February 2006

Equipment Spotlight

Plastic Granulators
by Irwin Rapoport

—View a list of manufacturers at the bottom of the page

With many jurisdictions enacting more stringent regulations regarding the recycling of consumer and industrial waste and by-products and as it becomes more fiscally sound to recover materials for re-use, re-processing or selling, increased demand by recyclers for plastic granulators and shredders is an unquestionable fact.

For some recyclers, shredding plastic prior to feeding the material into a granulator is a necessity.

Granutech SaturnGranutech Saturn Systems Inc. manufactures a product line known as Roto-Grind Shredders, a complete line of single-rotor horizontally fed shredders. With this machine design, material is horizontally forced via an electric hydraulic push ram into a rotor with multiple cutters.

“Typically, clients are processing plastic hard scrap or film in a bale form,” says Damon Dedo, Granutech’s sales director. “We commonly recommend our electric-hydraulic drive because it provides much more rotor torque. This satisfies the various demands in terms of system capacity and product sizing.

“Another benefit of this machine type is the large feed chamber sizes,” he adds, “As a result of oversized feed hoppers, operators can load material into the feed chamber and do other things. Our machines are very automated and are suited for minimal supervision.”

These shredders can provide product size reduction down to .5 inch particle size. The machines are available in 8 models, starting at 20 hp and upwards to 400 hp. In terms of capacity, the shredders can process materials at rates between 1,000 and 10,000 pounds per hour and more.

Roto-Grind shredders can process drools and purgings, injection molded parts and numerous types of film or fiber.

In terms of maintenance, the machines can operate 24/7 and are powered by 460 volt/3-phase electrical power. Typically these machines require a blade rotation every 8 to 10 weeks (when processing film) and the replacement of the blades after a similar time frame.

“For the most part, blade maintenance is the majority of the maintenance you should really expect,” says Dedo.

Rapid Granulator Inc. offers a selection of 46 different granulators, whose horsepower ranges from .5 to 400 and they have the capacity to process scrap material at a rate of 10 pounds to 10,000 pounds per hour.

“They are all based on the diameter of the rotor – the smallest is 6 inches and the largest is 32 inches,” said Kirk Winstead, Rapid Granulator’s president and CEO. “Custom design is our business. The cutting chamber itself is basically configurable among standard options. Getting complex parts to feed without producing flyback and noise are main challenges with design.”

The company also produces intake and evacuation systems. The most common intake system is the conveyer, which works well for basic parts and materials that have either passed through a shredder or are capable of being loosely stacked and fed. Continuous motion is used mainly for film, which is primarily handled by either a roll-feed system or the use of a hose feeder that pulls tubing from a reel.

The processed material is evacuated into boxes, silos or various other containers via negative or positive pressure. The company also produces equipment for dust containment, as well as dust separation that enhances the quality of the recycled product.

To protect the granulator, Rapid has feed sensors and metal detectors, and for conveyer systems, the ability to distinguish ferrous and non-ferrous materials. Machines can be shut down through a zero-speed switch.

“For example,” says Winstead, “if the normal rotor speed is 600 RPM and if it senses that the rotor speed has fallen below 200 RPM, it will anticipate a problem and shut down the machine automatically. That can be for metal or anything that is too big or hard to cut.”

As for maintenance, the majority is for sharpening the knives, replacing the knives and replacing the screens.

Rapid has clients and locations across the globe. “Rapid is the inventor and pioneer of adjustable rotating knives,” says Winstead. “Every machine we build is done with maintenance in mind – our clamshell-type opening and closing features – which gives plant personnel total access to the rotors, hopper and screen.”

Cumberland EngineeringCumberland Engineering Inc. offers more than 50 models of granulators, which range in horsepower from 2 to 600, have capacities between 100 and 15,000 pounds per hour and permit customers a choice between four primary types of rotors. The open wing rotor with its variations – the slant cut and twin shear is the most widely applied design. The staggered rotor is designed for lower RMP and less generation of sound. The hog rotor is a very large, massive and solid rotor, desirable for large or solid masses such as purging that comes out of an extruder or molding machine.

The granulators are driven by electric motors, although some applications have led to gas drives or diesel engines and hook-ups to generators.

“We supply fully integrated systems where we can provide the in-feed conveyers or any pre-staging equipment,” says John Farney, Cumberland’s national sales manager, “as well as extraction equipment. Our forte is providing the proper solution to any application, be it small, large, complex or simple.

Maintenance is essentially caring for knives, as well as replacing screens.

As well, you have to lubricate the bearings, otherwise they will seize up on you and you have to maintain belt tension on the drive belt. You also have to do some routine checks such as visual inspections to make sure that the safety interlocks are in place.”

Cumberland granulators are made of solid steel. “Solid steel makes a stronger, more massive machine and this mass is directly correlated to durability and safety,” says Farley. “Simply put, granulators are designed to destroy polymeric scrap and turn it into a usable commodity. This destruction demands the strongest and safest products and methods possible.”

Cumberland’s designs incorporate elements for added performance such as rotational side walls in cutting chambers and safety elements such as lockable/pinnable rotors to assist in maintenance operations.

Based in Toronto, Canada, Rotogran International Inc. manufactures a line of high-speed granulators with the majority of its customers located in North America.

Designed mainly for use on soft and hard plastics and rubber, the strength of the granulators ranges from 5 to 700 horsepower, have a capacity to process 300 to 400 pounds to 15,000 pounds per-hour and are powered by a totally enclosed electric cooled motor.

Similar to the other granulators featured, blade sharpening and replacement is the major maintenance requirement.

“Keeping the blades damage-free means keeping metal and contaminants away from them – one broken blade will in turn break the rest of the blades,” says Mike Cyr, Rotogran’s vice president of sales. “As blades wear down, they become dull and the machine has to work harder, the quality of the regrind drops and so does the quality.”

Rotogran InternationalAs with the other firms, Rotogran designs custom systems for its clients complete with in-take and evacuation systems.

Ensuring contaminated substances do not enter the granulator is an essential element for Rotogran products. To do this, Rotogran has a metal detecting system for the conveyer in-feed. This type of system is extremely sensitive and is commonly used in the food industry.

“To combat wear from dirty plastic, we offer replaceable inserts,” says Cyr. “When they start to wear down, you unbolt the inserts and put in a new set. Wear plates inside the chamber and along the sidewalls can be made from various materials such as mild steel, tungsten carbide coated steel, quenched and tempered steel or tool steel.”

A key feature for any size reduction system is the need to provide air-flow through the granulator with a blower/cyclone system.

By evacuating with a vacuum through the bottom drawer, the whole machine is cooled, plastic material is assisted through the screen area and production is increased while the quality of the regrind remains high.

“To increase efficiency,” says Cyr, “the system can be designed to have the in-take, granulator and evacuation system communicating with each other to monitor the feed, amperage draw and with sensors, inform you when the evacuation boxes are full.”

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