Reliable sludge removal for water jet cutting

Jon Lawson

A compelling case study that showcases how a robust rotary lobe pump can even pump highly abrasive residual water without any damage 

Cutting systems, which are based on high-pressure water jets and do not alter the material structure through their energy input like lasers do, are establishing themselves in more and more areas, such as robotics or automotive manufacturing.

A cutting aid, an abrasive, is mixed into the water to increase cutting performance. This abrasive is frequently a fine garnet sand.

After the cutting process, the water-sand mixture has to be separated again, so  that the sand can be disposed of.

The manufacturer of Waricut water jet cutting systems, H.G. Ridder, offers an automated solution for its systems to remove and separate the sludge from the water.

Because conventional pumps wear very quickly due to the abrasive medium, the company is using the particularly robust Tornado T2 rotary lobe pumps from Netzsch. Their condition is almost as good as new, even after double the operating time in comparison to the previous pumps.

Although the sand may be very useful as a cutting aid, it does lead to effort in terms of disposal. To relieve the burden on their customers in this area, the manufacturer offer an automatic removal system for its machines: the water-sand mixture is transported by pump to a cyclone that separates the solids from the water using centrifugal force and thus makes disposal easier.

Reversal of materials reduces wear

To find an efficient and cost-effective solution, the manufacturer has therefore been testing the Tornado T2 rotary lobe pump since the end of 2014. A characteristic feature of this type of pump is its combination of materials. Whereas other pump manufacturers normally have elastomer lobes rotating in a metal housing, steel rotary lobes are used here and the inside of the pump is lined with a rubber insert.

For its tests, the water jet cutting expert used the T2, a version of the Tornado that has a pumping capacity of 35m3/h. The final evaluation of the test pump was carried out after the device had circulated a total of 90t of the sandy abrasive. It was not possible to detect any wear in the pump chamber, in spite of the long operating time.

The insert and the mechanical seal were still in perfect condition. The shaft sealings, including contact pressure and lubrication, also showed no damage or impairments.

Only the rotary lobes showed slight traces of wear at the tips. The clearances still conformed to the dimensions at the time of delivery.

Overall, the loss of pumping capacity due to these signs of wear was so small that it was possible to compensate for this without any problem by slightly increasing the speed.

The rotary lobe pump continues to be used effectively, despite already having double the service life.

For even greater improvement of service lives, Netzsch technical experts have further optimised various aspects of their Tornado pumps for standard use in water jet cutting systems and tailored them to the specific application conditions.

The customers can in future fully concentrate on the demanding cutting process, with the removal of residual water and sludge taking care of itself.

Michael Groth is business field manager Environmental & Energy at Netzsch.  

Initial practical endurance tests have shown that the T2 is still almost as good as new, even after double the operating time of the centrifugal pumps used previously 

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