A Slower Approach
A number of shredding options beyond
high-speed hammermills are available to recyclers of materials ranging
from scrap tires to the lightest plastics.
By Brian Taylor
is more than one way to skin a cat, the old saw informs us, and there is
certainly more than one way to break an obsolete item into smaller pieces.
While hammermills can work quickly
to reduce all but the heartiest of materials into transportable pieces,
it is not the only configuration on the market for doing so.
In fact certain recyclables, such as
scrap tires and some types of plastic, would render a hammermill ineffective
and require a very different shredder configuration.
SHEARING WHILE SHREDDING
Shear shredders combine the cutting
action of shears with the rotating action of shredders.
Unlike hammermills, shear shredders
rely less on brute force and more on a cutting or scissoring action. The
machine’s advocates tout their quietness and energy efficiency when compared
to their louder counterparts.
The recycling industry, for the most
part, has matched the shear shredder with the processing and retained the
hammermill—noise, energy-consumption and all—as the favorite for the processing
of other materials.
Scrap tires, soft plastics (such as
plastic film) and nylon carpet are among the materials that are being processed
with shear shredders.
“They are very popular as the pre-shredder
in tire recycling,” says Mike Hinsey, director of sales with Granutech
Saturn Systems, Grand Prairie, Texas. “They are also widely used in nonferrous
metals recovery to process things such as aluminum and copper wire and
cable and with dealer grade scrap, where it acts as kind of a pre-breaker
in the cleaning process,” adds Hinsey.
Jeff Taylor, president of Hempstead
Industries, Troy, Mich., says his company has had success selling his company’s
shredders into the plastics industry, where manufacturers use the machines
to process their own prompt scrap. “They’re used to process automotive
plastic scrap, consumer goods factory trimmings, purgings, and skeletons
from die-cut material, among other things,” says Taylor. “The plastic industry
is as diverse as anything on Earth.”
Because of that diversity, a wide range
of shredders have been designed and marketed to handle different types
of plastic. “The ideal design is based on the size of the pieces being
processed, the type of material and the volume of material,” says Taylor.
“Are you running 500 pounds per hour, or 5,000?”
Perhaps most critical to consider is
the texture of the material being fed to the shredder. “A pliable plastic
requires a different configuration than, say, a PVC that is hard and that
fractures when you break it,” notes Taylor.
Among the variables that affect which
machine suits a given application are the type of drive system, the decision
between a keyed shaft or a hex shaft, and the amount of engine power required.
Sundance Products, Gainesville, Ga.,
is a custom compounder of recycled polypropylene resin (#5 plastic) that
uses a low-speed, high-torque shredder to process the scrap plastic items
it takes in as feedstock. The company purchases scrap #5 plastic in all
shapes and sizes, processes the material and then extrudes the plastic
into pellets for resale to injection molding businesses. Approximately
80% of the scrap it purchases goes through the low-speed shredders the
“We drop about 160,000 to 200,000 pounds
a day through our shredders,” says Steve Hungerford, vice president of
raw materials procurement and sales for Sundance Products. “The shredder
allows us to take large plastic sheets in different forms and bring them
down to a size that can be handled through the separation processes that
OPTIONS AND CONSIDERATIONS
Many shredders offer an option of using
either a direct electric drive or a hydraulic drive. Direct electric shredders
dominate the market for applications that require 100 horsepower or less,
according to Hinsey. The shredding of softer goods less likely to jam the
rotor is considered compatible with the electric drive. Hinsey lists textiles,
waste paper and secondary tire shredding as ideal applications.
Hydraulic drive shredders dominate
in those markets requiring shredders with more power and the ability to
reverse rotor direction quickly due to overloads. Among the recyclables
frequently processed in hydraulic-drive shredders are whole tires, nonferrous
metals, rigid and film plastics, and polyurethane foam.
“Some companies focus only on power
and the size of the cutter,” notes Hungerford of Sundance Plastics. “With
us the cutter configuration is very important. We look at how aggressive
the hook is, how much material it can grab, the hook height and width,
cutter material and the number of hooks per wheel. We place a lot of importance
in the cutter configuration so the shredder doesn’t take more than it can
Sufficient power supply does not have
to be a problem with hydraulic drive machines, which can be powered by
up to 800 horsepower for applications where large or tough material is
being processed, or for applications where the blades are reversing frequently.
Hydraulic systems, notes Hinsey, can
be either open-loop or closed-loop. The open-loop systems pumps fluid from
a reservoir through a valve package, out to the hydraulic motor and back
to the reservoir. A closed-loop system maintains a continuous flow of oil
between the hydraulic pump and the hydraulic motor. A small amount of oil
is continuously drained from the loop and cooled and is replenished by
a charge pump adding oil into the loop. Flow direction is controlled by
a swash plate in the hydraulic pump.
