Scaling Laws of Wear by Slurry Abrasion of Mild Steel

Applied Mechanics and Materials Vols. 446-447 (2014) pp 126-130 Online available since 2013/Nov/08 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.446-447.126 Scaling Laws of Wear by Slurry Abrasion of Mild Steel Avishkar Rathoda, Sanjay G. Sapateb and Rajesh K. Khatirkarc Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur -440010, Maharashtra State, India a [email protected], [email protected], [email protected] Keywords: Abrasion; Slurry; Cutting; Indentation. Abstract. Wear by slurry abrasion is very expansive problem that must be taken into consideration while selecting the material for the transportation of slurry through pipeline. Abrasive wear generally occurs when abrasive slurries come in contact with the industrial engineering components or slurry transporting pipes. The abrasive particles carried by slurries eventually remove the material from the encountering surfaces which results in the early failure of the component in service. In present investigation an attempt is made to study the effect of load, slurry concentration, sliding distance on the abrasive wear behaviour of mild steel. The slurry abrasion experiments were carried out using slurry abrasion test apparatus with silica sand slurry. The findings of the present investigation indicate that slurry abrasion volume increased with slurry concentration, load and sliding distance, although the magnitude of increase was different in each case. The SEM observation of worn out surfaces revealed micro ploughing and micro cutting as wear mechanisms. Introduction Transportation of mineral ores in the form of slurries through pipelines is proving the best way of transportation when compared to other means of transportation. It is not only cost effective but also is eco-friendly with less maintenance requirement, gives best option than conventional way of transportation [1]. World’s first longest pipeline was constructed in Samorco, Brazil and the second longest pipeline is constructed in India. ESSAR group of industries has constructed the 267 km long pipeline to carry iron ore in slurry medium. When examining slurry pipeline as an alternative transportation mode, the pumps and pipelines which constitute the system will experience extensive wear [2], [3]. Slurry abrasion is defined as progressive loss of material from the component in which liquid media carries abrasive particles. Wear by slurry abrasion occurs in extruders, slurry pumps, and pipes carrying slurry of minerals and ores in mineral processing industries, extruders, pump impellers and coal slurry nozzles. The wear life of components used under slurry abrasion conditions is influenced by the operational parameters; properties of abrasive particles in slurry and material properties. The evaluation of slurry abrasion under actual service conditions is often difficult and complicated due to interactive effects of different parameters such as slurry concentration, velocity and properties of abrasive medium on wear rate [4]-[9]. In present investigation wear by slurry abrasion of mild steel was studied. The calibration of slurry abrasion test apparatus was carried and then experiments were carried to study the effect of different test variables such as slurry concentration, load and sliding distance. Scanning Electron Microscopy studies were carried out on worn out surfaces to study the morphology. Experimental In the present study Mild Steel is selected for the experimentation. The chemical composition of as received Mild Steel was determined by wet chemical analysis method (Table 1). Total eighteen specimens were prepared for slurry abrasion test. The specimens were rectangular blocks measuring 57.2mm (length) X 25.4mm (width) X 12.5mm (thickness). All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 14.139.125.71-13/03/15,10:09:53) Applied Mechanics and Materials Vols. 446-447 127 Table 1 Chemical composition of mild steel (wt. %) C Si Mn P S Cr Ni Al Cu 0.118 0.229 0.869 0.0296 0.0174 0.0407 0.0094 0.0014 0.0065 The bulk hardness was measured by using Vicker’s Macrohardness tester of diamond tip indenter at a load of 30 kg, an average of eight readings is 245 HV30. The specimens for metallographic examination were of 10 X 10 X 10 mm (l X b X t) size which was cut from as received Mild Steel plate. Obtained specimen were ground and polished with conventional metallographic method. The polished specimens were etched with 2% Nital and examined under Optical Microscope for microstructure. Silica sand (+250-300 µm) was used as an abrasive particle for experimentation. The weight percent of elements present in the silica sand abrasives were found out by using XRF analysis (Table 2). Table 2 XRF Chemical Analysis of Silica Sand (wt%) Na2OMgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 MnOFe2O3 SrO 0.221 0.022 0.521 98.1650.0120.0200.0270.0940.0350.009 0.171 0.002 Fig. 1 SEM image of silica sand particles Fig. 2 Schematic diagram of slurry abrasion tester Using sieve analysis, the particles passed through - 300 µm and retained on +250 µm size sieve were collected for experimentation and few among them were coated with gold and observed under JEOL 6380A make SEM to study particle size distribution and shape (Fig. 1). The Gold coating of particles was done by using JFC -1600 Auto Fine Coater. Silica sand particles used in slurry were having (irregular to angular shape) as can be observed from Fig. 1. In the present work slurry abrasion test was carried out by using slurry abrasion test apparatus (DUCOM make, India) which is used to conduct test according to ASTM G105. The apparatus consisted of a slurry abrasive chamber enclosing the rubber lined steel wheel, slurry and test specimen firmly fixed in specimen holder. The wheel is made of steel disc with an outer layer of neoprene rubber (durometer hardness of 60 ± 2) molded to its periphery. Diameter of wheel is 178 mm and thickness is 12.7 mm. The maximum speed of the rubber lined wheel is 250 ± 5 RPM. The double walled jacket enables to maintain the slurry temperature by circulating coolant. The load was monitored by a load cell (450 N capacity) which was pre-calibrated to measure the force applied by the specimen over the rubber wheel. A schematic diagram of the slurry apparatus is shown in Fig. 2. This instrument is designed such that a flat test specimen is pressed radially against a neoprene rubber wheel with a known force. The test area is submerged in wet abrasive media (slurry). The arrangement is such that the wheel carries the abrasive media between the sample and the rubber wheel creating condition of three body abrasion wear whereas particles in slurry acts as third body. The specimens for slurry abrasive wear test were prepared by polishing upto 1000 grit silicon carbide emery paper followed by cleaned with ethyl alcohol and compressed air. The cleaned and dry specimen is then weighed using a digital electronic balance to the accuracy of 0.1 mg. The 128 Advanced Research in Material Science and Mechanical Engineering measured weight of specimen is considered as initial weight. The specimen was then placed firmly in the specimen holder assembly. The slurry chamber which is made of stainless steel material and having leak proof mechanism with double walled jacket is then closed. The inlet port was filled with required quantity of silica sand particles (- 300 +250µm size) in 1000ml distilled water. The load of 120N was placed on the loading lever and loading lever was released so that specimen comes in contact with neoprene rubber wheel. The slurry abrasion wear test of specimens was performed at different load, slurry concentration, and sliding distance. After test, the specimen was removed from the slurry chamber, cleaned with alcohol followed by compressed air cleaning and weighed. The weight obtained is considered as final weight. The loss in mass (gm) was calculated as the difference of initial and final weight of the specimen. In addition, wear volume loss (mm3) was also determined using mass loss data. Results and Discussion Fig. 3 shows the pearlite and ferrite in the microstructure of mild steel specimen when observed under optical microscope. To check the reproducibility of the test apparatus five mild steel specimens were tested under identical test conditions (120N,1117.84m,1.5g/cc) and the variation in mass loss was recorded as standard deviation. The results of these initial experiments are given in Table 3. The effect of load (30,60,90 and 120N), slurry concentration (0.4,0.8,1.2 and 1.6 gm/cm3) and sliding distance (279.46, 558.92, 838.38 and 1117.84 m) on slurry abrasive wear volume loss was studied. Figs. 4-6 show the effect of load, slurry concentration and sliding distance on abrasive wear volume of mild steel. Fig. 4 shows the linear effect of load on wear volume loss of mild steel at 1.6 gm/cm3 slurry concentration and at the load of 120N. Fig. 5 shows the linear effect of slurry concentration on wear volume loss. Similarly, Fig. 6 shows the linear effect of sliding distance on wear volume loss. Figs. 7(a, b and c) shows photograph of worn out surfaces and Fig. 8 (a, b and c) show SEM photographs of worn out surfaces under different test conditions. Fig. 3 Optical microscope image of mild steel (200x) Table 3 Mass loss of mild steel samples tested at same experimental conditions Sr. No. Initial Weight Final Weight Mass Loss Standard (gm) (gm) (gm) Deviation 1 142.0232 141.0246 0.9986 2 140.5954 139.5834 1.012 3 137.8376 136.7396 1.098 0.0468 4 142.0376 141.0544 0.9832 