January, 1924
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INDUSTBIAL A N D ENGINEERING CHEMISTRY
5
Mechanical Handling Devices' I-The
Grab Bucket
By A. E. Marshall 3034 ST.
T
PAUL S T . , BALTIMORE, MD.
H E growth of imMechanical devices for handling and mooing raw and finished Considering only the provements in the materials have become an essential feature of present-day chemical movement Of loose materials such as are met with in chemmethods for moving plant practice. materials from one place to The principles underlying fhe operation of such deoices permit icd manufacture, the early another closely the grouping info separate dioisions based on the characteristics of the applications Of machinery development of civilization, were simple improvements and a reasonably accurate The mooement of bulk material is one of the most important conon previous hand labor historica1 picture can be siderations in chemical engineering design and practice, so this first practice. Wheeled cars construoted without paper discusses briefly the history of material-handling methods and pulled along tracks by rate research. horses represented an addescribes certain applicafions of the grab bucket. DEVELOPMENT OF MATEaptation of early railroad practice to the plant needs, RIAL-HANDLING METHODS At the dawn of civilization man moved materials with and when the levels were favorable winding engines (copied natural equipment-his body and strength. Material which from the collieries and mines) were used to draw materials had to he placed on a higher elevation was lifted by the in- along an incline to the higher level which was Often the startdividual or by a group of individuals, the number being de- ing Point of a Process. termined by the weight and size of the pieces to be moved. NEEDOF HANDLING DEVICES IN CHEMICAL INDUSTRY Material which had to be transported-food for the larder, stones for the cave door, wood for the fires-was carried Chmical manufacture, in the early days, Was carried out on bodily, and then would follow the use of containers adapted a smaller scale than most other industrial operations. The to matoh the load to the individual's strength. Heavy result was a survival Of hand labor in chemical Plants, and objects were placed on sleds, and the sleds were pulled along an increasing use of m ~ h a n i c a lhandling methods in the other industries where considerable tonnages of raw and finby thongs or ropes of twisted fiber. Spade-like implements were a natural development of ished products had t o be moved through a cycle of operations. means for gathering up loose small material, and a conveying The chemical industry, as its development Proceeded, movement while the material was piled on the spade no doubt gave rise to a Series Of h'ge-SCale Operations inVOlViIlg tonsoon gave place to the use of the spade for filling a container, nage movements equal to other lines of manufacture, and in then moving the container to the new place for the material. recent Years the material-handfing equipment of chemical plants has become an essential Improvements on the spadefeature of low cost operation. plus-container method were, No single industry has such for many centuries, in detail only. The wheel brought in specialized needs in handling devices that its equipment is the wheelbarrow and the cart, peculiar to that industry alone, the horse having in the meanso the material-moving deGices time become a domestic animal of the chemical plant will be and an important part of the intermediate stage between found to be modifications of man and machinery. I n anequipment used generally in the manufacturing arts. other order of motion thewheel The general primary conbecame a pulley, and vertical siderations which underlie the movement with the aid of substitution of any form of forces located on the ground level displaced, or perhaps mechanical device for hand labor are saving in cost and paralleled, methods using the lifting and carryingpower of the increase in capacity. I n the case of material handling, a individual or the combined pull further factor is introduced and haul on a rope from the through the physical limits of higher and desired elevation. the employment of hand labor. Preceding our own timesConsider, as an instance, the that is, prior to the age of daily handling of a thousand machinery-the horizontal and tons of some dry material such vertical movement of material as soda ash or acid phosphate, by the most efficient methods and the difficulty, supposing was represented by the shovel labor could be secured, of argang and cart for horizontal ranging a satisfactory hand and the pulley plus a container for vertical movements. labor operation. If the operating cycle called for a movement Received October 23, 1923. FIG.~-TWO-HOPEG R A BBUCKET of the tonnage over a distance of
