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THE CONSIDERATIONS AND STAGES OF A SUCCESSFUL DESIGN

M. L. Puri (December 8, 1961)


In this case study, the various factors to be considered for designing a wagon are discussed from the pre-design stage to the final design, keeping in mind the functional, economic and maintenance requirements.



WAGON DESIGN - A CASE STUDY

INTRODUCTION

1. A wagon is very unobtrusive to look at. In the eyes of common public, it symbolizes slow and interrupted movement. As such, it does not get the popular prestige given to passenger coaches and more ‘modern’ members of the rolling stock family such as diesel and electric locomotives. In fact, quite often, our own engineers refer to a wagon as something inferior: a mere “box on wheels”, which could not require such designing skill or time. For the same reason, the number of amateur wagon critics is also large.

2. And yet, wagons are our most important revenue earners, vital for the national economy. Nor is wagon design as simple as it appears on the surface. A wagon has to move all over the country, where it is handled and maintained by a large body of unskilled and semi-skilled men. If these men do not understand or react favorably to any improvements made in the wagons, the same improvements may actually become draw backs. Further, every change in existing wagons for development towards new wagon designs is subject to the over-riding consideration that altered and new wagons will have to co-exist with the older wagons.

There should be no difficulties in forming trains with both old and new wagons in any marshalling order, or in re-marshalling such trains in the marshalling yards. The users who have geared their handling facilities to particular designs of wagons, must accept if not welcome the changes. The same applies to loading, unloading and trans shipment points on the railway system. Similarly, the changes should not upset existing permanent installations over which the wagons operate or in any way restrict the flexibility of operation. Last, but not the least, is the question of wagon production, which has to be progressively increased to meet the fast growing industrial demands. In course of time materials and manufacturing facilities have been developed in the country for wagon production on a large scale.

Any changes which dislocate or retard material availability or a steady flow in wagon production, cannot be justified unless they offer some very weighty over-all advantages. In this connection, we have to consider not only important steel mills and wagon builders but also the large number of units engaged in re-rolling, forging, casting and manufacturing components for wagon production.

These are fundamental considerations, which have far reaching ramifications; and even in making relatively minor changes in wagon design, meticulous study is necessary to examine the repercussions in different spheres and to ensure that the change will in fact result in an overall advantage.

To illustrate this point, we may take another example. The English copper Penny is unduly large, heavy and costly, and it would be very desirable to substitute it with a smaller and lighter and cheaper coin. Yet, this has not been done. Why? Because a very large number of telephone booths and other slot machines in the United kingdom are designed to operate on the existing Penny, and a change in the Penny would require a wholesale change of these booths and machines, which apart from being very costly could cause a major upset in the transition period. A change in the size of the Penny cannot, therefore, be considered in isolation. The same applies to standard wagon parts and standard dimensions which control coupling, buffer alignment, brake connections, floor heights etc.

It would be thus observed that though a wagon looks simple, its general design and details are closely linked to several external factors and, changes in wagon design have to be properly examined from the stand points of the user, indiscriminately pooled operation within the entire railway system, vastly scattered maintenance facilities, availability of wagon materials and manufacturing facilities for large scale production and, not the least, training and psychology of the large body of unskilled and semi-skilled men who have to handle and maintain the wagons.

3. In the background of what I have said, this lecture is intended to give you a general appreciation of what is involved in the design of a wagon from commencement of preliminary studies to the stage of standardization. I shall also touch upon the broad classification of wagons with particular reference to special types of wagons. Common items: bearings, suspension, brake- gear, draft gear and buffing gear will be dealt with separately. If time permits, we may also touch upon some other subjects of general interest.

4. Starting from scratch, design of a wagon incorporates the following stages:

4.1 Project study preceding design.

4.2 Wagon design proper leading to particular specification and key drawings for prototype manufacture.

4.3 Prototype testing and processing of modifications from the stand points of: fundamental effectiveness, structural strength, stability and riding characteristics, coupling, buffing and brake characteristics and any other features that are considered important.

4.4 Examination of design detail from the stand point of productibility and approval of builders manufacturing drawings, with such changes in Particular Specifications and connected Standard Specifications as may be considered necessary.

