Jacek Caban

Evaluation of Tribological Properties of Polymer Materials Used for Sliding Bearings in Agricultural Machinery

Abstract The continuous technological development requires the use of modern materials also in agricultural engineering. Knowledge of the characteristics of tribological materials pairs cooperating with each other is useful for developing sliding nodes of agricultural machinery. Tribological properties of materials should be assessed for selection of technological materials beyond the economic criterion. The article presents analysis of the characteristics of tribological ball-on-disc wear of polymeric materials used as sliding elements for farm machines. Tribological tests were carried out under dry friction for a polymer-metal pair, and a wear rate and friction coefficient of the sample; the signs of wear were submitted to SEM observations.

THE TRIBOLOGICAL CHARACTERISTICSOF Al-Si/GRAPHITE COMPOSITE

The paper presents the results of tribological research on AlSi12CuNiMg/5.7 wt.% Gr aluminium composite material (containing graphite particles in the amount of 5.7% wt.%) and on its matrix. This composite is used as high-tech construction material in the automotive industry, particularly for pistons, cylinder liners, and slide bearings. The tribological properties of these materials can be significantly changed as a result of the introduction of graphite particles. Therefore, wear tests have been carried out using the ball-on-disc tribometer. Microstructure and wear resistance of the matrix and composite alloy have been subjected to comparative analysis. It was demonstrated that the composite reinforced with graphite is characterized by a lower friction coefficient and lower wear in comparison to the matrix. Słowa kluczowe: aluminiowe materiały kompozytowe, grafit, tarcie ślizgowe, testy zużycia. Streszczenie: Artykuł przedstawia wyniki badań tribologicznych aluminiowego materiału kompozytowego AlSi12CuNiMg/5.7 wt.% Gr (zawierającego cząsteczki grafitu w ilości 5,7% wag.) i jego osnowy. Kompozyt ten znajduje zastosowanie jako nowoczesny materiał konstrukcyjny w przemyśle motoryzacyjnym, szczególnie na tłoki, tuleje cylindrowe i łożyska ślizgowe. Wprowadzenie cząstek grafitu znacząco może zmieniać właściwości tribologiczne tych materiałów. W tym celu wykonano testy zużycia na tribometrze typu kula-tarcza. Mikrostruktura i odporność na zużycie stopu osnowy i kompozytu zostały poddane analizie porównawczej. Wykazano, że kompozyt zbrojony grafitem charakteryzuje się mniejszym współczynnikiem tarcia i mniejszym zużyciem w porównaniu z osnową. * Lublin University of Technology, Faculty of Mechanical Engineering, Department of Materials Engineering, 36 Nadbystrzycka Street, 20-618 Lublin, Poland, e-mails: m.walczak@pollub.pl, j.bienias@pollub.pl. ** Wrocław University of Technology, Faculty of Mechanical Engineering, Institute of Production Engineering and Automation, 5 łukasiewicza Street, 50-371 Wrocław, Poland, e-mail: maciej.zwierzchowski@pwr.wroc.pl *** University of Life Sciences in Lublin, Faculty of Production Engineering, Department of Transporting and Agricultural Machinery, 28 Głęboka Street, 20-612 Lublin, Poland, e-mail: jacek.caban@up.lublin.pl INTRODUCTION Al-Si cast alloys are very popular in the transport industry due to their numerous attractive features, e.g., high strength to low specific gravity ratio, the low value of thermal expansion, excellent castability, and corrosion resistance [L. 1]. Al-Si eutectic alloys (i.e. AlSi12CuNiMg) are mainly used in the automotive industry for the manufacturing of pistons, cylinder liners, connecting rods, and engine blocks [L. 2, 3]. Recently Aluminium Matrix Composites (AlMC) reinforced with fine ceramic graphite particles, fly ash, SiC, and Al2o3 particles are increasingly gaining in importance in the scope of scientific research works and in implementation activities [L. 4–6]. From among the wide spectrum of metal composite materials, the materials based on the system consisting of aluminium alloy – graphite particles (Al/Gr) deserve a special mention. Excellent physicochemical and operational properties are achieved thanks to the presence of dispersed graphite particles in aluminium matrix [L. 7]. Moreover, the presence of solid, soft, and lubricating graphite particles in aluminium matrix leads to the significant improvement of anti-seizing properties and to better vibration damping [L. 7, 8]. The anti98 ISSN 0208-7774 T R I B O L O G I A 1/2017 seizing properties of Al/Gr composites are particularly important in the case of cold engine starting or the lack of proper lubrication. Casted pistons of compression-ignition (Diesel) engines made of Al-Si/Gr composites reduce the value of specific fuel consumption by 3% and the value of engine power losses caused by friction by 9% in comparison to applied conventional aluminium alloys of cast iron [L. 9]. It is possible due to the presence of lubricating graphite layer, high vibration damping capability, and the low value of thermal expansion coefficient. The high vibration damping capability of Al-Si/Gr pistons eliminates the piston slap and piston ring clearance as well as maintains a continuous hydrodynamic oil coating, reducing the friction between piston ring and sleeve surface as well as reducing the wearing of piston rings [L. 10, 11]. Aluminium is characterized by significant reactivity and by the local increase of mating elements temperature