Application Of Waterjet
Most of the main engines used by low-pressure water jets are centrifugal pumps, which have a relatively large flow rate. In addition to common firefighting, fountains, sprinkler irrigation and other uses, here is a focus on new uses.
Water jet has also been used in the field of fire protection for a long time. For example, water mist extinguishing is a new method. In fact, it replaces the high-flow water column with water mist, that is, a 10MPa high-pressure pump is used to generate a water mist column with a diameter of less than 0.1mm through the injection system. The evaporation of fine water droplets plays a role in rapid cooling. Generally, the volume of water droplets during the evaporation process Expanded by 1600 times to isolate the oxygen at the burning object to reach the fire extinguishing moon. In fact, water mist extinguishing is particularly suitable for fires in live areas, and it is difficult to use continuous water jets for such fires. At the same time, high-pressure and small-flow water mist fire extinguishing saves nearly 90% of water compared with commonly used faucet fire extinguishing.
There is also the impact of a large flow of water jets on the soil. An example is during the 1973 Egypt-Israel war, the Israeli side crossed the canal within 24 hours to build several bridges, and then piled up on part of the Barev line of defense. Giant sand barriers, they tried to block the Egyptian tank troops for 48h. If it is said that this solid sand wall is to be destroyed and the tank can move past, it is required to remove about 55m3 of yellow sand based on the frontal gap width of 6.8m. It takes about 60 such positions to pass the tank troops on the east embankment. If a bulldozer is used, it takes 10-12 hours. However, the Egyptian side used a high-pressure water jet to open the gap in less than 5 hours, destroying the Barev line of defense. His own army has won success.
High-pressure water jets such as cavitation jets have been widely used in ship descaling and industrial cleaning, which will be discussed in the following chapters. In general, the most widely applicable range of water jets is high-pressure water jets, the pressure range of which is 10-100MPa, and the upper pressure limit has now been extended to 250MPa. In fact, the characteristic of this pressure range is that as the power of the unit increases, it changes from a single unit to a complete set of equipment, from simple operations (such as cleaning) to complex operations (such as mining coal, etc.).
Another application of high-pressure water jet is crushing, which can be used to make grooves in materials. In the past decade, it has been developed to mechanically assist in stripping large amounts of materials. Recently, in almost all cases, research on equipment has focused on designed nozzles, as well as reliable rotating nozzles and rotating joints (they greatly increase the speed of the water jet on the surface of the object). The crushing function is used in airport runway degumming, bridge maintenance, coal seam mining, auxiliary tunneling, road damage, dam pouring and scouring, etc.
There are basically two main forms of ultra-high pressure water jet: the pressure range is 200-400 MPa, with the help of continuous medium flow, the flow rate here is mostly 2-6 L/min; and when the pressure reaches 700 MPa or higher, the device is In the form of a click water cannon. The ultra-high-pressure water cannon device is driven by a large amount of high-pressure compressed gas (nitrogen or air) to provide driving pressure. This is actually before the water cannon is fired, either by ignition or detonation, or by impacting the barrel with propellant, causing its energy to burst suddenly. In fact, due to the rapid wear of the jet barrel, the jet pressure rapidly decays over time, which has affected the popularization of this technology.
Ultra-high-pressure water cutting equipment and technology have been the hot spot in the development of water jet industry in various countries in the past 10 years. It is worth noting that from the papers of previous international water jet conferences, water cutting technology is the dominant content, which actually follows the water cutting equipment With the commercialization of the process, the application of water cutting has penetrated into many industrial fields and has obtained a broad application space. The continuous running jet cutting system of 200-300MPa is more satisfactory than many other cutting tools. It is characterized by non-selectivity of materials, narrow slits (0.3mm), good quality and no damage to the internal organization of the material, and it can cut two-dimensional and three-dimensional special shapes.
The flow rate of the water jet at a pressure of 70MPa is about 300m/s. In fact, when the pressure reaches ultra-high pressure, the flow rate is expected to reach 1000m/s, so that a very high cutting speed can be achieved. Once the water cutting achieves high pressure and small flow operation, it means that the force on the worktable is very small, which makes it easy to install the cutting nozzle on the robot arm and achieve high precision of three-dimensional complex shapes under computer control Cutting.
Water cutting is extremely important for the non-selectivity of materials, which means that it can cut both rigid metal sheets and flexible cloth paper. People have also used oil as a tool to cut soft candy.
However, the application of pure water jet cutting is limited by pressure. Blindly increasing the pressure means that the reliability of the equipment is difficult to guarantee and is not easy to achieve, so there is a 20-year history of development of abrasive water jets. It is worth noting that the jet pressure of more than 200MPa is used to guide the abrasive, which can be used in the cutting field when the target distance is short. This actually reduces the jet pressure significantly and makes the technology reliable to enter the commercial creation. good conditions.