How to reduce the rate of aging of galvanized sheet

The galvanized sheet may be aged if it is used for too long or not used for a long time. Why do you say that? Long-term construction or storage will inevitably expose to sunlight. After long-term light exposure, aging will occur, which is inevitable, but we can prevent and reduce the aging speed in advance, so what should we do?

A necessary condition for the aging or photochemical reaction of the color-coated board is that the surface components of the color-coated board can absorb radiant energy. Secondly, when the radiation energy absorbed by the molecules is greater than the bond energy of the molecules, the coating of the color-coated board will degrade. The shorter the wavelength of light, the more energy it contains.

According to the above theory, the aging of the color-coated board in the atmospheric environment is that the ultraviolet light band energy absorbed by the coating molecules is higher than the molecular bond energy in the sunlight, resulting in the degradation of the coating molecules. With the aging of the coating film, the body of the substrate is gradually lost, and the surface of the coating gradually becomes rough and loses its luster. The loss of binder eventually leaves stable pigment particles that remain on the surface of the coating film as an unbound powder, a process called pulverization.

To sum up, the aging resistance of polyester color-coated boards with different coating thicknesses varies greatly, the aging resistance of thin-coated color-coated boards is poor, and the aging resistance of ordinary coating thicknesses is relatively good.

Furthermore, it is not feasible to reduce the production cost of color-coated sheets by thinning the coating, which will inevitably bring about serious quality problems. At the same time, it is also demonstrated from the side that it is necessary to clearly indicate the coating thickness in the order contract of foreign color-coated sheet importers.

With the development of my country’s construction industry, the related building materials industry has a broader space for development. Galvanized sheet has been recognized by many users in the market for its unique advantages.

Galvanized steel sheet is cold rolled or hot rolled, and the slender steel sheet is coated with a layer of zinc of varying thickness. The production of galvanized sheet concentrates the advantages of galvanized sheet and strip, so that the product is not only corrosion-resistant and beautiful, but also has high dimensional accuracy, good surface quality, easy processing and material saving. To a certain extent, the products can meet the needs of the public and better meet the needs of users.

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Color selection and application advantages of color coated steel plate

Color steel plate is a steel plate produced after a series of treatments on a continuous line, such as cold-rolled strip. When designing the plates, HUNGTHAI will make various colors according to the needs of customers. Color selection of color steel plate coating: The color selection mainly considers the degree of matching between the user’s preference and the surrounding environment. However, from an application technology point of view, the choice of light-colored paints is larger. Inorganic pigments with better durability can be selected. In addition, the paint has strong heat reflection ability, and the temperature of the paint itself is lower in summer, which is beneficial to improve the service life of the paint.

Even if the color steel coating is discolored or chalked, the contrast between the light-colored film and the original color after the change is small, and the appearance has little effect. Dark colors are mostly organic. It can easily fade and discolor in as little as three months if exposed to UV radiation. For color-coated steel sheets, the thermal expansion coefficients of the coating and the steel sheet are usually different, especially the linear expansion coefficients of the metal matrix and the organic coating are quite different. When the ambient temperature changes, the bonding interface between the substrate and the coating will generate expansion or contraction stress, and if it cannot be properly released, coating cracks will occur.

Color steel plate is actually a kind of steel plate with special organic coating. Due to its excellent performance, it is widely used in construction, home appliances, transportation and other industries. What are the advantages of the color steel plate we often use? Let’s look at it from a few aspects:

  1. Since many building structures have seismic problems, in order to make them have better seismic performance, color steel plates can be used. The structural system has strong seismic resistance and anti-horizontal load capacity, and is suitable for areas with seismic intensity above 8 degrees.
  2. Wind resistance, color steel structure has the advantages of light weight, high strength, good overall rigidity and strong deformation ability.
  3. Durability, the color steel plate residential structure has a long service life compared with ordinary houses.
  4. The thermal insulation material for thermal insulation color steel plate is mainly made of glass fiber wool, which has a good thermal insulation effect.
  5. Sound insulation, sound insulation effect is an important indicator for evaluating residential buildings. The windows installed with color steel and light steel systems use insulating glass, which has good sound insulation effect.
  6. Comfort, the color steel plate wall adopts a high-efficiency energy-saving system, which has a breathing function and can adjust the drying and humidity of the indoor air; the roof has a ventilation function, which can form a flowing air room above the house to ensure the ventilation and heat dissipation requirements inside the roof.
  7. Environmental protection, color steel materials can be recycled to achieve green and pollution-free.
  8. Energy saving, all use high-efficiency energy-saving walls, which have good thermal insulation, heat insulation and sound insulation effects, and can reach 50% energy saving standards.
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Selection of coating materials for color steel coils

