Introduction to color coated board

Color plate to cold rolled steel and galvanized steel as the substrate, after the surface pretreatment (degreasing, cleaning, chemical conversion treatment), in a continuous process of coating, after baking and cooling and made.

Colour coated board introduction

What is painted board

Painted plate, also known as color steel or PPGI steel.

It is made of cold rolled steel sheet and galvanized steel sheet, after surface pretreatment (degreasing, cleaning, chemical conversion treatment), continuous coating (roller coating method), after baking and cooling.


Color coated steel features

Color coated steel is light and beautiful, with good anti-corrosion performance, and can be directly processed. It provides a new raw material for the construction industry, shipbuilding industry, vehicle manufacturing industry, furniture industry and electrical appliance industry, and plays a good effect of replacing wood with steel, efficient construction, energy saving and pollution prevention.


Color coated board structure

A color coating steel plate from the section is divided into five layers: steel substrate, metal coating (also some products directly use cold rolled substrate), chemical conversion layer, primary (primer), finish (finish)


Color coated board type

According to the substrate

According to the different substrates, there are cold rolled substrates, galvanized zinc substrates, hot galvanized substrates, aluminum zinc substrates.

Typical value of galvanizing layer is as follows (unit: g/m2) : electric galvanizing: 20/20, 36/36, etc.Hot dip galvanizing: 90/90/140/140, etc.;Hot aluminum zinc plating: 75/75, 90/90, etc.

According to the coating

Top coat: polyester (PE), silicon modified polyester (SMP), polyvinylidene fluoride (PVDF), high weather resistance polyester (HDP), functional coating (heat insulation, self-cleaning, anti-static, scratch resistance, etc.)

Primers: epoxy, polyester, polyurethane, etc

Selection of color coated steel for construction and coating

Architectural color coating board, coating options

The material requirements of buildings (roof panels and exterior wall panels) themselves can be divided into safety performance (impact, wind pressure and fire resistance), residential performance (water resistance, heat insulation and sound insulation), durability (pollution resistance, weather resistance) and manufacturability (economy, easy to work with, easy to maintain and repair).


Safety and service life are of Paramount importance to the ultimate owner of the building.For the design unit, the service life, bearing capacity, appearance, more important.And for the building wall and roof processors, color coated board processing (surface hardness, wear resistance, plate shape and steel strength) is the preferred requirements.


Of course, the quality of the color coated board mainly depends on the color coated board manufacturer, but if the processing and installation equipment and methods are not appropriate, will also cause different degrees of damage to the appearance of the final product and service life.

The performance of color coated board mainly includes:

Substrate: yield strength, tensile strength, elongation

Coating: coating weight, binding force

Coating: chromatic aberration, gloss, t-bend, impact, hardness, powder resistance, moisture and heat resistance, etc

Surface: visible surface defects, etc

Plate type: tolerances, irregularity, etc

1  The steel grade

For buildings, the bearing capacity (wind load, snow load, construction personnel thick wood), the span of the building, etc., depends on the hardness of the steel plate, for the building maintenance structure with color coating and aluminum zinc plate, there are corresponding standards at home and abroad.For example, Chinese GB/T 12754-2006, American astm653.a STM792, Japanese JISG3302, JISG3321, European en10215.en10147, etc.It is divided into CQ (ordinary commercial grade), D Q (general stamping), HSS (high strength structural steel) and FH (full hard steel).


Now the most commonly used, such as baosteel produced by the TDC51 class SU, yield strength between 260-320MPa, tensile strength between 350-400MPa, relative to the structural steel, its flexion ratio is slightly higher.


Due to the general construction color board are roller forming or composite sandwich, the requirements for the stamping performance of materials is not high, so the DQ class is mainly used in doors, Windows, pipelines and other industries.



High strength structural steel: according to European standard HSS, it can be divided into 4-5 kinds of steel with different strength. However, since ordinary CQ grade materials have been able to replace low-strength HSS steel, the steel with yield strength of 280MPa and 345MPa are widely used in the market. The TS280GD and TS350GD produced by baosteel are these two steel types.

Compared with CQ, HSS steel has several advantages:

1) as the flexion strength is relatively low, the steel has good fire resistance and shock resistance.

2) for thicker steel plates, it can be used to manufacture large-span arch plates.

3) for general external walls and roof panels, it can be thinner than CQ materials, thus saving material consumption.


Full hard steel: it is a kind of steel that can improve the yield strength of steel plate by controlling annealing temperature. According to the international general standard, the yield strength is greater than 550MPa, the tensile strength is greater than 570MPa.

