Galvanized Steel Manufacturing Process

Manufacturing process hot-dip galvanization process

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Manufacturing Process
Of
Galvanized Steel Frames

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Introduction

Corrosion and repair of corrosion damage are multi-billion dollar problems. Estimates show
metallic corrosion costs the United States approximately $297 billion annually, or about 3%
of the national GDP. Although corrosion is a natural phenomenon, and can never be
completely eliminated, utilizing adequate corrosion protection systems in harsh environments
can drastically reduce the costs. Hot-dip galvanizing after fabrication is a cost effective,
maintenance free corrosion protection system that lasts for decades even in the harshest
environments. For more than 100 years, hot-dip galvanized steel has been utilized
extensively to combat corrosion in major industrial environments including petro-chemical,
transportation, and public utilities.
Power grids are being rethought and rebuilt. The fast-growing requirement for transmission
capacity is driving the rapid expansion of transmission lines across the World. Transmission
infrastructure is being updated at an unprecedented pace. Meeting the challenge of today’s
fast-growing demand for quality, reliability and timely delivery requires a unique
combination of capability, capacity and experience. Whether the need is transmission
structures for the most severe terrains and environments, state-of-the- art advanced design
work, dependable tower testing, precision hardware or complete solutions covering the total
process from engineering through supply, we have what it takes to get the job done.

Flow Chart


Figure: 1 Overview of manufacturing of galvanized steel frames

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Planning and Design














Planning

Planning of this project was started when basic task of the project was received. For setting
up about the main idea of this project, several meetings were arranged among the team
members. The project scope was defined by discussing the problem and their solutions. It

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was decided to divide the project into phases to make it easy and explanatory. Information
sources concerning the research topic were analysed and it was decided to start research
immediately.

Design

The Company has in-house design centres with a strong team of over 100 design experts in
India and Americas who continuously develop innovative, construction friendly and cost-
effective designs. It is equipped with the latest software like PLS Tower, PLS Pole, PLS
CADD, AUTOCAD, MICROSTATION, BOCAD and Google Earth. It provides
computerized engineering solutions, 3D analysis and design depending on the size and
complexity of the project, voltage range, weather condition etc.



Figure: 2 Design Department

The Company has an unparalleled strength in the design of very complex and large towers
with a state of the art in-house Design centre. It has designed Multi circuit, River crossing
towers weighing approx. 300 M.T. with the height of more than 150 meters per tower.

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Raw Material

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Raw Material

The raw material used for manufacturing of self-supported power transmission towers are
steel angle bars. It can be in different sizes and different profile types i.e. L, V, T-shape and
flat angle bars iron net and other sheet metal etc. Steel in normal condition itself is corrosion
resistant but for further improvements HDG and paints are applied.
Raw material is chosen according to the structural parts, for example most heavy steel angle
bars are chosen for the purpose sizes for structural member of power transmission tower.
Raw material is directly purchased from the suppliers and as the company has mass
production so different suppliers supply raw mater is according to international standards and
specifications. Its quality is checked both by suppliers and company itself because in such
case of designing tower for the age of 25 years, the tower material must be chosen according
to standards. Steel angle bars are directly transported to company storage and they are further
sent to machine shop for further processes after quality check.

Figure: 3 Raw Material Yard

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Fabrication Process










Introduction

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The raw material is issued from the storage the next and first operation of manufacturing is
cutting of angle bars that are done with the presses. Before cutting the angle bars it needed to
measure and have to do some marking according to required sizes. There are three presses in
the factory which are used to cut different angle bars in different shapes and sizes and then
material is sent to machine shop.
Manufacturing processes of power transmission towers and the flow of material and products
can easily be understood by the following flow chart in fig.

Flow chart

Figure: 4 Flow Chart of Fabrication Process
Raw Material
Straightening
Cutting Bending
Punching
Stamping Notching

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Marking and Measurements

When the angle bars are cut in the size then the next process is about markings according to
measurements on it. Different drawings are used for each part and marking is done according
to the available drawings. At this stage, as it’s the first and main stage of the manufacturing
of telecommunication towers, the workers who do the marking job are well experienced and
they do the quality check themselves at same time during marking process. Different tools
like scribers, as shown in Figure 11 and different colour of chalks or temporary paints are
used for the purpose of marking.