At present, the types of coatings used for color-coated steel plates include polyester coatings (PE), fluorocarbon coatings (PVDF), silicon modified coatings (SMP), high weather resistance coatings (HDP), acrylic coatings, polyurethane coatings (PU), plastic Sol paint (PVC), etc.

  1. The polyester coating has good adhesion to the material. The color-coated steel plate is easy to process and form, the price is low, the product is many, and the color choice is large. Under direct exposure in general environment, the anti-corrosion life can be as long as 7-8 years. However, in industrial environments or heavily polluted areas, its service life will be relatively shortened. However, the UV resistance and film crush resistance of polyester coatings are not ideal. Therefore, the use of PE coatings still needs to be restricted. It is typically used in areas with less air pollution or products that require multiple molding and processing.
  2. Since polyester contains active groups -OH/-COOH, it is easy to react with other macromolecules and polymers. In order to improve the light resistance and pulverization of PE, silicone resin with excellent color retention and heat resistance is used for denaturation reaction, and the denaturation rate with PE can be between 5% and 50%. SMP provides better durability of steel plates, and its anti-corrosion life can reach 10-12 years. Of course, its price is also higher than that of PE, but due to the unsatisfactory adhesion of silicone resin to the material and the formability of processing, SMP color-coated steel plate is not suitable for occasions requiring multiple forming processes, and most of them are used for building roofs and exterior walls.
  3. The high weather resistance polyester coating is better than the ordinary silicon modified polyester coating, and the outdoor weather resistance is up to 15 years. In the process of synthesizing polyester resin with high weather resistance, monomers containing cyclohexane structure are used to achieve a balance between resin flexibility, weather resistance and cost. Aromatic polyols and polyacids are used to reduce the UV absorption of the resin and achieve high weather resistance of the coating. Add UV absorbers and steric blocking amines (HALS) to paint formulations to improve the weatherability of the paint film.

Fourth, the plastisol has good water resistance and chemical resistance. It is generally a high solid content coating with a coating thickness of 100-300 μM, which can provide a smooth PVC coating or a light embossing treatment as an embossed coating; since the PVC coating is a thermoplastic resin with a high film thickness, Therefore, it can provide good protection for the steel plate. But PVC has poor heat resistance.

  1. Due to the strong bond energy between PVDF chemical bonds, the coating has good corrosion resistance and color retention. It is a more advanced product in Baosteel’s color steel coil coatings for construction, with large molecular weight and direct bonding structure. Therefore, in addition to chemical resistance, its mechanical properties, UV resistance and heat resistance are also outstanding. Under normal circumstances, the anti-corrosion life can be as long as 20-25 years. In recent years, fluororesins copolymerized with chlorotrifluoroethylene and vinyl ester monomers have been widely used in my country, and are widely used in building exterior walls and metal panels. Due to the use of easily hydrolyzed vinyl ester monomers, the fluorine content is about 30% lower than that of PVDF, and its weather resistance has a certain gap with PVDF.
  2. Acrylic resin has good comprehensive performance and high price, and is only used in specific fields (such as containers).
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Maintenance of Color Coated Steel Coils

While factory pre-painted architectural panels last many years longer than regular painted panels, they still require thorough cleaning. If there is automatic washing of rainwater, such as roof slabs, no maintenance is required. Cleaning can remove accumulated corrosion and keep the building looking good without the need for painting. Places that need to be cleaned include brackets, side panels under drip eaves, warehouse door panels, grooves on the back of drip eaves, etc.

