Dissertations / Theses on the topic 'Determination of manufacture times'

This thesis deals with the efficiency improvement proposal of production of engineering component for agricultural machine. Firstly, the current production proces is described including description of the component and determination of manufacture times. The next part contains efficiency improvement proposal of production including determination of manufacture times. The last chapter contains a comparison of both variants in terms of production costs. The final provision summarizes results which were achieved and overall benefits of the thesis.

The presteaming of wood chips is an important step in the chemical pulping industry. It removes the air from within wood chips, allowing the cooking liquor to better impregnate wood chips, which leads to a more uniform cooking process, and lowers the amount of rejects. When steaming at atmospheric pressure, it is important that the temperature of the wood chips reach 100ᴼ C, as otherwise there will be an equilibrium leaving some air left inside. Having poorly steamed chips in a process could cause severe problems when it comes to reaching the targeted kappa number, or having the adequate retention time in the digester. There are a few different ways in which the wood chips are presteamed within the industry, however, there is little experimental data regarding the heating time of wood chips that can be used when designing these systems. Most studies have mainly focused on the air removal, or improvement of the impregnation step, and the few studies that have included the heating of the wood chips were limited to only one type of wood chip, or failed to specify the experimental details. Therefore, handmade wood chips pine and birch, two tree species commonly found in Sweden, were steamed in an ATEX designed digester with a steam jacket. The wood chips had thermocouples inside them and the temperature and time was recorded, and the effect of different parameters on the heating could thus be studied.The results revealed that there could be more than a minute in average time difference between wood chips of different thicknesses, both for birch and pine, although the difference in heating time was more linearly correlated to thickness for the birch chips. Pine chips of different thickness were also studied when the pressure inside the digester was allowed to build up, which showed that it is mainly thicker chips that have reduced heating time under such circumstances, as the thinner chips stop heating for a while when the steam condensates on colder surroundings. When comparing heartwood and sapwood chips, it was noted that the difference in heating time could be around 1 minute at most for pine, but only a few seconds for birch. This was most likely due to the pine heartwood and sapwood having distinct moisture contents, 25 % and 58 % respectively, while it was 41% and 42 % in birch heartwood and sapwood. Birch and pine chips wee also steamed together, however, the difference in heating time was only a few seconds on average. When comparing these experimental results with simulation data of the steaming of wood chips, it fit rather well when it came to the general heating time. However, the effect of increased moisture content had a much larger impact in the simulations, which predicted that more moist wood chips would need several minutes more steaming time, while the experiments only showed at difference of, at most, around 1 minute. When comparing with old experimental data, that has been the basis for the design of older steaming processes, it gave very distinct results, where the effect of thickness did not have as big of an impact as in the old data. No further comparison could be made, however, as the experimental conditions for the old experimental data were not known. Based on these results, it was noted that a steaming time of at least 5 minutes would be needed to ensure that even the largest and more moist chips could reach 100ᴼ C in this system. Finally, the condensate from the handmade birch and pine chips was analyzed. It revealed the presence of low molecular weight compounds like methanol, formic acid and acetic acid. Common metal ions were also present,although the amount of sodium ions clearly surpassed the rest. The pH of the pine condensate was measured and it was very high, which implies that the condensate was contaminated.
Basning av flis är ett viktigt steg inom kemisk massaindustri. Det avlägsnar luft från flisens insida vilket gör att impregneringen av luten blir bättre, vilket i sin tur leder till en jämnare kokning och färre rejekt. När basningen sker vid atmosfärstryck är det viktigt att flisen når en temperatur på 100ᴼ C, annars kommer det finna ett jämviktstillstånd där lite luft blir kvar på insidan. Att ha otillräckligt basad flis i en process skulle kunna orsaka stora problem när det gäller att nå önskade kappatal, eller att ha en önskad retentionstid i kokaren.Basningen görs på ett par olika sätt inom industrin, men det finns väldigt lite experimentell data tillgänglig angående flisens upvärmning, som skulle kunna användas när dessa system designas. De flesta vetenskapliga studier har fokuserat på luftborttagningen eller på förbättringar av impregneringssteget, medan de få studier som inkluderat mätningar av temperaturen ofta varit begränsade till ett slags trä, eller så har de inte inkluderat detaljer kring experimentet. Därför basades handgjorda flisbitar av björk och tall från Sverige i en ATEX-designad kokare med en ångjacka. Flisen hade termoelement inuti och temperaturen samt tiden kunde avläsas, vilket gjorde det möjligt att studera effekten av olika parametrar. Resultaten visade att det kunde skilja mer än en minut i uppvärmningstid mellan flisbitar av olika tjocklekar, både för tall och björk, även fast skillnaden i uppvärmningstid var mer linjärt relaterad till tjockleken för björkflisen. Tallflisen studerades också när trycket inuti kokar tilläts stiga vilket visade att det de tjockare flisbitarnas uppvärmningstid som kortas ned mest, eftersom de tunnare flisbitarna slutar värmas upp när ångan börjar kondensera på kallare ytor runt omkring. När flis av splintved och kärnved jämfördes visade det sig att skillnaden i uppvärmningstid kunde vara omkring 1 minut för tall, men endast ett par sekunder för björk. Detta beror troligtvis på att kärnveden och splintveden i tall hade stora skillnader i fukthalt, 25 % respektive 58 %, medan det för björk var 41 % och 42%. Björkflis och tallflis basades även tillsammans men det skillde bara ett fåtal sekunder i genomsnitt i uppvärmningstid. När den experimentella datan jämfördes med data från simuleringar visade det sig att de stämmer väl överens när det gäller uppvärmningstiden i allmänhet. Å andra sidan förutspådde simuleringsdatan att en ökad fukthalt skulle leda till flera minuters skillnad i uppvärmningstid, medan endast 1 minuts skillnad uppmättes. När jämförelser gjordes med gammal experimentell data som använts som grund för tidigare processers design, var resultaten ganska olika eftersom den gamla datan visade en större effekt av ökad tjocklek än den som uppmättes.Tyvärr kunde inte fler jämförelser göras eftersom detaljerna kring experimentet bakom den gamla datan inte var kända. Slutligen analyserades även kondensatet från de handgjorda flisbitarna av tall och björk. Det visade att det fanns små mängder av små polära organiska ämnen, såsom metanol, myrsyra och ättiksyra. Vanliga metalljoner detekterades också, där mängden natrium var klart större än övriga metalljoner. Tallkondensatets pH mättes och det visade sig vara väldigt högt, något som tyder på att det troligtvis var förorenat.

