IMPROVING THE TECHNOLOGY OF ELECTRO-SPARK ALLOYING THE COMPONENT PARTS FOR THE PUMPS OF NUCLEAR POWER PLANTS

Abstract

The paper deals with the technical challenge of seizing and sticking the tool electrode (TE) (anode) to the surface of the part (cathode) being alloyed. This is especially evident when it is necessary to carry out the electrospark alloying (ESA) process referring the parts made of corrosion-resistant stainless steels, which are mostly used in the pumps at nuclear power plants (NPP). The issue becomes more urgent while alloying under the so-called “coarse” ESA modes when the discharge energy (Wр) increases. To conduct the comparative tests, at the Елітрон 52А (Elytron 52A) model electrospark alloying unit, three (3) batches of 15x15x8 mm steel 12Х18Н10Т (12Kh18N10T) samples were processed. The rods of Ø3 mm and L = 30 mm made of steel 12Х18Н10Т (12Kh18N10T) and nickel were used as the TE. For the first batch, the samples were not pre-treated. For the second batch, the samples were pre-treated with a graphite TE, and for the third one, the surface to be alloyed was rubbed with molybdenum disulfide powder. The result of the research has become an improved ESA technology for processing the corrosion-resistant steels, which are used to manufacture the NPP equipment parts. According to this technology, molybdenum disulfide powder is applied by rubbing (smearing) to the surface to be alloyed. This dramatically improves the alloying process due to elimination of seizing (sticking) of the electrodes. In this case, at any values of the discharge energy while the ESA process, there is no seizing (sticking) events as for the anode and cathode electrodes. When comparing different processes by the ESA method of steel 12Х18Н10Т (12Kh18N10T) with the use of the TE made of steel 12Х18Н10Т (12Kh18N10T), it has been found that at the ESA method without pre-treatment of the surface of the sample, in comparison with the process including the pre-treatment of the surface with graphite and molybdenum disulfide, at the same values of discharge energy, respectively, the productivity is 35 and 44 times less, respectively, the roughness is 1.7 and 2.0 times more, and respectively, the continuity is 1.3 and 1.5 times less. When comparing different ESA methods for processing steel 12Х18Н10Т (12Kh18N10T) by the TE made of nickel, it has been stated that at the ESA process without pre-treatment of the sample surfaces, in comparison with pre-treatment of the above surfaces with graphite and molybdenum disulfide, at the same values of the discharge energy, the productivity is 177 and 197 times less, respectively, the roughness is 2.1 and 2.5 times more, respectively, and the continuity is 1.9 and 2.1 times less, respectively.