Grinding – the Smart Way


Sometimes, situations require us to reinvent the wheel. Taking another perspective, gaining new insights from an external user’s perspective, or getting to the bottom of an issue, can help us to find an original solution with an existing product.

During a kick-off meeting held at a Frewitt customers’ site in Germany, it was being discussed what grinding process the customer would like to use for preparing API products in a closed system. The initial assumption is to always grind product in one mill, and thereafter, the ground product would fill directly into containers or drums. The system would require cleaning using either a WIP or CIP procedure once a batch was completed in order to subsequently change over to a new product. The kick-off meeting by followed by talks and additional  meetings, layouts were developed, new approaches were established and modified until a surprisingly simple solution, albeit very practical, was finally found.

As easy as 1, 2, 3

Two factors have contributed to this solution: safety and time. As mentioned above, it needed to be  possible to completely clean, rinse and dry the system following completion of a batch so that it what thereafter ready for a new product batch,  of course, all in the name of safety.. On the other hand, due to the rapid, prerequisted, product changeover process; the company needed to minimise the time lost during switching without any expense to safety.

It had been concluded beforehand the Frewitt ConiWtt 150 would best meet the customer’s needs. The features of the ConiWitt 150 conical sieve mill, which won the customer over in this situation, included a large selection of sieves, infinitely variable regulation of the rotor speed from 400 – 2400 rpm and a rotor with either a rectangular profile for grinding dry products or a round profile for grinding moist products.

While equipping a mobile system with the ConiWitt-150’s grinding head had certainly led to good grinding results, this solution would have been too slow during the conversion process. By contrast, two identical systems – both featuring a CW150 grinding head with a drive system – proved to be the ideal solution with regard to the time saved during conversion and process safety.  

Two identical grinding systems

A WIP system and the Frewitt drive system were located on a static column, which was fastened to the production room floor by means of a plate. The ConiWitt-150’s grinding head could be docked to the FreDrive, which was mounted on a mobile frame as part of the entire grinding system.

This brought us to the heart of the solution: the grinding system, notably, the mobile part of the plant. The first element of the grinding system consisted of a two-part docking station. The docking process could be carried out either with the mobile vessel by means of the lifting column or using the active valve with automatic feeding. The mandrels for locking the system were used to centrally align the active and passive valves during the docking process. Product was fed contamination-free into the inlet vessel, which featured a sight glass and a level probe to monitor the process and product flow, via the active valve. A magnetic sensor prevented the motor from starting up unintentionally, as long as the feed hopper was not correctly assembled. Downstream of the feed hopper was the CW150 conical sieve mill that the customer required to grind product batches of max. 300 kg on. Dry, or moist powder, as well as or granulates could be disagglomerated or ground using sieves with different mesh sizes here. Under the sieve, two 

probes were installed for measuring the grinding chamber temperature, which would bring the ConiWitt-150 to a stop if and when a specified value were to be exceeded. The outlet hopper was assembled with a protective grating downstream of the ConiWitt-150. A specifically developed device connected the outlet hopper to the feed hopper and ensured balanced pressure throughout the grinding system. This les us to the last element of the mobile grinding system, specifically, the passive valve. Finally, the filling vessel (drum, container, etc.) was docked here to pick up the ground product.

As we have already seen, this mobile grinding system described in detail was ordered in duplicate – and with good reason.

Very carefully considered

The advantage of a twin grinding system was obvious: while one system was in operation, the second could be prepared for a new product with different properties. Inserting the correct sieve and choosing the right rotor (rectangular or round) are just two examples of the factors that would need to be considered. Once the batch in the first system was completed, cleaning was able to take place. To illustrate just how important details could be: once cleaning was complete, the spray nozzles were dried out with air so that water, well-known known to potentially cause product jams, could not get into the product under any circumstances.

Cleaning – the name of the game

Each of the twin systems were equipped with eight cleaning nozzles in total. One spray nozzle each was located in the active valve, the feed hopper, the outlet hopper and the passive valve, and a total of three spray nozzles were located in the conical sieve mill. Cleaning of the grinding system was able to be controlled and checked using a PLC. A mobile operating panel (HMI) was located on the static column. It was important to note here that the PLC not only handled the cleaning of the docking device (active valve and passive valve), but also the opening and closing of the valves.

A high level of flexibility and safety

Vessels (containers, drums) of various shapes and sizes could be connected to the mobile grinding system. A mobile lifting column was used to pick the vessels up, transport them to the production site and bring them to the correct height to then finally enable proper docking.

Flexibility and safety were both ensured throughout the entire system. The grinding chamber was designed for ATEX II 1 D (zone 20), while PTC probes ensured a controlled temperature in this critical area. All of the components, including vendor parts such as active and passive valves, complied with the ATEX directives. Both internal and external ATEX certificates ensured safety in the customer’s internal operations, at the same time while assuring the operator that their plant would keep running indefinitely.

Conclusion: Nothing ventured, nothing gained. This centuries-old adage has once again stood the test of time; even today, sometimes it’s just a matter of daring to try something that hasn’t been done before. In our situation, the solution was two identical grinding systems. The result was certainly one to be proud of, with unexpected time savings achieved during conversion, greater flexibility enabled during the process, and a system that met. All the safety requirements set in API production.


Frewitt fabrique de machines SA
Route du Coteau 7
1763 Granges-Paccot
Tel.: +41 (0) 26 460 74 00


Mr. Notker U Kling
Sales Manager Germany
Phone: +49 (0)6035 207 1261
Mobile: +49 (0)151 1145 4827