Evaluation of hoop residual stress variations in the thickness of dissimilar welded pipes by using the LCR ultrasonic waves

Mjerenje naprezanja pomoću ultrazvučnih valova temelji se na akustičnoelastičnom zakonu, t.j.odnosu između naprezanja i brzine valova u inženjerskim materijalima. Uzdužni kritički lomljen - Longitudinal critically refracted (LCR) val je popularni ultrazvučni val u primjeni ultrazvučnog mjerenja naprezanja. LCR val je masovni uzdužni val koji putuje na efektivnoj dubini ispod površine. U ovom radu procjenjuje se varijacija cirkularnog zaostalog naprezanja u debljini cijevi. Cijev je proizvedena zavarivanjem dviju različitih cijevi od nehrđajućeg čelika AISI 304 i ugljičnog čelika tipa A106-B. Varijacije zaostalih naprezanja u debljini cijevi mjere se pomoću četiri različite frekvencije pretvarača, dok su nominalne frekvencije 1 MHz, 2 MHz, 4 MHz i 5 MHz. Uporabom različitih frekvencija omogućeno je LCR valovima da prodru do različitih dubina i mjere veličinu naprezanja cijevi. Pokazalo se da se razlika u naprezanju između unutarnje i vanjske površine cijevi i također između strane cijevi od nehrđajućeg čelika i one od ugljičnog čelika može procijeniti pomoću LCR valova.Stress measurement by using ultrasonic waves is based on acoustoelasticity law, i. e. the relation between stress and wave velocity in engineering materials. Longitudinal critically refracted (LCR) wave is a popular ultrasonic wave in the ultrasonic stress measurement application. The LCR wave is a bulk longitudinal wave that travels within an effective depth underneath the surface. This paper evaluates hoop residual stress variation in the thickness of a pipe. The pipe is manufactured by welding two dissimilar pipes from AISI stainless steel 304 and carbon steel A106-B type. The residual stresses variations in the thickness of pipe are measured by using four different frequencies of transducers while the nominal frequencies are 1 MHz, 2 MHz, 4 MHz and 5 MHz. Using different frequencies enables the LCR waves to penetrate in different depths and measure the bulk stresses of pipe. It has been shown that the stress difference between inner and outer surfaces of pipes and also between the stainless steel and carbon steel side of dissimilar pipe can be evaluated by using the LCR waves

Strengthening Effect after Disintegration of Stainless Steel Using Pulsating Water Jet

The article deals with the measurement of micro-hardness of the track by the action of ultrasonic excitation of pulsating water jet. The cumulative effect of liquid matter in the form of droplets concentrated in waveform measurements was provided in horizontal and vertical direction to material core (AISI 304). The material was subjected to pressures of p = 40, 50 and 60 MPa with the actuator working at a frequency of 20,14 kHz and traverse speed v = 1,1 mm/s, v = 0,80 mm/s and v = 0,30 mm/s respectively. The micro hardness measurement was carried out after machining it by pulsating water jet. The values were recorded in the zone located transversally under the trace to the depth of 1,5 mm with 0,1 mm distance between successive points. It was found that the deformation of material was ascertained from the boundary to the outer environment created by pulsating water jet to the inner core of the material. The results indicate that the pressure was the most influential parameter, which was responsible for the deformation strengthening of the material

Material flow optimization – a case study in automotive industry

Danas je većina organizacija suočena s mnogim dilemama, bit kojih je određivanje načina postizanja ili održavanja stečenog položaja u konkurentnom okruženju. Poduzeća moraju neprestano povećavati svoju ekonomiju. Jedan od načina stjecanja nadmoći nad konkurencijom je analiza i optimizacija toka materijala, što doprinosi smanjenju troškova. Tok materijala u proizvodnoj organizaciji govori nam mnogo o organizaciji sustava. U radu se daje analiza postojećeg stanja toka materijala u jednoj proizvodnoj organizaciji motornih vozila. Predlaže se i projekt optimizacije toka materijala; projekt se sastoji od novog programa internog prijevoza i optimizacije položaja radnih štandova. U radu se opisuju postojeći problemi u internom prijevozu poduzeća i daju rješenja tih problema.Today, most contemporary organisations are facing many dilemmas, the essence of which is the determination of the ways of acquisition or maintenance of their position in the competitive environment. Companies have to continuously increase their economy. One of the ways to get competitive prevalence is analysis and optimization of material flow which contributes to the reduction of the company costs. Material flow in a production organization tells us a lot about how well the system is organised. The paper presents an analysis of the current state of material flow in a production company of the automotive branch. A project of the material flow optimization has also been proposed; the project consists of creation of a program of internal transport and optimization of the location of the working stands. The paper describes the current problems of the company internal transport and indicates solutions to those problems

Research on emulsion mist generation in the conditions of minimum quantity cooling lubrication (MQCL)

U radu se opisuje učinak parametara stvaranja emulzijske izmaglice i udaljenosti mlaznice od kontaktne površine reznog klina s obratkom na promjer i broj kapljica dospjelih u zonu rezanja. Dati su uvjeti stvaranja emulzijske izmaglice u kojoj su sve kapljice, dovedene u zonu rezanja u datom vremenu, u to vrijeme isparile. Opisana je analiza protoka topline u MQCL metodi i dokazano je da protok zraka i udaljenost mlaznice od zone rezanja imaju najvažniji učinak na promjer kapljica.The paper presents the effect of emulsion mist generation parameters and the distance of the nozzle from the contact zone of the cutting wedge with the workpiece on the diameter and number of droplets supplied into the cutting zone. The conditions of emulsion mist generation, in which all the droplets supplied to the cutting zone in a given time, are evaporated in this time. An analysis of heat flow in the MQCL method was presented and it was proved that the air flow and the distance of the nozzle from the cutting zone have the most significant effect on the diameter of droplets

