'I thought I knew a lot about retreads'
David Kolman, a former trucker and trade magazine writer, is associate director of the Tire Retread Information Bureau (TRIB). He joined TRIB in 2004 and works out of the organization's East Coast office. In this CTD exclusive, he describes what he recently learned at Bandag's Certified Retreading Technician Training program.
As a long-time trucker and trade journalist, I thought I knew a lot about retreads. But it's one thing to talk about doing something and another to actually do it. Bandag Inc. recently gave me the opportunity to "walk the walk" by inviting me to go through its Certified Retreading Technician Training program.
It didn't take long for me to realize that the retread process is more involved than I imagined. Those who think retreading is simply a matter of removing old tread and "gluing" on new tread are dreadfully misinformed. There are a lot of intricacies that go into retreading. As the class went on, my appreciation and respect for retreaders grew.
At the start of the program, my classmates and I picked the tires we would retread. I would retread two; my classmates would each be doing five. Here's what the rest of the process was like.
I. Initial inspection. I was surprised to learn that a tire's retreadability is not just a function of its age. Other considerations include application, how well the tire was maintained, the number of times it has already been retreaded, and customer specifications. I rolled the first of my tires onto an NDT-IIB tire tester, colored in the DOT number and wrote my name alongside the number. Accountability, I soon learned, is an important part of the process.
I raised the NDT machine's platform to bring the tire to a comfortable working height and spread the casing. Shining a bright hand-held light inside, I used a foot pedal to rotate the tire, carefully looking inside for injuries like cuts, bruises and punctures or other damage, such as wrinkles, splits or cracks. I then checked the outside of the tire -- the crown, beads and sidewalls -- for foreign material. Along with a visual inspection, I let my hand slide along each sidewall while rotating the tire, feeling for bumps and lumps. I also measured the remaining tread depth to make sure there was enough left to retread. (Instructors recommended taking a tire out of service for retreading when a tread measurement shows between 6/32-inch and 4/32-inch of tread remaining.)
Next I placed the NDT's probe inside the tire. The probe generates electrical impulses to detect nails, nail holes, cuts, tears and bad repairs. I found a nail hole in one of my tires. This meant I would get to perform a repair! A classmate, Kevin Smith of Premier Bandag in Alliance, Ohio, helped me mark the problem.
2. Shearography. Internal damage is a frequent cause of tire failure, according to Bandag instructors.
Bandag uses its Model 7400 Casing Analyzer (nicknamed the "clam shell" because of its appearance) to inspect a casing from bead-to-bead. For me, the mere look of the analyzer was intimidating. But when it was my turn, I bravely rolled each tire onto the machine's tire lift/centering table and marked the top center of the tire with a white crayon. This would serve as a reference point to locate and mark any internal damage that would be uncovered.
With the push of a button, the tire was lifted inside, the dome closed and the computer program began its self-controlled inspection cycle. It looked at the tire's top sidewall, top crown, bottom crown and bottom sidewall. Twenty-eight different pictures per section are played front-to-back like a slow-moving movie on the analyzer's display. We were told to look for something resembling a double bulls-eye, which indicates trapped air inside the casing.
I had a difficult time interpreting the animation. "Don't worry," classmate Joel Ayala of GCR Tire Centers in Norwalk, Calif., reassured me. "It's a matter of practice, practice and more practice." With his help, I saw that neither of my tires had internal damage.
3. Buffing. Bandag's technical learning lab has three buffers: the manual Model 8120, the Model 8200 and the Model 8400. All of them remove worn tread to the correct shape, size and texture while removing any irregularities. I selected the 8120 because I wanted to manually buff my tires. I used a hydraulic hand lift to transfer my first tire from the monorail to the 8120's rim.
After centering the tire, I hit the "inflate" button to air it up to its proper psi level. Then, with the help of an instructor, I dialed in the tire data. That done, I tried to operate a number of control mechanisms -- buttons, dials, switches and a joystick -- while also trying to stay within the lines and templates the machine produced as a guide. There is a real art to running the 8120 and being able to buff the casing to a particular shape and proper smoothness. I had a hard time.
