Force Control Rebuilds Fast Brake for Control on Downhill Conveyors

Conveyors are critical equipment at aggregate plants. Downhill conveyors, loaded with tons of material, don’t leave much room for error. When brakes fail and a belt gets away, the result is immediate and dangerous. Material moves where it shouldn’t, and equipment takes the hit. Unfortunately, that’s exactly what happened recently at an Oregon aggregate plant. A brake failure caused a loaded belt to let loose, damaging both the belt and sections of the conveyor framework. Operators responded with front loaders and dump trucks, making repeated trips up and down the incline to clear material. The plant was down. With replacement parts carrying lead times of up to 20 weeks, there was real concern about how long it might stay that way.

At aggregate operations, downhill conveyors are often responsible for moving large volumes of material continuously through the plant, so any loss of control can quickly affect multiple parts of the process and bring production to a halt. The conveyors in trouble were handling stone on an approximate 30-degree incline, each about 36 inches wide. In this type of application, consistent braking performance is critical to maintaining control of the loaded belt.

The system was originally equipped with Force Control Posistop brakes. By all accounts, they had run reliably for about fourteen years. The oil-shear design delivered reliable results with no adjustment and almost no maintenance, while the enclosed design kept dirt and debris away. But a few years back, the maintenance team changed, and fluid levels and system pressure were not consistently maintained. At the same time, issues with the hydraulic power units (HPUs) and valves led to inadequate pressure to fully release the spring-set brakes. In this condition, the system was effectively “driven through” the brake stacks, generating excessive internal heat and accelerating wear. Ultimately, the brakes failed, and on downhill conveyors, it doesn’t take much. Once a loaded belt starts moving uncontrolled, the impact adds up quickly.

Restoring Control After Failure [subhead]

After the failure, plant personnel worked with representatives from Motion Industries in Medford, Oregon to assess the damage and restore operations as quickly as possible. A bid was obtained for new replacement brakes, but the industry standard 20-week lead time was too long for the aggregate site to be out of production. 

“Knowing how important it was to get the plant back into production, we contacted Force Control to see if there was any way to speed the process – either with new brakes or by rebuilding the damaged ones,” said Motion Account Manager Todd Franklin. 

The team pulled two Posistop FA-20 brakes, including power units and valves, and sent them out to the Fairfield, Ohio factory. Teardown revealed significant internal heat damage consistent with the brakes being driven through under load, along with worn friction surfaces and compromised internal components. In both units, shafts required rebuilding, including machining undersized bearing journals and rebuilding shaft surfaces through a weld-and-grind process before returning components to final size.

Initial inspection also raised concerns about the condition of the valves and HPUs, which are critical to releasing the spring-set brakes. If these components fail to deliver sufficient pressure, the brakes will not fully release, leading to rapid heat buildup and potential repeat failure. Low or high fluid levels, faulty valves, or insufficient pressure (below 20 psi) can prevent proper release, leading to continued drag and heat buildup inside the brake stack. 

The work included evaluation, repairs, cleaning, and testing. Force Control maintains inventory of internal wear components, so the team was able to begin repairs at once rather than waiting on long-lead replacement parts. Both units were turned around in about four weeks, well ahead of the replacement timeline.

When the brakes were reinstalled, the system was brought back online within the scheduled outage window, bringing downhill conveyors back under control and stabilizing material flow through the plant. However, during initial startup, the system experienced added issues when the HPUs did not fully release the brakes, leaving them partially engaged and causing elevated operating temperatures above 220°F. Force Control personnel traveled to the site to troubleshoot, adjust brake stack clearances, and replace the HPUs. After these corrections, the conveyors were back up and running. While pressure spikes were observed, the system was evaluated and confirmed to operate safely without damaging the brakes. 

The shortened turnaround avoided an estimated 14 to 15 weeks of additional downtime and associated production losses, helping the operation return to normal production levels much sooner than expected. As part of the restart, the maintenance team received training on the system to support proper operation going forward. This included guidance on maintaining proper fluid levels and monitoring system performance to minimize heat buildup and prevent recurrence of the issue. With the rebuilt units in place, the conveyors returned to controlled operation. 

Braking without Breaking [subhead]

The key to the brakes’ previous long service life is a unique Oil Shear design. Unlike dry braking systems that use a sacrificial friction disc which contacts the drive plates to stop, Force Control features a boundary layer of transmission fluid in shear between the friction discs and drive plates. As the parts come together, the fluid transmits torque between the two parts while also absorbing heat. This eliminates direct contact of the friction discs and drive plates during high-speed slip and supports consistent braking performance. Heat from the friction surface is dissipated as the fluid circulates to the housing. 

Some systems use dry braking pads. When they wear, torque fade is introduced, which requires maintenance to adjust the gap. Systems that cut direct contact eliminate both the wear and the need for constant adjustment. Dry braking systems also generate high heat. With no good means of dissipating the heat, the friction plate glazes over, increasing torque fade and requiring further maintenance and adjustment. 

Force Control’s Posistop motor and coupler brakes are designed for long life with minimal maintenance in severe and critical applications, like downhill conveyors at mines and aggregate facilities. They are typically furnished as spring-set, pressure-release brakes, with pressure-set, spring-release configurations available in some models. The multiple disc design reduces inertia of the brake, placing less load on the motor and improving efficiency for each cycle.

Posistop motor brakes mount to the back of brake motors, while coupler brakes mount to the drive end of the motor, often between the motor and reducer. Various model sizes offer torque from 6 lb. ft. to 2,030 lb. ft. and fit 56 up to 440 frame motors, with special flange mountings available for IEC, servo, and other configurations. Spring-set configurations provide a fail-safe braking function, allowing the system to apply braking force in case of a loss of power or air pressure. Brake torque is sized to provide the holding force needed to control loaded conveyors under operating conditions.

The brakes use a totally enclosed sealed housing that keeps out dust, dirt, moisture, and fumes. This protects internal components from environmental damage and allows the system to operate in demanding conditions. Units can be configured for horizontal or vertical mounting and can be air or hydraulically actuated. When equipped with a hazardous duty valve, they can also be used in hazardous environments.

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