in the course of sliding resulting in surface oxidation [L. 10, 12]. Investigations [L. 13] on the impact of Si content on wear in aluminium casting alloys indicated that abrasion wear occurs at a Si content of 12%. The authors emphasize that mainly two abrasive wear mechanisms are present in such case: (1) ploughing action in the case of alloys subjected to heat treatment and (2) the combination of ploughing action and cutting in the case of alloys not subjected to heat treatment. Furthermore, they show that nucleation of Al alloy cracks takes place mainly on the Al/Si contact surface due to the high stress concentration on the interface between Si particles and Al matrix. Needle-shaped eutectoid Si will easily lead to the nucleation and propagation of cracks. This state is eliminated by the spheroidization of eutectic silicon as a result of heat treatment. In the course of the analysis of abrasive wear in eutectic Al-Si alloys, Mahato et al. [L. 14] observed Si decohesion from the matrix resulting in the occurrence of regional cracks. In all probability, this process is facilitated by high velocities of deformation in subsurface regions, and it causes the accumulation of dislocations on Si borders. Furthermore, the increasing occurrence of brittle oxides is observed in the region of micro-cracks occurrence due to increased oxygen diffusion. In the opinion of Omrani et al. [L. 10], graphite particles reduce the value of shear stress and plastic deformations in sub-surface area performing the role grease between the both slipping surfaces. Rajaram et al. [L. 15] indicate that wear progress in Al-Si/Gr composites takes place through the creation of sub-surface cracks, which locate at the previous location of separated Si particles in matrix alloy due to high shear stress. The wear is determined by occurring delaminations and the coalescence of these cracks. Then the wear process is carried out in the form of the removal of successive layers of material as a result of the delamination of sub-surface layers. The application of aluminium alloy graphite particles in combustion engines elements, e.g., cylinder liners, significantly reduces their wear, improves the efficiency, increases the engine power, and reduces operation costs. The reduction of losses caused by friction between the piston and cylinder liner can significantly contribute to the increase of mechanical efficiency [L. 11]. The cylinder liners used by Honda Corporation (staple fibre 12% Al2o3, 9% graphite) are integrated with the cylinder block. The thickness of friction layer has been reduced to 2/3 in comparison to previously used aluminium alloy and the previous mass was maintained. However, the mass has been reduced by 50% in comparison to cast iron inserts. Cooling effectiveness has been improved in a significant manner [L. 16]. The bearings characterized by lower weight, selflubricating, and generating lower production costs in comparison to currently manufactured bearings, e.g., made of copper, lead, tin, and cadmium alloys can prove to be the most promising application of casted Al/Gr composites [L. 8]. The friction joint and particularly the type of directly contacting materials are important in tribological processes. The knowledge of tribological characteristics and wearing mechanisms is essential in the course of designing, selection of materials and in the course of the selection of machine parts production technology. Therefore, the purpose of the research was to determine the impact of reinforcing layer (in the amount of 5.7 wt.% graphite) on wearing in dry sliding condition in regards to matrix alloy AlSi12CuNiMg. MATERIAL AND METHODS AlSi12CuNiMg casting aluminium alloy reinforced with fine graphite particles in the amount 5.7 wt.% has been used in tests. AlSi12CuNiMg/5.7 wt.% Gr composite was manufactured in the Foundry Research Institute in Cracow in the gravity casting process. Graphite particles coated with nickel (NOVAMET, 60 wt.% Ni) with average dimensions of 75–120 μm were introduced into liquid matrix alloy through mechanical mixing. Neareutectic AlSi12CuNiMg alloy constituting the matrix of composite to be tested was used as a comparative material. The tests were performed on raw specimens (not subjected to heat treatment). The chemical composition of AlSi12CuNiMg alloy is presented in Table 1. Disc shaped specimens with a diameter of 25 mm and thickness of 6 mm were used for tribological tests. Three (n=3) specimens from each test material group were used for wear test. The specimens were subjected to grinding on water abrasive papers with grains size of 220, 600 and 1200, sequentially. Then the specimens 99 ISSN 0208-7774 T R I B O L O G I A 1/2017 were subjected to mechanical polishing by means of a suspension of diamond particles (3 μm), a suspension of oxides particles (0.05 μm), washed with acetone, and dried in a warm air stream thereafter. The roughness Ra of the materials subjected to polishing reached level Ra≈0.05 μm. Surface preparation of the samples was dictated by the desire to obtain accurate results when determining the wear factor (according to ASTM G40) on the basis of measurements of profilometric wear volume. Wear tests were completed on a ball-on-disc tribometer manufactured by CSM Instruments. Dry sliding wear tests were conducted according to the ASTM G99-95c [L. 18] and DIN 50 324 standard [L. 19]. Balls with a diameter of 6 mm made of 100Cr6 steel with

