Facetting value of helical thread surface received by enveloping

В морской технике применяются различные резьбовые соединения. Детали судовых механизмов подвергаются в процессе работы вибрациям и переменным нагрузкам, которые приводят их к разрушениям, потере герметичности и к внеплановым остановкам судовых машин.. Для повышения эксплуатационных свойств и увеличения срока службы резьбовых соединений проводят анализ качества сопрягаемых поверхностей, в частности, параметров шероховатости. В предлагаемой статье исследуется величина огранки винтовой поверхности резьбы образующаяся при осуществлении нового метода изготовления резьбы огибанием. Процесс обработки металла, к которому относится новый метод нарезания, заключается в касании лезвия инструмента и обрабатываемого материала прерывистым касанием. Нарезание резьбы осуществляется, специальной червячной фрезой. При прерывистом резании обрабатываемая поверхность оказывается, как бы составленной из отдельных криволинейных площадок (граней), Линия стыка граней имеет определенную высоту по нормали к поверхности, при нарезании резьбы - к винтовой поверхности. Высота стыка граней определяет качественный показатель шероховатости поверхности, называемый волнистостью. При нарезании резьбы червячной фрезой высота стыка граней (волнистость винтовой поверхности) зависит от числа зубьев фрезы. Задача исследования состоит в том, чтобы выяснить, каким должно быть число зубьев фрезы для получение заданной шероховатости винтовой поверхности резьбы и как это влияет на качество поверхности резьбы. Так же в статье рассмотрено графическое описание процесса получения огранки резьбы и пример расчета числа гребенок фрезы. There are many different thread joints used on marine facilities. While in operation, components of the mechanisms undergo vibrations with repeated stresses that leads to their failures, loss of tightness, and unscheduled shutdowns of the equipment. The analyses of joint surfaces quality, e.g. roughness parameters, are conducted to enhance serviceability of the thread joints and to prolong their lifespan. The article studies facetting value of a helical thread surface while applying a new method of thread production – enveloping. The new method of cutting that is a process of metal treatment involves non-continuous contacting an instrument blade and the material being cut. The cutting of the thread is done with a special hob cutter. Due to the non-continuous cutting, a treated surface becomes as if consisting of curved pads or faces. The faces junction line has a specific normal line level towards the surface and towards the helical surface during the cutting. The height of the junction defines qualitative indicator of the surface roughness known as undulation. When cutting the thread with a hob cutter the height of the faces junction - undulation of a helical surface – depends on a cutter teeth number. The research objective is to specify the cutter teeth number needed to achieve the required roughness of a thread helical surface as well as to determine how it influences on the quality of the thread surface. The paper also provides several drawings illustrating the process of obtaining the thread facetting and the example of calculation of a cutter chaser number.

A Multiscale Accuracy Degradation Prediction Method of Planetary Roller Screw Mechanism Based on Fractal Theory Considering Thread Surface Roughness

The wear problems are vital to the planetary roller screw mechanism (PRSM) as they have a great influence on transmission accuracy, working efficiency, and service life. However, the wear characteristics of the PRSM have been rarely investigated in the past. In this paper, a multiscale adhesive wear model is established by incorporating the effective wear coefficient and considering the thread surface roughness. The variation of surface roughness is characterized by the two-dimension Majumdar–Bhushan (MB) function. The multi-asperity contact regimes are used to estimate microcontact mechanics of the rough interface. Moreover, the influences of surface roughness, material properties, and working conditions on the wear depth and precision loss of the PRSM are studied in detail. The results reveal that as the surface roughness increases, the total actual contact area, wear depth, and precision loss rate rise. In addition, the adhesive wear increases with the growth of the axial load, and decreases with the increase in the material hardness and material elastic modulus ratio to a certain extent. The investigation opens up a theoretical methodology to predict the wear volume and precision loss with regard to thread surface roughness, which lays the foundation for the design, manufacturing, and application of the PRSM.

The Main Directions of Improving the Reliability of Threaded Joints in the Nodes and Assemblies of Present-Day Cars

Приведён анализ результатов эксплуатации автомобилей отечественного и иностранного производства в условиях автотракторных предприятий Ярославской области с целью определения эффективности применения на них мероприятий, направленных на повышение надёжности резьбовых соединений и исключающих их самоотворачивание в процессе эксплуатации. К таким мероприятиям относятся: применение болтов и гаек новой конфигурации; нанесение клеев и гелей на поверхности резьбы элементов, соединяемых при сборке двигателей на заводах-изготовителях; затяжка резьбовых соединений в несколько приёмов (первый – по крутящему моменту и последующие – по углу поворота болтов). Последний метод чаще всего применяется для затяжки болтов крепления нижних крышек шатунов, крышек коренных опор коленчатого вала и головок цилиндров при сборке двигателей в заводских условиях, являясь наиболее эффективным из всех рассмотренных выше. Его применение на двигателях позволило изготовителям исключить из перечня операций технического обслуживания периодический контроль состояния крепления головок цилиндров. Данный метод рекомендуется применять при ремонте двигателей в условиях эксплуатации. The analysis of the results of operation of cars of domestic and foreign production in the conditions of automotive-tractor enterprises of the Yaroslavl region in order to determine the effectiveness of the application of measures aimed at improving the reliability of threaded joints and excluding their self-loosening during operation is given. Such measures contains the following: the use of bolts and nuts of a new configuration; application of adhesives and gels on the thread surface of the elements connected during the assembly of engines at manufacturing plants; tightening of threaded joints in several steps (the first – by torque effect and the following – by the angle of rotation of the bolts). The latter method is most often used to tighten the big-end bolts, crankshaft main support caps and the cylinder heads when assembling the engines in the factory environment being the most effective of all the above. Its use on engines allowed manufacturers to exclude from the list of maintenance operations periodic monitoring of the state of cylinder heads attachment. This method is recommended to use when engine repairing under operating conditions.

