Shieldseal® elastomers for radiation resistance and lead-free shielding
15 November 2006
Two ranges of Shieldseal® elastomers specially developed for use with ionising radiation have been introduced by James Walker - backed with evaluation results from independent test houses and individual customers in the nuclear sector.
Shieldseal® 500 is a range of lead-free elastomers for shielding x-ray and gamma radiation. These materials comprise specially formulated metallic fillers evenly dispersed throughout a base of either ethylene-propylene (EPDM) or polychloroprene (CR) elastomers. They are designed for duties where a resilient rubber-based flexible seal is needed to prevent shine paths in active areas.
A major advantage of these materials over traditional lead-filled PVC is that they are elastomers rather than thermoplastics, which allows them to maintain long-term sealing forces. Their inherent elasticity and high level of flexibility makes them ideal for door seals or flange joints, with sheets or strips easily folded, bent and draped for pipe wrapping. This flexibility is also a benefit in the manufacture of protective garments such as gloves and aprons.
With the two main lead-free materials, EPDM-based Shieldseal 561 and CR-based Shieldseal 551, a 2.4mm thickness has the same shielding effectiveness as 1mm of lead. In addition, attenuation properties for specific applications can be customised within certain constraints to meet special requirements: eg, to give a thickness of 1.8mm of Shieldseal that has the same shielding efficiency as 1mm of lead.
Product manager Mark Syer of James Walker explained: "We supply our Shieldseal 500 grades as 'O' rings, custom mouldings, sheets and cut gaskets."
Shieldseal® 600 is a range of four elastomers formulated to resist ionising radiation. Each material is available as mouldings or cut gaskets. The change in physical properties of each material was monitored over time when irradiated with gamma radiation. This proved their retention of compression-set resistance, long service life and excellent value for money.
Both Shieldseal 661 and 662 are ethylene-propylene (EPDM) based materials with a very low content of the ions that promote metalwork corrosion in a nuclear environment. Shieldseal 661 at 50 IRHD is a soft grade for sealing liquids and gases when a low closing force is required, whereas 662 is a medium hard grade of 70 IRHD for general sealing applications. They have excellent resistance to a wide range of chemicals.
Shieldseal 641 is a soft grade of fluoroelastomer (FKM) with excellent radiation resistance and the ability to work efficiently between -18°C and +200°C. Outstanding resistance to a wide range of chemicals as well as sunlight, ozone and atmospheric aging, make it ideal for many sealing applications at temperatures where other elastomers cannot operate effectively.
Nitrile (NBR) based Shieldseal 621 is a medium-soft grade of 60 IRHD, that offers excellent resistance to mineral oils, hydraulic fluids and a wide range of chemicals for general sealing duties in radioactive environments. This grade can be supplied as extruded profiles, in addition to mouldings and cut gaskets.
Commented Mark Syer: "James Walker has over 30 years' experience of supplying specialised elastomers to the nuclear sector. All our performance claims are soundly based on documentary evidence that we will supply to customers on request.
"We are willing to partner with equipment manufactures and end-users of radiation resistant and shielding elastomers to develop, prototype and evaluate materials or specific components for custom applications."
