A treatise on cranes. Descriptive particularly of those designed and built by the Yale & Towne manufacturing co

Front matter

strata, Uwi 'Bnrk

..Qiyll-Bagineering.. College

CORNELL UNIVERSITY LIBRARY

Preface

The subject of Cranes has had but little consideration from technical writers, and has never yet received from them the attention which its importance in the mechanic arts will justify. It is perhaps partly due to this cause that the value and economy of Cranes, as labor-saving machines, is as yet so little appreciated in this country.

The only English books descriptive of Cranes are that of Glynn, written more than thirty years ago, and the catalogues published by various English firms to advertise their products, none of which fully represent what is best in English practice, or affords any information as to the important details of construction embodied in the machines they illustrate.

The present treatise, although intended primarily to place before users of Cranes a description of those built by The Yale & TowNE Manufacturing Company, includes a careful study of the subject from an independent point of view, and will, it is believed, be found of interest to engineers generally by reason of its comprehensiveness, both as relates to the various types of Cranes and to the details of their construction, and because it carries the art it describes down to a more recent date than

VI

any previous publication. In its description of details and of actual construction, it embodies the results of the combined work of several skilled inventors and mechanical engineers, continued uninterruptedly, under the author's direction, during a number of years and applied, together with the resources of a large establishment, to the study and development of the art of Crane building as a distinct specialty.

It is the first publication descriptive of American, as distinct from European practice, in the specialty of which it treats. The class of machines which it describes has long been recognized in Europe as one of wide importance and interest. It is the purpose of this treatise to indicate to American readers the great variety of uses to which Cranes can be applied with economy and convenience, and to describe the latest and best results of American practice in this field of engineering work.

H. R. T.

September, 188S.

Vll

Part I. Page

Introduction i

Types of Cranes 3

Details of Cranes :

Hoisting Gear 6

Traverse Gear 9

Chains versus Ropes, and Chain Wheels versus Drums II

TroUeys and Trucks 15

PART II. Introduction 21

Crane Details 22

Chains 23

Chain Wheels 25

Spur Gearing , 28

Worm Gearing 30

Frictional Safety Ratchet 33

Clutches 41

Weston-Capen Clutch 47

Squaring Device for Movable Crane Bridges 54

Bridge Moving Device for Traveling Cranes 58

Squaring and Bridge and Trolley Moving Device for Traveling Cranes. ... 61

Trolley Traveling Mechanism 65

Gearing of Jib Cranes for operation by Hand 69

Gearing and Clutches of Power Traveling Cranes 73

Bridge Trucks 78

Bridges and Trestles of Traveling Cranes 85

Povirer Transmission 88

Take-ups 90

Hooks .' 91

Blocks and Bushings 94

Pillar Crane Foundations 97

Notice as to Rights Secured by Patent 99

List of Patents 103 viii Contents.

Part III. Page

Introduction 107

Swing Crane, with Winch, without Trolley 108

Light Jib Crane, with Differential Pulley Block and Trolley no

Light Jib Crane, with Winch, Trolley, and Traverse Gear 112

Jib Crane, Independent Trolley Travel 115

Jib Crane, Combined Hoist and Trolley Travel 118

Column Crane 122

Walking Crane 124

Derrick Crane 130

Pillar Crane 132

Locomotive Crane 135

Bridge Crane 136

Hand Traveling Crane, for Differential Pulley Block, Longitudinal Traverse Gear only 140

Hand Traveling Crane, for Differential Pulley Block, with Transverse and

Longitudinal Traverse Gear 143

Hand Traveling Crane (High Pattern), with complete Hoisting and Traveling Gear 146

Hand Traveling Crane (Low Pattern), with complete Hoisting and Traveling Gear 149

Hand Traveling Crane (Foundry Pattern), with complete Hoisting and

Traveling Gear 152

Power Traveling Crane 155

Power Traveling Crane, Double Trolleys 160

PART IV. Introduction 165

Relation of Power to Speed 167

Principle of the Weston Differential Pulley Block 16S

Differential Pulley Block, ' ' Direct " 176

"Geared" 177

Safety " Double Lift " Hoist 178

"Safety" Hoist 180

" " with "Governor" Action 181

Hoisting Crab 183

Derrick Winch ... 184

Dredging Winch ■ 185

Light Swing Crane, with " Double Lift " Hoisting Gear 186

Overhead Tramrails, Single Rail 187

" " Compound Rails 190

Contents. ix

Index To Illustrations

PAGE.