2  Selection of coating

Coating is to ensure the durability of the building, corrosion resistance and consideration, different USES can be selected by different coating, coating and thickness to meet its service life.


2.1 The plating

Construction with color coating now common coating for hot – dip galvanized and hot – dip aluminum zinc two kinds.For color coating, there is little difference between the two substrates. In the relatively acidic environment, aluminum-zinc substrates are a better choice.For wet, alkaline environment, the use of galvanized substrate notch corrosion resistance to reflect the advantages.

For coating thickness, on the roof panel and cladding the general requirements for hot dip galvanized is greater than 80 g/m2 (about 26 microns), aluminum zinc plating is greater than 100 g/m2 (about 27 microns), when using the environment in heavy industry or the beach, foreign related association has a minimum amount of galvanized, such as ECCA specification and Australian standard requirements zinc plating layer weight greater than 275 g/m2 (about 38 microns), aluminum zinc plating is greater than 150 g/m2 (about 40 microns).

Hot aluminized zinc substrate has excellent corrosion resistance and is suitable for the production of building panels.

Hot dip galvanized substrate has excellent corrosion resistance. It is suitable for making building exterior panels, and can be processed in general forming, stamping, deep stamping and other levels.

Electroplated zinc substrate has good corrosion resistance, thin zinc coating and good processing performance. Suitable for making household appliances, steel Windows or indoor saitama etc.

2.2 The coating

Must satisfy the user to the color demand and the durability request.For processors to meet its processing performance.So in order to explain the type of paint, color and gloss, coating thickness.

Now commonly used coil steel coating topcoat varieties are polyester (PE), polyurethane (PU), silicon modified polyester (SMP), fluorocarbon (PVDF), high weathering polyester (HDP), primer and back paint varieties are epoxy (EP), polyester (PE), polyurethane (PU) and so on.

The choice of color is mainly to consider the matching with the surrounding environment and the owner’s hobby, but from the perspective of the use of technology to say that the light color heat reflection ability is strong, coating film powder after the contrast is small, if cleaning and maintenance is appropriate, the service life will be long, will be more beautiful.

For the gloss, in the outdoor use of color coated board, the loss of light occurred the earliest phenomenon, especially the high gloss product its initial loss of light quickly.In glossiness falls to 20 or so can maintain relatively long time, this kind of phenomenon can appear in use a few months, accordingly, outdoor building USES colour to besmear board is low light commonly.


In addition, in the same building should use the same color coating factory produced products.Because different manufacturers of painted steel plate in the outdoor use of a certain number of years after the coating powder speed is different, even if the building seems to be the same, after a period of time will appear different colors of the visual effect and affect the beauty.

Microscopically, coatings are porous tissues.Water in the air and corrosive media (chloride ions, etc.) will invade through the weak part of the coating, causing submembrane corrosion, which causes the coating to bubble and flake.In addition, secondary coatings are denser than primary coatings, even with the same coating thickness.


According to the relevant corrosion test results, the front coating of more than 20 microns to effectively prevent the invasion of corrosive medium.PVDF products require a thicker film.Requirements for the back coating depend on the use, sandwich plate only requires a layer of adhesive primer, and formed steel plate due to indoor corrosion environment so also requires two layers, thickness of at least 10 microns.

[Aluminized/Aluminized-silicon Coating] Brief Introduction of Steel Plate

The aluminum plating process is carried out on a continuous production line similar to that of hot dip galvanized thick steel plate, in which cold rolled thin steel plate is hot dipped into the molten metal liquid of aluminum (aluminum plating) or aluminum (aluminum plating) with a silicon mass percentage of 5% ~ 11% to obtain the desired metal coating.

Aluminized sheet steel

The aluminum plating process is carried out on a continuous production line similar to that of hot dip galvanized thick steel plate, in which cold rolled thin steel plate is hot dipped into the molten metal liquid of aluminum (aluminum plating) or aluminum (aluminum plating) with a silicon mass percentage of 5% ~ 11% to obtain the desired metal coating.

Aluminized sheet steel is used in cases where heat resistance, heat reflection, or corrosion resistance are required, and the sheet steel is both attractive and economical.

A thick (usually 30-50 micron) coating produced by immersion in non-alloyed molten aluminum.


This product is usually used for outdoor structural purposes, such as roofs, culverts and grain silos, requiring a low formability requirement but with excellent corrosion resistance.

Aluminum – silicon alloy coating is relatively thin, the appearance quality has been improved.The commonly used thickness is about 20 ~ 25 microns.If the formability requirements are particularly high, a thinner coating thickness of 12 microns can be used.


