Consume Power Torque and Conveyor energy eciency for a Horizontal Screw Conveyor with three different Screw Flight –A Comparison

Material handling cost plays crucial role in any manufacturing industries. A judicious selection of material handling system or equipment can only help to enhance productivity and thereby increasing protability of an industry. Extensive studies require for establishing cost effective solution related to selection of right handling system. The objective of work is to nd out running cost associated with screw type horizontal conveyor through experimental investigation of consume power and associated torque against three different types of screw ight(Continuous, Ribbon and Cut Flight) of same nominal diameter and pitch while keeping conveying distance as constant with same material at different screw speed. The experiment was conducted against two different trough heights for nding out mass ow rate. The consume power, torque and conveying energy eciency calculated with three different screw ight and the results were compared for analysis. Hence on the basis of experimental results, conclusion was drawn. Present work conrming experimentally that the consume power at conveyor shaft and torque in case of ribbon ight was found to be 10 percent less than that of the continuous screw type of same nominal diameter, pitch and helix angle with same range of speed against single conveying material type in case of both the trough height(112 mm and 180 mm), which was in line with the statement made earlier[6]. In addition to that a trial has been made to establish a comparison in terms of consume power in between ribbon and cut ight against a constant trough height, which was not reported earlier. This comparative study may be helpful for taking decision in selecting material handling equipment type for specic application area. Now a day overall energy consumption becomes serious concern for different industries.


Introduction
A screw conveyor can be classi ed broadly into two categories; the U-shaped though type conveyor and the fully enclosed conveyor. The U-shape trough type casings are widely used in different industry.
However, their operation being restricted to low angle of elevation, low speeds and low ll ratio. There is various type of ight depending on the applications. Short pitch, single ight continuous screw is recommended for inclined or vertical con gurations while ribbon type ight is excellent for conveying sticky and viscous materials, eliminating collection and build up of material especially the space in between ight and shaft(both hollow or solid). On the other hand cut ight type screw design features is used for mixing and agitation of material in transit and very useful for moving material which have a tendency to pack. The summary of literature review as follows.
Nagel observed that the rotational velocity of a screw in rpm while raising water should not be more than 50/D 2/3 , where D is the diameter of the outer cylinder in meter. If the screw is rotated much faster, turbulence and sloshing prevent the cavities from being lled. Aston Fuch et al investigated a principle of reliable measurement of the mass ow of material through screw conveyor. He developed a novel, cost effective capacitive sensor which allows precise determination of the ll level and also speed of the Research has been carried out on "Design consideration and performance evaluation of screw conveyors" by Alan W. Roberts .This paper is concerned for screw conveyors with enclosed tubular casing. The throughput, torque and power were signi cantly in uenced by the vortex motion of the bulk solid being conveyed.
Yu.Y and P.C. Arnold [1] has discussed about the power requirements of the screw feeder which is a principal parameter and related to the feeder load, properties of bulk solid, screw material and constructional features. A theoretical model of power and torque calculation was outlined for which experimental studies on screw feeder are reported. Two types of bulk material, three types of trough with different inner diameter and screws with different con gurations are investigated. Indian standard speci cation IS:5563:1985 [2] has speci ed the dimensions of various parts and components of a screw conveyor with U-shaped trough, for various nominal sizes of the screw diameters, starting with 100mm diameter up to 1250 diameter. Indian standard speci cation IS:12960:1990 [3] has recommended the method for calculation of power requirement of both horizontal and inclined screw conveyor. The text books by Spivakovsky, A. and Dyachkov, V. [4], Ray, S. [5] and Alexandrov, M.P. [6] provide valuable information and operational data for designing as well as operating screw conveyors. Amla Kurjak described the powder properties of conveying materials in a vertical screw conveyor. He reported that the clearance and free length of intake has signi cant impact on screw capacity. Zareifrouh,H. [8,9] did review on screw conveyor performance during handling process of agricultural grains and bulk materials. He further studied the performance characteristics of screw augur as a function of screw diameter, rotational speed and inclination. The effect of percentage trough loading on horizontal screw conveyor was investigated by Dixit, D.K. [10]. Santanu Chakarborty et al developed a CAD model of semi exible screw conveyor and considered for adaptive design, which provides valuable information about different components of a screw conveyor. Ezzatollah et al [12] investigated the effect of screw speed, conveyor inclination with paddy grain verities on power requirement of a screw type conveyor. Present literature review reveals that few works has already been done on screw conveyor performance. The consume power, torque and conveying energy e ciency of different ight has not yet been reported experimentally, con rming the statement made by Alexandrov, M.P. [6]. In addition to that the trial has made to establish a comparison in between ribbon and cut ight type screw in terms of consume power and torque for 112 mm trough height, which was not reported earlier.

Mathematical Expression
Mass ow rate can be measured performing experiment for 30 s experimental run of the horizontal screw conveyor with the help of stop watch and digital weighing machine considering each screw type at a time. Four set of reading is taken to minimize experimental error at single speed.

