Crusher safety enhanced with new technologies

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 the typical approach.

However, recent developments have brought about the advent of new hydraulic systems in the latest modern crusher designs – innovations stimulated by the need for greater productivity, as well as a safer working environment.

The hydraulic systems in modern crusher designs are engineered to deliver greater plant uptime and enhanced safety, while reducing maintenance downtime and eliminating the risks associated with manual intervention.

Indeed the crushing arena is a hazardous environment. Large material and debris can jam inside the crusher, damaging components and causing costly downtime. Manually digging out the crusher before repairs or restarts puts workers in extremely dangerous positions.

The Mine Safety & Health Administration (MSHA) reports that numerous injuries and fatalities have incurred when workers climb in or under the jaw to manually clear, repair or adjust the typical older-style jaw crusher. Consider that fatalities and injuries can occur even when the machine is locked out and tagged out.

Examples include a foreman injured while attempting to dislodge a piece of steel caught in the primary jaw crusher. Another incident involved a fatality 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:

1. A hydraulic chamber clearing system that automatically opens the crusher to a safe position, allowing materials to pass.
2. A hydraulic overload relief that protects parts and components against overload damage.
3. 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 hydraulic systems illustrates how each affects safe operation and increased 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, and dislodging poses dangers to workers placed in harm’s way 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, uncrushables 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 being needed at any time (to shim is the act of inserting timber or other materials under equipment).

This is a key development, as many accidents and injuries have occurred during shim adjustment, a process that has no less than 15 steps as described in the primary crusher shim adjustment training program offered by MSHA.

Safe toggle maintenance

The hydraulics in modern jaw designs are integral to fast, safe toggle maintenance. Modern jaw designs eliminate the need for workers to go under the jaw until after the loose toggle is safely lowered.

To understand the above requires a few brief definitions. The pitman is the component that carries the moving jaw, and it moves in an oval path from the rotation of the eccentric shaft. The eccentric shaft translates circular motion into the crushing action of the moving jaw. The center portion of the shaft is eccentric and carries the pitman on two inner roller bearings. The toggle plate positions the lower end of the pitman.

On older-style crushers, toggle maintenance is performed manually, placing workers in harm’s way. Older jaw designs often require that the pitman be held forward with chains and a winching device that is not always easy to secure. Also a worker would be required to climb under the jaw to remove the tension assembly before the toggle could be lowered – a risky task that puts the worker directly under the loose toggle.

As for safe toggle maintenance on the modern crusher, the process is initiated by hydraulic adjustment cylinders that push the pitman forward where it is locked into position with lock-out pins that insert from the side. Then hydraulic tension cylinders, mounted on the side of the toggle, pull the toggle beam back, allowing it to be safely lowered away. Toggle lifting eyes assist in safe, speedy toggle removal.

Modern crusher design that incorporates hydraulic system technology is a major development in safe material processing – one that allows operations to maximize productivity while putting safety first.

 

Carol Wasson is a veteran freelance writer for the aggregates and construction equipment industries. Information courtesy of Telsmith Inc., manufacturer of mining and aggregate processing equipment.