Fig. I. Chain Wheel, Guide and Stripper 26

" 2. Teeth of Spur Wheels 28

" 3. Worm Wheel and Worm 32

" 4. " Double Lift " Safety Ratchet 34

" 5. Spur Pinion with Safety Ratchet 36

" 6. Safety Spur Pinion 38

" 7. Safety Worm Pinion 40

" 8. Model of Alternate Friction Plates 41

' ' g. Experimental Friction Brake 43

" 10. Frictional Shaft Coupling, longitudinal section 44

" II & 12. " " " transverse section 45

" 13. Friction PuUies with Capen Toggles 47

" 14. Simple Form of Weston Clutch 49

" I j. Weston Clutch with Capen Toggles 50

"16&17. CapenToggles 51

" 21. Device for Squaring Movable Bridges 54

" 22. Device for Squaring and Propelling Bridges 58

" 23. Device for Squaring and for Propelling Bridges and Tr611eys. . . . 62

" 24. Mechanism for Moving Trolleys 66

" 25. Gearing of Jib Cranes 69

" 26. Detail View of Chain Wheel in Jib Cranes 70

" 27. Gearing of Jib Crane 71

" 28. Top View of Reversing Mechanism 74

" 29. Side Elevation of Reversing Mechanism 74

" 30. End View of the Three Shafts of the Reversing Mechanism and

their Connecting Gears 75

" 31. Truck for I-Beam Bridge 78

" 32. Truck for Plate Girder Bridge 79

■' 33. Jib Crane Frame 82

" 34. Transverse Section of I-Beam Bridge 83

"35. " " " Plate Girder Bridge 83

" 35. Bridge of Hand Traveling Crane 85

"38. Rim of Wheel for Wire Rope 88

"39. " " " " Cotton Rope 88

" 40. Transmission of Power 89

" 41. Take-ups 90

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PAGE.

Standard Hook 92

Crane Block and Hook 94

Anti-Friction Bushing 95

Pillar Crane, and Foundation 97

Swing Crane, without Trolley 108

Light Jib Crane, with Trolley and Pulley Block no

Jib Crane, with Separate Trolley Gear 116

Heavy Jib Crane, with Combined Gear 118

Column Crane, or Jib Crane swinging around a Fixed Column. . 122

Walking Crane, as arranged for operation by Power 124

Derrick Crane, for Outdoor Use , 130

Pillar Crane, for operation by Hand 132

Bridge Crane, operated by Hand 136

Light Hand Traveling Crane, Longitudinal Traverse Gear only. . 140

" " " " Transverse and Longitudinal Tia-

verse Gear 144

Hand Traveling Crane, with Overhead Trolley 146

" " " " Underhung Trolley 150

" " " " Fixed Crab 152

Power Traveling Crane, with Single Trolley 156

" " " " " as applied to Foundry

Use 159

Power Traveling Crane, with Two Trolleys 160

Principle of the Weston Differential Pulley Block 169

a 4( t( <t (( tc It _

"Direct" Differential Pulley Block ' 176

Direct " Double Lift " Hoist 178

Geared " " " 179

" Double Lift," as Used for Hatchway 179

"Safety Hoist" 180

" " with "Governor" 181

Safety Crab 183

Safety Winch 184

Safety (Slip) Winch. .' 185

Light Swing Crane, with " Double Lift " Hoisting Gear 186

Single Tramrail 187

Patent Trolley, Side elevation 188

" " End View 188

Single Tramrail, with Switch 189

Compound Tramrail igo

Introduction

The contents of this Part consist of a general survey of the subject of Cranes, including an enumeration of the principal forms in which they are used, a definite system of nomenclature applied to the various forms, and finally a study of the most important elements of mechanism employed in Crane construction.