Hot cracking is a serious problem that encounters during welding of aluminium-magnesium alloys. In the present study, solidification and liquation type of hot cracks in weld metal and the heat-affected zones of 5086-H32 aluminium alloy were investigated by using Modified Varestraint Test (MVT) with TIG-AC and TIG-DC welding. With determining the size, type and number of cracks, a relation was established between welding line energy and strain on the hot crack formation. This information was used to determine the hot crack safe parameter ranges. The hot cracking tendency as a function of applied parameters were discussed in the frame of temperature fields around the moving heat source. Moreover, the characteristic hot crack locations on the 5086-H32 MVT specimens were generalized. The results of the study indicated that the increase in line energy and strain increased the hot cracking tendency of the specified aluminium alloy. In the low line energy range, the main hot cracking mechanism is the solidification cracking which could be overcome by the use of a suitable filler material. At high line energy range, due to the increased amount of interdendritic liquid, the amount of solidification cracking decreases by healing mechanism. However, because of the enlarged-temperature-field around the weld zone, fraction of HAZ cracking increases. The comparison between the hot cracking tendencies in low and high line energies indicates that the low line energy ranges with low augmented strains resulted in hot crack safer parameters.

碩士
國立中興大學
森林學系
87
The purpose of this study was to evaluate the manufacture processes that produced active carbon with larger surface area and higher yield. These processes included dehydration, carbonization and activation. Two species of bamboo, Phyllostachys heterocycla Mitf. and Bambusa atrovirens Wen were tested. The test conditions composed of five levels of heating rate, 0.5, 1, 2, 5, 10 ℃/min, three levels of activation temperature, 900, 1000, 1100 ℃, and two kinds of gas, CO2 and N2 at the rate of 100ml/min were evaluated. The results were found as follows: (1)It was proper to heat bamboo at the rate of 2 ℃/min in carbonization stage. (2)The yield of active carbon was higher for fully loaded bamboo without culm. (3)There were no significant difference in yield for varied moisture contents of samples, varied activation temperatures and gases. Therefore, The best condition to manufacture bamboo activated carbon of large sureface area, average diameter of pore and pore volume was that the samples were heated to 700 ℃ at the rate of 2oC/min, lasted for one hour at 700℃, reheated to 900℃, and added N2 at the rate of 100ml/min for one hour activation.

