It is therefore an object of the invention to provide a centrifugal pump. Bellows Seal ValvesIt is another object to provide a centrifugal pump having locally improved wear resistance. Another object is the provision of a pump and pump components which are locally and specifically improved in erosion wear resistance, particularly in the areas of the cutwater, the impeller, the wear rings and the volute, with a view to longer, more reliable pump operation. Balance ValvesThese and other objects of the invention to become apparent hereinafter are realized in a centrifugal pump adapted for pumping finely particulate slurries, comprising a steel housing having an inlet and an outlet and a volute therebetween, a motor mounted on the housing, and an impeller rotatably driven within the volute by the motor for pumping fluid through the housing along a flow path extending through the volute and between the inlet and outlet, the pump having surfaces conditioned against erosive wear along the flow path comprising iron carbide and iron boride formed in situ locally at pump steel surfaces subject to erosive wear.

In particular embodiments of the invention, the pump impeller is locally surface conditioned with iron carbide and iron boride; the volute includes a cutwater, and the cutwater is locally surface conditioned with the iron carbide and iron boride; the impeller is mounted in the housing with steel wear rings, and the wear rings are locally surface conditioned with the iron carbide and iron boride; and the steel housing comprises carbon steel or iron base stainless steel.

In further embodiments of the invention, there is provided the mentioned centrifugal pump in which the housing surfaces are coated with an erosion resistant coating comprising an inner layer of iron carbide and an outer layer of iron boride, and particularly wherein the outer layer of iron boride is iron carbide containing. REDUCING VALVESWhere carbonitriding is used in advance of the boronizing step, iron nitrides are also formed in the conditioned surface, along with the iron borides and iron carbides. In accordance with the invention, the pump coating is from 0.4 to 0.8 millimeter in depth, overall, and the outer layer of iron boride is from 0.5 to 0.06 millimeter in depth. Preferably, in the centrifugal pump according to the invention, the coating is formed by first diffusing carbon locally into the pump surfaces to be conditioned then after the carbon diffusion, diffusing boron from a diffusion pack at elevated temperatures and in the absence of oxygen, and thereafter quenching, to define an iron cabide layer outwardly relatively rich in iron boride as the coating.

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2011-12-13

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