4.5 Collection and scrutiny of service data (including both operation and repair / maintenance data) and alterations to remove service draw-backs.

4.6 Standardization to the extent practicable based on the prototype tests and production / service experience on the wagon.

5. It is not my intention to go into details. The main idea is to give you an outline of what we do and some food for thought, so that in your day to day working you may be conscious of the Design and Standards aspects of wagons. It is hoped that you attention to these aspects would provide value information and guidance to the design office and those of you who will be connected with the Design and Standards work are able to proceed along rational lines.

PROJECT STUDY PRECEDING DESIGN OF A WAGON

1. A wagon has to be considered as:

1.1 A carrier of freight
1.2 A rail borne vehicle
1.3 A unit to be produced, repaired and maintained.
1.4 An economic unit.

2. WAGON AS A CARRIER OF FREIGHT

2.1 Movement of freight by rail from one point to another involves:

2.11 Packaging.
2.12 Handling from point of origin to wagon.
2.13 Transportation by rail, including trans shipment.
2.14 Unpack aging.

2.2 All aforesaid operations in freight movement cost time and money. Besides, there is the over-head of damage to lading in transit, which the national economy has to bear and railways have to pay for. As such , railway wagons as carriers have to be designed for the most economical balance between the over-all time freight has to be in transit from origin to destination and the over-all cost of transportation including the loss through lading damage. This has to be with due regard to the prevailing environment for rail transport: ancillary packaging / unpackaging and loading / unloading methods employed; operating conditions obtaining on the railway system, particularly in the marshalling yards; and susceptibility of freight to damage through effects of weather or vibrations / impacts, as also the protection that the lading requires against pilferage in transit. These factors have a decisive influence on the design of space in the wagon provided for pay-load and facilities for loading and unloading the wagon.

2.3 Examples are:

2.31 In small quantities, liquids and gases are best transported in barrels or cylinders in general service wagons but for bulk transport, tank wagons are provided.

A special case is the LPG tank wagon, which is now being designed. At present, a major oil company is transporting the liquefied petroleum gas for domestic purposes from their refinery in Bombay to Delhi in Cylinders, which are crated and packed in covered wagons. In this manner, a covered wagon with a gross weight of 32 tons carries a pay-load of under 8 tons of liquefied petroleum gas. However, with the LPG tank wagon, the pay-load will be about 12 tons with the same gross weight. As such the cost of transportation which is substantial, would be cut down by about 1/3rd for the consumer.

2.32 Where rail transport has to be integrated in an industrial belt, special wagons such as hoppers are provided for mechanical loading and automatic discharge on bunkers.

2.33 For movement of extra heavy or over-sized consignments, special well wagons have to be provided. Such wagons are otherwise uneconomical, but they are justified when the alternative of dismantling the consignment such as a heavy machine or the necessity of fabricating at site a unit like fractioning column of refinery, are considered. In some cases, the aforesaid alternatives may not be practicable at all.

2.34 On considerations of cost and time involved in packaging / unpackaging and in handling for loading / unloading unit containers, which incidentally permit optimum utilization of pay-load space, are designed to be moved as such by road, direct on to the wagon and vice-versa.

The use of such containers has assisted several rail-roads to compete successfully with road traffic which offers the advantage of door to door delivery. Another use of similar containers can be considered for bulk movement of industrial products with change in gauge. For example, in changing over from 20 ton axle-load bogie wagons on broad gauge to 10 ton axle-load bogie wagons on meter gauge, the containers could be so designed that the number that is accommodated on a broad gauge 8-wheeler is double the number that can be accommodated on a meter gauge 8-wheeler, so that the number of meter gauge wagons required is exactly twice the number of broad gauge wagons and trans shipment can be carried out simply and expeditiously.

