A zinc layer on steel provides an efficient means of corrosion protection. Just how much protection does it offer, and how can galvanized-sheet formingoperations be optimized?

Think ZincThink ZincA zinc layer on steel provides an efficient means of corrosion protection. Just how much protection does it offer, and how can galvanized-sheet formingoperations be optimized?

Strip cools after exiting the zinc bath in a continous galvinizing line at Gregory Galvanizing & Metal Processing, Inc., Canton, OH.

by Louis A. KrenSenior Editor

The most economical method ofinhibiting corrosion on metal isgalvanizing—the coating of

sheetmetal strip with zinc prior toforming or the immersion of formedparts in a zinc bath. Gregory Galva-nizing & Metal Processing, Inc., Can-ton, OH, has provided pre- andpost-fab galvanizing for more than100 years. Galvannealing is anotherGregory service, where an addition-al furnace is placed in the galvaniz-ing line. Galvannealing offers essen-tially the same corrosion protectionas traditional galvanizing, but isoften specified where improved partpaintability and weldability is de-sired. Gregory also operates a num-ber of rollforming lines to producegalvanized fencing, structural prod-ucts and guardrail (see sidebar).

With such experience, the firm iswell-versed in the capabilities andlimitations of galvanizing. Metal-formers working with galvanizedsheet should be aware of these ca-pabilities and limitations as well. Byknowing what to look for and howto approach forming with galva-nized material, metalformers canproductively create parts that meetcustomer specifications.

Thicker Not Always BetterMost stampers buying galvanized

coil from Gregory specify accordingto automotive specs and really aren’tat all concerned with the galvanizingas long as it meets those auto specs,

22 www.metalforming.com MetalForming/March 2001

says Fred Zalenski, corporate vicepresident of sales and marketing forGregory. Typically, coating prob-lems in stamping galvanized sheetinvolve peeling or flaking of the zinccoating.

If stampers or rollformers experi-ence peeling or flaking, Zalenski rec-ommends that they use the lightestcoating allowed by the specification.

“Often someone will specify anA60 coating on the sheet we supplythem,” explains Zalenski. “That’s apretty thick coating, so we try to findout what the application is, and de-cide if the specification will allow anA40 coating. In that case, we’ll rec-ommend the lighter coating. Coatingwith A60 really doesn’t bring signifi-cant additional noncorrosive proper-ties as compared to A40, but thesheet will more likely peel with thatA60 thickness. During stamping orrollforming, the more brittle A60coating may flake as it runs throughthe dies.”

The use of thicker zinc coatingalso may lead to flaking or bendingat areas of severe bends.

“In such cases, we try to directmetalformers toward a lighter coat-ing,” continues Zalenski, explainingthe Gregory response to such aproblem. “Again, whatever youmight gain in terms of greater non-

corrosive protection on an A60 coat-ing can be negated by the increasedlikelihood of peeling and flaking.”

In automotive stamping, notesCurt Shaffer, Gregory plant manager,a minimum and maximum coatingthickness is specified. Adhering tothe minimum thickness spec canforestall problems resulting frommaterial being too heavy or thick forthe dies. Proper lubrication duringforming and punching operationswill reduce tool wear and heat,which can cause galling on galva-nized sheet.

Too Much Iron, Too Much BuildupPeeling and flaking can be caused

by the iron content of the zinc coat-ing itself. If the iron content of thecoating exceeds one percent, peel-ing may occur no matter what thecoating thickness. Therefore, galva-nizers should keep iron content intheir zinc coating below one percent.

Even without significant peelingand flaking of the galvanized surfaceoff of steel sheet, over time, zinc canbuild up on equipment.

“We do get some zinc buildup onthe rolls,” says Shaffer, describinghow the Gregory rollforming opera-tions work with galvanized sheet.“Here, we apply mainly heavy coat-ings, usually in the 4 oz./ft.2 range,whereas most rollformers work withthinner coatings. So we do get atremendous amount of buildup fromflaking. This is not detrimental to theproduct, but zinc does build up justbelow the rolls, so we have to cleanout the equipment a bit more oftenthan most rollformers do.”

Longer Tool LifeBecause Gregory rollforms heavy-

gauge galvanized steel to produceguardrail and fence material, tool lifeis a real concern. One marked bene-fit to stamping or rollforming withgalvanized sheet is that the relativelysoft coating reduces tooling wear.

“Galvanized coating definitelyhelps extend tooling life,” says Shaf-fer. “When working with the blacksubstrate, it acts as sandpaper towear and dull tooling quickly.”

Galvanized strip enters an accumulator after exiting the zinc bath. An overhead crane can place a furnace above the bath, providing customers of Gregory Galvanizing with galvannealed product.

Galvanized steel is an ideal material for the production of outdoor products.Gregory Galvanizing rollforms and punches guardrail in-house.

March 2001/MetalForming www.metalforming.com 23

Shaffer says inline punches lastthree to six months without sharpen-ing—longer than they would if usedon nongalvanized sheet. The savingsin tool life relating to using galva-nized material more than makes upfor the time required to remove ex-cess zinc.

Mind Your ToolingSome other problems in forming

galvanized sheet may have to dowith the tooling itself.

