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.
Let’s take a look at the galvanizing process from start to finish.
Hot-dip galvanizing is essentially a process that coats steel with a protective layer of zinc alloy to protect it from corrosion. Not only is it a relatively simple and cost-effective process, but the resulting benefits will last for decades.
The Process
Preparation
First and foremost, the steel itself must be thoroughly inspected to ensure that drainage and venting requirements are met. It wouldn’t do to have a flawed product at the outset.
Cleaning the Steel Prior to Hot-Dip Galvanizing
Before the galvanizing process can begin, the steel must be cleaned as thoroughly as possible. This isn’t just for appearances. The zinc coating simply can’t bond with a steel surface if foreign materials are present. There are several steps to cleaning:
The steel is submerged into a caustic tank at 180° F to remove any paint residue. It is then rinsed in a freshwater tank at ambient temperature to remove the caustic material.
The steel is pickled by being dipped into a tank of heated sulfuric acid at 140°-145° F to remove any mill scale. Afterward, it is again rinsed in a freshwater tank.
Lastly, the steel is washed in a flux tank containing a mixture of zinc chloride and ammonium chloride at 140°-170° F to provide protection against oxidation before galvanizing.
After these steps have been completed, the steel is ready to receive its new protective coating.
The Hot-Dip Galvanizing Kettle
The freshly cleaned steel is submerged into a kettle of molten zinc at 830°-850° F. The zinc then bonds with the steel in a diffusion reaction, creating a brand-new layer of metallurgically bonded zinc alloy. Before the newly coated steel can be removed from the tank, the surface of the molten zinc must be swept to remove any residue to ensure that the steel is exiting through pure zinc.
Cooling Down
As soon as it’s removed from the galvanizing kettle, the steel is quenched in aqueous sodium dichromate at ambient temperature to help cool it down before the final cleaning process. This also helps the galvanized steel retain its shiny surface for a longer period of time.
Final Cleaning
Once galvanized, the coated surface of the steel is cleaned of any dirt, drip marks or excess zinc to ensure the final product is ready for testing.
Testing Hot-Dip Galvanizing Results
The steel is then moved outside and placed on poles for millage tests. These tests verify that the process was successful and that the zinc coating is the proper thickness. Different applications for the steel can call for different coating thicknesses.
Other Key Considerations for Hot-Dip Galvanizing
Protection Against Rust via Hot-Dip Galvanizing
The main purpose of hot-dip galvanizing steel is to protect it against rust, the natural predator of steel. One of the main benefits of the zinc alloy coating, other than generally being very resistant to abrasion, is that zinc and rust are inherent enemies. Rust simply can’t eat through zinc, so it follows that it can’t eat the steel beneath the zinc. either.
A Long History of Hot-Dip Galvanizing
Galvanizing metal with zinc is a process that we’ve been using for over 150 years. The first known use was in 17th-century Indian armor, and the process was industrialized to protect the iron in British naval ships. Since then, it’s caught on in almost every application of steel and iron throughout the developed world.
Aesthetics
The crystallites of the zinc coating, or the grain, are a visible feature of galvanized steel. This feature is called “spangle” and can be varied and adjusted to taste by altering the number of particles added in heterogeneous nucleation, as well as the cooling rate during the hot-dip galvanizing process. If desired, the spangle can be made to appear uniform, and the grain will be too small to be seen with the naked eye.
Common Uses for Hot-Dip Galvanizing
Hot-dip galvanizing of steel is most often used for construction purposes. The process provides protection for building frameworks, walkways, staircases and more in major cities all around the world. Most of us have almost assuredly come in contact with hot-dip galvanized steel without even realizing it.
Galvanized piping is also used heavily in irrigation and other outdoor water storage and water transportation solutions due to its superior ability to withstand the corrosive forces of the elements and resistance to rust.
The Cost-Effectiveness of Hot-Dip Galvanizing
Hot-dip galvanizing is popular amongst farmers, engineers, architects and more for its protective qualities, but it also provides other more economic benefits.
Because of its longevity and toughness, hot-dip galvanized steel requires less maintenance and can span decades before needing to be repaired or replaced. The resistance to abrasion also makes for smoother surfaces that are more easily cleaned and painted.
Hot-dip galvanizing is a trusted solution for long-lasting corrosion protection, relied upon for its durability and unmatched performance. This video provides a step-by-step look at the galvanizing process, showcasing how steel is transformed with a protective zinc coating that stands up to the toughest conditions. From surface preparation to the final finish, see how this process ensures strength and longevity for projects of all sizes.
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies. If essential cookies are disabled, the website may not function properly.
This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
Cookie
Duration
Description
cookielawinfo-checkbox-analytics
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional
11 months
The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy
11 months
The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
