Colour-coated coils and sheets are widely used pre-engineered building materials. It is a versatile product used for various applications, including home appliances, furniture, airports, industrial, and warehouses.
Colour-coated steel sheets and coils use steel coils as substrates and are coated with various organic coatings. These pre Coloured steel sheets and coils are manufactured by the top structural steel company, APL Apollo Tubes. It also offers excellent electro-resistance as a high-quality PEBsteel structure solution.
The colour-coated steel coils are produced as pre-painted steel sheets and then cut to size and marketed as the finished products. The sheet’s colour comes from the steel colour-coated coils. Pre-painted steel coils are predominantly used to improve the aesthetic value of PEB structures. Apart from this, it offers other advantages such as durability and corrosion resistance.
Several companies that manufacture steel also produce colour-coated products. It is confusing to buy the best colour-coated products. This blog will share the factors to consider when purchasing colour-coated structural steel sheets.
How to Choose Color-coated Coils and Sheets from the market?
The construction material will not only meet your expectation but also reduce the purchasing costs. Consider the following factors when choosing pre-painted steel products:
Measure Coating Thickness
Whenever buying colour-coated sheets, it is important to check the coating thickness of the product. Substrate and coating thickness may vary depending on the application, use environment, and durability. The thickness of the coating will increase its durability and prolong its life.
Must be Hot-Dipped Galvanized Sheets
Before finalizing the structural steel coil/tubes, one major thing to consider is whether it is a galvanized sheet or a galvalume sheet. Manufacturers of color-coated sheets use hot-dip galvanized and galvalume sheets for their superior corrosion resistance. Its mechanical properties make Galvalume sheets suitable for industrial projects in highly corrosive environments.
Types and Colors of top/back paint
PE(polyethylene), SMP (mix of Silicon & Polyester), HDP, and PVDF are four popular top paints that differ in hardness, adhesion, durability, and other qualities. The most often coating used is PE which offers average durability, decent hardness and flexibility, and is available at a reasonable price. SMP is better than HMP because it is durable, glossy, and colour-retaining. However, it is less flexible. HDP is more durable than PE and also less expensive. PVDF has outstanding durability and flexibility, but it is less colourful and more expensive. The top coat should follow these factors such as the use purpose, the environment, the designed life, durability, processing method, etc. to prolong the life of the PEB steel sheets.
Back paint is often chosen based on the application and use environment. When the environment is not corrosive, one layer of paint is sufficient. The back paint must adhere well if it is pasted with thermal insulation materials.
Buy by Weight Rather than Per Piece
To construct their pre-Engineered steel building, you should purchase steel priced by weight rather than per piece. When working on large metal projects, precise weight calculation is crucial to reducing the weight economically and physically. Knowing the weight of steel sheets is essential if you plan to transport or lift them with cranes or hydraulic equipment.
In Summary!
Hopefully, the list of factors will help you to buy suitable colour-coated sheets from the market. APL Apollo is one of the leading structural steel manufacturers in India, with years of expertise in the structural steel sector. We offer safe and efficient structural steel tubes and pipes structures at reasonable pricing by leveraging our experience and cutting-edge technologies. To check out the entire range of APL Apollo structural steel products, please visit www.aplapollo.com and we will be happy to serve you.
Hunter Special Steel Co., Ltd supply professional and honest service.
1. What is the main use of hot-dip galvanized sheet?
Answer: Hot-dip galvanized sheet is mainly used in industries such as construction, household appliances, automobiles, machinery, electronics, and light industry.
2. What are the three types of galvanizing methods currently used in the world?
Answer: There are three types of galvanizing methods: electroplating zinc, hot-dip galvanizing and coating zinc.
3. What are the two types of hot-dip galvanizing according to different annealing methods?
Answer: They can be divided into two types: in-line annealing and off-line annealing, also known as protective gas method and flux method respectively.
4. What are the commonly used steel grades for hot-dip galvanized sheets?
Answer: Product categories include general commodity coils (CQ), structural use galvanized sheets (HSLA), deep drawing hot-dip galvanized sheets (DDQ), bake-hardened hot-dip galvanized sheets (BH), dual-phase steel (DP), TRIP steel (transformation-induced plasticity steel) etc.
5. What are the three forms of cooling towers usually used for cooling?
Answer: There are two kinds of cooling methods - air-cooled and water-cooled.
6. What are some common defects in hot-dipped zinc coatings?
Answer: The main defects include peeling off, scratches, passivation spots, zinc particles, thick edges, air knife marks/scratches/scrapes/exposed steel surface/inclusions/mechanical damage/poor base metal properties/wavy edges/cambering/out-of-size/embossing/zinc layer thickness out-of-specs/roll printing etc.
7. How many forms do zinc plating furnaces have?
Answer：There are three forms including vertical furnace，horizontal furnace，and vertical-horizontal combined furnace。
8.What is length tolerance for a piece of galvanized steel sheet?
Answer: The length tolerance should not have a negative value, and the maximum allowable deviation is +6mm.
