Do's and don'ts of OTR tire repair: Tire usage makes all the difference, say experts
There's more than meets the standard tire-repairing eye when it comes to fixing off-the-road (OTR) tires. "It's a whole other world," says Jerry Davis, director of heavy materials and retreading for Group 31 Inc. "There's considerably more load and flex involved in OTR tires."
Davis says there also is a great demand for accuracy due to their cost and, more importantly, the dangerous nature of many OTR applications.
"Over-the-highway truck tires basically have the same uses," says Bill Johnson, director of training for Tech International. "There are many different uses with OTR tires. You have to look at the load the tires are carrying, the distance they're traveling and haul road conditions. You also have to know your customer, how they operate and what kind of tire maintenance program they have."
There are critical factors to keep in mind during the OTR tire repair process itself.
1. Is it possible? "First, you have to decide if the repair is something you can do," says Davis. Measure the overall length and width of the damage and then refer to tire manufacturer-provided charts.
2. Start clean. If the injury size falls within range, spray a pre-buff cleaner over the entire repair area. Then use a hand-held hoe to scrape away silicone, which resides in every tire. "You have to get that silicone out to get the patch onto the tire," he says.
3. Buff out the injury. Buff down into the ply body until all remnants of the injury are removed. When working on a bias-ply tire, "go in just above the tire's body ply," Johnson says, "and don't leave any loose cord." When working on a radial tire, buff past the synthetic rubber inner liner -- which should be removed -- and then all the way down to the tire's natural rubber. Then extract all rusted or loose cables.
OTR tires are prone to stretching, so if you don't buff deeply enough "you'll get bulges that will cause rubber to crack" and cause dangerous flex points, according to Davis.
Always follow Rubber Manufacturers Association (RMA) specifications when buffing. The maximum speed the RMA recommends is 5,000 rpms, according to Johnson. "Most tools are between 2,400 and 4,000 rpms."
4. Prepare the repair area. After brushing and vacuuming the repair area, immediately coat it with cement to keep moisture from contacting with steel and creating rust (in radials) or causing plies to separate (in bias-ply tires). Davis recommends "stippling" the cement on so the substance works its way into every crevice. "Don't put it on too thickly."
5. Apply gum. Next, apply floater gum and stitch it to force air out so bubbles don't form. Most tire repair manufacturers include a sufficient amount of gum in the repair kits they sell.
6. Apply patch. When applying a patch, make sure the arrows on it are aligned with the tire's beads. "Patches are pretty much identified as to what area goes toward the bead," says Davis. "You want to center the patch whether it's a tread or sidewall repair." Failure to do so will cause cracks.
Also make sure the unit is applied flatly, says Larry Kinyon, OTR technical specialist for Rema Tip Top/North America Inc. "Don't bridge it. It has to be flat, especially in the shoulder (area)."
Davis and Johnson prefer using heat-cure patches, which they say are "more forgiving" than chemical patches. "You can get better adhesion," Davis says. The majority of OTR tire repairs today are heat-cure. Rema recently started offering heat-cure patches, according to Kinyon. "We'll still offer the chemical line."
Also during the patch application process, do not exceed tire repair manufacturers' repair chart limits.
7. Stitch and seal. Stitch the patch into place using an air hammer, or "tamper," if available, to ensure a tight bond and save labor. "I know a lot of people who still crawl inside these tires and stitch patches by hand," Davis says.
Line, or "strip," the patch's outside edges with cushion gum to seal the patch and liner on the edge. Then apply edge sealer over the top of it when using patches that are eight inches or smaller. With bigger patches, apply sealer to the edges "an inch on either side," Davis says. Then buff off excess rubber to the contour of the tire.
Techs should properly secure OTR tires, particularly giant ones, before starting the in-shop repair process, according to Rema's Kinyon. Most techs use tire stands that allow them to rotate, inspect and fix damaged casings; others use overhead crane systems with slings. "The days of sticking chock blocks underneath giant tires are over."
Properly remounting OTR tires after they've been fixed is critical, too. When possible, mount them on rear-wheel positions. "With loaders, (tires) need to go on the back to take the stress off of them," Johnson says. "With dump trucks, use them on the drive axle, not the steer, due to the weight of the machine."
Injury size also is a factor in remounting, says Kinyon. "If an injury is near the maximum size, you sure don't want to run the tire on a steer axle." Many mines handle their own mounting and demounting, "and have their own guidelines."
Minimizing downtime is a top priority in the mining and construction businesses. As a result, operators sometimes refuse to send damaged OTR tires back to the shop for a thorough repair job in favor of "fixing" them in the field by slapping on a patch.
Tire repair manufacturers see more "quick-fixes" at construction sites because builders "are not regulated nearly as closely as mining companies," Kinyon says. "It's hard for an OTR serviceman in that case, because the customer dictates what goes on. (Techs) are often between a rock and a hard spot."
That's where dealer salesmanship comes into play, Johnson says. Whether they want to hear it or not, end users must be told that fast, in-the-field patch jobs will cost them more in the long run by causing further separations that will spur extra service calls. "They should send their tires back to the shop for repair."
Bring it on, says new kid on the block: Tap-Rap targets 'extreme' tire injuries
Few would argue that bigger is better when it comes to OTR tire injuries. Quebec City, Quebec-based tire repair material manufacturer Tap-Rap International doesn't look at it that way. "We want the extreme repairs," says Dan Hunstiger, Tap-Rap director of sales and marketing in North America.
The company's repair system, which was introduced to the United States market earlier this year, can fix OTR tire injuries up to 30 cables wide and 19 inches long, according to Hunstiger, "big enough to put your head through." Tap-Rap's step-by-step process consists of applying the following:
* a thin layer of cushion gum following damage removal;
* a strip of flexible, directional steel with a thin layer of gum on it;
* a reinforcement layer made of fabric; and,
* a rubber "protector that looks like what most people would call a tire repair patch."
The system, invented 20 years ago in Italy, is more labor-intensive than standard patch repair jobs, and often takes longer to complete, Hunstiger says. Tap-Rap officials claim it can extend OTR tire service life by up to 4,000 hours in some cases, and gives a tech the ability to "custom make his repair right on the job."