The influence of PEEK (Polyether ether ketone) composite solid lubricant film on hybrid radial polymer bearing life, consisting of PEEK ring-PTFE (polytetrafluoroethylene) /graphite retainer-alumina ...balls, was investigated in terms of self-lubrication properties. A PEEK/graphite film layer formed around the ‘pure rolling contact’ track in the Hertzian contact area of the PEEK ring during rolling contact under dry conditions, and then covered the whole contact track. The PEEK/graphite film growth maintained smooth rotation of the bearings, avoiding seizure. Microgrooves on the PEEK ring strongly influenced the formation of PEEK/graphite film. This result helps effective tribological design of micro grooves for polymer bearings.
Wear of poly ether-ether-ketone (PEEK) radial ball bearing (composed of PEEK ring, PTFE composite retainer and alumina balls) was investigated. The PEEK radial bearings were produced by lathe ...machining, and their rolling contact wear tests were carried out at high rotational speed in dry condition. The PEEK adhesion film including PTFE and graphite wear particles was observed on the raceway of the bearing׳s inner ring during the test. Due to the PEEK–PTFE adhesion film accumulation, the wear rate decreased to one tenth of all-PEEK bearing. Moreover alumina balls were not stuck, and the operation temperature was less than glass transition temperature of PEEK. It was found that the PEEK–PTFE adhesion film improved dramatically wear and rotational performance of the bearing.
•PEEK–PTFE adhesion film covers a bearing׳s inner ring raceway under dry conditions.•Due to self-lubrication of the adhesion film, wear loss of the bearings was reduced.•The self-lubrication film consists of PEEK, PTFE and graphite particles.•Wear resistance of the PEEK–PTFE bearings is superior to all-PEEK bearings.•Temperature of PEEK–PTFE does not increase during operation.
In this study, the rolling contact fatigue (RCF) life of nitrided Cr-Mo steel, which has three types of different nitride compound layers, was investigated under contaminated lubrication. Specimen-γ’ ...has nitride compound layer which crystal structure is adjusted to γ’-Fe4N. Specimen-ε and specimen-εpor have the ε-Fe2-3N type nitride compound layer, however specimen-εpor has a porous layer on its outermost surface. To investigate the crucial factors on RCF life, material characteristics of the surface such as Vickers hardness, residual stress, resistance to indentations were evaluated. Changes of surface topography around Vickers indentation were measured through the RCF test under clean lubrication. As a result, the specimens with ε-Fe2-3N type nitride compound layer showed higher RCF fatigue life than that of specimen with γ’-Fe4N. The RCF life of specimen-εpor was the longest among the specimens, which was about 3-5 times longer than the RCF life of specimen-γ’. The rate of reduction in unevenness around the indentations was dramatically improved by the wear of the friable porous layer on the surface of specimen-εpor. Thus, the specimen-εpor with the hard ε-Fe2-3N type nitride compound layer and the friable porous layer kept the RCF life long under contaminated lubrication, because the stress concentration around the indentations decreased due to smooth indentation edge on the εpor surface.
The growth of flaking as tribological fatigue failure in PEEK was investigated through the one-point type rolling contact fatigue test between a machined PEEK polymer shaft and an alumina bearing's ...ball. Due to Hertzian contact of cyclic compressive stress, the subsurface fatigue cracks in the PEEK shaft propagated in rolling and axial directions. When the rolling fatigue life of the PEEK shaft reached 106 fatigue cycles, many narrow angled cracks occurred in the near-surface of the rolling track without flaking. On the other hand, when the flaking ocuurred on the PEEK shaft before 106 fatigue cycles, semicircular surface and subsurface crack propagations were observed. From these observations, it was found that micro-flaking occurred due to the linkages between subsurface and surface cracks. Flakingdeveloped due to the accumulation of these micro-flakings.
Tribological fatigue failure of the machined PEEK shaft was investigated through the one-point type rolling contact fatigue test between a PEEK shaft and an alumina ball, in order to explore fatigue ...fracture mechanism of frictional parts working at high frequency in various mechanical elements. Due to Hertzian contact of cyclic compressive stress, the subsurface crack occurred within approximately 300 mum depth from thesurface and propagated along the rolling direction. After that, the subsurface crack propagation direction changed toward the surface. The flaking occurred on the raceway of the PEEK shaft when the subsurface crack reached to the PEEK shaft surface.
In this paper, the thermal failure (seizure or melting) of hybrid radial bearing (PEEK ring-PTFE composite retainer and alumina ball) under rolling contact fatigue test was investigated. For ...effective operation of equipment in various environments such as dirty, harmful or corrosion situations, the radial PEEK-PTFE hybrid bearings were produced by machining. The PEEK accumulation layer containing carbon graphite was formed on the raceway of bearing's inner ring at 1200-1500 rpm rotation speed. Due to the self-lubrication of the PEEK composite accumulation layer as solid lubricant, the operation temperature in the hybrid bearing was lower than that of all PEEK radial bearing, and the load capacity of the PEEK bearings could be improved. Moreover, it was found that the PEEK composite film which is formed from the PEEK composite layer protected the raceway from the friction heat.
In our previous work, we designed a new joint system for humanoid sized robot. This system consists of a servomotor, a harmonic drive and a link unit. This link unit includes three components; ...polymer bushes, a metal cam plate and a metal camshaft. However elastic deformation of all-polymer bushes can cause a large backlash in the system. In the present work, a new bush was developed and its fatigue behavior was investigated.
Subsurface fatigue cracks under rolling contact area of the PEEK shaft against an alumina bearing’s ball were investigated for application of frictional part in mechanical element in special ...situations such as chemical environments. In order to explore the flaking process of the PEEK shaft, the rolling contact fatigue tests were carried out by using a one-point radial loading rolling contact machine. The flaking occurred on the rolling track of the PEEK shaft at approximate 4⨉105 fatigue cycles. The subsurface fatigue crack propagation was investigated by using 2.5-Dimension layer observation method. The flaking was caused by the propagations of surface cracks and subsurface shear cracks, and the flaking shape was half-ellipse. Moreover, beach marks as fatigue crack propagation in the flaking were observed.
In order to improve the radial load capacity and wear loss of the PPS-PTFE hybrid bearings, the groove shape of the PPS inner ring in the PPS-PTFE hybrid bearing was designed based on ceramic ...bearing’s ball radius (r). The rolling contact fatigue tests were performed by using the PPS-PTFE hybrid bearings with the original (r*1.0) and modified (r*1.1) inner rings. The radial load capacity of the bearing using the rl.1 inner ring was improved 150% over the capacity of the bearing using the r1.0 inner ring. While the operation temperature of the bearing with the r1.1 inner ring was stable at 40 °C, that of the bearing with the r1.0 inner ring incresed rapidly over 100 °C and thermal failure occurred. Moreover, the wear loss of the bearings with the r1.1 inner ring was lower than that of the r1.0. Thus the groove shape influenced the tribology performance of the PPS-PTFE hybrid bearings.
PDF