(1) Cleaning: Usually, most of the dust and residue accumulated on the surface of the steel plate can be removed with clean water. In theory, cleaning should be done at least every six months. More frequent cleaning should be done in coastal areas with more salt spray and in places with more industrial dust. For stubborn stains that cannot be washed off, use a weak detergent or household ammonia. In any case, before cleaning a large area, scrub in inconspicuous small pieces. Take a scoop of laundry detergent (or other detergent with less than 0.5% phosphate) and dissolve it in 5 gallons of hot water; or dissolve a cup of household ammonia in 5 gallons of room temperature water. Do not mix ammonia with any bleach; do not mix detergent and bleach without permission. If cleaning and bleaching is required, use a detergent that contains bleach. Using any of the above cleaners, clean the steel surface from top to bottom with a soft soaked cloth, sponge, soft brush or low pressure nozzle to avoid streaks and bright spots. Stain removal powders or industrial detergents are not recommended as they can damage the paint. Water-soluble detergents are effective and can be used. If fungus and mold cannot be removed by the above methods, a detergent containing bleach is recommended. After cleaning, the surface of the steel plate should be completely free of cleaning agent residues.

(2) Repainting: If scratches appear during installation and use, it may be necessary to repaint the defective parts. Improper or excessive patching can damage the entire surface. Scratches that are not apparent at 6 feet should not be repaired, as they may be covered by normal wind erosion. Only the peeling parts of the paint need to be repaired for paint repairs. Dirt, paraffin, and other grime will need to be removed with alcohol from the parts to be repaired prior to paint repairs. Touch-up paint is not recommended for repairing large areas, as touch-up paint does not air dry as well as factory pre-painted. Consult the building panel manufacturer or coating supplier for a suitable gunning system. Aerosol or spray repairs are not recommended for scratch defects. A better repair tool is a high-quality, 1/2-inch or smaller paint brush. If maintained as described above, color coated boards will retain their original color for a long time.

Hungthai Metal is a professional steel manufacturer and exporter. Color coated steel coil is also called prepainted galvanized steel coil, PPGI, PPGL in China, as a PPGI and PPGL manufacturer and exporter in China, we use our own high-quality galvanized steel coil and galvalume steel coil to produce color coated steel coil.

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Main uses and industries of galvanized sheet

The use of galvanized sheet industry has been very common, and many galvanized sheets are used in the automotive industry, refrigerated vehicles, construction industry, natural ventilation and heating equipment and furniture manufacturing and other industries, mainly including the following engineering construction, household appliances, furniture, transportation , steel products and other daily necessities and other industries.

Galvanized sheet is used in the construction industry: roofs, roof prefabricated components, living balcony control panels, balconies, newsstands, warehouses, electric rolling shutters, electric heaters, precipitation pipes, etc.

Galvanized sheet is used in electrical products: refrigerators, automatic washing machines, high-voltage switch cabinets, air conditioners, microwave ovens, bread machines, printers, vending machines, fans, vacuum cleaners, etc.

Galvanized sheet is used in the home improvement industry: lamp covers, wardrobes, dining tables, bookcases, bank counters, billboards, medical equipment, etc.

Galvanized sheets are used in the transportation manufacturing industry: trolley ceilings, car chassis, car box panels, large tractors, electric vehicles, shipping containers, highway courtyard walls, freighter compartment panels, etc.

Galvanized sheet is used in other aspects: traditional musical instrument casings, trash cans, billboards, clocks, photographic equipment, meters, etc.

Galvanized sheet is used in other steel product manufacturing industries: color-coated thick steel sheet should be based on hot-dip galvanized sheet, hot-dip galvanized sheet, electro-galvanized sheet, etc., after surface preparation Strips, electro-galvanized strips, electroplated tin plates, and galvanized plates are restrained and formed, and include connecting hooks, which can firmly connect the steel mesh and the pole without all spare parts. Galvanizing has become a key anti-corrosion method for steel, not only because zinc can produce a high-density protective layer thickness on the steel surface, but also because zinc has the actual effect of pipeline cathodic protection. to avoid corrosion of iron butt welds.

