6_Design_approach_for_transportation_equipment - Design...

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Unformatted text preview: Design approach for transportation equipment 1. Introduction In general, transportation equipment is used in transportation systems and thus the design requirements for equipment largely depends on the demands from the entire transportation process. The transportation equipment is part of an overall system and the performance of the total system is determined by the individual component performances and the interactions between the various components, forthcoming from the overall transportation process characteristics. Today system theory, systems analysis and operations research techniques are available as key tools for the analysis of overall transportation systems and these tools will contribute to determine the major design parameters for the various equipment types in the systems. Computer simulations will give information about dynamic behaviour and the sensitivity of variables, both for the complete transportation system and detailed sub-systems and equipment. This systems approach will result in an analysis of the total system and the required conditions to fulfil the agreed transportation system performance. Unavoidably there is a general demand to realise required capacities at the lowest possible cost per product unit (service performance) and so a systems approach always demands an estimate of the total investment and the operating cost for the transportation system and components. To determine the requirements for the various system components (handling equipment, vehicles, storage equipment, storage systems, control automation etc.) the following questions are relevant: • what time is available for the transportation system; • what is the effective production time, when the transportation system is in operation; • what is the effective productivity, when the system can really operate. The answers on the above questions, combined with the systems analysis will result in the requirements for each individual systems component (equipment, planning tools, control systems etc.). The next considerations will focus on the design approach for transportation equipment; which activities are required to present a proper design specification from where an equipment manufacturer can start the detailed design and manufacture of the specified transportation equipment. 2. Design requirements for equipment For the design of equipment the following areas of requirements should be considered: 1 a. b. c. d. Functional requirements (what?); Structural demands (how?); Economic requirements (total operating cost, life cycle cost?); Optimisation of the concept (priorities?). In more detail the following topics can be mentioned: Ad a Functional requirements What kind of performance is required from the equipment, under which system conditions and what are the quantitative expectations. This can be described as mentioned below: - Transportation performance (transported mass per time period). The basic performance is determined by a variety of factors: • speeds and acceleration/deceleration rates of the main drives (hoisting/lowering, trolley travel, crane travel, vehicle speed etc.); • transported volumes per second (conveyor belts); • fluid pressure in the equipment (pneumatic conveyors, hydraulic equipment); • attainable number of handling cycles per hour; • quality of the load pick-up devices (spreader, grab, vacuum equipment, special attachments); • load control (load suspended on wire ropes, guided load by means of mechanical devices, etc.); • delays between the various sub-cycles of the equipment handling cycle; • type of control for the equipment; • dynamic behaviour of the equipment (influences from equipment dead load, structural stiffness, drive control, etc.); • special provisions as an interface to the next transportation process. - Type of control Is the equipment manually driven or automated; what is the influence of the operator; is the equipment controlled in an overall automated system; what is the required control interfacing etc. Safety demands What provisions must be made to ensure a safe operation in a variety of operational situations. When working in an automated mode which requirements must be met to avoid accidents Environmental requirements The society tries to avoid the disadvantages of industrialisation and so equipment has to meet certain generally recognised requirements, (sometimes stipulated by law) with regard to noise levels, water and air pollution, the use of scarce material, the consumption of energy and the possibilities for the application of recyclable materials. The interfacing in the overall system These requirements determine how the equipment is interconnected in the overall system, which commands control the exchange of loads, which controls avoid damages to equipment etc. - - - 2 - - The availability of the equipment Requirements for maximum periods of ont-of-service must be specified. Required overhauls, periodic maintenance, functional checks etc. must be examined and specified. Reliability Especially in automated transportation systems the equipment reliability is of utmost importance. The MTBF (Mean Time Between Failure) and MTTR (Mean time To Repair) are the most important characteristics. The maintainability’s is a related functionality which determines the possibilities for maintenance during operations, the ease of access to vital equipment components and the possibilities to exchange components in running condition. Ad b Structural demands In order to enable the fulfilment of the functional requirements the equipment must be shaped, must have all kind of properties; some of them are given below: - The technical concept This describes the major technical systems, components and required characteristics as well as the structural concept, major dimensions etc. - Shape of design concept The customer may have specific demands for the main structural concept of the equipment (box girder, lattice girder, machinery trolley, rope driven trolley, continuous unloader, stacking and retrieval