Pub Date : 2017-07-17DOI: 10.5545/SV-JME.2017.4384
S. Park, D. Dang, T. Nguyen
Predicting machine tool performance at the design stage is one way to resolve the time issue and achieve cost savings. The objective of this paper was to develop a new non-hydraulic broaching machine using a servo motor, ball screw, and roll element linear guide using virtual prototyping technology. First, we developed a multi-body simulation model (MBS) of a servo-based broaching machine to investigate its dynamic behaviour. Then, an adaptive sliding mode proportional-integral-derivative (PID)-based controller (ASMPID) was proposed to conduct the broaching process. We then performed a co-simulation between the mechanical structure and virtual controller to investigate the ram body trajectory and identify the optimal control parameters. Finally, we manufactured a prototype machine to evaluate the simulation results and determine the benefits of the new system. Our results indicated that the proposed model, which includes a mechanical structure and intelligent controller, effectively improved broaching machine design. Therefore, this work is expected to improve the prototyping efficiency of new broaching machines.
{"title":"Development of a Servo-Based Broaching Machine Using Virtual Prototyping Technology","authors":"S. Park, D. Dang, T. Nguyen","doi":"10.5545/SV-JME.2017.4384","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4384","url":null,"abstract":"Predicting machine tool performance at the design stage is one way to resolve the time issue and achieve cost savings. The objective of this paper was to develop a new non-hydraulic broaching machine using a servo motor, ball screw, and roll element linear guide using virtual prototyping technology. First, we developed a multi-body simulation model (MBS) of a servo-based broaching machine to investigate its dynamic behaviour. Then, an adaptive sliding mode proportional-integral-derivative (PID)-based controller (ASMPID) was proposed to conduct the broaching process. We then performed a co-simulation between the mechanical structure and virtual controller to investigate the ram body trajectory and identify the optimal control parameters. Finally, we manufactured a prototype machine to evaluate the simulation results and determine the benefits of the new system. Our results indicated that the proposed model, which includes a mechanical structure and intelligent controller, effectively improved broaching machine design. Therefore, this work is expected to improve the prototyping efficiency of new broaching machines.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90122940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2017.4503
Marko Peternelj, B. Bizjan, B. Širok
In this paper, the industrial process of stone wool primary layer formation has been investigated. The blow-away airflow, collecting chamber suction pressure, and peripheral velocity of collecting member effects on primary layer area density have been investigated. In total, 27 operating points have been measured by means of primary layer visualization. Computer-aided visualization has been carried out by two digital cameras. Each operating point was monitored at two locations: the first one at the beginning of fibre accumulation, forming the primary layer, and the secondary one at the end of the formation zone. The mass attenuation coefficient was calculated for each operating point and then used to calculate the primary layer area density. It was determined that primary layer bulk density distribution and primary layer texture are significantly influenced by accumulation grid peripheral velocity and blow-away airflow; however, suction pressure has a less pronounced effect on those characteristics. At the highest accumulation grid velocity and blow-away flow rate, the area density was 37 % lower than at the lowest grid velocity and blow-away flow, with a corresponding increase in a standard deviation of 750 %. Multiple regression models suggest very good agreement with the measured data (R2 = 0.94 to 0.98).
