People who have seen trains by the railway always have a question mark in their hearts: how did that black, dusty wooden stake manage to withstand the repeated rolling of hundreds of tons of steel without even frowning? Although the sleepers looked like distant relatives chopping firewood, the train passed by and the steel rails trembled and the gravel jumped, making it as stable as if it had entered a stable place. This calmness is not innate from wood, but is cultivated after being completely 'straightened' once.
The most commonly used sleepers on railways are mostly made of pine wood. It's not a precious commodity, it grows freely all over the mountains and fields, but pine wood has a unique skill: its body is tough and elastic. When the wheels roll down, it can bend slightly and bounce back when the pressure passes, which is equivalent to having a naturally equipped micro shock absorption system. Pine wood has a fatal flaw - it's too tender. Termites use it as a dessert, decay fungi as a breeding ground, and leave it in the wild to be soaked in rain and bitten by insects. Within a few years, it can rot into a bag of debris. It is obviously impossible to expect such wood to last for decades under the track, so the hurdle of anti-corrosion must be overcome fiercely.
What kind of vicious method? Simply put, it is to throw pine wood into a giant "pressure cooker" and feed it with oil, which is commonly known as oil immersion preservation. First, evacuate and remove the air and residual moisture from the wood fibers. Then, the high-temperature anti-corrosion oil is pushed under high pressure and relentlessly drilled through the pores. It's not just about brushing a layer of paint on the surface, but about penetrating deep enough.
How deep is this penetration? Using a ruler to measure casually, the depth of immersion in oil is often above 13 millimeters. In other words, a thickness of three centimeters below the surface of the sleepers has been thoroughly "marinated" with oil, and even pinching it feels like touching a piece of old bacon soaked in oil.
This key number of 13mm hides the survival rules of sleepers. If termites and fungi want to gnaw on this piece of wood, they must first break through this layer of oil armor. For microorganisms, 13 millimeters is like a natural barrier, biting two bites is full of bitterness and spiciness, and the stomach is even more uncomfortable than swallowing industrial wastewater, so they naturally turn around and leave. The rain is even worse, falling on the sleepers like hitting old lotus leaves, rolling into beads and sliding down, unable to penetrate at all. Not afraid of direct sunlight, the oil seals the wood fibers tightly together, making it impossible to find any gaps even if they want to dry and crack. And all of this, without sacrificing the "resilience" in the pine wood bones, when the train approaches, it should bend and bounce, swallowing up the tremendous force completely.
Compared to concrete sleepers, oil immersed sleepers have a bit more rustic charm. Concrete is really hard, but the result of hitting it hard is strong vibration and the roadbed becomes stiff. Sleepers are different. They are greasy, silent, and capable of carrying and melting, like the old buddy who usually doesn't say a word, but once he carries things, he can hold his waist to the bottom. So even though concrete sleepers later became ubiquitous, many old dedicated lines and branch lines still have a row of oil immersed sleepers. The goods they have carried weigh tens of thousands of tons, and the wind and rain they have seen weigh ten years. The black oil seeping out from cracks is brighter than any paint.
In fact, when you think about it, a young pine tree was toppled from the mountains, peeled, sawn, and then thrown into a high-temperature and high-pressure oil tank to roll around. When it came out, it was already black all over, with a pungent smell, completely replacing its soul. What it loses is moisture and greenness, in exchange for at least 13 millimeters of tough oil armor underneath the outer skin. This armor can withstand trains weighing over a hundred tons, withstand decades of sun and rain, and hold up countless distant whistle sounds.
Those black bodies lying under the steel rails all day long don't need to speak up. The wind knows, the steel rails know, every time the train smoothly slides by, it is the sleepers silently embedding themselves deeply into the palm prints of the earth.
