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Letter 6056
Galvanealed VS. Hot dip
galvanized
.
Hello ,
Can anyone tell me the difference between a hot dip galvanize
steel from a galvanealed steel? Thanks.
Most likely, which is cheaper? can they both be powder coated?
Sharon S 
- Billerica, Massachusetts
First of two simultaneous responses-- .
Hot dipped galvanized steel is produced by immersing steel into a
bath of molten zinc, resulting in the formation of a pure zinc
coating on the steel surface. "Galvanneal" refers to steel with a
zinc-iron alloy coating. This is produced by heating a hot dipped
galvanized surface so that the zinc coating and the top layer of the
steel surface essentially meld together to form a zinc-iron alloy.
Galvanneal would most likely be more expensive because of the
additional processing. Either surface can be powder coated but you
should consult the powder coating manufacturer to determine what type
of pretreatment is required.
Patrick Patton
- Westlake, OH
Second of two simultaneous responses-- .
1. Both processes involve coating the object with molten Zinc in a
batch or continuous process. The main difference is that with the
Galvannealed steel, the object is then post-processed by heating in
an oven to induce diffusion alloying, creating the characteristic
Zinc-Iron (6-15%) coating. See ASTM
A653 [link is to spec at TechStreet],
A924 [link is to spec at TechStreet], and
A902 [link is to spec at TechStreet].
2. Expect the Galvannealed steel price to reflect the cost of the
extra processing (heat treatment).
3. Both can be effectively powder coated. Check with the steel and
powder coating vendors and reference ASTM
D2092 [link is to spec at TechStreet] for the most
effective surface preparation techniques.
Ted Bellinger
- Merrifield, VA, USA
+
Sharon,
I'm a metallurgical engineer working in a galvanizing plant and I
have to admit that Patrick and Ted answered your question very well.
Just to add a few details of my own, a galvanneal steel has better
paintability and weldability than galvanized steel. However it is
less resistant to corrosion since the coating is lighter and not as
adhesive to steel (because of the diffusion of iron in the zinc
coating).
Luc LeBlanc
galvanizing company - Windsor, ON, Canada
++++++
Dear Sir,
Kindly clarify as to what percentage extent is paintability and
weldability increased with galvanealed process compared to galvanised
sheet, and point out the technical differences of galvanealed to this
time electro-galvanised metal sheet.
Thank you for your assistance
Warm regards,
JOOMRATEE Yasseen
- Mauritius
+++++++
Hello, Joomratee. I've seen television commercials promising that
some cosmetic or other will "reduce the appearance of fine lines by
78 percent" and I chuckle that it is silly to try to rigorously
quantify such an obviously qualitative parameter.
Galvanneal is meant to be painted; galvanized is meant to be left
unpainted (although it is possible to successfully paint if the
chromic acid treatment is omitted) -- and I think that's the whole
answer. To ask by what percentage it's more paintable, forces us to
ask you whether you mean primary adhesion, secondary adhesion, or
something else, and exactly what pretreatments and final rinses you
will allow on each type of surface, etc., and exactly what formula
you want us to use to correlate all this disparate data into a single
index.
I guess my answer is that galvannealling improves paintability by
78 percent :-)
The zinc thickness of electrogalvanized sheet is far more
controllable than the thickness of hot dip galvanized, but it is
usual for the thickness to be far less -- perhaps 1/10 the thickness
of hot dipping. Patient application of the search engine will reveal
dozens of threads about that subject on this site. Good luck.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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