{"title":"The Influence of Airflow Characteristics and Accumulation Grid Velocity on the Formation of a Stone Wool Primary Layer","authors":"Marko Peternelj, B. Bizjan, B. Širok","doi":"10.5545/SV-JME.2017.4503","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4503","url":null,"abstract":"In this paper, the industrial process of stone wool primary layer formation has been investigated. The blow-away airflow, collecting chamber suction pressure, and peripheral velocity of collecting member effects on primary layer area density have been investigated. In total, 27 operating points have been measured by means of primary layer visualization. Computer-aided visualization has been carried out by two digital cameras. Each operating point was monitored at two locations: the first one at the beginning of fibre accumulation, forming the primary layer, and the secondary one at the end of the formation zone. The mass attenuation coefficient was calculated for each operating point and then used to calculate the primary layer area density. It was determined that primary layer bulk density distribution and primary layer texture are significantly influenced by accumulation grid peripheral velocity and blow-away airflow; however, suction pressure has a less pronounced effect on those characteristics. At the highest accumulation grid velocity and blow-away flow rate, the area density was 37 % lower than at the lowest grid velocity and blow-away flow, with a corresponding increase in a standard deviation of 750 %. Multiple regression models suggest very good agreement with the measured data (R2 = 0.94 to 0.98).","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83732184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2016.4159
M. O. Ogunlana, E. Akinlabi, M. Erinosho
Laser Metal Deposition (LMD) process is a means of producing metal composites with the aid of a laser beam, ejected onto the substrate with the participating powder and fused together after solidification. In this research work, Ti6Al4V alloy is fused with 20 wt % of B4C in order to form metal matrix composites (MMCs). Using the Ytterbium Fibre Laser System powdered at 3000 W, the laser powers were varied between 800 W and 2400 W while all other supporting process parameters were kept constant. The deposited Ti6Al4V-B4C composites were characterized through the surfacing microstructure, microhardness and dry sliding wear. The microstructural properties of the deposited samples were profound, with a Widmanstatten structure of α-Ti, β-Ti and (α+β) Ti phases. The microhardness tests revealed that the composites deposited with a laser power of 2000 W exhibited the highest hardness value and standard deviation of HV 445 ± 61. Furthermore, characterisation revealed that the sample produced with the laser power of 800 W had the lowest wear loss and wear rate of 35.2 × 10–3 mm3 and 6.42 × 10-4 mm3/Nm. However, the motivation for this work is to improve the material properties of the Ti6Al4V alloy for surface engineering applications.
{"title":"Analysis of the Influence of Laser Power on the Microstructure and Properties of a Titanium Alloy-Reinforced Boron Carbide Matrix Composite (Ti6Al4V-B4C)","authors":"M. O. Ogunlana, E. Akinlabi, M. Erinosho","doi":"10.5545/SV-JME.2016.4159","DOIUrl":"https://doi.org/10.5545/SV-JME.2016.4159","url":null,"abstract":"Laser Metal Deposition (LMD) process is a means of producing metal composites with the aid of a laser beam, ejected onto the substrate with the participating powder and fused together after solidification. In this research work, Ti6Al4V alloy is fused with 20 wt % of B4C in order to form metal matrix composites (MMCs). Using the Ytterbium Fibre Laser System powdered at 3000 W, the laser powers were varied between 800 W and 2400 W while all other supporting process parameters were kept constant. The deposited Ti6Al4V-B4C composites were characterized through the surfacing microstructure, microhardness and dry sliding wear. The microstructural properties of the deposited samples were profound, with a Widmanstatten structure of α-Ti, β-Ti and (α+β) Ti phases. The microhardness tests revealed that the composites deposited with a laser power of 2000 W exhibited the highest hardness value and standard deviation of HV 445 ± 61. Furthermore, characterisation revealed that the sample produced with the laser power of 800 W had the lowest wear loss and wear rate of 35.2 × 10–3 mm3 and 6.42 × 10-4 mm3/Nm. However, the motivation for this work is to improve the material properties of the Ti6Al4V alloy for surface engineering applications.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86873557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2017.4449
Yazan Taamneh, K. Bataineh
This work is focused on the steady laminar mixed convection flow in a lid-driven square cavity filled with Al2O3 water-nanofluid using computational fluid dynamics. The top lid of the cavity was kept at a higher temperature in comparison with the bottom wall and moving at a constant speed while the left and right walls were kept insulated. Simulations were performed using Fluent ver. 6.3 where the water based nanofluid was considered as a single phase. A parametric study was conducted, and the effects of the Richardson number (0.1 ≤ Ri ≤ 10), the volume fraction of the nanoparticle (0 ≤ φ ≤ 0.04) on the fluid flow, and heat transfer inside the cavity were investigated. It was found that when (1 ≤ Ri ≤ 10) the average Nusselt number increases accordingly for the whole range of solid volume fraction of the nanofluid. The simulation results showed that the presence of nanoparticles in the base fluid increases the heat transfer rate. The variations of isotherm and streamline patterns inside the cavity with different volume fractions of nanoparticle and Richardson number were discussed and demonstrated.
