PuK - Process Technology & Components 2022

Components Seals Approval of gaskets for our drinking water – despite the transitional regulation, haste is required Dipl.-Ing. Norbert Weimer With the KTW-BWGL (assessment basis for plastics and other organic materials in contact with drinking water), a new regulation has come into force that has a strong influence on the handling of gasket materials in drinking water. The effect specifically on the very often used fibre-based (FA) gasket materials and the resulting consequences for use in practice should be addressed here. What is drinking water? Drinking water is water intended for human consumption. Drinking water is the most important food; it cannot be replaced. Drinking water is defined as any water intended for drinking, cooking, preparing food and drink or, in particular, for the following domestic purposes: manufacture elastomers in contact with drinking water. This list also applies to fibre-reinforced gasket sheets bonded with elastomers (FA – fibrebased gasket sheets). Part 1 of the list contains the fully evaluated substances (monomers, fillers, plasticisers, anti-aging agents, processing aids, crosslinking agents, etc.). The positive list part 2 lists substances that have not been fully evaluated. The use of these partially assessed substances was only accepted until 31 December 2021. In the meantime, an additional “intermediate instance” has been introduced, the “preliminarily assessed starting materials”. Listed here is, among others, the p-aramid fibre used in FA gasket materials. How ever, no information could be found on how to deal with this part of the list and what “provisional” means. (e. g. heaters with gaskets for gas as well as heating and drinking water) and the “one for all – gasket” is no longer available. Despite a transitional regulation, all of this means that users and the supply chain should look for a wellfunctioning alternative at an early stage. Because new product assignments in production, different storage quantities and, if necessary, new logistics processes can take time – haste is essential. The possible gasket materials There are three basic sheet material types for the flat gaskets discussed here: 1) Flat gaskets based on graphite (GR) – (e. g. KLINGER ® graphite) – body care and cleaning – cleaning of objects intended to come into contact with food – cleaning of objects that, as intended, come into contact with the human body on a more than temporary basis Which materials will be permitted for use with drinking water in the future? The Federal Environment Agency (UBA Umweltbundesamt) has set requirements for a wide variety of components in the area of drinking water supply. In our area of soft fibre gaskets, the KTW-BWGL is authoritative. For this purpose, products and components made of organic materials are evaluated based on the starting materials used (primary materials) with regard to mass transfer into drinking water. The UBA’s positive list lists the raw materials that may be used to Impact on the supply chain For the manufacturer of FA gasket sheets, this situation means that they can no longer use their previous formulations for products intended for drinking water applications. The gasket materials from the previous formulations can, of course, continue to be used for other applications. However, it is painful that the usual range of applications is no longer guaranteed due to the reduction of the possible ingredients. This particularly affects processors, such as stamping workshops and technical distributors, who have to readjust (storage and costing) with regard to the utilisation of gasket plates during cutting and with regard to storage for different applications (e.g. drinking water, gas, temperature ranges, etc.). It could also become a problem for device manufacturers if it is not possible to allocate different gasket materials to different functions in production Up until now rarely used in the drinking water sector, these sheet materials are tested according to the KTW guidelines, even though they are not plastic. If the materials are not impregnated and consist only of pure graphite and stainless steel reinforcement, they should be able to meet the requirements. However, there is one major limitation for fitting gaskets – the twisting motion that often occurs when assembling fittings is not well tolerated by a graphite gasket. In addition, graphite particles can be flushed out more easily, which is hygienically harmless, but could be a visual problem. 2) Flat gasket based on PTFE (TF) – (e. g. KLINGER top-chem) These materials are also mainly tested according to the KTW guidelines and are hygienically very well suited for the drinking water area. But here, 110 PROCESS TECHNOLOGY & COMPONENTS 2022

Components Seals too, there are reasons why they are not used so often: The material PTFE is of very high quality and is therefore not used as a standard for the mass market. In addition, with the narrow-edged screw gaskets, higher setting amounts are often to be expected due to the flow behaviour. An exception here is the gasket made of KLINGER top-chem 2000, which falls under ceramic materials in terms of hygiene testing and offers the necessary stability. 3) Flat gaskets based on fibres (FA) – (e. g. KLINGERSIL C-4240, Fig. 1) Due to the binder (elastomer), these materials are mainly affected by the new regulation KTW-BWGL. On the one hand, they are the standard seals for the drinking water sector; on the other hand, the greatest encroachment on the possible choice of raw materials is found here. The reduction in the permitted ingredients for the production process is so great that the rolling and vulcanisation process requires the highest level of know-how in order to be able to produce a gasket sheet under these conditions at all. The gasket sheet mentioned as an example under point 3) is not just an example, it is currently the only one available on the market that meets the requirements of the KTW-BWGL. plication is the industrial production of composite components and devices from water filters to heaters. Exact assembly conditions and a high repeat accuracy of assembly processes are to be expected here. Table 1: Comparison of the previous and the new KLINGERSIL With the product KLINGERSIL ® C-4240, the Klinger company has developed a gasket sheet that is very similar to previous gasket materials in terms of its behaviour. It is precisely this behaviour that makes it Feature Requirements Unit KLINGERSIL C-4400 Compressibility ASTM F 36 J % 11 10 Recovery ASTM F 36 J % 55 45 Stress relaxation DIN 52913 Stability according to KLINGER 50 MPa Stability according to KLINGER 50 MPa 50 MPa, 16h/175°C MPa 37 35 Decrease in thickness at 23°C Decrease in thickness at 200°C % 10 10 % 10 15 Sealing performance DIN 28090-2 mg/(s x m) 0.02 0.01 Thickness swelling ASTM F 146 Thickness swelling ASTM F 146 OIL IRM 903: 5h/150°C % 3 5 Fuel B: 5h/23°C % 5 10 Density DIN 28090-2 g/cm 3 1.6 1.75 The gasket material must therefore have a consistent quality in order to ensure industrial production with consistent behaviour. In addition, it must have a wide range of applications in order to also enable manual assembly under different conditions. possible for the user to use the new gasket material without making any special adjustments. The compression behaviour and stability are just what the user wants. A comparison with the previous product makes this clear (Table 1): New: KLINGERSIL C-4240 Fig. 1: Fibre-based flat gasket What can the user expect from the new product? There are two different fields of application in drinking water installations. For one field there is the fitter, who visits his customers with his workshop trolley, replaces or reassembles components on site under often adverse conditions and stands for the craft with his experience and qualifications. The other field of ap- Gasket height [m m] 2,0 1,9 1,8 1,7 1,6 1,5 1,4 1,3 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 TEMESfl.ai1 Klinger A, 27.01.2022 Diagram 1: DIN 52913 pressure resistance curve DIN 52913 Pressure resistance curve KLINGERSIL ® C 4240 75x55x2 mm Q i = 50 MPa, T = 175 °C Time [s] Gasket height Surface pressue Temperature 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 Q R = 38 MPa 40 30 20 10 Surface pressure [MPa] Temperature [°C] PROCESS TECHNOLOGY & COMPONENTS 2022 111