Crusher Jamming: What Causes It and How to Clear It Safely

When a crushing chamber chokes, it is not only output that is lost; cleared the wrong way, a jam also puts the operator in danger. That is why a blockage should be treated as a genuine occupational safety risk. Most jams seen on site come from one of three sources.

1. Uncrushable foreign objects

When an excavator bucket tooth, a drill bit or a broken piece of steel gets into the crushing chamber, the machine can lock up. General cone crushers are fitted with hydraulic-cylinder overload protection for this case: on a sudden jam the system releases pressure, opens the setting and lets the object pass through, protecting the frame and liners from damage.

2. Feed that is too large or too much

Stones bigger than the crusher can accept, or material sent in without screening and without control, fill the chamber in no time. The largest permitted feed size for every model is stated in the catalogue, and it should never be exceeded.

3. A setting closed too far (CSS)

As the closed side setting (CSS) of a cone crusher is reduced hydraulically, the product becomes finer, but the load on the chamber rises. With damp material a narrow setting multiplies the chance of a blockage. The setting should therefore be changed step by step and the product curve checked after each change.

Safe sequence for clearing a blockage

(1) Stop the feed first. (2) Keep the crusher running until the chamber empties; if it does not clear, cut the power and apply lockout-tagout (LOTO). (3) Inspect the chamber visually from above; if the object has to be removed by hand, do so only with the energy lock in place. (4) On hydraulically protected models, open the setting to eject the jammed piece.

The feed limit: real catalogue figures

The warning about overfeeding is not abstract advice; every crusher has a specific feed opening listed in its catalogue. Below are figures from the GNRK jaw crusher series; the opening shows the physical limit of the largest stone the machine can take:

Two working habits that cut blockages

The first is to set the feeder speed according to the crusher's current draw: if the ammeter stays in the upper zone all the time, the chamber is full and the feed should be slowed. The second is to empty the crusher before stopping it at the end of a shift; a chamber left full will start the next run with a blockage.

Why it pays to record blockages

A jam that keeps recurring at the same point is usually a process problem rather than a machine fault. Causes such as oversize slipping past the screen, poor blast fragmentation or the grizzly bar spacing on the hopper must be fixed at the front of the line. A plain notebook with date, time and material details usually brings the underlying cause to light within a week.

Checks after the blockage is cleared

Once the object is out, the machine should not go straight back to full load. Work through the following in order: inspect the chamber and wear parts for damage; re-measure the setting, since the load during the jam may have shifted it; check belt tension and the coupling on the drive side; watch the machine running empty for the first minutes and then on reduced feed. If there is unusual vibration or noise, stop and inspect again. For recurring jams, also review screen leakage, blast size and grizzly opening; a simple date-time-material log makes the root cause visible quickly.

Maintenance needs vary with the machine model and its operating conditions. Get in touch with us to prepare a maintenance plan specific to your crusher.