{"title":"Mixed Convection Heat Transfer in a Square Lid-Driven Cavity Filled with Al2O3-Water Nanofluid","authors":"Yazan Taamneh, K. Bataineh","doi":"10.5545/SV-JME.2017.4449","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4449","url":null,"abstract":"This work is focused on the steady laminar mixed convection flow in a lid-driven square cavity filled with Al2O3 water-nanofluid using computational fluid dynamics. The top lid of the cavity was kept at a higher temperature in comparison with the bottom wall and moving at a constant speed while the left and right walls were kept insulated. Simulations were performed using Fluent ver. 6.3 where the water based nanofluid was considered as a single phase. A parametric study was conducted, and the effects of the Richardson number (0.1 ≤ Ri ≤ 10), the volume fraction of the nanoparticle (0 ≤ φ ≤ 0.04) on the fluid flow, and heat transfer inside the cavity were investigated. It was found that when (1 ≤ Ri ≤ 10) the average Nusselt number increases accordingly for the whole range of solid volume fraction of the nanofluid. The simulation results showed that the presence of nanoparticles in the base fluid increases the heat transfer rate. The variations of isotherm and streamline patterns inside the cavity with different volume fractions of nanoparticle and Richardson number were discussed and demonstrated.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73404906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2017.4366
B. Žugelj, M. Kalin
We present apparatus that allows in-situ optical measurements of the evolving real contact area between a rigid glass and a deformable Al6026 surface with 700 nm of lateral and 20 nm of vertical resolution. In previous experimental studies of multi-asperity real contact area this was investigated either with much less accuracy or did not include the full (loaded) nominal contact area, which can hinder the relevant sub-micron deformation phenomena. During experiments involving the real contact area, the contact load and asperity deformations are simultaneously measured. To show the relevance of the developed experimental procedure measurements are compared to the results calculated with the Greenwood-Williamson (GW) and a modified Abbott-Firestone (AF(H)) models, which represent the two extreme deformation-regime models. The AF(H) model shows relatively good agreement between the real contact area and the asperity deformations (< 60 %), while the GW model deviates by up to 10 times, depending on the deformation value. In contrast, the GW model shows better agreement for the relationship between the contact load and the asperity deformation (< 20 %), while the AF(H) deviates by more, approximately 30 %. The results also indicate that the real contact area is a non-linear function of the contact load, while theoretical models predict their linearity. Finally, it is demonstrated that the real contact area reaches only up to 9 % of the nominal value in the loading range up to the material yield strength, as calculated for the nominal contact parameters.
