It’s been a busy month: DCD Design have created a new how-to video for the Eagle Cable Lasher, demonstrating some of the features and showing you how to load the lashing wire. (This ties in to next month’s promotion. Subscribe to the mailing list and keep an eye out for updates.)
We put this one together on the workbench and outside on our ‘test line’ to show off the lightweight Eagle. Like the larger Lineman lasher, it uses tension from the lashing wire to drive the drum, not traction on the strand. As long as you’re moving forward, you’re spinning!
In other news, we’ve just finished an intensive four-day basic training for Solidworks 3D software. It’s astonishing what this software can do: if you can sketch it on a napkin at lunch, we can create a 3D model by the end of the day! DCD Design have always been progressive when it comes to listening to our customer’s requirements; now we can assess and turn around a new design faster than ever before.
AND! Direct Horizontal Drilling of Edmonton have been setting up for a river crossing in the neighbourhood: a new gas pipeline is going to be pulled under the Fraser River tonight! Good luck and smooth pulling to them.
Watch out for those innerduct pulling eyes – they’ve got sharp teeth!
We were making a short video for the various duct pulling tools last week: wire mesh grips, innerduct pulling eyes, the expanding shell pullers and the sealed “bullet” pullers. I was installing them onto typical pieces of duct to compare the time and methods involved.
Getting a Wire Mesh Grip onto a 1-1/4″ duct took some exertion, and then I picked up a 00604-series Innerduct Pulling Eye and threaded that on. (The tapered threads lead to the “carrot” nickname.) Cranked it on tight in a few seconds, but didn’t notice the sharp teeth imprinting themselves into my palm.
Picked up a 00620 Expanding Shell Puller next; slotted that in and cranked the eye tight to engage the shells– and noticed a few drops on the eye of the puller as I put it down again. Kept going, though; only one more puller…
I realized that my hand was shredded as I was socketing the 00650 Sealed Duct Puller over the end of the duct. The o-ring in the outer sleeve sealed down over the end of the duct and the eye was already smeared red. Turned the eye until the shells engaged the inside wall and gave it a tug to show that it had bit into the duct.
And there it is: four options from DCD Design. Each one has advantages, and one of them is particularly sharp! You can see about three bandages on my hand in this second take, and I make sure to mention gloves as an option.
I was tensile testing a batch of pins this afternoon and as I watched the load cell count up the pounds to fracture, I was reminded why you should never reuse pins that have previously been in service.
Typically, the load cell shows a linear increase as the crosshead applies strain to the sample. This stress vs. strain relation is constant up to a material’s yield point. At that point, the linear relation breaks down and the material enters the final plastic deformation phase. This phase is just like it sounds – the pin is being stretched like taffy and it won’t recover.
Watching the load cell, you can see the force flat-line while the crosshead is still moving – this is the moment before failure. If you were to stop the test right at this point, the plastic deformation would appear as a thinned-down neck in what was once a straight bar – see the photo. The atomic rearrangements at this point get pretty hectic, as dislocations start skipping through the crystal lattice and hanging up on the grain boundaries!
Similarly if you were using this pin in a breakaway connector: you can see the pin has deformed if it’s been loaded near its maximum capacity. But sometimes, the plastic deformation phase is brief and the pin breaks suddenly. It breaks at the expected load but there’s no plateau on the load cell and the necking is hard to spot.
A visual inspection won’t necessarily show a previously stressed pin and once a pin has entered the plastic deformation phase, it will pick up where it left off and continue to fail in short order. It’s better to start a pull with a new breakaway pin than risk the job.
DCD Design provides two Safe Working Load limits for our 00505 Series Line Swivels, depending on whether you’re pulling Underground or Overhead. What’s the difference? RISK.
A Safe or Maximum Working Load without a Safety Factor is incomplete – you don’t know where you stand. One company’s Overhead Swivels may only have a 3:1 Safety Factor, when every other component has been rated 5:1. Where’s the weak link?
When you’re stringing overhead lines, a 5:1 Safe Working Load is typically chosen to suit the safety factors applied to pulling rope and grips. I say “typically” because safety factors and the resulting safe working loads are user-dependent.
Occupational safety requirements are a minimum level of protection. Risk management demands a greater level of protection if a failure will have catastrophic consequences.
You don’t want to see a failure in an overhead job because when things fall down, they land on other things! You can reduce the risk of failure by choosing a larger safety factor, but you’re limiting your maximum load. There has to be a compromise!
Underground, a 3:1 Safe Working Load can typically be applied. A failure is still possible, but the risk of damage or injury is reduced. You can “afford” to increase your maximum load. So the same Line Swivel can have two Safe Working Loads, depending on the application.
If you’re comparing line stringing swivels for overhead use, know the Safety Factors built into your equipment and make sure you’re getting the whole story. DCD Line Swivels have a happy ending.
Inquiries for wire mesh pulling grips come in from all over the place, and it’s interesting to see how local tradition will affect terminology.