The latter portion is in some measure a record of the processes of reasoning and selection which resulted in the adoption of the forms of details employed in the Weston Cranes. In undertaking this new field of work the builders of these Cranes were untrammeled by any previous position or bias as to the details of the work, and many months of careful study were given to the consideration of the best forms to be adopted. The process usually resorted to in this effort was to give equal consideration to all possible plans and to select therefrom the one which gave the best promise of satisfactory results. The decisions thus reached were then subjected to the test of practice, and further modifications and improvements were introduced as experience was gained. The effort throughout was to reach the best practicable result, and to determine finally and reliably the best form or method of construction for each of the important details of Cranes.

The following pages, therefore, are not immediately descriptive of the Weston Cranes, but comprise a preliminary review of the whole subject which will enable the reader to understand the reasons upon which the selection of the chief elements in the Weston Cranes are based, and will assist him in judging for himself as to the soundness of the conclusions reached in the succeeding parts of this book.

A Treatise on Cranes.

CRANES;

A STUDY OF TYPES AND DETAILS,

BY

HENRY R. TOWNE.

A paper read before the American Society of Mechanical Engineers, at the Cleveland meeting, jpune, 1883.

In the study of any special class of machines it is often conducive to a better understanding of the subject clearly to enumerate the several types or forms in which the machine is used, and also to consider each of its more important details separately, rather than in their combination with other elements of the mechanism. It is proposed in the following pages thus to treat the subject of Cranes.

The only English text-books descriptive of cranes are Glynn's, which treats of English practice in crane building as it existed more than thirty years ago, and sundry catalogues published by English dealers in machinery as a means of advertising the products of the various builders of cranes for whom they act as selling agents. The practice represented in the former is now almost obsolete, by reason of the improvements which have been effected, and the latter consist of little but a series of pictures of various cranes, without descriptive text, and with no information as to the details of their construction.

The building of cranes has long been recognized in Europe as one of the most important subjects in the field of mechanical engineering, and cranes of many forms are there seen applied to an almost infinite variety of uses. In America, on the contrary, cranes are but little used or appreciated, in comparison, at least, with the extent of their application in European countries. It is

Types of Cranes. 3

the purpose of this paper to present to American readers a brief classification and description of the most important types of cj-anes, and a similarly brief study of the more important elements entering into their construction, the object of the latter inquiry being to determine, if possible, the best forms of elements to be adopted.

With a better knowledge of crane construction will surely come a better appreciation of their economy and value as labor-saving machines. In hundreds of mills and workshops heavy material is now being moved and handled by manual labor at an expense so much in excess of the cost of doing the same work far more rapidly and conveniently by cranes, that the saving effected by the latter would yield an annual profit of from twenty to fifty per cent, upon their first cost, while in many cases this outlay would be entirely repaid by the economy of one year's use.

CLASSIFICATION OF CRANES.

A hoist is a machine for raising and lowering weights. A crane is a hoist with the added capacity of moving the load in a lateral or horizontal direction.

All cranes, therefore, are provided with hoisting mechanism, and, in addition, must be capable of moving the load in one or more horizontal directions. This second function is effected in some types of cranes by simply pushing the suspended load, in others by the operation of a distinct mechanism.

Cranes are most clearly classified by reference to their modes of transferring their loads horizontally ; and, thus considered, are found to divide themselves into the following groups, viz. :

1. Rotary— In which the load is revolved around a fixed center, such as a mast or column.

2. Rectilinear — In which the load is moved in straight lines, in one or more directions.

Both types of cranes are subdivided into two general classes as to their movements, viz. :

(^.) Fixed— When their supporting members are fixed in some permanent location.

{£.) Movable — When the crane as a whole can be moved about.

And into four other general classes as to their source gf motive power, viz.:

(a.) Hand — When the motions, either vertical or horizontal, are effected by manual power.

{b!) Power — When the motions are effected by power derived from line shafting driven by a stationary engine or other fixed motor.

(c.) Steam — When the motive power is derived from a steam engine attached directly to the crane itself and moving with it.

(i£) Hydraulic — When the motive power consists of hydraulic pressure obtained from a pump or accumulator, and carried to the crane by pipes.

A further distinction is covered by the term locomotive, which is applied to cranes (usually of the rotary type) which are capable of propelling themselves upon a roadway or track.

