The forge I made many years ago and is folded up from 3 mm plate with the nozzle which is water cooled is made out of 2 pieces of thick wall tube , one inside the other with a thick washer at the fire end .
The fan is off an old Alldays and Onions forge which is long gone , I control the speed through a rheostat .
It was made to be light enough to be portable and when I was doing riverting on traction engine boilers it did sterling service .
The nozzle has lasted as long as a cast iron one and is easily fabricated at a fraction of the cost