For plate 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. But 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.
LIFETIME
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. |
Chemical Resistance
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.
High Temperature
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.
Low Temperature
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.
Food Applications
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. |
