Machine design - Hoists, Derricks, Cranes
MACHINE DESIGN - HOISTS, DERRICKS, CRANES
BY H. D. HESS
PHILADELPHIA AND LONDON, J. B. LIPPINCOTT COMPANY, 1912
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Machine design - hoists, derricks, cranes
PREFACE
The author believes that no class of problems afford as good general training and practice as may be had in the design of cranes. The larger portion of crane details being the simplest machine elements are common to a wide field of machine design. The stresses both in the frames and machinery are readily determined by the elementary principles of mechanics and the design thus easily carried out on a theoretical rather than on an empirical basis. The book is intended to aid the work of machine design in technical schools and colleges and it is hoped it may prove useful in drawing-rooms where a general field of machine design is covered. The problems have been selected with this in view rather than that of appealing to the specialist in crane design.
The engineering literature drawn upon includes the works of Bach, Bethmann and Ernst, and Machinery and Engineering Record among the periodicals. Through the kindness of several crane builders, catalogues, photographs, specifications and drawings, illustrating American practice, have been placed at our disposal.
The engineering literature drawn upon includes the works of Bach, Bethmann and Ernst, and Machinery and Engineering Record among the periodicals. Through the kindness of several crane builders, catalogues, photographs, specifications and drawings, illustrating American practice, have been placed at our disposal.
CONTENTS
- INTRODUCTION
- FRAMES AND GIRDERS
- BRAKES AND CLUTCHES
- WINCHES AND HOISTS
- PILLAR CRANES
- JIB CRANES
- UNDER-BRACED JIB CRANE
- INVERTED POST CRANE
- WALL CRANE
- OVERHEAD ELECTRIC TRAVELLING CRANES
- HOISTING ENGINES
- LOCOMOTIVE CRANES
PART XII - LOCOMOTIVE CRANES
Locomotive cranes are commonly steam-driven, but a few are electrically driven. Steam locomotive cranes are driven by double cylinder engines with the cranks set at 90. The several motions of rotation, transfer on the track, moving the load and boom are ordinarily accomplished by the use of friction clutches; the engine is then of the non-reversing type. The boiler is placed behind the engine, thus serving to counterweight the crane. The fuel-and-water tanks for the boiler are also placed to serve in this capacity. As previously explained for hoisting engines, the boiler should be large, so as to demand only occasional attention from the operator, and for the same reason ample fuel and water should be carried on the crane.
Owing to the limitations of the counterweight the crane will raise its greatest load when working at its shortest radius. The crane parts must therefore be designed for the stresses due to the maximum load.
The cranes are also designed to move several loaded cars along a level track, thus greatly facilitating loading and unloading cars.
The maximum direct stress will occur in the boom when it is in its highest position; the maximum lateral stress, however, may come upon it when in its lowest position and beginning to be rotated, as the accelerating force must then act upon it to produce the required velocity in the load.
To provide strength in the boom to resist this force, it is customary to spread the sections forming the boom at the lower end.
The force required to rotate the crane will be that needed to overcome friction plus the accelerating force.
The following clauses are taken from a specification of a locomotive crane built by Wellman-Seaver-Morgan Company:
PURPOSE. The crane will be designed especially for handling an automatic grab bucket, or can also be used for hoisting loads in ordinary yard service.
GENERAL DESCRIPTION. The crane comprises a car on which is mounted a revolving platform carrying boiler, engines, drums, boom and operating mechanism. The crane is provided with the necessary mechanism for propelling it back and forth on tracks, raising its load, and rotating the revolving platform; also for raising and lowering the boom to vary the radius, or to give it the necessary clearance in doors or archways through which it is designed to pass.
The crane has power strength and stability to safely handle these loads at the given radii through a full circle without fastening the crane to the track, or will move along the track with these loads hanging from the boom.
The lifting capacities are based upon the track being in good condition and with the counter-weight box filled with 15,000 pounds of counter-weight; the counter-weight to be furnished by the purchaser. By using track clamps provided with the crane, these lifting capacities can be increased.
BASE. The crane base will be a structural frame-work into which is bolted a turn-table. On this turn-table the rotating super structure rests. This turn-table has teeth cast on its periphery for meshing with the pinion which revolves the super-structure.
The crane has cast-iron track wheels with chilled treads. These track wheels are forced on hammered steel axles, which run in bronze bearings fitted with oil boxes.
REVOLVING PLATFORM. On the base is mounted a revolving platform, consisting of a heavy casting carried on two conical cast steel rollers at the rear end, and four conical rollers in pairs, in equalizing frames, at the front end. This revolving platform is pinned to the main base at the center by a heavy hollow cast steel pivot pin. The heel of the boom is carried at the front end of this platform. The housings for the engines and the hoisting mechanism are connected to this platform so as to practically make one rigid piece. The rear extension of this platform forms a support for the boiler, and is hollow, thus forming a tank for the crane water supply.
BOOM AND MAST. The boom will consist of 2 heavy channels securely braced together. The mast carrying the tackle for supporting the outer end of the boom will consist of heavy channels securely braced to and supported on the engine housings.