碩士
國立中興大學
食品科學系
87
The provincially aquacultured tilapia was used as materials to prepare a smoked dainty product. Tilapia fillets immersed with seasonings were semi-dried by hot-air and subsequently dried by smoking. The appropriate seasonings and processing process were investigated via hedonic sensory evaluation. Quality of the smoked dainty product was also determined. The results obtained were as follows: 1. Moisture content, water activity, salt content, and labelled storage life for several commercial products similar to the developed product were 6-40%, 0.6-0.8, 2-6%, and 8-12 months, respectively. 2. The higher salt content in immersed sauce, the higher rate of salt osmosis to fillets was observed. The moisture content of fillets reduced during immersion. Considering to both factors related to seasoning and microorganism growth, the immersion was controlled at 4℃ for 6 days. 3. During smoking, the Hunter L value of tilapia fillets decreased and Hunter a and b value increased. The fillet turned to brown color in appearance. This change resulted from the complicated effects with regard to curing agent, heating condition, and smoke components. 4. The process for preparation of smoked dainty products from tilapia was established. The water activity (Aw) of the products thus obtained was below 0.7. For reaching the Aw level of intermediate foods, the products could be distributed at normal temperature. 5. POV and TBA of the prepared products were not significantly changed during storage. Inhibition of microorganisms by drying combined with antioxidant action of smoke resulted in the storage stability. 6. Fatty acid composition of tilapia flesh was hardly not affected due to smoking or water-cooking. The two processes were better than frying to prevent from obvious decrease in ω-3 polyunsaturated fatty acids.

碩士
國立臺灣科技大學
工業管理系
96
In the scheduling literature about the two-stage assembly, the setup time is often ignored. However, an explicit consideration of setup time in the first stage is usually required in many practical manufacturing environments. This thesis considers a two-stage assembly scheduling of product problem with setup time to minimize the makespan (or maximum completion time). In this problem, the product consists of one or more common components. Since the problem is NP-complete, we propose a heuristic to solve the problem and evaluate the performance of the heuristic by a tight lower bound. Computational results show that the heuristic can obtain a near optimal solution in almost zero time and the average percentage deviation is only 0.714.

no
This study aimed to determine if response times gathered during perimetry can be exploited within a thresholding algorithm to improve the speed and accuracy of the test. Frequency of seeing (FoS) curves were measured at 24 locations across the central 30° of the visual field of 10 subjects using a Method of Constant Stimuli, with response times recorded for each presentation. Spatial locations were interleaved, and built up over multiple 5-min blocks, in order to mimic the attentional conditions of clinical perimetry. FoS curves were fitted to each participant’s data for each location, and response times derived as a function of distance-from-threshold normalised to the slope of each FoS curve. This data was then used to derive a function for the probability of observing response times given the distance-from-threshold, and to seed simulations of a new test procedure (BURTO) that exploited the probability function for stimulus placement. Test time and error were then simulated for patients with various false response rates. When compared with a ZEST algorithm, simulations revealed that BURTO was about one presentation per location faster than ZEST, on average, while sacrificing less precision and bias in threshold estimates than simply terminating the ZEST earlier. Despite response times varying considerably for a given individual and their thresholds, response times can be exploited to reduce the number of presentations required in a visual field test without loss of accuracy.

碩士
玄奘大學
企業管理學系碩士班
103
Abstract The demographic structure change in Taiwan, decrease in the younger age group and the increase of the excessive aging population, has led to many social issues. One of the most related issues to the demographic transition is the supply and demand in labor market as well as school recruitment, mainly caused by the low fertility rate. This research intends to investigate the issues in the labor recruitment among manufacturing industry in conventional industries. The results indicate that the differences of the salaries are based on three variables, i.e. job responsibility, technique and wage seniority, according to the participants. The recruitment channel has been reported more from web advertisement than from the introduction of friends and families. This research further divides all participants based on their working attitude into four groups, including company system, job satisfaction, salary rewards system and self achievement. The results of the analyses indicate that the competitive employees in conventional industries are more attracted if the company system is more realized and employees are led to a stronger job satisfaction as well as higher self achievement in addition to a reasonable salary reward system. The results of this research can help for future employee recruitment in conventional industries. Key words: Low Birth Rate, recruitment, salary reward system, conventional industries, manufacturing industry

