THE JOURNAL of the Worcester Polytechnic Institute
ORE-HANDLING MACHINERY AT THE N. Y. P. & O. DOCK AT CLEVELAND, OHIO
By Harry E. Scott, S.B., '99.
The plant herein described is located near the foot of West 25th St. on the old river bed.
Measured along the bed of the river the distance from the pier lights to the new unloaders is only 4,000 ft.; yet a boat entering the harbor with full cargo would consume from half an hour to an hour in covering this distance. Two steam tugs are required to tow and guide a vessel up the narrow, crooked channel, since deep draught vessels are not allowed to use their own propellers in the river, on accout of stirring up the mud and causing shoals.
The channel depth rangges from 20 1/2 to 25 ft. maintained by dredging; and as the ore carriers draw from 19 to 19 1/2 ft. of water, there is not muich depth to spare. The width of the channel does not exceed 200 ft. Where the channel is straight this width allows the mooring of one 10,000 ton carrier of 54 ft. beam on either side and towing one vessel between them.
None of the ore boats coming into Cleveland has less than three bridges to pass after entering the harbor. In this respet the N. Y. P. & O. dock offers the minimum number of obstructions. Ore docks farther up the river are at a disadvantage. For example: Corrigan & McKinney's dock 9,500 ft. from the pier lights, is reached by a carrier in an hour and a half or more.
The winding basin beyond the Jefferson St. bridge, 25,000 ft. from the pier lights, is from three to six hours up the river. From the foregoing, it will be seen that boats lose much valuable time along the river, which would be saved if the receiving docks were more favorably located. For example, by saving six hours on each of twenty trips during the season of navigation, a carrier would have five days to the good at the end of the season; which would probably enable the owner to send her on an extra trip, thereby increasing her tonnage five per cent.
Comparing our harbor facilities with those at Conneaut, we find that there they unload the largest cargo in the time the same boat would consume along the Cuyahoga River in getting in to Corrigan & McKinney's dock and out again.
The Conneaut channel is short and straight, fully as wide and deep as our river, and without a bridge to hinder the passage of boats.
The N. Y. P. & O. dock is of pile and timber construction. The part on which the new unloaders stand was rebuilt early in 1907, during their erection.
The piling consists of (1) a front row of 45 ft. piles on the face of the dock, spaced 10 ft. centers.
(2) A tight row, sheet piling, 12 ft. 6 in. back from the water front. This is made of three layers of 4 x 12 x 25 ft. long. Directly in front of the tight row, and separated from it by a 6 x 10 stringer, is a row of 40 ft. piles spaced 2 1/2 ft. centers.
(3) Under the front unloader's track is a triple row of 40 x 45 ft. piles, spaced 2 1/2 ft. centers in each row.
A similar triple row supports the rear unloader track, 51 ft. back from the front of the dock.
(4) Mooring piles are spaced 50 ft. centers, and 50 ft. long, along the front of the dock.
(5) The capping is 12 x 12 timbers. The stringers carrying the unloaders are 12 x 16, and the track rails 100 lbs. per yard.
Horizontal anchor rods 2 in. in diameter and about 6 ft. below dock level and 52 ft. long tie front and back runways together every ten feet.
The maximum wheel load running on this foundation is 52,000 lbs. The maximum static wheel load is 62,000 lbs., about 15,000 lbs. of which is due to 30 lbs. wind.
The timber in this dock is about 2,000 ft. board-measure per lineal foot of dock.
The first cost of a pile and concrete dock, designed for carrying the same loads, such as used at Fairport and Conneaut, would be from 12 to 15 per cent. more than for the timber dock.
The larger part of the ore received on the N.&. P. & O. dock is shipped direct to the furnaces in cars. Storage space is limited and confined to the far end of the dock, the principal business during the season of navigation being the unloading of ore directly into cars, weighing and shipping. The tracks are laid out with this end in view. A double track spur of the Erie R.R. leads into the dock, at the northeast end, running along the rear, where the weighing scales are located, to a dead end. From this spur sidings lead off, parallel with the water front and covering practically all the available space. There are seventeen parallel lines of track directly back of the new unloaders, and three lines runing under them.
