Dealing with Zinc


information from Wikipaedia

Metal fume fever, also known as brass founders' ague, brass shakes,[1] zinc shakes, galvie flu, metal dust fever, or Monday morning fever, is an illness primarily caused by exposure to certain fumes. Workers breathe in fumes from chemicals such as zinc oxide (ZnO) or magnesium oxide (MgO), which are themselves created by heating or welding certain metals, particularly galvanized steel. Other common sources are fuming silver, gold, platinum, chromium (from stainless steel), nickel, arsenic, manganese, beryllium, cadmium, cobalt, copper, lead, selenium. and zinc.

Welders are commonly exposed to the substances that cause metal fume fever from the base metal, plating, or filler. Brazing and soldering (a type of metal work in which only the filler is melted) can also cause metal poisoning from lead, zinc, copper, or cadmium in the filler metal. In extreme cases, cadmium[6] (present in some older silver solder alloys) can cause loss of consciousness within a matter of minutes.

Prevention

Prevention of metal fume fever in workers who are at potential risk (such as welders) involves avoidance of direct contact with potentially toxic fumes, improved engineering controls (exhaust ventilation systems), personal protective equipment (respirators), and education of workers regarding the features of the syndrome itself and proactive measures to prevent its development.

Particularly for cadmium, the design of the product may be changed so as to eliminate it. NiCd rechargeable batteries are being replaced by NiMH. These contain other toxic metals, such as chromium, vanadium and cerium. Cadmium plating is replaced with zinc or nickel. Silver solder alloys now rarely contain it.

Removal

There are at least two basic methods for removing zinc from galvanized steel

  1. physical
  2. chemical

Physical methods primarily involve grinding of some sort. Caution, when grinding galvanized steel wear a respirator. In my own case I use a knotted wire wheel to clean up the pipe I use. The knotted wire wheel is a lot tougher than the more common crimped wire wheel. I use a pair of leather gloves even though I've been taught not to use gloves around grounders, etc. that can grab the glove and pull you hand in. In one class I was using a disc grinder and had a pair of gloves on. The sander pulled my thumb down between the disc and the table flatteniing it more than I thought possible. While the glove caused the accident, it also protected my hand from any damage beyond the flattening which reinflated over the next couple of hours. With wire wheels, the glove protects me from occassional "touches" against the wheel. My basic aim is to get the zinc off before I powdercoat the pieces, knowing that the zinc otherwise would come off at least partially as a gas which would ruin the finish. At times I use a out gas forgiving undercoat and then apply a second transparent coat over top, even if I've already cleaned the zinc off.


Crimped Wire Wheel

Knotted Wire Wheel

Chemical removal basically relies on acids to strip the zinc from the underlying steel. A variety of acids are used ranging from vinegar to muriatic and hydrochloric acid. Personally I'm scared to death of muriatic and/or hydrochloric acids. The phobia probably goes back to high school chemistry where even thinking of using hydrochloric was a NO-NO. Even though I have a gallon jug of muriatic acid for use in my pool I still get spooked with the warnings not to put it in either a glass or metal container.

Two methods that I have used involve:

I've used both 20% and 30% vinegar (regular grocery store vinegar is only 5%) by basically putting the part to be degalvanized into plastic container and cover with vinegar then sealing the container. Usually I just let it go and come back the next day. To speed things up you can try heating the vinegar a little (i.e., solar) and/or adding some salt. Since my workshop is outside, our desert climate supplies sufficient heat.

I bought some citric acid in powder form (100% citric acid, food grade), disolved it in some water, and immersed the part in it. The next day the zinc was gone.




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