Conception of the Maritime Transport Safety in the Baltic Sea in 2009 to 2015

Abstract The maritime transport is particularly exposed to danger due to the environment of its operations. These are the threat dependent and independent of human e.g. environmental, safety health and life of humans or belongings. In spite of attempts to limit the risk of danger, it is impossible to completely eliminate it. The article presents some aspects of the state of transportation safety in the Baltic Sea from Statistical Yearbook of Maritime Economy and Helcom as well as attempt the undertaken to analyses the security state of this sea area in 2009 to 2015.

OVERVIEW OF SELECTED HYDRAULIC DEVICES SUPPORTING ROAD RESCUE OPERATIONS

The intense human activity determines the continuous development of systems and means of transport, which contributes to the intensification of existing road traffic risks and the emergence of new ones. Reduction in the number of fatalities of road accidents is dependent on investment in transport infrastructure, the development of safety systems for means of transport and the care for the technical condition of vehicles. Furthermore, the human factor is manifested in the growing awareness of hazards and improving skills of vehicle drivers. The article presents the construction, operating principles and technical capabilities of the most commonly used hydraulic rescue tools. All this was presented against the background of selected problems occurring during rescue operations while releasing victims caught in car wrecks.

Improvement of Harvesting Methods of Perennial Seed Grass

Abstract In case of traditional harvesting methods the losses of perennial grass seeds may reach 45-50% of the biological yield in unfavourable weather conditions. The paper presents the results of comparative assessment efficiency of various methods of harvesting of perennial seed grass. It was found that the use of special devices and structures in combine harvesters allows increase of yield of technological mixture to the combine tank, degree of seed threshing to 93% and limit the losses of crop to 20-29%. Harvesting of seeds in non-waste technology with harvesting of the entire yield with later transport, drying, threshing and seeds cleaning in stationary devices results in reduction of losses by 5 to 10% but it leads to the increase of energy inputs by 24-25% in comparison to traditional with threshing method. Harvesting with a combing method of plant seeds on a trunk in „Невейки” technology results in the increase of the seeds harvesting to 86-98% of a biological yield.

THE RESEARCH ON AGEING OF GLYCOL-BASED BRAKE FLUIDS OF VEHICLES IN OPERATION

The road safety depends on many factors, including the efficiency of the technical system and the disposal of the driver of the vehicle. As wear of most of the vehicle assemblies threatened only with a breakdown, excessive wear of the braking system components may pose a risk of a traffic accident. The article presents a study on the quality of the brake fluid conductivity as a function of temperature and water content conducted for a selected group of vehicles. This group of vehicles was characterized by different production date and had a different of vehicle mileage. We presented the methodology of statistical analysis of the quality of brake fluid tests in selected 38 passenger vehicles in operation.