A new method of assembling sliding bearings for centrifugal pumps operating in radiation exposure

Abstract

The article solves the problem of choosing construction materials for the formation of intermediate layers, which can be used in the sliding bearing (SB) responsible joints assembly of different types nuclear power plants (NPPs) centrifugal pumps. The following are taken into account as the main conditions: the number and magnitude of cyclic changes in mechanical loads; neutron irradiation and the effect of coolant on corrosion and corrosion-mechanical strength of materials. Analysis of the rotary machines SB assembling methods and the requirements for equipment, operating in radiation conditions allowed to identify reserves for improving of NPP centrifugal pumps SB assembling methods. The solution to the problem is that when assembling the SB, before installing the bearing liners (BL), on the housing and/or BL contact surfaces form a technological coating by electrospark alloying (ESA) with subsequent application to the alloy surface of reinforced metal polymer material (MPM) and its polymeri-zation. Nickel coatings are applied by ESA at a discharge energy Wp<0.13 J and a productivity of 1.0-2.5 cm²/min, and the alloyed surface is covered with MPM, reinforced with Nickel powder up to ~60%. Assembly of the bearing is carried out without waiting for the polymerization of MPM, while the remnants of MPM after compression of the contact surfaces are removed with a napkin. Metallographic and durometric studies have shown that the structure of the technological coating on the SB elements made of corrosion-resistant stainless steel 12Kh18N10T consists of 4 zones. On top is a dark zone with MPM reinforced with Nickel powder, 50-60 μm thick and with a microhardness in the range of 700-1000 MPa. Below is a "white" layer up to 20 μm thick with a microhardness of up to 4800 MPa. Even lower is the transition (diffusion) zone, in which the microhardness gradually decreases and at a depth of about 150-160 μm reaches the microhardness of the base - 1700 MPa. Comparative studies have shown that the use of a new SB assembling method, when the technological coating is applied simultaneously to the upper surface of the ВL and the lower surface - the "bed" of the housing, allows to reduce by 100% the running-in period of the centrifugal pump rotor pins babbit.