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
several hundred feet (and large tonnages mean long move. ments) it would be difficult to arrange even the start of the movement-loading into cars or carts-without lost time and low output per individual. The transportation and discharge of the vehicles might conceivably be arranged for hand labor with the aid of tracks and dumping devices, but the loading or initial stage would always be a limiting factor. Loading operations are usually a preliminary procedure in the movement of any loose material, so mechanical devices which will replace hand labor in this operation deserve early consideration in any survey of present-day methods. There are several available mechanical means for gathering loose material prior to its movement-as, for example, power shovels, suction gatherers, and grab buckets. SIMPLEGRABBUCKET The grab bucket is of general application and can be adapted to such a wide variety of uses that it claims first place as a gathering device and as a means for combining the operations of gathering and conveying. Fig. 1 shows a large size, heavy duty bucket of the tworope, link type being lowered from an overhead bridge onto a pile of material. Grab buckets differ in design, but not in the essential principle of their operation, so this illustration will be used for the general description of operating features. Other designs are shown in the subsequent illustrations which picture various uses, and, as will be noted, buckets for light duty work are designed to suit the load conditions, and so are of lighter construction than buckets intended for larger tonnages and heavy or dense materials. A grab bucket is relatively simple in construction. It is made up of two jaws (usually called spades), spade arms, the upper shell, head, and rope-controlled actuating mechanism. I n the operating cycle the open bucket is lowered onto the material so that the bucket weight rests on the edges of the spades. As soon as the spade-control rope is wound
FIG.LOCOMOTIVE
CRANE
Vol. 16, No. 1
further on its drum (the drum of course being located on the bridge or other similar device), the spades begin to close in and gather the material to the center. When the spades meet, the material is enclosed and will not be discharged until the operator permits the spade control rope to unwind from its drum. The second rope attached to the bucket is operated by another drum, the purpose of this rope being to permit the raising or lowering of the bucket. The control of a grab bucket is therefore carried out by ropes, which serve to raise or lower the bucket itself and to open or close the spades, Buckets are not always of the tworope type, as in some designs three or four ropes are used. Important features in bucket design are the shape and spread of the spades and protection of ropes and bearingsagainst abrasion. Spades provided with an insufficient back angle will skid over the material when closing, and so will not secure a useful load. Another feature which demands consideration in the usual run of chemical plant work i s the provision of a renewable nose plate or spade edge. Dense, hard material, such as pyrites, will wear down even alloy steels, and a spade without a renewable edge will, when worn, allow mat,erial to trickle out from the ragged edges of the closed spades. The grab bucket with its actuating mechanism forms a complete piece of equipment, as together they are capable of picking up material from one level, then hoisting and discharging it a t a higher or lower level as may be desired. Such an arrangement would operate over a small area only, and would only be suited to some special condition where, for instance, material was discharged into a pit and had to be delivered a t a higher level, Even then the fixed position of the actuating mechanism would call for the manual swinging of the bucket, which is not at all desirable. By providing a movable pulley arm or boom over which the ropes are reeved, or by arranging for the limited or free movement of the drum-winding device, the travel of the
FIG.%-STEAM
LOCOMOTIVI~ CRANE
ON C R a E P E R
