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Which sealing concepts are suitable for hygienic and dust-tight applications at the same time?

For applications that have to meet hygiene requirements (e.g. in accordance with EHEDG, FDA or the 3-A Sanitary Standards) and a high level of dust protection (typically IP6X to IP69K) at the same time, several sealing concepts are available. The choice depends above all on the cleaning method (CIP/SIP, washdown), media resistance, temperature range, type of movement (static/dynamic) and mechanical loading.

Suitable sealing concepts

Static O-ring seals with a hygienic groove geometry

Dead-space-free installation positions with a defined compression prevent deposits, the formation of germs and microbial growth. In combination with crevice-free transitions, the ingress of fine dusts is reliably prevented. A flush-mounted design without undercuts ensures that cleaning media reach all surfaces and no dust or product residues remain.

Radial shaft seals with an additional dust lip

Twin-lip concepts with a spring-loaded primary lip and a dry-running secondary lip protect rotating shafts both against the escape of media and against the ingress of dust. For hygienic applications, FDA-compliant materials and finely machined running surfaces with a surface roughness of Ra ≤ 0.8 µm are required, in order to reduce build-up and to ensure reliable cleaning.

Mechanical seals in a hygienic design

For dynamic processes with high purity requirements, mechanical seals with polished sealing faces, elastomer-free or PTFE-based secondary seals and flushable seal chambers are suitable. They combine high process reliability with dust tightness, since the sealing gaps can be executed in a defined, readily cleanable form and free of stagnant areas.

Diaphragm seals and bellows

These concepts enable an absolutely hermetic separation of the process and ambient spaces without a classic friction pairing. They are particularly suitable for aseptic processes with a simultaneous requirement for particle-free operation, since there are no leakage paths for dusts or microorganisms and CIP/SIP cleaning is possible without dismantling.

Profile seals with a metallic compression limit

Form and profile seals with a defined preload and a metallic stop ensure crevice-free, smooth-surfaced transitions at flanged connections, vessels and pipes. The controlled deformation prevents over-compression and the protrusion of the elastomer into the flow channel, whereby niches for dust deposits and microbial growth are avoided.

Inflatable seals for interfaces that are opened frequently

Inflatable seals are particularly suitable for flaps, doors and vessel lids with frequent opening cycles or irregular surfaces. In the activated state they expand uniformly by means of compressed air, closing tolerances and unevenness hermetically and dust-tight. In the depressurised state they retract without contact, whereby mechanical abrasion is minimised and particle contamination reduced.

Barrier air or air purge sealing concepts

With rotating or moving components, a barrier air seal can be used. A continuous overpressure of filtered air or inert gas in the seal chamber prevents the ingress of dust particles, cools the sealing faces and supports hygiene, since less mechanical abrasion arises and the sealing zone is flushed at the same time.

Level of protection and relevant IP ratings

  • IP6X: complete dust tightness against the ingress of dust into critical areas.
  • IP69K: additionally resistant to high-pressure and steam jet cleaning; particularly relevant for plants in which intensive washdown cleaning and dry dust processes are combined.

Sealing systems for hygienic and dust-tight applications should be designed so that these IP ratings are reliably met even after repeated cleaning cycles.

Choice of materials

For combined hygiene and dust applications, the following materials are preferred:

  • Elastomers: EPDM, FKM, HNBR, VMQ/silicone in qualities compliant with FDA, USP Class VI or (EC) 1935/2004.
  • Thermoplastic materials and compounds: PTFE compounds and further highly resistant plastics for abrasive or chemically aggressive media.

The materials must:

  • be chemically resistant to cleaning media (acids, alkalis, disinfectants),
  • reliably withstand the temperatures necessary for SIP processes (steam sterilisation),
  • have a high resistance to abrasion from abrasive dusts and
  • release no critical additives that could endanger product hygiene.

Basic design principles for hygiene and dust tightness

Irrespective of the type of seal, the following design rules apply:

  • Freedom from dead space: avoidance of cavities, crevices and undercuts in which the flow velocity of cleaning media approaches zero and dust or microorganisms can accumulate.
  • Crevice-free installation situations: flush-mounted seals without offset between the seal and the surrounding surfaces.
  • Surface roughness in the sealing area of Ra ≤ 0.8 µm: a high surface finish reduces build-up and facilitates residue-free cleaning.
  • Self-draining geometries: avoidance of horizontal surfaces and depressions in which cleaning liquids or product residues can remain standing.
  • Cleanability in the installed state (CIP/SIP capability): seals and adjoining geometries must be designed so that they can be cleaned completely and, where applicable, sterilised without dismantling.
  • Avoidance of ineffective metallic contact zones: designs in which metal surfaces are in contact without a seal being present can create dust nests and cleaning shadows and are to be avoided.

Through the targeted combination of suitable sealing geometries, certified materials and a hygienically compliant design, the requirements for hygiene and dust tightness can be reliably united in a single sealing system.

How amixon® solves seals and shaft passages – hygienic and dust-tight at the same time

In amixon® mixers, the mixing tool is mounted and driven exclusively from above. This eliminates the lower shaft passage, which in conventional mixers is often the most critical sealing point, because product bears against the seal there under the pressure of the bulk material. Sealing points arranged above the product level are subject to markedly lower mechanical and hygienic loading and can be managed far better.

The large inspection doors are manufactured by the Clever-Cut® process and seal permanently dead-space-free with the OmgaSeal® seal. The seal sits in a groove with an undercut, without a crevice to the product space. On request, the doors are executed vacuum-tight or against overpressure, so that hygienic cleanability and dust tightness are met with the same sealing concept.

Rotating passages and fittings too are consistently designed for tightness and cleanability. Cutting rotors, for instance for de-agglomeration or the distribution of liquids, run with a mechanical seal, including in pressure-tight and vacuum-tight mixer-dryer reactors that can hold a vacuum down to 5 mbar abs. Discharge devices are executed as dead-space-free standard connections with a discharge flap or as vacuum-tight and pressure-tight ball segment valves.

A further important design aspect is the high dimensional rigidity of amixon® apparatus. Even under maximum load, no perceptible deflection or relative movement occurs. This increases the functional reliability of all seals and contributes substantially to their particularly long service life.

The design advantage of this concept lies in the fact that fewer sealing points are needed, and thereby fewer wear parts, fewer inspection points and altogether lower maintenance effort. amixon® supplies selected wear parts together with the initial delivery, and most spare parts are held in stock at the Paderborn site, with a lifetime spare parts service.

amixon® develops and manufactures exclusively at the Paderborn works with a high depth of manufacture and all components from Germany. As a certified welding company with European, Japanese, Korean and American qualifications, amixon® designs every apparatus as a one-off on the basis of the operator's URS, and quality control remains entirely in-house without gaps.

For regulated environments, amixon® supplies the plant in qualifiable form and assists on request with DQ, IQ and OQ. Documentation and execution follow, on request, EU GMP and FDA 21 CFR Part 11. On request, the mixers meet the relevant standards such as EHEDG, the FDA hygiene guidelines, the 3-A Sanitary Standards, USDA, GMP, ATEX and ASME and are integrated into the operator's validation concept from the URS through to commissioning.

amixon® checks in advance in the pilot plant, with 35 test units, whether the specific formulation delivers the expected results. Trials with the original product under real conditions are carried out, evaluated and documented jointly and serve as a robust basis for decision-making before the investment.