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The difference between hot galvanized sheet and cold galvanized sheet

The difference between hot galvanized sheet and cold galvanized sheet

Hot-dip galvanized sheet: also known as hot-dip galvanized sheet and hot-dip galvanized sheet: It is an effective method of metal anti-corrosion, mainly used in metal structural facilities in various industries. It is to immerse the rust-removed steel parts in a molten zinc solution at about 500 ° C, so that the surface of the steel parts adheres to the zinc layer, so as to achieve the purpose of anti-corrosion.

Cold galvanized sheet: It is an electro-galvanized sheet with a small amount of zinc, only 10-50g/m2. It is a process of using electrolysis to attach a layer of metal film to the surface of metal or other materials. The process of forming a uniform, dense and well-bonded metal layer can prevent corrosion, improve wear resistance, electrical conductivity, reflectivity, and enhance aesthetics.

The difference between hot galvanized sheet and cold galvanized sheet:

  1. Different corrosion resistance, hot-dip galvanized sheet is dozens of times that of cold-galvanized sheet.
  2. The way of operation is different: hot-dip galvanized sheet is galvanized in a molten zinc solution of 450-480 degrees, and cold galvanized is galvanized by electroplating or other methods at room temperature.
  3. The thickness of the galvanized layer is different, and the thickness of the hot-dip galvanized sheet is much larger than that of the cold-galvanized sheet.
  4. The surface smoothness is different. The appearance of cold galvanized sheet is smoother and better than that of hot-dip galvanized sheet.
  5. The price is different, the price of hot-dip galvanized sheet is higher than that of cold galvanized sheet.
  6. The cold galvanized sheet can be plated only on one side, and the hot-dip galvanized sheet should be fully plated.
  7. The adhesion is different, and the adhesion of cold galvanized sheet is not as good as that of hot-dip galvanized sheet.
  8. The charging standards are different. Hot-dip galvanized sheets are charged according to the thickness of the material, and most of the cold-plated sheets are charged according to square meters.

The main application scope of hot-dip galvanized sheet process: industry, construction, power facilities, chemical facilities, machinery manufacturing, petroleum, municipal facilities, agricultural facilities, communication facilities, fire facilities, railways, highway transportation facilities and other fields.

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Precautions for storage of galvanized sheet

  1. Pay attention to the storage environment

After purchasing the galvanized sheet, the user needs to choose a suitable environment for storage. Generally speaking, galvanized sheet needs to be stored in a well-ventilated place in the house, and attention should be paid to prevent water leakage and moisture penetration. Especially if the wrapping paper of the galvanized sheet has been damaged, corresponding measures need to be taken, so it is necessary to check whether the packaging of the galvanized sheet is damaged before storage.

  1. Pay attention to the storage location and corresponding details

The galvanized sheet should be stored for as short a storage time as possible, because the long-term storage may be easily polluted by the environment and cause the surface to corrode. surface causing part of it to fall off. When storing the galvanized sheet, a dunnage or a support frame should be added below, and the number of layers should be as low as possible, and should not exceed two layers. In addition, it is necessary to pay attention to prevent oil powder or dirt from sticking to the surface of the galvanized sheet, thereby affecting the effect of galvanizing.

3, pay attention to rain

When storing galvanized sheets, pay attention to choosing an environment with good ventilation conditions, but do not choose an open-air environment. If you have to choose an open-air environment, you need to pay attention to rainproof measures, cover with rain cloth, and use rubber pads or wooden pads.

All in all, the storage of galvanized sheet should not only pay attention to the storage environment, but also pay attention to the storage location and corresponding details, and take measures to prevent rain in peacetime. In addition, the user should also pay attention to the corresponding anti-collision measures in the process of transporting the galvanized sheet, so as to avoid collision and scratch the surface of the galvanized sheet and affect the appearance.

