To start with, the seals and lubricants used have to be designed for the contact with food products - just like all the other equipment components. Permissible ingredients and compositions are laid down by the US FDA (Food & Drug Administration) or stated in the European regulation EC 1935/2004. There are also industry-specific requirements such as USP Class VI (United States Pharmacopeia) or 3-A Sanitary Standards for sealing materials, which have to be met.
Other than elastomer seals, lubricants are not subject to the EU regulation on ancillaries 1935/2004. Nevertheless they fall within the responsibility of the FDA. Lubricants registered as H1 conform with FDA 21-CFR-Sec-178.3570.
To prove they have been produced in a hygiencally sound way, lubricants should also be certified according to the international standard ISO 21 469. The certification organisation NSF (National Sanitation Foundation) uses its comprehensive, transparent NSF-ISO-21 469 programme for testing the production process of H1 lubricant manufacturers.
From a pool of suitable materials, those matching the specific application have to be determined. A primary criterion here is the product to be manufactured. However, the other process media including cleaning agents having the desired CIP/ SIP parameters also have to be considered. And, finally, sealing material and lubricant have to be compatible to ensure optimum product life and maximum maintenance intervals in operation.
Lube & Seal is an issue with autoclaves and steam sterilisers used in pharmaceutical or medical applications, e.g. where the right lubrication of their door seals has to be determined. For such applications, lubricants based on PFPE/PTFE such as BARRIERTA L 55/2 can be recommended since they combine resistance to high temperatures and media with elastomer compatibility. The choice of lubricant can significantly alter maintenance intervals: there has been a case where it increased from 200 to 600 or even 800 sterilisation cycles.
Lubricants based on mineral oil or synthetic oil may show disolouration after having been exposed to media and temperature (up to +135 °C in some applications) for some time. This not only looks unhygienic, but hints at a decomposition of lubricant ingredients, leading to deteriorating lubrication performance. The white BARRIERTA L 55/2, by contrast, retains its colour under the mentioned application parameters, and its function is not impaired.
The same applies to the selection of the sealing material: Using a more expensive, highly fluorinated elastomer may well pay off in terms of longer service life and hence higher productivity. The blue-coloured Fluoroprene XP can be used at temperatures up to +200 °C and offers resistance to a wide range of chemicals, which enables the material to be used also in industries other than pharmaceutical. They can be used in the dairy sector, with products containing a lot of fat, and in the beverage industry with its flavouring agents, without any restrictions as to the cleaning procedures.
Selection depends on the product
The chemical rule that "substances dissolve in like substances" is not so easy to take into account for the tribological systems encountered. Assuming a polar product, which is the most common in the process industry with its acqueous systems, a homopolar material such as EPDM will be selected for the sealing materials, according to the above-mentioned rule. EPDMs are not only available in the more common black colour, but in white as well. What remains is the question of the lubricant, which is to interact neither with the acqueous product nor with the seal. Practice has shown that a neutral product such as PARALIQ GTE 703 is the best option for lubrication.
For applications involving high temperatures and aggressive media, it is best to use inert products. A corresponding lubricant would be BARRIERTA L 55/2, and corresponding elastomers Fluoroprene XP 40 or Simriz (FFKM). Both are perfluorinated or highly fluorinated systems that are not susceptible to chemical attack. Some applications require the use of these high-end product since process media and parameters are too aggressive for less expensive products, or the products to be made are too sensitive or valuable.
Klüber Lubrication and Freudenberg Process Seals conducted several resistance tests to verify mutual compatibility of their products. In these tests, sealing materials were kept in containers containing lubricating greases at a temperature of +100 °C for more than 1000 hours. Fig. 2 illustrates the change in volume subsequently measured on the tested elastomers. Both the black EPDM 291 and the white EPDM 253815 are compatible with PARALIQ GTE 703. Fluoroprene XP 40 shows practically no change with this lubricant, while a minimal volume shrinkage of 0.1 % was registered with BARRIERTA L 55/2. The limit for volume changes in seals in hygienically designed grooves with no clearance is at 5 %. Results remained far below that threshold so the combinations tested can be used by operators without concerns about compatibility.
Christine Riebesell, Application Engineer, Freudenberg Process Seals
Helga Thomas, Market Manager Pharmaceutical and Chemical Industries
Jürgen Fett-Schudnagis, Market Manager Rubber and Plastics Industry