PSI - Issue 20

Nickolay Ovchinnikov / Procedia Structural Integrity 20 (2019) 113–118 Nickolay Ovchinnikov/ StructuralIntegrity Procedia 00 (2019) 000 – 000

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It should be noted that vibrodiagnostics is the most common way in the world to assess the technical condition of various electromechanical equipment, including pumping, what is stated by Fabian and Čačko (2013), Janicki et. al. (2014) and Yan et. al. (2015). The low correlation between the values of υ and Δ (see Fig. 2, a, b) probably due to the lack of noise immunity and frequent malfunctions of vibration sensors, which is confirmed by the results of vibration tests of the investigated pumps by highly qualified specialists from Mirny. Another important argument for the inexpediency of using vibration diagnostics to identify the critical axial shift of the pumps studied is the fact that in underground kimberlitic mines of the Company which usually has cause-and effect relationships with the vibration state of the bearing units, hydraulic values over time can change abruptly in one direction or another, which does not allow to reliably judge the technical condition of pumping equipment. It was found that the rotor axial shift is definitely correlated with the temperature (t) of the rear bearing assembly (Fig. 3, a), but not of the front (Fig. 3, b). In addition, Fig. 3, a it is clearly seen that in 6 out of 7 cases of reaching a temperature of 60 ÷ 63 º C by the rear bearing assembly, the pumps studied were just working at a critical axial shift of the rotor. It should be noted that the bearing units of the investigated pumps are equipped with a water cooling system, which distinguishes them from other sectional pumps operating in the underground kimberlitic mines of the Company. Full-scale tests conducted on one of the investigated pumps showed that under the same operating conditions, the temperature of bearing assemblies equipped with a water cooling system is on average 5 ÷ 7 º C lower than the value of t bearing assemblies not equipped with the cooling system. Thus, it can be assumed that the value t of the rear bearing unit of the sectional pump operating in the underground kimberlitic mines of the Company, in which the occurrence of a critical axial shift of the rotor is characteristic, lies in the range of 60 ÷ 70 º C, depending on the technical equipment of its design. It should be kept in mind, that the increase in the value of t to the above range of temperatures can be caused not only by the axial displacement of the rotor, but also by the ingress of shaft water from the flow part of the pump into the rear bearing assembly, contact with which leads to a deterioration of the lubricating properties of the oil, and according to this it leads to some heating of the assembly. In this case, when the rear bearing unit reaches a temperature t equal to 60 ÷ 70 ºC, it is also n ecessary to be guided by other accompanying signs of the sectional pump operation at a critical axial displacement of the rotor. Such accompanying signs can be an increasing of the water temperature in the discharge pipe over 20 ºC, which is noted by Link-Product LLC, the main supplier of pumping equipment for the Company's mines, as well as a critical decrease or increase in the flow of water (q) in the discharge pipe (production data).

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b

Fig. 3. (a) Linear dependences of the axial shift of the rotor on the temperature of the rear (a) and front (b) bearing unit of the pump and their approximation by a linear trend