thermite welding video

Date 05-16-2008 18:49

http://www.youtube.com/watch?v=nR6K90cR8Lg

I found this interesting video on thermite welding. I had an educational inspection job performing visual and UT of rail welds. It lasted about 6 months and i ended up walking about 100 miles over that time frame going from weld to weld. If you have never been around this type of welding it's unlike any other. It is more of a cast weld. Making these welds they will line up two rails, leaving a gap between them. next they build a mold around the gap. The job i worked they were using something like a sand mold. In this video they are using something different, it think. You can see a hopper above the weld. this is where the weld metal is put. It is in a powder form. It also has magnesium in it. this brings the powdered metal above it's melting point. It is a violent burning so this properly mixes the weld metal. The hopper that was used on my project had an igniter on it like a blank round. This was loaded and when ready it was struck with a hammer. This started the magnesium burning. Above the joint at the bottom of the hopper there was a special wax like plug that would melt at the desired temp. Allowing the contents of the hopper to pour into the sand mold. It was a very educational job and the UT took a lot of extra procedural work, but was only able to inspect the top flange and web, no btm flange. One draw back was that you are allowed no moisture in the joint prior to welding. My job had a much bigger hopper, about 5-6 hundred pounds. One connection had some moisture that was not removed. The water violently changes from liquid to gas, expanding 300 times it's volume. This was enough to send the hopper about 30 feet straight up. Another interesting piece of equipment they use is a grinder that is on a cart that rides along the rail. It can be adjusted up and down, at any angle forward and back, and any angle left and right. All running off of gears the operator can manipulate. You can see one of these in the video at about 3:03 going by in the back ground.

By aevald

Date 05-16-2008 19:45

Hello Hogan, a number of years ago one of our students ended up going to work for Burlington Northern Railroad as a track welder. He made arrangements for our summer class to take a field trip to see them perform some Thermite welds on the tracks near our college. Their process looked considerably different from the one that you attached from U-tube. As I recall they had a special friction saw that would clamp onto the rail and remove a 1" section from between the two pieces. Then they would apply specially formed ceramic molds to shape the weld and pack any cracks with some sort of clay, it may have also had some sort of clamp to hold the pieces in place, but I can't remember. Finally they would fill the mold cavity with the thermite mixture and in this case they would light a fireworks type sparkler and use that to ignite the whole thing. When all the action had ceased they would use sledge hammers to break the molds off of the weld area and then use one of the grinders that you commented on that would ride the rail to grind the proper profile and blend the weld to the top of the rail. I believe they also did a small amount of grinding on the sides of the top rail but not anywhere else. All of their equipment was operated with a portable hydraulic power pack. Great video, thanks for sharing. Best regards, Allan

By hotrodtodd (**)

Date 05-17-2008 05:53

yes aevald you are pretty close I was a welder for BNSF for 6 years till got hurt on job I was the thermite and electric welder. its a pretty involved process there are 2 manufacturers so there are some differences both use special clay molds shaped to fit the size of rail and has the contour preheat rail ends with monster propane rosebud then light the mixture off, when the molten metal reaches over 3200 degrees it will tap through a special plug and pour into the molds, 3 minutes after it pours you break the molds down and start rough grinding it leaving a small peak so when it cools it wont be low any questions ill answer any I can it is amazing to watch great to do in the winter horrible to do in the summer it is a very hot job ive literally melted dozens of faceshields off while preheating railends

By aevald

Date 05-17-2008 06:11

Hello hotrodtodd, thanks for commenting and clarifying, it's been a number of years since I had seen this, I didn't remember the preheating or the chamber with the tap, yet I have no doubt that it was exactly as you have described. Certainly a process that stands all by itself in the welding world. Possibly the only thing that comes close to the sparks and sounds and such of this process is one that was on a slightly larger scale that I witnessed at Oregon Steel Mills when they would melt down a new batch of material to cast their ingots. They had a crucible that would hold about 40 tons of material, I believe, and they would insert an anode into it and stir it in a circular fashion while they applied the current to it. It would melt the entire 40 tons in something like a few minutes. That was one that would make some thunder and sparks. Thanks for the reply and if you get a chance to describe the process in more detail I'm sure others would like to hear about it as well. Best regards, Allan

By jrw159