{"title":"In-situ Observations of a Multi-Asperity Real Contact Area on a Submicron Scale","authors":"B. Žugelj, M. Kalin","doi":"10.5545/SV-JME.2017.4366","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4366","url":null,"abstract":"We present apparatus that allows in-situ optical measurements of the evolving real contact area between a rigid glass and a deformable Al6026 surface with 700 nm of lateral and 20 nm of vertical resolution. In previous experimental studies of multi-asperity real contact area this was investigated either with much less accuracy or did not include the full (loaded) nominal contact area, which can hinder the relevant sub-micron deformation phenomena. During experiments involving the real contact area, the contact load and asperity deformations are simultaneously measured. To show the relevance of the developed experimental procedure measurements are compared to the results calculated with the Greenwood-Williamson (GW) and a modified Abbott-Firestone (AF(H)) models, which represent the two extreme deformation-regime models. The AF(H) model shows relatively good agreement between the real contact area and the asperity deformations (< 60 %), while the GW model deviates by up to 10 times, depending on the deformation value. In contrast, the GW model shows better agreement for the relationship between the contact load and the asperity deformation (< 20 %), while the AF(H) deviates by more, approximately 30 %. The results also indicate that the real contact area is a non-linear function of the contact load, while theoretical models predict their linearity. Finally, it is demonstrated that the real contact area reaches only up to 9 % of the nominal value in the loading range up to the material yield strength, as calculated for the nominal contact parameters.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77042274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2017.4332
Xiaofeng Wang, Jun Liu, W. Ge
To detect a transverse crack caused by fatigue or creep, most of the research has thus far paid attention only to resonances of steady-state oscillations created by the crack and proposed diagnosis systems utilizing these vibration phenomena. However, from a practical view point, these diagnosis systems have the following flaws: (1) the probability that a resonance occurs due to a crack in the rated rotational speed range is a lower position; (2) It is very dangerous to observe vibration characteristics in resonance ranges. In order to solve these problems, this paper uses a practical detection method utilizing the characteristic changes in a transient oscillation during the start-up, the shutdown, or the variable running speeds of rotating machinery. This method has great advantages, because it can check the occurrence signals of a crack in a wide speed range using a single sweep and avoid the operation in dangerous resonance ranges. Non-stationary characteristics during passages through the main resonance and various kinds of resonances are studied numerically and experimentally.
{"title":"A Practical Method to Detect a Transverse Cracked Rotor Using Transient Response","authors":"Xiaofeng Wang, Jun Liu, W. Ge","doi":"10.5545/SV-JME.2017.4332","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4332","url":null,"abstract":"To detect a transverse crack caused by fatigue or creep, most of the research has thus far paid attention only to resonances of steady-state oscillations created by the crack and proposed diagnosis systems utilizing these vibration phenomena. However, from a practical view point, these diagnosis systems have the following flaws: (1) the probability that a resonance occurs due to a crack in the rated rotational speed range is a lower position; (2) It is very dangerous to observe vibration characteristics in resonance ranges. In order to solve these problems, this paper uses a practical detection method utilizing the characteristic changes in a transient oscillation during the start-up, the shutdown, or the variable running speeds of rotating machinery. This method has great advantages, because it can check the occurrence signals of a crack in a wide speed range using a single sweep and avoid the operation in dangerous resonance ranges. Non-stationary characteristics during passages through the main resonance and various kinds of resonances are studied numerically and experimentally.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87379688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.5545/SV-JME.2016.4184
A. Yıldız, O. Kopmaz
The continuously variable transmission (CVT) system represents one of the best solutions to minimize the fuel consumption for vehicles that are driven by an internal combustion engine or an electrical motor. Hence, the theoretical analysis of a chain CVT is crucial in the optimization of the design and control strategy. This paper is concerned with the transient dynamics of a chain CVT with a speed ratio controller adopted from the Carbone-Mangialardi-Mantriota model and its experimental verification. To this end, a theoretical model is developed with a PI speed ratio controller, considering the momentary solution of a first order differential equation governing the shifting speed, which represents the whole dynamics of the CVT. To verify the developed model, the experiments are carried out on a chain CVT test rig. It is observed that the numerical and experimental results are in good agreement, which implies that the developed model embedded in a speed ratio controller is appropriate to predict the shifting dynamics of the chain CVT. Afterwards, the developed model is used to design the appropriate PI gains by numerical experiments in order to obtain the same slope of the time response of speed ratio for different input angular velocities. Therefore, the same shifting speed can be secured for the different working conditions in this manner. This paper contains very important results for manufacturers about the control parameter and gain effect on the shifting dynamics of chain CVT, and the developed model can be used for different control algorithms in automotive applications.