ENGINES. The engines will have two vertical cylinders with link-motion reversing gear. The engine shafts will be of forged steel and will have balanced disc cranks forced and keyed on. The engine shaft is geared to two intermediate shafts, one carrying the clutches for driving the drum shaft and for travelling the crane, the other carrying the clutches for the rotating mechanism.
GEARING. The engine pinion will be of forged steel with cut teeth. The gears meshing with the engine pinion will be steel castings with cut teeth. All boom-raising gears, except bevels, will be of steel castings with cut teeth. All remaining gears will be steel castings with cast teeth, from metal patterns. The main axle-driving bevel gears are split. Bearings for main axles and for conical rollers will be of bronze shells. All bearings not otherwise specified will be lined with babbitt metal, poured in place and accurately scraped to fit.
A few points in the design of such a crane will now be considered. The given specification will be followed in a general way.
ROPE. A 5/8-inch diameter extra flexible plow steel rope run- ning on a 24-inch diameter drum will be tried. The sheaves will be assumed at 21 inches diameter and the load of 20,000 pounds will be carried by 4 ropes.
DOWNLOAD FREE BOOK:
Machine design - hoists, derricks, cranes
Owing to the limitations of the counterweight the crane will raise its greatest load when working at its shortest radius. The crane parts must therefore be designed for the stresses due to the maximum load.
The cranes are also designed to move several loaded cars along a level track, thus greatly facilitating loading and unloading cars.
The maximum direct stress will occur in the boom when it is in its highest position; the maximum lateral stress, however, may come upon it when in its lowest position and beginning to be rotated, as the accelerating force must then act upon it to produce the required velocity in the load.
To provide strength in the boom to resist this force, it is customary to spread the sections forming the boom at the lower end.
The force required to rotate the crane will be that needed to overcome friction plus the accelerating force.
The following clauses are taken from a specification of a locomotive crane built by Wellman-Seaver-Morgan Company:
PURPOSE. The crane will be designed especially for handling an automatic grab bucket, or can also be used for hoisting loads in ordinary yard service.
GENERAL DESCRIPTION. The crane comprises a car on which is mounted a revolving platform carrying boiler, engines, drums, boom and operating mechanism. The crane is provided with the necessary mechanism for propelling it back and forth on tracks, raising its load, and rotating the revolving platform; also for raising and lowering the boom to vary the radius, or to give it the necessary clearance in doors or archways through which it is designed to pass.
The crane has power strength and stability to safely handle these loads at the given radii through a full circle without fastening the crane to the track, or will move along the track with these loads hanging from the boom.
The lifting capacities are based upon the track being in good condition and with the counter-weight box filled with 15,000 pounds of counter-weight; the counter-weight to be furnished by the purchaser. By using track clamps provided with the crane, these lifting capacities can be increased.
BASE. The crane base will be a structural frame-work into which is bolted a turn-table. On this turn-table the rotating super structure rests. This turn-table has teeth cast on its periphery for meshing with the pinion which revolves the super-structure.
The crane has cast-iron track wheels with chilled treads. These track wheels are forced on hammered steel axles, which run in bronze bearings fitted with oil boxes.
REVOLVING PLATFORM. On the base is mounted a revolving platform, consisting of a heavy casting carried on two conical cast steel rollers at the rear end, and four conical rollers in pairs, in equalizing frames, at the front end. This revolving platform is pinned to the main base at the center by a heavy hollow cast steel pivot pin. The heel of the boom is carried at the front end of this platform. The housings for the engines and the hoisting mechanism are connected to this platform so as to practically make one rigid piece. The rear extension of this platform forms a support for the boiler, and is hollow, thus forming a tank for the crane water supply.
BOOM AND MAST. The boom will consist of 2 heavy channels securely braced together. The mast carrying the tackle for supporting the outer end of the boom will consist of heavy channels securely braced to and supported on the engine housings.
ENGINES. The engines will have two vertical cylinders with link-motion reversing gear. The engine shafts will be of forged steel and will have balanced disc cranks forced and keyed on. The engine shaft is geared to two intermediate shafts, one carrying the clutches for driving the drum shaft and for travelling the crane, the other carrying the clutches for the rotating mechanism.
GEARING. The engine pinion will be of forged steel with cut teeth. The gears meshing with the engine pinion will be steel castings with cut teeth. All boom-raising gears, except bevels, will be of steel castings with cut teeth. All remaining gears will be steel castings with cast teeth, from metal patterns. The main axle-driving bevel gears are split. Bearings for main axles and for conical rollers will be of bronze shells. All bearings not otherwise specified will be lined with babbitt metal, poured in place and accurately scraped to fit.
A few points in the design of such a crane will now be considered. The given specification will be followed in a general way.
ROPE. A 5/8-inch diameter extra flexible plow steel rope run- ning on a 24-inch diameter drum will be tried. The sheaves will be assumed at 21 inches diameter and the load of 20,000 pounds will be carried by 4 ropes.
DOWNLOAD FREE BOOK:
Machine design - hoists, derricks, cranes
