ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE September 2020. Vol. 16(3):449-474 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 449 ORIGINAL RESEARCH ARTICLE DEVELOPMENT OF A LABORATORY SIZE SINGLE TOGGLE JAW CRUSHER FOR ARTISANAL MINERS AND STONE WORKERS C. Okechukwu1*, O. A. Dahunsi2, P. K. Oke3, I. O. Oladele4 and M. Dauda5 1Advanced Manufacturing Technology Programme, P. M. B. 1174, Jalingo, Taraba State, Nigeria. 2,3Department of Mechanical Engineering, Federal University of Technology, P. M. B. 704, Akure, Ondo State, Nigeria. 4Department of Metallurgical and Materials Engineering, Federal University of Technology, P. M. B. 704, Akure, Ondo State, Nigeria. 5Department of Mechanical Engineering, University of Maiduguri, P. M. B. 1069, Maiduguri, Borno State, Nigeria *Corresponding author’s email address: okerex2002@yahoo.com 1. Introduction Artisanal miners and stone workers in Nigeria today still use crude tools and methods in crushing and grinding comminution processes. Wills (2006) defined comminution as the process of size reduction of particles until the liberation of valuable minerals can be achieved. Value addition in mining and minerals processing industries has always taken the route of size reduction or comminution. While ores bearing specific minerals of interest are crushed and milled to reveal and concentrate the valuable constituents, rocks which have no mineral value such as stones, e.g. granite, are crushed to particular aggregate sizes. Stone aggregates are used in structural constructions of physical infrastructures such as buildings, roads, railways, bridges, dams, harbours, airstrips, drainages, wells, walkways and parks (Asbjörnsson, 2013; Ravindran, 2013). According to Pokrajcic (2010), comminution is the most energy intensive component of mining and mineral processing. The mineral sector accounts for about 15 % of the total electrical energy consumption in South Africa (Numbi et al., 2014). Small-scale stone crushing in underdeveloped countries is achieved through labour intensive and resource wasting activities such as breaking of the boulders using sledge and small hammers to aggregate sizes. Interaction with stone workers during a visit to a local quarry in Jalingo, Taraba State, Nigeria, revealed that a combination of elderly men in their fifties and young men in their twenties are involved in the rock burning, boulder separation and reduction to lump sizes that the women, male and female adolescents can break into aggregates. Furthermore, women and children carry out the sieving after the manual size reduction. It takes an average of three weeks to get ARTICLE INFORMATION ABSTRACT Comminution of minerals and stones in Nigeria is laden with myriads of resource challenges associated with other developing nations. A typical challenge is the need to import costly mining and mineral processing machineries or replace their components. To address this challenge, economic consideration was prominent in the development of components for the single toggle jaw crusher. Geometric modeling and structural/stress analysis of the components were achieved using Pro/Engineer® and Autodesk Inventor® computer applications. Designed eccentricity of 7 mm resulted in 5 mm throw and 0.01° angle of twist in the eccentric shaft. The designed base frame was statically stable, having yielded a maximum displacement of 0.008066 mm. Analysis of the compression spring indicated design compliance. Also, hardfaced crusher jaws and large diameter pulley and flywheel were developed. Selection of a three-phase, 3730 W electric motor resulted in a 0.24 ton/hr capacity jaw crusher in service. Optimal and maximum feed of the crusher were found to be 0.5 kg and 1 kg, respectively. Average eccentric shaft speed decreased with increased mass of granite lumps undergoing crushing. Therefore, the methods presented can be adopted in developing affordable and easily maintainable jaw crushers for artisanal miners and stone workers in Nigeria. © 2020 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 20 Sep., 2019 Revised 04 May, 2020 Accepted 20 May, 2020 Keywords: Artisanal mining, stone crushing, sustainable mineral processing, jaw crusher http://www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 450 a truck load (4m3) of the 31.75 mm aggregates; six weeks to get two trucks of the 31.75 mm aggregates and a pick-up vehicle load of 12.52 mm aggregates. The manual stone crushing activities in a local quarry are shown in Figure 1. Figure 1: Adolescent children and a woman breaking stones into aggregates in Jalingo quarry, Nigeria. Birabwa (2006) pointed out improved mechanization of small-scale stone quarrying as one of the ways to improve the livelihood of stone workers. Mohamed et al. (2014) designed a jaw crusher and advocated the need for affordable mechanized small-scale stone crushing machines. Furthermore, Alonge (2015) developed