3. WAGON AS A RAIL BORNE VEHICLE.

3.1 As a rail borne vehicle, a wagon has to be designed with the limitations imposed by permanent way, bridges, tunnel and signaling and inter-locking installations. These limitations are

3.11 Gauge : Broad (5’- 6”)
Meter (1 m.)
Narrow (2’-6”)
3.12 Axle – Broad gauge (22.5,20,16 tons)
Load Meter gauge (10, 12 tons)
Narrow Gauge (6 and 8 tons)
3.13 Intensity of track : Broad gauge – 2.3 tons / ft. run
Loading for trailing Meter gauge – 1.16 tons / ft. run
Load on M.L. Narrow gauge – 0.85 tons / ft. run
3.14 Moving dimensions.
3.15 Wheel base.
3.16 Projection of ends and ver sine on curves.
3.17 Ruling curves.
3.18 Ruling grades.

3.2 In order to provide complete flexibility for shunting, marshalling and train formation, standard designs of couplings, buffers and brake gear have to be employed and placed at standard locations. Similarly, the floor height has to be kept a standard in relation to the platform heights at which loading and unloading is done. Further, connections between one wagon and the other should be such that coupling is possible without regard to the direction in which the wagon is facing. Incidentally this is a disadvantage in the case of meter gauge couplers, where yoke end must face hook end and when this is not so, the wagon has to be turned.

3.3 In order to form goods train with optimum train loads to be run at optimum speeds, all goods wagons intended to be indiscriminately used in a pool, should have a uniform draft capacity and speed potential. In order to observe uniform impact speeds during marshalling, buff capacity should be regulated according to gross weight of wagons. Factors relevant to speed potential are riding characteristics with due regard to vertical and horizontal forces exchanged between wheels and the track and consequent damaging effects thereof on track, wagon structure and not the least, lading and adequacy of brake power.

4. WAGON AS A UNIT TO BE PRODUCED, REPAIRED AND MAINTAINED

4.1 At all times and particularly now, when the wagon fleet has be enlarged very fast to keep pace with the rapidly expanding demands of industrialization, our wagon designs should be such as can be produced in large number with indigenous materials and production facilities. What is needed is the maximum volume effect which is a function of effective ness of a wagon as a freight carrier and the number of such wagons that are available for carrying freight. Accordingly, a judicious balance has to be struck between modernization of design and the producibility aspect of design. We have to ensure that all methods of manufacture or fabrication available in the country are fully employed: forging, casting and welded fabrication in the manufacture of components; and riveted or welded construction in fabrication of the wagon itself. This would also apply to types of bearings (roller bearings or plain bearings), springs (laminated or coil springs), that can be produced in the country.

4.2 At the same time, designs have to be taken in hand keeping in view the future development trends in the country, so that when particular types of demands in freight movement materialize or when it does become possible to produce more modern designs of wagons economically in bulk, the necessary designs, duly tested and proved, can be released, can be released for production without delay. This would apply to special type of wagons that will be required to cater for future demands of industrialization on one hand and use of high tensile steels, light alloys, welded integral construction, and extended use of steel castings and roller bearings on the other.

4.3 Along with considerations of production, considerations for repairs and maintenance have to be taken into account. If the workshops are only geared for riveting work, it would not be prudent to rapidly place on line a large number of fully welded wagons. Even in day- to-day alterations, proper allowance has to be made for material and components that are available in stock and the losses that are likely to be incurred through obsolescence of materials or parts which are superseded. At the same time, it has to be borne in mind that material and components for the new design may not be readily available and that could result in loss of wagon availability.

Design side should, therefore, work in close collaboration with the railways, so that it can make a realistic appreciation of the practical implications of changes in wagon design and keep the railways informed of the future design trends, so that timely action is taken for controlling stocks and building up the necessary repair and maintenance facilities.

5. WAGON AS AN ECONOMIC UNIT

5.1Goods in transit means capital locked up for the owner. As such, less transit time is welcomed by users of rail transport. Faster freight movement also means fewer wagons for a given freight movement and, therefore, higher productivity of the transport system. Accordingly wagon design has to cater for the maximum through-put of traffic from available line capacity and the minimum requirement of time for loading, marshalling and unloading.

5.2The salient factors in the design of wagons which govern through-put of freight traffic from a given line capacity are:

5.21 Tare weight required per ton of pay load.
5.22 Intensity of track loading provided by the wagon.
5.23 Speed potential of the wagon with due regard to its riding characteristics and brake power.
5.24 Revenue earning potential as reflected by the ratio: empty wagon miles to loaded wagon miles in a repeating cycle.

