Wear of grinding rotors with thermally-sprayed coatings in a high-speed mill

Abstract

In this paper, the erosion behavior of three types of protective thermally-sprayed coatings and non-coated substrate steel was investigated under semi-industrial test conditions using a laboratory high-speed pin mill DESI-11. The grinding in the mill was performed by two counter rotors, on which protective coatings were deposited either by atmospheric plasma spraying (APS) (Cr3C2-NiCr and NiCrBSi coatings) or by high velocity oxy-fuel (HVOF) process (WC-CoCr coating). The grinding rotors with deposited coatings were used for milling of the Portland cement, and rotors' weight loss was monitored after milling of 1, 3, 5, 10, and 15 kg of this material. The lowest weight loss in the mixed impact erosion conditions was exhibited by WC-CoCr coating, which was followed by Cr3C2-NiCr and NiCrBSi coatings. The greatest material removal on the anterior and the right lateral faces of rotor pins was a result of erosion damage at high impact angles through surface fatigue wear and the following failure of protective coatings down to the substrate. In contrast, the top and the left lateral faces of the pins were subjected mostly to the ploughing and microcutting at oblique impact angles that resulted in significant erosive damage only if hardness of the pin was lower than that of the Portland cement (Cr3C2-NiCrcoated and non-coated steel pins). The study also found a significant disproportion between the volumetric wear losses of various rows of pins of grinding rotors. The central part of the grinding tool consisting of two counter rotors (both rows of 2-row rotor and a middle row of 3-row rotor) suffered more intensive erosion wear than the external part (outer rows of 3-row rotor). The design of the mill and the resulting variability in parameters of milled powder particles at different sites of the grinding tool (such as particle size, particle flux and particle velocity) were considered as main reasons of this phenomena.In this paper, the erosion behavior of three types of protective thermally-sprayed coatings and non-coated substrate steel was investigated under semi-industrial test conditions using a laboratory high-speed pin mill DESI-11. The grinding in the mill was performed by two counter rotors, on which protective coatings were deposited either by atmospheric plasma spraying (APS) (Cr3C2-NiCr and NiCrBSi coatings) or by high velocity oxy-fuel (HVOF) process (WC-CoCr coating). The grinding rotors with deposited coatings were used for milling of the Portland cement, and rotors' weight loss was monitored after milling of 1, 3, 5, 10, and 15 kg of this material. The lowest weight loss in the mixed impact erosion conditions was exhibited by WC-CoCr coating, which was followed by Cr3C2-NiCr and NiCrBSi coatings. The greatest material removal on the anterior and the right lateral faces of rotor pins was a result of erosion damage at high impact angles through surface fatigue wear and the following failure of protective coatings down to the substrate. In contrast, the top and the left lateral faces of the pins were subjected mostly to the ploughing and microcutting at oblique impact angles that resulted in significant erosive damage only if hardness of the pin was lower than that of the Portland cement (Cr3C2-NiCrcoated and non-coated steel pins). The study also found a significant disproportion between the volumetric wear losses of various rows of pins of grinding rotors. The central part of the grinding tool consisting of two counter rotors (both rows of 2-row rotor and a middle row of 3-row rotor) suffered more intensive erosion wear than the external part (outer rows of 3-row rotor). The design of the mill and the resulting variability in parameters of milled powder particles at different sites of the grinding tool (such as particle size, particle flux and particle velocity) were considered as main reasons of this phenomena.