Hot-dipped Galvanized Steel Coils(GI)

Introduction

Galvanized steel coil has excellent resistance to atmospheric corrosion of coated steel. cold-rolled sheet after the zinc can extend the service life for 15-20 years. Galvanised steel coils are successfully used in industries with stringent requirements for corrosion resistance, durability, strength and appearance, and can be formed or have various coatings applied. The key standards to be followed for the production of galvanised coils include EN 10346 (Europe), ASTM A653 / A653M (US). Manufacturers also have their own original standards.

Galvanized steel coil specifications

Hdg coil classification, product range and properties

Standards applied in different countries to set the requirements for hot dipped galvanized steel coils specify steel grade and size ranges for these products. Hot dipped galvanised coils are classified based on the following features:

● Application of coated steel (profiling, cold forming, manufacture of steel structures)

● Chemical composition of coating material (pure zinc, zinc-iron/zinc-aluminium/aluminium-zinc/zinc-magnesium alloys, etc)

● Thickness/weight of protective coating

►HDG coils according to European standards

Galvanised steel coils as per the European EN 10346, can be coated with zinc, zinc-iron alloy, zinc-aluminium alloy, aluminium-zinc alloy or aluminium-silicon alloy:

● Zinc coating (Z) is achieved by dipping the prepared strip into a bath with molten alloy, containing at least 99% zinc. This is the most common and traditional way of protecting rolled steel from corrosion.

● Zinc-iron coating (ZF) is formed by dipping a strip into a bath of molten zinc (at least 99% zinc) with further annealing to form a zinc-iron coating with an Fe content of 8-12%. Such coating is stronger than the traditional zinc coating and has better adhesion with substrate steel due to mutual diffusion between the iron and zinc in the surface layers. That is why this coating is less exposed to lamination or pitting under impact, mechanical stresses or deformation of treated products.

● Zinc-aluminium coating (ZA) is applied to rolled steel by dipping it into a bath of zinc and about 5% aluminium with a minor content of mishmetal (mix of metals). Rolled steel with such coating has better formability and corrosion protection properties compared with zinc-coated steel.

● Aluminium-zinc coating (AZ) is applied by dipping steel into a bath of molten metal consisting of 55% aluminium and 1. 6% silicon (with the remaining being taken up by zinc). The combined action of these metals ensures the best corrosion protection compared with other coatings.

● Aluminium-silicon coating (AS) is created by dipping steel into a bath of molten metal containing aluminium and 8-11% silicon. Galvanized steel coil with such coating is highly resistant to oxidation at high temperature (up to 650°C) and highly resistant to chemical corrosion.

Galvanised steel coils manufactured according to the EN 10346 can be made from the following steels:

● Low-carbon steel for cold forming (DX51D – DX57D). These products are classified based on suitability for cold forming: DX51D – bending and profiling quality; DX52D – drawing quality; DX53D – deep-drawing quality; DX54D – special deep-drawing quality; DX55D – special deep-drawing quality (only +AS); DX56D – extra deep drawing quality; DX57D – super deep drawing quality.

● Steel for construction and framing (S220GD – S550GD). Rolled products are arranged in increasing yield stress (Rp0. 2), which is indicated in the marking. Rolled products of S220GD – S550GD steel are mainly used in the manufacture of formed sections (Z-, C-, sigma-, U-shaped profiles, etc) for light-gauge steel structures.

● Steel with high yield strength for cold forming (HX160YD, HX180YD, HX180BD, HX220YD, HX300LAD, etc). Such rolled products are arranged in increasing yield stress (Rp0. 2), which is indicated in the marking. The marking also contains the following information: H – high-strength flat rolled products for cold forming; Х – as-rolled condition (hot-rolled or cold-rolled) is not defined; D – designed for hot-dip coating; B – heat-treated steel; Y – steel with higher formability; LA – low-alloy / micro-alloy steel.

● Cold-formable multi-phase steel (HDT450F, HCT490X, HDT590X, HCT780X, HCT980X, HCT780T, HDT580X, etc). Rolled products are arranged in increasing minimum tensile strength (Rm0. 2), which is indicated in the marking. The marking also contains the following information: H – high-strength flat-rolled products for cold forming; С – cold-rolled products; D – hot-rolled products; Т (nnn) – the minimum tensile strength in MPa. The last symbol: F – ferrite-bainite, Х – dual-phase; Т – TRIP, С – complex-phase; М – martensite.

Galvanised coils as per the EN 10346 standard can be coated with zinc, zinc-iron alloy, zinc-aluminium alloy, aluminium-zinc alloy or aluminium-silicon alloy. The coating weight is expressed as grams per square metre and characterises the weight of the coating deposited on the both strip surfaces. The coating type (Z, ZF, ZA, AZ, AS) and nominal weight are indicated in the coating designation. Depending on the type of protective layer, the minimum weight of coating on both surfaces of a galvanized product can be 100-600 g/m2 (average value for three spots).