It can be used for more applications, mainly for applications requiring formability and high temperature resistance, such as automobile exhaust pipe parts.

Characteristics of aluminized sheet

Corrosion resistance

The value of aluminum as a protective layer of thin steel lies mainly in its inherent corrosion resistance. In most environments, the long-term corrosion rate of aluminum is only 15-25% that of zinc.

In general, the value of aluminum coatings to steel substrates depends on thickness.As long as the coating remains undamaged, it provides long-term protection.

Aluminum coatings in most environments are especially exposed to the atmosphere without providing sacrificial anode protection.

Heat resistance

Aluminized sheet steel has excellent oxidation resistance at high temperature.

The aluminum coating protects the steel from oxidation and does not stain itself when the surface flap does not exceed approximately 510°C.

The coating still protects the steel at 510~675°C, but darkens the surface as the aluminum-iron-silicon alloy develops.The alloy layer is extremely resistant to heat, but because it has a different coefficient of expansion from steel, the coating becomes brittle and flaking when it exceeds 675°C.


Aluminized sheet steel can be connected by resistance welding (spot or seam welding), metal arc welding, spark butt welding or oxy welding.

Before connecting, it is recommended to use wire brush to thoroughly remove oil, grease, paint and dirt.Metal arc welding and block oxygen welding also require the use of specialized fluxes.

Aluminum may be attached to the electrode during resistance welding, so the electrode head or welding wheel needs to be polished more frequently.At the same time, the welding current density should also be greater than the welding of uncoated steel plate

Standard and grades for aluminized sheet

The JIS standard, for example, is included in the JISG3314, with typical grades such as SA1C and similar grades in other standards such as ASTM


SA1C Jis G3314 2010 aluminum or aluminum silicon

Brand interpretation

S steel,

A aluminum,

1 serial number, representing heat resistance

C commercial

The approximate number

DX51D OYN 4022 2015:aluminum or aluminum silicon alloy coated steel

DX51D EN 10346 2015:aluminum or aluminum silicon alloy coated steel

A463M CSTypeC ASTM A463/A463M 2010:aluminum or al-si alloy coating

The little knowledge of Aluminized

Aluminum plate has some other characteristics, may be different due to the production process or use conditions, there will be a special case, so as a small point remarks.

1, the surface of aluminum plate, not only beautiful processing, and has excellent reflection performance, at 500°C below the temperature, with about 80% light reflectance;The reflectivity in infrared is 95 percent.Therefore, the aluminized plate can be made into an efficient thermal barrier or heat reflector in high temperature applications, which can rapidly increase the temperature in the furnace through effective heat reflection.

2, aluminum plate between the substrate and the coating, because of the existence of iron and aluminum alloy, therefore, generally considered to be worse than cold rolled steel, galvanized steel plate processing.But for the various processing characteristics of aluminized steel plate, if it can be processed according to the method can obtain almost the same processing effect as other steel plates.

3, when coating on aluminum plate, in order to make the adhesion stable, the chemical coating needs to be pretreated.

4. The aluminized layer of aluminized steel plate is composed of aluminum, silicon and iron elements.Some authorities under the Japanese government have verified that the aluminum plate without chemical passivation complies with the food hygiene law, is harmless to human health, and can be directly applied to food processing.Test reports from many professional bodies prove that they are environmentally friendly and harmless to humans.

Description of Zinc Coating Thickness

We often see galvanized steel sheet, it is steel and zinc two kinds of composite material, combined with the advantages of both, both the strength and plasticity of steel, and corrosion resistant coating, in the field of construction, home appliances and automobiles have a wide range of applications.

In the atmosphere, zinc coating can give steel substrate excellent corrosion resistance, which is closely related to the thickness of zinc coating.How to identify the thickness of the zinc layer?Usually in the standard galvanized steel plate brand suffix.

For example, we often see the following suffix code

G90, Z27, Z275, 60, 90/90

These are labels for zinc thickness in different standards. To understand what they mean, you must know where they come from.

Then we have to understand what standard these coating suffixes belong to before we can make an analysis.

The above suffixes are classified into five standards, as shown in the table below:

Standard CodeUnitZinc Coating CodeZinc Coating Weight(both size)
ASTM 653/653M-13British systemOz/ft2G30 G40 G60 G90 G100…0.3 0.4 0.6 0.9 1.0…
Metric systemg/m2Z90 Z120 Z180 Z275 …90 120 180 275 …
EN 10327-2004Metric systemg/m2Z100 Z140 Z200 Z225 Z275…100 140 200 225 275
JIS G3302-2010Metric systemg/m2Z06 Z08 Z10 Z12 Z27…60 80 100 120 275…
GB/T 2518-2008Metric systemg/m260 80 100 120…60 80 100 120…
Q/BQB 420-2014Metric systemg/m240/40 50/50 70/70…80 100 140…

In the table from top to bottom are: American standard, European standard, Japanese standard, national standard and baosteel enterprise standard.