5.3 Tare weight per ton of pay load can be reduced through:

5.31 Economical use of material in the wagon structure. This requires as uniform stressing of the entire structure as possible.
5.32 Employment of high tensile steels and light alloys, whose load bearing capacity for the same weight is higher than that of ordinary structural steels.
5.33 Selection of a method of fabrication which is conductive to lightness. This indicates changeover from riveted to welded construction, so that the weight of riveting laps and rivets heads may be avoided.
5.34 Judicious disposition of different loads to which a wagon structure is subjected, so that as far as practicable, the loads may be direct tensile or compressive, avoiding bending to the maximum possible degree.
5.35 Employment of integral mode of construction, so that the ‘container’ part of the wagon may also be effective in resisting loads.

5.4 In order to obtain optimum intensity of track loading, particularly with low density freight, the approach has to be towards maximum cross section for pay-load practicable within the permissible moving dimensions. Similarly, the effort should be to reduce the empty space between the container portions of consecutive wagons in a given length of train. This would tend towards bogie wagons and a reduction in the projection of buffers without causing fouling of adjacent vehicles on curves and turn-outs. From the latter stand point, side buffers placed outside the headstock constitute a disadvantage.

5.5 Maximum permissible speed of a wagon is determined in terms of the vertical and lateral forces exchanged between the wagon wheels and the track. These forces are governed by the load pattern of the wagon, its suspension including damping and the controlling clearances between track and wheel set, wheel set and axle-boxes and axle boxes and their constraints in the wagon. Further, they are determined by irregularities in the track itself. They are not simple to estimate and guidance has to be taken from actual test results on different stretches of track.

5.6 In order to reduce the incidence of empty running, the wagon has to be made versatile to carry different types of freight. On the other hand, such versatility takes away the features that may be required for special type of freight e.g. the need for automatic discharge through hoppers. Accordingly, this aspect has to be carefully studied with due regard to volume of special demand, possibility of operating in close circuits, operational economics through reduced wagon turn round and guaranteed availability of special type of wagons for the purpose for which they are built.

SCHEDULE OF REQUIREMENTS FROM WAGON DESIGN

1. The preceding techno-economic Project Study would determine the broad basis for a Schedule of Requirements that the design of the wagon concerned will be expected to satisfy. Such a schedule will cover the following aspects:

1.1 Civil Engineering.
1.2 Operating.
1.3 Lading.
1.4 Production, Repair & Maintenance.
1.5 Standardization.
1.6 Economic.

2. CIVIL ENGINEERING

2.1 Track Gauge.
2.2 Maximum and minimum permissible moving dimensions.
2.3 Maximum permissible axle load ( for trailing load)
2.4 Maximum permissible intensity of track loading (for trailing load).
2.5 Ruling curves (including turn-outs) and grades.
2.6 Ruling length of loops for crossings.
2.7 Maximum and minimum permissible diameter of wheel and controlling dimensions pertaining to tread profile, distance apart of inner wheel faces, etc.
2.8 Maximum and minimum height of floor (excluding well wagons), height of buffers and couplings, and distance apart for centers of buffers (side buffers).
2.9 Maximum rigid wheel base for 4-wheelers, minimum rigid wheel base for bogie trucks, maximum permissible length of body or roof of stock, maximum distance apart between any two adjacent axles, maximum distance apart of bogie centers and ratio of distance apart of bogie centers to length of body of vehicle.
2.10 Maximum permissible values of vertical dynamic impacts and maximum permissible values of lateral forces on straight and curved track.

3. OPERATING

3.1 Closed circuit, limited pool or indiscriminately pooled operation.
3.2 Marshalling practice and maximum impact speed in marshalling.
3.3 Ruling train loads and type and disposition of motive power on the train.
3.4 Brake system, vacuum or air operated; whether supplemented by dynamic / regenerative braking, emergency braking distance.
3.5 Maximum speed potential required and standards of maintenance of track on which maximum speed is to be operated.
3.6 Range of temperature, humidity, atmospheric pressure, corrosive action of atmosphere, etc. to which the wagon will be subjected in operation.
3.7 Whether the wagon is required for mechanical loading, unloading or trans shipment and type of mechanical handling equipment to be used.

