Spare Parts Stock Research Articles

Optimization of spare parts for hierarchicall decomposable systems

Complex technical systems are often hierarchically composed of exchangeable modules, which themselves may be composed of exchangeable submodules. The hierarchy of modules of such systems can be represented by trees. Defective systems are repaired in a supply depot system by exchanging the defective modules from a stock of spare parts. The exchanged defective modules are repaired for resupply. In this paper, a dynamic programming algorithm for optimizing the stocks of spare parts, under a budget constraint, is presented. The optimization criterion is the minimization of the backlog of entire systems at the supply depot system. An implementation of the algorithm is described and some illustrative examples are given.

Yet Another Digression on Systems Analysis: The Great Spare Parts Fiasco

Top management of a well-known computer manufacturing firm recently became concerned with the growing cost of maintaining, across the country, local stocks of spare parts needed to repair and maintain the computers it typically leased, and sometimes sold, to users. This was obviously an inventory control problem, so the corporate OR/MS group was called in and told to do their thing to bring the inventory picture back into more acceptable proportions.

The optimum stock of spare parts in the basic shopsof metallurgical plants

The optimum stock of spare parts in the basic shopsof metallurgical plants

Mathematical analysis of metabolic networks

Although its important reaction sequences and cycles have been known for more than 25 years, we are still far from a satisfactory theory of intermediary metabolism. The empirical material is overwhelming and increases every year, but the development of a general conception is still in its infancy, although the conceptual progress of recent years has been considerable (for reviews, see [l-3] ). In our opinion, however, the emphasis is too much on static concepts which view the intermediary network as if it were a stock of spare parts, energy and material reserves to be used and filled up by appropriate enzymic reactions. The5 principal bias is towards optimization and control of this supply whereas the dynamic aspects are obviously neglected. There are preferences which testify to this tendency, for example the predominance of the feedback concept, or, in more general terms, of restrictive and repressive control at the metabolic and epigenetic level as a device to meet material demands and to prevent, or to cope with, sudden affluence. Activation and induction are likewise understood to have the same purpose. Indeed, the very concept of ‘con-

Improving the life, storage, and recording of spare parts

To reduce expenditure on acquiring and making spare parts and units and substantially reduce their consumption it is necessary to carry out more work on the standardization of components, replacing equipment and technical plant both in enterprises and in the industry as a whole. In all enterprises we should compile catalogs of components and equipment units, and determine the minimal required permanent stocks. Over a period of one to two years it will be necessary to carry out the complete centralization of the stocks of spare parts and guarantee their accountancy of consumption. To obtain a return of not less than 35–40% worn-out components for restoration and not less than 40–50% newly produced spare parts it will be necessary to subject them to strengthening by various techniques.

Miniseptor—A Modular Approach to Susceptor Design

MINISEPTOR is a susceptor for vacuum hear-treat and melting applications which is made up of a number of multisided polygons, (almost circular rings) primarily of graphite, stacked concentric with the axis of an induction coil. Its modular construction makes feasible hot zones, as large as 11 ft in diameter by 1712 ft high, for operating temperatures to 2750 °C (5000 °F). The reduced mass of the susceptor greatly reduces the stored energy in the susceptor resulting in brisk, temperature cycling. In addition, initial costs and operating costs are lower than for conventional systems. The modular construction of the susceptor and its thermal insulation allows replacement in sections as required, without complete removal, which simplifies maintenance and lowers the required minimum stock of spare parts. Variable configuration of the bars, pins, fit, and grade of the graphite used affect the overall resistance of each ring, the number and configuration of rings determining the power delivered to the susceptor at any given voltage and frequency. The multiplicity of independent concentric “rings” permits altering the spacing between “rings” so that it is possible to control the temperature gradient by distribution of the power along the length of the hot zone. Performance characteristics observed on a hot zone 35 in. in diameter and 51 in. tall are discussed. Uniformity of the temperature gradient across the hot zone and holding temperatures observed on this scale model of the large hot zone described above are reviewed.

Techniques for Optimum Spares Allocation: A Tutorial Review

In many modern complex systems the problem of achieving high reliability leads to the use of interchangeable modular components accompanied by a stock of spare parts. This paper examines, compares, and assesses several of the techniques presented in the literature for allocating the numbers of spares of each part type to be stocked in order to maximize the system reliability subject to constraints on resources (i.e., weight, volume, cost, etc.). The problem of optimum spares allocation is complicated since resources are consumed in a discrete fashion and the expression for the system reliability is a nonlinear transcendental function. The classical dynamic programming algorithm produces all optimal spares allocations; however, the solution can become computationally intractable even with the aid of a modern high-speed digital computer. In the case of multiple constraints the time problem is vastly exacerbated. In such a case one must turn to a procedure that yields a near-optimal solution in a reasonable amount of computer time. Two approximate methods discussed in this paper are the incremental reliability per pound algorithm and the Lagrange multiplier algorithm. These algorithms are readily adaptable to handle multiple constraints. Computer programs are developed for each of the three optimization algorithms and are utilized to obtain the spares allocation for a few systems. The optimization theory presented is directly applicable to series or parallel systems. A concluding example illustrates how this can be extended to certain series-parallel systems.

Maintenance operations in geothermal power plants

After a review of the differences in physical and chemical properties between the steam feeding the turbines in conventional thermal power plants and the endogenous fluid used by geothermal electric power plants, special corrosion problems are pointed out and discussed, together with the ensuing problems in selection of materials. The main points to be followed for a technically and economically sound operation are then discussed. They are: • - prearranged checking of the most vulnerable points of the machinery; • - internal organization of the power plants; • - planning for overhaul of the machines; • - minimal stocks of spare parts.