►Galvanised steel coils as per the EN 10346 standards are also classified based on:

●Types of surface quality:

   А – surface quality right after coating application

   В – surface quality improved by processing in a skin pass mill

   С – highest surface quality also obtained by processing in a skin pass mill; the controlled surface should allow for the application of a homogeneous layer of decorative paint, while the other surface should have minimum quality B

● Surface treatment:

There are some different surface treatment methods to reduce the risk of corrosion during storage and transportation.

1. Passivation

After being passivated, it can reduce rust (white rust) during storage and transportation. However, passivation hinders the adhesion of most coatings. In general, other types of galvanized layer, except for zinc-iron alloy coating, will go through passivation treatment atthe factory.

2. Oiling

Oiling can reduce the corrosion of steel sheets under wet conditions. Please note that theoil layer should be removed with a degreaser that does not damage the zinc layer.

3. Organic Coating Film

Using a thin transparent organic coating film on the surface can provide additional corrosion protection, as well as fingerprint resistance. It can also serve as the adhesion for subsequent coating.

4. Phosphating

Phosphating treatment also is able to improve the adhesion and corrosion resistance of zinc coating. And it can be coated without further treatment in addition to normal cleaning.

If you have special requirements about hot dip galvanized coils, please let us know.

● Surface finishing(spangles on Galvanized Steel)

Spangle is formed during the hot-dip galvanizing process. The size, brightness, and surface of spangles mainly depend on the composition of the zinc layer and the cooling method. According to the size, it includes small spangles, regular spangles, big spangles, and free spangles. They look different, but the spangles almost will not influence the quality of galvanized steel. You can choose according to your preference and use purpose.

(1) Big or Regular Spangles

Spangle-promoting elements are added to the zinc bath. Then beautiful spangles are formed as the zinc layer solidifies. It looks good. But the grains are coarse and there is slight unevenness. In a word, its adhesion is poor but weather resistance is good. It is most suitable for guardrails, blowers, ducts, rolling shutters, drain pipes, ceiling brackets, etc.

(2) Small Spangles

During the solidification process of the zinc layer, zinc grains are artificially restricted to form as fine spangles as possible. The spangle size can be controlled by cooling time. Generally, the shorter the cooling time, the smaller the size. Its coating performance is great. Therefore, it is perfect for drainage pipes, ceiling brackets, door columns, the substrate for color coated steel, car body panels, guardrails, blowers, etc.

(3) Zero Spangles

By adjusting the chemical composition of the bath, the coating has a uniform surface without visible spangles. The grains are very fine and smooth. It has excellent corrosion resistance and good coating performance. It is also ideal for drainage pipes, automobile components, back panels for home appliances, automobile body panels, guardrails, blowers, etc.

Geometry and size tolerances for steel sheets and strip coated by hot dipping should meet the requirements of the European EN 10143 standard.

 ►HDG steel coils according to US standards

The main US standard followed for the production of hot-dip galvanized coils with metallic coating is ASTM A653/A653M.

Hot dip galvanized steel can be produced from the following steels:

● Commercial steel (CS, types А, В and С)

● Formable steel (FS, types А and В)

● Deep drawn steel (DDS)

● Structural steel (SS)

● High-strength low-alloy steel (HSLAS, types А and В)

● Solution hardened steel (SHS)

● Bake hardenable steel (BHS)

Depending on the class of selected zinc coating (G01-G360 for British Imperial system, or Z001-Z1100 for international system of units SI), the minimum weight of protective material can vary from 90 tо 1, 100 g/m2 on both sides of the product.

Geometry and size tolerance for hot dipped galvanized coil produced to ASTM A653/A653M should meet the requirements of ASTM A924/A924M.

Hot dipped galvanized coil advantages

Due to the self sacrifice of zinc and good surafce, hot dipped galvanized coil has strong corrosion resistance, paintability, and processability, economical and practical.

Available to select and produce the desired amount of zinc gilded, in particular enables thick zinc layers.

Classified as either zero spangle or extra smooth depending on whether the galvanized sheet surface undergoes skin pass treatment.

