Recycled tires are the source for a growing
number of exciting new products today. In fact, turning
post-consumer tires into a valuable new resource is big
business, and it all begins with a tire shredder.
For most tire recycling operations, choosing
the right shredder can be a "make or break" decision.
The market has plenty to choose from with a variety of options
to match buyers' needs with equipment capabilities as closely
Operators considering a purchase should
first look at the end product they're after. "It's
a competitive market, so buyers need equipment that positions
them favorably as a low cost provider," said Michael
Weible, marketing specialist for Diamond Z Manufacturing
of Caldwell, Idaho. "Having the right equipment is
the key," he said.
To recycle tires, there are two distinct
types of shredder designs - high-speed, tub-style grinders,
and low-speed, high-torque rotary shear shredders. Either
type works, but there are some important differences.
Though not in widespread use for tires, tub-style
grinders feature a rotating "hopper" where scrap
tires are placed. As the tub rotates, guides direct the
tires toward the center where a cutting bar holds them in
contact with the hammermill. Through an arrangement of rotating
hammers - each one of which can weigh in excess of 100 lbs.
- the hammermill begins the process of reduction into a
various mix of shred, or "grind," depending upon
the end product in question.
"The tips of each hammer are equipped
with replaceable carbide cutting teeth, said Mike Weible.
"When the hammers are through, the primary grind is
a mix of shredded rubber ranging from six-inch pieces to
less. Further reduction takes place by grinding a second
time, or better yet, by directing the primary output through
a secondary rasper, granulator, or cracker mill," he
High horsepower, low-torque motors, typically
drive tub-style grinders. The horsepower is necessary because
the hammermill needs velocity to effectively break down
the rubber of the tires. Water lubricates the tires as they're
consumed by the hammermill.
The impact of the hammers also begins
to separate the rubber from the steel wire of the beads,
belts and sidewalls, depending on the tires being shredded.
In-line magnets remove most of the steel wire as the shred
is further processed.
One advantage of the tub-style grinder
is throughput. According to Diamond Z, "Larger tub
grinders can handle up to 4,000 tires per hour, producing
shred of 6" or less. Advanced controls allow a single
operator to run the machine over an eight hour shift."
Rotary Shear Shredders
The most popular type of shredder used for tires
is known as the rotary shear. Within the rotary shear group
though, there are the versatile, "hook-shear"
type shredders, and those dedicated to tire recycling, known
as the Holman-type shredder.
With a hook-shear shredder, conveyors
typically deliver scrap tires to a chute-like hopper. At
the bottom of the hopper are parallel shafts with hook shaped
blades, or knives. Spacers on the shafts, which are "nested"
with blades on adjoining shafts, separate the blades. As
the shafts rotate toward one another, the hook-shaped blades
grab the tire and draw it down through the blades, shredding
the carcass of the tire as it passes through. Hook-shear
shredders are driven by low-speed, high-torque drive systems.
According to Glenn Newton, president of
Granutech-Saturn, makers of hook-shear type shredders, "Most
hook-shear shredders feature blades made from heat-treated
4140 grade steel alloy. The blades, and spacers slide on
to the shaft, which is either hex-shaped or keyed, depending
on customer preference. The assembly is held in place on
the shaft by a locking nut or collar. The primary advantage
to this design is flexibility," he said. "Worn
blades can be re-welded, sharpened, and they can be configured
on the shafts in different ways to shred a variety of materials
- from tires, to wood to nearly all types of solid waste,"
Some rotary-shear shredders are purpose-built
for tire recycling, however. Equipment dedicated to tire
recycling is known as the Holman-type shredder. Charles
Astafan, general manager of Columbus-McKinnon's Sarasota,
Florida operation said, "The Holman shredder was specifically
designed for processing steel belted scrap tires. It is
similar in design to the hook-shear shredder, but it uses
knife rotors and rotor spacers that are permanently fixed
to the shafts by means of heat shrinking. The actual knife
is then attached to the rotor by bolting it in place. Wear
plates or liners are also secured to each side of the rotor
to protect them from wear," he said.
Holman-type shredders use blades made
from hardened tool steel. When they are press-fit onto the
shafts, they are aligned at extremely close tolerances to
the blades on the opposite shafts. According to Charlie
Astafan, "Since there's no deflection at the blade
tips, it enables the shredder to cut tires more like a pair
of scissors. The payoff to the operator is in reduced maintenance
costs on blades, per ton of tires processed. It also produces
a cleaner cut, with no wire exposed on the sides,"
It is also important to note that the
Holman design uses feeder rollers to align and feed tires
to the knives, unlike the hook and shear shredder that uses
the hooks on the knives to capture and pull the tire between
the edges of the knives. Notes Astafan, "The feeder
rollers are very simple, reliable and inexpensive. They
promote tire feed and reduce the chance of any jams when
feeding whole tires into the shredder, and they eliminate
tire bounce," he added.
Downstream from the primary shredder,
operators can choose from a wide variety of additional equipment
to further process the recycled rubber. Tom Wendt, Jr.,
Eldan product manager for Wendt Corporation, of Tonawanda,
New York said, "From the primary shred, material is
then further processed in a heavy rasper that produces a
much smaller chip, roughly 5/8", which is nearly wire-free.
Magnetic separation completes the steel removal, and then
a classifier further reduces chip size and begins the fiber
removal process. Size reduction continues with granulators
which can produce a wide range of crumb rubber sizes specific
to each end-user's specification."
Mark Diemunsch, president of Barclay Roto-Shred
in Stockton, California, makers of Holman-type tire shredders
observes, "There's lots of different ways recycled
tires can be used today, but three applications outnumber
the rest. There's shred for landfill acceptance, or use
as a daily alternative cover. There's the 2-inch chip for
TDF (tire derived fuel), drain fill or civil engineering
applications. And there's crumb rubber," he said. "Tire
recycling isn't for small operators anymore. You have to
be big to be in this business today. It takes trucking and
transportation, and an established market for your output.
Then, of course, it takes the right equipment."