Yuji Kashima

Wear Resistance Improvement of Titanium Bearings by Laser Gas Nitriding

The influence of gas nitriding on commercial pure titanium and Ti-6Al-4V (Ti64) alloy bearings by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter thin TiN coats of 0.5 to 3 µm were produced. Non-coated and coated bearings made of pure Titanium and Ti-6Al-4V alloy were tested in equal conditions and it was found that the titanium nitride layers significantly improve the rolling contact fatigue performance of titanium components. For tests up to 106 cycles the wear loss of the coated samples was at least ten fold lower than that of the uncoated ones and for 7.76 x 106 cycles, the wear resistance improved almost 100-fold.

Effect of PTFE Retainer on Friction Coefficient in Polymer Thrust Bearings under Dry Contact

Polyetheretherketone (PEEK) is a tough semi-crystalline thermoplastic polymer with excellent mechanical properties. While abilities of polyphenylenesulfide (PPS) are similar to PEEK, former material cost was lower than later. Polytetrafluoroethylene (PTFE) is well known because of its low friction coefficient and self lubrication ability. The objective of this study is to observe the friction coefficient of hybrid bearings, PTFE retainer sandwiched with PPS-races or PEEK-races. Rolling contact fatigue tests were performed and in situ friction forces wear measured. It is concluded that the PTFE retainer reduced friction coefficient.

Observation of Crack Propagation in PEEK Polymer Bearings under Water-Lubricated Conditions

Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in various types of industrial machinery. Due to the latest markets demands for elements capable of withstanding e.g. corrosive environment, metallic bearings are being gradually replaced by components produced from high performance engineering plastic polymers. In order to investigate the failure mechanism of polymer bearings and further improve their performance in practical applications in an underwater environment, in this research crack propagation in Poly-ether-ether-ketone (PEEK) was studied by rolling contact fatigue (RCF) testing under water. Crack propagation in the inner ring raceway surface and subsurface areas of PEEK bearings after testing was observed by a laser confocal microscope. Cracks and flaking failure were found on the bearing raceway surface. From the RCF tests results, it was found that the detected cracks could be divided into three groups: Main Surface Cracks, Semi-circular Cracks and Main Subsurface Cracks. It is concluded that flaking occurs on the inner ring raceway due to the fusion of semi-circular cracks and a main subsurface crack.

Surface Profile Observation of PTFE Thrust Bearings under Rolling Contact Fatigue in Water

The life of the PTFE thrust bearing under rolling contact fatigue (RCF) was investigated. The different conditions of axial loads and the rotating speeds under water were applied. The shapes of the bearing race before and after the tests were measured by a two-dimensional shape measurement sensor. The wear loss of PTFE bearing was rarely generated and the shape of the bearing changed slightly in the test. However, it was found that the lifetime of PTFE bearing depended on the temperature generated in the contact surface. In our testing machine condition, the bearing was collapsed over a load of 1600 N.

Effect of Thrust Load and Rotation Speed on Wear Loss in PPS Race - PTFE Retainer Hybrid Polymer Thrust Bearings under Dry Contact

In order to establish an optimal material combination for the production of polymer thrust bearings, two types of components: retainer and PPS races - PPS retainer were tested by rolling contact fatigue (RCF). The wear properties of both bearing types were investigated and a relationship between thrust load, rotation speed and wear loss was established. It is concluded that by using a PTFE retainer, it is possible to improve the

Observation of Wear on PEEK-PTFE Hybrid Radial Bearings

In this paper, the wear performance of hybrid radial bearing (PEEK-PTFE and alumina ball) was investigated. For effective operation of equipment in clean energy facilities environment, the PEEK-PTFE hybrid bearings was developed. Radial PEEK-PTFE hybrid bearings were produced by machining and their rolling contact fatigue (RCF) behavior under non-lubricated condition was carried out. PEEK accumulation layer with PTFE and graphite appeared on the bearings inner ring under 600-3000 rpm rotation speed. Due to the self-lubrication of PEEK layer, the wear loss of hybrid bearing cycles was lower than in the case of neat PEEK radial bearing. Moreover, It was found that the thin PEEK layer protected the raceway from the friction heat and wear.

Relationship between Load, Rotation Speed and, Strength in All - PEEK and PEEK Race – PTFE Retainer Hybrid Polymer Bearings under Dry Rolling Contact Fatigue

The production of bearings is focusing on polymers, such as polyether ether ketone (PEEK), a tough semi-crystalline thermoplastic polymer with excellent mechanical properties and polytetrafluoroethylene (PTFE), a material with low friction coefficient. The purpose of this study was to establish the properties of hybrid PEEK races – PTFE retainer bearings. Rolling contact fatigue tests were performed in order to investigate the wear properties of such components and the relation between load and rotation speed. It is concluded that by using a PTFE retainer, no wear occurs under thrust load ranging from 200N to 800N at 300rpm.

Influence of radial load on PEEK plastic bearings life cycle under water lubricated conditions

Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in industrial machinery. Usage of high performance engineering plastic polymers is increasing progressively as a replacement for metal components due to the latest markets demands. Poly-ether-ether-ketone (PEEK) is a promising material for precision-machined custom bearings, products that are expected to suit special market needs. In the present study, PEEK radial ball bearings were manufactured by lathe machining under different parameters and their rolling contact fatigue (RCF) resistance under water lubricated conditions was investigated. We observed the surface of the bearings prior and after testing by laser confocal microscope. The wear loss was measured by weighing the bearings before and after test. Cracks and/or flaking failures were identified on the bearing surface after testing. From the RCF tests results, we found that, at water lubricated conditions, crack initiation occurred later in the material that was machined at slower feed rate while at dry condition, the feed rate had little influence on the wear loss and cracking. Wear loss in the case of bearings tested under water was much less severe than that of bearings tested at dry conditions.

Influence of Radial Load on PEEK Plastic Bearings Life Cycle

Nowadays, due to strict environmental requirements, the automotive industry has been reducing vehicle weight in order to minimize the CO2 emission. This had led to an increase in the demand for plastic car parts as a replacement for formerly metal components. Poly ether-ether-ketone (PEEK) has a high glass transition temperature of 143°C, good friction and heat resistance, and can be easily machined. Due to these characteristics, PEEK is already being widely applied in the production of various car parts, such as seat adjustment parts, transmission parts, oil-pump parts etc. In the present study, PEEK bearings were produced by machining and their rolling contact fatigue (RCF) under non-lubricated conditions was investigated. Under high radial load, seizure in the inner bearing part occurred while under low radial load, there was failure by adhesive wear. Exposed to medium load between 85.6N and 93.1N, however, the bearings achieved relatively long lives of over 1.0x10E6 cycles, as well as a unique feature of self-lubrication that rid the raceway of micro depressions, deposits or smearing.

Observation of Fatigue Fracture on PEEK Shaft against Alumina Bearing’s Ball under One-Point Rolling Contact

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 μm 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.