Tag Archives: galvanized

Galvanized Steel Coil

galvanized steel coilBefore Steel Coil Can Be Coated

 I think far too often we take for granted the many processes companies spend lots of time and resources (not to mention money) to give us products with features we come to take for granted.  Like making sure metal such as steel does not rust and corrode after years of use.  Before steel can even be painted, it goes through a series of steps to ensure the coating (painting) process is top of the line.  And not just for today, but for many years down the road.

Unprotected steel corrodes quickly as oxidation activity consumes the metal, but this process is preventable by protecting the steel from water and oxygen, thus interrupting the oxidizing action. Surface coatings such as paint are permeable to water and oxygen and eventually permit rusting. Hot-dip galvanizing, however alloys molten zinc to steel metallurgically and forms an impenetrable barrier to water and oxygen. The zinc coating, which is much more durable than painted coatings which often chip during assembly or exposure to the elements, then acts as a sacrificial anode protecting the steel from rust and corrosion, even if the surface has been damaged. Unpainted galvanized steel parts can last 25 years or longer without maintenance.

 Galvanized steel coil is defined as a carbon steel sheet coated with zinc on both sides. Continuous hot dipping, or electro-galvanizing are the two processes used to produce both galvanized sheet steel and steel coil. Generally speaking, the hot dip process consists of passing the steel through a bath of molten zinc. The electro-galvanizing process consists of the application of zinc by electrolytic disposition. The result is a layer of zinc tightly adhering to the base metal through an iron-zinc bonding layer.

Continuous hot dipping is the process used in the application of zinc to steel coils which will later be roll formed into steel roofing and siding.

A zinc coating is one of the most effective and economical methods of protecting bare steel from a corroding environment. The zinc not only serves as a barrier between the steel and the environment, it will sacrifice itself to protect the underlying steel sheet. Sacrificial, or galvanic protection occurs when two dissimilar metals are in contact and coupled with water and oxygen. Zinc corrodes preferentially to the iron in steel. This protection prevents corrosion of the steel at areas not covered with zinc. Thus, the spread of corrosion from cut edges, drill holes, etc. is minimized.

Hot-dipped Galvanized products are manufactured to ASTM A-653 specifications, and are available in a variety of coating weights such as G-90, G-60, G-40, and G-30. With galvanization, the larger the “G” value, the thicker the zinc coating is. For related reading: https://www.hansenpolebuildings.com/blog/2014/02/steel-siding-2/

Typical applications for Galvanized Steel Coil and Sheet products include exterior building products (like steel roofing and siding for pole buildings), ductwork, HVAC products, flashing, electrical boxes and other electrical products, roofing, doors, sashes, automotive parts, appliances, commercial and residential steel framing, truss plates (read more on truss plates here: https://www.hansenpolebuildings.com/blog/2011/10/metal-connector-plates-have-teeth/ ), metal building purlins, and any other products requiring a corrosion resistant material.

Once the galvanized steel is protected, it moves on to the painting process – so stay tuned for tomorrow’s blog to learn the many magical steps of steel coil coating.

Steel Siding and Zinc

Galvanization refers to the coating of steel with zinc.  This is done to prevent rusting of the steel. The value of galvanizing stems from the corrosion resistance of zinc, which, under most service conditions, is considerably greater than steel. The zinc serves as a sacrificial anode, so it cathodically protects exposed steel. This means even if the coating is scratched or abraded, the exposed steel siding or roofing will still be protected from corrosion by the remaining zinc – an advantage absent from paint, enamel, powder coating and other methods. Galvanizing is also favored as a means of protective coating because of its low cost, ease of application and comparatively long maintenance-free service life.

The earliest cold roll formed steel siding and roofing panels were unpainted galvanized steel.

Sharon Glorioso writes in a Metal Roofing Magazine article:

zinc roofing“It’s common to find zinc roofs that have been in service for more than 100 years throughout the major cities of Europe.  For example, the famous German architect Karl Friedrich Schinkel (1781-1841) used zinc extensively for roofing and building ornamentation on several historical buildings and palaces, which still stand today.

The latest example of the longevity of zinc involves the renovation of St. Catherine’s Church in Reutlingen, Germany.  The church was built in 1890 in Gothic Revival style and utilized large portions of zinc tile roofing.  After approximately 120 years, it was determined that a restoration was needed.  The craftsman Wolfgang Huber was commissioned to conduct an assessment of the roof and a study to determine the feasibility of reusing the historic zinc tiles.  Huber, along with an industrial climber, ascended the roof and spires for a personal, up-close inspection of the effects of weathering and previous repair attempts.  “This climbing technique is a cost-effective method of accurately determining damage and planning the remediation,” Huber said.

The restoration plan called for dismantling and removing all zinc tiles for inspection and cleaning and salvaging as many tiles as possible.  Tiles determined to be too damaged for reuse were recycled.  The original tiles on the eastern portion of the roof, which was not exposed to the main west wind and weather were nearly all reusable.  Located at the old cemetery in Reutlingen, the church building has now been preserved to nearly its original state in 1890.

Two distinct but related attributes of zinc in buildings are major factors in its environmental performance: durability and recyclability.  The widespread application of zinc in roofing and wall cladding began in the 19th century.  These were often civic buildings and cathedrals–built to last for generations.  Today, zinc products used in architectural construction have an extremely long service life: an estimated 80 to 100 years for roofs and 200 to 300 years for walls.”

While most steel siding and roofing panels are now factory painted steel, the base coating beneath the paint is still either galvanized, or galvalume® (for more information on Galvalume®: https://www.hansenpolebuildings.com/blog/2013/04/galvalume/). For longevity and value combined with lifespan, steel siding and roofing just cannot be beat by any other product.