The length of a grip depends on where you’re standing. If you’re reading a North American catalog, the length of the mesh is taken at the grip’s nominal diameter. That is: it’s measured when it’s fitted around the cable it’s pulling. This is the engaged length of the grip; the eye and the overall length are measured separately.
Other locales will measure the “free length” of the grip, when it’s hanging on the wall. The free length can be half-again as long as the fitted length, so it’s not a clear indicator by itself of the size of the grip in service. The comparison below shows the difference: a free length of 35″ can contract the mesh to just 21″ when it’s installed.
The wire weave of a pulling grip is flexible, and the grip will contract as the tube diameter increases. Variation of a couple inches in the free length is typical, and the fitted length will vary depending on the actual diameter of the cable.
It’s a fairly regular request we get these days, “I’m wondering if I should service my swivel. What should I look for?”
Servicing the equipment you have is bound to be cheaper than buying new – in most cases! – and we’re seeing a lot of planning ahead this season. Things are tight; no one needs a surprise.
I’ve previously summarized what’s involved in swivel maintenance. This time, I’ve taken advantage of one of these on-line resources to boil it down to a step-by-step instruction on maintaining your Maxi DUB-Swivel.
Forward the link along to your crews so they can take care of their gear; and as always, give us a call or your local DCD distributor if you have any questions.
If you want to get your swivel factory serviced, we can do that too. We have the tools and material to return your swivel to prime condition. We built it; we can rebuild it!
Installation can be rough on a new electrical cable! A pulling winch can apply a few thousand pounds of tension. Bends in the duct can apply crushing sidewall pressure. Even the pulling eyes can chew through the cable jacket and permanently damage the cable ends. Cable manufacturers have a variety of physical limits for different cable constructions (tension, bending radius limits, end connections, etc).
Cable manufacturers limit the pulling force of wire mesh grips to a few hundred pounds for a reason: the wire mesh is gripping on the external plastic jacket of the cable. But you can’t expect the plastic jacket and rubbery insulation to support a structural load!
Typically, cable manufacturers require 10-15 feet of cable be cut away, beyond the end of the wire mesh grip. Why? Because the pulling forces exerted on the outside surface have applied shear forces through the jacket, the insulation and the outer strands of the cable construction – there is no way to ensure that the cable construction has not been damaged or deformed during the pull.
To take advantage of the cable’s maximum pulling tension, you have to get a grip on the conductor itself. The DCD Power-Grip is designed to lock onto the conductor strands and the harder you pull, the tighter your Grip! When you’ve completed your pull, cut away the portion of the cable conductor deformed inside the Power-Grip and that’s it.
Setscrews are used in a number of applications to clamp parts together: end fittings to fiberglass duct rod, fiber optic strength members, and electrical conductors into pulling eyes, for example. They’re a quick, simple and relatively strong connection, so long as you turn the wrench with some care.
Duct rodders can be spliced or ends replaced with new fittings – the setscrews can bite right into the fiberglass core to ensure a solid material interlock, or you can apply a redundant coating of glue.
Another application is our multiplex pulling eyes: three setscrews are used to clamp the free end of the each conductor into a pulling eye, for short, straight pulls of moderate tension.
However, the clamping force developed by the setscrews can’t be considered an exact science. The copper strands will shift as the setscrew descends, moving strands aside to fill the remaining bore space. But they may randomly shift to one side as the screw turns down, or they may not shift and just ovalize the conductor.
Fixed torque values are difficult to define for these somewhat random events! Practically speaking, “as hard as you can” works out to be a fairly comprehensive instruction for the guy turning the wrench.
DCD Design’s Power-Grips and Swivel-Grips are designed to make cable installation easy and secure. The re-useable Grips are sized to fit electrical cable from 1/0 through 2000MCM and really shine for the larger cables, where the pulling tension will approach the cable manufacturer’s allowance.
Assembly of the Power-Grip to the electrical cable is quick and easy: cut back the insulation to bare the conductor; mount the Threaded Cone Nut to suit the conductor size; screw in the Tapered Insert; and mount the preferred attachment Body. You select which Body suits your connections: the Lug, Clevis or Swivel Bodies share common threads to quickly mix and match.
The Power-Grip locks onto the conductor strands and the harder you pull, the tighter your Grip! When you’ve completed your pull, cut away the portion of the cable conductor deformed inside the Power-Grip and that’s it. You’re ready to re-use the Grip for the next conductor.
I responded to a customer inquiry recently that leads us into this month’s sales promotion on breakaway swivels and connectors:
“For your range of gas lines, we have a few breakaway connectors to choose from, with breaking loads from 200lb through 45,000lb.
The 00530 series Min-E-Max connector uses a single pin calibrated for loads up to 675lb. This would be put in series with a swivel.
The 00550 series breakaway swivels are available in three sizes for load ranges up to 2000lb; however, the compact size of these swivels limits the sealing capacity, so – while they do work – they’re not recommended for directional drilling work because mud will infiltrate over time and damage the swivel bearings.
We’ve found that the most flexible solution is a swivel that’s made for HDD, paired with a simple connector with plenty of break-point options. Have a look at the website, locate a distributor or give us a call directly if there’s anything more you need. Thanks!”
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