Comments by "ke6gwf - Ben Blackburn" (@ke6gwf) on "" video.
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@A.Lifecraft put your hand through a hole it barely fits through, then spread your fingers out, grab a tennis ball, and duct tape your fingers around it, and then try to pull your hand back through the hole. It won't go lol
There are styles of wedge sockets where the tension simply pulls a wedge in tighter, often used to terminate crane cables because it's easily removable, but the poured style are the ultimate termination for a cable.
The cable wires are splayed out to evenly fill the cone of the socket, and then they are mechanically and chemically cleaned.
The metal, zinc, or a zinc based alloy is then poured in, and it's like soldering or brazing to each individual wire strand.
So there is no way for it to loosen around the wires or corrode inside the metal plug, any more than a proper solder joint will loosen around the wires. It tins the metal and forms a metallurgical bond, actually forming an alloy layer of a combination of the base metal and the solder metal. This is in addition to any mechanical or adhesion bonds.
So the zinc is held to the base metal with as much force as its held to itself, as long as the formulation is correct to be able to wet the base metal.
So now, we have a tapered plug of solid metal bonded to thousands of wires inside.
When you apply tension to it, the taper wedges it deeper into the socket, which compresses the plug of metal, squeezing down on the wires inside it.
Since the potting metal is a little bit soft, it does compress the tighter it is pulled on, creating a very tight wedging action on the cable strands.
As long as it is done properly, you can't get corrosion inside the plug, and the wires can never slip out.
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@A.Lifecraft you seem to think that because you "studied physics" that you are smarter than 100 years plus of engineers and scientists and and end users finding every possible way to make one of these terminations fail.
There are only two ways to terminate a wire rope where the termination is stronger than the rope itself, and doesn't derate the cable due to bending it etc.
You 100%of the cable strength with pressure swaged ferrules and fittings, and with Spelter poured ends like this (using either a special epoxy or zinc/white metal/Babbitt metal, etc).
Since hydraulic ferrule presses are a newer invention, and a major investment, Spelter sockets are one of the most common methods to terminate cables, including bridges, crane support cables, rigging slings, barge tow lines, etc, and it's been that way for a very long time.
Tug boats will carry the stuff on board so if one of their giant tow lines gets damaged, they can easily cut off the bad end and put the Spelter socket back on the end.
They have been extensively tested and studied, by people with actual degrees, and the physics of how they work are well understood.
I went to Crosby and did some reading on their research, and I was wrong on one point.
It's almost entirely the wedging action of the tapered zinc or epoxy plug that holds the cable in.
Using epoxy for instance, when it cures you have two forces acting on the wires, adhesion and friction.
They found that either the adhesion or the friction by itself was adequate to seat the plug and create enough wedging action to break the cable.
However, if the plug didn't seat, the adhesion was not enough to hold the wires in, so these fittings are always proof tested after installation to ensure it seats the plug.
So they found that even if the wires were oiled so it would seem that they could slip out easily, there was still enough friction to pull the wedge in and exceed the breaking strength of the cable.
And that's the key point of this termination method, it holds the cable securely enough that the cable will break before it pulls out of the potting material, because of the wedge shape squeezing tighter the more load you add to it.
You also seem to think that zinc is a lubricant, which makes me wonder if you understood how Babbitt bearings worked, and I also suspect that the bearings you referred to are actually Babbitt metal, which is tin based, and not zinc.
Babbitt works by having hard crystals in a soft matrix, providing a low coefficient of friction when used with a polished harder shaft.
And it requires oil to make that happen.
If you run steel directly on babbitt, or zinc, it will tear it up, because it's not a lubricant.
And crimped wire rope wires are not a smooth surface, and so will not easily slide out of metal poured around it.
The fact that it has held for 30 years indicates that it was a proper joint, or it would have failed when originally loaded.
Also, the fact it failed after 30 years points to the likelihood of corrosion outside the potted section, which is a known and likely issue.
So instead of saying that one of the best and most thoroughly tested cable termination methods is a bad idea, maybe we wait for more data on the actual failure.
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@A.Lifecraft it sounds like maybe you have also heard of trapping monkeys by putting chunks of salt etc into bulb shaped holes? Lol
The reasons that they don't just solder the wires around the edges is, 1, you would be relying entirely on the shear strength of the solder to hold the load, and 2, the cables are giant, and you would have to have a very large ring to be able to terminate every strand to the anchor ring.
Instead, the cable end is simply expanded, like the sticks on a witches broom, and unlike my analogy with your hand, the center is also full of strands, all evenly spaced apart.
So basically you are forming the end of the cable into a wedge shape, and then filling it in with the potting metal to hold that shape.
It doesn't rely on the sheer strength of the metal, which is why it's a tapered shape, so that the tension increases the gripping force on the wires much like a wedge and socket, but it's even stronger, because instead of simply using friction to hold the wires, it also uses the intermetallic bonds to make the wires become part of the wedge.
In addition, and very important for such a large cable, it evenly distributes the load across all the strands and compresses them all evenly.
In a wedge socket design, the friction is only on the outer strands, and it loads the core unevenly, while relying on bends in the cable to transfer force, leading to high stress points, cable, bundle, and strand deformation, and thus loss of strength.
This method protects each strand, does not require any bending or deformation, and equalizes the compression forces and friction and actual metallic bonds across all the wires.
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