a prototype jaw crusher and identified the need for alternative and cheaper locally sourced materials for the jaws, he also called for the scaling-up of the crusher to industrial size. In addition, Elisante (2009) fabricated a jaw crusher for artisanal miners with engine prime mover but did not place adequate focus on the design and materials development for the machine’s critical components. UNDP (2014) summarily posited that there is need to bridge the gap between high capital intensity of modern mining production activities that the sector requires for significant value addition and reduction of hazard and drudgery associated with artisanal mining. This will shore up the profit of the small-scale operators, which currently dominate the sector. Access to modern technology, skills and finance are major factors in the gap that need to be addressed. Hence, this research is geared towards addressing technology and skills related challenges that are adversely affecting the profitability and sustainability of mining and minerals processing ventures in Nigeria. Economical methods of developing critical components of the jaw crusher for easy repairs and replacement by the small-scale operators have not been adequately addressed. Towards achieving sustainable comminution, it is pertinent to unveil the procedures for developing the critical components; which include: eccentric shaft, journal bearing and hardfaced jaws. Procedures used create room for easy maintenance of the jaw crusher. Consequently, the objectives of this study are to design a 0.1 tonne/hr capacity single toggle jaw crusher; develop critical components for easy and timely reparation; develop and evaluate the performance of the jaw crusher. http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 451 2. Materials and Methods 2.1 Materials The materials used in developing the components of the jaw crusher are presented in Table 1. Table 1: Materials Used in Developing Hardfacing Alloys and Crusher Parts Components Materials Hardfaced crusher jaws Ferro-alloy hardfacing insert, low carbon steel Pitman, crusher frame, rushing chamber, crushing chamber, journal bearings’ housing, toggle plate, shims Low carbon steel Pulleys and flywheel Grey cast iron Eccentric shaft Medium carbon steel 2.2 Design of the Single Toggle Jaw Crusher The design of the jaw crusher commenced from the crushing compartment, through the machine elements to the selection of a prime mover. 2.2.1 Determination of gape and lengths of movable jaw and pitman of the jaw crusher Ashok and Yan model for width (W) of the crusher jaw plate lies within the range: 1.3G < W < 3.0G (Moore and Rajpal, 2013); where, G is the gape. Also, the angle of nip must lie between 17o and 27o (Niemela and Kieranen, 2008). The width of the fixed jaw, W = 200 mm, the height of the fixed jaw, Lfj = 300 mm, and the angle of nip,  = 20o, then G can be calculated from Figure 2 as follows: Figure 2: Schematic diagram of the crushing compartment of a single toggle jaw crusher where, /BF/ is the Gape (G), /DE/ is the Set, /BD/ is the length of movable jaw, /JD/ is the length of the pitman, H1 is the thickness of the journal bearing base plate, and H2 is the radius of the bearing from its centre to the surface of the base plate. From Figure 2, it can be deduced that: �� � ��� cos� � 319.�5 mm (1) Notice that ZĴB =  (alternate angles), DĈE = (180-90- )o = 70o (angle on a straight line). Given that: H1 = 10 mm, H2 = 70 mm, and /DE/ = 12.5 mm, then: �1 � 1�.5 tan �0 � 4.55 mm file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 452 Therefore, the length of the movable jaw, Lmj is given by: �1 � �� � 3�3.8 ≈ 3�4 mm (�) Also, /AF/ = /CE/, which is given by: 1�.5 sin �0� � 13.3 mm More so, the length of /AB/ is given by: /AB/ � ��� ���� � 300tan�0° � 109.� mm This implies that the Gape, G equals G = /AB/ + /AF/ = 109.2 + 13.3 = 122.5 ≈ 123 mm. Notice that: 1.3 × 122.5 < 200 < 3 × 122.5 = 159.25 < 200 < 367.5 Hence, the width, W of the fixed jaw, which is the same as that of the movable jaw was properly selected within the range 1.3G < W < 3.0G. Additionally, �3 � �1 � �� ���� (3) � 10 � �0 cos �0° � 85.13 mm Hence, the length of pitman, Lp is given by: �� � �1 � �� � �3 (tt) (4) By substitution, Lp = 4.55 + 319.25 + 85.13 = 408.93 ≈ 409 mm 2.2.2 Determination of components of the crushing force contributed by the pitman, movable jaw, toggle plate and drawback rod Using the density of steel, 7.85 g/cm3, the weights of pitman-movable jaw sub-assembly (WP), toggle plate (WT) and drawback rod (WR) were determined with Pro/Engineer® software as 250.07 N, 31.06 N, and 28.95 N, respectively. The components of the crushing force contributed by movable jaw, toggle plate and drawback rod were determined from Figure 3: Figure 3: Contributions of the pitman, movable jaw, toggle plate and drawback rod to the crushing force http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 