DESIGN AND FABRICATION OF A SIMPLE SCREW CONVEYOR FOR TRANSPORTING INDUSTRIAL ABRASIVE MATERIALS

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1 DESIGN AND FABRICATION OF A SIMPLE SCREW CONVEYOR FOR TRANSPORTING INDUSTRIAL ABRASIVE MATERIALS M. Jason Daniel 1, S. Manoharan 2 and N.Nithyanandan 3 1,2,3 Department of Mechanical Engineering, Panimalar Institute of Technology, Chennai. Abstract The screw conveyor is one of the oldest equipments used for conveying materials known to mankind with the original design dating back to more than two thousand years. Nowadays, they are used extensively in food, plastics, mineral processing, agriculture and processing industries for elevating and/or transporting bulk materials over short to medium distances. Though the design appears to be a simple one, the operation is complex as the design heavily involves empirical relationships. Also, optimizing any component should be directed towards improving the life of the conveyor. This paper reviews a few scientific papers in this area and proposes a simple design by replacing a few materials using wear resistant materials. Some basic design calculations have been included to make the design more understandable. Keywords screw conveyor, SS 308, abrasive material, material handling. I. INTRODUCTION Though the screw conveyors came into existance a few centuries ago, its general use gained momentum in the last century. After the industrial evolution in the western countries, the conveyor finds a place in almost all the areas where full or partial auomation systems are implemented. It has come to occupy a unique place in the growing areas of material handling and processing today. The advent of technologies has made the screw conveyor one of the most efficient and economical way of moving bulk material. It is the simplest and most efficient transport system for the bulk materials and is widely used in all fields of industry. A screw conveyor consists of a shaft mounted rotating screw in the trough and a drive unit for running the shaft. The basic principle of material moving forward along the axis of is similar to the sliding motion of nut along a rotating screw when the nut is allowed to rotate. The material is moved forward by thrust of the screw thread or flight. A helical blade is attached to the drive shaft which is coupled with the drive unit; the shaft is supported by end bearings. The U shaped trough has a cover plate with an opening for loading the conveyor. A discharge opening is provided at the bottom of trough. The loading and discharge facilities can be located anywhere. This paper focuses on increasing the wear resistance of the auger in the screw conveyor to transfer the abrasive materials. Here, the stainless steel SS 308 flight replaces the conventional mild steel as per IS The properties of SS 308 make the component more wear resistant and corrosion resistant compared to mild steel as per IS II. LITERATURE REVIEW The history of the screw conveyor-one of man s simplest and most efficient tools for the conveying of bulk materials can be traced back more than 2,000 years. Archimedes, (240 B.C) a renowned Greek Mathematician and inventor, perfected a spiralled tubular device for transferring water from the hold of a large ship. In doing so, he became the first man to put the screw conveyor principle into practical application. Chang and Steele [1] investigated the inlet section of a screw conveyor and analyzed the performance characteristics for two corn lots. An auger with uniform rectangular cross section was designed and evaluated by Burr et al. [2]. The capacity, volumetric efficiency and power requirements for a conveyor used in transporting corn was determined by Nicolai et al. [3] for DOI: /IJMTER VS6SS 178

2 different speed range and inclination angles. One new 3D model was developed by Moysey and Thompson [4] for studying the local phenomenon of solids flow within the screw channel. Maleki et al. [5] evaluated the uniformity of the seed distribution of a multi flight auger. Bulk solid mechanics of a material element with in a pocket was considered by Dai and Grace [6] and a theoretical model for the torque requirement was developed. Asghariet et al. [7] studied the effect of auger speed and air flow discharge rate of bagasse. A better design of screw feeders for spacific materrials by using discrete element method (DEM) was proposed by Justin W. Fernandee et al. [8] to stimulate the particle transport in horizontal screw feeder system. Dixit et al. [9] determined the effect of percent trough load on horizontal screw conveyor. A few researchers have concentrated on the resesign of components for a specific purpose also. Ganesh S Sinare and Sanjay B Zope [10] modified and optimized the weight of a few components resulting in material savings. Pavlov et al. [11] presented a very detailed objective function that considers the self manufacturing costs of the whole structure. The cost function includes all essential fabrication and erection activities. The purpose of this work is to increase the life of the conveyor by repacing with SS ti handle abrasive materials in industries. III. DESIGN SPECIFICATIONS OF SCREW CONVEYOR The important components of a screw conveyor considered here are: Screws: Sectional type Trough: Angle Flanged U Trough Trough Cover: Flat End plates: Trough Ends without Feet Spouts: Standard Spouts Bearings: Ball bearings The designed screw conveyor is a horizontal type of screw conveyor. It is used for conveying materials along the same plane. The screws of the screw conveyor are sectional type with a diameter of 130 mm and a pitch of 55 mm between the two screws. The screws are fastened on to a pipe of 48.9 mm diameter. The screws and the pipe together are called the auger. Angle flanged U trough is 1000 mm long with a radius of 75 mm with a clearance of 10 mm to the screws. The trough is covered by a flat trough cover of 1000 mm long and 210 mm wide. End plates without feet are used and the trough rests on the supports. End shafts of 50 mm diameter fit the end bearings of diameter 50 mm. The end bearings are ball bearings as they have high radial load rating with good thrust capacity when compared to the roller bearings. The critical components are initially CAD modelled both in 2D and 3D levels. Two such models, the augur and the Trough are shown in Fig 1 and 2. The final assembly as modelled is presented in Fig 3. National standards like Indian Standard IS 2062 [12] and PSG Design Data Book [13] have been used for reference purpose Fig 1: Design of an All rights Reserved 179

