Hosokawa's proposal was to refit the two mixers, used in this process since the 1980s, with new rotating screws. Alternative tests carried out in the supplier's test centre included dual screws and increased rotor speeds, but these proved less effective.
Finally, Hosokawa made the following recommendations:
- Increasing the rotorspeed by adjusting the transmission ratios
- Replacing the mixing screw by a re-engineered one
- Placing a ball head bearing at the bottom of the mixer
This, in order to reduce mixing time by half. The new screw was engineered using Duplex stainless steel as explicitly requested by John Bervaes (see sidebar). "I'm a big fan of Duplex," comments Bervaes. "The old screws were made of Duplex and were indestructible. The new screws are also made of Duplex but have been engineered differently, using a bigger outside and a smaller inside diameter, the pitch was also altered."
The mixing vessel was still in very good condition and did not need any modifications except for an extra opening in the wall of the vessel for a new automatic product sampler. According to Jos Greven from Hosokawa, Nauta mixers are often modified and adjusted to suit their applications: "The vessel lasts a very long time but the ingredients tend to change over the years. Modifications can improve performance considerably as we can seen in this case."
Jongeneel is pleased with the results: "Mixing time has been reduced on both mixers from 30 minutes down to 12, which is a significant achievement indeed. In our calculations, we have adopted a 15-minute mixing time. Yet the reduction we have actually achieved is more than our initial goal of 50%. We have doubled our output and exceeded all of our original expectations." "Moreover," Jongeneel continues, "we have simplified the sampling process and extended the bearing's lifecycle from one year to four using the new bearing temperature monitoring system."
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