“Sometimes, problems result notfrom the lack of adherence of thezinc to the steel, but with improperinstallation of the tooling sets usedin rollforming and stamping,” saysZalenski. “For example, a customercame to us with a problem with flak-ing. It turns out the tooling was setup improperly and improperly tight-ened down. This basically causedgalling on the sheet and flaked offthe zinc. Slight errors in toolingsetup may have no effect whenworking with uncoated sheet, butcan mechanically remove zinc whenrunning galvanized sheet.”

Gregory Galvanizing and Metal Processing, Inc., Canton, OH,provides sheet galvanizing and galvannealing services to

metalformers and also operates five rollforming lines.The company is split according to capabilities. The Coil

Group manufactures slit, galvanized coil sold to automotivestampers, sold for use in tubing or stud applications or used inthe company’s rollforming operations. The Manufactured Products Group produces structural products, fencing and highway products such as guardrail.

Gregory operates two plants in Canton, OH, its headquartersand main manufacturing facility, which houses the galvaniz-ing/galvannealing line, slitters, a cut-to-length line and rollform-ing lines, and another facility that provides post-fabrication galvanizing.

Prior to galvanizing, master coils may undergo slitting in ei-ther a 36-in or a 72-in. slitter. Gregory’s cut-to-length line yieldssheet in lengths from 2 to 16 ft.

A zinc coating is applied to steel coil via a continuous hot-dip galvanizing line with in-line pickling, an atypical feature, accord-

ing to Gregory officials. If galvannealing is war-ranted, a furnace can be placed inline—just pastthe zinc bath—by an overhead crane. Upon exitingthe in-line zinc bath, computer-controlled airknives assure the specified coating thickness. Thecompany occupies a niche in the marketplace, of-fering heavier coatings than many other galvaniz-ers. Capabilities range from the application of verythin coatings such as 0.2 oz./ft.2 all the way to 4oz./ft.2

Rollforming capability includes in-house prod-uct design, steel coating, rolling and punching.Gregory can rollform sheet in gauges from 0.05 to0.187 in., widths from 3 to 30 in. and lengths to 60ft. Subcontracted pre- and post-punching, assem-bly, secondary stamping and secondary weldingsupport the main rollforming operation. Other in-house equipment includes several punch presses.

The breadth of capabilities leads Curt Shaffer,plant manager, to say, “We can bring in a master coil, slit it,coat it, reslit it and rollform it into a product within 48 hours.”

Think Zinc

Galvanized sheet causes zincbuildup in rollforming equipment,especially at Gregory Galvanizing,which specializes in forming sheetwith thick zinc coating.

Inside Gregory

24 www.metalforming.com MetalForming/March 2001

“Metalformers should pay carefulattention to tooling setup whenworking with galvanized sheet andclosely monitor wear on tooling andequipment,” adds Shaffer. “That canhave a greater effect when forminggalvanized sheet than when forminguncoated steel.”

Watch for Zinc BuildupBuildup of zinc on sheet edges is

another concern for formers.“As an example,” explains Zalens-

ki, “if you have a 5.5-in.-wide stripfor a rollforming application, wewould galvanize that as a 16- or 17-in. strip (the galvanizing line at Gre-gory handles a maximum strip widthof 19 in.), then reslit it into three 5.5-in. strips. We could, on the primaryslit, cut it down to a 5.5-in. widthand run it through the line, but thatwould cause edge buildup on eachstrip. So we prefer to galvanize awider strip and then slit it down. Be-cause edge buildup results in flaking

and peeling during rollforming, wetry to minimize those buildups.”

One thing formers should not beoverly concerned with, according toShaffer, is an edge condition wherepreviously galvanized sheet is slitinto smaller widths, thus leavingbare edges.

“That edge condition will not es-calate beyond rust formation on theedge—rust and corrosion will notspread,” he says. “Some of our cus-tomers try to protect that edge with anedge sealer, but that’s not necessary.”

Edge condition is an aestheticissue, not a functional issue, accord-ing to Zalenski. He explained that be-yond appearance, the condition willnot affect material integrity, nor itsability to be formed to specifications.

More Advice for MetalformersThose conducting continuous-

forming operations should be awareof the dangers of zinc poisoning,caused by exposure to zinc dust, cre-

ated when welding galvanized coilstogether. Proper personal-protectionequipment and a safety plan shouldbe in place to deal with the situation.

Parts cleaning is a must for post-forming galvanizing, another serviceperformed by Gregory. Mill varnish-es and oils can hinder adherence ofzinc. To head off that problem, in-coming parts at Gregory are cleanedand pickled prior to galvanizing.

Though galvanizing greatly in-hibits rust formation, it is not a cure-all, cautions Zalenski.

“Some people perceive that galva-nizing will retard white rust to the ex-tent that they can move such materialin the rain or store it in wet condi-tions. This is not the case,” he offers.“Exposing galvanized material to theweather, even if it is being offloadedfrom a truck in wet weather, causeswhite rust to form. If storing outside,properly stack galvanized product,with sufficient air circulation, tokeep white rust from forming.” MF

March 2001 25