Shelf life depends on how stored - it can be doubled or tripled or destroyed in a short time.
Carlisle belts made by Timken has this on their website:
With proper storage, normal shelf life is seven years. The quality of a Carlisle belt is not considered to change significantly within seven years when stored properly under normal conditions. Normal conditions can be defined as temperature below 85°F and relative humidity of 70% or less with no exposure to direct sunlight. Beyond seven years, assuming normal storage, a decrease in service life of approximately 10% per year can be expected. For belts not stored under “normal” conditions, the actual reduction in shelf life is difficult to measure due to lack of precise data and number of variables involved. When belts are stored under abnormal conditions, conservatism is recommended in estimating shelf life.
Simply put; stored in a sealed container devoid of oxygen in a cool dry place shielded from direct sunlight and ultraviolet light, the belt may be useful for 15 years or more, but it's 'in service' life will be shortened after appx 10% per each year over 7 years. So a belt over 17 years old may fail immediately upon installation, but I have seen belts on farm machinery (stored outdoors and only used seasonally) over 20 years old and still in service. A belt stored laying on a picnic table in an unshaded yard exposed to the ravages of weather or in a closed building with numerous electric motors (ozone generators), it may be unusable within a year or two. The service and shelf life will vary with the materials and construction of the specific belt.
Heat, sunlight, certain chemicals and gases will decrease the life of belt. A few belt specific dressing compounds may extend the life of a belt by a short time (extra year or two), but some products sold as belt dressing can decrease the life of a belt. Belt dressing products should only be used to get a last use out of a worn out belt.
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