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What are the advantages of galvanized steel sheet

  1. The adaptability of galvanized steel sheet is generally always very popular, and the anti-corrosion period is long, but the anti-corrosion period is different in different natural environments.
  2. The solution cost is low, and the cost of anti-rust treatment of galvanized steel plate is lower than that of other paint coatings.
  3. It is durable for a long time. In the natural environment of the suburbs, the standard hot-dip galvanized anti-rust treatment layer can be maintained for about 50 years without repairing. In urban areas or coastal areas, the standard hot-dip galvanized anti-rust treatment layer can be maintained for 20 years without repair.
  4. Good reliability. The hot-dip galvanized layer and the stainless steel sheet are integrated by the metallurgical industry, and become part of the surface layer, so the coating tolerance is relatively reliable.
  5. The ductility of the coating is strong, and the hot-dip galvanized layer produces this very metallurgical industrial structure, which can bear the damage of mechanical equipment during transportation and application.
  6. Comprehensive maintenance, every part of the plated parts can be galvanized, even in recesses, bevels and hidden places can be fully maintained.
  7. Cost saving, the whole process of hot-dip galvanizing is more convenient than other coating engineering construction methods, and it can prevent the time required for brushing on the construction site after installation.
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Causes of white rust and black spots on galvanized sheets

Galvanized sheet, immersed the thin steel sheet in a molten zinc bath, so that the surface of the sheet is adhered with a layer of zinc. It is mainly produced by continuous galvanizing process, that is, galvanized steel plate is made by continuously immersing the rolled steel plate in a plating tank with molten zinc. Alloy galvanized steel sheet. This kind of steel plate is also made by hot-dip method, but after it is out of the tank, it is heated to about 500 ℃ immediately to form an alloy film of zinc and iron. This galvanized sheet has good paint adhesion and weldability.

Its disadvantages are mainly falling off, scratches, passivation spots, zinc particles, thick edges, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of steel base, wave edges, buckling, and inappropriate sizes. , embossing, different thickness of zinc layer, roll printing, etc.
The black spot is formed by the further oxidation of white rust.

The main reasons for white rust are as follows:

(1) Poor passivation, insufficient or uneven thickness of the passivation film
(2) The surface is not oiled or there is residual moisture on the surface of the strip
(3) The strip surface contains moisture during coiling
(4) Passivation is not completely dried
(5) damp or rain-drenched during transportation or storage
(6) The storage time of finished products is too long
(7) The galvanized sheet is in contact with or stored together with other corrosive media such as acid and alkali.

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Classification and process production method of galvanized steel sheet

Galvanized steel plate is to prevent the surface of the steel plate from being corroded and prolong its service life, a layer of metal zinc is coated on the surface of the steel plate.

According to the production and processing methods, it can be divided into the following categories:
Hot-dip galvanized steel. The sheet steel is immersed in a molten zinc bath, and a sheet of zinc is adhered to its surface. At present, it is mainly produced by continuous galvanizing process, that is, galvanized steel plate is made by continuously immersing the rolled steel plate in a plating tank where zinc is melted;
Alloy galvanized steel sheet. This kind of steel plate is also made by hot dip method, but immediately after it is out of the tank, it is heated to about 500 ℃ to form an alloy film of zinc and iron. This galvanized sheet has good paint adhesion and weldability;
Electro-galvanized steel sheet. The galvanized steel sheet produced by the electroplating method has good workability. However, the coating is thin, and the corrosion resistance is not as good as that of the hot-dip galvanized sheet;

Single-sided and double-sided differentially galvanized steel. Single-sided galvanized steel sheet, that is, a product that is galvanized on only one side. In welding, painting, anti-rust treatment, processing, etc., it has better adaptability than double-sided galvanized sheet. In order to overcome the disadvantage that one side is not coated with zinc, there is another galvanized sheet coated with a thin layer of zinc on the other side, that is, double-sided differential galvanized sheet;

Alloy, composite galvanized steel sheet. It is made of zinc and other metals such as lead and zinc to make alloys and even composite plated steel sheets. This kind of steel plate not only has excellent anti-rust performance, but also has good coating performance; in addition to the above five kinds, there are also color galvanized steel sheet, printing coated galvanized steel sheet, PVC laminated galvanized steel sheet, etc. But the most commonly used is still hot-dip galvanized sheet.
Galvanized sheet should have a good appearance, and should not have defects harmful to the use of the product, such as no plating, holes, cracks and scum, over-plating thickness, scratches, chromic acid dirt, white rust, etc. Foreign standards are not very clear about specific appearance defects. Some specific defects should be listed in the contract when ordering. Galvanized sheet steel products are mainly used in construction, light industry, automobile, agriculture, animal husbandry, fishery and commercial industries.

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