Getting more tonnes from a set of blow bars

When blow bar life is disappointing, the first instinct is usually to change alloy. Sometimes that is right. Often the bars are fine and the machine is being asked to do something that wears them out prematurely.

Here are the factors that, in our experience, move blow bar life the furthest, roughly in order of how often they turn out to be the problem.

1. Apron gap

The gap between the blow bar tip and the impact apron sets how the machine breaks material. As bars wear the gap opens, and material that would have been broken against the apron is instead being hit repeatedly by the bar.

Plants that reset the apron as the bars wear consistently report better bar life than plants that set it once at change-out and leave it. It is the single most common preventable cause of poor blow bar life.

2. Turning bars at the right point

Most symmetrical bars can be rotated once to present a fresh face. The timing matters: turn too early and you waste usable material, turn too late and the wear has reached the mounting area, at which point the bar cannot be safely reused and may already be stressing the rotor pocket.

Set the turn point against a measurement rather than an impression. A simple depth gauge reading recorded at each inspection is enough.

3. Feed size and distribution

Impact crushers work best with a steady, evenly distributed feed across the full rotor width. Two problems recur:

• Feed concentrated on one side wears that region of every bar faster, so the whole set is scrapped when only part of it is worn out.
• Surging feed alternates between empty running and overload. Empty running is not free: the bars still take impact, without the material to distribute it.

A correctly set feeder that keeps the chamber consistently loaded is worth more than most alloy upgrades.

4. Removing tramp metal upstream

Every piece of tramp metal that reaches the rotor takes life out of the bars, and occasionally takes a bar out entirely. A magnet or metal detector on the feed conveyor pays for itself quickly on recycled feed. Where tramp metal cannot be eliminated, the alloy has to absorb it, which means accepting manganese steel and its higher abrasive wear rate.

5. Rotor balance and weight matching

Bars should be replaced as a full set of matched weight. Mixing new and part-worn bars, or bars of different alloys, unbalances the rotor. That causes vibration, accelerates bearing wear, and in serious cases cracks the rotor body, a failure far more expensive than any set of bars.

We weigh and match sets before despatch for exactly this reason.

6. Checking the pocket, not just the bar

A worn or damaged rotor pocket lets the bar move under load. That movement hammers both the bar and the rotor, and shows up as cracking that starts at the mounting seat rather than the wear face. If bars are cracking at the seat, inspect the pocket before ordering more bars.

Measure before and after

All of this is only useful if you can tell whether it worked. Record tonnes processed per set, not hours and not weeks, then note what changed between sets. A handful of data points is enough to show whether a change helped.

If you would like a second opinion on a wear pattern, send photographs of a worn bar together with the machine model and feed description. It is usually possible to say from the wear pattern whether the alloy or the machine setup is the limiting factor.