Figure: 5 Marking and Measurement by Design

Cutting of Material

After the raw material is issued from the storage the next and first operation of
manufacturing is cutting of angle bars that are done with the presses. Before cutting the angle
bars it needed to measure and have to do some marking according to required sizes. There
are three presses in the factory which are used to cut different angle bars in different shapes
and sizes and then material is sent to machine shop. Presses liken the one presented in Figure
10 that is used for cutting angle bars are either operated hydraulically or then mechanically.
They are from 1 to 3 tons in capacity

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Figure: 6 Steel Frame Cutting Machine

Machining and Drilling

When marking is finished, the material is ready for machining processes. For that, the factory
has about six drilling machines and different grinding machines. Actually, when the marks
are ready and points are located the holes in angle parts need to be done by drilling process
that is quite precise. Workers have to be well trained so that they can use exact tools and drill
the right sizes of holes because when the tower will go for site for erection then there should
not be any play between tower members. That can cause all tower breakage when it’s windy
or bad weather like storm etc.

Figure: 7 Machining of Steel Frame
Technical documentation work need to be done by using Auto Cad in which, the use of part
numbers in drawings and different scaling work need to be mention. Work need to be done

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according to the drawings and some inspection need to perform to check either if the parts
are manufactured according to drawings or if there are some mistakes. The work needs to be
done by workers under the guidance of foremen and some faulty parts have to be fixed under
the guidance of concerning supervisor and foremen. A typical drawing of the tower steel part
and the drilling machine used for the drilling purpose is shown in the Fig 12 and Fig 13 on
the next page.

Figure: 8 CNC Punching or Drilling of Steel Frame
Coolants are used for the devices to prevent its overheating, transferring the heat produced by
the device to other devices that use or dissipate it. For an ideal coolant it should have high
thermal capacity, low viscosity, is low-cost, neither causing nor promoting corrosion of the
cooling system either in a machine part or cutting tools. Coolant is commonly used in
automotive, some temperature-control applications. In industrial processing, heat transfer
fluid is used both in high temperature as well as low temperature manufacturing applications.

Figure: 9 Types of Notching

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Mostly the coolants used in ATL are cutting fluids. In other hand Cutting fluid is a type of
coolant and lubricant designed specifically for metal working and machining processes.
Different kinds of cutting fluids are used for different purposes i.e. oils, oil-water emulsions,
pastes, gels, aerosols (mists), and air or other gases. Cutting fluids may be made from
petroleum, animal fats, water and air, or plant oils etc. A good cutting fluid must have the
following properties: • A cutting fluid must keep the work piece at a stable temperature. • It
must ensure safety for the people handling it and for the environment upon disposal. • It
prevents rust and corrosion on cutting tools and machine parts. • It must maximize the life of
the cutting tip by lubricating the working edge or tip.

Figure: 10 Bending Machine

Figure: 11 CNC Punching Machine for generating holes on Steel Frames

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Figure: 12 Straightening Machine for keep Steel Frame straight

Figure: 13 CNC Punching Machine Arrangement

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Galvanizing Process







Introduction

Corrosion and repair of corrosion damage are multi-billion dollar problems. Estimates show
metallic corrosion costs the United States approximately $297 billion annually, or about 3%
of the national GDP. Although corrosion is a natural phenomenon, and can never be
completely eliminated, utilizing adequate corrosion protection systems in harsh environments
can drastically reduce the costs. Hot-dip galvanizing after fabrication is a cost effective,
maintenance free corrosion protection system that lasts for decades even in the harshest
environments. For more than 100 years, hot-dip galvanized steel has been utilized

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extensively to combat corrosion in major industrial environments including petro-chemical,
transportation, and public utilities.

The zinc of the hot-dip galvanized coating is more corrosion resistant than bare iron
and steel. Similar to steel, zinc corrodes when exposed to the atmosphere; however, zinc
corrodes at a rate approximately 1/30 of that for steel. Also like steel, zinc corrodes at
different rates depending on its environment. Therefore, the performance of hot-dip
galvanized steel varies from environment to environment. Environments in which galvanized
steel is commonly used include indoor and outdoor atmospheres, the storage of hundreds of
different chemicals, in fresh water, sea water, soils, concrete, and conjunction with other
metals, treated wood or extreme temperatures. Because of the many years galvanizing has
been used for corrosion protection, a wealth of real-world, long-term exposure data on zinc
coating performance in a wide variety of environments is available. Because hot-dip
galvanized steel is used in so many different applications.