Three hundred seventy-four cars, loaded and weighed out, is about the daily output during the busy season. Eight hundred empties have been stored in the yard at one time. The electric unloaders are designed to straddle three lines of track at the front of the dock; the empty cars, coming along these tracks from the sidings, pass out in the same direction, then, reversing their course, are switched back to the spur.
On the track system just described the cars are handled principally by yard locomotics, ample clearance being provided under the unloaders. There is also a car haulage system, desinged to move cars on the three front tracks. This system consists of two endless cables of 1 1/8 in. diameter, elctrically drived by the "Walker differential" drum arrangement, which is driven by a 35 H.P. motor. The cars are haulded by means of a hand-grip, which the operator attaches to the continuous running cable, and hooks on to the car, relaeasing the grip when the car reaches the desired point.
The speed of the cable is about 125 ft. per minute. The cable runs from the haulage house the length of the dock, to a 6 ft. bull-wheel and returns; thus providing a means of moving a car in either direction. Near the haulage house is a bull-wheel on a carriage, around which the cable passes. Initial tension in the cable is maintained by a counterweight suspended in a tower at this point, and pulling against the carriage. Where the dock front deviates from a straiaght line and the tracks are curved, deflecting sheaves are used for the cable; as is also the case where it is necessary to pass under tracks at runouts. Horizontal, wooden rollers are used to support the cable every 20 ft. at a height of a few inches above the dock level.
The haulage system has not given entire satisfaction. In the opinion of the writer the trouble is due partly to an excessive number of curves, and consequent deflecting sheaves, and partly to the too high speed of the cable, which gives an excessive pull in starting a car. The present system does not ordinarily supply enough cars to develop the full capacity of the unloading machines.
The power-house, which was built during the winter 1906-07, is a brick building, with steel roof trusses, about 100 ft. x 80 ft., with a brick stack. The house is divided logitudinally by a brick partition which separates the boiler room from the engine room. Coal is supplied from a track running parallel with the length of the boiler-room, and about 7 1/2 ft. abve the level of the boiler-room floor. The track is just outside this building.
The coal cars are unloaded here, by hand, and the coal is re-handeled by hand to get it to the boilers. About 6,000 tons of coal were used in running this power house during the seasn of 1906-07. The boilers are Stirling, equipped with chain-grates, which are of the Green Engineering Company's make. These boilers supply steam for operating the Hoover-Mason unloaders; but primarily are for running the
electric plant, which at present consists of three 350 kilowatt 250 volt generators, each direct connected to a Buckeye engine. Space in the engine room is proved for a fourth unit; but at present two units are sufficient for the usual work.
The electric power is used for operating the four Brown Hoist electrical unloaders, and for the car-haulage system and for electric lights on the dock. All the unloading machinery is used day and night during the busy season.
When running two units the power house circuit-breaker is set at 4,400 amperes; when three units are required the circuit breaker is set at 6,000 amperes.
Each machine has a guaranteed capacity of 300 tons during the first hour's work, in a full hatch. Ninety-five per cent. of the cargo can be unloaded without men in the boat. (This applies to modern boats with wide hatch openings, 24 ft. center.) Each machine is capable of unloading a hatch complete, with the assistance of five men in the hold, in 3 1/2 hours.
The machines are designed for a working hoist of 52 ft. 6. in., the lowest position fof the bucket being about 21 ft. below the cdock level. In its highest position the bucket clears the top of a 200-ton weighing-bin, into which it dumps. The height of the vin is such as to give 16 ft. clearance for cars and loclotives passing under it.
