanently adheres the new tread to the prepared casing.

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    Final inspection: A final visual check assures the retreaded tire is ready for service.

By Paul Abelson

Right after drivers and equipment operators, tires represent the largest expense for truck fleets. “Virgin” tires for snowplows, dump trucks, and other heavy equipment are quickly approaching $500 each.

Tire prices are directly linked to oil prices, since about 22 gallons of oil go into each new tire. Reusing casings, the structural body of the tire, saves 15 of those 22 gallons. The remaining 7 gallons represent tread that wears out in use, and intermediate layers between the casings' cords and the tread layer. In a retread, they are ground off to ensure proper geometry, then replaced.

Even with the time, labor, and equipment needed to prepare and retread tires, the cost can be 50% less than new ones. Tires are designed to be retreaded as many as two or three times, assuming they're properly used and maintained.

Preparing for retreads

The best candidates for retreading are your own tires, provided they have been well maintained, inspected periodically, and removed with at least 4/32 inch of tread left. Federal Motor Carrier Safety Regulation 393.75 requires tires to be replaced at a legal minimum tread depth of 2/32 inch (4/32 inch for steer tires).

Tire management also requires close attention to air pressure, tire balance, wheel alignment, and avoiding overloading. Adequate air pressure is critical to casing longevity. When air pressure is substantially low, heat begins to destroy tires.

Without enough support, the tire casing flexes more than it should and generates heat. If the tire's steel cord flexes enough, it melts the bonds that hold tire components together. That — not faulty retreading — is the primary cause of “road gators,” the strips of tire tread found along roads.

THE GOOD, BAD, AND UGLY

Not all retreads are created equal.

Working with the right vendor can help you avoid buying a “Maypop.” This is a tire “that may pop in 30 minutes or 30 miles,” according to Harvey Brodsky, director of the Retread Tire Association.

A good retread is made from a casing that has not been abused during its previous service life. It is thoroughly inspected using the latest industry-accepted methods, both before and after retreading. The tread is matched to the application for which it is intended. This retread will provide good service through several lifetimes.

A bad retread is given only a visual inspection. It is capped with a generic tread and put on the shelf for sale. You may be happy with it, but it could have defects that lead to early failure.

The ugly retread comes from the retreader with little or no inspection and qualification procedures. Some spray paint makes it look good, but underneath it could be a disaster.

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After a tire's worn surface has been removed and the casing is properly prepared, Bandag's 5400 OSM Builder automatically applies a new tread so it is straight, centered on the casing, and the end splices match. Photo: Bridgestone Bandag Tire Solutions

Underinflation is the reason for most tire failures, according to a recent National Highway Traffic Safety Administration study that physically examined thousands of tread strips. About three-quarters of the cast-off treads were from virgin casings. (If you see steel tire cord in a strip, it is from a casing, not a separated tread. There is no cord in the tread.)

Overloading tires by carrying too much sand or salt can lead to casing failures. Also, when a driver tries to “limp in” with a flat in a set of duals, it doubles the load on the remaining tire. This will quickly ruin the good tire.

Improper alignment will wear a tire unevenly, shortening its service life. But if cords aren't exposed and enough rubber remains, the tire can be retreaded. In fact, most damage, if quickly and properly repaired, will not prevent retreading a tire. A good retreader will determine a tire's suitability for retreading.

Choosing a supplier

The best way to start a long-term fleet tire program built around retreaded tires is to establish a relationship with your supplier. Both the Retread Tire Association and the Tire Retread and Repair Information Bureau advise visiting the plant of each supplier you are considering.

Observe and compare their nondestructive testing methods and equipment. Ask the following questions:

  • What happens to tires when they are brought in?
  • What happens to tires that are rejected?
  • Do they follow industry recommended practices for retreading?
  • Can they provide references? If so, call them.
  • What is their rate of tires returned under warranty vs. the number of tires sold? All good retreaders keep accurate records on returns.

    Don't hesitate to find another vendor if the answers aren't satisfactory.

    Finally, prices are important, but only in the final stage of decision-making. High-quality products are most important, followed by services that help you control total ownership costs.

    — Paul Abelson (truckwriter@anet.com) is a former director of the Technology and Maintenance Council (TMC) of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.