Experimental Methodology And Set Up
The experiment was conducted for three different screw having three various ight(Continuous, Ribbon and Cut ight) of identical nominal diameter, pitch and helix angle with easy replacement facility, so that each of screw type integral with tubular shaft installed within the same U-trough of interchangeable trough covers of different trough height (112 mm and 180 mm respectively) during experiment. The reading was taken for single ight type while using 112 mm trough cover at four level of screw speed (12,15, 21 and 26 respectively) as there was a provision for speed changing facility through variable frequency drive [7] installed with the conveyor itself. Then trough cover was changed with the same set up and reading was taken further for 180 mm trough cover at same four level of screw speed. Then screw type was replaced with another ight and the procedure was repeated for remaining ight type. During experiment for 30s run time the mass ow rate (Q) was measured with the help of stop watch and digital weighing machine of 50 kg with 1 gm resolution. The experimental methodology was expressed with the help of three no. of tables as follows.

Result Analysis And Discussion
The experiment was designed to perform with two distinct levels of trough height separately using two different trough cover(Th112 and Th180) along with three screw ight type(C, R and CF) having same nominal diameter, pitch and helix angle and keeping the conveying length as constant with single conveying material type(dry coarse sand) and against four levels of screw speed (12,15,21 and 26 rpm respectively). Following observations was found from experimental result cosidering six different cases (Case-1 to Case-6) which was further enumarated with the help of six graphical representations.

Variation of consumed power(P) with respect to screw speed(n)
The consumed power(P) in Case-4 lies in between Case-1 and Case-5 and Case-3 lies in between Case-2 and Case-6. More preciously, the value of consume power(P) for Case-4 was very similar to the mean of Case-1 and Case-5. The consume power(P) at conveyor shaft for Case-4 was near about 10 percent less than that of Case-1 and for Case-3 was near about 10 percent less than that of Case-2 against constant conveying distance for single conveying material, which was inline with statement [10].While increasing trough height from 112 mm to 180 mm consumed power(P) for Case-5 has a tendency to shift more towards Case-4, which was not reported earlier.

Variation of torque(M 0 ) with respect to screw speed(n)
Torque Characteristics(M 0 ) Case-4 lies in between Case-1 and Case-5 and Case-3 lies in between Case-2 and Case-6 and more precisely the value of the torque for Case-4 was very similar to the mean of Case-1 and Case-5 for Th112. While increasing trough height from 112 mm to 180 mm, torque characteritics for Case-5 has a tendency to shift more towards Case-4.

Variation of conveying energy e ciency(E) with respect to screw speed(n)
Conveying energy e ciency(E) found to be maximum value Case-2 and minimum against Case-5 for both the trough cover(Th112 and Th180). However it's value was slightly increasing trends with respect to screw speed for all ight types at both the trough cover. It has got more impact on screw speed rather than trough height. There was little variations of E with respect to ight type at various srew speed. The Loading [MathJax]/jax/output/CommonHTML/jax.js variation of E with respect to ight type was observed in case of Th112. However, the variation of E was not so distinct Th180.

Conclusion
Among three ight type, continuous ight was found to be expensive in terms of consumed power and associated torque characteristics in case of both the trough covers(Th112 as well as Th180 ) for constant conveying distance of 1480 mm with same conveying bulk material as dry coarse sand. Continuous type screw has got maximum power consumption while operating at 26 rpm against Th180 with same conveying bulk material. The consumed power at conveyor shaft in case of ribbon ight was near about 10 percent less than that of continuous screw type of same nominal diameter, pitch and helix angle with same speed range against xed conveying distance for single conveying material in case of both Th112 and Th180, which was con rmed experimentally. For Th112 the consume power(P) and torque(M 0 ) with CF was(8 to 10) percent less than that of ribbon type ight of same nominal diameter, pitch and helix angle. Which was not been published earlier. However, for Th180 the consumed power for ribbon and cut ight screw showed almost similar result, which was due to the fact that higher trough height(Th180 is equal to 1.6 times of Th112) was responsible for the vortex motion together with high degree of ll without the use of intermediate bearing hanger in a ood feeding condition with a short conveying distance(less than 2 m).Thus the throughput, torque and consumed power for ribbon and cut ight type screw was signi cantly in uenced by vortex motion of bulk material being conveyed. Trough height probably has got signi cant impact on consumed power as well as torque in case of short (less than 2 m)horizontal screw conveyor with ood feeding condition. At Th180 mm trough height(1.6 time than another trough cover) found to be expensive in terms of consumed power and torque rather than Th112 in case of all three ight type. The effect of screw speed on conveying energy e ciency was observed and found slightly increasing trends with respect speed. It's value was found to be within a range of 0.048 to 0.058 t/w-h at experimental range against both the trough cover. Throgh height has got little impact on conveying energy e ciency rather than speed and ight type.

Future Scope
A similar experiment may be conducted for higher speed range and the effect needs to be studied. Present experiment was conducted with a bulk solid (dry sand), the experiment may be conducted with free owing material. The dependence of power factor need to be investigated further. Figure 1 Typical experimental set up    Variation of E with respect to n for Case-2, Case-3 and Case-6