4. LADING

4.1 Type if freight: packed, en-bulk or both: carrying capacity.
4.2 State of lading, solid, liquid, gas or any intermediate state.
4.3 Condition of lading: temperature, pressure.
4.4 Properties of lading: handling hazard, corrosive action, combustibility, expensive characteristic, and poisonous characteristic.
4.5 Fragility of lading: effect of vibration and shock.
4.6 Method of loading, unloading and trans shipment.
4.7 Special requirements: security against pilferage, water tightness, air tightness, air-conditioning, refrigeration, etc.

5. PRODUCTION, REPAIR & MAINTENANCE

5.1 Material availability.
5.2 Development of ancillary industry for manufacture of wagon components.
5.3 Production facilities available with wagon Builders.
5.4 Repair and maintenance equipment available in central repair workshops and sick-lines, with particular reference to capacity of traverses and overhead cranes, height of crane gantries, size of wheel lathes, length of repair belt stages, lifting facilities in sickliness etc.
5.5 Stocking facilities and impress levels on the districts.
5.6 Training of repair and maintenance staff.

6. STANDARDIZATION:

6.1 Use of standard components to ensure inter-culpability: buffers, draw books, screw couplings, center buffer couplers and brake connection.
6.2 Use of standard components to permit maximum interchangeability with minimum variety in respect to replaceable components: wheels, axle boxes, spring gear details, brake gear details and body details. This is calculated to improve wagon availability with minimum capital investment in spares and minimum cost of repairs and maintenance.
6.3 Use of standard sections and sizes of materials to standard specifications in wagon fabrication. This is calculated to reduce cost of materials, ensure their quick delivery and simplify procurement, stocking and distribution.

7. ECONOMIC:

7.1 Tare weight per ton of pay load.
7.2 Wagon utilization and availability.
7.3 Requirements if wagon reliability and limits of lading damage.
7.4 Resistance to movement in train working per ton of gross weight.
7.5 Limits of loading, unloading and trans shipment times.
7.6 Cost of repairs and maintenance in service life.
7.7 First cost per ton of pay load.

WAGON DESIGN PROCEDURE

1. After formulation of the Schedule of Requirements for design of a wagon, processing of the design proper is taken in hand.

Progress of a design is not along a straight line. It is rather in progressively diminishing concentric circles where each successive circle represents a step in giving concrete shape to the general concepts, while retaining all the essentials. The development process rests both on analysis and synthesis, with such verificational tests as may be required from time to time.

2. Since the primary purpose of a wagon is to serve as a carrier, the first step is to tentatively fix the shape and size of the ‘container’ part in the wagon. The next step is to select or develop a suitable under frame for the container and decide upon the method of mounting the container on the under frame.

Note: In integral construction the container may become part of the under frame, partially or completely.

The container cum under frame unit has then to be provided with running and suspension gear to move on rail track. The next stage is to fix its ancillary equipment, namely, draft gear, buffing gear and brake gear. Treating the wagon as a whole, both in the empty and loaded conditions, its position of center of gravity and load pattern have to be studied from the stand point of stability and other riding characteristics. Any obvious changes or adjustments that may be called for in these regards have to be incorporated.

3. In the second round, the container, it’s mounting, under frame and the different gears on the wagon are examined separately in their relative juxtaposition, as indicated in the first stage. This enables each unit being examined in greater detail and taken towards more concrete shape. The units, as revised, are again examined from the standpoint of the wagon as a whole and necessary adjustments made. This process is carried on till a functionally successful design is evolved. In the process, a series of studies, investigations, calculations and exploratory / confirmatory tests have to be carried out.

The final functional design is described in Particular Specification and a set of key drawings pertaining to the wagon in question. The processing leading up to Particular Specification and key drawings is kept on internal documentation of the design; general write-up, study drawings, stress calculations, results of tests, etc.