3 Fig 2: Design of a Trough Fig 3: 3D Model of the Screw Conveyor IV. DESIGN CALCULATIONS As mentioned earlier, the design of a screw conmveyor is highly complicated. However in recent days, lot of design data are available which come handy for any design engineer. Also, the field experience and feedbacks collected have resulted in the refinement of conveyor design. Using the following steps, the specifications of a horizontal screw conveyor are determined. Step 1: Conveying requirements: To properly design a conveyor it is important to know several parameters. A few are as follows: Material to be conveyed: Sand in our case (Dry Silica) Capacity: 0.35 TPH (as a proto type) Length of the conveyor: 1000 mm Diameter of the screw: 130 mm Pitch of the screw: 55 mm. Step 2: Material Characteristics: The material to be conveyed is characterised based on its bulk density, lump size, flowability and abrasiveness. The data are presented in Table All rights Reserved 180

4 Table 1, Sand Sand (Dry Silica) Characteristics Bulk Density kg/m 3 Lump size Fine Flowability Average Abrasiveness Moderate The conveyor is made up of Mild Steel and Stainless Steel. The screws are made up of Stainless Steel and other components are made up of Mild Steel. The physical properties of Mild Steel (IS 2062, Grade 2) are listed in Table 2 and for the Stainless Steel in Table 3. Table 2, Mild Steel Mild Steel (IS 2062 Grade 2) Physical Properties Density 7850 kg/cu.m Tensile Strength 410 MPa Yield Strength 240 MPa Elongation 20% Table 3, Stainless Steel Stainless Steel (AISI 308L) - Physical Properties Density 8000 kg/cu.m Tensile Strength 550 MPa Yield Strength 270 MPa Elongation 60% Also, the required chemical composition of Mild Steel (IS 2062 Grade 2) and Stainless Steel (AISI 308L) is collected and tabulated in Tables 4 and 5 respectively. Step 3: Volume: Volumetric capacity Table 4, Chemical Properties Mild Steel Mild Steel (IS 2062 Grade 2) Chemical Properties Element % C 0.12 Mn 0.5 Si 0.08 P 0.05 S 0.05 Table 5, Chemical Properties Stainless Steel Stainless Steel (AISI 308L) - Chemical Properties Element % Cr Ni C 0.03 Mn 2 Si 1 P S 0.03 Area of the screw (A) = π R 2 = (Capacity X Factor) / (Bulk density of sand) = (350 X 1.25) / ( ) = m 3 All rights Reserved 181

5 Area of the pipe (a) = π r 2 = π (0.065) 2 = m 2 = π ( ) 2 = m 2 Area of the flight (A * ) = A a = m 2 Area of flight at 30% filling (A ** ) = A * (0.3) = m 2 Volume per revolution = A ** X Pitch = X = m 3 Volume per rpm = X 60 = m 3 /rpm Step 4: Speed: Speed Step 5: Power: = Volumetric Capacity / Volume per rpm = / = rpm Material Horse Power is the power required to move the material. It is calculated by the following equation: Material Horse Power (MHP) = [L X (DS+QF)] / 10 6 Where, L = overall length (in ft) D = friction factor S = speed (in rpm) Q = quantity of material conveyed (in lbs hr) F = horse power factor of sand MHP = [3.281(1X X 2)] / 10 6 = HP Frictional Horse Power is the power required to move the conveyor empty. It is calculated by the following equation: Frictional Horse Power (FHP) = L (DSH) / 10 6 Where, L = overall length (in ft) D = friction factor S = speed (in rpm) H= hanger bearing factor FHP = [3.281(1 X30X 1)] / (10 6 ) = All rights Reserved 182

