How to Optimize Dry Cleaning Methods for Bulk Residues in Mixers

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Hosokawa Micron B.V.

These observations can help to find the ideal cleaning approach. The dust in zone one can often easily be blown away with compressed air. Residues in zone two might still be cleanable with a cloth in a relatively short time. The mixing screw in some cases could take the operator over an hour to clean, calling for higher friction forces to break the adherence bonds, and cleaning equipment like brushes and tools.

Three Solutions for Mixer Dry Cleaning

Hosokawa specialists suggest three solutions how to enhance the dry cleaning of conical screw mixers:

• Large inspection door: The operator sized inspection-door in the vessel wall offers a large entrance opening, through which the operator can easily access all surfaces that should be cleaned. Surfaces requiring special care and thorough cleaning are the welds connecting the screw flights to the screw shaft, and the lower surface of the screw. A large door makes these surfaces both visible and accessible for cleaning. Off course, the door will be shut tightly when mixing powders. To ensure tightness, a large silicone o-ring is used as the sealing element, combined with several quick release clamps on the door (in fact, this door is used for some cases of wet cleaning too). Since safety of the operating personnel is an important aspect of such doors, a safety switch should be a standard part of the design, preventing the door from opening, as long as the screw is rotating. When the door is closed, special care is taken in the design to have the door flush with the vessel wall.

• Semi domed cover: The inside surface of the cover can be reached when the access door has been opened. To further enhance cleanability, the customer often selects a semi-domed cover which is welded to the cone, offering a large radius and no crevices in which bacteria can settle.

• Isem outlet valve: The third feature that facilitates dry cleaning is Hosokawa’s Isem ball segment valve in the outlet opening. The interior of this valve consists of rounded surfaces, reducing the possibility for material deposition to a minimum. In the standard layout of this ball segment valve, an inspection port is available. In case deposits have to be removed, this can be done by using special cleaning tools.

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More about dry cleaning? Read also an interview Hendrik Freije, application engineer of Hosokawa Micron’s Food & Pharma team, about the Do’s and Dont’s of dry cleaning.

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