Rotary Lobe Pump Meets the Challenge of Abrasive Bonding Primer

Contributed by: PumpScout Staff

One of the products which the building materials manufacturer, Knauf of Iphofen, Germany produces is a concrete primer. What is intended to ensure that plaster evenly bonds onto smooth walls in construction does however create problems during con-veyance: the plaster primer contains dispersion and has a mineral solid content of around 60 percent, which has an emery paper effect in the rotary lobe pump feeding the filling station.

The newly developed TORNADO® T2 of NETZSCH Pumpen & Systeme GmbH from Waldkraiburg has been in use since April 2012 – and very successfully.

The concrete primer is filled from a storage tank using frequency control and a rotary lobe pump that fills various large barrels. The operating mode is intermittent; the pump is started up and shut down for each filling process – 5 seconds of stationary follows 20 seconds of opera-tion. The speed of the pump is raised as the wear increases.

The conventional rotary lobe pump previously been used by Knauf was able to convey approx-imately 600 tons of highly abrasive plaster primer containing dispersion before the rotary lobes and wear plates were so badly affected that the required capacity was no longer achieved.

The high annual production capacity on the mixing system resulted in a considerable mainte-nance effort. "At busy times we were repairing the pump every 3 to 4 weeks," reports Mainte-nance Manager, Armin Ryba. Rotary lobes and wear plates had to be replaced at every repair and at every second repair the shaft seal was changed. Clearly this was a reason to search for an alternative which was provided by NETZSCH, the pump manufacturer from Waldkraiburg in Upper Bavaria.

Engineered for challenges of this kind, the entire materials concept of conventional rotary lobe pumps was reversed when the TORNADO® was redesigned: two lobes made of hardened steel that rotate in a geometrically adapted elastomer insert are used instead of the standard elastomer lobes. This bi-lobe rotor design creates a considerably longer sealing line to the housing providing more wear padding. A specially developed pulsation reduction system en-sures that the most minimal pulsation or shear forces are generated, despite this straight, bi-lobe rotor design. Elastomer inserts are vulcanized onto the edges of the lobes to create a permanent hard-soft contact between the lobes throughout the 360° rotation cycle. This avoids high-wear contact between elastomer parts. The elastomer insert acts as a stator and is subject to considerably less dynamic load and deformation than in the traditional rotary lobe pump design when the elastomer functioned as a rotor. Ultimately, energy is saved; wear is reduced and the service life of the pump is increased overall.

Additionally, the drive of this new pump design was radically modified. The complex timing gear was replaced by a robust synchronized gear with belt drive. This means that not only is the danger of transmission damage greatly reduced, but the weight and installation space required are decreased. The drive requires no lubrication, eliminating the chance oil leaks. Typical re-pairs or maintenance are simplified because the conveying and gear chambers can easily be opened. The cover and attachment of the components are designed for easy access and every component can be replaced with standard, commercial tools in just minutes.

The first inspection of the TORNADO® T2 at Knauf has already demonstrated the value of these features after double the capacity had been conveyed: cover and elastomer inserts could be easily disassembled and the conveying elements could be easily disassembled and re-moved.

In comparison to the conventional rotary lobe pump previously used, there was evidence of significantly less wear, even after double the service life. The cover and housing inserts were practically good as new. They showed only minor leaching and were definitely still usable. The lobes showed consistent material removal with grooves in the front end however, the lobe in-serts on the edges were hardly worn. The inspection of the belt drive was also impressive. There was no wear to note on the double-toothed belt nor on the belt pulley. The belt tension had only reduced slightly and not in any critical way with respect to the condition on delivery – in spite of demanding, non-continuous operation with around 60,000 load changes since commis-sioning.

At the time of the first inspection, the new Tornado T2 pump had already delivered double the volume of the previously used, conventional rotary lobe pump with only 60% of the maximum speed having been reached. "So we still have a lot more potential," said Dirk Schmalz of NETZSCH. "Based on the operating time so far, the T2 can certainly achieve three times the ser-vice life."

This supposition has now been confirmed after six months' operation: with 3-4 times the con-veyance there has been more than three times the service life.

There is a high level of satisfaction with the investment in the new rotary lobe pump at Knauf Iphofen. Maintenance Manager, Armin Ryba comments that they are very satisfied with the new purchase: "The long service life means that we now only incur around half the previous costs for spare parts, repairs and downtimes."

About NETZSCH

For 60 years, NETZSCH Pumpen & Systeme GmbH has served markets worldwide with its NEMO® progressing cavity pumps, TORNADO® rotary lobe pumps, grinding machines, dosing systems and accessories, providing customised, sophisticated solutions for applications in every type of industry. With a workforce of more than 1,600, "Pumps & Systems" is the largest business unit with the highest turnover in the NETZSCH Group, alongside "Analyzing & Test-ing" and "Grinding & Dispersing".

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