Rotary cranes comprise the following principal types, viz. :

1. Swing Cranes — In which the central mast is pivoted to the floor and roof of the building, and the load is suspended from a block fixed at the outer end of an arm projecting horizontally from the mast, the only horizontal motion being one of rotation.

2. Jib Cranes — In which the central mast is pivoted to the floor and roof of the building, and the load is suspended from a trolley traveling in and out upon an arm or jib projecting laterally from the mast.

3. Column Cranes — Which consist of a jib crane constructed to revolve around or upon a fixed column forming the support of a building or floor.

4. Pillar Cranes — In which the central column or pillar is entirely supported by a heavy foundation built at its base, and the load is suspended from a boom projecting from the pillar and revolving with it or around it.

5. Derrick Cranes — Which consist of a jib crane for yard use, the upper end or pivot of the mast being held in position by guy-rods or stays, instead of by attachment to a roof or ceiling.

6. Walking Cranes — Which consist of a pillar or jib crane

Types of Cranes. 5

mounted on wheels, and arranged to travel by power or by hand upon one or more rails.

7. Locomotive Cranes — Which consist of a pillar crane mounted on wheels, and provided with a steam engine and boiler, the power of which is available for operating the crane and for propelling it upon its tracks.

Rectilinear Cranes comprise the following principal types: —

1. Bridge Cranes — In which a fixed bridge spans an opening, and the load is suspended from a truck or trolley capable of moving across the bridge.

2. Tram Cranes — In which a truck or short bridge, from which the load is suspended, is arranged to travel longitudinally upon a pair of overhead rails, but is without capacity for transverse motion.

3. Traveling Cranes — In which a rectangular space is provided with overhead tracks upon two of its opposite sides, and is spanned by a bridge arranged to travel longitudinally upon these tracks, the load being suspended from a truck or trolley capable of moving transversely across the bridge, so that the load may be moved to or from any point within the entire rectangle.

4. Gantries — In which an overhead bridge is supported at each end by a frame, or trestle, extending downwards, and having wheels in its base to permit of travel upon two longitudinal tracks laid upon the ground, so that the entire structure can move endwise upon the latter, and the load, which is suspended from a truck or trolley on the bridge, can be moved transversely across the bridge.

5. Rotary Bridge Cranes — Which combine a rotary with a rectilinear movement, and consist of a bridge having one end pivoted to a central pier or post, while the other or outer end travels on a circular overhead track, or is supported by a gantry frame traveling upon a circular track upon the ground, the load being suspended from a truck or trolley traveling transversely across the bridge.

The above nomenclature will be adhered to in the following descriptions of crane construction.

CRANE DETAILS.

HOISTING GEAR.

The most important factor in the economy and convenience of a crane is the mechanism by which the load is lifted and lowered, as it must necessarily come into action every time the crane is used.

In all applications of power, from whatever source derived, it must be remembered that the gearing of a machine can only modify the power applied in one of two ways, viz. :

(i). By reducing its velocity, and proportionately increasing its force or " pull."

(2). By increasing the velocity, and proportionately decreasing the intensity of the power transmitted.

Under no circumstances, unless the motive force is increased, can power be gained except by a sacrifice in speed, or can speed be increased, except by a sacrifice in power. If either or both must be increased without diminishing the other, it can only be accomplished by supplying more motive power.

The function of gearing, then, is to change the force or direction of the power applied, If it is well designed and constructed, this may be done with only a small loss from friction; while, if badly made, the gearing may absorb much power in wasteful friction of its moving parts.

In machinery for hoisting, the " purchase " or conversion of velocity into lifting power, is usually effected partly by a multiplication of the ropes or chains of the tackle through which the load is suspended, and partly by gearing within the machine, which latter thus becomes an important feature in crane work. The gearing ordinarily used for this, purpose consists either of spur wheels and pinions or of worm wheels and worms, or both combined, and the smoothness and economy of power of the machine depend largely upon the manner in which the gearing is made.

Crane Details. — Hoisting Gear. 7

A second feature of prime importance in the hoisting gear of a crane is the mode of sustaining the load, and guarding against its " running down " when the application of the motive power is discontinued. This has heretofore been accomplished, in machines having spur gearing, by a ratchet-wheel, the pawl of which has to be entirely disengaged to permit lowering to occur, or by a brake, which, when on, prevents all motion of the machine, and which requires to be held or thrown off, both in hoisting and lowering. In machines having worm gearing, the end is attained by a construction of the worm wheels such that the friction between the worm and the wheel is sufficient to prevent the ba-ckward rotation of the worm under the pressure of the teeth of the worm wheel caused by the load, the resistance thus generated sufficing to prevent the running down of the load.

