New requirements for cutting tools in turbine blade machining
December 18, 2022
At present, the domestic steam turbine industry is generally faced with a large increase in orders and a serious shortage of production capacity. The production and processing efficiency needs to be continuously improved, and the large-scale application of high-efficiency tools undoubtedly provides a solution. Shanghai Turbine Co., Ltd. is also increasing the investment and promotion of high-efficiency tools. At the same time, it is actively developing some highly technical tools to meet the needs of gas turbine, ultra-supercritical and nuclear power equipment processing.
Difficult to process materials
At present, in order to reduce the heat consumption of the generator set, the steam pressure and temperature of the steam turbine are getting higher and higher. For example, the steam pressure of the million-class ultra-supercritical unit is up to 26 MPa, the temperature is increased to 600 ° C; the initial temperature of the F-class gas turbine is 1300 ° C, thus The requirements for part materials are also higher. Because high temperature alloys have excellent high temperature strength, thermal stability and special resistance to thermal fatigue. Therefore, it is more and more widely used in steam turbines and gas turbines, so that there are many problems in cutting by the original tools.
The high and medium pressure blade of 600MW supercritical unit is a kind of new material containing niobium (Nb). It is difficult to process. The iron scraps processed by the original tool are red color and the temperature is very high (previously processed iron without niobium material) The swarf is light blue, and the blade wears very badly. Originally a tool can complete the processing of one blade, now it needs to replace 4 blades. In this way, not only the processing cost is high, but also the production efficiency is difficult to improve. It is urgent to update the tool materials. We have been looking for a number of tool suppliers to try out the system, and finally chose the indexable inserts of the new material that Iskar repressed. . In addition, the material of the valve stem of the 600MW supercritical unit has also been updated. Now the GH901 high-temperature nickel-based alloy material is used. Deep hole processing also faces many difficulties. The deep hole gun drill of Sandvik Coromant is selected.
Shanghai Steam Turbine Co., Ltd. imported the American ring-tooth milling cutter as early as 1997. At present, there are also tool suppliers in China, but it is impossible to realize the spiral groove and the front angle. We are currently using a zero degree rake angle. The cutting performance is poor and the processing efficiency is low. Recently, our company used the newly purchased German SAACKE machine to manufacture a ring-shaped milling cutter with a helix angle and a front angle, which can improve the processing efficiency by 2~3 times.
High precision requirements
The production and processing problems of steam turbines are not only reflected in the high-temperature and difficult-to-cut materials. With the continuous improvement of user requirements, the accuracy level of the products has been increased again and again, and the accuracy requirements must be managed in production.
In the gas turbine project of the National 863 Program undertaken by our company, the precision of the roulette processing is very high. The material is GH2674 iron-based superalloy. At present, the turning of the roulette is basically realized by the tools of Walter and Iskar. However, the precision of wheel milling is even higher, and the machining is more difficult. The pitch tolerance is ±4μm, which is difficult for domestic tool suppliers to guarantee. We are preparing to import from ALDEN. In addition, the company has also developed its own SAACKE machine tool and Zaller measuring instrument, and the current self-made wheel groove milling cutter can achieve a pitch tolerance of 1~5μm.
Of course, in general, the accuracy guarantee depends mainly on the equipment, but in the turbine processing, especially the wheel groove of the rotor is finally realized by the cutter. Turbine processing is not like mass production in the automotive industry. It is a single-piece small batch. The various precision requirements may be different. For new requirements, it can only be tested and tried. If the supply cycle is tight, only the existing tools can be used. If you have time, you can make full use of various channels, including seeking suppliers and independent research and development.
