Number Three Shovel

A descriptive essay written in 1986 by Herb Daum, Shovel Operator, 1979-1982

It is 8:15 A.M. on top of a mountain in the Cassiars in northern British Columbia and the autumn sun is rising over an open pit mine. A pickup crummy discharges two men. The men are wearing steel-toed boots and company-issued dark green coveralls. They also wear dirty red hard hats equipped with muff-type hearing protectors. The men, carrying their lunch boxes, walk towards Number Three Shovel. This shovel is a P&H Nineteen Hundred, an electric shovel, dipper type, that towers above the two men.

One of the men, the shovel operator, is responsible for the safe operation of this one-million-dollar mining machine. He is also responsible for maintaining high production of truck loads of waste rock. With his helper, the shovel oiler, he approaches the bright yellow and dull black shovel. They both examine the conditions they will be working in during their eight-hour shift. They inspect for damage to the bucket resting on the uneven ground. They also inspect the sticks, the carbody, the boom, and the condition of the work face of the rock pile. Satisfied with their inspection, they pull down the counterweighted ladder. The ladder comes squeaking and squealing down to provide the crew access to the lower walkway. Then, ascended and released, it shoots with a slam back up in its track, to where it will be out of harms way. The crew enters the machine room via a heavy steel door.

The machine room, commonly referred to as the house, is painted white inside and contains the complex inner organs of this mighty beast. All is quiet except for the humming of electrical transformers and the hissing of minor air leaks. The crew recognizes the familiar smells of lubricating greases, cleaning solvent, and the vague yet acrid smell common to electrical motors and generators. A pulled dipstick reveals the oil level of the air compressor to be within proper levels. A turn of a gate valve releases a floor-wetting gush of milky liquid, a mixture of condensed water, compressor oil, and methanol. Its release precedes an ear-piercing blast of compressed air. With the voluminous tank now purged of condensate, the oiler closes the gate valve. The air compressor, ever faithful, senses the drop of air pressure and noisily starts. It pumps briskly, restoring air pressure to within operating range. The oiler carries on with his inspection, and while he is ensuring an adequate supply of greases for the automatic greasing systems, the air compressor stops with a sigh. The operator has examined the black greasy hoist cables. The two cables, which are symmetrically wrapped around the hoist drum, lead away over long log-like rollers to the outside.

Satisfied with this portion of their inspection, the men step out, latch the house door and proceed up the narrow steep stairs. The stairs lead to a small square landing behind the operator's cab. The operator takes a minute to inspect the external upper rigging of the shovel. This rigging is composed of gantries, heavy three-inch thick cables, and big cable clamps. The gantries are black heavy steel structures, that combined with the cables and clamps, form the strong framework that supports the massive boom.

Nothing unusual attracts the trained eye of the operator, so he enters the operators cab. The cab, fairly clean and white inside, is bright with windows. There are windows on both sides and the front is almost entirely glass. The offensive odour of the previous operators cigarette smoke still lingers in the cab. There are four small storage lockers, one for each shifts crew, and there are the many electric heaters required to keep the glass free of frost during the frequent blizzards of the long cold winters. The metal floor is also heated to ward off the icy chills. The center of the cab is dominated by a large operators seat, which is flanked on each side by a control console. The view out the front windows, twenty feet above the ground, reveals the boom, the sticks, the cables, and the bucket. They are all quietly waiting. The quiet is occasionally broken by a gob of black grease splattering down on the rocky ground below.

A glance at the voltmeter on the cabs left side wall indicates to the operator that the normal voltage of four thousand, one hundred and sixty volts alternating current (4,160 A.C.) is available to feed the shovel. The operator pushes the green start button and the cab lights dim as the big A.C. motor surges to life with a huge thirst for energy. This motor, six feet high, is shafted on one end to the chain drive which spins two barrel-sized direct current (D.C.) generators. The other end of the motors shaft spins the rotors of the twin magnetorques. These magnetorques, which are electromagnetic torque convertors, supply the required torque, when desired, to turn the big gear-driven hoist drum. As the spinning machinery approaches operating speed the cab lights gradually return to normal brightness. The twin house fans then start up and pressurize the house with filtered air. The high pressure of clean air bars entry of airborne rock dust. The rock dust, abrasive to bearings, can cost many thousands of dollars in lost production as well as in repair costs due to premature equipment failure. Finally, about three minutes after the push of the start button, the trip motor, located at the base of the boom and below the cab, suddenly springs to life, turning its small trip cable drum. It reels in the slack of the dangling trip cable. The trip cable, finger-thick and stretching forward and down to the bucket, is now taut. This signals to the waiting operator that his beast in now wide awake and at his command.

Meanwhile, the oiler has descended to the ground equipped with his life-protecting linemans gloves, and has pulled extra slack in the power cable, towards the rear of the shovel. The black heavy cable is wrist-thick and is carrying the high voltage electricity feeding the shovel. The linemans gloves are required because such high voltage can easily kill an unprotected person if the cables thick rubber insulation is damaged. The cable is attached to the rear of the shovels carbody. Once cable slack is adequate for the expected amount of forward travel by the shovel, the oiler inspects the entire string of connected power cables leading away from the shovel.

The operator has seated himself and adjusted his seat forward. He places his feet on the pair of swing pedals protruding from the floor in front of him. He places each of his hands on one of the control consoles. His wrist watch shows 8:30 A.M. A button push releases the hoist/crowd brake and a switch thrown releases the swing brakes. The air brakes depend on the air compressor for their supply to release the brakes and strong springs automatically apply the brakes in the event of a power failure. The operator pulls back gently on the short hoist control lever. In the house below, in the wind tunnel air flow of the house fans, where normal speech would now be drowned out by the roar of the house fans, generators and motors, something stirs.

