Why water can also “cut iron like mud”?

Water is a liquid, has no fixed shape. People often use the phrase “soft affection like water” to visualize the degree of tenderness. But scientists have made the water hard like a “knife,” which is used not only for excavating soil, mining but also for cutting steel sheets.

It was discovered that in the first few milliseconds, when high-pressure water sprayed on the surface of an object, its instantaneous pressure was enormous. Humans have taken advantage of that characteristic of high-pressure water used in coal mining. When a high-pressure pump puts water pressure up to several hundred megapascals (MPa), it can erode the coal layer for coal to fall. Using a pump, bring the water along with the eroded coal up to the surface. This method is called coal mining by water pressure.
Using water to cut steel sheets is a far more complicated issue than coal mining. Because of the limited strength of thin steel sheet can withstand a pressure of about 700 MPa. When the pressure is brought up to such pressure, the good sealing device is very easy to be broken and cause leakage. To solve the sealing problem, the scientists put in water 5% of the soluble cutting oil. This has both a lubricating effect and enhanced sealing performance. Simultaneously, special treatment is applied for the high-pressure sealing pump, pouring the oil solution into the two-layer sealing ring, taking advantage of the oil solution’s adhesive properties to become very large under high pressure, ensuring seal of a high-pressure water pump.

Secondly, the country has no fixed form. Therefore, after the water comes out of the pipe, it will immediately disperse. Once the water column is dispersed, not only can the water pressure be lowered, but it cannot be cut properly. So the scientists arranged to put in water a few long-chain polymers of polyvinyl oxide. The water molecule that clings to this material causes the water from the nozzle to stick together like a long thread; it doesn’t disperse and maintains a strong pressure over a very long distance.
The third problem is the high water pressure, the intensity of the nozzle’s intensity is high compared to the nozzle, and the diameter of the nozzle must be small so that the water spray can hit the target properly. The body is not wrong. High-pressure water jet nozzles are currently made of high-grade hard alloys, jade, diamonds, etc. The nozzle diameter is only 0.05 mm. Moreover, the spray hole’s inner wall is smooth and smooth, able to withstand water pressure up to 1700 MPa (17,000 atm).

Using water as a “knife” has many advantages. Its use is very wide; steel plate, copper plate, glass, plastic, etc., can use “water knife” to process. Next is the smooth section of the material, without the roughness of the sawed material or the laser and acetylene, causing the cut’s temperature to rise but deform. When cutting some fused materials, it will not emit toxic gases or generate dust, will not even wet the material because the speed of water penetration is extremely fast.

Currently, some countries have put high-pressure water cutting technology into practical use. According to the progress of science and technology, the application of “water knife” will become more and more widespread. Such as using a “water knife” to remove the ceramic paint on components, using a water knife to punch and smash the material, scrub the object on the surface of the hull and propeller, and can even be used for surgery.