Wettability of stern-tube tribopairs materials with water

The wettability of materials used for manufacturing water-lubricated stern-tube bearings — polyamide and rubber 8130 as well as materials used for propeller shaft journal linings — stainless steel 12Ch18N10T and tin bronze BrO5Ts5S5 — was investigated. Wettability was evaluated by measuring the contact angle. Based on the experimental results, second-order models were developed to describe the contact angle as a function of water salinity and arithmetic mean deviation of the profile. A similar influence of the investigated factors on the wettability of bronze and stainless steel was revealed, which, for polymers, not only differs significantly from that of metallic alloys, but also the change in wettability of polyamide differs from that of rubber with a change in these factors. It is noted that the salt content in seawater has a weak influence on the wettability of lining materials, but the surface roughness has a noticeable influence on it; moreover, there is a value of the height parameter Ra at which the wettability reaches a maximum value. For rubber, on the contrary, the surface roughness has a weak influence on the wettability by water, but the salt content in water has a very strong influence on it (in fresh water, rubber exhibits pronounced hydrophilic properties, while in seawater it becomes hydrophobic). The hydrophilicity of polyamide shows a moderate increase both with an increase in the salt content in water and with an increase in the roughness of its surface. It is proposed to use a hydrophilic material for the bearing in a stern-tube tribopair lubricated with water, in combination with a pronounced hydrophobic material for the lining; accordingly, in seawater, it is advisable to use polyamide bearings instead of rubber-metal bearings. Based on the results obtained, it seems reasonable to conduct research on replacing bronze and stainless steel in the manufacture of linings with other materials exhibiting pronounced hydrophobic properties.