Water-Lubricated Journal Bearings by Litwin Wojciech;

Author:Litwin, Wojciech; [Litwin, Wojciech]
Language: eng
Format: epub
Publisher: Elsevier
Published: 2024-12-15T00:00:00+00:00

The surface roughness of a co-working friction pair has a large influence on the resistance of motion, energy losses, and thermal processes taking place especially intensively in the run-in phase (Figs. 6.2.1 and 6.2.2).

Figure 6.2.1 Coefficient of friction of water-lubricated bearing with polymer bush, before (A) and after (B) running-in process.

Figure 6.2.2 Coefficient of friction of water-lubricated bearing with three-layer bush with PTFE sliding surface before (A) and after (B) running-in process.

The below-mentioned example consists of the experimentally acquired resistance of motion in the form of the friction coefficient as a function of a rotational speed of a 100 mm diameter shaft working in a polymer, elastic bush, in which lubrication grooves are machined only in the upper, non-loaded half of the bush, that is, in the way that is currently considered to be optimal. This bearing was characterized by good hydrodynamic properties, but a significant reduction of the resistance of motion could also be seen after a few hours of the running-in process. One should also note that, after smoothing the bush’s sliding surface, the start-up friction increased. This is connected with the stickslip processes occurring when, as a result of the acting adhesive forces, two sliding surfaces that remain at rest become attached to each other (Chapter 6.4).

In a bearing with inferior hydrodynamic properties due to having lubrication grooves present along the entire bush circumference, the running-in process will also be visible, although the coefficient of friction graph displays a different shape, typical for a bearing working in a mixed-friction zone (Fig. 6.2.2).

The significance of the surface condition on the hydrodynamic properties of sliding bearings was first noticed by researchers as early as the 1960s. Probably the first research works were carried out by Tzeng and Saibel in 1967 and concerned a flat sliding pair [14]. Based on the work conducted, the authors concluded that surface roughness may have a significant impact on the hydrodynamic capacity of a bearing; however, local changes (oscillations) should not be expected in the lubrication film. The results of calculations performed for roughness placed perpendicularly to the sliding direction were especially promising. These led to the conclusion that, in this specific case, one might expect a significant increase, as high as over 60%, in the hydrodynamic capacity of the bearing [15].

In the late 1970s, Patir and Cheng published a paper in which they analyzed a three- dimensional model of surface roughness [16–21], and the majority of their work concerns rolling friction, and therefore different contact conditions from those that appear in a radial bearing.

The author’s own research on the impact of the surface condition on the bearing’s hydrodynamic properties was carried out on a test stand meant for conducting detailed tests of a single sliding bearing (Fig. 4.3). In selecting the bearing, an attempt was made to choose diverse materials with differing physical properties. That is why it was decided to use homogeneous materials such as polyamide, PET, and composite.

It was important, from the perspective of the ability to compare the experimental results with theoretical calculations, to test a bronze bush bearing.

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