Comparison Of Sliding Frictions Of Different Materials .

ICMIEE-PI-140425International Conference on Mechanical, Industrial and Energy Engineering 201426-27 December, 2014, Khulna, BANGLADESHComparison of Sliding Frictions of Different Materials Using a DigitalSliding Friction TesterKamrul Hasan Chowdhury, Md. Nafis Soyaib and Dr. Sobahan Mia*Department of Mechanical Engineering,Khulna University of Engineering & Technology, Khulna-9203,BANGLADESHABSTRACT: Friction Tester has a greater importance in the field of fundamental friction studies such as frictiontesting of metal surfaces, soft and hard coatings, plastics, glasses, polymers and different types of fabrics with orwithout lubricants. So it has been decided to construct a friction tester and measure the coefficient of friction of variousmaterials in different conditions. In order to do that, various types of friction tester has been studied and finally it hasbeen decided to design and construct a Digital Sliding Friction Tester. In this construction a 24 Volt dc motor was usedwhich elevates a sliding plate. A gear mechanism was used to transfer the motion from motor to shaft. Afterconstruction performance test has been done with respect to various parameters and conditions. The obtained resultfrom Digital Sliding Friction Tester was compared with manually calculated friction tester and standard ASTM chart.This showed a very good accuracy with a deviation of negligible amount of 1-6%. Results showed that the coefficientof friction is independent of load and is totally dependent on material and surface roughness.Keywords: Friction, Static Friction, Coefficient of Static Friction, Friction Tester, Lubrication.1.IntroductionFriction is the force resisting the relative motion ofmagnitude of kinetic frictional force is always less thansolid surfaces, fluid layers, and material elementsmagnitude of static frictional force. When value ofsliding against each other. As a consequence ofapplied net external force, F is more than fk then bodyfriction, the process of motion and the dynamicmoves with a net acceleration and when these forcesbehavior of the whole system are influenced orare equal then body moves with a constant velocity.disturbed and some part of the energy of motion isRolling frictional force is a force that slows down thedissipated [1].motion of a rolling object [2]. Basically it is aThere are four types of friction namely. Static frictioncombination of various types of frictional forces atis friction between two or more solid objects that arepoint of contact of wheel and ground or surface. Whennot moving relative to each other.Static frictionala hard object moves along a hard surface then staticforces from the interlocking of the irregularities of twoand molecular friction force retards its motion. Whensurfaces will increase to prevent any relative motion upsoft object moves over a hard surface then its distortionuntil some limit where motion occurs. It is thatmakes it slow down. When a body moves in a fluid orthreshold of motion which is characterized by thein air then there exists a resistive force which slowscoefficient of static friction. The magnitude of staticdown the motion of the body, known as fluid frictionalfriction depends upon µs (coefficient of static friction)force. A freely falling skydiver feels a drag force due toand N (net normal reaction of the body). Kineticair which acts in the upward direction or in a directionfriction denoted as µkcomes into play when a body justopposite to skydiver’s motion. The magnitude of thisstarts moving along a surface. When external applieddrag force increases with increment in the downwardforce is sufficient to move a body along a surface thenvelocity of skydiver. At a particular point of time thethe force which opposes this motion is called as kineticvalue of this drag force becomes equal to the drivingfrictional force.force and skydiver falls with a constant velocity.µk is coefficient of kinetic frictionalforce and N is the net normal reaction on the body. The*Corresponding author. Tel.: 88-01711951400E-mail address: smia@me.kuet.ac.bd

Coefficient of friction is the ratio of the weight of anobject being moved along a surface and the force thatmaintains contact between the object and thesurface[3]. The coefficient of friction is not always thesame for objects that are motionless and objects thatare in motion; motionless objects often experiencemore friction than moving ones, requiring more forceto put them in motion than to sustain them in motion.The static coefficient of friction is the coefficient offriction that applies to objects that are motionless.The kinetic or sliding coefficient of friction is thecoefficient of friction that applies to objects that are inmotion.2.2 Design DetailsStudy of mechanics of friction dates back to thesixteenth century, after the invention of Newton’s lawof motion. The variation of friction depends oninterfacial conditions such as geometry, relative surfacemotion, surface roughness of contact surfaces, type ofmaterial, lubrication etc. Among these factors materialand surface roughness are two major factors whichplay significant role for the variation of friction. And inthis observation it ishigh lightened to observe thevariation of static friction for different material. Inorder to determine this observation a Digital SlidingFriction Tester has been designed. This machine is not2. Design and Constructionavailable in our country. In foreign countries such as2.1 General ComponentsChina and Canada analog version of this machine isThe general components of a Digital Sliding Frictionused. Different type of Friction Tester has been studiedTester are:on internet and learned about the analog version of thisBase Plate: The Base Plate is the part which supportsmachine. Then the machine has been designed in Solidthe whole foundation and the other parts of the FrictionWorks 2013.Tester are mounted on it.Sliding Plate: Sliding plate is that part on which thetest specimen is placed. It is welded with the mainshaft.Main Shaft: The main shaft is welded with the SlidingPlate. The two ends of the shaft are attached to theBase Plate. For smooth rotation of the shaft twobearings are mounted at the two ends of the shaft.Motor: In this machine the motor is the mainmechanical power source to elevate the sliding plate byA schematic diagram of the design has been shown onthe Fig.1. Here, the base of the structure is constructedwith 0.0625 inch thick galvanized iron sheet. Thesliding plate is attached to the rotating shaft. The gearis attached at the middle of the shaft. This wholearrangement is further attached with the base with thebearings. The electric motor is used as a source ofmechanical power. A pinion is attached with the motorshaft to transmit power from motor to shaft. Theexperiment was carried out for different materials.rotating the main shaft. For smooth elevation of thesliding plate a motor of low rpm and high torque isused.Gear arrangement: For transmitting the power frommotor to main shaft a 2:1 spur gear arrangement isused.Bearings: A pair of 6202 bearings is used to supportthe main shaft.Electronic components: Microcontroller ATmega8,16x2 LCD Screen, Motor Driver L298N, IR Sensoretc.Fig.1Aschematic diagram of Digital Sliding FrictionTester.

