Plate Heat Exchanger Gasket Materials
For plate (and frame) heat exchangers, the standard materials are EPDM and Nitrile rubber (NBR). EPDM is used normally for non-fatty/oily applications, and NBR for oil/fat applications. However, there are no rules without exceptions. An "oil" and fatty application may have a low fat content, making the application more suitable for EPDM instead of NBR.
Other rubbers used for PHE's are Hydrogenated Nitrile Rubber (HNBR), Fluorocarbon rubber (FKM), Butyl, Chloroprene Rubber (GR), Chlorsulphonated Polyethylene (CSM), Styrene Rubber (SBR), Natural Rubber (NR) and Silicone Rubber (Q) are less common ones.
All additives matter for the product properties, and not only effect the quality level of the product, they also influence the consistency of the quality level.
Eventually all rubber materials will degrade, loosing their properties, making them unsuitable for further use. It is all a matter of time and the original quality of the product. The lifetime of rubber products is dependent on the environment (chemical types, concentrations) and temperature. Also, temperature changes and pressure changes effect the performance and lifetime of the rubber product.
Each rubber material has its unique resistance towards various chemicals. Polymer used, as well as additives, effect which chemicals each rubber material is suitable for. WCR compounds rubber materials for optimum performance.
At high temperatures the rubber will be attacked faster by the chemicals in use, and the surrounding oxygen. The oxidation process will either make the rubber harder (the most common one) OR make it softer (less common), OR both at the same time. Either way the change in properties will reduce the performance. All rubber materials have a maximum continuous temperature, which should not be exceeded to maintain good performance and to achieve a reasonable lifetime.
At low temperatures the stiffness increases, and the elasticity decreases. This influences the sealing force of the gaskets. All rubber materials have a certain lowest temperature that have to be exceeded to be able to perform well enough as a gasket.
For food applications there are demands according to national standards. The usual one for PHE gaskets is FDA (USA). This standard regulates what additives are allowed to be used in the rubber and to what content. It also sets demands on what tests have to be done to ensure the quality level.
WCR develops rubber compounds to maximize nominal quality level, and minimize variation.
EXPLANATIONS: RUBBER PROPERTIES/TEST METHODS
Hardness: Measured normally as Shore A or IRH D. Both methods are based on the penetration of a needle into a rubber surface. The less the penetration is, the harder the rubber is.
Elongation at break:How much a rubber can be stretched until breaking. Measured in % of original length. Tear strength: How much force is needed to break a rubber sample with a specified crack. Measured in force per thickness.
Compression set:The idea of measuring the compression set is that the lower the compression set is, the higher the sealing force is. It is measured in % of the deformation. Heat Resistance/Heat Ageing: is measured through measuring the change in various mechanical properties.
Chemical Resistance: Is measured through measuring the change in volume, weight, and various properties. Low temperature resistance: Is measured either through compression set of tensile retraction test, which is a test or elasticity at low temperature.