In the world of cable making, nothing lasts forever—especially potting compounds. This article serves as a quick PSA to remind you that the compounds you rely on for creating splices have a shelf life, and they come with specific storage requirements.
Creating a splice typically involves a few hours of preparation: soldering all the cores, preparing the mould, and finally pouring in the compound. After that, the splice is left to cure overnight. Altogether, the process can take upwards of a day. The last thing anyone wants after investing all that time is to end up with a failed splice.
Bad potting compound can manifest in a couple of telltale ways:
- Clumping of the resin: This is often evident by hard lumps in the resin, as shown in the left-hand side example.
- Outgassing and crystallization of the hardener: This can cause the bag to expand and the hardener to appear crystalline, as seen in the right-hand side example.
When the resin clumps, it makes mixing the hardener difficult, leading to incomplete mixing. These lumps won’t flow properly in the mould, potentially causing air pockets. On the other hand, outgassing in the hardener is a sign that its effectiveness is compromised, making it unreliable.
Using compounds in these compromised states can result in incomplete curing, leaving the splice sticky, with uncured polyurethane that lingers for weeks and never fully cures.
However, it's not all bad news. In some cases, and with certain compounds, this degradation process can be reversed with the application of mild heat, typically via a water bath. But be cautious—when it comes to cable making, the stakes are high. Consider the potential time and cost of re-splicing, and the impact a cable failure could have once deployed.
To avoid these issues, always store your compounds in a warm, dry place, away from direct sunlight and temperature fluctuations. And if you have any doubts about the condition of the compound before use, it’s wise to open a new bag.