Figure: 14 Galvanized Mild Steel Frames

History Of Galvanizing

The recorded history of galvanizing dates back to 1742 when P.J. Malouin, a French chemist
described a method of coating iron by dipping it in molten zinc in a presentation to the
French Royal Academy. Thirty years later, Luigi Galvani, galvanizing namesake, discovered
more about the electrochemical process that takes place between metals. Galvani’s research
was furthered in 1829 when Michael Faraday discovered zinc’s sacrificial action, and in
1836, French engineer Sorel obtained a patent for the early galvanizing process. By 1850, the

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British galvanizing industry was using 10,000 tons of zinc a year for the protection of steel,
and in 1870, the first galvanizing plant opened in the United States. Today, galvanizing is
found in almost every major application and industry where iron or steel is used. Hot-dip
galvanized steel has a proven and growing history of success in myriad applications
worldwide.

How Zinc Protects Steel from Corrosion

The reason for the extensive use of hot-dip galvanizing is the two-fold protective nature of
the coating. As a barrier coating, it provides a tough, metallurgical bonded zinc coating that
completely covers the steel surface and seals the steel from the corrosive action of the
environment. Additionally, zinc’s sacrificial behaviour protects the steel, even where damage
or a minor discontinuity in the coating occurs.

The Hot-Dip Galvanizing Process

The hot-dip galvanizing process consists of three basic steps: Surface Preparation,
Galvanizing, and Inspection.

Surface Preparation

Surface preparation is the most important step in the application of any coating. In most
instances, incorrect or inadequate surface preparation is the cause of a coating failure before
the end of its expected service lifetime. The surface preparation step in the galvanizing
process has its own built-in means of quality control because zinc wills not metallurgical
react with an unclean steel surface. Any failures or inadequacies in surface preparation will
immediately be apparent when the steel is withdrawn from the molten zinc, because the
unclean areas will remain uncoated and immediate corrective action must be taken. Surface
preparation for galvanizing consists of three steps: Degreasing, Acid pickling, and Fluxing.

Degreasing - A hot alkali solution, mild acidic bath, or biological cleaning bath
removes organic contaminants such as dirt, paint markings, grease, and oil from the steel
surface. Degreasing baths cannot remove epoxies, vinyl, asphalt, or welding slag; thus,
these materials must be removed by grit-blasting, sand blasting, or other mechanical
means before the steel is sent to the galvanizer.

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Figure: 15 Degreasing Tank

Pickling - A dilute solution of hot sulphuric acid or ambient temperature hydrochloric acid
removes mill scale and iron oxides (rust) from the steel surface. As an alternative to or in
conjunction with pickling, this step can also be accomplished using abrasive cleaning, air
blasting sand, metallic shot, or grit onto the steel.



Figure: 16 Pickling Tank

Rinsing Tank - The material is cleaned and cooled by dipping it in water tank because
HCL acid sticks on it.

Figure: 17 Rinsing Tank

Fluxing - The final surface preparation step in the galvanizing process serves two
purposes. It removes any remaining oxides and deposits a protective layer onto the steel to
prevent any further oxides from forming on the surface prior to galvanizing. Flux is
applied in two different ways; wet or dry. In the dry galvanizing process, the steel or iron
is dipped or pre-fluxed in an aqueous solution of zinc ammonium chloride. The material is
then dried prior to immersion in molten zinc. In the wet galvanizing process, a layer of
liquid zinc ammonium chloride is floated on top of the molten zinc. The iron or steel being
galvanized passes through the flux on its way into the molten zinc.

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Figure: 18 Fluxing Tank

Galvanizing

In the true galvanizing step of the process, the material is completely immersed in a bath of
molten zinc. The bath contains at least 98% pure zinc and is heated to approximately 840 F
(449 C). Zinc chemistry is specified by ASTM B 6. While immersed in the kettle, the zinc
reacts with the iron in the steel to form a series of zinc/iron intermetallic alloy layers. Once
the fabricated items coating growth is complete, they are withdrawn slowly from the
galvanizing bath, and the excess zinc is removed by draining, vibrating, and/or centrifuging.
The metallurgical reaction will continue after the articles are withdrawn from the bath, as
long as the article remains near bath temperature. Articles are cooled either by immersion in
a passivation solution or water or by being left in open air. Hot-dip galvanizing is a factory-
controlled process performed under any climate conditions. Most brush and spray-applied
coatings depend upon proper climate conditions for correct application. Dependence on
atmospheric conditions often translates into costly construction delays. The galvanizer’s
ability to work in any climate conditions provides a higher degree of assurance of on-time
delivery; furthermore, no climate restrictions means galvanizing can be completed quickly
and with short lead times.
Zink Bath - There is mainly ZN in this bath at 460’c temperature. AL & Lead also
present these for surface finishing of material. The material is dipped into it and after
Certain time it is raised from it. Thus the Zn coating is made.

