Putting safety around crushers front and center

The following is an excerpt from the Pit & Quarry University lesson on crushing and secondary breaking. For the full lesson, visit pitandquarry.com/pquniversity-crushing.

Little has changed in basic crusher design over past decades, other than that of improvements in speed and chamber design.

Rebuilding and keeping the same crusher in operation year after year has long been a typical approach. Still, recent developments have brought about the advent of new hydraulic systems in modern crusher designs – innovations stimulated by the need for greater productivity and a safer working environment.

Importantly, the hydraulic systems in modern crusher designs are engineered to deliver greater uptime and eliminate the risks associated with manual intervention.

The crushing arena is undoubtedly a hazardous environment. Large material and debris can jam inside the crusher, damaging components and causing costly downtime. Over the years, the Mine Safety & Health Administration has reported a number of injuries and fatalities occurred when workers climbed in or under the jaw to manually clear, repair or adjust typical older-style crushers.

Examples from recent years include a foreman injured while attempting to dislodge a piece of steel caught in the primary jaw crusher. Another fatal accident occurred when a maintenance man was removing the toggle plate seat from the pitman on a jaw crusher. The worker was standing on a temporary platform when the bolts holding the toggle seat were removed, causing the pitman to move and strike him.

The hydraulic systems on modern crusher designs eliminate the need for workers to place themselves in or under the crusher. An overview of hydraulic system technology points to three key elements:

• A hydraulic chamber-clearing system that automatically opens the crusher to a safe position, allowing materials to pass

• A hydraulic overload relief that protects parts and components against overload damage

• A hydraulic adjustment that eliminates the maintenance downtime associated with manual crusher adjustments and maintains safe, consistent crusher output without the need for worker intervention.

A closer look at these systems illustrates how each affects safe operation and increases productivity.

Hydraulic chamber clearing

Whether a crusher is jammed by large material, tramp iron or uncrushable debris – or is stalled by a power failure – the chamber must be cleared before restarting. Manual clearing is a lengthy and risky task, especially because material can be wedged inside the crusher with tremendous pressure. Dislodging poses a tremendous danger to workers placed inside the crusher.

Unlike that of the older-style jaw, the modern jaw will clear itself automatically with hydraulics that open the crusher to a safe position and allow materials to pass – again, without the need for manual intervention. If a feeder or deflector plate is installed under the crusher, uncrushable material will transfer smoothly onto the conveyor without slicing the belt.

Hydraulic relief

To prevent crusher damage, downtime and difficult maintenance procedures, the hydraulic overload relief system opens the crusher when internal forces become too high, protecting the unit against costly component failure. After relief, the system automatically returns the crusher to the previous setting for continued crushing.

Hydraulic adjustment

The modern crusher is engineered with oversized hydraulic cylinders and a traveling toggle beam to achieve reliable overload protection and simple crusher adjustment. All closed-side setting adjustments are made with push-button controls, with no shims needed at any time. This is a key development, as many accidents have occurred during shim adjustment.