bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Laser Heat Treatment Efficiency Evaluation in Multi-Track Surface Hardening
Authors: Campana Giampaolo , Ascari Alessandro , Tani Giovanni
Published: September 2010

Laser surface hardening is nowadays an industrial emerging technique, which is gradually substituting induction and flame surface hardening thanks to its advantages related to power saving and process versatility. This manufacturing technology is a challenging process especially when it has to be applied on surfaces larger than the beam spot. In this case several adjacent passes must be performed in order to scan the whole surface to be treated. This strategy involves inevitably an intrinsic tempering effect due to the re-heating of the previously hardened material. The extent of the softening occurring depends on several parameters. First of all, it depends on the material and its initial state, then on process parameters related to the laser source, such as type, optical path and spot dimension and further on the adopted surface scan strategy of the beam. This last set of process parameters is represented by: laser beam speed, number of tracks, pass overlapping degree and tracks sequence. The hardness uniformity of the heat treated layer and the consequent effectiveness of the process depend strictly on the tempering degree occurring in the material. According to this it is important to find a practical method devoted to quickly characterize the result of a laser surface treatment in terms of tempered zones extension and distribution. This article proposes, then, the definition of a “Covering Uniformity” index (CU) which represents an engineering approach to this problem and it allows to easily determine the effectiveness of a particular laser hardening treatment. The CU index is based upon hardness measurements and it is related to the ratio between the extension of the tempered zone and the total extension of the treated area. In order to underline and demonstrate the intrinsic value of this parameter a set of experimental trials was carried out on AISI 1070 carbon steel, AISI 1040 carbon steel and AISI 420B martensitic stainless steel.
Finite Element Analysis for Orthogonal Cuttings of Hardened AISI 52100 by Advanced cBN-TiN Composite Coated Tools of Two Depositing cBN Particle Sizes
Authors: Nakkiew Wasawat , Liu C. Richard
Published: September 2010

A finite element model is developed to predict the temperature distribution and stress distribution in orthogonal machining of hardened AISI 52100 steel (62HRC) from using advanced cBN-TiN composited coating cutting tools. The advanced cBN-TiN composited coating tool is made of innovative two-stage composite coating methods: ESC (electrostatic spray coating) and CVI (chemical vapor infiltration). For a cBN-TiN composite coating on WC substrate cutting tool used in hard turning process, the ESC of nano-to-micron cBN particles forms a layer over WC-Co and TiN-TiC cermet tool inserts. CVI introduces TiN as binding material through the porous matrix to form a very dense coating. The finite element model is developed for hard turning simulations of composite coating cutting tools with different particulate particle size distributions. In this paper, two different size distributions of depositing cBN particles are investigated: cBN particle sizes of 0.5 and 2μm. Since solid Poly-crystalline Cubic Boron Nitride (PCBN) tool is the dominant cutting tool used for hard turning applications, a comparative study of this advanced composited coating tools to solid PCBN can suggest a possible comparable alternative cutting tool for hard turning applications. Solid PCBN tool provides a lower maximum temperature than cBN-TiN coated tools. A better surface finish on cutting tool surface also has a significant role in lower the maximum temperature in this study.
Spot Friction Welding Joint Strength Improvement Using Localized Metal Matrix Composite Formation
Authors: Arul Senthil G. , Kruger Grant H. , Miller Scott F. , Pan Tsung-Yu , Shih Albert J.
Published: September 2010

This study investigates the application of metal particles in spot friction welding (SFW), a semi-solid state sheet metal joining process, to create the localized metal matrix composite (MMC) for the improvement of lap-shear strength. Ancorsteel® 1000 particles, compressed around the axial center-line of the tool between the upper and lower sheets, was demonstrated to form a localized MMC and effective as the reinforcement particles in aluminum 6111-T4 alloy sheets. Results revealed that the particle MMC in SFW increased the maximum lap-shear by 20%. In the stir-zone, steel particle sizes were significantly reduced due to breaking by mechanical action. Analysis revealed an aluminum-ferrous solid solution formation around the steel particle and aluminum matrix interfaces. In the heat-affected zone along the joint line, steel particles retained their original sizes and reinforced the joint interface. The load deflection curve and cross-section micrographs of the failed lap-shear tensile specimens indicated that, for steel particle MMC samples, the crack path was longer. This was due to a localized MMC forming along the joint interface and was identified as the primary factor responsible for the increase in SFW lap-shear strength.
High Temperature Characteristics of Lap Joint of 15Cr Ferritic Stainless Steel
Authors: Lee Younggi , Lee Gyeongcheol , Kim Jaeseong , Lee Boyoung
Published: September 2010