Table1: Coefficient of static friction of variousmaterials without lubricationStatic Coefficient ofFriction, 22Cast GI dGI Sheet0.590.580.500.700.700.800.603. Testing ProcedureGI SheetBrass0.360.360.352.78To determine the influence of surface roughness ofCast IronGI Sheet0.630.640.653.08various materials on static coefficient of friction wereWoodBrass0.650.620.603.33carried out under both dry and wet condition. At firstWoodWood0.480.480.504.00Cast IronWood0.600.591.67WoodGI rdBoardGI 0.352.78maintained at a range of 0.3-0.5 rpm. A certain timePlywoodBrass0.530.543.64later for a certain angle the weight block started 600.500.600.70load, the load shouldn’t exceed 5N. A photo sensorGlassCarton0.700.720.754.00was used to facilitate that immediate action. After thatCarton0.600.590.601.67the angle was taken on account and doing the tIron0.580.590.603.33Fig.2 A Digital Sliding Friction Tester afterconstruction.the testing specimen was placed on sliding plate whichwas in initial position (0º angle) and another specimenof same material was attached with a sliding block andplaced on top of that material. Then the machine wasswitched on and the sliding plate started to lift at anangle with a constant velocity. For accurate results theangular velocity of the sliding plate should bemove on and the sliding plate stops at that angle1.001.671.543.332.86immediately. Since the motor speed varies with thecalculation with the help of microcontroller the finalresult was showed on LCD screen. That was the resultof static coefficient of friction for that specific material.Finally, another switch was used to bring back thesliding plate in its initial position.4. Experimental Data5. DiscussionThe data collected during the performance test at 70%The main goal in this project was to investigate therelative humidity are as follows:influence of surface roughness of various materials oncoefficient of friction. The nature of friction is to

Table2: Coefficient of static friction of variousmaterials with lubricationStatic Coefficient ofDM1M2Friction, µs(%)µs3[5]µs1µs2humid condition, for a pair of metal the water particlesGlassGlass0.210.220.25.00Lubricants play a great role in reducing the friction.CastIronGlassGlass0.280.290.33.33The co-efficient of static friction varies with nWoodGlass0.340.362.86From tables 1 and 2 it can be seen that for both withBrass0.240.260.350.400.254.00and without lubricants the digitally obtained 0coefficient are different for different sliding pairs andCastIronWoodWood0.370.392.5lubricants, therefore maintaining appropriate level .370.405.00value to improve mechanical processes.0.240.260.254.006.0 0.330.330.355.71HardboardBrassBrassof the air act as lubricant at the contact surfaces. Butfor glass and polymers the coefficient of frictionincreases with the increase of relative humidity.lubricants with different additives. The viscousproperties of the lubricants vary with the temperature.vary at a range of 1-6% in comparison to the standardvalues from ASTM chart. The magnitudes of frictionrelative humidity as well as appropriate choice ofsliding pair, friction may be kept to some optimumFrom the study and within the experimental setup, thefollowing conclusions may be drawn:The Coefficient of static friction of various materials atdifferent conditions has been measured. From the test itcan be concluded that-increase with the increase of normal force. Frictionalforce is independent of apparent area of contact. It hasI. The co-efficient of friction depends on contactsurface condition of material.been found that by applying lubricant between tly. For wet condition the friction is alsoreduced between the contact surfaces. For changing theII. The frictional force is independent of apparentarea of contact.III. Test result is satisfactory with 15% variation.angular position of the sliding plate smoothly a motorof low speed and high torque was used. TheNOMENCLATUREconstruction was made such a way so that theN: normal reaction force, Nspecimens can be loaded and unloaded easily. SinceF: force, Nvibration has a great effect on frictional phenomena,Ө : angle, ºthe main basement was welded with legs. During theµs :coefficient of static friction.performance test for keeping one surface fixed clampsµs1 :coefficient of static friction obtained digitally.were used. The relative humidity of the atmosphere hasa great effect on the static friction coefficient. Atµs2 :coefficient of static friction obtained manually.