453 where, WP, WT, and WR were the weights of the pitman-movable jaw sub-assembly, toggle plate and drawback rod, respectively. Also, FP, FT and FR are the forces acting along the length of the pitman-movable jaw sub-assembly, toggle plate, and drawback rod due to their weights, respectively. FSC is the slanted component of the crushing force along the movable jaw, while FHC is the horizontal component of FSC. The movable jaw is inclined at 20° to the vertical line /AO/, while the toggle plate is inclined at 30° to the horizontal line /AE/. The angle of inclination of the drawback rod is calculated thus: � � tan−1 50 430 � 6.63° From Figure 3, FP, FT and FR and their horizontal components FPX, FTX and FRX, respectively, can be calculated as follow: �� � �� �t��0° � �50.0� 0.939� � �66.1� N ��� � �� ����0° � 91.0� N Similarly, �� � �� �t�30° � 6�.1� N ��� � �� ���30° � 53.80 N Likewise, �� � �� �t�6.63° � �50.65 N ��� � �� ��� 6.63° � �48.9� N The horizontal component of the crushing force is given by: ��t � ��� � ��� � ��� N (5) By substitution, FHC = 91.02 + 53.80 + 248.97 = 393.79 N The slanted component of the crushing force along the pitman-movable jaw subassembly is given by: ��t � ��t ����0° � 1151.43 N Furthermore, the contribution of the pulley-eccentric shaft-flywheel subassembly is as follows: Given that: mass of grey cast iron pulley is 18.4 kg, mass of grey cast iron flywheel equals 18.4 kg, and mass of medium carbon steel eccentric shaft is 13.211 kg; then, mass of pulley-eccentric shaft-flywheel = 18.40 + 18.40 + 13.211 = 50.01 kg, weight of pulley-eccentric shaft-flywheel sub-assembly, WPF = 500.10 N; this can be resolved to the slanted crushing force direction as shown in Figure 4: file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 454 Figure 4: Contributions of the pulley, eccentric shaft and flywheel to the crushing force From Figure 4, FPF can be calculated as follows: ��� � ��� ����0° � 53�.19 N where, FPF is the component of the crushing force from pulley, eccentric shaft and flywheel. Therefore, total force available along the pitman-movable jaw sub-assembly for crushing is given by: �t� � ��� � ��t N (6) Substituting the values of FPF and FSC into equation (6), gives FCF = 1151.43 + 532.19 = 1683.62 N 2.2.3 Estimation of power required by the jaw crusher to crush a given feed According to Zhang (2014), the power required to crush a given feed size of ore or stone to product, PR (kW), is given by the modified Bond’s equation: �� t� � 0.3161�t 1 �� − 1 �� kWhr tonne (�) Given that: material to be crushed is granite, Df = 100 mm, Dp = 12.5 mm, t� = 0.1 ton/hr, Wi = 15.83 kWhr/ton (Kelly and Spottiswood, 1982), then, PR (kW) can be calculated as: �� � 0.1 × 0.3161 × 15.83 × 1 1�.5 − 1 100 � 91.5� W Also, the reduction ratio, RR is given by: �� � �t�� �� ���� (mm) �t�� �� �耀��䀀�� (mm) (8) By substitution, �� � 100 1�.5 � 8:1 http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 455 2.2.4 Estimation of power available from the crushing force and eccentric shaft The eccentricity, e, of the eccentric shaft can be determined from Figure 5 as the difference between the radii of 60 mm diameter and 74 mm diameter parts of the shaft; hence, e = 7 mm. Figure 5: End view of the eccentric shaft. The throw or stroke of the pitman-movable jaw sub-assembly is given by the difference between the eccentricity (7 mm) and the difference between the internal diameter of eccentric shaft housing (76 mm) and the diameter of the eccentric lobe (74 mm); hence, Stroke = 7 – (76 – 74) = 7 – 2 = 5 mm The crusher stroke is the displacement of jaw between the widest and narrowest points on an eccentrically gyrating cycle (Karra et al., 1992). Alternatively, Donovan (2003) defined the throw as the stroke of the swing jaw or the difference between the open side set and the closed side set. The open side set is the maximum discharge aperture, while the closed side set is the minimum discharge aperture. Open side set = 15 mm; Closed side set = 10 mm Stroke = 15 – 10 = 5 mm; Set = aggregate product size = 12.5 mm According to Karra et al. (1992), the mechanical power required to drive the crushing mechanism can be calculated from equation (9) as follows: ��耀����⹉�耀 � �t� . � .