New sealing concept for roller dryers

A German plant of an international pharmaceutical company uses multiple roller dryers for the production of pharmaceutical powder. The dryers used to be equipped with typical liquid-lubricated mechanical seals. These proved to be very maintenance-intensive in the respective application, however.

The brittle silicon rings in the seal proved to be the weak point. They could not withstand the sudden deflections of the shaft and the resulting vibrations that occurred while drying the coarse-grained product. 

For that reason, the manufacturer decided to upgrade the roller dryers. The process began with the search for a new sealing concept that would enable efficient, fault-free operation.

The dryers each have two heated rollers, which are operated in a vacuum. The product is applied evenly to the rollers and dried within a half rotation. Then it falls past wipers into the paddle dryer situated below. This process ensures rapid and gentle drying of the product.

The seals are installed horizontally on the driven and non-driven sides of both rollers with side entry drive.

It quickly became clear that dry-running seals would be a good choice for the moderate operating conditions.

In comparison with liquid- or gas-lubricated mechanical seals, these seals can even be operated without a supply system. Faults due to barrier medium or flushing medium and the task of selecting an appropriate barrier medium are eliminated. Plus, the investment and operating costs are significantly lower.

The next step was to ensure that the sealing solution could handle the shaft deflections and prevent the high levels of wear previously observed on the sealing rings.

This is exactly where the newly developed SeccoLip lip seal from EagleBurgmann can demonstrate its strengths.

The seal has been fully reconceived and now combines the functional principle of shaft seal lips with the reliability and safety of a mechanical seal. The combination of a sealing lip of special PTFE compound and a sliding part is patented and can directly and reliably compensate for any deflections in the agitator shaft. This means that the seal gets by without compensation elements such as O-rings, expansion disks, or metal bellows.

The sliding bearing compensates for shaft movements by following the movement with the entire sealing element. The installation of U-caps instead of dynamic O-rings reliably compensates radial deflections up to 3 mm. At the same time, the sealing gap between the shaft and the sealing lip remains constant. Because the contact force of the lip against the sleeve is also minimized, the heat production, wear, and leakage are low. An additional bearing is unnecessary, eliminating the associated costs and maintenance effort.

Perfect fit thanks to modular design

The arrangement of the sealing lips is variable with the SeccoLip and can be tailored to the needs of the specific customer. Four lip elements were integrated for the roller dryer application.

The first and second sealing lips each face towards the product. These ensure that no product penetrates the seal. They also permit the seal to be flushed. Hot steam at 4 bar can be supplied through a flushing port for regular cleaning.

The third and fourth sealing lips face the atmosphere. This arrangement protects the processed product from external contamination and makes vacuum operation possible. The sealing capability of the SeccoLip is ensured at regular intervals by a defined period of vacuum in the roller dryer.

In the pharmaceutical industry, all production systems, plants, and components are subject to strict regulatory requirements. In this case, the manufacturer required verification that the materials met the requirements of the U.S. Food & Drug Administration (FDA). Furthermore, the seal had to be certified for use in ATEX zone 2 with temperature class 2. The new design was able to meet these requirements as well.

Since the successful conversion of the roller dryers to the dry-running SeccoLip seals at the end of 2020, they have been operating reliably and without issues. Regular maintenance is no longer necessary. The conversion quickly paid for itself thanks to the savings.
 

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