For my second tire, I decided to go with the easier-to-use Model 8400, which is automated. Once I mounted the tire and pressed "start," the computer controlled the entire buffing process. After three minutes, the machine slowed to a stop. I hit the "deflate" button and was done. Effortless!
It is very important that the buffed area of a tire be kept clean and never touched. Dirt and oils from one's hand can contaminate the buffed surface, adversely affecting the adhesion of new tread. Keeping my hands off the buffed surface was challenging; I instinctively tried to move a tire along the monorail by pushing on the buffed area. The first time I touched the surface, I received a lecture from one of the instructors. He kept a close watch on me after that. He shouted "Hands off, David!" so often that my classmates started calling me that!
4. Skiving. Skiving is the process of removing all injuries or scorched materials from the tire's surface to prevent injuries from growing. I rotated the tire to check for obvious injuries. Then I used a probe to determine if an injury should be skived. I found a couple of rock drills (small holes made by stones) that needed to be skived but weren't deep enough to require repair. Using a low-speed air tool fixed with a rasp, I ground out the hole, trying to not damage the casing's steel cords or scorch the buffed surface. But I was too heavy-handed. On several of the holes, I broke the protector ply, the top belt that protects the other belts.
Seeing what I had done, classmate Efrain Jauregui of Cross-Midwest Tire in Kansas City, Kan., helped me correct the problem. Using an air tool fixed with a stone, I carefully trimmed the steel back to where it is tightly embedded in the rubber. This allows for better adhesion of new tread, he told me. The nail hole puncture in my other tire was left alone to be repaired next.
5. Repairing. While trying to fix my nail hole puncture, I came to realize that tire repair requires the utmost precision and accuracy. With the help of my instructor, I repaired the nail hole injury, but it wasn't an easy task. In drilling out the hole, we discovered rust in the steel belts and had to enlarge the hole to ensure that all of the problem steel was removed. Otherwise, rust would grow and the tire would fail. As a result, the spot repair turned into a section repair, which required a B120 patch.
6. Building. After placing my tire on the Model 6400 extruder's rim, I fed a roll of cushion gum into the machine and heated the gum to the proper temperature. Another classmate, Alvin Jackson of Southern Tire Mart in Shreveport, Miss., helped me set various guides and work the touch screen display to begin automatically applying a uniform coating of cushion gum, filling in all of the skives.
Using the monorail, I then moved the tire to the Model 6400 builder, which applies the new tread. After the tire was set and inflated, the machine measured the tire's circumference. At the other end of the machine, I loaded in the new tread rubber. Using the device's cutter, I cut the lead end of the tread in the middle of a tread design. I applied cement and double-sided cushion along the cut end.
I next pressed a button that advanced the tread to the proper length, according to the circumference measurement. I adjusted the trailing end to match the tread design and then made a cut. This end also received some cement. I pressed the "advance" button, and the tread was automatically centered, aligned and applied to the casing. I physically pushed the tread together, making sure to match the tread design on the two ends. With the push of another button, automatic rollers pressed the tread evenly onto the cushion gum. I then attached a wick strip over the splice.
From here, the tires were moved to the enveloping station, where they were encased in a flexible rubber envelope and sealed. Then they went through the curing process. After curing, the completed retreaded tires were inspected one more time. I rigorously inspected each tire. "This is the final opportunity to make certain that everything has been done to produce a quality, safe and attractive tire," my instructor said.
Once approved, tires were branded with a code to identify their status as retreads, in addition to who manufactured the retread and its date of manufacture. The code was placed near the tire's original DOT code. The tires were now ready to be prepared for delivery.
Each tire was cleaned of all markings while excess rubber was trimmed away. Tires that complied with all finished specifications were painted and labeled for a "like new" appearance. Meanwhile, all paperwork was completed.
My time participating in Bandag's Certified Retreading Technician Training program was well-spent. It was an awakening to realize that despite all the high-tech equipment involved, much of the retread process work still boils down to the talent, skill and experience of retread professionals.