Industrial facilities that engage in plastics processing utilize a lot of different equipment in their operations, such as plastic pelletizers, granulators, plastic grinders, shredders, and more.
Companies who are new to the industry, or those who are looking to expand, may wonder about the differences between some of these types of equipment, however. In this post, we’ll look at the key differences between a granulator machine and a shredding machine to help you determine which is best for your needs.
Here are some fast facts to know about shredders and their operation:
Shredders take larger materials and shred them to more manageable units, with some models able to reduce chosen materials to a uniform size.
Shredders are less efficient at low throughputs, with some units struggling to work well in these scenarios as heavier loads in the feed bin are easier to push forward into the rotor
The rotors used in shredders are usually composed of solid steel, or are made of heavy-duty weldments
Because shredders produce larger pieces as an end result of operation, there can be considerable variation in these pieces and a lot of dust, with granulators needed to further process and reduce the material
Here are some fast facts to know about granulators and their operation:
Granulators reduce materials to much smaller sizes compared to shredders and even grinders, with sizes of 0.2 mm or lower being possible
These small sizes are made possible due to the open-rotor design of granulators that helps to facilitate the processing of lighter materials, compared to the closed-rotor operation of shredders and grinders
The open-rotor functionality of granulators also means more air space is present facilitating product agitation and cooling
Because granulators further refine and reduce materials, they are often used in conjunction with other processing equipment such as grinders and shredders
Granulators tend to require a more specialized feeding process, either by hand, conveyer, or robot, to avoid jamming, in comparison to shredders which do not necessitate as much oversight and can simply be fed material that has been dumped in the feed hopper.
Some scrap can put a considerable strain on size-reduction equipment. Purgings, for example, can be several inches thick and weigh thirty or forty pounds. Putting one in a granulator, even a central granulator with a hog rotor and plenty of horsepower, can be noisy, can cause power spikes and can potentially damage the granulator. To avoid these problems, companies who recycle purgings with granulators often cut them into smaller pieces using a band saw or a similar tool.
Big scrap like purgings are no problem for shredders. In fact, a bin full of purgings can be dumped into a shredder hopper and the machine will devour them quite efficiently. The same holds true for a bale of crushed laundry detergent bottles—a shredder would love them. However, in undensified form, a shredder wouldn’t handle them very efficiently; the loose bottles would bounce around too much. But loose, lightweight scrap would pose no problem if it was manually or conveyor-fed to the cutting chamber of a granulator.
Off-spec rolls of plastic film and fiber, some weighing hundreds of pounds each, are another example of scrap that is ideal for shredding—the whole roll can simply be dropped in. To process the same scrap in a granulator, the roll stock would have to be cut into slabs or unrolled. Special cutters are available for these shredder applications to ensure that long strips of film and fiber strands do not wrap themselves around the rotor.
If you need to process high-volumes of heavy, dense scrap (whether it is purgings or thick-wall pipe or sheet), and you want to avoid the labor-intensive prep work needed to use a granulator, a shredder is likely your best choice.
As you’ve probably noted already, shredders don’t require careful feeding. They work just fine when heavy, dense scrap is simply dumped into the feed hopper, where a hydraulic ram built into the bottom of the hopper pushes the scrap into the rotor. When the ram retracts, the weight of the remaining scrap above tends to force it downward, so the next ram cycle can move it forward. Thus, shredders are “dump-and-forget” when it comes to feeding.
Most granulators are just the opposite. To avoid jamming, they need to be fed smaller amounts of scrap continuously, either by hand or by an automated feeding system—a robot or conveyor.
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