Last week in the hot humid weather we had I had occasion to case harden a couple of gudgeon pins for a veteran Triumph motorcycle. I have never had problems with corrosion in my workshop up till this point.
Once the pins had been soaked for a few hours at 900 degrees Celsius I opened the furnace door to remove them from the pot containing the case hardening compound, then I returned them to the furnace to bring them back up to temperature before qrenching them. This was done with the door open at one end of the workshop.
The next day when I went into the workshop I was greeted with all steel and iron surfaces coated in a layer of rust, All of the TTS nooling for the Tormach Mill had rust on the mandrels that are gripped in the spindle were affected. I spent the whole morning carefully removing the rust with very fine wet or dry paper and giving them all a smear of oil.
I found that the closer to the section of the workshop that houses the furnace the worse the rust coating. I can only assume that this has happened as a result of the very high humidity, lack of air circulation (there was not wind whatsoever on the day) and the fumes from the case hardening compound.
Once bitten, Twice Shy I resolved to not having this happen again so yesterday I ordered a 14" industrial extractor fan. It arrived this morning and I chain drilled a hole in the brickwork for it, knocked out the bricks so that I could fit the fan, fitted it and wired it up.
The neighbours aren't going to like it one bit, it's really noisy but boy does it shift some air. You can feel the draught coming through the curtain doors, hopefully from now on when I use the furnace I won't have a future recurrence of the corrosion.
The fumes from the case hardening compound must be very acidic because even some brass pipe fittings on my model aircraft engine turned a copper colour, as though the zinc near the surface had been eaten away leaving them looking more like copper than brass.