Effect of Porosity on the Friction Properties of Porous Polyimide Impregnated with Poly-α-Olefin in Different Lubrication Regimes

Abstract

Porous polyimide materials (PPIs) having different porosity with a constant pore size were fabricated to further understand the effect of porosity on the friction properties in the boundary lubrication, mixed lubrication and elastohydrodynamic lubrication (EHL) regime, respectively. The tribological behaviors of non-porous polyimide (PI0) immersed in poly-α-olefin oil bath and PPIs impregnated with poly-α-olefin were firstly compared, and the effects of load and porosity on the friction performances were investigated. Results show that as the speed increases, the PPIs impregnated with oil exhibit the same friction coefficient (COF) change trend as PI0 immersed in poly-α-olefin oil, which is consistent with the stribeck curve, but the COFs in whole velocity range are higher, and the EHL arrived at a higher speed. The EHL critical speed of PPIs impregnated with oil, as well as the COFs during whole lubricating regime are closely related to the load and the porosity of the material. It mainly depends on two opposite effects of porosity on the friction properties. On one hand, PPIs with higher porosity will release more oil from pores under compression to form a lubricating film, on the other hand, higher porosity will lead to higher contact pressure under the same load, and provide larger contact areas as a result of the increase in the elastic collapse area, which will aggravate the solid-solid direct rubbing and increase the COFs.

Reinforcement of nanoporous lanthanum-doped zinc borate by vanadium selenide nanosheets for improved tribological activity

“…The porous structure of LZB plays a crucial role in enhancing lubricating properties by acting as an intelligent oil reservoir that makes it a self-lubricating system to facilitate the pore structure for discharge of the base oil, which is already stored in pores to the contacting surfaces consistently. 37,38 Meanwhile, through capillary imbibition, it can reuse the additional base oil into the internal pores in between and aerward the work. 38 Thus, the self-lubricating porous LZB shows the benets of high accuracy, high consistency, and enduring lubrication.…”

“…37,38 Meanwhile, through capillary imbibition, it can reuse the additional base oil into the internal pores in between and aerward the work. 38 Thus, the self-lubricating porous LZB shows the benets of high accuracy, high consistency, and enduring lubrication. Mesopores of LZB ll with only base lube, which is released when required, while the macropores severely affect the mechanical properties because of their merger with the neighbouring ones.…”

“…36 Further, it has been reported that the tribological functioning under a ravenous condition can be enhanced by improving the lubricating oil-storage capability of the system. 37,38 In the case of porous G-Ni composite, it has been noted that the porosity adds to lubrication behavior in oil. 39 Xiao et al have observed improved mechanical and tribological properties of porous metallic cubic boron nitride reinforced with graphene nanoparticles.…”

Molecular Dynamics Simulations of Lubricant Recycling in Porous Polyimide Retainers of Bearing

“…In this study, the model system consists of a 60 × 60 × 20 (l x × l y × h l ) nm 3 oil reservoir and a nanopore with a diameter of 10−50 nm. The model is generated using software Packmol.…”

Molecular Dynamics Simulations of Lubricant Outflow in Porous Polyimide Retainers of Bearings

“…In space, due to the limit of environment, the lubricant replenishment is difficult compared with earth conditions. It is found that the porous polyimide material impregnated with lubricants can continuously supply lubricants, , which is attributed to the porous structure that can be used to store and recycle lubricants to reduce lubricant loss. − Our recent work on the lubricant imbibition process demonstrates that the porous polyimide material indeed can recycle lubricants by the capillary effect and press in the bearing system . Thus, porous polyimide materials have been widely used as bearing retainer materials to improve lubricant supply performance in space. − To improve the performance of the lubricant supply, it is suggested to increase the pore size for storing more lubricants, and different sizes of pores were prepared by the pore-foaming agent, laser, − and forming technology. , However, it is difficult to ensure a stable supply of lubricants for a large pore.…”