During the Chinese New Year holiday, I took a train trip with my child. The child pointed to the neatly stacked ballast stones outside the window and asked me how the sleepers were made. The child has seen that dark and heavy wood and has always been curious about why it can withstand it for decades without rotting.
I explained to him all the way and remembered that I should write these down.
The sleepers on the railway may seem inconspicuous, but they are actually quite interesting. It is mostly pine wood - unfortunately, pine wood itself is not a durable material. This type of wood grows quickly and is easy to process, but it is naturally afraid of water and insects. If left in the wild, it will deteriorate in two or three years. But if it is sent to the processing plant for a walk, it can lie under the railway tracks for decades, exposed to wind and rain, and remain motionless.
This process of transformation is called "oil immersion" in the jargon.
The newly cut pine wood needs to be dried for a while to evaporate the moisture in the wood. At this moment, the sleepers are called "plain pillows", with a simple appearance but already prepared inside - the spaces that were originally occupied by moisture are now empty and waiting to be filled.
Next is the crucial step.
The plain pillow is pushed into a huge steel tank and sealed. First, evacuate, then inject anti-corrosion oil, combined with high temperature and high pressure, allowing the oil to drill in an non-negotiable manner. After this process, the penetration depth of oil can reach over 13 millimeters. What is this concept? It is equivalent to every fiber of the wood being soaked in oil within a depth of over one centimeter from the surface of the sleeper. It is no longer a layer of oil brushed on the surface of the wood, but the oil and wood have grown together, becoming another material.
I have seen sleepers that have just come out of the can, covered in oil and black, with heavy hands. That strong smell is unforgettable after smelling it once.
What's the point of tinkering with it like this?
The railway looks tough, but it actually moves every day. When the train starts running, the tracks are impacted, and the sleepers are the cushioning layer. Wood has natural elasticity, which can dissipate vibrations, making the car run steadily and reducing the disturbance of the underlying roadbed. Replacing with cement sleepers, although more durable, has too much rigidity and requires much higher requirements for the roadbed. So to this day, many critical road sections still use wooden sleepers.
The soft ribs of wood are afraid of corrosion. If it were ordinary wood, once the railway track cracked, rainwater would seep in, and insects would gnaw on it again, it would scatter in a few years. But the sleepers soaked in oil are different. Even if the surface cracks, the layer inside is still soaked in oil - insects don't want to touch it, fungi can't survive. It's like wearing a thick layer of armor on itself, and it's the kind that grows inside the flesh.
As an old saying goes, this is called 'combining strength and softness'.
The hard part is that it can withstand the repeated crushing of a hundred ton train, and the soft part is that it always maintains the elasticity of wood. The railway tracks pressed up, causing it to sink slightly and release that strong force; The pressure passed, and it slowly bounced back, day after day.
Interestingly, from the outside, this thing looks dark and greasy, and cannot be washed off with just one hand. Every old railway worker knows this smell. But it is these inconspicuous woods that carry tens of trillions of tons of goods and billions of people year after year, from south to north, from east to west.
I think this may be the charm of industry. Transform an ordinary pine tree into something else. Inject its soul into it, and then let it carry the weight that belongs to it.
Decades later, they will age and be replaced. But before that, they will carry countless people and arrive safely at the place they want to go.