Ferritic stainless steels have excellent stress corrosion resistance and a low coefficient of thermal expansion compared to austenitic stainless steels. Ferritic stainless steels of the 400 series have been available for automotive exhaust systems, heat exchangers, radiators etc. in various industries. Automotive exhaust manifolds especially require good heat resistance because the typical operation temperature(800°C) of the exhaust system is exposed to during engine operation. In this study, the effects of high temperature(800°C) characteristics on the mechanical and microstructure properties were investigated for lap joint of ferritic stainless steel(STS 429) mainly used as the automotive exhaust manifolds. The microstructure of lap joint was characterized by optical microscopy(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The mechanical property of lap joint was evaluated by tensile test. The tensile test results show that a significant decrease in ultimate tensile strength(between 82 and 85%) was observed for aged STS 429 when tested at the evaluated temperature(800°C). The tensile strength was significantly influenced by growth of grain in the heat affected zone(HAZ). The XRD results show that chromium carbide and chromium nitride phases such as Cr23C6, Cr7C3, Cr2N and TiN were precipitated in the heat affected zone(HAZ).
A Three-Dimensional Transient Modeling and Experimental Analysis of Laser Transformation Hardening by Using High Power Direct Diode Laser
Authors: Santhanakrishnan S. , Kong F. R. , Kovacevic R.
Published: September 2010

Laser transformation hardening (LTH) based on rapid heating and cooling cycles produce hard and wear-resistant layers of the metallic component. A high intensity moving laser beam heats up the thin layer of the external surface of the component without damaging the bulk of material. The metallurgical transformations taking place in the material during the thermo-kinetic cycles could effectively improve the mechanical properties of its surface. Nowadays, a high power direct diode laser (HPDDL) has been accepted by industry as a valuable tool to carry out this process. A three-dimensional (3-D) transient thermo-kinetic model has been developed to predict the temperature profile of the hardened layers of the material surface. The temperature-dependence of the thermal properties of the material is taken into account in the model. The laser beam is considered as a moving line heat source with a uniform distribution of laser power. The numerical solution is obtained by using a transient 3-D heat conduction equation with convection boundary conditions at the surfaces of the workpiece. A number of experiments have been carried out to harden components of AISI S7 tool steel by a continuous wave (CW) HPDDL at different power levels (1200 W – 2000 W) and different scanning speeds (5 mm/s – 20 mm/s). The main processing parameters such as laser power and scanning speed are optimized based on the numerical analysis of the heat conduction involved in this process. The numerical simulation results are compared with results produced experimentally by a HPDDL laser operating in CW, showing good agreement.
Model-Based Control of an Advanced Actuated Part-Fixture System
Authors: Bakker O. J. , Popov A. A. , Ratchev S. M.
Published: September 2010

In this paper the dynamical behavior of a part and an actuated fixture system is studied. The part is modeled using the finite element method. Subsequently, a reduced model is established using the Craig-Bampton reduction method in order to create a small-sized model, accurately describing the dynamic behavior of the part. The clampers and locators of the fixture are modeled as springs. The fixture frame is considered to be much stiffer than the locators such that it provides zero displacement boundary conditions to the locators. An electromechanical actuator is utilized to provide the adaptive clamping forces. After investigating proportional control, integral control, the three term classical PID controller and a lag filter for dynamic compensation, the analysis shows that position feedback can be used effectively in combination with integral control action to minimize unnecessary displacement of the workpiece and increase the bandwidth of the actuated fixture system.
Study on Mechanical Properties of Al Metal Matrix Nanocomposites Processed Using Ultrasonic Vibration
Authors: He F. , Han Q. , Chen Y. C. , Xu C. , Shao L.
Published: September 2010

High intensity ultrasonic vibration was applied to disperse SiC nano-particles into molten A354 during solidification process to fabricate metal matrix nanocomposite (MMNCs). MMNCs: A354/SiC/1p was obtained by dispersing 1% SiC particles into the molten A354. The distribution of the nano-SiC particles in this material was investigated using scanning electron microscope. The mechanical properties of this nano composite were tested. A354/SiC/1p-T6 samples were also fabricated and tested. Mechanical properties of A354/SiC with different weight percentage of SiC particles were also investigated to find out the optimized content of particles. The results suggest that A354/SiC/0.5p-T6 with extra 15 minutes ultrasonic treatment has shown the highest mechanical properties.
Environmental Sustainability of Laser-Based Manufacturing: Case Studies on Laser Shock Peening and Laser Assisted Turning
Authors: Zhao Fu , Naik Gautam , Zhang Li
Published: September 2010