4. On the basis of Particular specification and key drawings one or more prototype wagons are built. These prototypes are subjected to functional tests, static load (vertical, horizontal and oblique) tests, impact tests and oscillation tests. Functional tests establish the suitability of the wagon as a carrier and as a vehicle for operation in the manner envisaged. Static load tests are intended to stimulate the loads to which the wagon would actually be subjected in service, including, where practicable, the static equivalent of dynamic loads. Impact tests are intended to stimulate the conditions obtained during marshalling. Oscillation tests are to assess the stability and riding characteristic of the wagon at different speeds with different standards of track maintenance. They indicate the value of dynamic augments that may be expected in service and, give a quantitative measure of vertical and horizontal forces exchanged between the wheels and the track, as also various parasitic oscillations during run. Another important type of test is with regard to damage to lading due to vibrations, impacts or effects of weather.

5. Weaknesses of design revealed during prototype tests are overcome through suitable modifications, a process which continues till a successful functional design is obtained. Particular Specifications and key drawings revised to incorporate the aforesaid modifications are then issued for bulk production. The Wagon Builder examines these drawings and specifications closely from the standpoint of producibility and offer alternatives wherever considered necessary. These alternatives are normally accepted, provided they do not compromise the functional requirements or disturb the standardization aspect. The Wagon Builder then goes into production and on completion of the contract, furnishes a set of ‘as made’ drawings, which accurately describe the wagons that are produced by the Builder against a particular contract.

6. Wagons of the same basic design manufactured by different builders will have differences in detail, depending upon the materials and methods of fabrication adopted by different builders. At times the design department deliberately introduces variations in wagons coming from different builders to obtain experience on alternatives. Performance of new wagons in service is monitored and experience of different railways in respect of service effectiveness, repairs and maintenance is obtained. In the light of experience so gathered, the question of standardization is taken up and design features, which have given the best overall advantage from standpoints of service effectiveness, production, repairs and maintenance, are recommended for adoption as standards. Broadly speaking, the total period from commencement of techno-economic Project Study of a new design to the stage of standardization would run up to say 10 years: Project Study – 6 months, Particular Specification and key drawings – 12 months, Prototype manufacture and testing – 24 months, Release of Particular Specification and key drawings for bulk production – 6 months, Approval of Manufactures’ drawings and commencement of bulk production – 12 months, service trials and collection of data for standardization – 5 years.

WAGON DESIGN PRACTICE

1. WAGON CLASSIFICATION

1.1 Freight stock is broadly divided into two categories: 4-wheelers and 8- wheelers. For special requirements, wagons with a larger number of wheels are also built. They are usually for extra heavy consignments, where with 8-wheels the permissible axle loads are exceeded. Selection of axle load and whether the wagon should be 4 or 8- wheeled is with due regard to the optimum carrying capacity required of the wagon, as also the anticipated value of tare weight per ton of payload.

1.2 In each of the two categories, namely 4-wheelers and 8-wheelers, there are different classes of wagons:

1.21 Covered.
1.22 Open.
1.23 Flat.
1.24 Tank.
1.25 Hopper.
1.26 Well.
1.27 Special.

In each class there are different types to suit different requirements. For example, a covered wagon may be of the ordinary type made suitable for live stock by providing wooden flooring, breast bars and ventilators; or it may be lined with timber or other insulation material to make it suitable for transport of explosives.

2. CARRYING CAPACITY

2.1 In the context of rapid industrialized development, the prime requirement is maximum throughput of freight with the available line capacity. As such, the trend is towards maximum possible axle loads and intensity of track loading. This calls for maximum cross- section of the payload space, particularly for low density freight. As such, new designs of open wagons for movement of bulk materials are wider and have higher body sides and ends. In broad gauge ‘O’ type wagon, internal width is 9’-4” and internal height 5’3”. In the BOX wagon, on the other hand, internal width is 10’-10” and internal height 6’-6”, which increases the cross-sectional area for pay load by nearly 33%.

Measures are also under consideration to remove the relatively less costly infringements in moving dimensions, such copings of good platform, to permit more width in the wagon cross-section and thereby further increase the payload cross-section.

2.2 With the available moving dimensions on broad gauge, the ratio “width of goods wagons to track gauge” is 1.82. The same ratio on meter gauge is 2.74. In other countries this ratio varies between 2.2 and 3.2. It would be thus observed that the moving dimensions on our broad gauge handicap the Wagon Designer in obtaining the optimum proportions that may be otherwise possible.

