Knife shredder technology is enabling recyclers to simultaneously shred, chip and size onsite, speeding production and reducing processing costs.
By Doug Bartelt and Del Williams

Traditionally, recyclers have shredded paper, fiber, textiles, carpet, mattresses and plastic products, followed by granulating them to a size suitable for further processing and use as a recovered manufacturing input.

However, the process of shredding, screening and grinding such materials to size with different equipment in separate processes can not only be inefficient, but also a bottleneck to processing.
Now, for the recyclers of these materials, there is a more efficient alternative—a shredder knife technology that can cut, screen and size in a single pass with one machine onsite.

Because the sizing of reduced scrap can be specified, uniform and even tailored to suit the manufacturing process, more material can be successfully processed by recyclers with less labor, boosting profits. Shipping costs are also reduced for scrap transported offsite to buyers since any voids (i.e., empty spaces) within the container are minimized.

In addition to these materials, a knife system design effectively shreds and sizes a wide variety of others, including rubber, wood, copper wire, aluminum, fiberglass, and even garbage and batteries.

Since knife technology simultaneously does the work of both a typical shredder and granulator, it is also more energy efficient and takes less space on the production floor. The technology is flexible enough to be incorporated into the smallest to largest recycling, shearing and grinding equipment.

BCA-Triplus-Shredder-knife-

Conventional Equipment Limitations
For decades in recycling, the reduction of large paper, fiber, textile, carpet, and mattress scrap or unusable product has usually involved shearing equipment such as dual or quad shaft shredders. To further decrease size, this is typically followed by the use of grinding machinery such as granulators, stone mills, tub grinders or chippers.

Screeners are often used at various points, which decreases processing speed. As an example, a standard dual shaft shredder typically turns shredder material into strips and requires the use of a re-screening device to reduce the material to a specific size.

Conventional shredders like this are usually used in conjunction with granulators. A single shaft granulator is a simple device consisting of a knife (or multiple knives) attached to a shaft which mates with a stationary bed knife. Material is chopped and continues to be cut until small enough to fit through a sizing screen in the bottom of the machine. Both the shredder and granulator create various sized material.

Usually, this is determined by how the material is fed into the system in terms of speed, timing, etc., which results in a percentage of incorrectly sized material.

Efficiently Reducing Scrap to Size
Seeking a better way to size scrap material, a knife system technology changes a standard shredder to a hybrid between a dual shaft rotary shear shredder and a single shaft granulator.

The approach uses the precision grabbing action of the high torque, dual shaft shredder to cut the width of the material, while the bed knife design of the shredder sizes the length. This is accomplished in one operation, which produces accurately sized material in one pass without a screen. The end-product size is based on the size and geometry of the knives.

Unlike traditional equipment, a knife system is capable of shredding, chipping and sizing any kind or size of material in a single pass without using a screen. A shredder using this design can produce more than 85 percent correctly sized material in one pass with less than 10 percent oversized material.

With a knife system, a recycling operator just specifies the chip size needed, and it produces chips in the specified size. The design works with wet or difficult to screen materials, and clean cuts those that normally create fines and dust.

Functionally, for recyclers looking to streamline paper, fiber, textiles, carpet and mattress scrap processing, a knife system increases efficiency and throughput that surpasses the typical granulators, hammer mills, chippers and quad shaft shredders used in the industry. By eliminating separate equipment and steps to shred, screen and grind scrap to size—and combining this into a single function—the manufacturing process is expedited.

Another factor increases production output for recyclers: the RPMs of the knives can be adjusted to the load needed for optimal production efficiency. Typical shredders tend to operate at low speed and high torque; this type of system uses a knife design that can be operated at high speed and low torque for higher production speeds. When more torque is required for anything tougher to grind like large mattresses, the system automatically provides the RPMs necessary; it then readjusts to the higher speed and lower torque setting for faster production within seconds.

Additionally, a knife system can reduce scrap to the appropriate size with less energy than typical shearing and grinding equipment. Power efficiency approaches 150 percent over any standard shredder or granulator. As an example, with this technology, a 50-horsepower single pass shredder can produce the same amount of recyclable product per hour as a standard 100 to 150 horsepower conventional system. This can reduce recycler energy costs by $1,500 to $5,000 per month while producing a consistently sized product, ready for cost-effective transport to a purchaser.

Recyclers needing to reduce the size of paper, fiber, textile, carpet and mattress scrap, plus a wide variety of other materials, have traditionally used a combination of in-house shredding, screening and grinding processes as well as dealt with shipment costs to customers. However, with industry innovation, recyclers now have the ability to quickly and efficiently cut these scrap materials to size onsite. This has the potential to both simplify production and reduce shipping costs to boost the bottom line. | WA

Doug Bartelt is President of Milwaukee, WI-based BCA Industries, a developer and manufacturer of industrial shredding and recycling equipment. For more information, call (414) 353-1002, e-mail j[email protected] or visit www.bca-industries.com. Del Williams is a technical writer based in Torrance, CA.

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