When it comes to manufacturing food and beverages, pharmaceutical products and cosmetics, the health of the consumer takes top priority – an approach that affects all design and operational aspects of production facilities. Seals and lubricants, which were once ignored in such considerations, are now painstakingly tested and selected on the basis of their suitability and functional reliability.
The authors: Christine Riebesell Application Consultant, Freudenberg Process Seals Helga Thomas Market Manager Pharmaceutical and Chemical Industry, Klüber Lubrication Jürgen Fett-Schudnagis Market Manager Rubber and Thermoplastics, Klüber Lubrication
First of all, seals and lubricants – just like all other components in production facilities – need to be designed for contact with food and beverages. The US FDA (Food & Drug Administration) and European regulation EC 1935/2004 determine which substances and compositions are allowable. In addition, numerous industry-specific criteria like USP Class VI (United States Pharmacopeia) or 3-A Sanitary Standards for sealing materials need to be satisfied.
Unlike elastomeric seals, lubricants are not covered by the European regulation EC 1935/2004 on materials and articles intended to come into contact with food, but are instead regulated by the FDA. Lubricants in category H1 are compliant with FDA 21 CFR Sec. 178.3570. Furthermore, they are certified according to the international standard ISO 21469, which confirms that they were manufactured under hygienic conditions. Fi-nally, the NSF ISO 21469 programme, a battery of tests designed by the NSF (National Sanitation Foundation), offers a comprehensive and transparent means of assessing the production processes used by H1 lubricant manufacturers.
Once this pool of generally suitable materials has been established, the next step is to filter out those types best suited to the application concerned. Though this is primarily determined by the product to be manufactured, the other process media involved, including cleaning agents with the desired CIP/SIP parameters, also have to be taken into account. Last but not least, the sealing material and lubricant need to be mutually compatible in order to ensure optimal service life and the longest possible maintenance intervals.
Critical applications
Lube & seal is an important topic for autoclaves and steam sterilisers used in the pharmaceutical and medical fields, e. g. when it comes to finding the right lubrication for their door gaskets. PFPE/PTFE lubricants like Barrierta L 55/2 are ideal candidates for this type of application, as they are not only stable when exposed to heat and various media but also highly compatible with elastomers. Using the best lubricant for the job can greatly affect maintenance intervals: in a concrete example, switching to another lubricant extended the interval from 200 to an impressive 600 to 800 sterilisation cycles.
When exposed to a wide variety of media and high temperatures (operating temperatures up to +135 °C), lubricants based on mineral or synthetic oils may become discoloured after a certain time. This not only looks unhygienic; it also indicates a chemical breakdown in the lubricant, which is accompanied by decreased performance. In contrast, the white Barrierta L 55/2 grease maintains its original colour under these operating conditions and shows no loss in function.
The same is true when selecting the right sealing material: the longer service life and higher productivity offered by more expensive, highly fluorinated elastomers can make them a worthwhile investment. Blue Fluoroprene XP can be used in temperatures up to +200 °C and is resistant to a broad range of chemicals. This not only makes it a good choice for pharmaceutical applications; it is also suitable for high-fat products in the dairy industry or beverage bottling processes involving flavouring agents without any restrictions on cleaning procedures.
It all depends on the product
The basic chemical principle of “like dissolves like” isn’t quite as easy to apply in this three-part system. If we have a polar product, which is quite common in the process industry’s aqueous systems, the above principle suggests that we should choose a non-polar sealing material like EPDM, which is available in both standard black and white variants. Now we still need to select the right type of lubricant, which should ideally not interact with either the aqueous product or the seal. Experience shows that a neutral choice like Paraliq GTE 703 is best here. For applications linked to high temperatures and corrosive media, inert products should be preferred wherever possible. Barrierta L 55/2 is a good candidate for the lubricant; as regards the elastomer, Fluoroprene XP 40 or Simriz (FFKM) would fit the bill. Both materials are highly fluorinated or perfluorated, making them extremely resistant to chemical attack. In some applications it becomes necessary to fall back on these high-end products because the process media and parameters involved are simply too aggressive for more economical products, or because the product being manufactured is too sensitive and valuable.
Klüber Lubrication and Process Seals have conducted an extensive series of endurance tests in order to determine and verify the mutual compatibility of their products. The sealing materials were immersed in lubricant at +100 °C for a period of 1000 h. Figure 2 clearly shows the volume change subsequently observed in the elastomers. Both black EPDM 291 and white EPDM 253815 are perfectly compatible with Paraliq GTE 703. Fluoroprene XP 40 showed practically no change beyond a minimal volume loss of 0.1 % in Barrierta L 55/2. As the maximum allowable threshold for volume changes in seals intended for hygienically designed and dead-space-free grooves is 5 %, this minute difference is well within the limits; plant operators can therefore use these material/lubricant combinations without any reservations.
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