Have you noticed a pattern: only in astm653/653m is there an inch marking method, and G90 is an inch marking method.

Characters in different standards have different meanings.

Is G90 equivalent to baosteel target 90/90?As can be seen from the table above, there are essential differences between them.

The value of comparison is only when the standards of measurement are consistent

The imperial value is certainly not the same as the metric value

The G90 USES the British unit, which must be converted to metric for comparison.

In the standard, G90 refers to the mean minimum weight of 0.9oz/ft2 (oz/ft2) measured at three points on both sides of galvanized sheet, namely 0.9oz/ft2.

1 oz = 0.0284 kg

0.9 oz = 0.02556 kg = 25.56 g

1 ft2 = 0.093 m2

25.56 g/m2 = 0.093 275 g/m2

G90= double side sum 0.9oz/ft2= double side sum 275g/m2 / baosteel enterprise standard 90/90 g/m?(90+90= the two-sided sum of 180g/m2).The relationship between zinc layer and thickness of zinc layer

The conversion relation between weight and thickness of each coating is different, which is described in the standard. The pure zinc coating 50g/m2 is approximately equal to 7.1um.

Then, for example, in G90, the total thickness of the zinc layer on both sides =275/50*7.1 =39.05um (micron).

Steel sheet product process


Iron ore is reduced to molten iron, and the specified chemical composition of molten steel is obtained by adjusting the content of alloying elements in the molten iron.

The C, Si, Mn, P, S and other alloying elements we see in the warranty have been basically fixed in this link.


Continuous casting

Direct casting of molten steel into rectangular billets eliminates the traditional “ingot – billet rolling” process.(like 300 tons of molten steel in a furnace, cast into 10 or so rectangular billets.)

The steel blank is the raw material for the hot rolling process.


Hot rolled

Hot rolling, or hot rolling.After the billet is heated, it is rolled in a specific temperature range to obtain the desired properties.Main applications: container, engineering machinery, steel structure, etc.



A process after hot rolling and before cold rolling is to remove iron oxide from the surface of hot rolling products.The full name of pickling products is “hot rolling pickling material”, which belongs to a kind of hot rolling products.Main applications: automotive chassis parts, wheel hub, electric water heater components


Cold rolled

On the basis of the hot rolled raw material, further thin, to achieve the desired thickness of the finished product.After cold rolling steel strength, hardness, toughness and plastic index decline, processing performance is very poor. 

Main applications: cold rolled coils are used as raw materials for subsequent annealing and galvanizing processes.


The rolled coil is slowly heated to a set temperature, held for a certain time, and then cooled at a specified rate.Annealing is a form of heat treatment designed to obtain desired product properties (mechanical properties).

Main applications: automobiles, home appliances, etc.


Hot dip galvanized

Also known as hot dip galvanizing, the process of dipping the annealed steel strip into a zinc pot containing liquid zinc to obtain a pure zinc or zinc ferroalloy coating on the surface of the steel strip.Main applications: automotive, home appliances, parts with high corrosion resistance.


Electric galvanized

The process of obtaining a thin layer of zinc on the surface of steel strip by electrolysis reaction.

Main applications: computer cases, copiers and other parts of high surface quality requirements.


Colour Coated

The process of coating steel strip with organic or inorganic coatings. 

Main applications: industrial plants, mobile buildings, etc.


Horizontal bright stripe of galvanized roll

The possibility of horizontal stripes, and their characteristics

DX51D+Z environmental protection passivated galvanized coil head out of horizontal bright stripes, this stripe thick is not easy to determine whether it is crease print, roller print, mill vibration stripes, horizontal stripes, etc., as shown in the figure below:


Learn more product information from defect photos, warranty, brand, specifications, implementation standards, defect morphology, appearance and other aspects, then eliminate other defects from multiple perspectives, and then narrow the scope of possibility from several features.

Defect description

The DX51D+Z zinc-friendly passivating coil has a continuous horizontal bright stripe defect, and only the upper surface has a horizontal bright stripe, the lower surface does not.

Defect possibility analysis

We exclude several possibilities from several aspects:

First, it is impossible to be a crease print, the crease print should appear on the thick specification, and should be in the inner ring, and this is the direct delivery futures, the specification is 0.8*1250, the thickness is relatively thin, the possibility of producing crease print is not large, and the direct delivery, the possibility of rewinding crease print found in the inner ring is not large.In addition, the crease print should be the top and bottom, not a single side.

