Elastomer seals are built to handle a wide range of demanding hydraulic and pneumatic applications. A seal’s design and its material properties are two keys to lasting performance. The engineers at Parker Hannifin’s Engineered Materials Group in Germany also offer some important recommendations on how to store, handle and clean seals prior to use.
Dr Heinz-Christian Rost
Technology and Innovation Manager
Prädifa Technology Division
Parker Hannifin, Engineered Materials Group
High-quality elastomer seals meet the most exacting demands in a wide range of applications. Aside from the appropriate seal designs, the material properties of seal compounds are crucial to ensuring that seals deliver the desired performance. However, there are a few rules to be observed in the event that seals are installed after longer storage periods or if cleaning should be required.
Factors such as heat, humidity and UV radiation can degrade seals in storage.
The properties profile of an elastomer seal typically remains constant for years if the seal is properly stored. Improper storage conditions, on the other hand, can drastically reduce a seal’s potential shelf life due to a large number of influencing factors. Ultimately, the seal will no longer be fit for use due to hardening, softening, permanent deformation, cracks, surface damage or other detrimental factors.
To avoid this, engineers at Parker’s Engineered Materials Group in Germany recommend, based on DIN 7716 and ISO 2230 standards, that the following guidelines be observed for storage, storage periods and cleaning of elastomer seals. (Note that many suppliers and users of elastomer seals in the U.S. prefer to follow SAE ARP 5316D recommendations, which are similar but not the same as the DIN and ISO standards.)
Factors that influence seal storage
- Temperature. The preferred storage temperature for elastomer products is 15 °C (59° F) and should not exceed 25° C (77° F). Accordingly, avoid sources of heat such as radiators, boilers (minimum distance: 1 meter) or direct sunlight. Temperatures should not drop below -10 °C (14° F). In this case, elastomer products will stiffen, and seals should be handled with special care to prevent deformation. Chloroprene materials should not be stored below -12 °C (10.4° F).
- Humidity. Ensure that the relative humidity in storage facilities is below 65%. Storage in humid rooms and condensation must be avoided. Likewise, elastomer seals should not be stored in extremely dry conditions.
- Light/radiation. Elastomer seals must be protected against sources of light with a high UV content that could damage the products. Examples of light sources with a high UV content include intense artificial light or direct sunlight. Light-induced (photo) damage can be avoided by adequate application of UV filters to the window panes in the storage room. All types of radiation such as gamma or radioactive radiation must be avoided.
- Oxygen/ozone. Generally, elastomer seals should be protected against circulating air by suitable packaging such as airtight containers. This is particularly important for very small seals with a large surface-to-volume ratio. Mercury vapour lamps, fluorescent light sources, electric motors—generally any device that is capable of producing ozone through sparks, electrical discharges or high-voltage fields— must be strictly avoided. Ozone is harmful to many elastomers so storage rooms must be ozone-free. This also applies to organic gases as well as combustion gases, as they are capable of producing ozone via a photochemical process.
- Solvents/greases. Greases, oils and solvents may damage elastomer seals. Therefore, ensure that the seals cannot come into contact with these media in storage (unless packaged in this fashion by the manufacturer).
- Deformation. Elastomer seals exposed to tensile or compressive strain, or other types of deformation, may be damaged. Cracking may occur. Therefore, the seals must be stored without being subjected to strain and deformation.
- Storage period. A key criterion for the storage period of elastomers is the time at which the product was vulcanized. Parker indicates the date of manufacture on the packaging bags: “1Qxx” stands for parts produced in the first quarter of the year 20xx. The recommended maximum storage period depends on the type of elastomer.
Recommended maximum storage period per ISO and DIN guidelines for the following elastomers is:
Thermoplastic urethane (TPU): 4 years
Hydrogenated nitrile (HNBR), nitrile (NBR) and chloroprene (CR): 6 years
Ethylene propylene (EPDM): 8 years
Fluorocarbon (FKM), silicone (VMQ) and fluorosilicone (FVMQ): 10 years
Perfluorelastomer (FFKM): 13 years
Elastomer seals should preferably be used within the statutory liability period of 24 months.
Fluid-power engineers and users of elastomer seals should be aware that the DIN 7716 and ISO 2230 standards tend to be more stringent than the ARP 5316D guidelines for seal storage duration often used in the U.S. For example, ARP 5316D recommends a maximum storage period of 5 years for polyurethane; 15 years for HNBR, NBR and CR; and “unlimited” for EPDM, FKM, VMQ, FVMQ, and FFKM.
In addition to these recommendations, there are a few other aspects to observe when storing elastomer seals:
• Elastomer products should not come into contact with metals such as iron, copper and manganese, as this may result in damage. The same applies to respective alloys such as brass and non-metals.
• Avoid contact with materials containing plasticizers, such as PVC.
• Elastomer seals of various types (such as material or colour) should be stored separately.
Inspection after storage
Generally, elastomer products should be checked to ensure their proper condition prior to installation. Negative changes due to improper storage can usually be detected by visual inspection. The main characteristics discernible in a visual inspection are: dirt deposits, cracks, hardening, softening, stickiness or discolouration.
Following an inspection of these characteristics, the recommended maximum storage period may be extended. For small elastomer seals, due to the greater surface-to-volume ratio and the resulting risk of oxidative attack, for example, the inspection cycles should be shortened. Parker’s laboratories offer these examinations as a service to users. Storage ends after installation. As mentioned above, further recommendations can be found in the standards DIN 7716, ISO 2230 and DIN 9088.
Elastomer seals should be cleaned swiftly using a clean cloth and lukewarm water. Exceptions are fabric-reinforced elastomer seals. In this case, avoid contact with water. Gasoline, benzene, turpentine and similar substances are not suitable for use as cleaning fluids.
Finally, elastomer products must not come into contact with sharp-edged or pointed objects such as steel brushes or sanding paper. Drying near radiators is not recommended.
By observing these simple but important recommendations users can ensure that the properties of Parker-manufactured elastomer seals are maintained at the highest level even after prolonged storage and subsequent cleaning. Application engineers are always available to offer advice in case of special or unusual conditions.