Once the metal is cleaned, treated, and painted, the strip is rewound into a coil size prescribed by the customer. From there, the coil is removed from the line and packaged for shipment or additional processing.
After the primer is applied and cured, then the metal strip enters the finish coat station where a topcoat is applied. Topcoats provide color, corrosion resistance, durability, flexibility and any other required physical properties. Like primers, the topcoat is cured using thermal cure ovens.
Oven
Coil coating ovens can range from 130 feet to 160 feet and will cure the coatings in 13 to 20 seconds.
During this stage, the strip enters the prime coat station whereby a primer is applied to the clean and treated metal. After the primer is applied, the metal strip travels through a thermal oven for curing. Primers are used to aid in paint adhesion, improve corrosion performance and enhance aesthetic and functional attributes of the topcoat.
S Wrap Coater
The S wrap coater design allows for primers and paints to be applied to the top and back side of the metal strip simultaneously in one continuous pass.
The cleaning and pretreating section of the coil coating process focuses on preparing the metal for painting. During the cleaning stage, dirt, debris, and oils are removed from the metal strip. From there, the metal enters the pretreatment section and/or a chemical coater whereby chemicals are applied to facilitate paint adhesion and enhance corrosion resistance.
Dried-In-Place
In this stage a chemical that provides enhanced corrosion performance is applied. This treatment can be chrome free if required.
The accumulator is a structure that adjusts up and down to store material, which makes continuous operation of the coil coating process possible. This accumulation will continue to feed the coil coating processes while the entry end has stopped for the stitching process. As much as 750 feet of metal can be collected.
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
The process, provided by AZZ Surface Technologies, received its name because the part to be treated forms the anode electrode of an electrolytic cell. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. Anodic films can also be used for several cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add reflected light wave interference effects.
Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminum alloys, although processes also exist for titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum. Iron or carbon steel metal exfoliates when oxidized under neutral or alkaline micro-electrolytic conditions. [1]
1. Anodizing was originally used to prevent seaplane parts from corrosion.
Aluminum components commonly utilized on marine vessels, offshore rigs, shipyard components and parts frequently exposed to saltwater spray often benefit from anodizing. In fact, the process was first adopted on an industrial scale in the 1920’s to safeguard Duralumin seaplane components from the dangers of corrosion. If you’re curious, the early chromic acid-based process was outlined in British defense specification DEF STAN 03-24/3 and is still utilized in modern times.
2. The protective layer is “grown”, not simply applied.
The anodized aluminum layer is grown by passing a direct current through an electrolytic solution, with the aluminum object serving as the anode (the positive electrode). The current releases hydrogen at the cathode (the negative electrode) and oxygen at the surface of the aluminum anode, creating a build-up of the protective aluminum oxide layer. [2]
3. Anodizing facilitates a major pop of color. Just don’t ask for white.
The most common anodizing processes produce a porous surface which absorb dye and enable a vast array of color options. Standard colors include yellow, green, blue, black and red, but custom colors are also available. Interestingly, white color cannot be applied due to the larger molecule size than the pore size of the oxide layer.
4. Anodizing is one of the more environmentally friendly metal finishing processes.
Except for organic (aka integral color) anodizing, the by-products contain only small amounts of heavy metals, halogens, or volatile organic compounds. Integral color anodizing produces no VOCs, heavy metals, or halogens as all of the byproducts found in the effluent streams of other processes come from their dyes or plating materials. The most common anodizing effluents, aluminum hydroxide and aluminum sulfate, are recycled for the manufacturing of alum, baking powder, cosmetics, newsprint and fertilizer or used by industrial wastewater treatment systems. [3]
5. There are different types of anodizing.
Anodized Type I: Type I utilizes chromic acid to produce a thin, pliable anodized layer on an aluminum component.
Anodized Type II: Instead of using chromic acid, Type II relies on the utilization of sulfuric acid in order produce a thicker anodized layer on the component. The additional thickness allows for maximum coloration.
Anodized Type III: Similarly to Type II, this method also uses sulfuric acid at a lower temperature and higher voltage, produces an even thicker and more dense anodized layer that is also suitable for coloration. It’s also commonly known as “hard anodizing” and is ideal when friction between components is present.
Interested in learning more about AZZ’s anodizing capabilities? Contact us today to learn more!
Sources:
[1] Sheasby, P. G.; Pinner, R. (2001). The Surface Treatment and Finishing of Aluminum and its Alloys. 2 (Sixth ed.). Materials Park, Ohio & Stevenage, UK: ASM International & Finishing Publications.
AWS D – 19.0, Welding Zinc-Coated Steel, calls for welds to be made on steel that is free of zinc in the area to be welded. Thus, for galvanized structural components of a fabrication, the zinc coating should be removed at least one to four inches (2.5 – 10 cm) from either side of the intended weld zone and on both sides of the work piece. Grinding back the zinc coating is the preferred and most common method; burning the zinc away or pushing back the molten zinc from the weld area also are effective.