Second, it is not rolling, flat roll printing, if it is rolling, it should be periodic, and may be rolled out, and the bright streak is a continuous number of a straight 40m, so also excluded.

Third, the mill vibration stripe is not, because this defect is also mostly double-sided, single-sided possibility is very small.

Finally, horizontal streaks produced by the coating spores of the coated passivator are more likely because the two surfaces are coated separately during the coating process, so the single bright streaks are most likely to be produced.If the bright streaks have a raised feel, and if you sandpaper the passivated film, it will disappear with the polishing, that’s very likely.

Can you raise the quality objection?

According to the steel mill enterprise standard, the surface quality grade of FB is allowed to have streaks, among which horizontal streaks also belong to streaks.

Can I use it?

So can we use this 40-meter material?From the perspective of use, if it is the horizontal stripe caused by passivating liquid coating, the uneven coating will not affect the corrosion resistance, but it is not very good-looking, but there is a problem with the single side, the side can be used as the inner surface, or can be used.

Of course, if the passivating liquid is not applied, then another, so we want to see is raised or sunken, raised is passivating liquid is applied too much, sunken should be tested, whether to apply.

Washing their own plate:Self-cleaning color board

Self-cleaning color coated board introduction


Many buildings are complex in shape and high in height, so the human and material cost of cleaning once is very high.We often see “spiderman” outside buildings, and safety at high altitude is a big problem.

Now the haze is so serious, the air quality is low, and the surface is more vulnerable to pollution.So there is no such a material, can achieve self-cleaning.

As we mentioned earlier, color coated panels are now used in many buildings because of their superior performance and low cost.There is a special variety of color coated, we call it will give their own bath color coated plate – self-cleaning color coated plate.

Self-cleaning color coated steel plate structure

Self-cleaning color coating board is also composed of substrate, coating, chemical conversion layer, primer, finish.


Self-cleaning principle


The surface of the color coating plate is enriched with hydrophilic additives and forms a dense paint film structure in the paint surface.Let’s compare the difference between ordinary color board and self-cleaning color board.

Stain resistance contrast

1 ordinary color board


The surface contaminant of ordinary color plate is easy to permeate from the small crack on the surface and cannot be removed by conventional cleaning method.

2 self-cleaning color board


The surface of the self-cleaning color board because of the existence of a layer of cross-linked dense paint film, can effectively resist the pollutants permeate into the paint film inside, and play a role in protecting the color board.

The hydrophilic

1 ordinary color board


Ordinary color board because is the surface of the water, when the rain wash, there is no way to adhere to the color board in the surface of the dirt to wash away.

2 self-cleaning color plate


Self-cleaning color plate has excellent hydrophilic surface, to ensure that the rain fully auxiliary development, wash away the surface of the pollutants.

Types of paint

According to different environmental requirements, commonly used coating has the following four kinds:

1. Self-cleaning polyester (PE)

2. Self-cleaning silicon modified polyester (SMP)

3. Self-cleaning high weathering polyester (HDP)

4. Self-cleaning fluorocarbon (PVDF)

Above four kinds of coating from top to bottom weather resistance is better and better, of course, the price is also more and more expensive.

Features and applications

1. Excellent decorative performance

2. Special finish design to achieve self-cleaning function

3, according to the different environment, there are a variety of topcoat to choose

4. Various medium and high strength substrates + different coating combinations

Analysis and control method of surface defect of hot dip galvanizing

Hot dip galvanizing is one of the effective methods to improve the corrosion resistance of steel because of its excellent coating performance and long service life.

The surface of hot dip galvanizing layer has many common quality defects such as leakage plating, stripe feather white pattern, coating super thick, rough, gray, tear streaks, turtle crack, crystal raised grain, “white rust”, etc., the influencing factors are many, and the control is relatively difficult.

In order to improve the surface quality of hot dip galvanizing, the process control should be strengthened and necessary measures should be taken.

Surface pretreatment

Poor surface pretreatment is the main cause of plating leakage.

Steel in the factory, storage, transportation, processing inevitably stained with paint or mineral fat, sometimes welding parts need to daub difficult to clean special grease, most of the enterprise and no degreasing process, only by pickling to remove surface impurities, which is easy to cause leakage plating (iron).

The other case is due to the pickling process pickling parts more concentrated, piled up dense, heavy and other factors, resulting in underpickling and line clamping, or because the pickling concentration is too high so that the acid salt precipitation on the surface, groove, not washing or washing is not complete, it is also easy to form leakage plating, empty plating phenomenon.

