Deionised Water Requires Special Sealing Solutions

Elastomers comprise a large number of different ingredients. Low-molecular weight organic compounds in particular can be dissolved out of the matrix by certain solvents and sometimes even by water. This effect, also known as leaching, is even more marked in applications involving deionised water. The material 70 EPDM 291 from Freudenberg is a reliable choice for sealing challenges in deionised water plants.

The extraction of elastomer ingredients always goes hand-in-hand with a measureable shrinkage of volume, which in turn affects the sealing effect of the product. At the same time, the various solvents can — depending on their polarity — diffuse into the elastomer matrix, resulting in a measurable increase in volume. If both effects occur simultaneously as a result of superimposition, the composition of the sealing material and, consequently, its properties undergo a fundamental change despite the fact that there is no noticeable change in volume.

In addition to purely physical processes, chemical processes such as post-curing, the breaking of crosslinks and even chain degradation can occur, resulting in striking consequences for the properties of the seal. Such reactions generally lead to changes in the seal’s mechanical properties. In order to be able to register these changes in a reliable manner, it is important that not only changes in mass and volume but also changes in mechanical properties are closely and accurately measured and analysed. The key parameters in this context are hardness, elongation at break, tension at 100% elongation and tensile strength.

Depending on the application in question, a variety of threshold values for changes in properties have proven useful for the assessment of suitability. The threshold values for changes in mass and volume are +/-5% and +/-10% respectively; for changes in mechanical values, they are +/-15% for dynamic applications and +/-30% for static applications.

The elastomer compound 70 EPDM 291 boasts very good properties in contact with both water and deionised water. The most significant property of 70 EPDM 291 in this context is the fact that there are no significant increases in mass and volume even when the material is submerged in water at 200˚C over long periods. Nor were any significant effects noted after a prolonged period in deionised water at 100˚C.

O-rings, O-ring type seals in special shapes, or seals for valves and fittings made of 70 EPDM 291 remain reliably resistant in water up to 180 °C, deionised water up to 160˚C and air up to 150˚C.

70 EPDM 291 meets the specifications of the European standard DIN EN 681–1 WB and the American standard NSF 61, the requirements of the drinking water regulations in Germany, Great Britain and France without restrictions and the strict requirements of the FDA for both food and pharmaceutical products. The high purity of this material is also further emphasised by its USP Class VI approval.

Freudenberg will be highlighting 70 EPDM 291 at TechnoPharm 2013, 23–25 April, Nuremberg, Germany, Hall 6, Stand 227.

Freudenberg Sealing Technologies GmbH & Co. KG, +49 6201 80 3631, michael.scheuer@fst.com, www.fst.com.