Підвищення ефективності нагнітання тіста обертовими валками у формувальній машині
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Дата
2018
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Анотація
Дисертація на здобуття наукового ступеня кандидата технічних наук зі спеціальності 05.18.12 «Процеси та обладнання харчових, мікробіологічних та фармацевтичних виробництв». Національний університет біоресурсів і природокористування України. Київ, 2018. Дисертацію присвячено обґрунтуванню конструктивних і технологічних параметрів при проектуванні нових валків вузла нагнітання для формування тіста заданої якості, форми та розмірів. Розроблено реологічну модель для розв’язування задач, пов’язаних з оцінюванням пружно-деформованого стану тіста у вузлі нагнітання. Встановлено критичну швидкість течії, за якою вперше настає пластична деформація. Розроблено і запропоновано методику визначення оптимальних параметрів валкового нагнітання. Встановлено, що одним із пріоритетних чинників розрахункової течії тіста є кут затягування β, який залежить від конструктивного виконання валків. Тривалість t повороту тіста на поверхні валка залежить від даного кута і становить 2,36–1,8 с. Здійснено математичне моделювання впливу зазору між валками та індексу течії на корисну потужність і питомий тиск. Розраховано моменти на валах у початковий і кінцевий моменти дискретного нагнітання тіста. Проведено порівняльний аналіз впливу геометричних та кінематичних параметрів різних типів валків на якісні показники напівфабрикату й готової продукції. Одночасно відображено органолептичні показники бублика «Подільський» та розкрито його структуру згідно з розробленою методикою
Опис
Dissertation with a view to obtaining the academic degree of Candidate of Sciences in the specialty 05.18.12 «Processes and Equipment of the Food, Microbiological and Pharmaceutical Production». National University of Life and Environmental Sciences of Ukraine. Kyiv, 2018. Dissertation is dedicated to the substantiation of structural and technological parameters when designing new shafts of the injection unit for forming a test of a specified quality, shape and size. It has been performed the analytical review of influence of constructive parameters of shafts working bodies of different class of machines on a viscous fluid, behavior of the specified fluid. It has been examined methods of rolling and performed contrastive analysis of constructions. It has been revealed the main essence of the influence of the surface of shafts working bodies on the structural and mechanical properties of viscous fluid. It has been determined the prospects of the shafts working bodies using during injection, rolling, transportation and ways of their modernization and construction. Shafts working bodies have been classified by features in machines of different classes which determine in the result the course of the technological process. It has been discovered the general plan for conducting theoretical and experimental investigation on the developed physical model of the injection unit. The subjects and materials of the research have been determined provided research methods of the structural and mechanical, rheological characteristics, quality indicators, as well as the experiment planning scheme and using of the mathematical and computer processing of experimental data. It has been developed a rheological model for solving problems connected with the evaluation of the stress-strain state of the dough in the injection unit. It has been discovered the work of the injection unit which characterized by the discretization of the process. It has been defined critical flow velocity whereby time plastic deformation occurs for the first. Thus, parameters start change when the speed comes up to 1.3 radian per second, the shearing stress comes up to 1.02 kPa g and the density comes up to 1180 kg per cubic meter. It has been developed and proposed a method for determining of the optimal shaft injection parameters. To minimize the structural parameters it has been determined specific area of the shaft and influence of changes of its diameter on this area. It has been defined that one of the priority factors of the dough calculated flow is the contact angle β, which depends on the structural performance of the shafts. Consequently, the duration t of the dough turning on the surface of the shaft depends on this angle and is 2.36–1.8 s. Considering the different designs of injection units has been given their comparative characteristics in the forming machine, which are used on the enterprise. The research confirms the advanced preconditions and the optimal, theoretically substantiated dependence of the influence of deformation on the quality of the dough. It has been considered thermophysical properties of the dough (thermal conductivity, thermal capacity), which determine the nature and speed of the flow of thermal processes. It was founded that the thermal conductivity of the dough depends not only on its condition, but also on the direction of the heat flow with regard to the action of the shafts. On the basis of Fourier's law has been developed a mathematical model for determining the temperature fluxes in the dough flow. On the basis of data about the temperature distribution in the dough thickness, thermal capacity of the area, its volume, with using the mathematical model has been defined amount of heat which generated during injection for each of the investigated shafts with taking into account their structural and technological parameters. It has been performed the thermal-imaging shooting by means of the FlukeTi25 thermal imager in order to confirm the theoretical calculations and a qualitative assessment of the dough temperature change during the technological process of injection. Such temperature change of the dough with the mass of 40 kg loaded into the working camera has different values for each injection unit. The greatest values of temperature change occurs in the unit of the machine which was constructed in the year 1968, in other words temperature increase very rapidly to the 31,5 оС for 15 minutes of the process, and beginning from the 15th minute it decreases by 0,5 оС until the completion of overall cycle time. If take into account constructive changes of the machine of the year 2015, dough has the increasing of temperature to the 28 оС on the 12 minutes of the process. The dough gradually reduces its values to the completion of the overall discrete cycle with the beginning of the specified period. The value of the temperature practically does not change during the process on the shafts of the developed construction and they keep in the range of 24–23 оС. It has been performed a mathematical simulation of the influence of the gap between shafts and the flow index on the net power and specific pressure. It has been calculated moments on shafts in the initial and final moment of the discrete injection of the dough. On the basis of the research data of equations was constructed graphic dependencies and performed analysis of the polynomial regression curves. It has been found the relationship between the parameters of the new shafts and the productivity of injection unit of the dough. It has been performed comparative analysis of the effect of geometric and kinematic parameters of different types of shafts on the qualitative indicator of semifinished products and finished products. At the same time, the organoleptic parameters of «Podilskyi» doughnut-shaped bread roll was indicated and was discovered its structure in accordance with the developed methodology. It has been defined that the process of the dough injection can be controlled by means of providing the temperature stability; increasing of thermal exchange surface; production of a shaft from a material which has the maximum thermal conductivity; increasing of the thermal losses in the environment (the return of heat to a shaft surface which does not contact with the dough). The effectiveness of the introduction of cylindrical-screw shafts is confirmed by the act of introduction into production with an annual economic effect of 87.3 thousand UAH. This construction of the shafts working bodies is protected by the patent of Ukraine on the utility model
Ключові слова
тісто, теплообмін, валкові робочі органи, в’язке тертя, обробка, цикл
Бібліографічний опис
Підвищення ефективності нагнітання тіста обертовими валками у формувальній машині: автореф. дис. ... кандидата тенічних наук 05.18.12 "Процеси та обладнання харчових, мікробіологічних та фармацевтичних виробництв" / А.В. Деркач ; Національний університет біоресурсів і природокористування України. - К., 2018. - 25 с