Wear resistant PTFE thin film enabled by a polydopamine adhesive layer

The self-lubricating performance of the two types of modified, angular-contact 25-mm-bore ball bearings, i.e., a hybrid ceramic bearing with Si3N4 ceramic balls and an all-steel bearing, was evaluated based on wear inspection as well as X-ray photoelectron spectroscopic (XPS) analysis of transfer films. These bearings had been tested in liquid hydrogen (LH2), liquid oxygen (LO2), or liquid nitrogen (LN2) at speeds to 50,000 rpm and thrust loads to 2840 N. In LH2, both the hybrid ceramic and all-steel bearings demonstrated excellent wear performance made possible by the thick transfer film consisting of PTFE (polytetrafluoroethylene)/CaF2 or CaF2/FeF2, in which CaF2 and FeF2 were tribocatalytically formed by the reducing ability of LHτ This film was generated from a glass cloth-reinforced PTFE retainer. In LO2, the all-steel bearing exhibited excellent wear performance as the result of the intense formation of a Cr2O3 layer beneath an extremely thin PTFE transfer film. By contrast, the hybrid ceramic beari...

Tribo-Characteristics of Cryogenic Hybrid Ceramic Ball Bearings for Rocket Turbopumps: Bearing Wear and Transfer Film©

Synergism of an MoS2 sputtered film and a transfer film of a PTFE composite

Experiments were conducted to evaluate effects of an iron fluoride (FeF2) layer on the self-lubrication and durability of the modified 25-mm-bore ball bearings made of SUS 440C. The modified bearings had a single outer land-guided, glass cloth-reinforced polytetrafluoroethylene (PTFE) retainers with elliptical ball-pockets. An FeF2 layer was chemically formed by means of a passivating surface treatment of fluoridation. The untreated and fluorine-passivated bearings were tested in liquid oxygen (LO2), liquid nitrogen (LN2) or liquid hydrogen (LH2) at a speed of 50,000 rpm with thrust loads up to 2740 N for total operation times up to 11.7 hours. Under sufficient cooling conditions, the untreated bearing tested in LO2, as well as the fluorine-passivated bearing tested in LN2, exhibited excellent self-lubrication and durability, demonstrating sound surface conditions with hardly any wear. The fluorine-passivated bearing tested in LO2 showed a reduction in self-lubrication. In contrast, even under poor coolin...

Effects of Iron Fluoride Layer on Durability of Cryogenic High-Speed Ball Bearings for Rocket Turbopumps

Sliding performance of binary metal-PTFE coatings

Tribological characteristics of transfer films from polytetrafluoroethylene (PTFE)-based, glass-fiber reinforced composites to 440C stainless steel disks were evaluated in an ultra-high vacuum, using a dual-pin-on-disk friction tester. The transfer film was formed by rubbing a composite pin against a 440C stainless steel disk. A friction test was then carried out using the other 440C stainless steel pin. Three types of composites with the additives, Mo, Ag or MoS2 were tested. Outstanding tribological performance was obtained with the composite containing molybdenum. X-ray photoelectron spectroscopy (XPS) analysis of the transfer film showed both PTFE and metal fluoride to exist on the disks for all the composites tested. Therefore, metal fluoride is not the reason for the outstanding performance observed using the composite with the molybdenum additive. Electron probe micro analysis (EPMA) studies showed that, for the case of the composite containing molybdenum, considerable transferred fluorine was foun...

Masami Minami

Papers

Evaluation of tribological characteristics of PTFE composite transfer films in ultra-high vacuum