Replacing Hot-Melt Flooding Compound in a Copper Pair Cable

Twenty-five pairs, 1.4 grams of flooding compound per metre in the core, and a drip test at 80 degrees Celsius for four hours with no more than a defined bead at the lower end. The weight is the easy part of the specification. The drip test is the one that decides whether a substitute is acceptable, because hot-melt compound passes it simply by being a solid at service temperature. A water-absorbing powder has to be persuaded to do the same job with a completely different mechanism.

The substitution is being pushed by cost and by process. Hot-melt requires a heated pressure pot, a heated die and a cleaning routine that consumes a shift every week. Powder needs a dosing unit and a dust extractor. Whether the swap works depends on which failure you are willing to manage.

What the compound does that powder must copy

Three functions, in order. It fills the interstices between insulated conductors so water cannot travel longitudinally. It stays where it is put at 80 degrees, which rules out anything that flows under its own weight in a hot cabinet. And it does not migrate into the splice closure or creep along the conductor during thermal cycling, because a compound that reaches a connector turns a repair into a re-termination.

Powder handles the first function well and the second by a different route: it does not flow because it is a solid granule, and it only becomes a gel when water arrives. That is an advantage in service and a problem in the filling head, where a granule that does not flow will bridge.

Powder, yarn or tape

Three ways to put super absorbent into a cable, and they are not interchangeable. Powder blown into the core is the cheapest per metre and the hardest to control. Water-blocking yarn wrapped around the bundle is easier to place, adds volume, and works well in small pair counts. Tape is the most consistent and the most expensive, and it is what most fibre designs use.

Where the swap fails

The gap size decides everything. A 25-pair core has interstitial channels around 0.3 to 0.5 mm wide, and a granule that has been screened to 30/60 mesh has a mean size near 0.4 mm. It will sit on top of a channel rather than enter it, and the water test finds a path through the gaps in under a minute. The fix is a finer cut, 100/200 mesh, which enters the channel but then dusts, bridges in the nozzle and coats the workshop.

One plant solved it by switching to a 60/100 cut and adding a vibratory feeder with a 2 mm screen ahead of the dosing head, which removed the agglomerates that were causing the bridging. The first attempt, without the screen, stopped the line every ninety minutes and the trial was abandoned after two days. The powder was not the problem; the feeding was.

The other failure is thermal. A powder that has absorbed moisture in the hopper will form a crust on the die face at 90 degrees, and the crust breaks off in flakes that end up under the sheath. Dry air over the hopper, a hopper level that never runs below 20 percent, and a daily purge are the three habits that keep this from happening.

Before committing a line, run a 500 m trial with the actual cut, the actual die temperature, and a water penetration test on the finished cable rather than on a sample of powder. The water blocking granule grades page lists the mesh cuts used in cable work. A gram per metre figure means nothing if the granule never reaches the channel it was meant to block.