{"title":"Control-Oriented Modelling with Experimental Verification and Design of the Appropriate Gains of a PI Speed Ratio Controller of Chain CVTs","authors":"A. Yıldız, O. Kopmaz","doi":"10.5545/SV-JME.2016.4184","DOIUrl":"https://doi.org/10.5545/SV-JME.2016.4184","url":null,"abstract":"The continuously variable transmission (CVT) system represents one of the best solutions to minimize the fuel consumption for vehicles that are driven by an internal combustion engine or an electrical motor. Hence, the theoretical analysis of a chain CVT is crucial in the optimization of the design and control strategy. This paper is concerned with the transient dynamics of a chain CVT with a speed ratio controller adopted from the Carbone-Mangialardi-Mantriota model and its experimental verification. To this end, a theoretical model is developed with a PI speed ratio controller, considering the momentary solution of a first order differential equation governing the shifting speed, which represents the whole dynamics of the CVT. To verify the developed model, the experiments are carried out on a chain CVT test rig. It is observed that the numerical and experimental results are in good agreement, which implies that the developed model embedded in a speed ratio controller is appropriate to predict the shifting dynamics of the chain CVT. Afterwards, the developed model is used to design the appropriate PI gains by numerical experiments in order to obtain the same slope of the time response of speed ratio for different input angular velocities. Therefore, the same shifting speed can be secured for the different working conditions in this manner. This paper contains very important results for manufacturers about the control parameter and gain effect on the shifting dynamics of chain CVT, and the developed model can be used for different control algorithms in automotive applications.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77214075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-08DOI: 10.5545/SV-JME.2017.4324
M. Finžgar, P. Podržaj
In this paper we present a study of vision-based, human-recognition solutions in human-oriented, mobile-robot applications. Human recognition is composed of detection, tracking and identification. Here, we provide an analysis of each step. The applied vision systems can be conventional 2D, stereo or omnidirectional. The camera sensor can be designed to detect light in the visible or infrared parts of the electromagnetic spectrum. Regardless of the method or the type of sensor chosen, the best results in human recognition can be obtained by using a multimodal solution. In this case, the vision system is enhanced with other forms of sensory information. The most common sensors are laser range finders, microphones and sonars. As medicine is expected to be one of the main fields of application for mobile robots, we give it special emphasis. An overview of current applications and proposal of potential future applications are given. Without doubt, properly controlled mobile robots will play an ever-increasing role in the future of medicine.
{"title":"Machine-Vision-Based Human-Oriented Mobile Robots: A Review","authors":"M. Finžgar, P. Podržaj","doi":"10.5545/SV-JME.2017.4324","DOIUrl":"https://doi.org/10.5545/SV-JME.2017.4324","url":null,"abstract":"In this paper we present a study of vision-based, human-recognition solutions in human-oriented, mobile-robot applications. Human recognition is composed of detection, tracking and identification. Here, we provide an analysis of each step. The applied vision systems can be conventional 2D, stereo or omnidirectional. The camera sensor can be designed to detect light in the visible or infrared parts of the electromagnetic spectrum. Regardless of the method or the type of sensor chosen, the best results in human recognition can be obtained by using a multimodal solution. In this case, the vision system is enhanced with other forms of sensory information. The most common sensors are laser range finders, microphones and sonars. As medicine is expected to be one of the main fields of application for mobile robots, we give it special emphasis. An overview of current applications and proposal of potential future applications are given. Without doubt, properly controlled mobile robots will play an ever-increasing role in the future of medicine.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85771758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-08DOI: 10.5545/SV-JME.2016.4188
G. Gupta, S. Chattopadhyaya
This paper highlights a methodology for failure investigation of superheater tubes made of the material T-22 of a coal-based boiler. The process includes visual observation, the identification of sampling locations, the determination of the bulk chemical composition of the base alloy, microstructural investigation using optical microscopy, the exploration of finer structural details using a scanning electron microscope (SEM), the evaluation of hardness over samples obtained from different locations, the fractographic analysis of different failed locations, the X-ray diffraction (XRD) study of corrosion products adhered to inner surfaces, and the determination of the nature of the failure. Within a span of four months, three successive failures of superheater tubes were reported. The tubes were observed to have undergone significant wall thinning. Microscopic examinations using SEM on the failed region and a region some distance away on the as-received tubes were conducted in order to determine the failure mechanism. Layer-wise oxidation corrosion (exfoliation) in the inner surface was observed. Apart from major cracking, a number of nearly straight line crackings were observed in the longitudinal direction of both tubes. Close to cracking/bulging, void formation/de-cohesion of grain boundary indicated creep deformation under service exploitation. The failure mechanism was identified to be a result of excessive oxidation corrosion along the inside wall to reduce thickness, the spheroidization of alloy carbides and the coarsening of precipitate as well as creep void formation along grain boundary leading to inter-granular cracking with material flow near regions covered with thick scales. Moreover, there was a drastic reduction in bulk hardness of alloy and finally ‘thin lip fish mouth’ fractures.