Effect of oil adhesion on the measurement of screw thread with machine vision

In the process of screw thread manufacturing, the cooling liquid or lubricating oil will adhere to the screw thread surface, which affects the vision measurement results of the screw thread parameters. To simulate the adhesion behavior of oil on the thread surface during the actual measurement, four different attachment states were set in this experiment. An image measuring instrument was used to collect the screw thread images of different adhesion states. Then, the distribution of the oil film on the screw thread surface was analyzed with computer image processing. The visual inspection method was used to obtain the relative influence rate of the oil adhesion on the measurement result of the screw thread parameters. Finally, an experiment-based pitch diameter compensation method was proposed, and the compensation effect of this method was verified with the test method. Experiments showed that the effect of oil adhesion on the measurement results of the diameter parameters is greater than 7 µm, and the effect on the measurement result of the thread angle is greater than 0.1°. The compensation experiment showed that the compensation efficiency was above 70% for the pitch diameter.

Innovation technologies in metal pressure forming for transport engineering

Modern innovation technologies in metal pressure forming for transport engineering are presented. The analysis of the blank stress-strain properties impact upon parts quality is carried out. A method for thread surface layer strengthening is considered. The impact assessment of an elongation ratio and anisotropy upon ear values is carried out.

Examination of a Low-Profile Spinal Implant

Most spine implant devices are fabricated outside Japan, and therefore do not always fit the bodies of Japanese people. This causes a quality-of-life (QOL) problem in which patients feel the embedded implant devices on their back. The aim of this study was to develop more compact and lower-profile spine implant devices. Three types of devices with different heights and different screw threads were created, and the removal torque (fitting force) of the devices was measured after a static load test and cyclic load test. In addition, the screw thread surface was observed in detail after the tests. The results indicated that the mechanism of the reduction in the fitting force was related to partial contact due to abrasion or plastic deformation of the screw thread surface and decrease in the contact area between the screw threads caused by the increased diameter of the upper opening of the implant device after tightening. Therefore, we concluded that lowering the height of the implant device, securing the number of the screw threads, and securing the contact area of the threads are important in developing a low-profile spine implant.

In Vitro Laser Treatment Platform Construction with Dental Implant Thread Surface on Bacterial Adhesion for Peri-Implantitis

This study constructs a standard in vitro laser treatment platform with dental implant thread surface on bacterial adhesion for peri-implantitis at different tooth positions. The standard clinical adult tooth jaw model was scanned to construct the digital model with 6 mm bone loss depth on behalf of serious peri-implantitis at the incisor, first premolar, and first molar. A cylindrical suite connected to the implant and each tooth root in the jaw model was designed as one experimental unit set to allow the suite to be replaced for individual bacterial adhesion. The digital peri-implantitis and suite models were exported to fulfill the physical model using ABS material in a 3D printer. A 3 mm diameter specimen implant on bacterial adhesion against Escherichia coli was performed for gram-negative bacteria. An Er:YAG laser, working with a chisel type glass tip, was moved from the buccal across the implant thread to the lingual for about 30 seconds per sample to verify the in vitro laser treatment platform. The result showed that the sterilization rate can reach 99.3% and the jaw model was not damaged after laser irradiation testing. This study concluded that using integrated image processing, reverse engineering, CAD system, and a 3D printer to construct a peri-implantitis model replacing the implant on bacterial adhesion and acceptable sterilization rate proved the feasibility of the proposed laser treatment platform.

TRIBOLOGICAL WEAR OF WHEEL RIMS IN RAIL VEHICLES IN OPERATING CONDITIONS

Wheel sets as elements determine the reliability and safety in railway traffic demand ensuring high technological and quality standards at the stage of production and exploitation. Not satisfying these conditions may result in, among others, premature wear of wheels in the wheel sets, in turn a shortening between-repair running periods and increasing the exploitation costs of rail vehicles. The authors, based on carried out tests, analysed the influence of not satisfying proper parameters of heat treatment of wheel rims on tribological wear on their surface. This especially concerns abrasive wear of wheel rims and damages of the spalling type on the wheel thread surface in wheel sets.

A Study of Surface Characteristics of Flank Lock Type Precision Locknut Under a Vertical Installation

The study attempted to observe the surface characteristics of the flank lock type precision locknut which was assembled in a vertical type and operates under different tightening speed. The speed setting was in according with the specifications of 4rpm, 6rpm and 8rpm conditions to set up this experiment. A type of 2TML lubricant was used. The experiment investigated the surface characteristics of a locknut, including contact surface flatness, contact surface roughness, and thread surface roughness before and after the designed test. According to the contact surface flatness of the locknut obtained from this study, it was found that the surface of the locknut contacting with the bearing resulted into a deterioration of the surface flatness and surface roughness during the tests. Furthermore, the thread surface roughness has been changed at different thread for different tightening speed during the test, especially at threads 1, 2, 7 and 8. The study found that some of variations occurred in the values of Ra, Rz and Rmax at different thread of a locknut. The variation of Rmax is the most among them.