Laser assisted manufacturing (LAM) processes, when compared with traditional manufacturing processes, have the potential to reduce cost, increase surface finish, extend part/tool life, and expand the range of manufacturable materials. However, very limited research has been done to evaluate the environmental performance of laser assisted processes and it is generally not clear how LAM processes compare with traditional methods. This paper conducts case studies on two representative laser based processes, i.e. laser shock peening of 7065 T7351 Aluminum and laser assisted turning of compacted graphite iron. Life cycle assessment is used to benchmark the environmental performance of these two processes to conventional processes, i.e. shot peening and dry turning, respectively. The life cycle inventory of both the laser based processes and conventional processes are developed using SimaPro v7.1 and Ecoinvent 2.0 and life cycle impact assessment is performed using US EPA TRACI. It is found that environmental performance of laser based processes varies significantly from process to process due to materials and energy consumption. Laser shock peening of aluminum has much better performance when over all environmental impact categories considered. Contribution analysis indicates that this is mainly due to the fact that laser shock peening does not need shot medium and at the same time significantly extends fatigue life of the workpiece. However, due to high electricity consumption and use of absorptive paint, laser assisted turning of compacted graphite iron has much higher environmental impacts than traditional dry turning, even after extending the tool life significantly.
Improvement of Surface Flatness in Face Milling by Varying the Tool Cutting Depth and Feed Rate
Authors: Tai Bruce L. , Stephenson David A. , Shih Albert J.
Published: September 2010

This paper explores two approaches to improve the flatness of face milled surfaces by modifying the tool cutting depth and feed rate based on the 3D holographic laser measurement. The tool cutting depth compensation method generates a cutting path which is the mirror image of the measured error profile to reduce the flatness errors. Issues of back-cutting and the interference due to cutter size limit the range of applicability of this approach. The feed rate is varied to match the axial force on the cutter with the local compliance of the workpiece to further improve the surface flatness. Using a flat plate workpiece and 50.8 mm diameter face milling cutter, the surface flatness can be reduced from around 15 μm without compensation to lower than 10 μm by varying tool cutting depth. Modification of feed rate further reduces the flatness errors from 10 μm to 6 μm. Automatic tool path compensation based on holographic feedback is also discussed.
Experimental Study of Lapping Using Mixed Abrasive Grits
Authors: Chung Chunhui , Melendez Glenn , Kao Imin
Published: September 2010

Wafers made of materials such as silicon, III-V and II-VI compounds, and optoelectronic materials, require high-degree of surface quality in order to increase the yield in micro-electronics fabrication to produce IC chips and devices. Measures of properties of surface quality of wafers include: nanotopography, surface morphology, global planarization, total thickness variation (TTV) and warp. Due to the reduction of feature size in micro-electronics fabrication, the requirements of such properties become more and more stringent. To meet such requirements, the wafer manufacturing processes of brittle semiconductor materials, such as slicing, lapping, grinding, and polishing have been continually improved. In this paper, the lapping process of wafer surface treatment is studied with experimental results of surface roughness and material removal rate. In order to improve the performance of lapping process, effects of mixed abrasive grits in the slurry of the free abrasive machining (FAM) processes are studied using a single-sided wafer-lapping machine. Under the same slurry density, experiments employing different mixing ratios of large and small abrasive grits, and various normal loadings on the wafer surface applied through a jig are conducted for parameter study. With various mixing ratios and loadings, observations and measurements such as the total amount of material removed, material removal rate, surface roughness, and relative angular velocity are presented and discussed in this paper. The experiments show that the half-half mixing ratio of abrasives removes more material than other mixing ratios under the same conditions, but with a higher surface roughness. The results of this study can provide a good reference to the FAM processes that practitioners use today by exploiting different mixing ratios and loadings of abrasive slurry in the manufacturing processes.
Laser Assisted Finish Turning of Inconel 718: Process Optimization
Authors: Tavakoli Salar , Attia Helmi , Vargas Raul , Thomson Vincent
Published: September 2010

Generally, superalloys have superior strength and toughness compared to conventional engineering material. However, while applications for such materials are growing, the improvement of their machinability has not been improved in parallel. Of particular interest to the aerospace industry, are nickel-based superalloys. Inconel 718, which is one type of nickel-based superalloy, is considered difficult-to-machine at room temperature due to the fact that it retains much of its strength at high temperatures. Conventional machining methods applied to these materials results in excessive tool wear and poor surface finish. One approach, which is becoming increasingly popular with difficult-to-machine materials, is laser assisted machining (LAM). This study assesses the effect of LAM on the machinability of Inconel 718 using a triple-layer coated carbide tool in terms of cutting forces, tool wear and surface finish. A focused Nd:YAG laser beam was used as a localized heat source to thermally soften the workpiece prior to material removal. Finishing operations were assumed throughout the experiments. Cutting tests were performed over a wide range of cutting speeds (ranging from 100 to 500 m/min) and feeds (ranging from 0.125 to 0.500 mm/rev) to determine the optimum cutting speed and feed for each tool material. Results showed a significant drop in all three components of cutting force when thermal softening caused by the laser power was in effect. A two to three fold improvement was observed in terms of surface finish and tool wear under LAM conditions when compared to conventional machining.
Diode Laser Cure of Thermosetting Powders for Writing on Painted and Unpainted Metallic Surfaces
Authors: Santo Loredana , Tagliaferri Vincenzo , Trovalusci Federica
Published: September 2010

