The common railroad spikes are divided into two categories, blacksmithing railroad spike and the mechanical railroad spike. Both of them are easy to handle and use, just use the railroad spike hammer to fix. But in term of the manufacturing technique, they have many differences. Blacksmithing railroad spike is the use of the hand-made way to make the railway spike. So the use of this production process will have a certain defect. For example, the surface will be partially raised, the weight of railroad spike will be more or less and the like. Mechanical railroad spike can be a good way to avoid these problems. But the corrosion is an inescapable topic.
Due to the railroad spikes are exposed to the atmosphere, the active anions (such as Cl-ions in the feces) are contained in the media. These active anions are adsorbed at certain points on the root surface of the railroad spike so that the passivation film of the metal surface is destroyed that resulting in the corrosion. Due to the anode area is very small, so the corrosion rate is fast.
When the iron and iron or iron and other non-metallic surface forms a narrow gap, the movement of the material has been blocked in the gap, which will form a concentration of batteries, resulting in local crevice corrosion. In the medium, the oxygen concentration increases and the crevice corrosion increases; the pH decreases, the anodic dissolution rate increases and the crevice corrosion increases.
The rail is pressed against the sleeper by the railroad fasteners, and the railway fastener is pressed by the railroad spike, which is anchored to the sleeper and formed integrally with the sleeper. When the train through with high-speed, that will produce strong pressure, friction, horizontal force and elastic vibration to the rails. The railroad spike is both subjected to static tensile stress and the role of the cyclic stress when the train passes.
The process of the railroad spikes has three stages. The first stage is the incubation period. During this period, due to the localization of the corrosion process and the effect of tensile stress, the cracks disappear.
The second stage is the development of corrosion cracking. In the third stage, due to the local concentration of tensile stress, the rapid growth of cracks led to the destruction.
Generally, the greater the relative humidity, the more likely to form a water film on the surface of the railroad spike, the longer the membrane remains, so the more likely the atmospheric corrosion.
Because the existence of temperature difference will promote the water vapor in the iron surface to form a water film, that provides a corrosion conditions.