Granulators and shredders are both types of equipment used for size reduction. On the surface, it seems like they have similarities, but in reality, they are completely different types of machines.

You can't just trade out a shredder for a granulator, or vice versa, and expect the same results on the shop floor. These are fundamentally distinct types of machinery with several different design and operational considerations. In other words, they are built differently and work differently.

In recycling, every minute counts and every pound of material matters. The nature of the business is all about production, preventing downtime, and keeping machines running all the time.

The industry is moving away from fancy and toward functional. Recyclers and plastic processors have become more sophisticated and have upped their game. Understanding the key differences between granulators and shredders can help operations get the utmost production out of their machines. Believing they are interchangeable can be costly.

There is a place for both machines in the marketplace, and sometimes they even work together. But again, it's all very specific and materials-focused. Let's take a closer look.

What to know about granulators

Granulators are high-speed, inertia-driven machines that typically run around 500 rpm. These machines utilize speed and inertia to cut material into progressively smaller pieces. They are typically metered-fed by a conveyor or simply by hand. A steady, controlled flow of material maximizes the production rate of a granulator.

There's lots of physics involved as the flywheel and rotor carry stored energy into each cut, so the machine isn't relying solely on the motor for every pass of the blade. The heavier and more solid the flywheel and rotor assembly, the more cutting work it can do before the motor needs to kick in.

There's also an energy advantage. Because the machine carries all that inertia, stored energy powers through the cut first. Only once that energy is used up does it go directly to the horsepower motor — that's when amps go up, and the motor draws more electricity.

While many granulators were designed for light-duty in-house scrap, many plastic processors and recyclers are now seeking high-performance granulators as part of a complete package. Things have evolved quite a bit from the days when a granulator just sat beside an injection molding machine waiting for the next sprue.

There is also a greater demand for customization, especially when it comes to recycling and handling a wide range of scrap material. Custom-built granulators and systems help recyclers and manufacturers keep materials in use longer, reduce waste, and close the loop on production.

A common misperception is that materials must first pass through a shredder in a two-stage process; a well-built, tough granulator can take on those materials on its own as long as the wall is thin. The right granulator can tackle large parts, thin-walled material (such as thermoforming sheet), scrapped parts, and more.

This is where utilizing inertia, solid flywheels, geometry, and build quality all matter. With this level of engineering, you don't need to go to a pre-size step just because parts are larger. These strong granulators can even process larger parts, such as a 55-gallon drum, without the need for pre-shredding. The solution is to make the grinder big, strong, and narrow enough so that the granulator can handle it.

Granulator output is a more consistent, evenly sized regrind since it is a high-speed cutting machine. This is especially ideal for plastics processors who typically put the material back into a plastics machine (such as an extruder or injection molding machine) without additional steps. Recyclers, meanwhile, are more focused on throughput and cost per pound, and a well-built granulator delivers on both.

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Heather Caliendo

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The real difference between granulators and shredders

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