Most shear shredders have a twin-rotor
configuration, with each rotor containing affixed blades that act as scissors
as the two rotors move in opposite directions to pull in and cut material
that is fed in.
At least one manufacturer is now offering
a single-rotor shredder that still relies on shearing as a key part of
the processing function. “It’s a relatively slow-speed shredder at 80 to
120 rpm,” says Granutech Saturn’s Hinsey of the company’s Grizzly shredder.
“It consists of a rotor that contains more than 200 30mm square knives
as well as a stationary row of bed knives. As the shaft turns, it is cutting
the material against those bed knives as well as with the rotor knives.
A screened discharge allows you to control the product that comes out,
with screens available down to one-inch in size.”
Hinsey notes that the Evergreen Nylon
Recycling Inc. facility established by AlliedSignal Inc. in Augusta, Ga.,
is using three Grizzly units to process a stream of nylon-bearing materials
ranging from carpet to harder nylon scrap objects. “The horizontal configuration
of the machine allows them to load whole bales and gradually feed the product
into the loader. They can go from bales to a consistently sized discharge
product,” says Hinsey.
Makers of low-speed shredders have
continued to seek out new uses for their machines, with some of those in
the recycling industry and others in solid waste.
Portions of the growing stream of obsolete
electronic scrap is finding its way into low-speed shredders, according
to SSI Shredding Systems Inc., Wilsonville, Ore. “Shredders are used as
part of a multi-step recycling process to recapture the precious metals
commonly embedded in electronic scrap from computers, circuit boards, motors
and switching drives,” says Chris Nichols, SSI senior engineer.
Butler-MacDonald, Indianapolis, is
an electronics recycling firm that uses a SSI low-speed high torque shredder
in its operations. The company first shreds or pulverizes their stream
of scrap electronic and telecommunications equipment to segregate the steel,
aluminum, plastics and nonferrous copper-bearing materials. Later, they
use pulverizers and granulators for further size reduction, prior to final
“Taking a product and trying to reduce
it to half-inch or smaller pieces can’t be done in one bite,” says Mike
Thierault, production manager at Butler-MacDonald. He credits the company’s
low-speed shredder as being “very effective at taking that first bite and
giving us a sized product that the downstream machines can digest.”
Solid waste generators and handlers
have also turned to slow-speed shredders to process bulky items so they
will take up less cubic feet in the landfill.
Art Van, a furniture sales company
based in Detroit, uses low-speed shredders to help economically dispose
of old box springs, mattresses, couches and debris generated at its 26
stores. As a customer service, the company takes back mattresses from customers
to ensure that they don’t end up in the secondary “gray” market.
“We were using open-top containers
from disposal companies that cost about $400 each, and we were filling
about 15 of them per day,” says Art Van maintenance supervisor Ed Michael.
“By shredding the mattresses, we can get away with three to four per day.
The shredder helps us provide a service to our customers without overloading
TURN IT UP TO MEDIUM
Medium-speed shredders or grinders—with
speeds from 100 rpm to 400 rpm—also use knives or cutters to process material.
The machines, as mentioned by Granutech
Saturn’s Hinsey earlier, feature just one rotor and usually have small
cutter tips on the rotor. Plastics recyclers and recyclers of electronic
scrap, wood waste and light nonferrous metals are among the target markets
for this type of machinery.
According to Hinsey, plastic mold shops
will use a medium-speed shear shredder to process batch-fed rejected molded
plastic parts, which are screened and fed back into the extruder for repelletizing.
Generators of prompt scrap wood, such
as furniture makers or pallet manufacturers, will also grind scrap through
these machines to make a fuel-quality product.
Larger medium-speed machines, which
can use up to 400 horsepower drives and rotors weighing as much as 10 tons,
are typically vertically fed and rely as much on the rotor force as on
the cutting edges to perform the work. “The mass of the rotor is very much
part of the reduction process, unlike lower-speed machines which are more
dependent on the shear cutting action,” says Hinsey.
They are often used as a secondary
process. For scrap tires, they can reduce rough-shredded tires to nearly
steel-free chips less than ¾-inch in size. “We’re seeing that there
is a larger demand for a low-steel content tire-derived fuel (TDF),” says
Hinsey, noting that many TDF users are demanding less than 3% steel content.
“We’re seeing more and more processors
whose buyers aren’t satisfied with nominal fuel chips with too much steel,”
Other emerging markets for the machine
include processors of asphalt shingles, nylon and carpet recycling, and
as a secondary step for wire and cable processors. RT