Моделирование закономерностей формообразования конических поверхностей

The scheme of processing conical surfaces by grinding them to a flat tool is considered and a technical solution for the implementation of such processing is proposed. Using the created device allows implementing the group method of forming conical parts with a deviation of the generatrix of the cone from straightness of not more than ± 0.00012 mm. A mathematical model of the patterns of removal of stock from a conical part with a flat tool is developed. A formula is obtained for calculating the modulus of the sliding velocity at any point on the processed conical surface, which implements engineering methods for controlling the shaping of conical parts without conducting preliminary labor-intensive experimental studies. An optimization technique for the adjustment parameters of technological equipment was proposed. The most effective axicon processing modes were revealed at the stages of preliminary, medium and fine grinding, as well as at the polishing stage, depending on the technological heredity of the workpiece from the point of view of distribution of the stock to be removed over its surface. It has been established that changes in the eccentricity between the axes of rotation of the tool and the faceplate as well as the amplitudes of the reciprocating rotational movements of the latter practically do not affect both accuracy and processing productivity, therefore, in practice, these parameters can not be optimized, but their average values can be assigned. The operating modes of the basic lever grinding and polishing machine are established, at which the required accuracy of the working surface of the tool is provided, which directly affects the straightness of the generatrix of the cone. Studies of the regularities of the shaping of the side surface of a conical lens in the conditions of free grinding are carried out and the adjustment parameters of technological equipment that affect the quality and productivity of the processing process are determined.Рассмотрена схема обработки конических поверхностей посредством их притирания к плоскому инструменту и предложено техническое решение для реализации такой обработки. Использование созданного авторами устройства позволяет реализовать групповой метод формообразования конических деталей с отклонением образующей конуса от прямолинейности не более 0,00012 мм. Разработана математическая модель, устанавливающая закономерности съема припуска с конической детали плоским инструментом. Получена формула для расчета скорости скольжения в любой точке обрабатываемой конической поверхности, реализующая инженерные методы управления формообразованием конических изделий без проведения предварительных трудоемких экспериментальных исследований. Предложена методика оптимизации наладочных параметров технологического оборудования. Выявлены наиболее эффективные режимы обработки аксиконов на стадиях предварительного, основного и окончательного шлифования, а также на этапе полирования в зависимости от технологической наследственности заготовки с точки зрения распределения подлежащего удалению припуска по ее поверхности. Установлено, что изменения эксцентриситета между осями вращения инструмента и планшайбы, а также амплитуды возвратно-вращательных движений последней практически не влияют как на точность, так и на производительность обработки, поэтому на практике эти параметры можно не оптимизировать, а назначать их средние значения. Определены режимы работы базового рычажного шлифовально-полировального станка, при которых обеспечивается требуемая точность рабочей поверхности инструмента, непосредственно влияющая на прямолинейность образующей конуса. Выполнены исследования закономерностей формообразования боковой поверхности конической линзы в условиях свободного притирания и установлены наладочные параметры технологического оборудования, обуславливающие качество и производительность процесса обработки

The risk to develop tuberculosis and efficacy of its preventive treatment in labor migrants residing in the Republic of Tajikistan

Objective: to study the prevalence of latent tuberculosis infection (LTBI), risk factors for LTBI to develop into active tuberculosis, the efficacy of preventive treatment in those with LTBI among labor migrants, residing in the Republic of Tajikistan.Subjects and methods. In the Republic of Tajikistan, 500 residents were followed up as Main Group, they all were labor migrants for more than 3 months and returned to their homeland within one year before inclusion in this study. All of them participated in a questionnaire survey to identify risk factors for developing tuberculosis and had the examination that included Mantoux test with 2 TE and chest X-ray. Comparison Group (CG) consisted of 500 citizens of compatible gender and age who did not travel as labor migrants; they all participated in the same survey and had the same examination.Results. The positive results of Mantoux test with no abnormalities on X-ray were observed in 40% of people in Main Group and 33.4% of people in Comparison Group.The following factors were found to be more frequent in Main Group versus Comparison Group, respectively: frequent and continuous exposure to a TB case – 78.2 and 23.1% (p < 0.01); no tuberculosis prevention – 83.1% and 48.4% (p < 0.01); poor accommodation and work conditions 87.9 and 13.6% (p < 0.01); inadequate diet and lack of proper clothes – 79.4 and 24.3% (p < 0.01); limited access to medical care – 85.4 and 22.6% (p < 0.01). MG was found to have a higher summarized risk coefficient (r = 4.75) versus CG (r = 2.0), p < 0.01. During 2–3-year follow-up of those with LTBI who had no preventive treatment with isoniazod, tuberculosis was diagnosed in 44.4% of people from MG and 18.5% of people from CG. The introduction of the integrated approach to tuberculosis control among people preparing for labor migration allowed reducing the proportion (from 19.7 to 13.7%) of labor migrants in the structure of TB incidence