9. What are the main reasons for zinc layer shedding?
Answer: The main reasons for zinc layer shedding include surface oxidation, silicide compounds, dirty cold rolling emulsion, oxidizing atmosphere in NOF section and high dew point of protective gas, unreasonable air-fuel ratio or low hydrogen flow rate during production process; oxygen infiltration into furnace; too low entry temperature of strip; low furnace pressure in RWP section or air intake at door；low temperature in NOF section，incomplete evaporation of oil/grease，low aluminum content in zinc pot，too fast line speed，insufficient reduction reaction time and short residence time of strip in molten zinc bath etc.
10. What are the causes of white rust and black spots?
Answer: Black spots are formed by further oxidation of white rust. The main causes of white rust formation include poor passivation film quality or uneven thickness; insufficient drying after passivation treatment; residual moisture on the surface before coating application or during coiling operation；moisture absorption due to poor ventilation conditions during storage/transportation；long-term storage under unfavorable environmental conditions such as exposure to acid/alkaline/salt media etc.
11. How long can finished products be stored? Why?
Answer: Finished products can be stored for up to three months to avoid excessive oxidation caused by prolonged storage.
12.What is the length tolerance for hot-dip galvanized steel sheets？
Answer：The length tolerance should not have a negative value, and the maximum allowable deviation is +6mm。
13.What is big flower pattern？What is small flower pattern？
Answer：Big flower pattern refers to normal spangle which can be produced through normal production process with crystal nucleus diameter no less than 0.2 mm while small flower pattern refers to spangle with crystal nucleus diameter less than 0.2 mm which is difficult to identify by naked eyes.
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14.What is the protection principle of hot-dip galvanized coating?
Answer: Zinc can form a corrosion-resistant film on its surface in corrosive environments, which not only protects the zinc layer itself but also protects the steel base.
15.What is the passivation principle of hot-dip galvanized sheet?
Answer: Passivation treatment with chromate solution can form a passivation film on the surface of galvanized sheet. The chemical reaction formula is as follows: Zn + H2CrO4 - ZnCrO2 + H2
The trivalent chromium in passivating solution has low solubility and chemical activity, acting as a skeleton while hexavalent chromium easily dissolves in water and plays a role in re-passivating when scratches occur on passivated film, thus having healing effect. Therefore, within certain limits, passivation film can prevent direct erosion of steam or humid air into galvanized sheet and protect zinc layer.
16. What are the methods for testing the corrosion resistance of hot-dip galvanized sheets?
Answer: There are three methods for testing the corrosion resistance of hot-dip galvanized sheets: salt spray test, wet test, and immersion test.
17. Why is rust prevention treatment necessary for hot-dip galvanized products?
Answer: When hot-dip galvanized sheets are exposed to humid air, especially when the air contains acidic substances such as SiO2, CO2, NO2 and NO, a loose white rust will quickly form on the surface of the zinc coating. The main components of this white rust are ZnO and Zn(OH)2. This kind of white rust not only affects aesthetics but also brings great difficulties to future use.
18. What are the reasons for white rust formation?
Answer: The reasons for white rust formation include putting hot-dip galvanizing together with other corrosive media such as acid-base or salt; damage to passivation film or anti-film; poor passivation or oiling effect; poor ventilation in storage warehouse causing humidity; water splashing on galvanized sheet during transportation; transportation at low temperature and storage at high temperature resulting in condensation.
19. How do you calculate coating thickness?
Answer: The formula for coating thickness is Dz = Gz (Sz * dz), where Dz represents coating thickness in mm, Gz represents weight per square meter of coating in g/m² , Sz represents area covered by coating in mm² , dz represents density of zinc. This formula can be simplified as Dz = 0.Gz.
20.What causes zinc particles to appear?
Answer: Problems with raw materials mainly involve cleanliness and iron content levels within them；the temperature being too high which causes slag floating up from bottom；Aluminum content being too high affecting solubility level of iron.
21.What does it mean when a hot-dip galvanized sheet is smooth?
Answer: With the continuous expansion of the use of hot-dip galvanized sheets, in modern strip steel continuous hot-dip galvanizing units, the following objectives can be achieved by smoothing the strip:
① Improve the flatness and straightness of thin plates. At the same time, zinc particles on surface can also be flattened to make it smooth. This is particularly advantageous for deep drawing and other high-precision applications in future.
② The smoothing roller used has been pre-treated with shot blasting, so that after being smoothed, there is a certain roughness on the surface of plated plate. It can improve coating adhesion and store a certain amount of grease which will benefit lubrication during deep drawing processing;
③ For plated plates that will undergo painting treatment later on, even if their surfaces are controlled to have small zinc flowers but these small zinc flowers still show through paint layer. Therefore, for some high-demanding galvanized sheets, their surfaces need to go through further smoothing treatment so as to obtain a more uniform silver-white appearance;
④ Through smoothing process，yield point can be lowered，making yield platform disappear or less obvious，which could prevent slip lines from appearing when stretching or deep drawing processing takes place in future thus improving its deep drawability.
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