PeachParts Mercedes-Benz Forum - View Single Post

jay_bob · #5 04-04-2016, 01:33 PM

I have looked at the assembly plant videos on YT and based on what I have seen and my experience with the industry at that time...

I think the 124 was assembled from mild steel and then the entire body was dipped in zinc primer. The first gen 124s were painted with traditional "wet" solvent based enamel without clear coat. I think they added clear coat to the later 124s since I have seen later 124s with clear coat that is totally shot.

I think the 210 was assembled from steel that was galvanized at the mill and then welded. Then they did a primer dip and then powder painted the body. The clear coat was wet but low VOC. Also they probably changed the formula for the undercoating to lower VOCs as well. I think all these things conspired to decrease the rust resistance of the 210s.

BTW my 210 is totally rust free except where there was a big rock chip in the hood. I got hit in a parking lot and part of the repair involved replacing the hood so now I am rust free again...and this car lived its first 15 years in Maryland.

Reason I suspect this is that in the mid 90s the steel industry figured out how to do continuous galvanizing of steel strip coming off the mill. It is a very complex process. Basically the strip is reheated and then plunged through a vat of molten zinc at around 800 degrees. Then air knives (think a Dyson AirBlade restroom dryer on steroids) blew off the excess coating before it was rolled to a finish thickness.

The problem was that sensor technology at the time would not allow the thickness of the coating to be measured until it was below a couple hundred degrees. This meant that the strip had traveled several hundred feet down line between the vat and sensor. The feedback control algorithms required processing power that was just becoming available in the early 90s. They used a special PLC with 6 CPUs performing parallel processing if I recall correctly.

Unfortunately I did not get to mess with that part of it, my job was to make sure the system got its power source.