Study on Lubricant Release-Recycle Performance of Porous Polyimide Retainer Materials

Abstract

Oil-impregnated porous polyimide (PI) materials can provide continuous lubricant supply, which is widely used to manufacture space rolling bearing retainers. The lubrication performance of porous polyimide materials mainly depends on their ability to release and recycle lubricants, which is closely related to pore size. In this paper, to investigate the effect of pore size, porous polyimide materials with different pore sizes were prepared by preheating the retainer tube billet during the limit pressing process. The lubricant content rates at each stage were measured by the lubricant immersion and centrifugal release experiment to show the variation of the lubricant content rate in the porous PI sample during a working cycle. At first, the lubricant can be absorbed into the pore. It is found that the absorption rate is faster for lubricants with a smaller viscosity. Moreover, lubricant thinning caused by temperature rise also improves the absorption rate. After lubricant absorption to saturation, the lubricant is released under the centrifugal effect to provide the lubricant. Increasing pore size and using low-viscosity lubricants are the main ways to improve lubrication. Finally, the lubricant on the surface can be recycled into the pore by capillary effect. The smaller the pore size, the faster the lubricant recycles to saturation. These insights gained in this study can provide guidance for the choice of an oil-impregnated porous retainer in different working conditions.

Tribofilm Formation of Zinc Dialkyldithiophosphate as Oil Additives Impregnated in Porous Polyimide under Different Contacts

“…Raman spectroscopy (wavelength 532 nm) was adopted to further analyze the chemical composition of the tribofilm on the worn surfaces of steel balls and discs, as shown in Figure . In almost all Raman test results of worn surfaces lubricated with pure PAO4, characteristic peaks of Fe 2 O 3 at 223, 292, 409, and 1317 cm −1 and strong peaks of magnetite (Fe 3 O 4 ) at 665 cm −1 appeared. , However, their peaks are relatively low or even absent in the spectra of worn surfaces lubricated by ZDDP, indicating that the generation of iron oxide is inhibited by ZDDP.

12 Raman spectral analysis of the worn surface in the (a) double-contact, (b) upper single-contact, and (c) lower single-contact.

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“…In the bearings lubricated by the oil-impregnated PPI retainer, there may sometimes be a transient lack of oil, which increases friction and wear. It has been found that iron oxide particles produced by the wear of the rolling elements and the grooves can penetrate inside PPI, also increasing friction and wear. , If a tribofilm was formed on the rubbing surfaces, the transient severe wear could be prevented. Therefore, ZDDP was selected as an oil additive to improve the tribological performances of PPI.…”

“…In almost all Raman test results of worn surfaces lubricated with pure PAO4, characteristic peaks of Fe 2 O 3 at 223, 292, 409, and 1317 cm −1 and strong peaks of magnetite (Fe 3 O 4 ) at 665 cm −1 appeared. 23,32 However, their peaks are relatively low or even absent in the spectra of worn surfaces lubricated by ZDDP, indicating that the generation of iron oxide is inhibited by ZDDP.…”

Preparation and tribological behavior of high‐temperature oil‐containing porous polyimides

“…A common PI raw material grade YS-20 with about T g value of 250 C was composed of 4,4'-Oxydiphthalic anhydride and 4,4 0 -oxydianiline were frequently applied in fabricating porous materials via cold compaction sintering or hot foaming method. [10,11,16,[25][26][27][28][29][30] Wang [25] prepared PPIs via cold compaction sintering at a certain temperature followed by hot pressing again to adjust the density of PPIs. Ruan [29] developed a hierarchically porous oil-containing material via cold pressing and hot sintering process simultaneously retaining excellent mechanical properties and high oil retention.…”

“…Ruan [29] developed a hierarchically porous oil-containing material via cold pressing and hot sintering process simultaneously retaining excellent mechanical properties and high oil retention. Chen [30] prepared PPIs with different pore sizes by adjusting the pressing pressure, sintering temperature, and sintering time. Jia [12] prepared multi-hole self-lubricating materials which were regulated and controlled by adding pore-foaming agent to PI matrix which also possesses a T g value of 260 C and processable T m value of 350 C. Fewer investigations, however, pay close attention to the fabrication of porous materials using hightemperature pulverulent PI materials with T g value exceeding 300 C and even with no processable melting point.…”