In addition, due to solvent aging, failure, in addition to the drying process did not put the workpiece in time, or drying time is longer so that the steel surface appears secondary micro-oxidation, the formation of acid iron salt cover on the surface, also prone to plating leakage, especially in the relative humidity of the climate and fog weather is more common.This situation is often overlooked.

In addition, when using solvent hot dip galvanizing, the most commonly used ZnCI2 and NH4CI mixed aqueous solution is not the right ratio, no eutectic point is formed, especially in the case of too high concentration, in the support plate welding Angle seam circular hole is prone to occurrence of ash trap leakage plating.

The zinc coating is not thick enough

The thickness of galvanized layer is not up to the standard requirements will directly affect the service life of the product.The reasons for the insufficient thickness of the galvanized layer are as follows.

(1)Effect of zinc liquor temperature.When the temperature of zinc solution is lower than 430°C, the diffusion rate of zinc and iron is low, it is not easy to generate enough iron and zinc alloy layer, the whole coating is thin;When the temperature is 460°C, the zinc layer thickens; when the temperature continues to rise, the zinc solution becomes thinner and the zinc layer becomes thinner.Therefore, the temperature of zinc liquid must be strictly controlled to ensure the stability of quality.

(2) influence of dwell time of strip steel in zinc solution.The dwell time of strip steel in zinc solution has a certain time range.According to the thickness of strip steel, with the extension of galvanized time, the coating thickness will increase, but excessively prolonged galvanized time will make the zinc layer brittle, but affect the quality.

(3) influence of zinc extraction method from zinc solution.The zinc coating should be thin when the strip is slanted out.Therefore, when the strip leads out the zinc pot, it should be vertical.

Other components in zinc solution

The zinc solution contains many other metal components or harmful elements, which may cause defects such as zinc slag particles adhering to the surface of the coating and some abnormal patterns, cracks and other defects.

(1) iron

Hot dip galvanized for a period of time, the steel surface will appear zinc accumulation and small zinc slag particles, resulting in the coating surface rough, smooth also declined.Such fine particles are generally Fe – Zn alloy particles.

At 450 ° C galvanized, zinc iron in the saturated solubility of 0.02%, iron content in liquid zinc exceeds this value, can form zinc slag, due to the difference of zinc slag particles and density is not large, the gathered sinking slowly, suspended in the liquid zinc alloy slag will clip in zinc liquid out of the parts, inlaid in the coating, which affect the quality of the galvanized layer surface.The sources of iron in zinc solution are generally the corrosion of zinc pot, the dissolution of the parts, the iron ions in the plating agent and the iron salts on the parts.

Therefore, in order to obtain a flat and smooth coating, it is necessary to strictly control the iron content in the zinc solution, reduce the iron ion, control the temperature of the zinc solution, to avoid the zinc solution temperature of the rise and fall, reduce the corrosion rate of the zinc pot.Generally, when the content of iron in zinc solution should be 0.20%, it is necessary to cool down and stand still and salvage zinc slag.

(2) aluminum

Aluminum is the most commonly used additive element in hot dip galvanizing.Different properties of zinc coating can be obtained by adding different concentrations of aluminum to zinc solution.

It is generally believed that hot galvanizing, adding < 1% aluminum in the zinc solution can play the following role: improve the coating brightness;Reduce the oxidation of zinc liquid surface;The coating with good adhesion was obtained by inhibiting the formation of brittle Fe – Zn phase.

However, in the actual production, the zinc solution containing 0.005%~0.020%AI can achieve the purpose of bright coating, and can reduce the surface oxidation of zinc solution and the generation of zinc ash.

It must be pointed out that Zn – AI intermediate alloy should be used to add aluminum.Often due to add the quality problems in the middle of the alloy and the method of adding aluminum and zinc alloy inappropriate or too fast, leading to a large number of generated in zinc liquid aluminum, iron compounds, the density of liquid zinc is less than the zinc aluminum iron three yuan “surface slag” or zinc particles suspended in a liquid surface and very thick, very easy to stick on the iron and steel parts, serious damage to the coating quality, only by cooling in dregs is useless at this time.

Once found this situation should immediately stop adding alloy, at the same time to take zinc solution purification measures, aluminum content down, when the situation is not serious can consider the appropriate extension of air cooling time, in order to prevent the appearance of bubbles and wrinkles coating surface sharp water cooling.

(3) the tin and lead

Generally, zinc ingots contain no tin, only trace amounts of lead.In recent years, some suppliers of zinc alloy have added tin and lead to the so-called multi-alloy in order to reduce the temperature of zinc plating and obtain white and bright coatings.