TRUCKS
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1924
bucket can be changed from the vertical plane only to any desired combination of vertical and horizontal movements. It is this elasticity of travel which makes the grab bucket of universal service in the industries. Buckets supported by their ropes from the end of movable, pivoted booms and with the drum mechanism set close to
FIG. 4 - M O N O R A I L
CRANE
the base of the boom are familiar objects on any large construction job. The boom may ha\-e a free movement through 360 degroes, and by provision of another winding drum and pulleys can be held at any desired angle from horizontal to vertical, thus giving the bucket a range of action determined by the distance from the pivot to the end pulley mounting. The strength of the boom introduces certain essential safety factors into the angle to which the boom can be lowered. I t is, of course, obvious that a boom used a t 10 degrees from the vertical is considerably stronger than when used a t 60 degrees. For this reason, plates showing safe loads at various angles or different distances from the pivot (radius of action) are usually attached to all devices in which booms are atilized. A similar arrangement of bucket, boom, and winding drums is often used a t waterfront plants for the discharge of vessels. LOCOMOTIVE CRAKES If we consider the addition of another movement to the entire device-horizontal travel-we then have the grab bucket locomotive crane. Fig. 2 shows a two-rope bucket attached to a crane transferring material from a car (not shown) to a storage pile. The radius of action in this case is represented horizontally by the length of track and the safe distance of the bucket from the pivot, and vertically by the length of the boom. Loconiotive cranes provide the chemical manufacturer with a useful means for handling outdoor storage of materials like coal, pyrites, limestone, phosphate rock, etc. I n recent years a desire to extend the useful radius of action of locomotive cranes has resulted in the creeper track type. These cranes are similar to the railroad track type in all respects except that creeper tracks, such as were used during the war for propelling tanks, field guns, etc., are substituted for the driven flanged wheels. Fig. 3 shows a creeper track crane and indicates the increased radius of action. The creeper crane permits an entire pile of material to be cleaned up without recourse to a shovel gang or the relaying of trackage, and as a general utility machine for yard work has some distinct advantages. Reference to Fig. 2 will illustrate one of the advantages. A pile of material made by a railroad track type of locomotive crane will have as its apex a point which represents the highest discharge elevation of the bucket. The angle of repose of the material will usually permit a wide
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slope to the pile, and when the material is regained at a later date the crane boom will not be capable of reaching the tail of the pile remote from the tracks. For this reason, piles are often made between parallel tracks, and when excess outdoor storage has to be provided some plants use a single track,
F I G . B-MONORAIL
CRANES IN
FERTILIZER PLANT
but permit the pile to center over the track, the crane, of course, backing away as the pile extends. Such a system permits the cleaning up of the pile as an end operation only and involves excessive movements of both cars and crane. The creeper track cranes are free to move in any horizontal direction, and can therefore gather piled material from any part of the pile. The handling of materials by locomotive or creeper track bucket cranes involves separate movements for picking up and for any subsequent conveying to another desired place, such cranes being in effect a substitute for hand shoveling. The buckets discharge material into cars or trucks, and the final movement is completed as a distinct and separate operation. The crane could, of course, move off under its own power with a loaded bucket and so avoid the second handling, but this would be a slow process and decidedly uneconomical.
PIG.6 - M O N O R A I L
C R A N E WITH CONVERGIWQ
TRACKS AND
SWITCHES
As the grab bucket is a satisfactory piece of equipment for holding material which it has gathered, the idea of conveying the loaded bucket to the discharge point inetead of using a second and subsidiary equipment for movement came along as a logical development.
