The oil resistance of rail pads and their compatibility with the oily environment of turnout areas
Why do oil stains corrode under-rail pads and what is the mechanism?The main materials of under-rail pads are rubber or polyurethane, which are polymer materials. Mineral oil and lubricating oil components in oil stains undergo a like-dissolves-like reaction with polymer molecules and penetrate into the pad. For rubber pads, oil stains damage the vulcanized cross-linked structure of rubber, relaxing the molecular chains; for polyurethane pads, oil stains cause chemical degradation. This corrosion changes the micro-structure of the pad, making it lose its original elasticity and mechanical properties and unable to perform the buffering function normally.
What typical failure phenomena occur when pads are corroded by oil stains?
Rubber pads corroded by oil stains show obvious swelling, with increased volume, reduced hardness, and become soft and easy to deform, resulting in excessive settlement when trains pass. Some rubbers also crack and powder, losing elasticity. Polyurethane pads become hardened and brittle, with a sharp drop in elasticity and loss of buffering capacity. Both swelling and hardening will cause the permanent deformation rate of the pad to exceed the limit, making it difficult to maintain the stability of the track geometric dimensions in the switch area.
What special designs are there in the material formula of special under-rail pads for switch areas?
Special pads for switch areas use rubber varieties with excellent oil resistance, such as nitrile rubber and fluororubber, or oil-resistant modified polyurethane materials. Oil resistance agents and reinforcing agents are added to the formula to enhance the resistance of polymer materials to oil stains. At the same time, an oil-resistant isolation coating is added to the pad surface to form physical protection and prevent oil stains from penetrating into the interior. These special designs can extend the service life of the pad in an oil-contaminated environment to 3-5 times that of ordinary pads.
Can ordinary pads for ordinary-speed lines be temporarily used in oil-contaminated sections of switch areas?
Temporary use is not recommended. Ordinary pads do not have special oil-resistant design and will fail quickly in an oil-contaminated environment. Even for short-term use, swelling and deformation will occur within a few weeks, leading to excessive deviations in switch gauge and level, affecting the normal conversion of point machines. The switch area is a key part of the line with extremely high requirements for pad performance, and temporary replacement will bring great safety hazards. If emergency use is necessary, oil stains must be cleaned in a timely manner, and special oil-resistant pads for switches must be replaced as soon as possible.
How to quickly judge whether the pad has failed due to oil stain corrosion on-site?
First, observe the appearance of the pad. If there is volume expansion, sticky surface, cracking or darkening, it indicates corrosion by oil stains. Press the pad by hand; if it feels obviously soft and inelastic, or hard and brittle, it is invalid. Combined with the geometric dimension detection of the switch area, if the rail settlement and gauge variation in the point machine area frequently exceed the limit and there are oil stains in the area, it is highly probable that the pad has failed due to poor oil resistance. After finding a failed pad, it must be replaced immediately, and the oil source must be cleaned to prevent the new pad from being corroded again.