Anti-corrosion solutions for cold-sprayed zinc coatings in construction steel structures

The application of corrosion-resistant coatings in steel structures in municipal public facilities takes into account not only long service life and aesthetic decoration, but also environmental protection, i.e. the best combination of performance, aesthetics and environmental regulations.
1. The requirements of anti-corrosion and low-paint construction steel structure and the development of
1.1 anti-corrosion primer zinc powder requirements
Commonly used rust-proof primers have zinc-rich primers and thick paddle-type epoxy coatings,
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. Zinc-rich primers have the following regulations for zinc powder.
different countries and regions have different specifications for zinc powder content in zinc-rich primers. BS 4652:1995 stipulates that the zinc powder content in dry paint film should not be less than 85% (mass fraction).
ISO 12944-5: Section 5.2 of 1998 stipulates that zinc-rich primers, whether organic or inorganic, do not volatilized zinc powder content of not less than 80% (quality score), zinc powder standards to comply with ISO 3549.
HG/T 3668-2000 on the non-volatile zinc content of the metal, inorganic zinc-rich primer is not less than 80%, organic zinc-rich primer is not less than 70%.
two types of zinc-rich primers are specified in SSPC-Paint 20: 2002, type I is inorganic zinc-rich paint and type II is organic zinc-rich. And according to the weight of zinc powder in the dry film specified three types of paint: Level1 equal to or greater than 85%; Level2 is equal to or greater than 77%, less than 85%; Level3 is equal to or greater than 65%, less than 77%. The main pigment component in these coatings must be the metal zinc powder requirements set out in ASTM D 520.
steel structure anti-corrosion construction site
1.2 anti-corrosion primer zinc powder nature requirements
zinc powder used in coatings can not be 100% pure metal zinc, it will contain certain zinc oxide, lead oxide and other non-metallic components and metal elements. According to GB/T 6890-2000, its chemical composition can be found in Table 8-40.
ASTM D520 specifies three types of metal zinc powder as paint pigments. The maximum limit of lead content in category 1 is not specified, which is the general grade, the quality ratio of lead content stipulated in type 2 is not greater than that of high purity grade, and the quality ratio of lead content in type 3 is not greater than 0.002%, which is the highest purity grade.
1.3 The lead content standard in zinc powder
The ASTM D520 specifies three types of metal zinc powder as paint pigments. The maximum limit of lead content in category 1 is not specified, which is the general grade, the quality ratio of lead content stipulated in type 2 is not greater than that of high purity grade, and the quality ratio of lead content in type 3 is not greater than 0.002%, which is the highest purity grade.
high-purity zinc powder
2, the development of anti-corrosion primer
building steel structure anti-corrosion primer mainly includes zinc-rich primer, epoxy anti-corrosion primer, metal thermal spraying.
2.1 zinc-rich primer
zinc-rich primer is mainly epoxy-rich zinc-rich primer, alcohol-soluble inorganic zinc-rich primer and water-based inorganic primer. Epoxy zinc-rich primer is mainly epoxy resin as the base material, polyamide as curing agent, ultra-fine zinc powder as the main anti-rust pigment two-part coating. Adding a certain amount of aluminum silver paste and iron oxide red can increase weather resistance and prevent zinc powder from producing.
inorganic zinc-rich primer consists of alkyl silicate polymers, zinc powders, additives and solvents, and typical alcohol-soluble inorganic zinc-rich primers are below Table 8-41. Inorganic zinc-rich primers have better performance in heat, solvent, chemical and electrostecturical conductivity than epoxy-rich primers. However, the construction requirements of inorganic zinc-rich primers are very high, and steel surfaces must be blasted to Sa 2.5. The curing of alcohol-soluble inorganic zinc-rich primers is done by absorbing moisture from the air for hydrolytic shrinking, so the relative humidity of the air is best maintained at more than 65% after spraying. Inorganic zinc-rich must be completely cured before coating the backdoor paint, otherwise it will cause separation between the coating layers.
inorganic zinc-rich primer surface is porous, requiring special closed paint or fog spray technology before spraying the rear paint layer. Inorganic zinc-rich primer for the thickness of the paint film has strict requirements, too high dry film thickness will lead to cracking of the paint film, alcohol-soluble inorganic zinc-rich primer is generally considered safe below 125pm.
Water-based inorganic zinc-rich, water instead of solvents and thinners, does not contain any organic volatiles, non-toxic, non-flash fire point, damage to construction personnel is significantly lower than solvent-based inorganic zinc-rich paint, small environmental pollution, VOC zero, no fire hazard, in the construction, storage and transport process is more safe. It mainly uses carbon dioxide and moisture in the air to react with potassium silicate, in the production of carbonate, zinc powder and potassium silicate fully react to produce zinc silicate high-concentration, its curing is greatly affected by temperature and humidity. Water-inorganic zinc-rich primer requires blasting to Sa3, and the film thickness can be as high as 150 to 200 microns.