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Today there are several ways of arranging the travel of loaded buckets in a horizontal direction, each method being dictated by the requirements. MONORAIL CRAKE One solution was to reduce the bulk and weight of a locomotive crane by substituting electricity for steam, and to
FIG.7-TROLLEY
C R A N E UNLOADING COAL
hang the crane from an I-beam by an electrically propelled trolley. Such an arrangement constitutes a monorail crane. Fig. 4 is a three-rope monorail crane handling pyrites and sulfur in an acid plant. Current for the various motors which drive the drums and trolley is picked up from a conductor, which can be seen at the right of the illustration. The radius of action of a monorail crane is limited vertically by the height of the bucket in the raised position and horizontally by the length of the overhead tracks. The side limitsof gather of material are, of course, rather narrow, as in the case of its prototype, the locomotive track crane. Monorail construction, involving as it does the support of the crane and its load from an I-beam, is confined to relatively small loads, with, however, an advantage in permissible speed of travel. The difficulty of gathering up the tail of a pile is more pronounced with monorail than locomotive cranes, as the monorail pulley is fixed and has no circular
Vol. 16, No. 1
sweep like the pulleys on a boom. The effect of two locomotive crane tracks on opposite sides of a pile can be secured by using two monorails, Fig. 5 being an illustration of this adaptation to fertilizer factory practice. The bucket on the righthand crane of Fig. 5 is equipped with replaceable teeth to enable it t o dig into “set” acid phosphate. This illustration also shows clearly the conductor rail and trolley driving mechanism. Fig. 6 shows another method of overcoming the limited side radius of a monorail. Converging tracks and switches enable the crane to cover practically the entire floor of the factory. Whenever switches are employed to increase the radius of action of a II)‘ norail, it is important to provide a safety stop so that the crane cannot proceed through an open switch. Several fatalities have been recorded through lack of this obvious precaution. The use of monorail cranes is not restricted to the simple process of gathering and directly conveying materials. Fig. 7 shows an arrangemgnt designed for leveling the peak of receipt and use of a raw material. This crane unloads the incoming cars and either delivers to the point of use inside the plant or puts the excess in storage. When storage material is being used the crane acts as a direct transfer. There are obviously many combinations of usage for the monorail crane, and its application t o chemical plant work seems to be limited only by the ingenuity of the designer. As an example, movement of a material to points at right angles to the main line of travel can be arranged by providing trackage at different elevations and a transfer pit. When large tonnages have to be handled, a group of monorails is not a satisfactory method, as each crane has to have an operator, This same duplication of skilled workmen would occur if monorails were used to handle material over the entire floor surface of a building.
BRIDGECRANE The ability to cover an entire floor and to handle large tonnages are combined in another device which utilizes the grab bucket as a gathering mechanism. This equipment is the bridge crane, so called because the bucket mechanism is carried on a structural or girder bridge which rests on and can be propelled along elevated parallel tracks. Fig. 8 shows a typical bridge crane of the girder type. Except for size, the mechanical arrangements are quite similar to a monorail crane. The bucket-operating mechanism and operator’s cab form a unit which is capable of movement the full length of the girder-in other words, considered without relation to bridge movement, the device is equivalent to a heavy duty monorail carried on girders instead of an Ibeam and limited in travel to the length of the girder. The movement of the bridge adds the feature of free travel in all
I
F I o . S-BRIDGE
C R A N E OX T E E
GIRDERTYPE
F I G . 9-BRIDGB
C R A N E AND
BUCKETFOR HANDLING ACID P H O S P H A T E
January, 1924
I N D U S T R I A L B N D ENGINEERING CHEMISTRY
planes within the liniits of maximum bucket height, span of girder or bridge, and length of elevated tracks. Bridge cranes are a comparatively recent introduction in chemical engineering practice, and so far have found their principal field in the fertilizer industry. Fig. 9 shows a bridge crane and bucket used for handling acid phosphate from the dens t o storage and from storage t o either the milling or shipping departments. The bucket mechanism is usually capable of simultaneous travel in both directions-that is, along the bridge and by reason of bridge travel, along the building. The bucket can also be raised, lowered, opened, or closed while the other movements are taking place.
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I n this survey of the grab bucket and its associated operating mechanisms, no attempt has been made to describe all of the mechanisms which are in use today. Certain examples have been selected to show the development of one form of handling device, and the lack of mention of other known means of utilizing this same device does not imply a lack of appreciation of their merits. ACKNOWLEDGMENT The author is indebted to the Brown Hoisting Machinery Company, Shepard Electric Crane & Hoist Company, and Sprague Electric Works for the illustrations used in this article.
T h e Solvent-Index of Refraction Method of Determining Oil in Wax' u
By Robert E. Wilson and Robert E. Wilkin STANDARD OIL COMPANY (INDIANA),WHITING,IND.
