How to decide between two-mass and brute force vibratory screens

Vibratory screens are a critical component of material recovery systems, but not all screens are created equal. Beneath the motion lies an important design distinction: whether the screen is powered by a two-mass system or brute force. While both approaches aim to separate material effectively, the way they generate and manage vibration can significantly impact energy use, maintenance, and throughput, especially in demanding environments like scrapyards, C&D facilities, and MRFs.

"When you add weight to a brute force system, performance goes down," explains Bob Huffer, director of recycling at General Kinematics (GK). "But with a two-mass system, it actually improves."

Huffer has spent decades helping recycling operators choose the right screen for the right material stream, whether that's high-tonnage C&D, scrap, or municipal solid waste. While both systems serve the same purpose, the design differences are substantial, and those differences show up in everything from energy efficiency and scalability to how they respond under load.

Understanding the differences between two-mass and brute force vibratory screens

Brute force systems operate on a simple principle: a motor is mounted to a single mass, essentially a steel box, supported by isolation springs. When powered on, the eccentric motor shakes the entire unit.

"The bigger that box gets, the more energy, the more horsepower you need to drive that," says Huffer. Additional or larger motors are required to maintain performance.

Two-mass systems take a more engineered approach. Rather than forcing vibration through a single body, they use two masses connected by springs. One mass contains the motor where the vibration is created. That vibratory energy is then amplified through springs into the second mass, where the material is handled. This configuration allows the two-mass system to operate near its natural frequency, where a minimal amount of energy is needed to do the same or more work than a brute force machine. The result is a more efficient transfer of motion and significantly lower energy demand.

"In general, you're looking at 40 to 60 percent less horsepower [for two-mass] compared to brute force," says Huffer.

Comparing the performance of vibratory screens under high-volume conditions 

Where the two systems really diverge is in how they respond to changes in material load. In brute force systems, increasing the weight of the load dampens the stroke, essentially reducing the amplitude of the screen's motion. This results in reduced material movement, slower processing, and lower overall capacity.

Two-mass systems behave differently. As more weight is added, the stroke increases due to the natural frequency effect. This effect makes them better suited for high-volume or heavyload applications, such as C&D recycling, scrap processing, and mining, where material surges are common.

Selecting the right screen design for recycling efficiency

Two-mass systems are a good choice for large-scale, fixed recycling facilities. According to Huffer, GK's systems can weigh upwards of 85,000 pounds and are designed to handle up to 1,400 tons per day of construction and demolition material. These installations often include custom finger screens and integrated components tailored to the plant's material flow and space constraints.

Brute force screens are more common in compact or mobile applications, such as aggregate screening trailers or under-crusher feeders. Their simplicity makes them easy to maintain in tight quarters or when weight and space are limiting factors.

"There are still cases where brute force makes sense," says Huffer. "It's a simpler design with fewer components,

Managing vibration and structural impact 

Another advantage of the two-mass design is its ability to manage dynamic forces. Because the two masses move in opposite directions, they cancel out a significant portion of the vibration that would otherwise be transmitted to the foundation.

According to Huffer, this cancellation effect can reduce dynamic forces by up to 80 percent. This is a crucial benefit when installing heavy equipment on lighter foundations or in older facilities. It also minimizes the risk of vibration damage to nearby structures or equipment.

Maintenance, scalability, and lifespan of vibratory screens

Brute force screens offer a simpler mechanical design, with fewer components and no counterbalancing mass. With fewer moving parts and a straightforward drive mechanism, brute force systems are often easier to install, troubleshoot, and maintain in compact or remote setups.

However, that doesn't necessarily equate to longer life or lower maintenance over time. Brute force systems hit design limitations when scaled up, making them less suitable for larger or high-tonnage operations.

Two-mass systems, by contrast, are built for scalability. Their design allows machines to be constructed wider and longer without losing stroke or efficiency. This means operators can process more material in a single unit, increasing throughput without expanding their equipment footprint. It also opens the door to custom configurations tailored to high-tonnage applications, where brute force designs would struggle to maintain consistent performance.

When it comes to wear and maintenance, both systems are comparable, provided they're processing similar volumes. "Wear is probably equivalent if you're comparing the same tonnage," says Huffer.

Different vibratory screen types and customization options

General Kinematics offers three primary screen designs under the finger screen category: Traditional, Free-Flow, and Velocity (formerly known as FINGER-SCREEN 2.0). Each is built on a two-mass platform but optimized for different materials and system configurations.

Traditional finger screens use a counterbalance beneath the screen to stabilize motion and are ideal for high-volume, rugged applications.

Free-Flow screens eliminate the lower conveying pan, allowing all material to drop through onto a belt. This open-deck design minimizes material buildup and simplifies maintenance, making it especially effective when processing sticky or wet fines.

Velocity screens use multiple screen bodies running out of phase to maximize stroke and movement, making them well-suited for light or bulky materials like cardboard.

Choosing between screen types depends on feedstock, separation goals, and plant layout. "It's about the type of material, the size you're trying to separate, and how much volume you're dealing with," says Huffer.

Processing wet, heavy, or inconsistent feedstocks efficiently

Both systems can be used with wet or sticky materials, but the longer stroke and higher energy of two-mass systems make them more effective in these scenarios. The increased vibratory energy helps prevent material from clumping or clogging. When feedstock is inconsistent or surging, as is often the case in MRFs and C&D facilities, the responsive stroke of twomass systems enables them to adapt in real-time, spreading material more evenly and maintaining throughput.

Upgrading and expanding vibratory screens for higher throughput

For facilities that currently use brute force systems, upgrading to two-mass can offer a path to greater capacity without increasing footprint. In some cases, a plant can handle significantly more throughput simply by swapping in a two-mass system tuned to the existing space.

Huffer notes that upgrading to a two-mass system is often a natural step for facilities looking to modernize or expand. For operations aiming to boost capacity by 20 to 40 percent, switching to a different screen design can be the most effective solution.

What's next for General Kinematics? 

As customer demands evolve, GK is continuing to scale its technology. In 2023, the company built its largest finger screen to date: seven feet wide and 50 feet long, weighing in at 130,000 pounds. It was developed to meet growing demand for high-throughput screening in a single unit.

Increasingly, the company is designing integrated systems that pair shredders, screens, and downstream sorting equipment into cohesive, high-efficiency workflows. According to Huffer, the shift reflects a broader trend across the industry: reducing manual labour while maximizing material recovery.

"Whether it's through robotics, optical sorting, or better front-end screening, customers are looking for ways to reduce headcount while increasing throughput," he says.

Designing effective recycling systems isn't just about choosing a screen. It's about engineering for the feedstock, footprint, and future growth. With two-mass systems, greater efficiency, foundation protection, and scaling potential are clear advantages. But in more compact or mobile applications, the simplicity of brute force still brings value. And for operators evaluating upgrades, the right screening system can be a powerful tool for addressing existing limitations without tearing up the plant.

This article originally appeared in the September/October 2025 issue of Recycling Product News.