Indirect utilization of liquid nitrogen cooling
By：adminauthor：admin Date:2020-03-20 15:14 View：
We take advantage of the low temperature brittleness of some steel materials to perform liquid nitrogen low temperature cutting and grinding processing, which can improve its cutting processability and improve processing quality. The direct application of liquid nitrogen as a cutting fluid can significantly reduce the cutting temperature, improve the machining accuracy and surface quality, and prolong the service life of the tool (grinding wheel). .
The indirect use of liquid nitrogen cooling is mainly the tool cooling method, that is, the tool is continuously cooled during processing, so that the cutting heat is quickly taken away from the tool, especially the tool tip, and the tool tip is always kept at low temperature. Scholars at the University of Lincoln in the United States used a CBN (PCBN) tool with a new cooling system produced by Sandvik for experimental research. This tool stores liquid nitrogen in a square box on the top of a turning tool. It is imported and imported from Outflow.
Tests show that when liquid nitrogen is cooled, the cutting life of the turning tool is increased by 10 times, the wear is reduced by 1/4, and a smaller surface roughness can be obtained.
Another special indirect utilization method is jet cooling. Some Japanese scholars have developed a jet cooling system. The cooling gas used in the system is cooled by liquid nitrogen in a heat exchanger, and its temperature is lower than -50 ° C. The cooling gas is sprayed directly onto the grinding point. The experiment found that the residual compressive stress of the workpiece material after grinding was larger than that with grinding fluid, and the distribution area of the residual compressive stress became wider. The residual compressive stress can improve the fatigue life of parts, which is very important for some parts, such as aircraft parts. CBN wheels treated with solid lubricants, or a very small amount (10 l / h) of super-refined vegetable oil added during processing, can play a better lubrication role in processing.
The use of liquid nitrogen to cool low-temperature (ultra-low temperature) processing solves some difficult-to-machine problems of difficult-to-process metal materials, non-metal materials, and composite materials. When using liquid nitrogen cooling and cutting, some lubricants need to be used to solve the problem of poor lubricity during chip formation. At the same time, the newly formed metal surface on the workpiece has strong chemical activity and will rust quickly when exposed to air. Therefore, it is necessary to use some rust inhibitors to prevent the workpieces and machine tools from rusting.
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