Storage and Shelf Life
Storage and Shelf Life of Seal Items
Seal system components just like wiper seals, seals (dynamic and static), wear rings and anti-extrusion rings are made of different polymers. Seals are considered as spare parts, which are often stored on shelf for a longer time before installation.
Typical materials are elastomers (vulcanized rubbers), polyurethanes, fluoroplastics, and hard plastics what tend to change their properties as a result of either chemical reaction or physical impact. Such changes in material properties can lead to degradation of seal conditions and they can become unserviceable. This might be due to aging, hardening, cracking, softening, crazing, and other possible degradations.
Seal material characteristic changes can be the result of different physical and/or chemical factors: heat, humidity, light, oxygen, ozone, and exposure of chemicals or physical contact with different metals, further physical impact, which can result in permanent deformation of the components.
Polymers will maintain their original properties for a certain, limited time without significant changes in case, if they are stored and protected properly. Otherwise faster degradation can be occurred.
Useful information and guide on packaging, storage and cleaning of polymer components are provided by industrial standards, such as ISO 2230 and DIN7716. Polymer products should be stored according to described suggestions, helping to maintain the optimum, serviceable properties of the seals through the entire recommended shelf life.
Contact with metals
Direct contact with certain metal gardes should be avoided, as they can degrade elastomers. Such metal are iron, copper and its alloys (brass) ,and manganese.
|Material grade||Typical shelf life|
|Thermoplastic polyurethanes||10 years|
|Hydrogenated nitrile (HNBR), nitrile (NBR) and chloroprene (CR)||6 years|
|Ethylene propylene (EPDM)||8 years|
|Neoprene with cotton||1 year|
|Nitrile with cotton||1 year|
|Fluorocarbon (FKM), silicone (VMQ) and fluorosilicone (FVMQ)||10 years|
|Perfluorelastomer (FFKM)||13 years|
|Polytetrafluoroethylene (PTFE) virgin and filled||unlimited|
|Polyether ether ketone (PEEK) unfilled and filled||unlimited|
|Ultra-high-molecular-weight polyethylene (UHMWPE)||20 years|
|Polyester resin||5 years|
|Polyacetal (POM)||5 years|
|Polyamide (PA)||5 years|