The Dixon technique is a well-established method in magnetic resonance imaging for obtaining separate images of water and fat. Here we present a generalized solution to the two-point Dixon problem with a geometric interpretation, allowing for flexible echo times and a multi-peak fat model. By simulation and experiment, we have analyzed the dependence on the echo times of the error in the water, fat, and relative background phasor values due to both signal noise and T2* decay. Furthermore, we have demonstrated that broken symmetry due to the multi-peak nature of fat enables direct water and fat determination without phase correction, and we have quantified the reliability of this technique as a function of the echo times. The results may provide valuable guidance for selecting scan parameters to balance the objectives of optimizing fat-water identification, minimizing error in the pixel values, and minimizing total scan time.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Medicine in Pharmaceutical Affairs Johannesburg, 2014
Aim The first step in a wet granulation process is dry mixing. This step has the objective of ensuring that all the raw materials are mixed such that the end product is homogeneous. Dry mixing in a high shear mixer instead of a blender saves cost. However, the mixing parameters have not been well researched. Dry mixing parameters that are currently used, have been established through experience, trial and error and in-process testing. Alexander and Muzzio (2006) confirms this by stating that there are currently no mathematical techniques to predict blending behaviour of granular components without prior experimental work; therefore, blending studies start with a small-scale, try-itand- see approach. Even though they are referring to blending, the same is also true for dry mixing. Both processes are the mixing of powders. Therefore the aim of this research was to develop parameters for dry mixing, based on experimental work. Methods Using a Saral rapid mixer and wet granulator (Saral Engineering Company, India), experiments were performed according to a 24 two-level Plackett-Burman Design method, to determine the effects of different blades (mixer/impeller and chopper) speeds and mixing times on the homogeneity of the mixtures containing different ratios of two powders that have different densities and particle sizes. One of the powders mixed, was enalapril maleate. This was chosen as it can be assayed. Samples were taken from the bowl and tested for assay. The mix for a specific experiment is homogeneous if the results of all 7 assayed samples are within 10 % of the target % w/w value and the % Relative Standard Deviation (% RSD) of the 7 results is less than or equal to 5,0 %. The outcome was being measured in % RSD. A lower % RSD indicates a more homogeneous mix. The parameters developed, will be beneficial to pharmaceutical companies as it can assist them to improve accuracy, consistency and quality of granular mixes. The experimental method used can serve as an example for future experiments. Results The results indicated that impeller blade mixing speed and mixing time are the two factors that have the biggest impact on the homogeneity of a mix in a high shear mixer. Chopper blade speed was also found to be significant, but less than the above two parameters mentioned. Optimal parameters were predicted. Conclusion As there are many parameters to be controlled during dry mixing in a high shear mixer, a statistical design method is suitable to establish the parameters that would have the most impact on the end result. Statistically it was found that mixing speed of the main impeller and chopper blades and overall mixing time are the three factors that have the biggest impact on the homogeneity of a mixture. The mixing time and impeller blade speed have proven to be more significant than the chopper blade speed. Concentration was found to be insignificant. For our experiments and for the specific granulator used the following optimal parameters could be deduced: Impeller blade set at 191 rpm, chopper blade set at 2002 rpm and mixing time set at 3.01 minutes.

This work reports the results of a systematic study of the factors that affect the bridging behaviour of bagasse. It shows that traditional bulk solids theory is inappropriate for predicting bagasse flow mainly because of the impossibility of obtaining a reliable measure of internal friction. It demonstrates the significant influence of fibre length and moisture content on its handling charateristics. Correlations of pertinent bulk properties such as compactibility, tensile strength, surface friction and translation of vertical into horizontal pressure have been developed. These were derived as a result of measurements in equipment that was designed for the purpose. Finally, an empirical model utilising these correlations is proposed by which the likelihood of bridge formation in any piece of bagasse handling equipment can be determined. The validity of the model is assessed by comparison with bridging tests that were performed under controlled conditions.
Thesis (Ph.D.)-University of Natal, 1996