What is CADweld?
Technically, it's called exothermic welding, but the name CADweld is a registered trademark of Erico, which manufactures the product line. On their web site, look on the left for Online Catalogs and then choose "CADweld - Americas".
It's a pretty cool method to weld electrical conductors together. I'm sure it can do a lot more, but the most common use for hams is to weld ground cables to ground rods. For instance, I use #4 stranded copper wire for all my ground connections outside, and have 10 ground rods in my grounding system so far. Most of those rods are literally welded to the ground wire using CADweld.
Here is a sample weld, which was later buried in my yard:
Why Would I Use It?
The traditional method of doing ground rods is pretty flaky, often isn't done right, and requires frequent inspections and touch-ups. The ground rods normally stick out above the ground, and use compression connectors to squeeze the ground wire for a "good" joint. Can you say "corrosion?" That exposed connection WILL deteriorate, no matter how much Penetrox you slop on it. And, since it needs to be inspected, you have to keep the connections above ground. Yuck!
With a couple little kids running around the yard, and with poor soil that needs lots of ground rods, I needed something better. Besides, I want to make QSOs, not spend time checking/cleaning ground connections. Enter exothermic welding.
CADweld basically melts a metal around the joint where the ground rod and wire meet. It's a molecular bond, which means no corrosion between the wire and rod. It's a solid joint, a blob of metal. All of my ground rods are buried, so there is nothing to see except from the base of the tower to where the wires go under ground. The copper will rot before the CADweld connection fails.
What Do I Need?
First, there are two basic groups of these things: one-shot and re-usable. Their names describe them well. I have the most experience with one-shot molds.
No matter what type you use, you'll always use some sort of mold (either ceramic or graphite), a "shot" (some sort of powdered metal) an ignitor (a fine powder that burns like crazy) and a flint igniter (to ignite the whole thing).
Here's the best part... you get the mold set up, pour in the shot, and then ignite it... WHOOOSH! A flame shoots out for about 1/2 second, then inside the mold it'll glow bright red as the molten metal forms around the wire/rod. It takes only about 10 to 15 seconds for a solid weld, but the mold will be brutally hot for quite a while.
This consists of a kit to do one weld. Included in the small cardboard box are the mold, the mold top, the metal thingy, and the shot. If you look at the picture below, you'll see a typical one-shot mold. The mold is in the upper right. The metal disc goes into the bottom of the mold, then the shot (the powdery stuff being poured out of the blue container) gets poured on top. Finally, the disc with the hole in the middle goes on top.
I need another picture here. Below is a picture of the XXXX clamp that you'll definitely need to hold the mold in place. The clamp is used to hold the mold in place; you need to buy the appropriate mold for you application. You'll then need one shot per weld. When you're done, the mold and clamp can be re-used, although there is a limited life of the mold.
Here's a picture of the reusable clamp and mold, ready for the shot to be poured in:
After the magic, the mold is released and this is the end result:
Where Can I Get It?
I'm sure there are a number of places that sell it, but I found the R. F. Connection first. They stock the CADweld one-shot molds, and can order other products for you. They've gotten me shots, re-usable molds, etc.
I screwed up a few molds, and had a pretty poor success rate at first. I kept bugging the folks at R. F. Connection until they got me in touch with the experts at Erico. Erico has a few products that I would highly recommend to anyone consideringthis product:
- How to CADWELD, An Easy Connection to Make (videotape)
- CADWELD ONE-SHOT Connections (videotape)
- Booklet: Installers and Inspectors Guide for CADweld Electrical Connections
- Booklet: Contractor Tips for the Use of CADweld Products
Contact a dealer or Erico for pricing on these. I had fouled up a number of one-shots before getting this material, then had a 100% success rate after looking at the data.
Reusable molds are expensive (about $90 each) and you need the XXXX clamp (shown above, another $40). Keep in mind that molds don't last forever, so you might get 50 welds from one. Assuming you get 40 welds and each shot is $3 (about right), that's about $6.25 per weld. One-shots are $7-$9 each, so this still works nicely.
For one-shot molds, there is a rubber gasket on the bottom that fits around the ground rod. If your ground wires are pulling up on the mold, it'll be a disaster. The molten metal will cause the rubber to pull away from the mold, and it'll ignite. Molten metal pours out the bottom, setting almost anything on fire. When I did my rods, they were all down in holes so the whole thing could be under ground. This really was a case of "fire in the hole!"
So, make sure the mold is pressing down on the ground rod. Easy to do with little effort. This makes every weld a perfect one.
Use an Erico flint igniter. There's a long explanation for why, but trust me, it does work better than a torch.
Storage, Handling, Etc
The boxes with the shots and one-shot molds are marked which end has to be kept up. Pay attention to that! If you toss them around, the igniter material will mix with the shot and won't light.
Keep them in a dry place for obvious reasons.
It Won't Ignite!
My biggest problem, but it was easy to solve with a few steps. First, when you dump out the shot, the igniter at the bottom probably won't come out. I use a little screwdriver to just scrape loose the material, and then pour it out.
If you're using a reusable mold, make sure you put some of the igniter on the lip of the mold. Get that started and the rest of the shot will ignite without a problem.