This report describes a method developed in the laboratories of the Standard Oil Company (Indiana) for determining the oil content of parafin wax. I t is believed that this should supplant the present press method for "oil and moisture." which has proued inaccurate and unsatisfactory. The new method consists essentially in dissolving a 5-gram wax sample in ethylene dichloride, cooling to ubout 0" F.. filtering 09the wax, washing, and evaporating the solvent from the filtrate plus washings. This leaves a residue containing all the oil and the small amount of low melting wax which is soluble even at 0" F. The amount of oil present therein is determined by adding enough of a special soluent to dissolve the residue and measuring the index of refraction, the corresponding oil content being determined by reference to u predetermined curve given in this paper.
The method gives good checks on samples containing known amounts of oil, and seems to be quite satisfactory as f a r as it has been tried on oil and wax f r o m Midcontinent crude. It should, howeuer, be checked u p in other laboratories with wax and oil made f r o m other, crudes. While the method is not as simple as might be desired, attempts to simplify it further have not been successful. Its accuracy is certainly f a r superior to that of the press method. The new method was used to show u p the magnitude and sources of the errors in the ordinary press method by determining the amount of oil and wax contained in the residual wax cake and in the cloths and the blotting papers used in that method. These tests showed that the error in the press method may readily amount to as much as 2 per cent of oil on samples containing 2 or 3 per cent oil.
H.E method most commonly used at present for deter-
into the blotting paper in solution in the oil from the wax. The precise magnitude of the errors involved is shown to be as high as 2 per cent by data presented in the latter part of this paper. Even this error might be overlooked, in the absence of a better method, if different laboratories could obtain check results, but comparative tests in a number of different laboratories have shown very wide variations. , Furthermore, the method requires the use of an expensive press in a special room, the temperature of which can be accurately controlled, and such facilities are not available in many laboratories, particularly those of consumers. I n the light of these facts it is obviously desirable to find some other method for the determination. This need has already been recognized, but rather extensive investigations in this laboratory and others have not disclosed any simple scheme which could be considered a t all satisfactory. This paper discusses further efforts in this direction, and outlines a method which seems to be reasonably satisfactory.
T
mining oil (and moisture) in wax is the press method, .where a small amount of wax (15to 35 grams) is placed between two cloths with blotting paper on the outside, and then subjected to high pressure (around 1000 pounds per square inch) at a definite temperature (60" F.) to squeeze out the oil. Originally, as much wax as possible was scraped off the cloth and the total gain in weight of the cloth and blotting papers was taken as a measure of the oil and moisture present. This tended to make the results high on waxes containing small amounts of oil, because a considerable amount, of wax was pressed into the cloth. For samples of higher oil contents, however, this error was counterbalanced t o a considerable extent by the amount of oil which could not be pressed out of the cake under the prevailing conditions. I n an effort to get more reasonable and reproducible results on samples with lower oil content, the subcommittee on paraffin wax of Committee D-2 of the American Society for Testing Materials2has suggested that this method be modified by leaving the cloths with the wax after pressing, and determining only the gain in weight of the blotting papers. The results of this method would obviously be in error by the amount of oil which is held in the cloth and left in the cake. For very high oil contents this serious error is partly counterbalanced by the fact that small amounts of wax are carried 1 Received August 15, 1923. Presented before the Division of Petroleum (!hemistry at the 66th Meeting of the American Chemical Society, Milwauktse. Wis.. SeDtember 10 to 14. 1923. 8 Proc..Am. Soc.-Tesling Materials, 22, 422 (1922).
ATTEMPTSTO SEPARATE WAX FROM OIL
From time to time suggestions have been made that it ought to be possible to separate the oil from the wax by the use of some solvent which would dissolve one-preferably the oil-without dissolving appreciable quantities of the other, and thus permit a separation, possibly involving repeated fractionation. Methods of this type-e. g., that of Holde3have indeed been found reasonably satisfactory for products 8
Holde-Mueller, "Examination of Hydrocarbon Oils," 1915, p. 87.