The worm-wheel system is usually safe against accidents, but is not economical of power if the worm gears are proportioned, as above explained, to hold the load suspended without running backwards when the application of power ceases, as is usually the case. The spur-wheel system, on the other hand, is a constant and inevitable source of great danger, both to the load and to the operator. With the least carelessness in lowering, the load begins to descend with great velocity, and the mechanism is driven backwards with corresponding speed and violence. If not checked the load then practically falls as if unsupported. If too suddenly checked, violent strain is thrown upon the entire frame of the crane and on its gearing, which latter is thus liable to damage, and even to " stripping " or fracture, in which event the load falls. Where spur-geared cranes are operated by hand this " running down " of the load involves a reversing or " flying back " of the cranks, which then frequently strike the men before they can escape beyond their reach. Accidents of this kind, resulting in injury to limbs, and even to life, are constantly happening with common cranes, and are reported almost daily in the newspapers.

It is possible, however, so to proportion worm gearing as to place it almost, if riot wholly, upon a parity with spur gearing in regard to economy of power transmitted, and, by the use of cut worm wheels, driven by turned worms or pinions (the teeth of the wheel being formed by means of a chasing hob or cutter), so to construct worm gearing that it becomes the best and most convenient form of gearing for use in crane mechanism. It is found that gearing thus made will not automatically support the load, and that the latter, if left suspended, will drive the worm gearing backward, but in this case the descent of the load is quite slow, and no perceptible acceleration takes place, so that the worm gears thus act as a governor to control the load. By the application of a small brake to the worm-shaft this tendency is counteracted, and, by connecting this brake with the levers which control the motions of the mechanism, the brake is easily made automatic, and thus securely holds the load whenever the crane mechanism is at rest.

In all cranes, except those of small size, provision should be made for one or more changes of speed in hoisting and lowering, so that the speed may be varied according to the load and the nature of the work to be done. Cranes operated by power may be so constructed that the maximum load can be lifted at the quickest speed ; but they are usually so proportioned that this can be done only at a slow speed. By this plan" much economy of gearing, space and cost is effected, and the practical efficiency of the crane for all ordinary uses is not impaired. The most perfect construction is one that permits a change of speeds to be made whether the hoisting gear is in motion or at rest, and which sustains the load automatically while a change of speed is being made.

The hoisting gear of a crane should therefore attain the following results, viz. :

(i.) Such changes in direction and velocity of the power applied as will give the desired motions to the load.

(2.) The accomplishment of this with a minimum loss of power through friction.

(3.) The safety, both of the operator and the load, under all conditions ; to insure which the load must be always self-sustained and incapable of " running down."

Crane Details, — Traverse Gear. 9

(4.) Capacity for changes of speed and for convenient transition from one of these to another at will, whether the gearing is in motion or at rest, and for the automatic support of the load during the act of changing speeds.

TRAVERSE GEAR.

In this, as in the hoisting gear, good design and construction are essential to economy of power, and frequently to safety against accidents.

In some types of rotary cranes no traverse mechanism exists, except an arrangement of parts which provides for the rotation of the crane. In others, such as jib and 'derrick cranes, provision must also be made for moving the truck or trolley horizontally on the jib, and the same provision is required for moving the trolley of bridge and traveling cranes transversely on the bridge. In all such cases a separate mechanism, distinct from the hoisting gear, has heretofore been employed, and is still sometimes desirable or convenient. When employed, its parts should be as few and simple as possible, and it should be so far independent of the hoisting gear as to permit either to be used at any time separately or conjointly. In power cranes provision should be made for accelerating the speed of the trolley travel whenever the nature of the work admits of it. The best possible result is attained when travel of the trolley is effected without varying the vertical position of the load, and without causing useless movement of the hoisting chain or rope over the sheaves through which it supports the load, which movement would involve much additional friction, and cause rapid wear of the chain or rope.