Touch-up of Weld Area
Any welding process on galvanized surfaces destroys the zinc coating on and around the weld area. Restoration of the area should be performed in accordance with ASTM A 780, Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings, which specifies the use of paints containing zinc dust, zinc-based solders or sprayed zinc. All touch-up and repair methods are capable of building a protective layer to the thickness required by ASTM A 780.
The restored area of the zinc coating will have no effect on the overall lifetime of the part. Repair materials and their coating thickness have been chosen to give comparable lifetimes to the coating minimums required by ASTM A 123/A 123M, Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products. There may be some visual differences between the original hot-dip galvanized coating and the restored area, but, over time, the natural weathering of the galvanized coating and the repair material yield similar appearances.
Quality of Welded Joints
It is recommended in AWS D – 19.0 to remove all zinc from the weld area prior to welding because burning through the zinc slows the welding process, generates zinc fumes (see “Safety and Health” at right) and creates an unsightly burn area around the weld. However, as studies performed by the International Lead Zinc Research Organization (ILZRO) have shown, the tensile, bend and impact properties of welds on galvanized steel are equivalent to the properties of welds on uncoated steel.
Fracture Toughness
Tests establish that the fracture toughness properties of welds are unaffected by the presence of galvanized coatings.
Fatigue Strength
The fatigue strength of arc welds on galvanized steel is equivalent to welds on uncoated steel made by CO2 welding.
Porosity
The extent of weld porosity is a function of heat input and the solidification rate of the weld metal. Not always possible to eliminate, porosity affects the fatigue strength and cracking tendencies of welds. When welds are subject to fatigue loading, welds on galvanized steel should be made oversized to reduce the influence of any weld metal porosity.
When evaluating the effect of porosity on the fatigue strength of a fillet weld, it is necessary to consider both the function of the joint and the weld size. When a fillet weld on galvanized steel is large enough relative to plate thickness to fail by fatigue from the toe of the weld in the same manner as in uncoated steel, the presence of porosity in the weld does not reduce the fatigue strength of the joint.
Where the dimensions of the weld are just large enough to cause fatigue failure from the toe in a sound weld, a weld containing porosity at the root may fail preferentially through the throat of the weld. Intergranular cracking of fillet welds containing porosity, sometimes referred to as zinc penetrator cracking, does not significantly affect the strength of non-critical joints. For more critical stress applications, it is advisable to carry out procedural tests on materials and samples.
Safety and Health
All welding processes produce fumes and gases to a greater or lesser extent. Manufacturers and welders must identify the hazards associated with welding coated and uncoated steel and workers must be trained to maintain work practices within Occupational Safety and Health Administration (OSHA) regulations. In general, welding on steel with the zinc coating ground back away from the weld area will produce lead and zinc oxide emissions below OSHA permissible exposure limits (PELs) for zinc and lead. When welding directly on galvanized steel is unavoidable, PELs may be exceeded and every precaution, including high-velocity circulating fans with filters, air respirators and fume-extraction systems suggested by AWS, should be employed.
Fumes from welding galvanized steel can contain zinc, iron and lead. Fume composition typically depends on the composition of materials used, as well as the heat applied by the particular welding process. In any event, good ventilation minimizes the amount of exposure to fumes. Prior to welding on any metal, consult ANSI/ASC Z-49.1, Safety In Welding, Cutting and Allied Processes, which contains information on the protection of personnel and the general area, ventilation and fire prevention.
Summary
With proper preparation of the weld area, selection of a suitable welding material and process, and careful touch-up of the weld area, welding on galvanized steel provides an excellent product for use in myriad applications, from bridges, towers and grating to handrail, trusses and guardrail.
Have additional questions? Contact AZZ today and we’ll put you in touch with a galvanizing expert!
Let’s take a look at some of the key materials used, how they differ, and which might be the best long-term solution for utilities looking to keep pace with increasing demand.
Steel vs Wood Utility Poles
Wood utility poles can be made of many materials, though woods like southern pine are common. However, this isn’t the only material that contributes to the final product – chromated copper arsenic (CCA) is often used to treat wooden utility poles to prevent termite infection and overall decay.
Still, even with these measures – which can have adverse effects on the environment to begin with – wood utility poles are certainly not permanent installations. An Electric Power Research study estimated that wood utility poles can last up to 50 years, though 30 to 40 years of true service life is more common.
Steel utility poles can be manufactured to the same dimensions as wooden poles but require no harsh chemical treatments. They’re often galvanized to protect them from corrosion and other harsh elements. It’s been estimated that steel utility poles can exhibit service lives of 50-80 years.
While wood is generally considered a green material, the actual impact of wood utility poles on our shared environment is greater than you might imagine.
In addition to their treatment with CCA, the harvesting and manufacturing of wood utility poles can actually release more greenhouse gases and aerosols than that of steel utility poles. Electricity is required to produce CCA in the first place, and shorter lifetimes mean more truck rolls, more emissions, and more destruction of the habitats of potentially endangered species.
Steel utility poles, on the other hand, exhibit far less environmental impact. Though steel production and galvanization is not without environmental impact whatsoever, it is generally lesser, and the longer lifespans of steel utility poles also leads to key energy savings.