equipment supported from the top etc.). - The absorbtion of and resistance to loads This asks for the specification of required stiffness, maximum allowable stresses, the resistance to fatigue loads, required stability under various operating conditions, the absorbtion of dynamic influences. - Manufacture and erection The customer may have specific demands about the manufacture of components and the assembling of sub-systems. The applied materials and painting system as well as the preferred electrical sub-systems should be described as well. Special attention must be given to the erection of large equipment. Erection method, preferred support equipment, maximum area for the erection site etc. are of importance. - Maintenance demands Lay-out of machinery rooms, accessibility to components, selection of components, lifetime and performance of sub-systems etc. should be described. If a minimum maintenance-free operating period (e.g. 1000 operating hours) is required, this must be indicated. Ad c Economic requirements A systems analysis may have learned that a specific balance between technical functionality and economic requirements should be met. Some examples are listed below: - Equipment lifetime The longer a required lifetime, the more important is the resistance for fatique loads, properly designed drive systems, quality of manufacture and a proper surface protection (painting). These aspects also positively influence the residual value at the end of the economic lifetime and thus the yearly deprecations. 3 - - - - Potential for future capacity expansion Already built-in provisions for a future increase of performance or adaptation to new technological developments may contribute to an extended feasible lifetime. Sensitivity to handle various products (services) Flexibility to perform under changing operational circumstances helps in maintaining the projected economic lifetime even when the operating conditions for the equipment have changed. Energy consumption, durability Drive-line concepts (electric, hydro-static, diesel etc.) determine the resulting fuel demand. A high drive-line efficiency and a direct electrical supply system will be beneficial to control energy consumption. The application of recyclable and durable materials is of increasing importance. Overall operating cost These are determined by the yearly fixed cost (depreciation, capital interest, inspection cost, insurance, painting) and the variable cost per operating hour (energy, maintenance, spare parts, lubrication, labour cost, tires, wire ropes, tools etc.). In many cases more expensive quality products result in lower yearly total operation cost, due to a higher availability/performance and lower variable cost (less maintenance, less break-downs). Ad d Optimisation of the concept After finishing the first three major design requirement area’s some first design concepts can be realised and assessed (analysed) on their fulfilment of functional, structural and economic requirements. After that an essential activity should be made: the optimisation of the concept(s) covering the following elements: - Test the fulfilment of the user’s philosophy. The user may have various goals such as * striving for the lowest initial investment; * looking for the lowest overall life cycle cost; * the equipment must show the lowest environmental pollution; * the equipment must have maximum flexibility to operate with the materials under other conditions; * the equipment must be maximally dedicated to the operator’s requirements (comfort, control, accessibility); * the equipment must allow a gradual automation in the future; * the equipment must have a modern, good looking shape resulting in a maximum appeal and environment for employer. Some of these topics will dominate the design concept and in general the concept is a compromise, however it is a must to analyse the major criteria that will be used in the assessment of a design - Cost/performance ratio After defining one or some typical operational situations (load cycle, one-day operation, representative load-pattern, etc.), the concept can be analysed on its cost/performance ratio which requires estimating capacity for maintenance cost, operating cost, energy consumption, availability etc. The determination of the future performance under operating conditions is quite difficult and requires the 4 support form the operational staff and data about operational disturbances which will decrease the designed technical capacity. Although it could be considered as a separate design topic the selection of load handling devices is an important topic for the overall equipment performance. Examples of such load handling devices are: clamshell (grab), container spreader, pallet hook, magnet, paper roll clamps. - The requirements for such handling devices are: * proper positioning onto/over the load * quick release from the load * easily adaptable to various dimensions of the load * quickly exchangeable (in case of break-downs; for various types of loads) * a low mass (saves energy in every load cycle) * shock-absorbing; shock resistant * capabilities to function in automatic mode. In many cases the characteristics of a load handling device may influence the operational capacity with ± 25%. Equipment size (required capacity/performance) Terminals, transportation companies etc. are faced with the question: many smaller units or only one or a few large units. Although large handling (transportation) units can benefit from economies of scale (lower cost per unit handled), there are some more aspects to decide on the optimal size of equipment: * the allowed loads on quay wall, site surface * clearance dimensions on the site * ratio between peak demands and average capacity * utilisation rate of the equipment * restrictions in various operating conditions (vessel sizes, transportation track etc.) * (future) requirements for automation. When it comes to handling and storage there is a tendency to install larger (and thus less) equipment to benefit from the economies of scale (lower life cycle cost per unit handed). In automated processes the application of smaller equipment is sometimes preferred due to a better redundancy and maintainability (MTBF, MTTR). Optimisation of the concept is a real itirative process and requires a broad knowledge of all interfering aspects in the design of equipment. 