Role of surface to volume ratio of zinc oxide arrester on energy absorption capability

Functional life of a zinc oxide arrester block is largely dependent on its energy absorption capability which is an important characteristic in ensuring enhanced reliability of a surge protection system. An arrester block is usually cylindrical in shape with two flat surfaces. Injected energy from the stroke of transient electrical surge into the arrester body is transformed into heat and dissipated through the surface of the disc body. This study has been conducted to observe whether the higher surface to volume (S/V) ratio of an arrester block enhances the capability of energy absorption or not. The round side or C-surface of the cylindrical disc was ground by diamond wheel to transform into hexagonal shape. By making this geometrical modification an increase of about 11% in S/V ratio was achieved for the hexagonal discs. Ten ZnO arrester blocks of both shapes were tested and the average energy absorption capability for the hexagonal discs was found to be 483 J.cm-3 compared to that of 357 J.cm-3 for the cylindrical discs. Thus, for the hexagonal discs a significant increase (35%) in energy absorption capability is observed which is attributable to increased S/V ratio of the arrester facilitating greater heat transfer. This knowledge can be useful in designing the geometry of the device for improved functional reliability of electrical system. Ke

Possible cost reduction by applying MRP in a transformer manufacturing company of Bangladesh

Local manufacturing industries generally do not pay adequate attention towards applying the state-of-the-art operations management techniques in inventory control, scheduling, material requirements planning (MRP) etc. The main identifiable reasons are lack of exposure to the concurrent techniques and facilities, exorbitantly high price of commercially available software and inadequate indigenous support systems. Moreover, the lack of knowledge about the benefits of using MRP in various aspects hindered its wide spread diffusion. Most of the local firms assume that the procurement of raw materials either in huge quantity at a time or in small amount from period to period without adopting any mathematical approach would not have any remarkable effect on the total inventory cost. Practically the situation is different and it has been found that the procurement of material applying an established algorithm instead of current practice could significantly reduce the total incremental inventory costs. In this respect educational software was used. This paper highlights the salient features of MRP application in a local transformer manufacturing industry and makes a comparison of the total inventory costs determined by following the user-defined approach and the standard lot-sizing approaches

Optimization of product mix in a typical yarn manufacturing industry

In a typical yam manufacturing company different types of yams are produced and usually a schedule of production is prepared and followed for smoother production. However, company's taking decision regarding order receiving and scheduling become tougher when it gets simultaneous orders of different yams. A compromise is required between profit and capacity. An LP model has been formulated for some selected yams and solved and this paper presents an analysis to find the optimum product mix indicating the quantity (tons) of each category of yams to be produced and the duration of machine hours to be allocated. It would also help to identify the abundant or scarce resources. Moreover, through the analysis it is possible to prioritize the expansion of the scarce resources in allocation of additional investment, if required. A sensitivity analysis in this regard provides the information of increment of the scarce resources and maximum change in marginal profi

Dimensions of job satisfaction of library professionals: a qualitative exploration

This research is aimed at investigating the underlying causes of job satisfaction of the library staff at a large public university in Malaysia. A qualitative methodology, namely, hermeneutic phenomenology, approach is undertaken with Herzberg’s two-factor theory employed in designing the interview protocol. Twelve full-time librarians take part in the interviews for this purpose. Despite in a few cases, the study reveals a general concord with Herzberg’s reasoning vis-à-vis the factors leading to staff satisfaction or dissatisfaction. One striking feature of the finding relates to the religious values and environment contributing to the staff satisfaction to a great extent. Some recommendations and possible future research areas are also suggested

Electrical performance of zinc oxide varistor using powders processed by different latex binders

The critical electrical parameters such as I-V characteristics, watt-loss and energy absorption capability etc. are the determinants for performance evaluation of ZnO varistors. In this regard there are a large number of contributing variables. Selection of proper binder in the processing of electro-ceramic powder is also a crucial factor. It imparts green strength, enhances compressibility and reduces density gradient within the green discs. Grain growth during sintering and subsequent microstructure of the varistor is also highly influenced by the binder system. It is envisaged that a disc with higher mechanical strength could be capable of withstanding more thermal stress due to temperature gradients. The energy absorption capability as well as high current performance can thus be enhanced. It was possible to generate varistor discs from the powder processed by the latex binder with better electrical performance than that of the powder processed with conventional binder of polyvinyl alcohol. Factorial analysis showed that the level of binder and solid concentration in the slurry had great influence on the energy absorption capability of ZnO varistor

