A THERMAL ANALYSIS OF THE THREADED SPINDLE BEARING ASSEMBLY IN NUMERICALLY CONTROLLED MACHINE TOOLS

A threaded gear in machine tools is a mechanical actuator that converts rotary motion into linear one of the machine axis using a recirculating ball-nut. It provides positioning accuracy, uniform motion, silent operation, reduced wear and an increased service life. The bearing assembly of the threaded spindles should provide load transfer (cutting forces and friction forces) while maintaining high guiding accuracy. Due to a high number of the threaded spindle revolutions and the presence of tension in the bearing and a high axial force originating from the cutting and friction forces, the increased heat load due to friction in the bearings is normally expected. For this reason, this paper presents a thermal analysis of the bearing assembly of the threaded spindle which is realized via an axial ball bearing with angular contact of the ZKLN type, produced by the German manufacturer Schaeffler (INA); in other words, a numerical thermal analysis has been performed

Technology of hardfacing applied to the tramwayswitch-hearts channels

Reparatura oštećenih delova šina i skretničkih srca postupkom navarivanja je standardna metoda održavanja šina u svetu. Beograd je jedini grad u Srbiji u kome postoji tramvajski saobraćaj. Zbog konfiguracije terena po kome su postavljene tramvajske šine i zbog točkova tramvaja nove generacije od austenitnog materijala, sa povišenom tvrdoćom, pojavio se problem habanja skretničkih srca. Na zahtev Vossloh-a iz Niša urađena je tehnologiju navarivanja kanala šina na tramvajskim srcima u Nemanjinoj ulici u Beogradu, a firma Vossloh izvršila navarivanje. U radu je dat pregled tehnologije navarivanja, kao i rezultati ispitivanja tvrdoće, makro i mikro ispitivanja na probnom uzorku, na osnovu koga bi bilo moguće praćenje eksplotacionog veka ovako navarenih kanala skretničkih srca.Reparation of damaged tramway tracks and tramway switch-hearts by hardfacing method is standard procedure of tramway tracks maintenance in the world. Belgrade is single one city in Serbia with tram traffic. Regarding on terrene configuration, where tramway tracks are laid on, and regarding on new-generation-tram-wheels, made of austenite hardened steel, problem of tramwayswitch-hearts wearing has appeared. Requested by Vossloh, hardfacing technology has been applied on tramwayswitch-hearts in Nemanjina Street, Belgrade, by Vossloh. This paper gives overview on hardfacing technology and result of hardness testing, micro and macroprobe testing, which enable exploiting work rate investigation for tramwayswitch-hearts

Technology of hardfacing applied to the tramwayswitch-hearts channels

Reparatura oštećenih delova šina i skretničkih srca postupkom navarivanja je standardna metoda održavanja šina u svetu. Beograd je jedini grad u Srbiji u kome postoji tramvajski saobraćaj. Zbog konfiguracije terena po kome su postavljene tramvajske šine i zbog točkova tramvaja nove generacije od austenitnog materijala, sa povišenom tvrdoćom, pojavio se problem habanja skretničkih srca. Na zahtev Vossloh-a iz Niša urađena je tehnologiju navarivanja kanala šina na tramvajskim srcima u Nemanjinoj ulici u Beogradu, a firma Vossloh izvršila navarivanje. U radu je dat pregled tehnologije navarivanja, kao i rezultati ispitivanja tvrdoće, makro i mikro ispitivanja na probnom uzorku, na osnovu koga bi bilo moguće praćenje eksplotacionog veka ovako navarenih kanala skretničkih srca.Reparation of damaged tramway tracks and tramway switch-hearts by hardfacing method is standard procedure of tramway tracks maintenance in the world. Belgrade is single one city in Serbia with tram traffic. Regarding on terrene configuration, where tramway tracks are laid on, and regarding on new-generation-tram-wheels, made of austenite hardened steel, problem of tramwayswitch-hearts wearing has appeared. Requested by Vossloh, hardfacing technology has been applied on tramwayswitch-hearts in Nemanjina Street, Belgrade, by Vossloh. This paper gives overview on hardfacing technology and result of hardness testing, micro and macroprobe testing, which enable exploiting work rate investigation for tramwayswitch-hearts

Analytical Algorithm Expressions in Simulation of the Temperature Field in Electric Resistance Spot Welding

The paper presents the method of obtaining mathematical equations named "Analytical algorithm expressions" which enable simple creation of computer programs for simulation of the temperature field in the weld zone in electric resistance spot welding. Knowledge of these equations and the manner of their formulation make creation of program packages easier but they do not change anything with respect to the structure and scope of necessary input data which determine concrete initial and boundary conditions. In addition to providing algorithm description of the temperature field, the considered approach is applied for mathematical description of the field of any other physical value relevant for the welding process (specific current, electric potential, density, etc.). In this paper they are realized in temperature fields, as hierarchically superior to the fields of stress and current density, i.e. fields of physical properties of materials of the sheet and the electrode (superiority refers to the algorithm domain). Results of simulation for the non-stationary period of the welding process at two extreme discreet moments are presented at the end

