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Acoustic switch deals with blocked chutes

A relatively new, large export thermal coal mine was experiencing production problems. Located in the Hunter Valley, this mine produces in excess of 10 million tonnes per year.

The Coal Handling Preparation Plant (CHPP) was experiencing problems in production because of intermittent tripping of conveyors caused by the blocked chute switches in the head conveyor transfer chutes. The head conveyor transfer chutes are critical to the CHPP plant, as all new coal feed enters through these chutes and conveyors.

The problems were caused by coal fines build-up, clay build-up and water sprays in the chutes. This build up was occurring around the blocked chute probes. Each production shift experienced up to six intermittent trips, causing a production downtime loss, of up to 1.25 hours per shift. The cost per hour of lost production was approximately $100,000.

The technology specified for the (head chute) conveyor transfer chute’s blocked chute switches cost less than $1,000 each. The selected blocked chute switch technology was affected by build-up and false triggering.

Clearly, the blocked chute switch selected did not take into account the chute operating environment, cost of downtime for production when originally being specified. Price is a small component in the technology selection for these head chute applications.

When specifying a blocked chute switch, Hawk takes into account the operating environment as the most important parameter. The company supplied the low frequency (15 kHz) acoustic switch with titanium diaphragms that provided a self cleaning capability for the application.

The low frequency transducers emit a pressure wave with each pulse that atomises water and fines build-up off the diaphragms.

As water allows for the excellent transfer of acoustic sound waves, wet environments actually increase the signal amplitude of the acoustic switch’s ability in conveyor transfer chutes, wet product and reject screens, truck detection, run of mine (ROM) bins and any application where moisture or water spray is used for dust control.

The acoustic switch can also be tested remotely, through a PLC, in critical applications, to guarantee the switch’s ongoing capability. Additional alarms can be provided to support routine maintenance of these switches.

The Hawk Gladiator Acoustic Switch has a maximum operating range of 150m depending on the hardware selected. Applications include conveyor transfer chutes, wet and dry screens, reject screens, head chutes, crusher blocked chute switch and boom protection for stackers and reclaimers.

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