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Figure: 19 Zink Bath Tank
Rising Tank - This tank consist water. The material is dipped into it for cooking,
cleaning after Zn coating.

Figure: 20 Rising Tank
During the actual galvanizing step of the process, the material is completely immersed in a
bath of molten zinc. The bath chemistry is specified by ASTM B6, and requires at least 98%
pure zinc maintained at approximately 840 F (449 C). While immersed in the kettle, the zinc
reacts with the iron in the steel to form a series of zinc/iron intermetallic alloy layers. Once
the fabricated items’ coating growth is complete, they are withdrawn slowly form the
galvanizing bath, and the excess zinc is removed by draining, vibrating, and/or centrifuging.
The metallurgical reaction will continue after the articles are withdrawn from the bath, as
long as the article remains near bath temperature. Articles are cooled either by immersion in
a passivation solution or water or by being left in open air. Temperature of molten bath is
around 860°F (460°C).

Zn+O₂=ZnO

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ZnO+CO₂=ZnCO₃



Figure: 21Batch Hot-Dip Galvanizing Process



Figure: 22 Withdrawal of a steel article from the zinc bath

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Quality Check and Inspection

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Inspection

The inspection of hot-dip galvanized steel is simple and fast. The two properties of the
coating closely scrutinized are coating appearance and coating thickness. A variety of simple
physical and laboratory tests may be performed to determine thickness, uniformity,
adherence, and appearance. Products are galvanized according to long-established, accepted,
and approved standards of ASTM, the Canadian Standards Association (CSA), the
International Organization for Standardization (ISO), and the American Association of State
Highway and Transportation Officials (AASHTO). These standards cover everything from
minimum required coating thicknesses for various categories of galvanized items to the
composition of the zinc metal used in the process. The inspection process for galvanized
items also requires minimal labour. This is important because the inspection process required
assuring the quality of many brush- and spray-applied coatings is highly labour-intensive and
requires expensive skilled labour. Once a job has been delivered and accepted at the
galvanizer’s plant, there is one point of responsibility for ensuring the material leaves the
plant properly galvanized. That point of responsibility is the galvanizer.


Figure: 23 Inspection of Zinc Coating

The last process after HDG and before sending it to storage is quality check and final
inspection where all the galvanized parts of tower are finally inspected by QC department.
In the final inspection zinc coated parts are inspected and it is made sure that there is not any
faults i.e. blowholes, porosity, black spots and missed zinc coated places because it is
necessary to galvanize parts in proper way. Otherwise there can be rusting and corrosion with
the passage of time. Zinc coating thickness is important to consider in point because of cost
and safety factors. For checking zinc coating thickness, a special tool, positector is used.
Thickness of zinc varies from 2 µmm to 1 mm, depending on the part and size of the tower
member. Electronic magnetic gages (e.g. PosiTector 6000 F Series, PosiTest DFT Ferrous)
come in many shapes and sizes. They commonly use a constant pressure probe to provide
consistent readings that are not influenced by different operators. Readings are shown on a
liquid crystal display (LCD).

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Loading and Tower Erection

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Loading

In case when quality department is ok with angles, they directly go for loading, than they
dispatched to their desired location.

Tower Erection

The last operation after manufacturing is erection of simply supported towers. When the
towers are transported to site, the foundation of tower is ready before the tower structure is
unloaded. The foundation of the part is constructed by company's civil engineers who make
the foundation ready two weeks before the erection of tower. The foundation consists of
concrete and works as base of tower. Heavy cranes and different fork lifters are used for the
handling the tower members. As they are heavy in weight, it is not possible to lift them
easily. Different pulleys are used too during the erection of power transmission towers and
safety precautions are adapted for the safe work. Different tools are used step by step for the
quality work and it takes about a week to completely erect a 60 meter high
telecommunication tower. The lower joints and legs of the tower are fitted with the
foundation with anchor rods and bolts. And then whole tower is fitted upward by starting
from foundation. Some heavy working cranes are used for that purpose and of course some
fitters and workers under supervision. It takes about a week to erect one tower and the rest of
the telecom devices are fitted later by client's own engineers. When erection of mechanical
structure of telecommunication tower is finished then different power transmission
companies install the power transmission unit along with the tower. For that they use a
control room (processing unit), antennas and some cables for the purpose of communication.
The whole tower from its erection to the final working takes about a month.

