material deposition (LDM) of metal-matrix composite (MMC) layers made of 316L and SiC has also shown promising results (Holzer et al 2023). The cylinder drum can be phosphated or nitrided, with or without post-oxidation, the sliding-shoe components DLC coated, etc. In radial piston hydraulic motors, rollers and pistons are often DLC coated in order to improve wear resistance and to mitigate the risk of seizure between rollers and roller cages at high power output. DLC coatings also bring improvements in mechanical efficiency at low speeds. A variety of new seal materials also avail themselves, allowing engineers to push the performance limits.
Triboconditioning®
to hard coatings Triboconditioning®
CG process as an alternative CG is a patented mechanochemical
surface finishing technology developed by Tribonex AB. The Triboconditioning®
CG treatment can be carried
out using standard mass-finishing equipment, such as vibratory tub finishers, centrifugal barrel finishers, and steam, and drag-finishers (Zhmud et al 2025). Compared to traditional mass-finishing processes, the major difference is the use of special chemically reactive process fluids and media types. The technology is used as the final finishing operation bringing about a triad of effects (Figure 3): (i) surface roughness profile optimisation, (ii) compressive stress buildup, and (iii) tribofilm priming, which greatly improves the tribological performance of treated parts. An ongoing joint project between Tribonex and Bosch Rexroth on commercialisation of the Triboconditioning® process sponsored by the Swedish Energy Agency has demonstrated that the treatment delivers a positive impact on the endurance and efficiency of Bosch Rexroth’s Atom radial piston hydraulic motors (Figure 4). The improved wear resistance of surfaces finished using this process prevents leak development and efficiency loss due to wear.
Figure 4: The effect of Triboconditioning®
CG treatment on surface
roughness and wear-resistance of the pistons used in Bosch Rexroth’s Atom radial piston hydraulic motor. LHS: The changes in the surface roughness parameters due to the Triboconditioning®
process.
The changes in the surface roughness profile bring about significant friction reduction in the mixed lubrication regime (Figure 5). As a result, a significant reduction in start-up friction and an improvement in mechanical efficiency at low speeds are expected.
Figure 5: Dependence of the coefficient of friction on the surface finish quality for the roller/roller cage tribocouple (redrawn from Isaksson
et.al. 2011).
It should also be noted that the this treatment reduces not only amplitude roughness, as does, for example, polishing, but also gradient roughness that characterises the slopes of surface asperities (see Figure 6). Previous research showed that gradient roughness has a significant impact on boundary friction (Brodmann and Bodschwinna, 2019).
Figure 3: The surface effects brought about by the Triboconditioning® treatment.
CG
Figure 6: The effect of Triboconditioning®
treatment on gradient roughness (the Aq parameter) of piston surfaces in the Bosch Rexroth Atom motor.
28
LUBE MAGAZINE NO.189 OCTOBER 2025
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