Manufacturing process

Hot-dip galvanising (HDG) technology is used to create a protective layer by immersing a steel strip into a bath of molten zinc. Hot-dip galvanised steel coils can be produced by continuous galvanising lines with non-oxidising annealing furnaces (the Sendzimir method and its variations) or by applying wet or dry flux (the Cook-Norteman method and its modifications). Hot- or cold-rolled non-annealed (full-hard) steel coils are used as feedstock for continuous hot-dip galvanising lines with non-oxidising annealing furnaces. The production process involves electrochemically cleaning, drying and annealing the strip to obtain the required mechanical properties, followed by immersing the material into a bath of molten zinc and controlling zinc thickness. The strip then undergoes forced cooling and finishing (passivation, oiling, levelling, drying and coiling the galvanized coil). When using lines that apply wet or dry flux, feedstock (before it is galvanized) should have the required set of mechanical properties since such lines do not have annealing furnaces. The strip is first degreased with an alkali solution and pickled in acid, following which a smooth layer of flux composed of a combination of zinc chloride, ammonia chloride and various additives is applied to the strip. The strip is then put into a strand furnace with a protective atmosphere, where the flux is dried, and is immersed into a bath of molten zinc. The flux completely removes residual pickling substances and moisture from the metal surface, and the thin film reduces the surface tension of zinc and ensures the best moistening of the metal surface. Hot-dip galvanising technology is fairly universal and is widely used in construction, machine building and other industries. It is used by both large steel mills and re-rollers/coaters.

Inspection of Hot-Dip Galvanized Steel

The inspection of hot-dip galvanized steel products includes the base metal material and mechanical properties (tensile test/bending test), thickness, width, length, zinc coating thickness, spangles (surface), packaging, profiles, etc. In our company, we have a strict quality inspection system. Also, Jinbowantong hot dipped steel coil is subject to third-party quality tests. Moreover, we can offer samples for your inspection. Welcome to contact us for more details!

Packaging details

The standard seaworthy package includes waterproof kraft paper and plastic film inside and GI sheets outside. Then it is bound with steel strips. extra reinforcement before shipment to ensure that the goods are safer and less damaged to customers.

Below are some pictures for your reference.

Application of hot dipped galvanized coil

Hot dipped galvanized coil is widely used in the following industries:

● In the construction industry: to manufacture structural elements low-rise construction, light steel thin-walled structures, sandwich panels, lining of heat pipelines and various heat insulation, conditioning systems, metal roof shingle, profiled sheeting, culvert pipes, cladding of entry doors, elevators, reinforcement profiles for PVC windows and plastic doors, European-type fasteners for plasterboards, light steel keel, interior and exterior wall panels, door panels and frames, the surface sheet of the balcony, ceiling, railings, partition walls, windows, and doors, gutter, sound insulation walls, ventilation ducts, rainwater pipes, rolling shutters, agricultural warehouses, Scaffolding, CZ purlin and so on.

● In the automotive industry: to manufacture external and internal car body parts, as well as to repair external public transport body parts, eg for buses and trams). decks of trains or ships, containers, road signs, isolation fences, ship bulkheads, etc.

● In the machine building and instrumentation industries: to manufacture cases for electrical and mechanical equipment, home appliances, metering devices and packing

● To manufacture houseware (tableware, bowls, buckets, tanks, baths, etc)

● To manufacture colour-coated (and other type of coating) rolled steel

Why Choose Galvanized Steel Coil?

1. Cost-effective Solution

Compared to GL or color coated steel coils, the galvanized coil is the most cost-effective solution but with similar features, such as great corrosion resistance, good appearance, etc.

2. Wide Applications

GI sheet roll is easy to process for different purposes. Galvanised steel sheet is widely used in construction, home appliances, automobile containers, transportation, etc. Besides, china coil has good coating adhesion and weldability. That's why hot-dipped galvanized steel is also an ideal base metal for PPGI products.

3. Easy to Transport

Compared to GI steel sheets, coils are easier to transport. In this way, it will save your shipping cost.

FAQ

A. How long is the service life?

It is 5-8 years for regular zinc coating—more zinc coating, more service life.

B.Type of galvanized spangle:

Galvanized with regular spangle: zinc coating from 30g to 275g, thickness from 0. 15mm to 2. 0mm. it usually be used for building and automobiles. Such as roofing, door, car board fence and so on.

Galvanized with zero spangles: this kind of GI with brightly surface, zinc-coated from 30g to 275g, thickness from 0. 12mm to 0. 25mm. It could be used outdoor also. Currently mainly exported to Southeast Asia and Africa. It is cheaper than galvanized with regular spangle. This product can be processed later, for example, processed into stone coated tiles, light steel keel and so on.

C. Galvanized steel coil could be oiled?

Yes, it could be oiled, Oiling can prevent the oxidation of galvanized sheets in a short time.

D. How can you guarantee the coils' quality?

We accepted any testing. We could send samples to the laboratory that the clients required, or customer arrange third-party testing, such as SGS, BV and so on.

GI coil is a profitable investment project, which can be used in many areas. jinbowantong Steel is a qualified galvanized steel coil manufacturer in China, which has 12 years of industry experience and 8 years of export experience. During the two decades, we have developed full systems from pre-sales consulting to after-sales service, roofing solutions and coils. That's why our products are well-received by customers around the world. Except for GI coils and sheets for sale, we also have PPGI, PPGL, GL steel sheets and coils, strips and plates, etc. to choose from. Welcome to contact us for more information!

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