� (9) Let, crushing force, FCF = 1683.62 N, stroke, x = 0.005 m, shaft speed in r.p.m., N = 400 r.p.m. ������耀t� �݄��� ����� � ��� 60 (rad/s) (10) � 41.89 rad/s The amount of power consumed during crushing (i.e. driving the mechanism) is calculated thus: �t � 1683.6� × 0.005 × 41.89 � 35�.63 W 2.2.5 Estimation of reaction forces at the bearings Let, weight of the eccentric shaft be WE = 132.11 N, Vertical component of slanted force, FSC, beWSC, WSC = FSC cos20° = 1151.43 × 0.9396 = 1081.88 N Also, let reaction at each bearing support be RB, weight of pulley, WL = 184 N, weight of flywheel, WF = 184 N. Then, RB can be determined from the force diagram shown in Figure 6 as follows: file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 456 Figure 6: Force diagram for the calculation of reactions at the journal bearings. Note: All distance dimensions in Figure 6 are in mm. Summing vertical forces, we have: �� � �� − �� −�� −��t −�� � 0 (11) By substitution, we have: �� � � 184 � 13�.11 � 1081.88 � 184 � 1581.99 �� � �90.995 ~ �91 N 2.2.6 Design of flywheel Let, mf be the mass of the flywheel, then, mf = 18.40 kg, speed of flywheel, Nf = 400 rpm, angular speed of the flywheel is given by: �� � ���� 60 (rad/s) (1�) By substitution, �� � � × 3.14� × 400 60 � 41.89 (rad/s) Radius of gyration, rg is taken as the mean radius of the rim, because the thickness of the rim is very small compared to its diameter (Khurmi and Gupta, 2005); rg is calculated from Figure 7 as follows: Figure 7: Schematic drawing of the flywheel for the calculation of the mean radius 耀� � �00 � 180 � � 0.19 m Mass moment of inertia of the flywheel about the axis of rotation, I is given by: � � t�耀�� (kgm�) (13) � 0.66 kgm� Mean kinetic energy of the flywheel, Ef is given by: �� � 1 � ��� � � 1 �t�耀���� � (J) (14) � 58�.80 J http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 457 Maximum fluctuation of energy, ���, is given by: ��� � ��� �t� � t�耀���� �t� � ���t� (J) (15) According to Khurmi and Gupta (2005), coefficient of fluctuation of speed, Cf, for crushing machines is 0.2. Hence, ��� � � × 58�.8 × 0.� � �33.1� J Energy consumed per second due to the inertia of the flywheel, PF = 233.12 W. Then, power required to drive the crushing mechanism and reduce the feed to product, i.e. reduce 100 mm granite feed to 12.5 mm is the sum of PR, PC and PF. Therefore, total power consumed during crushing is given by: ��t � �� � �t � PF (16) � 6��.3� W 2.2.7 Selection of prime mover for driving the crushing mechanism Given that: R1 is the radius of the driving or driver pulley (m), R2 is the radius of the driven or follower pulley (m), D1 is the diameter of the driver pulley (m), D2 is the diameter of the driven pulley (m), N1 is the speed of the driver pulley (r.p.m.), N2 is the speed of the driven pulley (r.p.m.), V1 is the velocity of the belt while passing driver pulley (m/s), V2 is the velocity of the belt while passing driven pulley (m/s), T1 be the tension of the tight side of the belt (N) and T2 is the tension on the slack side of the belt (N). According to Khurmi and Gupta (2005); Juvinall and Marshek (2012), the angle of contact or lap on the large diameter driven pulley is given by: �� � 180° � �� � 180 rad. (1�) � � �t�−1 �� − �1 � ° (18) where, X is the centre to centre distance between the driver shaft and the driven shaft, (m). Then, �1 � ��1�1 60 (m/s) (19) �� � ����� 60 (m/s) (�0) If there is no slip, V1 equals V2, which implies the velocity ratio of the belt is given by: �1 �� � �� �1 (�1) The ratio of the tight side tension (T1) to that of the slack side tension (T2) is given by the expression, �1 �� � ���������� (��) where, μ is coefficient of friction between the belt and the pulley, which equals 0.3 for cast iron and rubber belt. � equals half of the angle formed by the slanted sides of the V-belt or the grooved pulley. From the Pro/Engineer® software, �� � 33.86° which implies, � � 16.93°. The effective turning force at the circumference of the driven pulley is the difference between the two tensions, i.e., file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 458 ������t�� �䀀耀�t�� ��耀�� � �1 − �� (N) (�3) Therefore, power transmitted by a belt is given by: �� � �1 − �� �� W (�4) Torque exerted on the driven pulley equals torque transmitted by the eccentric shaft and can be calculated from the equation: ��� � �1 − �� �� N.m (�5) Output power available at the driven pulley is given by: ��t � �π����� 60 W (�6) Input power transmitted from the prime mover is given by: �� � �� × �� W (��) where, �� is the number of belts. Efficiency of the pulley-drive system is given by: � � �䀀��䀀� ��⹉�耀 ���䀀� ��⹉�耀 (�8) Given that: PPC = 677.32 W, D2 = 0.4 m, D1 = 0.102 m, R1 = 0.2 m, R2 = 0.051 m, � � 16.93°, μ = 0.3, X = 0.666227 m and N2 = 400 r.p.m., then, from equation (18), � � sin−1 0.� − 0.051 0.666��� � 1�.9�° Also, from equation (17), �� � 180° � � × 1�.9� × 3.14� 180 � 3.593 rad. This implies that: ��������� � 0.3 × 3.653 × cosec 16.93° � 3.�0� Then, from equation (22), �1 �� � ���������� � e3.�0� � 40.53 Hence, �1 � 40.53�� (N) (�9) More so, from equation (26), torque on the driven pulley can be calculated as follows: ��� � 60��t ���� � 60 × 6��.3� � × 3.14� × 400 � 16.1� Nm From equations (23) and (25), the effective turning force is given by: http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 459 �1 − �� � ��� �� � 16.1� 0.