Forming
| Joining
| Sealants
| Painting
Forming
Electrogalvanized sheet can be formed in a variety of ways,
from simple bending to complex operations involving combined deep
drawing and stretching.
Although the steel substrate for electroplated sheet has
mechanical properties similar to cold rolled sheet, the
characteristics of the zinc and zinc-iron coatings have
considerable influence on the sheet's performance during forming
operations. For example, the surface finish and relative softness
of pure zinc coatings, compared with uncoated cold rolled steel
sheet, cause differences in frictional behavior in dies. Thus for
optimal forming, it is generally advantageous to use dies that are
harder and smoother for electrogalvanized sheet than those used for
cold rolled sheet. Other forming parameters, such as die clearances
and hold-down forces, also may have to be adjusted. Because the
zinc-iron alloy coating is significantly harder than a pure zinc
coating, there is usually not as much adjustment needed for this
product. In some cases, lubricants that are effective with
uncoated cold rolled sheet of similar metallurgical quality perform
less satisfactorily with electrogalvanized sheet. Therefore, care
must be exercised in choosing forming lubricants.
Joining
Welding
Electrogalvanized sheet can be readily welded by the
resistance, arc and oxyfuel gas welding processes, usually with the
same equipment used to weld the uncoated underlying steel.
Joining and safety precautions are similar to those described for
hot-dip
galvanized sheet. Because of lower surface contact resistance,
the welding parameters must be adjusted for electrogalvanized sheet
to achieve successful resistance welding. Spot welding of
electrogalvanized sheet has been thoroughly developed by the
automotive industry and is being used extensively in assembly
plants.
Electrogalvanized sheet also has two features that allow
consistent spot weldability. First, the exceptionally uniform
coating thickness achieved by electrogalvanizing allows fine tuning
of the welding operation with assurance of good results that can be
reproduced time after time. Second, electrogalvanized sheet users
often specify relatively thin coatings since thinner coatings enhance
electrode life.
Soldering
Electrogalvanized sheet can be readily soldered with many types
of conventional solders and fluxes. Flux residues should be removed
after soldering to prevent corrosive damage to the coating.
Materials and methods similar to those used to solder hot-dip
galvanized sheet can be employed.
Adhesive Bonding
Adhesive bonding is a proven technique that can join steel
effectively to many materials. It can also improve product
design and performance. Electrogalvanized sheet can be
fastened readily by adhesive bonding in the same way and with the
same adhesives as hot-dip
galvanized sheet.
Sealants
Sealants are often used between overlapping areas of steel
sheet to form watertight joints and to achieve superior
environmental durability. Neutral-cure silicone rubber
sealants are recommended for use with electrogalvanized
sheet. These materials need no primer. They are
flexible, non-corrosive and resistant to heat, cold, water and
ultraviolet rays.
Other types of sealants, like butyl rubber and styrene butadiene
rubber, may also be considered for certain applications. For
more information about sealants for specific applications, consult
a sealant manufacturer.
Painting
U. S. Steel Electrogalvanized Sheet can be readily painted to
develop good paint adhesion, high corrosion resistance and a
quality surface finish. Although most experience in painting
U. S. Steel Electrogalvanized Sheet has been with automotive
postpainting systems (after fabrication and assembly), the
technology for coil line prepainting (before fabrication) is well
known (prepainted
coated sheet).
Excellent paintability and corrosion resistance
are achieved by the automotive industry when electrogalvanized
sheet is applied for exposed body panels. Automotive paint
technology is very advanced today, and painting over
metallic-coated steels is very successfully done on a routine
basis.
GALVA-ONE® and GALVA-TWO® are
registered trademarks of United States Steel.
|
