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Message No 42 from welding of Galvanized rebars

 
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inchak at tatasteel.com
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PostPosted: Sat Jul 09, 2005 3:45 am    Post subject: Message No 42 from welding of Galvanized rebars Reply with quote

QUESTION
Dear Mr Chakraborti:
How does one weld galvanised bars in the event of having to do so without
affecting the galvanising?
Regards,
Alpa

ANSWER
Thanks for raising a very important issue.
Galvanized bars are indeed weldable.
An excellent note on welding Galvanized rebars by Dr. Tom Langill,  the
technical director for the American Galvanizers Association is available in
the following URL:
http://www.precast.org/publications/mc/TechArticles/03_Winter_Galvanized_Rebar.htm

I reproduce the relevant part for the ready reference of everybody
QUOTE
"Welding galvanized steel. Welding can be accomplished by either grinding
away the zinc coating and directly welding the base metal, or by welding
through the galvanized coating. Materials that have been galvanized may be
welded easily by all common welding techniques. In general, anything that
can be welded before galvanizing can be welded after galvanizing, but some
minor changes to the welding technique need to be incorporated to ensure
full weld penetration. These changes are primarily intended to allow the
galvanized coating to burn off at the front of the weld pool.

For normal flat welds on galvanized steel, the welding current can remain
the same as on bare steel, but for fillet welds, the current may need to be
increased about 10 amps. Butt welds may require a slightly wider gap since
the penetration of the weld for galvanized steel is less than for uncoated
steel. Travel speeds on the root pass should be reduced by 10 percent to 20
percent, and the electrode drag angle should be increased. All these items
are intended to increase the weld penetration and to stabilize the arc that
can be disturbed by the evolving zinc vapor.

When galvanized steel is welded, fumes of zinc oxide are produced. If
inhaled in sufficient quantity, the fumes can result in "metal fume fever"
or "zinc chills." In severe cases, vomiting can occur. These flu-like
symptoms are of short duration and typically pass within a 24-hour period.
Adequate ventilation or fume extraction should be used and the welder's
head should never be in the plume. If adequate ventilation is not possible,
the welder should be fitted with a respirator. "
UNQUOTE

Trust this answers your question


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