{"title":"Critical Failure Analysis of Superheater Tubes of Coal-Based Boiler","authors":"G. Gupta, S. Chattopadhyaya","doi":"10.5545/SV-JME.2016.4188","DOIUrl":"https://doi.org/10.5545/SV-JME.2016.4188","url":null,"abstract":"This paper highlights a methodology for failure investigation of superheater tubes made of the material T-22 of a coal-based boiler. The process includes visual observation, the identification of sampling locations, the determination of the bulk chemical composition of the base alloy, microstructural investigation using optical microscopy, the exploration of finer structural details using a scanning electron microscope (SEM), the evaluation of hardness over samples obtained from different locations, the fractographic analysis of different failed locations, the X-ray diffraction (XRD) study of corrosion products adhered to inner surfaces, and the determination of the nature of the failure. Within a span of four months, three successive failures of superheater tubes were reported. The tubes were observed to have undergone significant wall thinning. Microscopic examinations using SEM on the failed region and a region some distance away on the as-received tubes were conducted in order to determine the failure mechanism. Layer-wise oxidation corrosion (exfoliation) in the inner surface was observed. Apart from major cracking, a number of nearly straight line crackings were observed in the longitudinal direction of both tubes. Close to cracking/bulging, void formation/de-cohesion of grain boundary indicated creep deformation under service exploitation. The failure mechanism was identified to be a result of excessive oxidation corrosion along the inside wall to reduce thickness, the spheroidization of alloy carbides and the coarsening of precipitate as well as creep void formation along grain boundary leading to inter-granular cracking with material flow near regions covered with thick scales. Moreover, there was a drastic reduction in bulk hardness of alloy and finally ‘thin lip fish mouth’ fractures.","PeriodicalId":49472,"journal":{"name":"Strojniski Vestnik-Journal of Mechanical Engineering","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2017-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85778670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-08DOI: 10.5545/SV-JME.2016.4247
M. Di̇rek, Alper Keleşoğlu, A. Akın
This paper presents the experimental comparative performance analysis of an automotive air conditioning (AAC) system using R1234yf and R134a. For this purpose, an AAC experiment setup used for R134a was built to obtain the drop-in performance of a new refrigerant R1234yf. Among the low global warming potential (GWP) refrigerants, R1234yf was particularly chosen due to its similar thermo-physical properties with R134a. However, the system with R1234yf could not perform as efficiently as R134a can. Therefore, an internal heat exchanger (IHX) was employed to enhance the performance of the R1234yf system. After that, the performances of R1234yf and R134a were compared under various compressor speeds and air stream temperatures. The results showed that the cooling capacity and COP of the system with R1234yf were 17.1 % and 12.4 %, respectively, lower compared to the one with R134a. However, when the IHX was introduced into the system with R1234yf, the cooling capacity and COP values were significantly enhanced by 7.9 % and 4.1 %, respectively.
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