5 138.7289 137.7334 0.9954 Fig. 5 Effect of slurry concentration on volume loss of Mild steel Fig. 4 Effect of load on abrasive wear volume loss of mild steel Applied Mechanics and Materials Vols. 446-447 129 Fig. 6 Effect of sliding distance on wear volume loss of mild steel Fig. 7 (a-c) Worn Out surfaces of Mild Steel at varying conditions a) Normal load (b) sliding distance and (c) Slurry concentration Fig. 8 (a-c) SEM photographs of worn out surfaces after slurry abrasion of Mild steel at (a) Normal load of 120N (b) sliding distance of 1117.84m and (c) Slurry concentration of 1.6 gm/cm3 From Table 3 it can be observed that the reproducibility of the slurry abrasion apparatus is excellent as indicated by standard deviation .It can be observed from Figs 4-6 that slurry abrasion volume loss increased with load, slurry concentration and sliding distance. The wear volume loss increased linearly with load thus obeying Archard’s Wear law, Q = K S L / H where Q is wear volume loss , S is sliding distance, L is load , H is surface hardness and K is Arcahrd’s wear constant[5],[7]. The abrasive wear volume loss increased more than 2.5 times for fourfold increase in load from 30 to 120 N. The abrasive wear volume increased more than twelve times when the slurry concentration was increased from 0.4 g/cm3 to 1.6 g/cm3) whereas with increase sliding distance from 279.46 m to 1117.84m abrasive wear loss increased three times. With increase in load the depth of cut caused by silica sand particle on the specimen surface increased leading to increased wear volume loss. With the increase in slurry concentration more number of slurry particles making contact with surface and causing material removal by grooving abrasion as compared to rolling abrasion caused by silica sand particles at lower slurry concentration leading to lowest wear volume loss at lower slurry concentration [10]-[14]. The photographs of worn out surface of mild steel with increase in normal load shows the increase in wear scar length and depth of parallel grooves also increases with load. The same features are observed visually in wear scar obtained after variation in slurry concentration. However, when sliding distance is varied the length of wear scar remains constant but the depth of groves formed increases with increase in sliding distance. When these samples were observed under Scanning Electron Microscopy (SEM) the mechanism of removal of material was revealed (Fig. 8 (a-c)). At 120 N load material removal occurs predominantly by micro cutting process whereas at lower loads material was removed by ploughing process. The deep grooves were observed on the surface of 130 Advanced Research in Material Science and Mechanical Engineering worn out specimen with width of grooves was seen as around 10 µm. as can be observed from Figs. 7 (a-c). Conclusion The scaling laws of wear by slurry abrasion of mild steel were investigated in the present study. The standard deviation in slurry abrasion mass loss of mild steel was observed to be 0.0462. The effect of experimental variables such as load, slurry concentration and sliding distance on slurry abrasion volume loss of mild steel exhibited increasing trend, however the magnitude of increase was different in each case. The slurry concentration has strongest influence on abrasive wear volume loss as compared to other test parameters. The morphology of worn out surfaces indicated ploughing and micro cutting as important wear mechanisms of material removal. Acknowledgement The authors are thankful to Director VNIT for providing facilities for experimentation. References [1] B. E. Abulnaga: Slurry Systems Handbook (2002), McGraw-Hill, p. 533. [2] Ahmed, Elkholy: Prediction of abrasion wear for slurry pump materials, Wear, Vol 84, (1983) p. 39 – 49. [3] T. Akira, T. Takaoka, H. Furukawa, H. Hori, T. Fukui, Y. Minami: Development of abrasion resistant pipe for slurry transportation. NKK Tech Rev, Vol. 85, (2001), p. 16. [4] G. W. Stachowiak, A. W. Batchelor, Engineering Tribology, Butterworth Heinemann. [5] I. M. Hutchings, Tribology, Friction and Wear of Engineering Materials, Edward Arnold; 1992. [6] P. J. Blau, Friction, Lubrication and Wear Technology, ASM Handbook, Vol 18, (1992) ASM international, The Materials Information Society. [7] S. G. Sapate, Avishkar Rathod, S. 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Misra, Finnie: On the size effect in abrasive and erosive wear, Wear, Vol. 65, (1981), p. 359. [14] Sevim I, Eryurek IB: Effect of abrasive particle size on wear resistance in steels, Mater Des;27 (2006) p. 173. Advanced Research in Material Science and Mechanical Engineering 10.4028/www.scientific.net/AMM.446-447 Scaling Laws of Wear by Slurry Abrasion of Mild Steel 10.4028/www.scientific.net/AMM.446-447.126