What are the Different Types of Rotor Materials?

December 7, 2017

Try and name some different rotor material types. There are the perfectly balanced metals that resist the effects of thermal expansion, plus the alloyed additives that toughen those metals. We've only just begun, and we're doing so well already. What about progressive cavity pumps? Equipped with solid helical rotors, the materials used here require abrasion-resistance muscle. After all, that tight mechanical seal exacts a cost, isn't that true?

When Pump Actions Exact a Cost

Abrasion is the culprit we're referring to at the moment, although the characteristics of the system-assigned fluid also impact rotor functionality. In that latter case, the thermal and chemical properties of the viscous material are at fault. A hot stream causes metal fatigue. Then, just to add insult to injury, a caustic chemical further weakens the alloy. Ideally, the corkscrewing rod operating at the heart of the pump is made from a toughened but ever so slightly elastic steel alloy.

Steel-Reinforced Rotors Excel

Three factors control the different rotor types. First of all, we're looking for a machine element that's sourced from a forged facility, one that's made from a hardened or stainless steel. Next on the agenda, that material requires heat treatment toughening. Cooked in a furnace and quenched in water or oil, the surface-hardened steel is polished and free of microcrystalline defects. This is already a formidable rotor candidate, but it's not quite ready to be mounted in its progressive cavity housing just yet.

Only the Finest Coatings

Sure, that stainless steel core is undeniably strong, but it will age as it comes in contact with some of the most challenging fluid streams in any industry. Food acids are an issue, as are the solids suspended in mining aggregate surges. Then there're the effluent rivulets that crush lesser rotors. No, that hardened steel alloy is durable, but it requires something extra. What's required is a special coating, a double-applied layer of nickel or chromium. Then, when the outer casing wears away, the rotor's underlying steel core will remain undamaged. Called back to the manufacturing factory, a new jacket of nickel is applied.

Out on the frontier, progressive cavity pump rotors are appareled in tungsten carbide then sent into the depths of the Earth. Meanwhile, in mines and sanitation stations, food mixing facilities and grain conveyance silos, it's pure hardened steel that functions within the elastomeric seal. Coated in several layers of bonded nickel, the protected rotor is injected with extended life. Incidentally, for those potentially extreme applications, there are tungsten carbide coatings and even word of a ceramic finish.

Contact Alpha Pumps:

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Fax:          (03) 9364 9554
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