Study of TiC cutting tool insert using microwave synthesis

Microwave processing ceramics is emerging fast as a new field of ceramic processing and material synthesis. The past year has witnessed significant progress in the aspects of commercialization and application of the technology to new areas. Further research states that Titanium Carbide (TiC) is the best cutting tool due to its high melting point and by that reason this project aims to show the difference between conventional sintering, microwave sintering and Hot Isostatic Pressing (HIP). Two different compositions consisting of 97TiC3Ni and 93TiC7Ni were sintered using conventional furnace, microwave furnace and HIP. Density, hardness and microstructure analysis were carried out on these TiC inserts. 97TiC3Ni produced higher density and hardness values compared to 93TiC7Ni for all three different methods. Microwave sintering produced the highest density and hardness values compared to conventional sintering and HIP. Microwave produced samples with improved density and hardness in a shorter processing time which is 93% faster than conventional sintering and 50% faster than HIP

Multi-criteria optimization in end milling of AISI D2 hardened steel using coated carbide inserts

This paper proposes a multi-criteria optimization technique using the mathematical models developed by the response surface methodology (RSM) for the target responses combined with desirability indices for the determining the optimum cutting parameters in end milling of AISI D2 hardened steels. Different responses may require different targets either being maximized or minimized. Simultaneous achievement of the optimized (maximum or minimum) values of all the responses is very unlikely. In machining operations tool life and volume metal removed are targeted to be maximized whereas the machined surface roughness need to be at minimum level. Models showing the combined effect of the three control factors such as cutting speed, feed, and depth of cut are developed. However, a particular combination of parameter levels appears to be optimum for a particular response but not for all. Thus adoption of the method of consecutive searches with higher desirability values is found to be appropriate. In this study the desirability index reaches to a maximum value of 0.889 after five consecutive solution searching. At this stage, the optimum values of machining parameters - cutting speed, depth of cut and feed were determined as 44.27 m/min, 0.61 mm, 0.065 mm/tooth respectively. Under this set condition of machining operations a surface roughness of 0.348 μm and volume material removal of 7.45 cm3 were the best results compared to the rest four set conditions. However, the tool life would be required to compromise slightly from the optimum value

Enhancing mechanical and structural properties of TiC inserts using microwave energy

Two different compositions of Titanium Carbide (TiC) inserts consisting of 97%TiC3%Ni and 93%TiC7%Ni were synthesized using conventional sintering(CS), microwave sintering (MS) and Hot Isostatic Pressing (HIP). The influence of sintering time and sintering temperature on the mechanical and structural properties of this TiC inserts were examined. The compaction load of 103 MPa was used to produce the green samples. Different time-temperature combinations were used for each type of heat treatment. 97TiC3Ni composition produced inserts with higher density, hardness and strength compared to the 93TiC7Ni composition for all three different sintering methods. Meanwhile, hybrid microwave sintering produced TiC inserts with the highest density, hardness and strength compared to conventional sintering and HIP. Improved mechanical and structural properties were observed using microwave energy in just 10 minutes of sintering compared to 10 minutes using HIP and a total processing time of 150 minutes (30 minutes holding time) using conventional sintering

Cost Model for end-milling of AISI D2 tool steel

In this research paper, user-friendly and accurate mathematical model for estimating the cost of end-milling of AISI D2 tool steel using Polycrystalline Cubic Boron Nitride (PCBN) cutting tool inserts is developed. Initially, the different components of machining cost were identified, followed by establishment of equations to determine their values. Then, the required experimental and non-experimental data were collected and the bottom-up approach was adopted for evaluating the cost of machining corresponding to each of fifteen experimental runs. The Response Surface Methodology (RSM) was used to develop the model in which the cost of machining is given as a function of the machining parameters; cutting speed, feed per tooth, and depth of cut, and expressed in Ringgit Malaysia per cubic cm (RM per cm)3. Analysis of Variance (ANOVA) was utilized to check the adequacy of the developed model. The developed model was found to be statistically adequate

Analysis of end crack in boiler tube

Boiler tube failures usually result in frequent forced outages, and ultimately in costly extended outages for major tubing replacement in a plant. There are several failure modes that may occur in a boiler tube, i.e. stress-corrosion cracking, pitting, water-side corrosion, fire-side corrosion, fatigue failure, overheating, dissimilar metal weld fatigue, mechanical fatigue and erosion. In this research the failure modes of boiler and its end cracks due to the dissimilar metal weld is analyzed. Hence data are collected and explored to determine the cause of failure and as a solution ceramic ferrule is suggested. The use of ceramic ferrule in boiler tube can eliminate the crack occurrence or delay the process due to thermal properties. The prevention of crack will reduce frequent maintenance and thus the cost of operation can be minimized