2.2 epoxy zinc-rich
thick-mounted modified epoxy coating is also an important anti-rust primer, they usually contain zinc phosphate or aluminum powder and other anti-rust pigments, paint film strong and durable, strong adhesion to steel. These products have been used in marine environments for decades and have excellent corrosion resistance.
hydrocarbon resin modified epoxy resin coating has a common type, aluminum powder type and glass -piece reinforced type and other products, a single spray can reach 100 to 400 microns of dry film thickness. General wear-resistant epoxy paint with modified phenolic amine as a curing agent, as a true universal epoxy anti-rust paint, it can be used all year round, winter without the use of low temperature curing agent, for workshop primer surface, steel, aluminum, stainless steel, galvanizing and thermal spray metal surface, etc. have good adhesion, and can be coated with alcoholic acid, epoxy, acrylic, polyurethane and other finishes. The product passed 4200h salt spray, ultraviolet cycle test, is recognized as the need for zinc-rich primer and can achieve more than 15 years of service life of heavy anti-corrosion coatings.
2.3 Metal thermal spraying
Many large steel structures require a design life of 50 years or more, and a single coating system is unlikely to meet this requirement. Therefore, in the outdoor atmospheric corrosion environment, the steel structure is thermally sprayed with zinc or aluminum coating, combined with coating closure, is the best way to protect the steel structure long-term maintenance without maintenance or less maintenance.
in a corrosive environment, the zinc or aluminum coating is corroded as an anode, and its corrosion product is covered on the coating surface, which acts as a seal. As a result, thermally sprayed zinc or aluminum coatings provide cathode protection and shielding, ensuring that when the coating breaks, the metal spray coating can sacrifice itself. Effective protection for up to 20 years maintenance-free and 40 years less maintenance.
for metal thermal spraying and inorganic zinc-rich primers, a epoxy-enclosed paint/connection paint should be constructed separately, with a dry film thickness of about 30 microns. The main function of closed paint and connecting paint is to penetrate and seal the porous surface of metal thermal spray and inorganic zinc-rich primer, which plays a role in preventing foaming pinholes, and also plays a good connection role in the subsequent intermediate coating.
2.3 Cold Zinc Spray
Zinc is an ultra - fine zinc powder treated by atomic method. A single-part product consisting of resins and volatile solvents, with a zinc content of up to 96%. Zinc powder purity is above 99.99%. Zinc powder particle size of 3-6 m. created a cold zinc spray coating on steel excellent corrosion resistance. A material protection technique for painting zinc powder on the surface of a substrate. Hot galvanizing can be achieved under natural conditions at room temperature. Spray zinc. A new anti-corrosion process with anti-rust effect of aluminum spray. Its anti-corrosion principle, like hot galvanizing, has the dual function of cathode protection and barrier protection. Cold zinc spray is the best material to replace traditional hot dip zinc, hot galvanizing, hot zinc spray (aluminum).
Cathode protection cold spray zinc paint film high purity zinc content of more than 96%, the purity of zinc raw materials used as high as 99.995 percent, special treatment of zinc powder surface, shape and particle size complement each other, to provide the best cathode protection capacity, even if the cold coated zinc protective layer has a little damage, zinc layer of steel will not rust, until zinc consumption, at the same time, effectively prevent the spread of rust.
the special reaction mechanism of self-enclosed barrier protection makes the cold-sprayed zinc coating can also be applied over time, further self-enclosed, forming a dense barrier, effectively isolating corrosion factors, greatly improving corrosion resistance. Cold-sprayed zinc combines the advantages of two anti-rust methods, double protection in one, breaking through the traditional paint base ratio limit, to obtain excellent long-lasting corrosion resistance.