This paper describes an innovative system to make writings or patterns on painted or unpainted metallic surfaces by diode laser cure of thermosetting powders. The process is very interesting to personalize objects such as automotive components and others. An electrostatic deposition of commercial thermosetting powder is performed on metallic surfaces, the laser beam passes on the deposited powder following a fixed path and cures it. A process map was found in terms of laser power and scan speed. The laser power is in the range 55–70 W for a scan speed of 1 or 2 mm/s in the case of metallic surfaces, while the power is in the range 35–50 W for the same scan speeds in the case of painted surfaces. Visual inspection and scratch tests were performed in order to evaluate the aspect and the adhesion to the substrate. Very good results were found demonstrating that the diode laser is a useful tool to make writing.
Reactive Process Planning: Incorporating Machining, Inspection, and Feedback
Authors: Zhao Yaoyao F. , Xu Xun W. , Xie Sheng Q.
Published: September 2010

Closed-Loop Manufacturing (CLM) techniques include machine tool self-checks, automated setups, tool measurement, in-process probing with process adjustment, on-machine final inspection, data collection and data analysis. All of these elements and more are utilized to collect data in a mostly automated fashion to subsequently correct and adjust undesired conditions that can affect part quality. Inspection process planning plays an essential part of CLM. As G&M codes that contains low-level information or vendor-specific bespoke routines is the primary programming language, inspection process planning is mostly isolated from machining process planning. With the development of new data model standards such as STEP and STEP-NC providing high-level product information for the entire manufacturing chain, it is conceivable that both machining and inspection process planning are considered hand-in-hand to generate optimal machining and inspection sequences with real-time measurement feedback for the CLM scenario. This paper introduces an reactive process planning system architecture that incorporates machining, inspection, and feedback. In order to provide real-time inspection feedback, On-Machine Measurement (OMM) is chosen to carry out inspection operations. Implementation of the proposed architecture has been partially carried out with newly developed data model and interpreter. A case study testified the feasibility of the proposed architecture.
Ultrasonic-Vibration-Assisted Grinding of Titanium: Cutting Force Modeling With Design of Experiments
Authors: Qin Na , Pei Z. J. , Guo D. M.
Published: September 2010

Titanium and its alloys (Ti) have wide applications in industry. However, since Ti is notorious for its poor machinability, their applications have been hindered by the high cost and low efficiency. Ultrasonic-vibration-assisted grinding (UVAG) is a hybrid machining process that combines the material removal mechanisms of diamond grinding and ultrasonic machining, and it is a cost-effective machining process for Ti. The relations between cutting force and input variables have been investigated and reported. But these relations have been studied by changing one variable at time. Therefore, the interactions between cutting force and input variables have not been revealed. In this paper, a two-level five-factor full factorial design is used to study the relations between cutting force and input variables based on a cutting force model for UVAG of Ti. The main effects of these variables, and two-factor interactions and three-factor interactions of these variables are also revealed.
Picosecond Laser Ablation of Polydimethylsiloxane (PDMS)
Authors: Zeng Hansong , Zhao Yi , Wu Benxin , Taylor Chris , Jacobsen Ronald L. , Gao Yibo
Published: September 2010

Picosecond laser ablation of Polydimethylsiloxane (PDMS) has been studied experimentally. The measurements show that laser ablation rate per pulse increases with laser fluence and pulse number. The laser-drilled hole diameter increases with pulse number, and it saturates above certain pulse number for low fluence. The study shows that picosecond laser ablation may provide a good solution for micromachining PDMS, which is more flexible and versatile than the replica molding technique.
Integrated Sensing of Pressure Distribution at the Workpiece-Tool Interface in Sheet Metal Stamping
Authors: Sah Sripati , Gao Robert X.
Published: September 2010

To improve process monitoring in the sheet metal stamping process, it is of interest to measure the contact pressure distribution at the workpiece-tool interface. This paper presents the design and performance evaluation of a tooling integrated sensing method that estimates the pressure distribution on the contact interface through an array of force sensors embedded in the stamping tool. Experiments were conducted to evaluate two techniques for integrating force sensors into the tool structure. The spatially discrete nature of the sensor measurements necessitates the use of a numerical interpolation model to construct continuous pressure distribution maps from the discrete sensing locations. Experiments conducted on a customized panel stamping test bed confirmed the effectiveness of the tooling-integrated sensing method for improving the observability of the process with benefits to process designers.
Multistage Machining Process Design and Optimization Using Error Equivalence Method
Authors: Chen Shaoqiang , Wang Hui , Huang Qiang
Published: September 2010