3. Purchase specifications Especially the procurement of large, expensive equipment asks for a proper description of the equipment to be purchased, and such specifications are normally presented by the purchaser (the end user or its representative e.q. an engineering consultant). The specifications form the basis for the purchasing (negotiating) process, however the specifications presented by the purchaser should never release the manufacturer from his responsibility to provide a safe and properly designed piece of equipment. 5 An outline of such equipment specifications is presented below, based on handling equipment for terminals in seaports. Purchase specifications 1. general requirements 2. special requirements 3. design 4. manufacture and erection 5. options Input from operations, engineering, maintenance, equipment operators, manufacturers, controller, purchasing department is essential. 1. General requirements • definitions • intent • general description • ownership of joint developments • patent indemnification 2. Special requirements • scope of delivery (deliverables, delivery date, acceptance) • progress (delays, additional work efforts, modifications, schedule) • management (project, quality assurance, inspection plan) • insurance • indemnification on liability • disputes (“Raad van Arbitrage”, FEDIC) • liquidated damages (“Penalties”) • compliance with regulations (law, taxes, duties, fees) • warranty • design responsibility • bankruptcy • ownership of equipment and components • terms of payment 3. Design • drawings, certification, documentation • referenced specifications (AWS, ASTM, DAST, DIN, NEN,FEM, VDI, VDE) • general design aspects (site + operating conditions, main characteristics) • design criteria (classification, loads, duty cycle, calculations) • main drive systems (characteristics of drive systems will influence the design of mechanical, structural and electrical components • mechanical design • electrical design • miscellaneous (auxiliary drives, load limiting device, name plates, tools, etc.) 3a. Mechanical design • general directives • criteria for mechanical calculations • wheels, trucks 6 • gearing, bearings, seals • brakes, couplings • wire ropes, sheaves, rollers, drums • hydraulic systems • lubrication systems • stowage devices • equipment alignment, rail track tolerances 3b. Structural design • general directives • fabrication, inspection (welding) • structural design calculations (allowable stress, deflections, frequency calculation, fatigue calculations, buckling, stability) • housing(s) for machinery • operators cabin(s) • stairs, ladders, platforms and walkways (important for the operators access, the maintainability) 3c. electrical design • general directives • criteria for electrical calculations • control systems (schematic, bus-systems, standard interfaces) • wiring and conduits • motors, generators, transformers, electric brakes • power supply, distribution, festoon cables • master switches, operator’s information (influencing the operator’s control and so the cycle time) • limit switches, operator’s information • protective and safety devices • lighting, communication, convenience and welding outlets • electrical control room, cubicles, enclosures • auxiliaries (air-conditioning, fire protection, earth brushes etc.) 4. Manufacture and erection • workmanship (qualification of welders, grading of machinery) • material quality • inspection (conformity with drawings, sub-assemblies, inspector’s office) • shop assembly and testing • shop cleaning and painting (surface preparations, coating applications, coating system) • field erection (site, provisions, regulations, maximum loads) • final testing for acceptance (commissioning) • packing and marking (reference codes, mass, packing list) 5. Options • elevator • equipment for data communication • automatic positioning, location control • remote control • maintenance monitoring system 7 • • • tele-diagnostics, tele-service recommended set of spare parts operator’s training program 4. The procurement process The entire process from the first initiative to acquire new equipment until the day the equipment is satisfactorily running into operations may take several years. This is often performed as a project approach with one dedicated team responsible for the whole process. In more detail: • Motive or inducement The motive for the procurement of new equipment can be a new service addition, the expansion of capacity, the replacement of old equipment, a change in handling process, the introduction of automation, the improvement of working conditions for the operator, new requirements for the environment, a decrease in handling cost etc. • Objective After the recognition of the motive the objective with the procurement should be defined: what’s the required capacity, which type of equipment, what’s the company’s philosophy etc. • Feasibility study In this analysis it should be checked whether the assumed equipment concept will be technically feasible, will meet some economic demands, does fulfil societal demands etc. Such a feasibility study may cover the analysis of various proposed concepts and might encompass the impact on the existing operations (required modifications, a process redesign) • Decision on project responsibility In an early stage it should be decided which person or team (with one team manager) will be responsible for the entire procurement process and this person or team must be announced in the company including a brief description of the objective and related responsibilities and authorities. • Draft of the equipment specifications After some fact finding some design concepts must be considered including a basic engineering of each concept. From there the preliminary specifications can be written down, including some general arrangement drawings and a brief description of the required functionality. • Invitation for pre-tendering In this stage preferred suppliers (contractors) are invited to present a proposal for the delivery of the requires equipment. Depending on the local situation and the type of financing it must be decided whether the pre-tendering will be on invitation, will be in public, will be directed only to one preferred supplier or will be directed to a consortium that should present a BOT-arrangement (Build, Operate and Transfer). • Presentation of proposals Based on the presented specifications, the selected tenderers will submit a proposal for the equipment including a description of the major characteristics, the related cost, delivery time etc. The contractor may propose alternative concepts that will fulfil the requirements, and may be advantageous over the described concept in the tender documents. 