As previously stated, the unloader straddles three tracks, running as close as possible to the front of the dock. The ore, however, is drawn from the bin into cars on the central track only. A 60-ft. apron, designed to be raised and lowered over a boat of broadest beam, together with a fixed track over the bin, provide a total trolley travel of 92 ft. The height of the structure resulting from these conditions is 110 ft. to the top of the apron latch on the mast head. The
over-all width of the unloader is slightly less than 24 ft., the unloaders being designed to work 24 ft. center to center, which is the standard distance between hatches on many of the Lake boats.
From the foregoing it will be seen that the structure is high in porportion to its width, and that more than half its trolley travel overhangs the water.
With the bin full of ore the approximate weight of one unloader is 450 net tons. With the bin empty the weight is reduced one-half. The moving load on the bridge is about 84,000 lbs. Under working conditions, therefore, the position of the center of gravity of the whole plant would change considerably; and for the condition with bin empty and trolley and load in extreme position over boat, the center of gravity would be so near the front of the dock as to make the plant unstable. This condition is obviated by using a counterweight on the rear sill, which is sufficient to insure stability under the worst conditions of wind pressure and over-hung live load combined.
The speeds of the varous motions of the unloaders are as follows:
The voltage at the unloaders is nominally 220 volts. The amperes passing motors under working conditions are as follows:
This is for a 60-second cycle, (one round trip,) performing each motion separately. The average current used, per machine, performing each motion separately, and making one trip per minute, would be about 400 amperes. In actual practice the operators combine the different motions, especially the hoisting with the trolley travel, and the lowering with the trolley travel; so that the current used is more than as above stated, and the time of a round trip is sometimes reduced to 35 seconds, under the most favorable condiionts.
The bucket is the two-rope grab, of 70 cubic ft. capacity, having a spread of 14 ft. and a width of 5 ft. The closing ropes have a purchase of three to one. The sustaining ropes are attached directly to the shell, having no opening power. The weight of the ore picked up by the bucket varies widely, ranging fom 15,000 lbs. per trip in the soft, heavy grades of group ore, to less than 6,000 lbs. in hard, lumpy grades. The bucket average also varies with the percentage of cargo unloaded. For example, taking a series of fifty-one boats, the percentage of cargo unloaded was 36.08 per cent.; the remainder being unloaded by other machinery, and the average weight of ore per bucket was 4.37 tons.
From a series of thirty boats, the percentage of cargo unloaded was 75.8 per cent.; the remainder being unloaded by other machines. The average weight of ore per bucket was 4.00 tons, showing that the bucket average decreases as the percentage of cargo unloaded increases. The same thing is shown by observations made at differenct stages during the unloading of the same cargo. For example: during the first hour in a certain boat 13 per cent. was unloaded, the bucket average being five tons; during the tenth hour 4 1/2 per cent. was unloaded, the bucket average being two and six-tenths tons.
The main features of the trolley can best be seen by reference to accompanying cuts.
The motions of the trolley and bucket, as well as the bridge travel and apron hoist, are under separate control, one operator having all the necessary levers and controllers within reach from his position in the cage. The motors and mechanism for hoisting, racking, and rotating are also carried on the trolley.
The 200-ton ore bin is rectangular in plan, 27 ft. 4 in. by 18 ft. 6 in. Its sides and ends are curved, being of the bag-plate construction. The bin is suspended at each of the four corners by two 2 3/4 in. [symbol?] rods, the maximum corner load being
about 130,000 lbs. In the bottom of the bin are two chutes, each opening 2 ft. by 7 ft. The gates on these chutes are arranged to operate simultaneously, and draw ore into the same car. The slope of the end plates at the flattest point is 45 degrees with the horizontal. This means that the valley slope is 33 degreees with the horizontal at then flattest point. The valleys are too flat, especially for a bin with gates, i.e., where the ore is likely to stand and become packed together for twenty-four hours or more before being drawn out.