In design of a multistage machining process, process tolerance allocation at each stage and design of process layouts, in particular, the fixture layouts, should be optimized considering dimensional tolerance stackup or variation propagation. When multiple error sources contribute to the tolerance stackup, the dimensionality of the design space could be large and design solution may not be unique. One strategy is to prioritize the allocation of tolerances to different error sources at each stage through proper selection of cost functions. Considering the fact that the cost function selection can be very subjective and the knowledge regarding cost structures is very limited, we propose a hierarchical process design method using error equivalence concept to aggregate multiple error sources together. The main idea is to allocate tolerances to the aggregated error sources at each stage and then further distribute the tolerance to individual error sources through cost analysis. The advantage is two-fold: (1) limiting the impact of cost function selection within individual stages to avoid overhaul of process design caused by subtle change in cost functions, and (2) enabling the optimization of fixture layouts to reduce the overall tolerance stackup due to multiple error sources. To reduce computational load in optimizing process layouts, a computer experiment model is developed to explore a large number of process design alternatives. The robustness of the optimal tolerance is evaluated through sensitivity analysis, which provides guidance for process design. We illustrate the error-equivalence-based process design method by a multistage machining process. The results have shown that the proposed method could significantly reduce the design space and increase the design efficiency.
Selective Zone Search Method for Evaluation of Minimum Zone Sphericity
Authors: Soman Kedar G. , Ramaswami Hemant , Anand Sam
Published: September 2010

Accuracy, robustness and speed are essential components of every precision engineering procedure. With the availability of high speed inspection machines and the ability to generate large datasets with minimal effort and time, the evaluation algorithm becomes a critical component of the inspection time. This paper presents a new approach for evaluation of minimum zone sphericity tolerance using a selective zone search method. The method uses geometric constructs to identify the five extreme points required to generate the two minimum zone spheres. Four different models have been developed to investigate all possible combinations for the tolerance evaluation, viz. 4-1, 3-2, 2-3 and 1-4 models. The robustness of the algorithm has been tested using various simulated and reported datasets and the results have been found to be comparable to existing methods. The presented algorithm has also shown considerable savings in time compared to a nonlinear optimization formulation for minimum zone sphericity evaluation.
AE Signal Evolutions in Machining by Diamond Coated Tools
Authors: Lu Ping , Chou Y. Kevin , Thompson Raymond G.
Published: September 2010

Diamond coated cutting tools have a potential to replace costly polycrystalline diamond tools. However, coating delaminations remain the primary wear mode that often results in catastrophic tool failures, causing to poor part quality and possible damage to machine tools. Moreover, delamination events are difficult to be precisely predicted. Thus, tool delamination identification is necessary for process monitoring. Following a previous work, this study examines the acoustic emission (AE) signal evolutions during machining by diamond coated tools, in particular, the frequency response along cutting time as well as during a specific cutting pass. The intent was to correlate the characteristics of the AE spectral components with coating delaminations. The results are summarized as follows. Though AE root-mean-square values have been used to monitor tool failure, it may not show clear transition registered to coating delamination in some cases. The fast Fourier transformation (FFT) spectra of AE data along cutting time generally show decreased intensity for low frequency peaks, but increased intensity for high frequency peaks. In addition, the AE FFT spectra of sub-divided time zones during one cutting pass may clearly indicate the coating failure transition.
Modeling of Thermoelastic Stress Wave in Laser-Assisted Cell Direct Writing
Authors: Wang Wei , Huang Yong , Lin Yafu
Published: September 2010

Laser-assisted cell direct-write technique has been a promising biomaterial direct-write method. For safe and reproducible cell direct writing, the cell damage due to process-induced external stress must be understood in addition to biological property research. The objective of this study is to model the thermoelastic stress wave propagation inside the coating in laser-assisted cell direct writing when the vaporization or optical breakdown of coating materials is not available. It is found that a bipolar pressure pair has been developed within a finite thin coating medium, locations near the laser focal spot experience higher stresses, and shorter duration laser pulses lead to higher thermoelastic stresses. This study will help understand the photomechanical stress and its relevance with biomaterial damage in laser-assisted cell direct writing.
Feasibility Study of the Effectiveness of Cryogenically Treated Ceramic Inserts for Pocket Milling Maneuvers
Authors: Milner Justin L. , Beers Jeffrey A. , Roth John T.
Published: September 2010

