Product category:
Industrial Drives/Controls
News Release from: BSL Engineering | Subject: Drives
Edited by the Engineeringtalk Editorial
Team on 07 June 2000
Siemens smooths out the shocks at Welsh
quarry
BSL Engineering has supplied a 37kW Siemens MidiMaster drive system and Flender geared motor to control a quarry's large Apron Feeder.
The problems of disrupted production and shock loading on power transmission equipment, resulting from sudden unplanned stops of a large rock crusher line at Graig Quarry in North Wales have been overcome since BSL Engineering supplied a 37kW Siemens MidiMaster drive system and Flender geared motor to control the quarry's large Apron Feeder Graig Quarry is part of the Lafarge Redland Aggregates Group
It is situated squarely in the middle of hill walking country near Ruthin in North Wales.
The quarry produces dry stone and coated stone, mostly for use in road making.
The process of preparing the dry stone starts with large quantities of rock being deposited onto an Apron Feeder.
The latter is the main feed mechanism to transfer quarry rocks up to 1cu.m.
into the Crusher.
It is essentially a heavy duty steel plate feeder - resembling a large excavator track - which carries the run of quarry rock on top of it to the crusher.
With a full hopper the weight of rocks to be moved by the Apron Feeder may reach 80 or 90 tonnes.
As a result, it requires an exceptionally large starting torque to set it in motion.
The Apron Feeder was installed in late 1960's.
Until recently it had one operating speed only.
Consequently, the feed rate of material into the Crusher could not be optimised to take advantage of instances when the stone was cleaner than normal or closer to the ideal size.
Since the Crusher capacity exceeds that of the feeder at its fixed speed, considerable advantage could be gained if the feed rate could be varied.
Addressing the problem of fixed speed, whilst important, was one of many priorities at the quarry.
In terms of importance it was surpassed by the need to overcome the disruption to production resulting from sudden unnecessary stops of the Apron Feeder.
These were the result of operator intervention from the plant control room.
Then as now, closed circuit TV cameras were used to monitor the outflow from the Crusher.
The comprehensive pictures provided enabled the operator to check that rock at the Crusher outflow did not build up to unacceptable levels.
If it did, then the operator pressed a button to stop the Apron Feeder - a matter of subjective judgement rather than measurement and control.
In an effort to smooth the production difficulties level sensors were fitted to the Dump Hopper, Grizzly Feeder and Primary Screen to monitor and measure process flows.
These, together with the existing CCTV, provide accurate assessment of conditions allowing for semi-automatic control.
This feedback and flexibility of variable speed control smoothes the process cycle and optimises throughput.
The choice of which drive to use was simplified by the previous experience of Lafarge's Electrical Engineer, Barry Pitt.
He had completed several successful projects, mostly on energy saving projects, with BSL Engineering using the Siemens MidiMaster range of drives.
After consultation with Richard Sanderson, the Manager at Graig Quarry, it was decided to use a Siemens drive on this latest application too.
The 37 kW MidiMaster unit supplied by BSL Engineering forms part of a complete packaged control system installed to optimise, modernise and upgrade the Primary section at the quarry.
Since installation the drive system has proved to be a complete success.
It has now been operating for over a year and to-date.
"The drive has performed exceptionally well from day 1 and we continue to reap the benefits of variable speed control both in quantity and quality of production" according to Richard Sanderson.
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