The balls and raceways in a rolling bearing are separated by a very thin oil layer that is critical to performance. There are several models for predicting the layer thickness and some lab-based methods for studying individual contacts in model apparatuses. However, techniques for in situ measurement of oil films in real bearings are scarce, especially at the level of detail of the film profile. The purpose of this study was to experimentally measure the film thickness profile between the outer ring and balls in a rolling element bearing using an ultrasonic reflection method. A 25-MHz ultrasonic immersion transducer was installed in a water bath above the bearing and the incident pulses were focused onto the moving contacts. The oil film thickness profiles across the ball passage are presented for a 6410 deep-groove ball bearing under loads up to 49 kN and speeds up to 600 rpm. The spatial resolution of an ultrasonic pulse is relatively low, so it is not possible to pick out the detail of the horseshoe constriction at the contact exit. However, there are some indications of its presence and the central film thickness measurement agrees well with theoretical solutions. For a range of loads and speeds, oil films of between 0.1 and 0.7 µm were measured. Data storage limitations mean that the measurements are limited to low-resolution profiles across several balls or a detailed profile over a single ball. The oil films were also measured for successive balls and found to be identical within the accuracy of the method.
The use of mineral and synthetic lubricants will have long-term impact on the environment. Vegetable oil can be an alternative for substitution due to having significant environmental benefits. In addition, vegetable oils also offer renewable resources and have proven to have excellent lubrication performance for automotive and industrial application. Coconut oil is one of vegetable-based oil that would have prospective characteristics to be exploited as bio-lubricant oil. The origin of coconut oil would distinguish its characteristic, hence differentiating its performance as a lubricant. Indonesia is well known as having abundant source of coconut oil which is made with different extraction methods. Extraction method can be envisaged for improving the performance of coconut oil as lubricant oil. Indonesian coconut oils that had been extracted through dry and wet methods would be a primary concern in this study. The prospective of extracting method of coconut oil as lubricant in term of physicochemical and tribological properties will be investigated. hydrogenated coconut oil (HCO), virgin coconut oil (VCO), and refined coconut oil (RCO) are product of coconut oil extracted from wet and dry, respectively. Results indicated that RCO and HCO posed high viscosity index, high ratio unsaturated to saturated fatty acids, and low wear and friction coefficient which are prospective as base fluid in lubricant industries.
Due to increased environmental sensitivity, renewable-based lubricants, and food grade lubricants are being considered potential alternatives to petroleum-based lubricants. Understanding of bio-lubricant in relation to abrasive wear is essential for using ball bearings in industrial implementation. This study focused on wear mechanism on ball bearings lubricated by bio-lubricants. Palm oil and coconut oils were used in this study. Coconut oils were made by two processes, namely dry and wet processing, resulting in three types of oil (virgin coconut oil [VCO], refined coconut oil [RCO], and hydrogenated coconut oil [HCO]). Full-scale bearing life tests were conducted with 300 N load with 2,840 rpm for 6 hours. Method of lubrication was circulating oil by using pump injection to the self-aligning ball bearings. The results show that the main wear mechanism, which impacted on the surfaces of inner race, outer race, and ball for different bio-lubricants, were abrasive and adhesive wear. It found that the abrasion rate was the least severe for VCO. The discrepancies of worn surfaces are thought to be as a result of the physical and chemical properties of bio-lubricants.
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