The arrangement of the plant is such that the bucket can rest on the ore, packing it down in the bin. This often happens. The bin is suspended from scale beams, in such a manner as to weigh the ore as it is drawn out into cars, one operator having control of the gates and the scale beams.
The weighing feature has proved very satisfactory, doing away with the need of yard-scales, trimming machines and car guessers. This means a great saving of labor. A saving of freight is also made by weighing direct into cars. The railroad company allows a ten per cent. over-run on the capacity of each car. The scale operator has a list of capacities and over-runs before him, and loads his cars to the limit. The weighing feature is sure to become a part of the ore unloader of the future; but the requirements of unloading on to several tracks will proably develop a movable weighing hopper, holding about a carload. The sixteen feet head-room under the gates, which is provided in the case of the fixed bin,
would not be necessary in the case of a movable hopper, as the hopper can be moved to one side when a locomotve passes under the unloader. Where the cable haul is used for handling cars on the front of the dock, a clearance of eleven feet under the hopper gates would be sufficient for the largest ore cars.
The scale-beams from which the ore bin is suspended are of especial design, having been designed and built by the Brown Hoist Compnay. These beams are built of structural shapes. The main knife edges, which carry a load of 132,000 lbs. each, are made of tool steel, tempered to a hard, cold-chisel temper, and ground to a sharp 90 degree edge. The length of the knife edge is 24 in. the pressure per lineal inch being 5500 lbs. The knife edge was originally made in one piece, but it was found that the tempering caused it to warp so badly that it was finally cut into three parts, each about 8 in. long. The knife edges are suppported in steel castings, which are securely riveted to the structural beams.
The scale beams are hung from four ball-and-socket connections provided in the structure of the unloader.
Multiplying levers connect the scale beams just described with a special set of scales built by Fairbanks, Morse & Company. These scales have a double beam arrangement, called the plus-and-minus beams. To draw out and weigh a certain amount of ore, the scale operator first sets the minus beam on zero, and balances the plus beam. This shows the amount of ore in the bin. He then sets the balance weight on the minus beam, at the weight to be drawn out, and opens the gates. Watching for the motion of the beams, he closes the gates at the proper time, and if the beams do not exactly balance, he balances them by moving the balace weight on the minus beam, which then reads the exact amount drawn out.
The accuracy of the scales compares well with the yard scales installed in the railroad yards at the dock, in the spring of 1907, by Fairbanks, Morse & Company.
During the season of 1908, thre was noticed considerable difference between weights recorded by the unloaders and those obtained from the three sets of yard scales used at the docks. At the request of the dock company the writer investigated the causes of variation. Eight empty, carefully cleaned cars were selected and weighed on the three sets of yard scales. The total weight of the eight cars was as follows:
The cars were then loaded with ore drawn from the bin of the unloader and agina weighted on the yard scales with the following results:
The cars were then sent to Randall, Ohio, and weighted on a certain track scale considered one of the best on the Erie Railroad.
Weight by Randall scales, 1,210,300 lbs.
After making the customary deduction of stenciled weight, for tare in the case of the track scales, the net weights of the ore are as follows:
In order to give a complete comparison, the differences were found from all possible combinations of two each. This gave ten different differences, using stenciled weights for tare; and nine, using track scale weight of empty car for tare. From the nineteen differences thus obtained, the greatest
was found to be 13,800 lbs. between the Randall scales and the B scales, and the smallest variation was between the A scales and the unloaders.
The weights were obtained from the unloaders under working conditions, with the trolley and bucket operating on the latter half of a cargo.
The main causes of variation were shown to be as follows:
1. All track scales compared have Streeter Ammet attachments for reading weights; these either cover up the zero point or act as a drag on the pointer, imparing the accuracy of results.
2. The zero point on the track scales is sometimes not properly adjusted.
3. In getting railroad weights the stenciled weight of car is ordinarily used for tare. This often disagrees with actual weight for the reason that the so called empty car will be found to contain from 100 to 500 lbs. of coal or waste material.