In traveling cranes a point of great importance is the parallelism of the bridge travel with the longitudinal tracks. Any defect here results in increased resistance to traction, and any considerable error might cause derailment. In traveling cranes^ as heretofore built, the use of flanged wheels has been relied upon to prevent derailment, and the propulsion of the bridge has been effected by a transverse shaft extending the whole length of the bridge, and connected by gearing with the truck-wheels suplo A Treatise on Cranes.

porting each end of the bridge, so that, by revolving the shaft, the truck-wheels would be rotated, arid the bridge be thereby propelled, provided the adhesion between the wheels and the rails was sufficient. In some instances, where the adhesion has not been sufificient to prevent slipping, a cast iron rack has been laid adjacent to the longitudinal tracks, and extending their whole length, and pinions, gearing into this rack, attached to the axles of the truck-wheels, so that propulsion is effected independently of the adhesion of the truck-wheels to the track. If the load were always central on the bridge, and the motive power always applied to this shaft at the center of its length, this plan would answer well, although it is somewhat clumsy ; but in practice the load is constantly varying in position, and the motive power is applied at one end of the long transverse shaft, so that torsion of the shaft induces a considerable variation in the travel of the opposite ends of the bridge. This error is a constantly varying one, according to the portion of the load resting upon each truck, as determined by the position of the trolley, the load being never equally distributed between the two trucks except when it is exactly in the center. It follows, therefore, that this system of bridge travel, although operative, is radically defective, and that its use involves a constant loss of power by needless friction, and entails a proportionate amount of wear and tear of rails, wheels, and driving gear.

A better and more simple method of bridge propulsion has lately been introduced, by means of which the longitudinal motions of the bridge are effected by pulling each of its ends, simultaneously and at equal speed, in the desired direction. For this purpose light wire cables are used which, by a very simple and ingenious arrangement of guide sheaves, are made to act as a " squaring device " to hold the bridge at all times perpendicular, or square, to the tracks upon which it travels. By this system the friction of traction is reduced to a minimum, and the danger of derailment from unequal travel of the opposite ends of the bridge entirely obviated.

From the above facts it becomes evident that a perfect system of bridge propulsion must hold the bridge always absolutely

Crane Details. — Chains versus Ropes. 1 1

square with its tracks, and must propel the opposite ends of the bridge in the same direction, at the same time, and at the same speed, however unequally the load may be distributed. It is desirable also that, in large cranes at least, provision be made for starting the bridge slowly from a state of rest, and then increasing the speed, and also for varying the speed while the bridge is in motion.

CHAINS versus ropes,

AND CHAIN WHEELS VCrSUS DRUMS.

In almost every type of crane the load is primarily carried upon a flexible cord of some kind. This usually consists of rope, either hemp or wire, or of chain. Each of these has distinctive merits and objections.

Ropes have the advantage of being formed of many parts or fibres, so that no splicing or welding is necessary in their manufacture ; and they thus have an assured and practically uniform strength throughout their length.

Chains, on the contrary, consist of a series of independent links, each of which is formed from a straight bar, and welded, so that a single imperfect weld injures the whole, the strength of a chain being obviously limited by the strength of its weakest link. By care and good workmanship, however, this danger can be avoided, in which case the chain becomes as safe as the rope, and much more durable.

Where a rope is used, the hoisting gear must necessarily include a drum or barrel upon which the rope is wound up when hoisting takes place. Chain may also be thus wound up on a barrel, and this has heretofore been the common practice when chains have been employed in crane construction, and a prominent feature in cranes of large capacity has usually been a proportionately large " winding-barrel " to receive the chain. A chain, however, admits of another mode of construction, which consists in substituting for the wide barrel or drum a pocketed " chain-wheel," consisting of a narrow wheel or sheave, of a width only slightly greater than that of the chain, and having formed upon its periphery a series of indentations or "pockets," exactly corresponding in size and shape with the links of the chain, so that the chain and the pockets fit together accurately, and slipping of the chain upon the chain wheel becomes impossible. It thus follows that rotation of the chain wheel causes positive motion of the chain at a speed equal to the circumferential velocity of the wheel, in a manner precisely similar to the motion of a rack driven by a pinion, or of one spur wheel driven by another.