Helsinki tram maintenance? (may be curve-specific)

Explanation needed - I am a railfan visiting Helsinki and as luck (your choice) would have it, I am staying in a second-floor apartment along the #7 tram line, where it goes around a corner. The track is set into cobblestone. For the past two nights, starting at 11pm, the following has happened. I can´t leave my kids alone, and my Finnish is just bad enough that I probably wouldn`t be able to find out by asking, so I thought I'd post here.

Just as tram service ends, a truck which contains a generator (I think) pulls up and two guys get out with two stools and three pieces of equipment
1. a grinding machine
2. a machine which sits in the gauge and has a spool of wire in the front, what looks like a vacuum on one side. and a funnel on the other. attached by double cables to the truck
3. a third machine I haven't stayed up late enough to see what they're doing with.

Step one: They weld a shoe to the rail on the inside of the curve. The shoe is connected to a cable which runs into the truck.
I'm guessing this grounds the rail.

Step two: They take the grinding machine and appear to grind out the flange between the running rail and the guard rail (I'm guessing this because of what happens next) from the tangent through the curve into the next tangent.

Step three: They pour a white powder into buckets which they line up along the side of the track.

Step four: They take machine #2 and run it along the ground-out portion of the rail. pouring the powder from the bucket into the funnel, which appears to dispense it into the flange, I am guessing on top of wire which it is also dispensing. The machine appears to be welding the wire into the flange because there is arcing and the rail appears to be glowing orange (unless that's some laser device for calibration). They sit on the stools on either side of the rail and one guy vacuums up the powder, and the other guy appears to be picking out excess pieces of fused something or other. When they have finished the process, they repeat it. After last night, I don't see any evidence of their work, and I don't think it would be fair to my family to inflict myself on them after an all-nighter of maintenance-of-way supervision.

They're on the third go 'round of this process - would anybody be able to tell me what this is, and particularly what the white substance is? A woman walking her dog stopped to look, and the men working did not shoo the dog away, so it can't be that toxic, but what is it?

Thanks - by the way, the tram is very efficient, and the curves are very quiet, so my first guess was that they would be laying rubber or some kind of lubricant ...

That may be a location-specific operation, a definitive answer to only be found with that transit operator. I would cold call their customer relations office and ask them if it might be possible to speak with someone in English about this process. I have found that English is spoken world-wide now, so chances are that someone there who knows what this is that speaks English may be able to help you. If that doesn't work, just walk into their headquarters, pick a door, and ask. Either way, your chances of getting an answer are pretty good, especially if you do both.

It sounds to me like the white powder would be a flux of some sort, in order to perform either Thermite or Submerged Arc welding to join rails or build up a flange section. Both should have articles on Wikipedia for you to explore.

Shame, too - I took a railroad engineering class whose professor was Finnish, and it even involved a trip to Finland. He'd be conversant in rail maintenance as well as the language. If I knew he was in Helsinki, I'd send you his contact information, but he's probably teaching in Michigan right now.

Thanks very much - from the Wikipedia articles, it appears that they are doing submerged arc welding, which explains not only the powder but the spool of wire, and why they have to grind before and after the welding.