Machining is a popular and versatile manufacturing process that is widely used in today’s industry when producing metallic parts; however, limited tool life can make this an expensive and time consuming fabrication technique. Consequently, methods that decrease the rate of tool wear and, thus, increase tool longevity are a vital component when improving the efficiency of machining processes. To this end, cryogenically treating cutting tools (especially high-speed steel tooling) is becoming more commonplace since research has shown that the treated tooling exhibits significantly higher wear resistance. At this point, however, the effect of cryogenic treatments on ceramic tooling has not been established. Considering this, the research herein presents a feasibility study on the effectiveness of using cryogenic treatments to enhance the wear resistance of WG-300 whisker-reinforced ceramic cutting inserts. To begin, the effect of the cryogenic treatment on the insert’s hardness is examined. Subsequently, tool wear tests are conducted at various cutting speeds. Through this study, it is shown that cryogenically treating the ceramic inserts decreases the rate of tool wear at each of the cutting speeds that were tested. However, the degree of wear resistance introduced by cryogenically treating the inserts proved to be highly dependent on the cutting speed, with slower speeds exhibiting greater improvements. Thus, based on this initial study, the cryogenic treatment of ceramic tooling appears to produce beneficial results, potentially increasing the overall efficiency of machining processes.
Effect of Controlled Modulation on Chip Formation and Interface Tribology in Machining
Authors: Mann J. B. , Saldana C. , Compton W. D. , Farris T. N. , Trumble K. P. , Chandrasekar S.
Published: September 2010

Based on consideration of mechanics of chip formation, it is shown that the application of a controlled modulation fundamentally changes the nature of the extreme deformation underlying chip formation, and the severe contact conditions at the tool-chip interface. Important consequences are significant reduction in the energy of chip formation, and control of chip shape and size for improved chip management. Implementation of modulation-assisted machining for industrial machining processes is discussed.
Dynamic Similarity of Multistage Compressor Control: Analyses of Energy Utilization
Authors: Elmandouh Waleed A. , Khalil Essam E.
Published: September 2010

The balance between safe efficient process control and low instrumentation cost is quite hard to achieve. It was found that design of process control systems plays an important role for achieving the optimum process safety and efficiency beside the minimum required instrumentation costs. This paper is mainly intended to describe a new approach to compressor control aimed principally at achieving increased controllability during start-up which optimizes safety and control of a multistage gas compressor. It highlights the importance of the proper compressor control, introduces some recommendations for compressor control to facilitate the development of optimum process control and also stresses on the factors that improve the safety and efficiency of compressor control for already existed systems. Surge phenomenon causes and effects on compressors were explained together with Universal Performance Curve anti-surge control method and the Minimum Flow Strategy used to compensate for pressure transmitters failure. A detailed study was performed on a specific common problem that occurs in petrochemical plants, gas compressor first stage suction pressure measurement. Conventional solutions were discussed and disadvantages were highlighted. The main contribution of this paper is a novel idea to overcome the problem without affecting either safety or efficiency of operation and absolutely no extra instrumentation cost. A new dimensionless parameter was invented, Ratio of Pressure Ratios. Relation between ratio of pressure ratios and compressor speed is being investigated experimentally and numerically. Experimental results show that there is a relation between ratio of pressure ratios, the results were fitted to second order polynomial trend lines using least squares method. The numerical calculations are compared with experimental data and good agreement is found. The results also suggest direction for further investigations. Ratio of Pressure Ratios method was implemented for a propylene gas compressor turbine train, the results of calculation were collected and compared to actual measurements, and it was found that calculation error is less than 1%.
Fuel Gas Conditioning System Modularization and Optimization
Authors: Kauffman Bradford A.
Published: September 2010

Siemens Energy, Inc. has developed a modular approach that standardizes the components and configuration of the fuel gas conditioning system, while allowing for customization to meet site-specific requirements. The intent of this approach is to: • Lower engineering costs (design only has to be done once). • Allow for interchageability (long-lead components purchased for one project can be used on another project if necessary). • Simplify installation and commissioning at the site. In the past, fuel gas conditioning system components have been purchased from various suppliers. In cooperation with these suppliers we developed a modular fuel gas conditioning system that would lower engineering costs, standardize design, and allow for interchageability of components. The result was the development of three standard fuel gas conditioning systems that accommodate several combined cycle power plant sites. Design 1 is for sites that require compression, but no pressure regulation. Design 2 is for sites that require regulation, but little or no compression. Design 3 is for sites that require both compression and pressure regulation. Site specific customization is minimized, since the standard designs encompass most of the foreseen site conditions. We have developed control technologies to accommodate high variability in site gas pressures and minimize the impact of pressure spikes. We also reviewed the optimum placement of the compressor gas cooler. Installing the cooler in the recycle stream rather than as an aftercooler can reduce capital costs. Additionally, this configuration improves gas turbine heat rate. This paper will describe in detail the design of the fuel gas conditioning system, the various applications, and the benefits to the customer.
Power Savings in Simple and Combined Cycle Power Plants Using Closed-Loop, Evaporative Cooling Systems
Authors: Jenkinson Rob
Published: September 2010