When adding the liquid zinc alloy, zinc liquid level can appear mirror under 430 ° C and can maintain 10 ~ 20 min, but in hot steel plated parts, the coating on the surface of the plume tinea and small white spot, tin, lead alloy added content once reached 0.5%, zinc flower will occur and zinc ash significantly raised, production efficiency is also decreased, caused losses to the enterprise.

Lead and tin, due to their low melting point and high content, rapidly reduce the solidification temperature of the zinc solution. During the cooling process of the zinc layer, it is easy to form coarse crystals and turtle cracks, which affect the surface smoothness and corrosion resistance of the zinc layer.

Intergranular corrosion is the most sensitive to aluminum impurities, and the corrosion rate is accelerated with the increase of lead content in the coating. When the lead content reaches 0.02%, intergranular corrosion will occur. The coating will break along the grain boundary and lose adhesion.Therefore, we must make clear the content of lead, tin and aluminum in the application of zinc-aluminum alloy or multiple alloy, and decide whether to add it in the zinc solution.

Galvanized process

The main problems of the imperfect hot-dip galvanizing process are as follows:

(1) after pickling, no washing or insufficient washing can directly enter the solvent pool, so as to increase the acidity of the solvent and increase the iron ion;Or with hydrochloric acid as a plating agent, so that the strip steel surface covered with a layer of iron salt, into the zinc solution, the formation of melting slag attached to the surface of the workpiece;

(2) solvent aging, more iron ions, more impurities, if not filtered or with the strip into the zinc solution, the viscosity of the zinc solution increased, making the coating thicker and rough, poor adhesion;

The workpiece does not dry, the solvent with water for hot galvanizing will form zinc (0H)2 particles, affecting the product appearance quality;

(4) the solvent is generally weak acid, no heating or low temperature will prolong the drying time, will also corrodes the surface of the workpiece and form adhesion of iron salt, zinc alloy slag formed on the surface of the workpiece, so that the surface of the coating rough

“White rust” is the galvanized layer of the common defects, the main reason is because the zinc plating passivation of the lack, strip with water or do not remove passivation passivation technology is unqualified, strip after water-cooling not completely dry, stored in a damp and electrochemical corrosion in the poorly ventilated environment “white rust” and gray powder corrosion deposits, a direct impact on product and engineering quality, type of this kind of white or grey powder if owner by alkali carbonate zinc compounds, etc

In a word, after hot galvanizing strip steel surface defects are more complex, the causes are more, the solution is a variety of, need to do a lot of hard if meticulous work, so that the hot plating technology to improve one step.

The difference between cold rolling and hard cold forming pickling

Definition of product

In the analysis of the varieties, the first thing to make clear is the definition of these products, these commonly referred to are usually referred to as low carbon steel coil:

Pickling: usually refers to the hot-rolled steel coil after the pickling unit to remove the surface of iron oxide products.

Rolling: usually refers to the product of hot rolled steel coils that have been thinned by a cold mill after pickling, but have not been annealed.

Cold rolling: usually the product of a rolled coil that has been completely or partially annealed.

Cold forming: usually refers to hot-rolled, acid-washed strip steel produced by the ESP continuous casting and rolling process.

Cold forming steel sheet and strip


This standard specifies the classification, code, order content, size, shape, weight and allowable deviation, technical requirements, test methods, inspection rules, packaging, marking and inspection documents of cold-formed steel sheet and strip.

This standard is applicable to the cold formed copper strip of 0.50mm ~ 4.00mm thickness produced by rizhao baohua new material co.

Grade Naming Method

The brand consists of four letters, the first two of which are “RE”, representing the copper plate and steel strip produced by the ESP production line of rizhao baohua new materials co., LTD.The latter two represent the use of steel.

Production process differencesTo understand these four products, you must understand the difference in the production process.Continuous Casting 

ProductsSteelmakingContinuous Casting Hot RollingPicklingCold RollingAnnealing
Picklingmolten waterContinuous Casting SteelHot RollingPickling coil

Rollingmolten waterContinuous Casting SteelHot RollingPickling coilCold Rolling
Cold rollingmolten waterContinuous Casting SteelHot RollingPickling coilCold Rolling
Cold formingmolten waterESPPickling coil

Pickling rolls have no change in base material compared with hot rolling, and are often used in occasions where hot rolling has higher surface quality requirements.Common brand SPHC

Rolled coil is not cheap, formability and surface quality are not good, so usually only used in some thin specifications and performance requirements of the specific industry, such as umbrella bones, or factory trunk.Common brand cdcm-spcc, commonly known in the industry as “cold hard C material” cold rolled coil comprehensive performance is very good, but the disadvantage is the most expensive price (the most processes, the highest cost).Common brand SPCC, commonly known in the industry as “cold rolled C material”.

