Glossary: J
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Jar-bar Feeder
The jar-bar grizzly feeder is a heavy-duty feeder which may form the bottom of the feed hopper of a primary crusher. It consists of a series of bars of elliptical cross-section with the major axes of adjacent bars at right-angles. Material is moved forward by the rotating bars, with a tumbling, rocking motion which makes this type of feeder suitable for applications where fines and clay have to be removed from the feed.
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Jawstock
The swing jaw of a jaw crusher.
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Jet-piercing
The use of high-velocity jet flames to cut blastholes in hard rock.
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Jig
A machine in which the feed is stratified in water by means of a pulsating motion and from which the stratified products are removed separately, the pulsating motion being usually obtained by alternate upward and downward currents of water.
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Jigging
A mineral-processing operation in which particles are separated on a density basis by water pulsation.
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Jim Crow
A rail bender operated by hand.
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Job Evaluation
The techniques of helping to determine a fair day’s pay for a particular job. It is the assessment of the value of the job not the individual and must reflect fairly the skill, experience, responsibility and condition of the job.
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Jointing Sleeves
Insulating thimbles placed over the connected ends of detonator leads coupled in large rounds of shots, and over the connections between the detonator leads and the shotfiring cable.
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Joist
A beam which supports a floor or ceiling.
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Joule
The work performed when the point of application of a force of one newton is displaced through a distance of one metre in the direction of the force.
Symbol: J (=1Nm)
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Journal
The part of a shaft which is supported and held by a bearing.
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Jumbo
A drill carriage usually holding several drifters for tunnelling work.