DETERMINATION OF LOAD SPECTRUM OF BUCKET WHEEL EXCAVATOR SRS 1300 IN COAL STRIP MINE DRMNO

Toothed gear power transmissions are complex mechanical systems and their design is a very challenging engineering task that requires the application of common calculation procedures and contemporary designing methods. Operating conditions of the gear power transmission are important for the design process from the aspect of overload prediction and they are defined within the design process by the operating condition factor KA, which has a wide range of values (1 to 2.5), prescribing various operating situations. However, a good design of the toothed gear power transmission can be achieved if operating conditions are simulated and as such implemented in the calculation/design procedure. Such improvement in the design process can be done with the use of defined load spectra that accurately describe realistic operating conditions. The paper presents the results of tensiometric measurements of torque at the output shaft of the working wheel gearbox of the bucket wheel excavator SRs 1300 TAKRAF in the coal strip mine Drmno, and gives a definition of appropriate load spectra based on these tensiometric measurements. The load spectra are defined by applying the full cycle discretization method and as such afterwards used for the calculations/design of the working wheel of the bucket wheel excavator (gears, shafts, shaft keys etc.)

DYNAMIC BEHAVIOUR OF HOT WATER BOILERS DURING START UP

The most commonly used central units in the district heating system are most certainly hot water boilers. Experience in exploitation as well as their former development have given rise to new demands and possibilities of using hot water boilers for achieving a more efficient utilization of fuel. Yet, the current trend is not only for an efficient operation in terms of energy efficiency of primary fuel, but it also comprises many strict requirements when it comes to a cost-effective, reliable and safe operation. A mathematical - empirical model of the hot water boiler during the start-up process is presented in this paper. The dynamic behavior of the object will be discussed in the start-up regime because it represents one of the most critical transient regimes during the operation

Experimental studies of parameters affecting the heat generation in friction stir welding process

Heat generation is a complex process of transformation of a specific type of energy into heat. During friction stir welding, one part of mechanical energy delivered to the welding tool is consumed in the welding process, another is used for deformational processes etc., and the rest of the energy is transformed into heat. The analytical procedure for the estimation of heat generated during friction stir welding is very complex because it includes a significant number of variables and parameters, and many of them cannot be fully mathematically explained. Because of that, the analytical model for the estimation of heat generated during friction stir welding defines variables and parameters that dominantly affect heat generation. These parameters are numerous and some of them, e. g. loads, friction coefficient, torque, temperature, are estimated experimentally. Due to the complex geometry of the friction stir welding process and requirements of the measuring equipment, adequate measuring configurations and specific constructional solutions that provide adequate measuring positions are necessary. This paper gives an overview of the process of heat generation during friction stir welding, the most influencing parameters on heat generation, constructional solutions for the measuring equipment needed for these experimental researches and examples of measured values

Supplementary data for article: Petković, B. B.; Stanković, D.; Milčić, M.; Sovilj, S. P.; Manojlović, D. Dinuclear Copper(II) Octaazamacrocyclic Complex in a PVC Coated GCE and Graphite as a Voltammetric Sensor for Determination of Gallic Acid and Antioxidant Capacity of Wine Samples. Talanta 2015, 132, 513–519. https://doi.org/10.1016/j.talanta.2014.09.025

Supplementary material for: [https://doi.org/10.1016/j.talanta.2014.09.025]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1654]Related to accepted version: [http://cherry.chem.bg.ac.rs/handle/123456789/3363

Basic terms in friction stir welding according to AWS D17.3/D17.3M:2010 i ISO 25239-1: 2011

Zavarivanje trenjem sa mešanjem - ZTM (eng. Friction Stir Welding - FSW) je relativno mlad postupak zavarivanja u čvrstom stanju nastao na Institutu za zavarivanje (TWI) u Londonu, krajem 1991. godine. Prva primena ZTM postupka se vezuje za železnicu i zavarivanje aluminijuma i njegovih legura ali se sa vremenom proširio opseg primene tako da se danas ovim postupkom uspešno zavaruje veliki broj čistih metala, legura, ali i nemetala, u svim industrijskim granama (železnica. avioindustrija, automobilska, brodogradnja itd.). Dve decenije po nastajanju, ZTM postupak se ipak, najviše koristi za zavarivanje aluminijuma i njegovih legura, te nije iznenađujuće što su prvi koraci standardizacije ZTM postupka vezani za zavarivanje aluminijuma. Ovim radom se skreće pažnja na osnovne pojmove kod ZTM koji su dati u postojećim standardima i predlažu odgovarajući pojmovi na srpskom jeziku.Friction Stir Welding is relatively young welding process in solid state which is created in The Welding Institute - London, during 1991 year. The first application is connected with railway and aluminum and aluminum alloys welding but later the application range is extended, so today this process successfully welded many pure metals, alloys also, non-metals in all industrial branches (railway, aircraft, automotive, shipyard etc). Two decades after formation, FSW process is the mostly used for aluminum and aluminum alloys welding, so it is not surprise that the first step in FSW standardization is connected to aluminum welding. The aim of this paper is to draw attention to basic terms for FSW which are presented in actual standards and suggested appropriated terms on Serbian language