The twin magnetorques sense the delicate manipulation of the controls in the cab above, and cause the hoist drum to revolve, rather slowly, pulling in the hoist cables. The two-inch thick hoist cables, oozing life-prolonging black grease, string over rollers, out and up to the top of the boom, where forty feet above the ground, they snuggle in twin six foot diameter pulley sheaves. From there they plunge down towards their point of attachment at the bail, near the ground. The bail is C-shaped and connects the bucket to the ascending hoist cables. The bail slowly pivots upwards on the bucket till it is in line with the cables and then the cables begin to creak softly as they tighten under the strain. The cavernous bucket is squarish shaped and is armed with six hardened-steel teeth, wedge-shaped. The bucket resists the pull of the hoist cables with its large mass, but its initial resistance is overcome with the operators application of more hoist power. The bucket begins to arc upwards, pivoting on the crowd pinion gears, on which the sticks rest. The arc is defined by the hoisting of the cables and the extension of the sticks. The large sticks, which are twin gear-racked, black and grease-dripping, are retracted back or crowded out by the twin pinion gears of the crowd mechanism. The pinion gears are pail-sized and also grease-dripping. They are turned by their shaft connection to the crowd motor which is located on the boom. The boom is the shovels largest component and angles up from the base of the house. It supports the crowd pinion gears, the sticks, and the hoist cables with their lofty sheaves; they all control the bucket.

The bucket, now hoisted high enough to clear the ground safely, stops as the operator sets the hoist/crowd brake. With his foot he pushes the right-hand swing pedal. This action causes the swing motors down in the house below, to slowly turn the swing pinion gears which are meshing with the ring gear crowning the carbody. The house, cab, boom, bucket and all, are revolving slowly clockwise. The moving mass pivoting above the stationary carbody is supported by dozens of greasy rollers.

When the operator sees the oiler giving him the "all clear" signal from the ground, behind the shovel, he switches another lever to redirect electrical power from the crowd motor to the propel motor. He pushes the left swing pedal till the shovel faces the work face of the rock pile, then pushes the crowd/propel lever forward causing the propel motor in the carbody to turn the twin tracks. The tracks, shoulder high and three feet wide, slowly pull this monster towards the rock pile.

After the shovel has lurched and rumbled to within digging range, the operator switches from propel mode back to crowd mode and then releases the hoist/crowd brake with another blast of compressed air. Released, the heavy bucket, eager to eat, is pulled by gravity and descends. It descends slowly, then faster, and even faster yet, pulling out the hoist cables, the cables spinning the hoist drum, the drum spinning the magnetorque stators, all hoist machinery now screaming and whining in angry protest. The experienced operator, by judiciously applying just the correct amount of hoist power, counters the powerful pull of gravity and the tremendous momentum of all this falling and spinning steel. The bucket stops falling at precisely the right place to gently engage the bottom of the work face. Then with little human effort, the operator applies full hoist and crowd power. The bucket surges up, skimming blasted rock over its teeth and into its capacious ten cubic yard interior. The bucket, having nearly reached the top of the boom, is now filled to capacity and excess rock is spilling over its sides in a dusty clatter. The operator lowers and retracts the bucket a bit. He hovers the bucket, counterbalancing gravitys pull with exactly the right amount of hoist power, while he swings the suspended full bucket to his right. He places the bucket in a truck-loading position and sets the brakes while waiting for the first truck of the shift.

Shovel loading a 75-ton Wabco truckAn empty eighty-five-ton (or smaller seventy-five-ton) dump truck is backed under the bucket. The shovel operators stop signal to the truck driver, an air horn blast, is facilitated by his squeezing a small secondary lever on the crowd control. This coincides with his squeezing the trip control, another secondary lever, this one on the hoist control. This activates the trip motor, which by turning its drum, powerfully yanks on the trip cable. The cable jerks up the trip lever on the bucket. The lever pulls the latch bar out of the dutchman, which is a small hole in the heel of the bucket. Released, the door, which is the entire rear wall of the bucket, suddenly pivots back and dumps the contents of the bucket. Twenty tons of rock crash down into the waiting truck in a cloud of dust. By the time the truck has stopped bouncing from the impact the bucket has been refilled and is swinging over the truck again to dump another load. Then, filled and dumped, filled and dumped again, the bucket has loaded a truck full. Another blast of the air horn sends the truck away. The truck, filled with eighty tons of rock, trundles off to the waste dump site. Another empty truck, waiting for its first ration of rock, backs up alongside the shovel. Every few bucketfuls of rock removed from the work face unleashes a minor avalanche of rock. The rock cascades down to the shovels feet with a roar. Each time, clouds of dust rise to envelop the shovel, but the house fans do their protective task ceaselessly. Soon the bottom of the rock pile is beyond optimum digging range of the bucket, so the operator walks the shovel forward a bit. He starts to dig again, loading trucks. The returning trucks eagerly queue up for getting loaded and then hauling their cargo away.

This process is repeated continuously, all shift long, except for two coffee breaks and a short lunch break. Occasionally excessive accumulation of spilled rock impairs the backing up of trucks, so a rubber-tired dozer or tractor dozer is brought to the scene to clean up the area by pushing the spillage to the foot of the workface. At the end of the shift, having loaded approximately one hundred to one hundred and fifty truck loads, the shovel is backed away from the work face. Backed to a safe distance, and with the bucket lowered to the ground, it is shut down with a push of the red stop button. The crew disembarks. Silenced, the shovel, now a sleeping beast, awaits the arrival of the relief crew for another shift of loading rock.

All rights on text reserved. 1987


This page was last edited Friday, September 18, 2015

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