Granulators vs. Pelletizers

The plastics processing industry relies on specialized machinery to cut and grind material to a specific size or shape. Granulators and pelletizers are commonly found in plastic processing plants.

However, they perform two very different tasks. Read on to learn more about the differences between granulators and pelletizers.

Granulators

Granulator machines are used mainly to recycle plastics. They’re often found in plastic recycling plants or other manufacturing facilities where recycling scrap from their products can add up to significant cost savings. Other times, companies will purchase plastic scrap, use a granulator to chop it down to a specific size or shape, and then put the finished product back on the market for resale.

The size of the recycled granular flake varies depending on the screen size inside the machine. We often refer to this as the “back end” of the process as the material has been made and formed into one of thousands of plastic products such as bottles, car bumpers, and computer keyboards.

Granulator Blades

The design of the knife itself not only determines the quality of the granulate but the overall production rate as well. There are a few considerations for selecting the right granulator blade:

• How the blades are arranged — This depends on the type and size of plastic being processed. For example, if you’re cutting softer materials, a smaller space in between the blades produces a cleaner, more efficient cut.
• Tip angle — The angle of the tip is determined by the material you want to process. A scissor cutting action improves efficiency while lowering noise and dust.
• Speed — Slower knife speeds allow for efficient cutting of same-size granulates. It also helps reduce noise and wear and tear on the blade.
• Sharpness — Softer materials require higher angles and sharper blades. For more brittle materials, a blunter tip with a lower angle is optimal.

Pelletizers

Unlike granulators, which chop up plastic that’s already been created, pelletizers are used in the manufacturing of plastics. Polymers are mixed and then extruded through a die face and come out in long spaghetti-like strands. They’re then fed into a pelletizer, which cuts the strands into small pellets whose size is based upon the customer’s product.

This process is highly technical and involves a fair amount of science. This ensures that the pellet being fed into the molding machine or next extruder will melt, flow properly, and come out as an acceptable part.

There is another type of pelletizing process that’s referred to by one of several different names, such as “underwater pelletizing,” “hot face,” or “die face pelletizing.” In this process, the mix is fed into an extruder and flows through to a die face located at the end. The material is then cut at the face of the die. The process is similar to a meat grinder that a butcher uses.

Pelletizer Rotors and Knives

Pelletizers can use either knives or rotors, depending on the application. There are several materials used to manufacture pelletizer knives and rotors:

• Ceramic
• CPM
• Stellite
• D2 Steel
• Stainless Steel
• Carbide (multiple grades)

There are a few different types of pelletizer rotors, such as wedge lock, bolt-on, and solid helical. Solid rotors can range anywhere from two to forty inches, while wedge lock rotors are from four to forty inches.

Which One is Right For Your Application?

Granulators and pelletizers perform two entirely different tasks. Granulators assist with the recycling process while pelletizers chop up new plastic to form pellets.

Click below to learn more about granulators and the various custom knives and blades they use.