Auto Trends

Yeah, our own lives can be pretty tough, but they are nothing compared to the thankless horrors of a treaded tire. Well, actually the treaded tire has it easier than the old worn out tire. Day after day of traveling over the hot and cold asphalt, wearing itself inevitably down to the day that we simply take them into the tire shop and have them disposed of.

But today we are living in the green age, so this story does not exactly end here. Most tire shops recycle old tires, which means that it goes into a warehouse for sorting. The good tires get sent to an area for retreading, while the bad tires get sent to an area for shredding and grinding.

The tires fit for retreading are literally given a second chance at life. Sort of a toupee fitted to a balding tread spot if you will. Most of the time at low speeds the retread does just fine (just like a toupee’d driver in a convertible Chevrolet Corvette). But on the open highway they occasionally fly right off, leaving those tread strips (and roadkill toupee’s) that we often see on the sides of highway.

When this happens, these tires are often sent straight to the shredding halls. A tire that has been marked for shredding with either go through what is known as ambient shredding or cryogenic chopping.

Ambient Processing-

Ambient shredding refers to the crackermills that process old “ambient temperature” rubber by using two large counter rotating rollers with serrating cutters that literally chew the rubber into rubber particles. The actual size of rubber chunks is controlled by different sized screens that can be inserted into the cutting machine.

Generally this method produces long rubber slivers or crumbs that have a cut surface shape and rough texture. The uses for this crumb rubber include such products as car mats, insulation, construction products, hoses, horse arenas, garden mulch, and safety cushioning for walking/jogging paths and playground surfaces.

Cryogenic Processing-

The breakdown of rubber can also be accomplished through a Cryogenic process. This process uses liquid nitrogen to freeze the rubber tire particles at temperatures below -80° F. This causes the rubber to become brittle like glass and break into smaller particles easier.

The cryogenic method is a more effective way to get “clean” rubber consisting of low steel and fiber content, due to the prior freezing which allows for cleaner breaks in the rubber. The difference in quality can best be described by the difference in shredded beef versus chopped sirloin.

Micromilling-

Micromilling (or wet grinding) consists of running the rubber crumbs from either of the above steps through another set of closely spaced grinding wheels while the rubber is submersed in a liquid medium, such as water. The liquid aids in chopping of the rubber into finer particles.

Such Fine ground rubber is suited for ingredient aids in asphalt, roofing products, various rubberized coatings/sealants, and even as an ingredients in numerous automotive products, such as new tires.

Now you know more about the life of your tires than you probably ever wanted to know!

Source:
TIA (Tire Industry Association)