� � 80.85 N Hence, �1 � 80.85 � �� (N) (30) Equating equation (29) to equation (30), gives 40.53�� � 80.85 � �� �� � 80.85 39.53 � �.05 N Therefore, T1 = 80.85 + 2.05 = 82.90 N The speed of the driver pulley can be determined from equation (21) as follows: �1 � ���� �1 � 400 × 0.4 0.10� � 1568.63 r.p.m. Velocity of belt, V1 = V2 = VB is calculated thus: �� � ��1�1 60 � 3.14� × 0.10� × 1568.63 60 � 8.38 m/s Power transmitted by a belt is calculated as follows: �� � �1 − �� �� � 80.85 × 8.38 � 6��.5� W Most crushing mechanisms are driven with a minimum of two belts, since the crusher to be developed is of laboratory size, two belts were selected. Given that: �� = 2, PB = 677.52 W, substituting these values into equation (27), gives �� � 6��.5� × � � 1355.04 W Efficiency of the pulley-driven system is determined thus: � � �䀀��䀀� ��⹉�耀 ���䀀� ��⹉�耀 � 6��.3� 1355.04 � 0.4999 ~ 0.5 � 50% Considering power losses due to friction, inertia forces, voltage drop, heat and vibration, the power rating of the prime mover can be taken as two and half times input, i.e., Power rating of prime mover � �.5 × 1355.04 � 338�.60 W At this stage, decision was made to use an electric motor as the prime mover and the selection criteria are outlined below: Speed should be normal at about 1600 r.p.m. Torque should be greater than the output torque of 16.8 Nm. Power output should be at least 3.4 kW. It must be a three-phase A.C. motor. Based on the criteria above, the motor bought has the following specifications: Power rating = 5 hp = 5 × 746 = 3730 W, speed = 1600 r.p.m., torque = 22.26 Nm, number of phases = 3. 2.3 Stress Analysis of the Components of the Jaw Crusher Stress analysis of the eccentric shaft, base frame and spring were carried out with Autodesk Inventor® as outlined by Waguespack (2014). file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 460 2.3.1 Stress analysis of the eccentric shaft Given that the shaft material is medium carbon steel, with modulus of elasticity, E = 206000 MPa, modulus of rigidity, Gr = 80000 MPa, density, ρ = 7860 kg/m3, radial load = 184 N, continuous load on the eccentric shaft = 1151.43 N / 200 mm = 5.757 N/mm, direction of the continuous load = 20°, and torque = 22 Nm. Using these values and machine elements’ positions shown in Figure 8, the stress analysis of the eccentric shaft was achieved. Figure 8: Positions of radial loads, bearing and continuous load on the eccentric shaft 2.3.2 Stress analysis of the base frame The base frame was drawn and welded in Autodesk Inventor®, prior to the stress analysis. Fixed joints and constrained points are shown in Figure 9. Additionally, the weights of the crushing chamber and its accessories were determined, divided into six and distributed as illustrated in Figure 10, while the weight of the motor-small pulley sub-assembly was determined, divided by four and distributed as presented in Figure 11. Figure 9: Fixed joints and constrained points on the base frame Figure 10: One-sixth of the weight of crushing chamber and its accessories http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 461 Figure 11: One-fourth of the weight of the motor-small pulley sub-assembly 2.3.3 Design of the compression spring Springs are designed to provide a push, a pull, or a twist force (torque), or to primarily store energy. The spring index is the ratio of the mean coil diameter to the wire diameter; the preferred range of the spring index is from 4 to 12. If the spring index is less than 4, the spring is difficult to manufacture, when the index is greater than 12, it is prone to buckling and also tangles easily when handled in bulk (Norton, 2000). Properties of the heat-treated wire carbon steel spring that was analysed in Autodesk Inventor® are listed in Figure 12. The spring check analysis was carried out with the minimum load as the horizontal component of the crushing force, while the working load is the component of the horizontal component when resolved along the drawback rod or at 6.63°. Figure 12: Properties of the compression spring 2.4 Development of the Eccentric Shaft Using a medium carbon steel shaft of Ø74 mm, the following dimensions where considered prior to production of the eccentric shaft by machining: diameter of the hole in hubs of the large diameter pulley and flywheel = 50 mm, diameter of the bearing bore = 55 mm, eccentric lobe diameter = 74 mm and stopper diameter = 60 mm. The working drawings of the machining steps 1 to 9, taken towards producing the eccentric shaft are presented in Figure 13 to Figure 22. The machining steps are as follow: file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 462 Step 1: A straight line was drawn through the centre of the ends of the Ø74 mm solid shaft and along its length; Step 2: An offset of 30 mm was marked from the opposite ends of the shaft and each point was centre-punched; Step 3: A hole was drilled at one end of the centre-punched point; with a radius of 25 mm, a circle was drawn with its centre at 30 mm from the edge of the opposite circular end; Step 4: About 100 mm length of a Ø50 