Milling System How pharmaceutical manufacturer could fulfill Atex in grinding processes

Author / Editor: Roy Housh* / Manja Wühr

Milling products is one matter. Finely milling products in compliance with Atex to a particle size of 75 µm is another. In order to ensure perfect Atex compliance when finely milling different products, all the conditions have to be in concert.

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Challenge, which has been taken up – milling sugar in compliance with Atex to a particle size of 75µm.
Challenge, which has been taken up – milling sugar in compliance with Atex to a particle size of 75µm.
( © Coprid - Fotolia)

A French pharmaceutical manufacturer had already validated a system to finely mill crystal sugar (saccharose), however they were missing the final aspect. Atex compliance. Never had they realized that they would have to take such an arduous path and have it done by other suppliers. Crystal sugar was originally milled with a vibrating-sieve machine, and sequentially manually filled. In order to simplify the process and make it safer; a hammer mill was purchased from one of Frewitt’s competitors. The product to be milled was fed via a pneumatic conveyor, and thereafter manually filled.


The system worked perfectly albeit required considerable manual handling. The validation results were satisfactory, but they stumbled at the step of Atex compliance evaluation. Realizing the existing system could not comply to Atex standards, they initiated a search for an alternative solution.

A process expert from Frewitt visited the pharmaceutical manufacturer in order to obtain important, on-site information, to analyze the existing system, the process and finally the product. The existing process did not need to be completely revised, instead, the same product could be finely milled with the same sieve execution and the same parameter settings, notably the identical rotor tip speed. Following this conclusion, various Frewitt milling processes were tried. The customer decided to entrust his fine milling to the Hammerwitt, as it achieved the same results as the competitor’s hammer mill, while providing significant improvements in the granulometry and throughput.

New Performance Characteristics

The first and most important step was done, notably defining the hammer mill as the size reduction process. Logically, conceiving the new process followed. A pivoting post hoist column, a pneumatic conveying system, and the Hammerwitt with the containers to be filled, are all located in the Atex zone; whereas the switch cabinet and control panel are outside the Atex hazard zones.

The characteristics of the individual system components contributed to a significant performance improvement in the entire system. The Hammerwitt made an important contribution by doubling throughput and its ability to mill the product with a rotor execution of 24 blades (the competitor’s rotor was fitted with 16 blades) in order to mill a finer product (75 µm).


The Profi-Valve, another Frewitt component, replaced the feed screw. It reduces the risk of blockage to zero due to its completely new rotary valve design, and provides constant product feed due to it’s volumetric dosing capacity explicitly designed for the capacity of the Hammerwitt milling chamber.

The final benefits are provided by the Frewitt Profi-Clean filter, which regulates the pressure in the milling chamber, and provides constant filtered exhaust through the particle separator. It monitors and regulates the exhaust air to ensure that the product does not heat up, which contributes to constant, high throughput. The Profi-Clean system is outfitted with an H13 filter which prevents the escape of the finest dust or powder. The filter is continuously cleaned via an efficient back-blow system.

The user was at the center of the system’s concept. A lifting column could accommodate containers up to a height of 2700 mm, resulting in containers with capacities of 300, 600, 1200 and 2000 liters can be quickly and safely filled in compliance with GMP standards.

Another advantage: The new milling design provides unparalleled flexibility, being quickly changeable from the Hammerwitt hammer mill to Frewitt's Turbowitt cylindrical mill. It is now child’s play to mill Product A, then switch to deagglomerating Product B within minutes, thanks to Frewitt's Fredrive system and its interchangeability.

How pharmaceutical manufacturer could fulfill Atex in grinding processes

Atex design Makes it Possible

There are many technical process solutions behind the Atex concept to convey, finely mill or disagglomerate, as well as dose and fill various products. The milling chamber and the milling head area were in Atex 3D (Zone 22).

The rest of the equipment is installed outside the defined Atex zone, bringing the customer the advantage of safely manufacturing the product with a safe, cost effective solution. Having installed the rest of the system outside the Atex zone ensured greater safety and enhanced affordability.


Summary: The customer was completely satisfied with the execution of the entire project: planning, engineering, installation and operation. The system operators were satisfied with the overview of the process monitoring, due to its simple and safe operation.

Despite the difficult properties of saccharose when milling (such as sticky, smearing, heat-sensitive), the hammer mill runs without blockage and provides high, trouble-free throughput of dry product. The safety gains clearly more than paid for themselves for the customer, and for Frewitt, a satisfied customer.

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