Tread On Me
Tire casings are designed to last much longer than the original tread
Retreaded tires got a bad rap a long time ago, but tire manufacturers and large retreaders have figured out how to make the retread process all but flawless today. The best way to judge a retread plant is by asking how technicians are trained, how much experience each has and how quality is monitored. We toured the Wingfoot retreading plant in Wilkes Barre, Penn., to find out how it’s done.
1. Every tire is bar-coded in two places so it can be tracked at every step in the process.
2. The casing is then inspected. The inspector will condemn casings that can’t produce a safe retread and will mark where repairs will be needed. The tire is mounted onto a machine that opens it up and rolls it around so the inspector can check it both inside and out. It finds nail holes by attempting to pass an electrical current through the casing from the inside.
3. The tire is then mounted on an automatic buffer, where the technician inputs its size and other data. It then buffs the tire as it is spun, removing the old tread rubber gradually. A device with a roller on it measures its diameter. This leaves the tire with the right thickness of rubber, termed the “undertread,” where the pre-cured tread will be installed.
4. At the skive station, the inspector examines the buffed surface, smoothes out any damaged or rough areas and applies rust protection anywhere the steel cords ride right along the surface.
5. He then makes repairs, cutting out damaged rubber, filling gaps in the casing with fresh rubber that will cure in the process and sealing the “inner liner,” which keeps moisture out of the casing, with the proper-size patch.
6. Next, the tire is mounted on a machine that applies the AZ cushion gum — a layer of rubber adhesive that will hold the tread on by curing it to the surface of the casing. You can see the layer of cushion gum where it has been flattened to the proper width and evenly applied.
7. Next, the tire moves to the pre-cure builder, where the pre-cured tread is evenly rolled onto the tire straight by machine. Since the tire’s diameter is programmed in, the machine stops the rotation at the right point, then the operator cuts the tread to exactly the right length. Once the tread is rolled all the way around and the ends butt together, the technician gently taps the tread to remove any bulges.
8. As the casing rotates, these rollers apply gentle pressure from the center outward to remove air and ensure the pre-cured tread section is flat against the layer of cushion gum, a process called “stitching.”
9. After a thin layer of poly is applied over the tread, another machine opens up a rubber envelope so the tire can be put inside, then allows the tread to close over the tire.
10. Sealing rings are installed to seal the envelope edges at the bead on either side.
11. The tire is placed in a curing chamber. Each envelope is pressurized to 75 psi, and the chamber to 85 psi, to ensure the green tread section is held snugly against the casing. The oven is heated to 260 degrees Fahreheit by steam and held there for 150 minutes. This cures the green tread rubber and vulcanizes it to the tire, a process like welding. Gauges allow continuous monitoring of the pressure inside each tire’s envelope.
12. At the end, the tire is inspected again and pressure-tested at 125 psi inside this machine to ensure the casing is sound.
Truckers News thanks Wingfoot Production Manager Bob Bohn, Center Manager Rich Matson and Reatread Plant Manager Rick Christman for their help with this article.