Piyas Palit

Bio: Piyas Palit is an academic researcher from Tata Steel. The author has contributed to research in topics: Bearing (mechanical) & Ultimate tensile strength. The author has an hindex of 3, co-authored 16 publications receiving 32 citations.

Analysis of a Progressive Failure of a Work Roll in Hot Strip Mill

Abstract: In hot rolling mills, premature failure of rolls is a major concern as it adversely affects the mill operation as well as production. Analysis of failed roll materials and actual rolling conditions in service are therefore necessary to understand the roll failure mechanism and thereby improve the service life of rolls. The hot strip mill referred here consists of two stands in a roughing mill and seven stands in a finishing mill. Indefinite chilled double poured cast iron rolls are used in the finishing mill for rolling of the sheet in the last two stands. HSM produces coils in the thickness range of 2–25 mm. This present case describes one of the finishing stand work roll failures and analysis which was carried out using destructive as well as nondestructive testing techniques. The spalled roll showed fatigue arrest marks in a smooth continuous path along the circumferential direction. Characteristic features of the fracture surface were similar to those of surface-initiated spalling which is known as ribbon fatigue spalling. The fracture or spalled region was analyzed with Ultrasonic test to identify the origin of the crack. Past data and roll schedule were also studied for root cause.

Development of AISI A2 Tool Steel Beater Head for an Impact Crusher in a Sinter Plant

Abstract: Failure analysis of a tool steel (AISI A2) beater head of an impact crusher and development of suitable heat treatment process to improve its performance have been presented. The beater heads were failing prematurely by brittle fracture from its pin-hole locations. The investigation consisted of visual inspection, fractography, chemical analysis, characterization of microstructures using optical and scanning electron microscopes (SEM), EDS analysis, and determination of micro-hardness profile. Microstructural characterization using SEM and EDS analysis revealed significant amount of coarse continuous Cr-carbide networks in the martensite matrix. It increased hardness (64 HRC) as well as heterogeneity of the matrix as depicted by the micro-hardness profile, and decreased the toughness (3 J) since coarse carbide networks are very hard and brittle. The austenitizing temperature as well as tempering temperature of heat treatment was found lower at the manufacturer’s end. The new recommended heat treatment resulted in lower amount of discontinuous Cr-carbides along with significant amount of fine precipitates uniformly distributed throughout the matrix which led to an optimum combination of both hardness (59 HRC) and toughness (6.5 J) required for the application. The beater heads manufactured following the recommended heat treatment exhibited better performance (life increased by 4 times) compared to the earlier ones.

Six-sigma application in tire-manufacturing company: A case study

Abstract: Globalization, advancement of technologies, and increment in the demand of the customer change the way of doing business in the companies. To overcome these barriers, the six-sigma define–measure–analyze–improve–control (DMAIC) method is most popular and useful. This method helps to trim down the wastes and generating the potential ways of improvement in the process as well as service industries. In the current research, the DMAIC method was used for decreasing the process variations of bead splice causing wastage of material. This six-sigma DMAIC research was initiated by problem identification through voice of customer in the define step. The subsequent step constitutes of gathering the specification data of existing tire bead. This step was followed by the analysis and improvement steps, where the six-sigma quality tools such as cause–effect diagram, statistical process control, and substantial analysis of existing system were implemented for root cause identification and reduction in process variation. The process control charts were used for systematic observation and control the process. Utilizing DMAIC methodology, the standard deviation was decreased from 2.17 to 1.69. The process capability index (C p) value was enhanced from 1.65 to 2.95 and the process performance capability index (C pk) value was enhanced from 0.94 to 2.66. A DMAIC methodology was established that can play a key role for reducing defects in the tire-manufacturing process in India.

Application of Desirability Approach to Optimize the Control Factors in Cryogenic Diamond Burnishing

Abstract: Cryogenic diamond burnishing is an impactful method to enhance the functional performance of the product. In this article, an experimental study on the diamond burnishing of 17-4 precipitation hardenable stainless steel in a cryogenic cooling condition has been presented. This material has excellent corrosion resistance, high strength and enormous applications in the manufacturing industries. The control variables were namely burnishing force, burnishing feed and burnishing force have been studied and modeled for the output responses explicitly surface hardness and surface roughness. The influence of control variables on performance features has been analyzed using response surface graphs. The significant influence of burnishing conditions on the output responses was established by analysis of variance. Desirability function approach has been employed to optimize the multi-performance characteristics. At the corresponding highest desirability, the optimal process parameter combination was found to be burnishing feed = 0.053 mm/rev, burnishing speed = 31.29 m/min and burnishing force = 200 N which yields a minimum surface roughness = 0.199 µm and maximum surface hardness = 397.48 HV. The maximum percentage of error among the predicted and experimental results was found to be 10% and 2%, respectively, for surface roughness and surface hardness. The investigational findings were observed to be in agreement with the predicted value with permissible deviation.

Resistance to High-Temperature Oxidation and Wear of Various Ferrous Alloys Used in Rolling Mills

Abstract: Various materials are commonly used to manufacture work rolls for hot rolling mills, such as ICDP (Indefinite Chill Double Pour) cast irons, high-chromium white cast irons, and high speed steels (HSS). Various chemical compositions and microstructures are studied in order to optimize the in-use behavior of those grades of rolls. In this paper, six grades of ferrous alloys (an ICDP cast iron; an ICDP cast iron enriched in vanadium, niobium, and molybdenum; a HSS; a graphitic HSS; a high-chromium white cast iron (Hi-Cr); and a niobium-molybdenum-doped high-chromium white cast iron) were investigated. High-temperature oxidation tests with gravimetric means at 575 °C in water vapor atmosphere and sliding wear tests were carried out. The oxidation kinetics was followed during oxidation test. The microstructure was observed by optical and scanning electron microscopies. The oxides formed on the surface of the samples were analyzed by XRD and EDS. The thickness of the oxide scales and the mass gain were measured after oxidation test. The results showed that the behavior of all the grades differed. The oxide scale of HSS and HSS-G grades was fine and their friction coefficient was low. The weight gain after oxidation test of HSS was high. Hi-Cr and M-Hi-Cr grades presented highly porous oxide layer and an important increase of the friction coefficient during wear test. ICDP and M-ICDP had intermediate behavior.