Robust joints mean longer service life

Louise Smyth

Safety in mining and at construction sites where explosives are used was a problem for a long time, because the storage and transport of ‘volatile’ explosives always constitute an enormous risk. To reduce the danger and achieve a better explosive performance, there has for some time been greater use of pumpable emulsion explosives.

Since the year 2000, a global explosives manufacturer had been using a progressing cavity pump to fill storage silos with the ready-to-use NH4NO3 emulsion. However, the pump did not provide the required level of performance and delayed the supplying of the mines and customers due to regular breakdowns. The pin joint could not withstand the torque nor the deflection on the coupling rod and therefore often failed. The shortness of the coupling rod also increased the angle for which the joint had to compensate. That not only increased the stress on the joint itself, but also the dynamic load on its seal system. The lubricating effect of the lubricant used for the pin joint was not sufficient either.

Since the pump had a crucial role to play in the process chain and every breakdown led to increased cost and delivery delays, the emulsion manufacturer searched for a more reliable pump with a larger capacity and found Netzsch. The company’s mining specialists proposed a Nemo progressing cavity pump for the job. Due to the special displacement principle allowing smooth conveyance with little shearing effect and pulsation, this type of pump is particularly well suited to this application. The consistency and viscosity of the medium are insignificant here in terms of the product flow. It is therefore ideally suited for ammonium nitrate emulsion, which has a temperature of 50°C and a viscosity of 18,000-22,000 mPa-s.

More reliability through V-joint
Instead of being fitted with the standard version – the B-Universal model – the progressing cavity pump was also fitted with the Nemo V-pin joint. To achieve a long service life, it is filled with oil and also encapsulated using the Nemo SM sealing collar. To increase the service life of the pin joint even in the toughest operating conditions, it also has hardened bushes, in contrast to the B-model. These are pressed into the boreholes of the coupling rod and the rotor head or drive shaft head and can be easily replaced during maintenance work. Because the NH4NO3 manufacturer had problems with the previous pump involving the coupling rod joints, it wanted to have the option of also being able to replace the wear bushings when there is major stress or high maintenance intensity. However, this turned out not to be necessary. The pump proved to be extremely reliable.

Tyron Adam is with Netzsch.


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