Figure: 24 Tower Erections

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Application

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Application of Galvanized Steel

The selection of a steel coating system is an integral part of all engineering design. The main
consideration for the engineer in the selection of the most suitable corrosion protection
system would be the performance of a steel coating and the economics of the application of
the steel coating system. There is no other corrosion protection system that could match the
performance and economics of hot dip galvanizing.

POWER GENERATION AND POWER TRANSMISSION

In the building of a power station for power generation, steel is a major construction
material. Galvanized steel is used in platforms, equipment buildings, stairs and handrails. In
the area of fuel supply to the main power generating plants galvanized steel conveyor
systems are common in a coal fired power station. Cooling water, water reticulation and fire
protections systems consume huge amounts of galvanized steel in the form of piping and it
fittings. As for power transmission every piece of steel in a transmission tower is completely
galvanized from the main steel frame, every piece of bolt and nut used to fasten the angles
together to the cable support systems are completely galvanized. They are now many
transmission towers that are also painted with special paint system for identification
purposes.

INFRASTRUCTURE DEVELOPMENT

Government of many countries now invest and spent huge part of their budgets in improving
the infrastructure such as road highways and expressways, railways, Light Rail
Transport system (LRT) and Mass rapid Transportation system (MRT) , Port terminals and
airport facilities. These projects consume huge amounts of exposed steel and as such hot dip
galvanizing is the preferred corrosion protection system.
As for other developments such as schools, hospitals, community halls and other public
places galvanized steel are mainly in galvanized products such as galvanized water tanks for
fire protections systems, street lights, safety barriers and road and drain covers.
Hot dip galvanized reinforcement steel was only used in critical construction areas such as
coastal or marine concrete structures. In the last decade the use of hot dip galvanized
reinforcement steel increased with the rapid expansion of the road, highways and
expressways. Steel rods and strips for reinforced earth (RE) walls and soil nails
are always hot dip galvanized. Guardrails, crash cushions, decorative street lights, high
masts, pedestrian overhead bridges, noise barriers,
parapet handrails are some of the other products that are corrosion protected with hot dip
galvanizing


TELECOMMUNICATION TOWERS

Telecommunication steel towers are difficult structures to maintain considering its location
which normally are difficult to access since it is situated on hills slopes and on top of
mountains. For easy installation these Steel Towers are fabricated from Steel Tubes in

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different sections and steel Angles of various sizes and lengths, Hot Dip Galvanized and
fastened with Centrifuged Hot Dip Galvanized Bolts, Nuts and Washers. These 3 Leg
Telecommunication Towers are 100% Hot Dip Galvanized and Duplex coated for long term
corrosion protection and aerial Identification.

BUILDING AND CONSTRUCTION

The Twin Tower in Kuala Lumpur and the Kuala Lumpur Tower are prestigious projects in
Malaysia. For durability most steel are Hot Dip Galvanized and Duplex coated. Commonly
found in the open areas are Forged Welded Gratings hot dip Galvanized, Garden Lighting
Poles Hot Dip Galvanized and Children Play Stations all Hot Dip Galvanized and Duplex
Coated.


Figure: 25 Tower Transmissions and Telecom Tower Application of Galvanized Steel



Figure: 26 Industries and Building Application of Galvanized Steel

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Figure: 26 Tower Application of Galvanized Steel

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Reference
 www.kecrpg.com
 https://en.wikipedia.org/wiki/KEC_International
 www.rpggroup.com/our_business/infrastructure/kec_international.aspx
 www.theseus.fi/bitstream/handle/10024/41511/Ishtiaq_Muhammad.pdf?sequence
=1
 https://en.wikipedia.org/wiki/Hot-dip_galvanization
 https://en.wikipedia.org/wiki/Galvanization
 www.steeldoor.org/res/SDI_112.pdf
 www.galvanizingasia.com/pdfs/page9-25.pdf
 www.buzzle.com/articles/use-of-galvanized-steel.htm
 Google Images galvanized steel application
 www.azom.com/article.aspx?ArticleID=2629

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