mm shaft was turned on the lathe and its circular end welded to the Ø50 mm circle on one end of the Ø74 mm shaft; Step 5: The attached Ø50 mm shaft was mounted in the jaw chuck of the lathe and the other centre-punched end on the tailstock; the job was set with the aid of a tool; Step 6: 200 mm length was marked-out at 265 mm offset from the tailstock end; with a cut of 0.5 mm, shaft was step-turned to Ø60 mm from the both ends of the 200 mm lobe and parallel-turned to the ends of the shaft; Step 7: An offset of 5 mm was marked out from both ends of the 200 mm lobe, step-turned to Ø55 mm from the Ø60 mm and parallel-turned to the ends of the shaft; Step 8: Ø50 mm was step-turned at 80 mm from 5 mm offset, and parallel-turned 180 mm on the tailstock side and 200 mm on the headstock side; and Step 9: Unclamp the machined part and part-off of the welded part. Figure 13: Geometric model of machining step 1 Figure 14: Geometric model of machining step 2 Figure 15: Geometric model of machining step 3 Figure 16: Geometric model of machining step 4 http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 463 Figure 17: Geometric model of machining step 5 Figure 18: Geometric model of machining step 6 Figure 19: Geometric model of machining step 7 Figure 20: Geometric model of machining step 8 Figure 21: Geometric model of machining step 9 Figure 22: Eccentric shaft after machining Grooves were made along the Ø80 mm sections for retaining rings, after turning the eccentric shaft. Also, keyways were cut along the Ø50 mm section as shown in Figure 23. Knurling operation along the Ø80 mm section of the eccentric shaft is depicted in Figure 24. file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 464 Figure 23: Third angle orthographic and isometric projections of the eccentric shaft with keyways and grooves for retaining rings Figure 24: Knurling of the bearing part of the eccentric shaft for force fitting 2.5 Development of Hardfaced Jaws The fixed and movable jaws of the jaw crusher were developed by welding a ferro-alloy hardfacing insert to mild steel substrate using manual metal arc welding at a welding speed of 120 mm/min and current of 100 A. Stringer hardfacing pattern of the insert was used to form the corrugations, while dot hardfacing pattern was made along the groove to protect the base plate as shown in Figure 25. The hardfacing insert contains mainly 72.8 % Fe, 12.32 % Mn, 7.38 % Cr and 4.35 % C. Detailed hardfacing procedures have been presented by Okechukwu et al. (2018). Geometric models of the movable and fixed hardfaced jaws are shown in Figure 26 and Figure 27, respectively. http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 465 Figure 25: Hardfacing of mild steel with hardfacing insert to form hardfaced jaw (Okechukwu et al., 2018) Figure 26: Exploded view of the pitman-movable jaw sub-assembly Figure 27: Fixed jaw-support plate sub-assembly and exploded view 2.6 Development of the Journal Bearings The eccentric movement of pitman-movable jaw sub-assembly contributes significantly to the failure of bearings in jaw crushers. Frequent replacement of the bearing results in longer downtimes in quarries; hence, the journal bearings are critical components. Based on the eccentric diameter of the eccentric shaft and the bore diameter in the hubs of the pulley and flywheel, a decision was made to use a bearing whose bore diameter falls between the two diameters. This led to the selection and purchasing of four 6311-2RSC3 ball bearings, with Ø55 mm internal diameter, Ø120 mm external diameter and 29 mm thickness. file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 466 Consequently, a steel pipe of internal diameter Ø120 mm, external diameter Ø140 mm and length 200 mm was used to form the bearing housing, while 10 mm thick mild steel plate was used as the journal bearing base. Arc welding was used in joining the bearing housing to base plate and end plates. Exploded view of the journal bearing is presented in Figure 28. Figure 28: Exploded view of the journal bearing sub-assembly 2.7 Assembling of Jaw Crusher Components The assembling sequence of the single toggle jaw crusher is summarized in steps A to D and the corresponding geometric models are presented in Figure 29 to 32. Assembling steps are as follow: Step A: Crushing chamber was positioned on the base frame and fastened with bolts and nuts Step B: Cheek plates were attached to inner side walls; thereafter, fixed jaw-support plate sub- assembly was fastened adjacent the cheek plates, while the toggle socket was attached opposite the fixed jaw Step C: The pitman-movable jaw sub-assembly was hung on the eccentric shaft, the journal bearings were positioned on the eccentric shaft, and the toggle plate was attached to the lower end of the pitman prior to positioning the journal bearings on their sitting positions on the crushing chamber. The drawback rod was attached