Topographic inspection as a method of weld joint diagnostic

U radu se demonstrira topografsko ispitivanje u specifičnom kontekstu triju vrsta inspekcijskih metoda zavara od austenitnog nehrđajučeg željeza. Vizualna i metrološka kontrola provedena je tijekom ispitivanja zavarivanja TIG postupkom, primjenom ne-destruktivnih metoda: rendgensko ispitivanje, kompjuterizirana tomografija i profilometrija površine. Rad je reakcija na nedostatak informacija, posebice u području ne-destruktivnih metoda prikladnih za široku primjenu u praksi. U radu se prezentiraju prednosti i nedostaci analiziranih dijagnostičkih metoda i klasifikacija uobičajenih i specifičnih mana zavarenog spoja. Najvažnija neispravnost u praktičnim primjenama kod određivanja pouzdanosti zavarenog spoja su pukotine. Ova vrsta dijagnoze zasnovana je na dobivenim podacima o promatranom anizotropskom i nehomogenom volumenu u dijelu zavara pod utjecajem topline.The paper demonstrates a topographic inspection in the specific context of three kinds of inspection methods of austenitic stainless steel welds. Visual and metrological inspection was analysed during tungsten inert gas (TIG) welding tests, showing the non-destructive techniques: X-ray, computed tomography, and surface profilometry. The article is a response to the lack of information, especially in the area of non-destructive techniques suitable for wide practical application. The Paper presents advantages and drawbacks of the analysed diagnostic methods and a classification of conventional and specific welded joint flaws. The most important defect in practical applications determining reliability of a welded joint is cracks. This kind of diagnostic is based on the obtained information about anisotropic and inhomogeneous volume under consideration in the heat-affected zone of a weld

Characterization of Friction Surfaced Coatings of AISI 316 Tool over High-Speed-Steel Substrate

Nowadays friction surfacing (FS) has become a popular solid state surface coating technology suitable for a range of substrates. The technology has the ability to produce coatings with marginal dilution and good metallurgical bonding. The present study has aimed at producing a single-track and a three-track overlapping coatings on high-speed steel substrates using an AISI 316 consumable rod. Microhardness of coatings was examined by a Vickers micro hardness tester. Coatings of all the friction surfaced samples in as-deposited condition showed significant hardness. The infrared thermography showed that the peak temperature achieved by the AISI 316 coating was about 1020 ͦ C. The coatings, thus attained, were further analysed for their microstructural features and interfacial characteristics by using FE-SEM. The EDX analysis showed the presence of nickel, chromium and oxygen, which indicates the formation of oxide compounds. The formation of AISI 316 deposits on the HSS substrate and the effect of coating overlapping are discussed in this article

Experimental Analysis by Measurement of Surface Roughness Variations in Turning Process of Duplex Stainless Steel

The objective of the investigation was to identify surface roughness after turning with wedges of coated sintered carbide. The investigation included predicting the average surface roughness in the dry machining of Duplex Stainless Steel (DSS) and the determination of load curves together with roughness profiles for various cutting conditions. The load curves and roughness profiles for various cutting wedges and variable cutting parameters were compared. It has been shown that dry cutting leads to a decrease in friction for lubricated surfaces, providing a small initial contact area where the surface is contacted. The study has been performed within a production facility during the production of electric motor parts and deep-well pumps

Effect of the disc processing technology on the vibration level of the chipper during operations

Svrha ovog rada je prikazivanje tehnologije reparacije stroja za usitnjavanje drva koji se koristi za usitnjavanje drva u čestice određene veličine. Mobilni stroj za usitnjavanje drva koristi se u proizvodnji papira i postrojenjima za proizvodnju vlakana. Rad prikazuje tehnologiju popravka i balansiranje stroja. U članku se također predstavlja utjecaj djelovanja neuravnoteženih strojnih elemenata na ljudsko tijelo.The purpose of this article is to present the technological repair process of the mobile disc chipper used for crushing raw wood into chips of a certain size. Mobile disc chippers are used in the pulp - paper industry and fibreboard manufacturing plants. The paper presents the technology of repairing the disc chipper and the balancing process of the disc chipper in its own bearings. The article also presents the influence of unbalanced machine elements on the human body

Investigation of wear and tool life of coated carbide and cubic boron nitride cutting tools in high speed milling

The objective of the investigation was analysis of the wear of milling cutters made of sintered carbide and of boron nitride. The article presents the life period of the cutting edges and describes industrial conditions of the applicability of tools made of the materials under investigation. Tests have been performed on modern toroidal and ball-end mill cutters. The study has been performed within a production facility in the technology of high speed machining of 55NiCrMoV6 and X153CrMoV12 hardened steel. The analysed cutting speed is a parameter which significantly influences the intensity of heat generated in the cutting zone. Due to the wear characteristics, two areas of applicability of the analysed tools have been distinguished. For v c  ≤ 300 m/min, sintered carbide edges are recommended; for v c  > 500 m/min, boron nitride edges. For 300 ≤  v c  ≤ 500 m/min, a transition area has been observed. It has been proved that the application of sintered carbide edges is not economically justified above certain cutting speed