From Lower Life Cycle Cost to Ease of Installation: Steel Utility Poles Provide a Vast Number of Benefits
In addition to the environmental benefits, steel utility poles also exhibit:
More uniform dimensions
No need for treatment with harsh chemicals (that eventually end up in landfills)
Easy installation
Greater durability, particularly when galvanized
Lower overall life cycle cost due to longer service life
Superior strength and resistance to damage during service
Lower weights – often 30% lighter and as much as 70% lighter
Clean, appealing aesthetics
100% recyclability
Steel Utility Poles Excel in Comprehensive Study
A study commissioned by the Steel Market Development Institute and conducted by SCS Global Services sought to analyze the performance of 45-foot-tall, Class 2/Grade B steel utility poles and wood utility poles in the southeastern U.S. over the course of a 40-year horizon.
As the study outlines, “two different scenarios were compared – one in which wood poles were taken out of service as a result of pole failure and continued to be replaced by Class 2 wood poles, and the other in which wood poles taken out of service due to pole failure were replaced by galvanized steel utility poles.”
The study confirmed the general belief that steel utility poles, over the totality of their service life, exhibit a much smaller environmental impact than their wood utility pole counterparts, which were assumed to need replacement every 40 years. The steel utility poles were assumed to have an 80-year service life.
The study’s key findings were that:
The steel utility pole scenario would use 300,000 fewer barrels of oil over 40 years
The steel utility pole scenario would impact the habitats of three species, whereas the wood utility pole scenario would impact seven
Approximately 15 acres of terrestrial biome would be disturbed by the steel utility pole scenario compared to 12,000 for wood utility poles
In the wood utility pole scenario, the CCA used would result in nearly 600,000 tons of waste over 40 years
Steel Utility Poles Ready to Shine as Utility Demands Grow
The demand for energy has asked a lot of utility companies, and that means saving money wherever possible. By choosing more cost-effective steel utility poles, utilities can not only save resources and money, but lower their environmental impact and install solutions set to last much longer than wood utility poles.
To learn more about AZZ’s role in the galvanization of steel utility poles, contact us today.
Spin galvanizing is a hot-dip process that utilizes a centrifuge anchored to a galvanizing kettle (or a spinner located above it) for immersing small to medium scale components in molten zinc. A tightly bonded alloy coating forms on the steel, providing long-term, durable protection from the devastating effects of corrosion, while the centrifuge or spinner removes excess molten zinc to ensure coating uniformity, quality fit, and precise functionality.
AZZ is pleased to bring state-of-the-art spin galvanizing capabilities to our AZZ Galvanizing-Houston location. We are operational and equipped to serve a broad range of customers – and, for added convenience, transportation to and from D/FW, San Antonio, Austin, Waco, Baton Rouge and the Beaumont Golden Triangle!
AZZ’s Spin Galvanizing Process Delivers:
• 100% complete and consistent coverage • Cathodic protection • 3,600 psi coating bond strength • Hardness – difficult to damage during tightening • Temperature range: continuous exposure in arctic climates to the extremes of 392°F • Paintable – prepared according to ASTM D 6383
To learn more about our capabilities in Texas, please call our plant directly or complete our online contact us form today!
AZZ Galvanizing – Houston
7407 C E King Pkwy Houston, TX 77044 Phone: 281.458.1550
Powder coating your critical components offers a variety of benefits in terms of performance, long-term cost savings, and more, and AZZ has an expansive network of powder coating facilities ready to help you take advantage.
We have the experience and tools you need to realize those decorative and functional benefits, and that network helps us do it without vast turnaround times you’ll experience with smaller operations.
Powder Coating: A More Durable, Protective Option
Powder coating provides:
Corrosion Resistance Chemicals and moisture can eat away at metals like steel, but powder coating provides key resistance against those elements by acting as a barrier that prevents corrosion.
Chemical Resistance Depending on a finished product’s unique application, oils, gasoline, harsh cleansers and much more can come into contact with finished solution. Powder coating helps parts resist the negative effects of these chemicals.
Electrical Insulation Resistance Powder-coated components can be specifically designed and tested for use on electrical components, helping ensure safety and performance.
Heat Resistance While in use, coatings can face elevated temperatures either constantly or during intermittent use, and powder coating can help finished products stand up to those harsh environment factors in applications from residential barbecues to automotive engines and beyond.
Abrasion, Impact and Marking/Mar Resistance Powder coating is known for its durability in the face of forces that would wear it down, cause damage due to significant impact or mark the coating with scratches or other marring. Not only does this maintain the coating’s integrity and resistance to other elements – it also helps maintain an attractive finish for longer durations of use.
Powder-coated parts are also attractive, with consistent, quality finishes that stand the test of time and make parts stand out.
AZZ’s Flexibility in Powder Coating
AZZ has facilities that can powder coat everything from the smallest parts to parts up to 60 feet in length, offering tremendous flexibility in meeting all of your powder coating needs.
AZZ has also earned the following certifications in heavy equipment, aerospace and defense, and more:
AS9100
Caterpillar
General Dynamics
ISO 9001
NADCAP Quality
PACCAR
We back our versatility and experience with a commitment to a durable, long-lasting and attractive finish. To learn more, visit azz.com/powder-coating .
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