to the lower end of the pitman before the fastening of the compression spring to the back of the crushing chamber. Step D: The 5 hp electric motor was fastened to the base frame; the Ø400 mm pulley and flywheel were positioned on the eccentric shaft and secured with taper keys, while the Ø102 mm pulley was also secured with a taper key. The pulleys were connected with two B82 V- belts. Figure 29: Geometric model of assembling step A http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 467 Figure 30: Geometric model of assembling step B Figure 31: Geometric model of assembling step C Figure 32: Geometric model of assembling step D file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 468 2.8 Determination of the Capacity of the Jaw Crusher The crusher capacity was determined by crushing 80 kg of granite lumps with sizes ranging from 30 mm to 75 mm, and the crushing time in minutes was recorded. 2.9 Determination of the Variation of Eccentric Shaft Speed with Load The effect of crushing varying quantities of granite on the eccentric shaft speed and the crusher stability was determined with the aid of a digital tachometer. Different quantities of the granite ranging from 0.1 kg to 0.6 kg were crushed and the corresponding eccentric shaft speeds were recorded. 3. Results and Discussion 3.1 Result of the Eccentric Shaft Design Table 2 shows the results generated for the eccentric shaft when it was subjected to stress analysis in Autodesk Inventor®. Table 2: Summary of Results of the Analysis of the Eccentric shaft Design parameters Symbol Value Maximal bending stress σB 1.679 MPa Maximal shear stress τS 0.254 MPa Maximal torsional stress Τ 0.896 MPa Maximal deflection fmax 9.323 microm Angle of twist Φ 0.01 deg The result showed that the angle of twist was insignificant; hence, there was no noticeable twisting in service. Shear force and bending moment diagrams of the eccentric shaft along the yz plane are presented in Figures 33 and 34, respectively. Figure 33: Shear force, yz plane http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 469 Figure 34: Bending moment , yz plane From Figure 33, highest shear force value of 789.776 N occurred between the eccentric lobe and journal bearings. Maximum bending moment of magnitude 26.2341 Nm occurred at the centre of the eccentric shaft as presented in Figure 34. 3.2 Base Frame Stress Analysis Static analysis of the base frame yielded the result shown in Table 3, while directional stiffness values are presented in Table 4. The directional stiffness values were calculated from the generated force and displacement. Table 3: Result of Displacement of the Crusher Frame and Directional Forces Table 4: Determination of Directional Stiffness Force (N) Max. displacement (mm) Directional stiffness (N/mm) Fx 578.346 0.008066 71,701.71 Fy 586.004 0.008066 72, 651.13 Fz 400.771 0.008066 49,686.46 file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 470 The result of the frame’s displacement when subjected to the weights of the crushing chamber accessories and the electric motor is shown in Figure 35. The frame is said to be statically stable or satisfactorily stiff considering the maximum displacement value of 0.008066 mm or 0.000008066 m, which is insignificant. High stiffness recorded can be attributed to the diagonal bracing below the crushing chamber position. These results are in agreement with the work reported by Rusiński et al. (2013), who posited that incorporating diagonal bracing inside a crusher frame increases the stiffness. Figure 35: Static analysis result for the displacement of the jaw crusher base frame The weakest part of the frame or the part with maximum displacement falls around the position of the electric motor-small pulley sub-assembly, where there is no diagonal bracing; the z-direction has the least stiffness as evidenced in Figure 36. http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 471 Figure 36: Force acting along z-direction due to components’ weights 3.3 Result of the Spring Design The results of the spring design are tabulated as shown in Table 5. Table 5: Spring Design Parameters Spring design parameters Values Spring constant 35.241 N/mm Total spring deflection 17.026 mm Spring limit force 2256.678 N Endurance in shear 726.000 MPa Min. load stress 178.149 MPa Max. load stress 185.636 MPa Critical speed of spring 14.600 mps Natural frequency of spring surge 129.034 Hz Spring check result Positive The spring check result is positive, indicating design compliance. It is clear that the spring will not fail when subjected to the forces specified. Furthermore, the spring index of 7.294 was within acceptable range of 4 to 12, while the total spring deflection of 17.026 mm favoured the designed crusher stroke of 5mm. Also, the spring limit force of 2256.678 N was greater than the total crushing force of 1683.62 N. 3.4 Capacity of the Jaw Crusher The developed single toggle jaw crusher showing the evaluated hardfaced jaws and other critical components are shown in Figure 37. file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Okechukwu et al: Development of a Laboratory Size Single Toggle Jaw Crusher for Artisanal Miners and Stone Workers. AZOJETE,16(3):449-474. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 472 Figure 37: Side and front views of the single toggle jaw crusher After crushing the specified quantities of granite, the aggregate product size ranges from 5 mm to 15 mm, with majority falling around 12.5 mm. The average quantity of granite crushed, corresponding crushing time, and the calculated capacity of the crusher were 20kg, 5min and 0.24 ton/h, respectively. The increased capacity beyond the designed capacity of 0.1 ton/hr can be attributed to the use of a higher horse power motor; this implies increased feed rate and throughput. Variation in the crushing time despite crushing the same quantity was due to voltage fluctuation, shape of granite lumps, friction and heat between the metal parts. It was observed that wedge-shaped granite lumps were easily nipped and crushed, while irregular-shaped lumps took longer crushing time. 3.5 Variation of Eccentric Shaft Speed with Load Result of the analysis of effect of crushing increasing quantities of granite on the eccentric shaft speed of the jaw crusher is shown in Figure 38. Figure 38: Variation of average eccentric shaft speed with quantity of granite crushed by the jaw crusher From Figure 38, it is clear that the speed of the eccentric shaft decreases with creasing quantity of granite undergoing crushing in the crushing compartment of the laboratory size jaw crusher. http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 449-474. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: okerex2002@yahoo.com 473 The shaft speed decreases more when the stone shape is irregular; hence, a longer crushing time as observed earlier during the capacity determination. Furthermore, it was observed that the higher the quantity of granite undergoing crushing, the higher the noise and vibration of the crusher parts; this imposes stress on the electric motor. Crushing of 1 kg of granite resulted in an average eccentric shaft speed of 340.30 r.p.m. and a near breaking stress on the motor; hence, 1 kg was taken as the maximum load. Additionally, a moderate load of 0.5 kg will ensure reduced stress on the electric motor and other components since there was a sharp drop in the shaft speed when 0.6 kg of granite was undergoing crushing. 4. Conclusions Geometric modeling and stress analysis of the single toggle jaw crusher were achieved with Pro/Engineer® and Autodesk Inventor® softwares, respectively. Stress analysis revealed that both the angle of twist of the eccentric shaft, 0.01° and the maximum displacement of the base frame, 0.008066 mm, were insignificant; also, spring check result was positive and summarily indicated design compliance. Method of developing critical components of the jaw crusher such as: eccentric shaft, by welding a removable offset shaft before machining; journal bearing, by the use of fabricated journal housing and detachable ball bearings; and crusher jaws, by hardfacing ferro-alloy hardfacing alloy inserts to low carbon steel substrate, were found economical for easy repairs and replacement. Performance evaluation of the machine showed that the actual capacity of the crusher was higher than the design capacity, owing to the selection of a higher capacity electric motor as prime mover. It was observed that the average speed of the eccentric shaft decreased with increasing mass of granite undergoing crushing and when crushing irregular-shaped than wedge- shaped lumps of granite. The methods used in developing the critical components of the jaw crusher can be adopted in developing affordable jaw crushers for artisanal miners and stone workers. More so, these offer shorter reparation time and will reduce the proliferation of moribund quarries in Nigeria. Recommendation The methods used in developing the critical components of the single toggle jaw crusher are sustainable and should be adopted by machine builders to boost the productivity and livelihood of artisanal miners and stones workers, and increase the profitability of small and medium scale enterprises in the minerals sector. Acknowledgement The authors are grateful to the management and technical staff of Advanced Manufacturing Technology Programme, Jalingo, Taraba State, Scientific Equipment Development Institute, Enugu, Enugu State, Union Foundry Industries, Port Harcourt, Rivers State and M. K. Technical Enterprises, Jalingo, Taraba State, Nigeria, for their technical assistance in the course of this research. References Alonge, A. 2015. Development of a prototype jaw-type rock crushing machine. M. Eng. 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