8 • • • • • • • Explanations of the proposals by the tendering suppliers. In this stage the suppliers are invited to further elucidate their proposals. It may include visits to the suppliers manufacturing plant (to check the potentials, quality design and manufacture capabilities etc.) and a verification in the suppliers support of the presented specification. In some cases visits are made to relevant installations earlier supplied by the potential contractor. Evaluation of the presented proposals This is the most crucial stage in the whole procurement process. The evaluation will comprise a large number of technical features (such as: design approach, component types, sizing of major elements, dimensions of components, etc.), commercial conditions (delivery time, payment periods, warranty, liabilities, currency etc.) and some secondary aspects (quality of communication, language, flexibility, appearance in the proposal stage, reputation, etc.). It is recommended to prepare a complete overview for the various assessment criteria and in many cases a consulting engineering company is invited to support in this stage in order to assure an objective assessment of the various proposals. Confirmation of available budgets After the evaluations it will be clear which consequences will result from the planned ordering of equipment (total value, payment terms, project team, travel expenses etc.). Then it must be checked whether the organisation who wants to install (acquire) the new equipment is really prepared to provide the funding, to guide the implementation and accommodate the commissioning. This is necessary before the final contracting can start. Finalising the contract After negotiating the definite technical specifications and all commercial conditions, a contract should be made in such a way that both parties feel satisfied with the final result. The intent of the contract must be clearly described and all the expected deliverables must be clear to both parties. For large procurements (> 0.5 mio Euro) it will be necessary to inform the works council. In many cases it is recommended to start informing the works council in a very early stage especially when new equipment will support automation or when new equipment will change work procedures, will require less people etc. The contract will describe how the supplier will conform with the pending CE-directives (“Machinerichtlijn”). A relevant flow diagram is given in appendix A. Design stage The supplier will deliver a complete set of design drawings including a listing of all sub-contractors for the major components. In this stage the supplier and the principal will cooperate very intensively. Manufacture, erection and commissioning During manufacture the principal will monitor the quality and progress of the work and will check whether the applied materials and components conform with the specifications and the design drawings (quality assurance). The erection plan will be checked with the pending characteristics of the site and for the commissioning an acceptance test plan will be made. In this acceptance test it must be checked that the equipment does fulfil the requirements (technical, operational. user’s interface etc.) Transfer to operations and maintenance department 9 • • After a successful acceptance test, the equipment can be transferred to the operations and maintenance department, including the handover of all relevant operating manuals, maintenance manuals, spare parts list etc. In many cases employees from operations and maintenance are represented in the procurement team and they are keen that the acceptance test is in line with the required characteristics under operating conditions. After sales From the acceptance date until the end of the warranty period the contractor is liable for the quality and proper functioning of the equipment. In this stage there is still an intensive contact between the supplier and the principal’s project team and of course the impact from operations and maintenance which guide the new equipment very careful in the first period of operation. Formal end of the procurement It is recommended to release the original project team of their duties and to assure that al data is transferred to that organisation which is from then responsible for the control of the equipment (either an operations or maintenance department or even an outside contractor). In many cases this is the end of the agreed warranty period. The more attention is paid to a properly described and well communicated procurement process the more successful the introduction of new equipment will be. 10 Appendix Machinerichtlijn • voor werktuigen van kracht sinds 1994 (veiligheid + gezondheid) • opgesteld door Europese Commissie t.b.v. gelijke voorwaarden • geldt voor iedere leverancier (wereldwijd) • leverancier kan zelf verklaring afgeven • risicobeoordeling staat centraal • risico-analyse vereist voorkomen van gesignaleerde gevaren • voldoen aan geharmoniseerde normen is een belangrijk aspect (CEN) • samenstellen technisch dossier (tekeningen, berekeningen, handboeken, risico-analyse, evaluatie, testresultaten • minstens 10 jaar archief, bij schade/letsel overleggen • tijdens gebruik regelmatig keuren/testen (zelf, onafhankelijke instelling) 11 ...
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