Uncured compound contains curatives and keeps reacting slowly even when idle. Finished parts age more slowly but they do age. Good storage extends shelf life and protects consistency.
Uncured compound and gum
- Keep it cool. Heat shortens scorch time and shelf life. Stable cool storage is better than a hot warehouse. Specific limits depend on the compound, and peroxide-containing compounds are the most sensitive, so follow the supplier's instructions.
- Keep it clean and dry. Moisture causes porosity and variable cure. Keep sheets and slabs covered and off the floor.
- Avoid contamination. Separate compounds of different polymers and cure systems. Peroxide and bisphenol compounds must not be mixed up, and dust from one on another can cause trouble.
- First in, first out. Record the date of manufacture and use the oldest lot first.
- Do not leave it near heat sources such as ovens, hot pipes and sunlit windows.
- Test before use if it is old. Run a cure curve on stock past its stated age and compare it with the original.
Raw materials
Peroxides, coagents, silanes and some fillers are sensitive to heat and moisture. Store them in their original packs, in the conditions on the safety data sheet. Peroxides are hazardous and must be kept away from acids, amines and reducing agents.
Finished parts
ISO 2230 gives guidance on storing vulcanised rubber products. In summary: cool, dark, dry and clean surroundings, away from ozone sources such as electric motors and arc equipment, kept free from stress or deformation, and away from oils, solvents and contact with metals such as copper that can attack rubber.
Shelf life
Shelf life depends on polymer, cure system and storage. Fluoro-rubber parts and many cured HNBR parts keep for years in good storage, but your customer's specification or the part maker's policy may set a maximum age for use. Record the cure date on the package.
Sources and further reading
- ISO 2230, guidelines for storage of rubber products.