Closed-loop, evaporative cooling systems are a cost-effective heat transfer technology in simple and combined cycle power plants. Utilizing proven technology, a closed-loop, evaporative cooler provides lower outlet temperatures, uses less plot space, and offers the ability to use poor quality water along with requiring significantly lower parasitic energy usage.
Improving Plant Operations With Performance and Condition Monitoring Systems
Authors: Hicks Jonathan , Kerber Donald
Published: September 2010

Business operations in the power industry, as with every other industry, require payback for the resolution of process problems. In order to achieve this payback many plant monitoring systems are used such as Performance and Condition Monitoring Systems. Performance Monitoring systems use first principles calculations for a baseline and test performance case, both of these calculations can then be reconciled to give a cost associated with off design operation. Condition Monitoring systems operate on the Advanced Pattern Recognition Algorithm (APR) and can be used to identify slight variations in the performance of a system largely independent of the quality of the inputs. The process to identify deviations is as follows: a predicted value is calculated for every modeled parameter, a difference between the predicted value and actual value is calculated, the difference is compared to an allowed threshold, and then problems are reported. The purpose of the following report is to identify the strengths and weaknesses of each monitoring system and show how they may be used together for a more thorough analysis of off design operation. Performance monitoring systems provide a reliable and actionable assessment of Heat Rate deviations when they occur in the field. The calculations provided by these systems can lead directly to the diagnosis of real performance problems as well as instrument inaccuracies and provide the financial implications of each issue. Performance monitoring systems, however, are highly dependent upon input quality as their results are found using first principles calculations. Condition Monitoring systems can be used to identify smaller deviations from normal at an earlier time. The major strength of the APR process is its ability to identify these deviations regardless of input quality. As with Performance Monitoring Systems the APR process will identify real problems as well as instrument problems. However, it will not provide a financially quantifiable result as to the effect of the deviation. Monitoring systems should be able to provide quantifiable results with minimal personnel use in order to achieve a payback for more operational problems. This paper will discuss how the use of Performance Monitoring Systems in conjunction with Condition Monitoring Systems will provide the complete analysis needed by the power industry today.
Varnish Removal and Control in Turbine Lubrication Systems
Authors: Farooq Khalid
Published: September 2010

Varnish deposits on metal surfaces in turbine lube system results in a number of adverse operational issues, especially the restriction and sticking of moving mechanical parts such as servo or directional control valves. The oil has limited solvency for the material, hence a typical turbine will have the majority of the material as deposits and a relatively small portion as suspended material in the oil phase in quasi-equilibrium with the deposits. The lube system needs to be cleaned by removing the suspended varnish precursors from the oil phase, which allows the deposits to re-entrain into the oil phase, until the majority of the transferable deposits from internal surfaces are removed and the oil carries no significant amount of the material to have any adverse effect. The methods used for the removal of varnish from turbine lube oil systems include chemical cleaning - flushing, and electrostatic charge induced agglomeration - retention and the adsorption of the oil suspended varnish on an adsorbent medium. The paper discusses an absorption based removal method that utilizes a fibrous medium that has pronounced affinity for the removal and retention of the varnish forming material from the oil and the deposits from surfaces that are in quasi-equilibrium with the varnish precursors in the oil. The filtration medium is composite cellulose with specially formulated, temperature cured binder resins. The absorptive medium that exhibits high structural and chemical integrity has been thoroughly tested on operating turbines, showing reduction in varnish levels from critical range to below normal range in a relatively short time. The experiences with the utilization of the absorptive medium in laboratory tests and in two operating turbines are presented.
Reliability Estimation Techniques Applied in ALSTOM
Authors: Raza M. , Hutchison K. , Mishra S.
Published: September 2010

Many organizations and industrial sectors have created databases containing the histories of critical events affecting items of equipment to determine unreliability of equipment. The intention is to record and maintain data about the root cause analysis of such events and to determine the main component / equipment or cause of error which triggered the forced event. Failure rate evaluations are the basis for this estimation. For confidence in these estimations large and accurate resources of data are necessary. When the event information is limited or not enough, the application of mathematical concepts is the only way forward. In this paper the ALSTOM approach to such failure rate estimation using a number of methods is presented. These include development of statistical methodologies that combine frequentist and Bayesian ideas as well as using information that is available as standard industry-wide. An overview shall also be provided on the methodology and application of reliability concepts as developed and customised to the requirements of its product development within ALSTOM power business.
Best Practices: Multi-Ton Component Removal/Replacement Utilizing Air Casters
Authors: Farmer Jesse , Massenburg John , Pitsch Terry
Published: September 2010