, the application of cold-sprayed zinc coatings in anti-corrosion of construction steel structure
In view of the rapid development of construction steel structure, the application of cold-sprayed zinc should be discussed in particular. The dual function requirements of corrosion and fire protection - based on the characteristics of building steel structure in its own structure and use function, it is determined that most steel structure construction in the protection work, not only need long-term anti-corrosion protection, but also need to have fire protection function. However, due to the completely different characteristics of these two functions, the current lack of protection materials to meet both functions, at home and abroad are used (anti-corrosion and fire prevention) combined methods. Therefore, it is necessary to reasonably carry out the design and construction of dual-function protection, in the selection of long-lasting anti-corrosion materials, in the construction steel structure to replace the traditional hot-soaked zinc steel, not only easy to build, but also give the steel structure a viable - as large environment non-permanent steel structure, according to the requirements, the use of single-layer cold zinc spray protection. The current practice is to coat the steel base, medium coating, apply fireproof layer and then paint, in order to protect the weak fire layer with the help of paint, increase the protection performance of the whole system. The author believes that this is not very long-term use of the occasion is protective, the use of hot-soaked zinc steel buildings, once the zinc layer is damaged, it can no longer be repaired For feasible, but for those semi-permanent and permanent steel structures, may not be the most reasonable design, because without the need for fire protection, it is easier to design a better long-lasting corrosion protection system. Once the fire prevention function is required at the same time, there must be a weak link located in the system, if the above plan for protection, first of all, the barrier protection effect of the paint layer is always limited, after a period of time the outside world moisture, moisture and other constant intrusion, itself more loose fire layer, easy to swell, bubble, cracking and other ills, these strains will inevitably cause damage to the paint layer. With the destruction of the paint, the corrosive medium is very easy to directly erode the coating, the bottom coating. In the face of such a situation, the maintenance work will not only involve paint and fire protection layer. If we can make the fire layer on top of the paint, and then according to the design life and maintenance plan, a small part of the original paint layer on top of the fire layer, appropriately strengthen the barrier protection, extend the life of the fire layer, to ensure the normal use of the design period. To the maintenance period, because the bottom-medium-surface three coating is a strong combination system, maintenance only involves fire layer, and fire layer strength is low, maintenance is also easy to remove, basically does not hurt the bottom coating and medium coating, only need to maintain the fire layer, and re-use the appropriate thickness of the surface layer closure, maintenance works are easy to carry out, and anti-corrosion system is not major damage, to ensure the entire design life.
Cold spray zinc can be used as the base or surface layer of heavy anti-corrosion coating system of various construction steel structures such as sports center, airport terminal, high-speed railway station, exhibition center, high-rise steel structure building, etc., to provide long-lasting anti-corrosion coating protection layer for construction steel structure.
3.1 Guangzhou New Baiyun Airport
Guangzhou New Baiyun International Airport terminal pressed steel plate using hot galvanized steel courgettes, galvanized volume of 275g/m2, thickness of 1.2mm, 1.52mm, 1.9mm and 2.0mm. After pressing and molding 2 and a half pieces, the assembly is welded and molded. Roof combination pressure plate bottom surface local need to hit a diameter of 3mm small holes, horizontal spacing of 10mm, vertical spacing of 8mm, as sound absorption. Welding, punching and cutting can cause varying degrees of damage to the galvanized layer of the surface of the pressed steel plate. In order to ensure product quality, meet the requirements of design anti-corrosion performance, in accordance with the Design Requirements of Guangdong Architectural Design Institute and the relevant provisions of the New Baiyun International Airport Command, pressed steel plate molding, welding and cutting parts for cold galvanizing anti-corrosion treatment, galvanizing amount of not less than 275g/m, anti-corrosion age of not less than 30 years.
Guangzhou New Baiyun Airport
3.2 Shanghai Five Corners Around the Island Decoration Project
Shanghai Five Corners Around the Island Decoration Project is located in the urban and industrial atmosphere, with moderate sulfur dioxide pollution, according to ISO 12944 standards, the corrosion environment of steel structure in this project can be defined as C3 that is, medium corrosion environment. The project was originally designed to use hot-dip galvanizing plus finish paint, but due to the high cost of hot-dip galvanizing and the size limitation of hot galvanized steel structure, the owner and the design institute finally chose to use cold-sprayed zinc scheme, the coating scheme for cold-sprayed zinc 50 microns and epoxy cloud iron intermediate paint 100 microns plus re-coatable polyurethane paint 60 microns
Shanghai Five Corners around the island decoration
3.3 National Grand Theatre underwater corridor steel structure anti-corrosion coating
According to ISO 12944, the corrosion environment of steel structure in this project can be defined as the C4 environment of higher corrosion category. According to the requirement that the project anti-corrosion protection period is more than 30 years, the owner and the design institute choose to use the cold zinc spray scheme, the coating scheme is the cold spray zinc 50 m and epoxy cloud iron intermediate paint 100 m and polyurethane paint 60 m.
National Grand Theatre underwater corridor steel structure
3.4 Guangzhou new TV tower Ferris wheel steel structure cold-coated zinc supporting anti-corrosion coating project
project location: Guangzhou. Coating scheme: cold-sprayed zinc 80 m plus epoxy closed paint 30 sm plus re-coatable polyurethane finish 60 sm. Completion date: September 2010.
Guangzhou New TV Tower Ferris Wheel
3.5 Shenzhen Dayan Center Stadium steel structure cold-coated zinc anti-corrosion coating project
project location: Shenzhen. Coating scheme: cold-sprayed zinc 80 m. Completion time: December 2010
Shenzhen Daye Center Stadium