Have you ever noticed the pieces of wood lying horizontally under the tracks while taking the train? They may seem unremarkable, but they are the true "behind the scenes heroes" in the railway system, known as sleepers. Don't be fooled by the fact that it's just a piece of wood, it has to withstand the heavy pressure of the steel rails, the vibration of the train, and be exposed to the sun and rain for decades. Ordinary wood has already rotted. So, railway sleepers must undergo special treatment, and the most critical step is anti-corrosion. In anti-corrosion technology, oil immersion and oil foam are often compared, but when it comes to choosing, only oil immersion is recognized on railways. Why? Today, let's talk about the tricks behind this.
Let's first talk about what kind of wood to use. Sleepers cannot be used simply by taking a piece of wood, they must be sturdy, pressure resistant, and not easily deformed. Pine wood is the mainstream choice because of its uniform texture, easy processing, and most importantly, its wood grain structure is particularly friendly to the absorption of anti-corrosion oil. But pine wood itself is afraid of water and insects, so if left in the wild, it will rot in three to five years. So, anti-corrosion treatment is a necessary path.
In common anti-corrosion methods, oil soaking and oil immersion sound similar, as if wood is soaked in oil, but in actual operation and effect, there is not a single difference.
Oil foam, as the name suggests, is soaking wood in anti-corrosion oil for a while. The duration varies, some may only soak for a few hours, or even shorter. During this process, the oil mainly adheres to the surface of the wood and seeps in at most a little bit. Over time, the surface oil is slowly evaporated and washed away by wind, sun, and rain, greatly reducing the anti-corrosion effect.
And oil immersion is another approach. It is not simply "soaking", but a complete process of vacuuming, pressurization, and re infiltration of wood in a sealed high-pressure tank. This process truly allows the anti-corrosion oil to "drill" deep into the wood. Pine wood treated with oil immersion has a depth of over 13mm. This depth means that even if the surface of the sleepers is worn or rubbed by ballast during use, there is still sufficient anti-corrosion protection layer inside, which can resist the erosion of moisture, fungi, and pests for a long time.
The advantages of oil immersion technology are precisely reflected in its durability and reliability. Because oil is truly 'pressed' into the interior of wood, it binds more tightly to the wood fibers and is less likely to be lost. Even in harsh environments, it can maintain its anti-corrosion effect for a long time. In contrast, the anticorrosive coating of the oil bubble is like a "facial mask", which falls off when used, and the protection period is naturally much shorter.
Another point that is easily overlooked is that oil immersed sleepers not only prevent corrosion, but also enhance the stability of the wood to a certain extent. Oil fills the gaps inside the wood, reducing the opportunity for water to enter and exit. As a result, the expansion and contraction changes of the wood are reduced, making it less prone to cracking and deformation. For sleepers that require precise support for steel rails, this is crucial. The smoothness of the track is directly related to driving safety and comfort. If the sleepers themselves are crooked or cracked, the geometric dimensions of the track cannot be maintained.
Of course, the cost of oil immersion is definitely higher than that of oil foam, and the equipment is also more complex, but railway engineering has always been a typical example of "you get what you pay for". Safety, durability, and low maintenance are the ultimate goals. Looking at heavy-duty railways and high-speed railways both domestically and internationally, almost all use oil immersed anti-corrosion technology for wooden sleepers. This is not a decision made on a whim, but rather the experience accumulated from decades or even centuries of engineering practice.
At the end of the day, oil bubbles are "surface work", while oil immersion is "deep into the bone marrow". The railway, which is a major safety project, naturally chooses the latter. After all, when it comes to safety, there is never any room for carelessness.