Power plants originally designed to be decommissioned at 20–30 years are extending their service life by removing/replacing major power plant components. This requirement is contrary to the original floor and workspace designs engineered for power plants. Feedwater heaters, casks, heat exchangers, and other very large (50′ ±) and heavy (20–100 Ton) components can overcome floor and space restrictions by using a combination of air casters and cranes. This proven methodology saves in excess of 75% of the cost of a standard crane-only operation and significantly reduces the possibility of permanent floor damage. Air caster transport systems are low profile and easily insert under industrial heaters, exchangers, transformers, etc. The casters raise components and carry them across the floor, spreading the multi-ton weight across the surface area without damage to the floor or component. Air casters are frictionless even with the heaviest loads, and significantly reduce ergonomic risk while also providing the benefit of requiring a reduced workforce to move the component across the floor. Controlled drive systems allow a single operator to easily move components omni-directionally without wheels or rails, and into position within .5″ (13mm) accuracy. The air caster methodology for moving heavy loads was referenced as proven effective in existing nuclear plants in the 2004 ICONE paper presented by Tokyo Power. Air casters, often coupled with cranes, significantly lower material handling costs associated with new installation and repair/refurbishment of components up to and over 5000 tons. Air casters operate on normal compressed air and have very few moving parts, resulting in low ongoing maintenance costs.
Influence of deposition parameters on the microstructure and properties of nitrogen-doped diamondlike carbon films
Authors: Sun L. , Li H. K. , Lin G. Q. , Dong C.
Published: September 2010

CN x films were prepared on cemented carbide substrates by a pulsed bias arc ion-plating method with two graphite targets and using N2/Ar mixture gases. The effects of the deposition parameters, such as substrate negative-bias voltage, duty cycle, and nitrogen flow rate, on the structures and properties of CNx films were investigated using Raman spectra and nanoindentation. The properties of CNx films are closely related to the film structures. For CNx films deposited at a different bias voltage, the CNx film deposited at a bias voltage of −300 V had the highest hardness. The ID/IG ratio and G peak position decreased and then increased with increasing bias voltage, and the minimum values, which correspond to the highest sp3 content, were obtained at a bias voltage of −300 V. For the CNx films deposited at different duty cycles, the hardness and elastic modulus decreased with increasing duty cycle. For the CNx films deposited at different nitrogen flow rates, the results show that first the ID/IG ratio decreases and sp3 content increases with increasing nitrogen flow rate, and then the ID/IG ratio increases and sp3 bond content decreases after the nitrogen flow rate exceeds 10 SCCM (SCCM denotes cubic centimeter per minute at STP). The hardness and elastic modulus of the CNx film prepared at a nitrogen flow rate of 10 SCCM reached the maximum values of 32.1 and 411.8 GPa, respectively.
Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition
Authors: Huang Yen-Chin , Li Zhen-Yu , Weng Li-Wei , Uen Wu-Yih , Lan Shan-Ming , Liao Sen-Mao , Lin Tai-Yuan , Huang Yu-Hsiang , Chen Jian-Wen , Yang Tsun-Neng
Published: September 2010

The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H2O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio=0.55; however, p-type ZnO films with the hole concentration of the order of 1017 cm−3 could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm2/V s and the lowest resistivity of 0.369 Ω cm have been achieved for the specimen fabricated at the VI/II ratio=1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zni) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (VZn) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic defects was further confirmed by low temperature PL measurements conducted at 10 K. Conclusively, the conduction type of undoped ZnO films deposited by AP-MOCVD is resolved by the VI/II ratio used, which causes the formation of various kinds of intrinsic defects, Zni otherwise VZn. p-type ZnO films with the hole concentration in the range of (1.5–3.3)×1017 cm−3 can be achieved with good reproducibility by modulating a VI/II ratio the range 1.0–2.2 for the AP-MOCVD process.
Numerical simulation of turbomolecular pump over a wide range of gas rarefaction
Authors: Sharipov Felix
Published: September 2010

A gas flow through a turbomolecular pump is modeled by the direct-simulation Monte Carlo method over a wide range of gas rarefaction covering the free-molecular, transitional, and hydrodynamic regimes. Several values of the rotor speed are considered. The main characteristics of the pump, such as maximum pumping speed and compression ratio, are reported. It is pointed out that in the range between the free-molecular and transitional regimes, the pump characteristics change slightly, but they vary significantly in the hydrodynamic regime. It is shown that the pumping speed increases in the hydrodynamic regime when the rotor speed is high, but it decreases for a small value of the speed. The compression ratio always decreases when approaching the hydrodynamic regime.