4. The timbers supporting scales A are insecure.
5. Vibrarion of the unloader, resulting from operating the trolley and bucket simultaneously with the weighing is equally likely to cause plus or minus variation.
6. Wind blowing on the side of the bin while the ore is being weighed could cause considerable variation; for the reason that the area of one side of the bin is approximately 270 sq. ft., inclined with the horizontal at an angle of about 45 degrees. This variation, caused by the wind on the suspended bin is probably more than offset by the effect of ore and other material accumulated on the platform and in the scale pit of the track scales.
Since the above report was submitted to the dock company no further complaint has been receive.
The heavy truck loads, occasioned by the addition of the 200-ton bin to the new unloaders, gave rise to a special six-wheeled and equalizing truck, which was designed and built
especially for the new conditions, and which is used only at the front of the dock, there being no rear cantilever on the plant.
Aside from the new trucks, the moving gear is practically the same as on the older machines, and consists of a 75 H.P. motor, centrally located at the top chord level, driving a line of shafting which connects with a vertical shaft at each leg of the plant, driving four wheels of each truck. The truck wheels are 24 in. in diameter.
A solenoid brake on the moving gear shaft automatically locks the moving gear mechanism when the current is turned off. The machinery for raising and lowering the apron is driven by the same motor that drives the moving gear the two mechanisms being connected or disconnected with the motor by means of a jaw-clutch.
Eight parts of 9/16 wire rope are used to hoist the apron, the purchase being four to one. The two hauling parts are wound up on two eighteen-inch drums, on the same shaft, which is connected with the motor by a train of gearing.
A safety brake with a ratchet and prawl arrangement is used to check the motion of the apron in descending, and to hold the load at any point when the power is turned off. In other words, power is ordinarily required to lower the apron, the motor and apron both working against the safety brake. A foot brake is also provided, so that a man can lower the apron without the use of the motor.
In taking the ore out of the hatch of a boat, the bucket is first used to dig a trench directly under the hatch-opening the unloader being placed centrally over the hatch.
Working with the bucket in position to enter the hatch, that is with the fourteen-foot spread across the boat, the trench is dug to the bottom of the boat, or to a point where the framing in the hold will permit of rotating the bucket. The bucket is then rotated below the deck, widening the trench. Work is continued in this manner until a point is reached, where in addition to the rotation of the bucket, a further reach under the deck can be accomplished by traveling the whole plant. The plant is then moved from its central position, a distance equal to half the width of the hatch, thus allowing the bucket to reach seven feet under the deck. With the bucket in this position the hoist ropes touch the hatch combings.
Before hoisting the bucket out of the hatch, the plant is moved back to its central position, and the bucket rotated back to its original position.
In 1904, when this type of unloader was first used, four machines were installed at Conneaut. During that season the machines were worked only on the day shift, working eleven hours out of every twenty-four. It was considered doubtful if the machines would stand up under double-shift work.
During this single shift season, which was a short one, the four machines unloaded approximately 700,000 tons. During the next three years the machines worked night and day, during the season of navigation and thoroughly demonstrated their capacity. Exact data for this time are not available, but 4,000,000 tons is probably not too high an estimate for the ore unloaded during that time.
Six machines of the same type were recently installed at Fairport, and worked double-shifts during the season of
1907, unloading from boats 1,750,000 tons of ore. During the same season the four new unloaders at the N. Y. P. & O. dock unloaded 838,000 tons.
The four Hoover Mason machines on the same dock unloaded 536,000 tons; and the nine old, standard bridges, each handling a one-ton tub, unloaded 300,000 tons, making a total of 1,674,000 tons, for the season's work at he N. Y. P. & O. dock.
During the season of 1908, at different points along the Lakes, twenty-five of these unloaders were operated, representing a capacity of 7,500,000 gross tons; but of all these machines only the four new ones weigh the ore as it is loaded into cars.
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Last updated September 28, 1998