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Grinding Technology

There is no alternative to testing when it comes to grinding new products

| Author / Editor: Notker Kling* / Manja Wühr

During test series one and two and the subsequent tests on the Coniwitt-150, the team needed to dig deep into their box of tricks to achieve anything close to the expected results. The tests with a rasp with 1 mm openings led to unsatisfactory results, both at a speed of 800 rpm and at a speed of 2,000 rpm. While 10.8 kg of the 12 kg of product in total were indeed ground in three minutes and 50 seconds at 2,000 rpm, the temperature rose to 34 °C. For test series three to seven, the rotor arm was replaced, first by a rasp, and then by a special sieve with 0.5 mm openings. The results were similar to the first test series, except that the temperature only rose to 28 °C at lower speeds. During each round, the product was too hard to pass through the sieve openings and ultimately heated up to 38 °C at higher speeds, which was to be avoided. Conclusion: Further tests were required.

Next, it was the turn of the Oscillowitt-3: During the eighth test, a sieve with 0.71 mm openings and a circumferential speed of 1 m/s were used. For the ninth test, the Oscillowitt was switched from rotating to oscillating, and product was ground. Both tests revealed similar results: From a 5 kg batch, 2.9 kg of ground product passed through the sieve during the oscillating movement, but led to blockages due to the lower speeds.

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Somehow, there was a hope that better results would be achieved with the Coniwitt-150, despite the insufficient outcomes. Test number 10 on the Coniwitt-150 with a different rotor arm and smaller sieve openings led to 2.4 kg of ground product out of a 5 kg batch passing through the sieve in two minutes and 20 seconds, which was also unsatisfactory.

Last but not least was the Hammerwitt-3, which was used for tests twelve and 13. At a speed of 3,500 rpm, during the first round 5 kg of product passed through the Conidur sieve in four minutes and 25 seconds. The product temperature did not exceed 29 °C during this process. During the second round, 25 kg passed through the same sieve at a throughput of 64 kg/h and a product temperature of less than 29 °C, so the goal was achieved! The throughput, the temperature and, therefore, also the product properties were fully in line with the customer’s specifications.

The final hurdle

During the tests, the Hammerwitt-3 was fed with a 5 kg batch first of all, and then a 25 kg batch. But on the customer’s premises, the mill was supposed to be able to grind continuously, a requirement which was met using the Profi-Valve 80 dosing system, a frequency converter and a PLC. The system, equipped with retractable WIP nozzles, is easy to rinse once the grinding process is complete, and therefore quickly equipped for the next run.

Conclusion: The same number of product tests do not need to be performed for each product. However, if the product properties so require, it is certainly beneficial to know that the team at Frewitt will always be ready to lend an ear along with their wide range of mills and test lab fitted out with the latest equipment.

* The Author is Sales Manager Germany at Frewitt, Granges-Paccot/Switzerland.

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