Proceedings of SerbiaTrib '13

tg( ) tg 100, [%] (2)tgwhere are: relative error of measurement; -angular error of measurement . If I one takes intoaccount that the frictioncoefficient tg , thenthe diagramgiven in Figure 2 candetermine therelative measurement error ()which is, amongother, function of coefficient of friction.Friction coefficient µ [-]Relative percent difference ε [%]21.81.61.41.210.80.60.40.2004 8 12 16 20 24 28 32 36 40Rotation of steep plane [ ]°Figure 2. Graphical representationof the relativeemeasurement error of the coefficient off friction over r thesteep planeOn the basis of eqquation (2) and the diagram(Figure 2) can be noted that values of thecoefficient of sliding friction μ> 0.1 with Δα = 1'correspond to the measurement error which is lessof 0.3%. This means that theprinciple ofmeasurement can be efficiently used to determinethe static friction coefficient at higher temperatures,especially if one takes into accountt that the slidingcoefficient of staticfriction at elevatedtemperatures for most materials is greater than n theabove values.44tops of some asperities a and in that case betweenmost asperitiess there is noo real physical contact.Block and the rollers are made of same material(theaforementioned). Experiments weree carried outwith increase of temperatures by 50⁰ C, startingfromthe temperature T 1 =50 ⁰ C up to temperatureeT 2 = 350 ⁰ C, andd after heating samples were left tocool to room temperature.Each measurement wasrepeated 10 times, so that a total of 350independent experimentsis performed at roomtemperature after heating the contact pair.Figure 3. Schematic representation of the contact pairThe coefficient of friction was determined usingspecially designed devicess (Figure 4). Workingprinciple of designed d Tribometer iss based onrotation of steep plane, which is done on amechanical principle to the accuracy of the readingsof 1’. Namely, rotation steep plane is carried out bymanually turning of nonius. . Leveling off Tribometerris done using level whichh provides precision ofreading which is i less than 0,02/1000 ⁄ .3. EXPERIMENTAL RESEARCHExperimentalstudieswere performed onsamples made of steel EN X160 CrVMo12 1 whichis subjectedto heat treatment hardening, with theaim to obtain the highh hardness of 64 HRC andwear resistance. Tribological contact pair is realizedby setting the rollers of diameters 4 mm, 6 mm, 8mm, 10 mmm and 12 mm, length 20mm, on prismblock (Figure 3). This simulates tribological contactwhich is, theoreticaly,realized on line. If we takeinto account that the mass of the rollers is smallthen we have small values of contact pressure.When rollers are in contact on flat surface s block, inthe absencee of temperature, contactt is achievedd on13 th International Conference on Tribology – Serbiatrib’13Figure 4. Measuring equipmentContact pairs were heated to temperatures from50 ⁰ C to 350 ⁰ C with the step of 50 ⁰ C, after whichhthey are cooled to roomtemperature.So,determining the size of the static coefficient offriction was performed withh contact pairs that wereeheat treated at temperatures indicated. This meansthat contact pairs in the process of determining thestatic coefficient of friction weree at roomtemperature. The T results of measurement of thecoefficient of friction f depending on the weight of149