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Commercial Tires

Flat-Out Progress?

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One of the new technologies introduced recently by a major tire company really has the trucking industry talking – at least in certain vocational segments that have consistent problems with downtime due to tire punctures.

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In the commercial truck tire market, the problem of punctures peaked as the era of tube-type bias ply tires drew to a close. Two of the highly touted advantages of tubeless tires were a reduction in punctures and a shift from an expected “blowout” to a more controlled “slowout.”

Later, the introduction of steel reinforced tubeless radial tires further diminished the incidence of tread area punctures, but the basic problem has remained. In fact, there has been a renewed interest in preventing puncture-caused flats in the last several years due to greater emphasis on equipment utilization (reduced downtime), and wider acceptance of tires as “assets” that must generally be retreaded to keep tire program costs under control. This latter concern emphasizes longer-term casing durability.

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Countless efforts have been made over the years to address the issue of flat tires caused by punctures. Tire manufacturers, retread and repair material makers and a variety of well-meaning entrepreneurs have offered up solutions ranging from undefined goo sprayed from aerosol cans to liquid solutions mixed with polymer particles.

Many of the products actually do offer some sealing capability, although the results vary widely. All, however, have significant downsides. First, many conventional sealants are liquids with sealing “particles” in a solution. Any liquid inside a tubeless tire is undesirable, as moisture can permeate into the casing after long periods of time/temperature cycling and cause steel belts to rust and weaken, a factor that can be accelerated when actual punctures occur.

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Since the liquid portion of these sealants must work in a variety of seasons and temperature conditions, some type of antifreeze solution is employed to prevent freezing when the weather turns cold. Most contain solvents or other compounds that can, under certain temperature and pressure conditions, become flammable.

Regardless of makeup, many of these products create added problems when it comes time to retread a worn casing, including the time, labor and process modifications required to prepare casings that have contained liquid sealants.

Sealant Shortcomings

Another issue is that liquid-based sealants settle to the bottom (footprint) area when the tire is at rest, sometimes leaving a new puncture unsealed if it happens to be positioned in another part of the tire. Even when rotating, sealant coverage inside a tire is dependent upon the tire profile, inflation pressure, speed, innerliner design and other factors. Care must also be taken to avoid getting any of the sealing “particles” into the small annular sealing area of the tire valve, as this can create a different type of slow leak.

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Other internal sealing efforts have produced a more semi-solid type of material that is sprayed or painted on the tire innerliner, with a goal of keeping the sealant consistently positioned for maximum effectiveness and avoiding some of the other problems associated with a liquid carrier. Such materials, however, tend to be less uniformly distributed around the tire circumference and can cause vibration in high-speed service.

One problem common to all internal sealant solutions/compounds is the difficulty they create for a technician inspecting the tire interior while preparing a casing for repair or retreading. Generally, the sealant material must be removed so that any punctures, liner damage, or other injuries can be detected and permanently repaired.

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In spite of these shortcomings, sealants still make economic sense in some vocational applications. Slow-speed service with high downtime potential, combined with high exposure to punctures, accounts for many of these. Underground mine tires and refuse hauler tires are especially common applications. Intermodal trailer tires that operate in ill-maintained or debris-heavy terminal areas, and on-/off-highway tires operating in construction zones are also good candidates.

A Feasible Solution?

With this background, it’s easy to see why the use of sealants has not expanded widely into most over-the-road or mixed-service (on-/off-road) applications, but that may change, given the technology recently presented by one major tire manufacturer.

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This new approach places a thin layer of gel-like rubber sealing compound between the innerliner and the tire body plies. Since this material is installed as part of the tire building process, the sealing compound is permanently located, uniformly distributed and remains in place through retreading for the life of the casing.

Because of this placement, it does not inhibit visual or any other non-destructive inspection of the casing. There is nothing to be cleaned from the tire interior, and there is no concern of moisture inside the inflated tire/wheel assembly. Plus, there is no fear of chamber fires when retreading.

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Goodyear claims that its new DuraSeal technology will seal multiple tread area punctures up to 1/4-inch in diameter and that sealant properties are essentially constant from ambient temperatures of -40ºF to 100ºF.

The company also presents test results showing dramatically higher success rates of puncture sealing vs. liquid sealants and data showing that fewer subsequent repairs are required with DuraSeal technology vs. liquid sealants.

Fuel economy is a common concern in most highway applications, and Goodyear data indicates that DuraSeal has a negligible effect on rolling resistance. Of course, the added component increases the weight of a finished tire, and Goodyear says this amounts to 5 to 7 pounds in a typical mixed service tire, depending on the particular tire size. Prior to January 2005, this would have related to an excise tax increase of $2.50 to $3.50 per tire, but because the new excise tax structure is based on tire load capacity, cost is not affected by the small amount of added weight.

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There are many more positive aspects of this technology, Goodyear says, most of which are in favor of this self-contained approach. Therefore, one might wonder why something this simple has not been accomplished and made commercially available before now. There are many reasons for this, involving bonding of dissimilar chemistry rubber compounds, physical properties of heat generation/dissipation, flow properties, component curing challenges, etc., that are subjects for study by industry engineers.

One thing that is certain is that this new technology seems likely to force a very significant change in the way the trucking industry addresses the issue of lessening tire punctures and the accompanying problems they create. Once proven on a broad scale, this new technology could very well represent significant flat-out progress.

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