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Sizing and recycling incoming material streams are standard practices at waste processing facilities across the country. Facility managers use sizing equipment to reduce the volume of material, to separate materials that can be repurposed and to create valuable end products, so it’s important to choose the most efficient processing equipment for handling specific material streams.

The two most common equipment types for processing wood (both organic and processed), construction and demolition (C&D) material and municipal solid waste (MSW) are low-speed shredders and high-speed grinders.

Understanding the differences between these two categories of machines and the type of material each is best at processing can optimize a facility’s throughput significantly.

Waste sizing equipment categories

Low-speed shredders and high-speed grinders commonly are used to process various materials. The categorization of low-speed shredders typically depends on the number of shafts they have, ranging from one to four. High-speed grinders include horizontal grinders and tub grinders.

The choice between these machines is determined by several factors, including the type, size and shape of the material to be processed, the location of the facility and the desired end product. For example, shredders are a good choice for recycling operations and for dealing with materials that could contain contaminants, such as metal objects. Tub and horizontal grinders often are used for processing clean organic wood waste given their ability to efficiently reduce materials to smaller sizes compared with most shredders.

When to use a low-speed shredder

Low-speed shredders are versatile machines, excelling in processing material with contaminates because of their low rotor speed and high torque configuration. They can handle a wide range of material streams, including C&D debris, contaminated green waste, MSW, storm debris and materials from land clearing operations where crews could encounter more than just organic material. These shredders often are used as primary grinders because they are less likely to be damaged when encountering ferrous contaminants in the material stream.

Shredders also are highly effective at processing materials such as railroad ties and heavy C&D debris. They can process materials while removing ferrous metals when equipped with crossband magnets, which allows companies to process a wider range of materials and potentially create new revenue streams for their operations. Once the metal is separated from the organic material, companies can use a horizontal grinder or tub grinder for final product sizing.

In addition, shredders can process certain types of synthetic materials mixed with other material streams more efficiently than high-speed grinders.

For smaller waste facilities or those in urban areas, shredders can be a good option for sizing material. These machines are fuel-efficient, operate quietly, help minimize dust and, because of their low speed, are less likely to throw objects long distances. L

Imitations of shredders

The slow rotor rotation speed is one of the qualities that make shredders more tolerant of contaminants. However, those slow speeds also mean shredders take longer to process material than high-speed grinders. Shredders also produce chunky, inconsistent product sizes that could require additional processing depending on the intended use of the final product.

Maintenance accessibility is another area to pay attention to. On many shredders, access to the engine compartment, rotor and comb is restricted, but models like the Vermeer LS3600TX low-speed shredder prioritize serviceability.

The LS3600TX design enables access to its components, including large doors to the engine bay, multiple ladder points and a service platform. This design allows clear access to the rotor and comb. Additionally, the shredder is equipped with a reversible mechanical transmission for efficient power transfer and a torque limiter that automatically disengages the drive when maximum torque is experienced, helping to protect critical machine components.

When to use a high-speed grinder

High-speed grinders, including tub and horizontal grinders, are designed for speed and productivity. They use hammer mills that spin rapidly, from 800 rpm to 1,300 rpm, allowing for faster material processing than low-speed shredders. This makes them suitable for facilities prioritizing throughput. They deliver consistent material sizing with adjustable cutter tips and screen sizes, providing operators with control over the final product’s size.

Horizontal grinders are efficient at handling longer material. For waste streams that include a large volume of long-cut tree branches and limbs, a horizontal grinder can reduce the cutting time before processing the material. This efficiency can lead to significant time savings in waste processing operations.

Tub grinders, on the other hand, can handle bulkier materials, such as tree stumps, and processed wood materials, such as pallets. They also have proven efficiencies in processing loose green material. This flexibility makes them a valuable asset for facilities dealing with a variety of material types.

• compost, which must be under 4 inches in length and width;
• mulch, typically sized to 1.5 inches to 2.5 inches; and
• biomass/biofuel, which has varying size requirements depending on the power plant burner type and conveying system being used.

Swapping out screens on a grinder allows for the production of varying material sizes based on an operation’s needs, providing a level of control that isn’t achievable with low-speed shredders. This flexibility enables operators to meet specific size requirements for different markets, which can contribute to the profitability and versatility of material processing operations.

Grinder limitations

Because of their high rotational speed, grinders are more prone to component damage than slow-speed shredders when exposed to contaminants. They also produce more noise and could project objects further compared with low-speed shredders. Therefore, grinders require more operating space.

Using high-speed grinders and low-speed shredders together

Facilities also might want to consider using high-speed grinders and low-speed shredders in conjunction. By using a low-speed shredder as a preshredding stage, facilities can remove contaminants and improve the overall efficiency of their operations.

This combined approach can be especially useful in waste facilities that allow public dumping, as these locations often have higher contamination rates within the material stream. By employing a low-speed shredder as the primary shredding stage, facilities can more safely remove contaminants before sending the material to high-speed grinders for final sizing.

Additionally, using high-speed grinders and low-speed shredders in tandem can extend the life of the wear parts on the secondary grinders by removing contaminants early in the process that could cause excessive wear and tear.

Ultimately, whether it’s low-speed or high-speed, carrying out these operations as efficiently as possible will help an organization ensure the investment in waste sizing equipment, fuel and labor outweighs the expenses associated with the process.

Ted Dirkx is a sales manager for Vermeer Corp. He can be reached at tdirkx@vermeer.com.