The forming performance of cold forming coil is much better than that of hard rolling coil, but not as good as that of cold rolling coil (mainly due to the influence of hot processing capacity and large leveling after pickling).

Common ESP cold forming grades include RECC, RECD, MCFC, etc.

Prepainted Galvanized Steel Knowledge 2

Comparison of properties of different coatings

Painter TypeHardnessBendingAnticorrosionWeatherabilityCostPaint Thickness/um
Acrylic ResinGoodNormalOkOkBad20
PVC PlastisolNormalGoodGoodOkBad200

The two most important factors in the selection of primers are,

One is the adhesion of the primer and the finish substrate,

The second is that the primer provides most of the corrosion resistance of the coating.

From this point of view, epoxy is the only choice.

If considering flexibility, considering uv resistance, can also choose polyurethane primer.

For the back coating, the most correct choice is to choose a two-layer structure if the painted steel plate is used in a single layer.

Namely a back primer, a back finish.The primer is the same as the front, and the top coat is a layer of polyester in a light color (such as white).

If the painted steel plate is in composite or sandwich condition, an epoxy resin with excellent adhesion and corrosion resistance on the back will do.

Coating Gloss Selection

Effect of coating thickness on corrosion resistance of color coated plate


Gloss does not belong to the coating performance index, and color, it is just a characterization.In fact, coatings (coatings) are easier to achieve high gloss.

However, the high reflectivity of the high-gloss surface to sunlight during the day will cause light pollution (many of them do not use glass curtain wall now because of light pollution). In addition, the friction coefficient of the high-gloss surface is small, which is easy to slip.Color coated steel plate in the outdoor use of aging is the loss of light, if need to repair, between the new and old steel plate is easy to distinguish, resulting in poor appearance;

If the back paint is high gloss indoor lighting easy to produce halo and cause visual fatigue.Therefore, under normal circumstances, the color coated steel plate used in the construction of medium and low gloss (30-40 degrees).

Coating thickness selection

At the micro level, the coating is porous tissue.Water in the air and corrosive media (chloride ions, etc.) will invade through the weak part of the coating, causing submembrane corrosion, which causes the coating to bubble and flake.

In addition, secondary coatings are denser than primary coatings, even with the same coating thickness.According to foreign reports and related corrosion test results, the front coating of more than 20 um can effectively prevent the invasion of corrosive medium,

Due to the different anti-corrosion mechanism of primers and topcoats, the total film thickness shall be specified, and the thickness of primers (5um) and topcoats (15um) shall be required respectively. Only in this way, the corrosion resistance of different parts of painted steel plates can be ensured to be balanced.

PVDF products require a thicker film.Because to provide a longer life guarantee.The requirements for the back coat depend on the use, the sandwich plate only requires a coat of adhesive primer.The formed steel plate because of indoor corrosion environment therefore also requires two coating.Thickness at least 10um.

Coating Color Selection

The choice of color is mainly to consider the matching with the surrounding environment and the owner’s interests, but from the perspective of the use of technology to speak light color paint pigment selection,

Can choose inorganic coating with superior durability (such as titanium dioxide, etc.), and the thermal reflection ability of coating is strong (the reflection coefficient reaches T tone of dark coating) the temperature of the coating itself in summer is relatively low, which is beneficial to the extension of coating life.

In addition, even if the coating color or powder, light color coating film changes after the contrast with the original color is small, the impact on the appearance is not big.

And dark color (especially more bright-coloured color) use organic color is in the majority, encounter ultraviolet radiation to fade easily, the shortest 3 months change color.

According to relevant experimental data, in summer, when the outside temperature at noon is the highest, the white surface is 10 degrees lower than the blue surface temperature, 19 degrees lower than the black surface.

Different colors reflect different amounts of sunlight.The following table lists the reflectivity of different colors


Color reflectivity reflection effect

For color coated steel plate, the thermal expansion rate of coating and steel plate is usually different, especially the linear expansion coefficient of metal substrate and organic coating is quite different, when the ambient temperature changes, the substrate and coating interface will occur expansion or contraction stress, if not properly released will occur coating cracking.

Baosteel has done the same coating variety in hainan, the same coating supplier, different colors of the 8 years of exposure test, the results also confirmed the light color coating color change is small.

ColourOriginal LusterReal LusterChromatismOriginal ThicknessReal ThicknessDusting
Light Yellow26%2%1.2624172