6 Total Horse Power (THP) Required Power Step 6: Deflection: Screw deflection = MHP + FHP = HP = (THP X Factor) / Efficiency = ( X 1.25) / 0.85 = HP = 5/384 [WL 3 / EI] Where, L = length between two bearings (1140 mm) E= Young s Modulus (2.15 X 10 5 N/mm 2 ) W= w 1 + w 2 +w 3 (12.59 kg) w 1 = weight of pipe (4.82 kg) w 2 = weight of flight (5.31 kg) w 3 = weight of end shafts (2.46 kg) I = moment of inertia (16.4 X 10 4 mm 4 ) Screw deflection = 5/384 [(12.59 X ) / (2.15 X 10 5 X 16.4 X 10 4 )] = mm V. FABRICATION The entire components have been fabricated in a conventional machine shop. The fabrication of a few critical components is described below: AUGER: An auger includes the screw flights and the screw pipe. The screw flights are sectional type and are made up of Stainless Steel SS308. The screw pipe is Electric Resistance Welded pipe and is made up of Mild Steel conforming to IS The sectional flights are blanked from a steel plate, formed in to a helix and then welded together to form a continuous helix on the pipe. The flights are fastened to the pipe by continuously welding on one slide with the help of Super Stainless 308 L (AWS A5.4:E308L-16), a low carbon rutile coated austenitic stainless steel electrode with 8% ferrite and very low moisture pick up. TROUGH: An angle flange troughs is fabricated using a structural steel angle welded flush with the top of the trough edge. The welds are intermittent with Rasi E6013 (AWS E6013), a rutile based medium coated general purpose electrode, ideally designed for welding structural steel works. The angle flanges are welded for perfect alignment with other sections. TROUGH COVER: A flat trough cover is not considered weather or dust tight. Due to the lack of flanges, it is less rigid than the preceeding types. Inlet spout is fabricated and intermittent welded to the trough cover by Rasi E6013 (AWS E6013) electrode. SUPPORTS: The supports are made of steel construction. They are welded to the bottom of the trough by intermittent weld with Rasi E6013 (AWS E6013) electrode. They are stiffened with an angle structure. END PLATE: The U end plate without feet is made up of steel construction. It is welded to the trough ends by intermittent weld by Rasi E6013 (AWS E6013) electrode. It holds the end bearings on which the end shafts are mounted. END SHAFT: The end shaft connects the screw shaft with the handle in the inlet end with the bearing in between them. And the end shaft connects the screw shaft with the bearing in the outlet end. The end shaft is made up of EN-8 grade Steel and machined accordingly. END BEARINGS: The end bearings are of FYH F210 ball bearing type. The units have a high radial load rating with good thrust capacity. They are bolted to the end plate using 4 bolts. The final assembly of the conveyor, before and after painting is shown in Figures 4 and All rights Reserved 183

7 Fig 4: Screw conveyor before painting Fig 5: Screw conveyor after painting VI. CONCLUSION The objective of this paper is to model a screw conveyor capable of handling abrasive materials. The Mild Steel is replaced by Stainless Steel. Though this increases the initial cost, as the life of the conveyor goes up, this will result in long term financial gains, Also, the product can be manufactured and assembled in a conventional machine shop which may encourage the small scale manufacturers to produce the same as a Specific Purpose Equipment. The working has been observed to be satisfactory. The screw conveyor is capable of handling a great variety of abrasive materials from sluggish to free-flowing. Abrasive materials can be conveyed and distributed to various locations as required. The screw conveyor can also be used for mixing two or more abrasive materials in a homogenous manner and also for breaking up large lumps. The screw conveyor is very compact and adaptable to congested locations. It does not have a return similar to a belt or drag conveyor. It is totally enclosed to contain the product and prevent spillage. The abrasive materials are transferred or conveyed with a minimum wear on the auger and giving a homogenous mixture when two or more abrasive materials are used. REFERENCES [1] Chang, C. S., and J. L. Steele. "Performance characteristics of the inlet section of a screw conveyor.", Applied Engineering in Agriculture, 13.5, , [2] Burr, M. S., Kocher, M. F., & Jones, D. D., Design of tapered augers for uniform unloading particulate materials from rectangular cross-section containers, Transactions of the ASAE, 41(5), , All rights Reserved 184

8 [3] Nicolai, R., Ollerich, J., & Kelley, J., Screw auger power and throughput analysis, ASAE/CSAE Annual International Meeting. Ottawa, Ontario, Canada, , [4] Moysey, P. A., & Thompson, M. R.., Modelling the solids inflow and solids conveying of single-screw extruders using the discrete element method, Powder Technology, 153, , [5] Maleki, M. R., Jafari, J. F., Raufat, M. H., Mouazen, A. M., & Baerdemaeker, J. D., Distribution uniformity of a multi-flight auger as a grain drill metering device, Biosystems Engineering, 94(4), , [6] Dai, J., & Grace, J. R., A model for biomass screw feeding, Powder Techn, 186, 40 55, [7] Asghari, A., Alimardani, R., Akram, A., & Karparvar, H., Effect of auger speed and air Flow on discharge rate of bagasse, American-Eurasian Journal of Agricultural & Environmental Science, 3(5), , [8] Fernandez, Justin W., Paul W. Cleary, and William Mcbride, "Effect of screw design on hopper draw down by a horizontal screw feeder.", Seventh International Conference on CFD in the Minerals and Process Indistries, [9] Dixit, Kishor, A. S. Rao, and P. Vasudevan, "Effect of Percent Trough Load on Horizontal Screw Conveyor.", International Journal of Engineering Development and Research. Vol. 2. No. 1, [10] Ganesh S Sinare1 and Sanjay B Zope, Redesign of Roller Conveyor System for Weight Reduction, International Journal of Modern Trends in Engineering Research, Vol. 02,No. 10, [11] L. Pavlov,A. Krajnc and D.Beg Cost function analysis in the structural optimization of steel frames [12] Indian Standard, IS 2062:2011, Hot Rolled Medium and High Tensile Structural Steel Specification [13] PSG Design Data, Kalaikathir All rights Reserved 185