3. LENGTH OF WAGON

3.1 The length of the wagon over couplers is equal to the length of the container part of the wagon plus the minimum clearance required between adjacent containers to prevent fouling on curves and turn- outs, plus any additional length that may be necessitated on account of buffers, couplings or other end fitments.

3.2 The clearance between adjacent containers reduces the intensity of track loading and therefore the freight throughput. As such, in a good design practice the actual clearance should not be more than the minimum clearance required from the consideration of fouling on curves and turn-outs. For the same reason, it is preferable to use bogie wagons instead of 4-wheelers, since the same clearance is then required for a much greater length of the container, and thereby the total effective length of the container in a given length of train is increased.

3.3 From the above considerations, buffers which are accommodated completely or partially behind the headstock like the center buffer couplers have an advantage over those which are completely outside the headstock such as side buffers.

3.4 The length of the container itself is so fixed that the payload plus tare weight will equal the number of axles multiplied by the selected axle load. However, at times, for example in the case of extra dense freight, the actual length of the wagon may have to be made more than the indicated length, in order to accommodate brake and other gearing between the bogies or from considerations of suitability and riding.

4. WHEEL BASE OF FOUR WHEELERS AND BOGIE CENTER DISTANCE FOR BOGIE WAGONS

Broadly speaking the wheel base of a four-wheeler and center to center distance between bogie pivots in the case of bogie wagons is approximately two-thirds the length over headstocks. This permits a reasonably even displacement of the ends and center of wagon on curve track. (The ends of the wagon are displaced outside the curve and the center of the wagon is displaced inside the curve). At the same time the aforesaid proportion reduces the maximum value of bending stress in the under frame, thereby permitting a lighter under frame. It is also conductive to good riding.

5. HEIGHTS OF BUFFER, COUPLER AND FLOOR.

For wagons which have to be operated in a general pool, standard heights of buffer, coupler and floor have to be observed to permit couplability and enable loading, unloading and trans shipment on existing platforms and with existing floor heights of road vehicles used for freight movement.

However, if wagons are required to work for special purposes along close circuits, variations in these dimensions can be made to improve their service effectiveness, but then such wagons cannot be used in the general pool and their proportion of empty running usually increases.

6. WHEEL DIAMETER

6.1 The wheel resting on the track stresses the rail in two ways: local stressing stresses the rail and itself in two ways. The wheel and the rail are locally deformed at the point of contact to a radius (with the present materials used for rails and types); and the rail as a whole is bent as continuous beam. The aforesaid local deformations get severer with the reduction in wheel diameter. Accordingly, from considerations of rail and wheel life and in order to prevent plastic flow of the tyre / rail material, there is a minimum limit prescribed for wheel diameter. Correctly speaking, this limit of wheel diameter has to be linked to the axle load and the speed at which the particular axle loads have to operate.

6.2 There is also a limit for the maximum wheel diameter which is prescribed from considerations of the wheel fouling the under frame members or wagon floor. Further, to permit wheel interchangeability it is not desirable to have several standards for wheel diameters. Accordingly, on Broad gauge we have three standard wheel diameters for freight stock: 3’-7”, 1 meter (recently introduced), and 3 meters. The matter is being further examined but we may standardize the one meter wheel for all future designs of freight stock, the same as on the continent, where metric systems is in force.

6.3 Along with the question of initial wheel diameter, is the question of wear allowance on the tread. A small wear allowance would necessitate frequent wheel changes and a large wear allowance would necessitate a higher value of up sprung tare weight and a reduction in the permissible change in floor, buffer and coupler heights due to spring deflection and spring settling. In effect it would mean harder springs with adverse repercussions on riding and stability. In U.S.A. hard wearing unit wear wheels are also employed. In our environment they may not be practicable but a compromise may be made giving wear allowance for wheel life of say 10 or 20 years. With modern wheel lathes, working with car bite tools, which can take fine cuts for reconditioning, the total value of wear allowance can be bro ught within about 25 mm. Another alternative is to weld on the whole tread profile, as is done in West Germany and thereby have much greater wheel life with limited wear allowance.

 

 

 
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