Anticorrosive coatings are generally used for anticorrosion protection of railway steel bridges at home and abroad.
The anticorrosion technology of railway steel bridge coatings in China is also developing constantly and gradually improving.
In 1950s, the coating protection life of steel beams was only (2~3) years; From the end of 1960s to 1980s, the matching system of red lead antirust primer and gray aluminum zinc alkyd topcoat (i.e. 66 alkyd topcoat) or gray mica iron oxide alkyd topcoat was adopted successively, and the protective life of the coating was improved to about 10 year. Zinc-rich epoxy antirust primer, micaceous iron epoxy intermediate paint and gray aluminum graphite alkyd topcoat (i.e. 0 18 alkyd topcoat) were used in 1990s, and the protective life of the coatings reached 15 years.
At present, the supporting systems of zinc-rich epoxy antirust primer, micaceous iron epoxy intermediate paint and fluorocarbon topcoat are being promoted to further extend the maintenance cycle of railway steel bridges. It is estimated that the service life of the system will exceed 30 years.
Railway steel bridge coating is used together with primer and topcoat to give full play to the antirust function of primer and the aging resistance of topcoat.
The following table is the reference table of coating varieties used at home and abroad 1.
Commonly used steel bridge coatings at home and abroad
In the national primer, the topcoat is China Hongdan antirust paint, zinc-rich primer micaceous alkyd topcoat, gray aluminum graphite alkyd topcoat, polyurethane topcoat, fluorocarbon topcoat and other German Hongdan alkyd primer and oily Hongdan paint.
Mica aluminum alkyd topcoat British zinc yellow phenolic primer, zinc-rich primer
Mica phenolic topcoat, mica polyurethane topcoat, French red lead primer
Mica iron topcoat: American zinc-rich primer leveling topcoat, epoxy paint aluminum powder phenolic topcoat, aluminum powder polyethylene topcoat, polyurethane topcoat zinc-rich primer, oily red lead primer, zinc-rich primer mica iron epoxy paint polyurethane topcoat, chlorinated rubber topcoat, alcohol ester topcoat and fluorocarbon topcoat.
Coatings for China Railway Steel Bridges: 1
Red lead antirust paint
Red lead antirust paint is a traditional antirust primer with excellent performance and low price.
It is generally believed that its corrosion resistance comes from lead soap formed by fatty acids and lead in oil, and lead soap is a corrosion inhibitor; However, some people think that the protective effect of red lead pigment is related to the polarization of cathodic and anodic corrosion reactions.
The cathodic reaction of iron matrix is polarized by the formation of lead compounds with low solubility, while the anodic reaction is polarized by the formation of insoluble iron compounds by soluble iron, which is deposited in the metal lattice together with lead oxides and hydroxides.
Due to lead poisoning, in order to protect the environment, red lead antirust paint is gradually replaced by other antirust primers, but railway steel bridges are still widely used as permanent and important steel structures in China.
The red lead antirust paint can be red lead phenolic antirust paint or red lead alkyd antirust paint, wherein the content of red lead in nonvolatile matter is not less than 65%.
2
zinc rich primer
Zinc-rich primer is a cathodic protection heavy-duty anticorrosive coating, which can be divided into two categories: inorganic zinc-rich primer and organic zinc-rich primer.
Inorganic zinc-rich primer includes sodium silicate and hydrolyzed ethyl silicate, in which sodium silicate is used as steel bridge primer.
Water glass type inorganic zinc-rich primer is also called water-borne inorganic zinc-rich primer.
The waterborne inorganic zinc-rich primer used in China is mostly secondary curing type, which is composed of sodium silicate and zinc powder. After the coating is formed, it needs to be cured by brushing curing agent.
At present, waterborne self-curing inorganic zinc-rich coatings are used on railways in China, which are mainly composed of potassium sodium silicate and zinc powder. The coating can completely self-cure in a few hours and is not afraid of rain, which greatly shortens the construction period.
It has been applied to Lilac Bridge and Changshou Bridge on the newly-built Qinhuangdao-Shenyang Passenger Dedicated Line in China.
Organic zinc-rich primer is mainly epoxy zinc-rich primer.
Due to the good adhesion between epoxy resin and steel matrix, the dosage is large.
3 Grey micaceous alkyd topcoat
According to the idea that flake pigment can prolong the weatherability life of topcoat, 1978 successfully developed gray mica iron alkyd topcoat.
The top coat is mainly made of mica iron, and its flaky structure and chemical inertness make the weather-resistant life of the coating reach 10 years or more.
4 gray aluminum powder graphite alkyd topcoat
1993 developed the railway steel beam topcoat-gray aluminum graphite alkyd topcoat (also known as 0 18-2 alkyd topcoat).
Among them, the pigment is flaky aluminum powder graphite composite material, and its weather resistance life can reach 15 years or more.
five
Acrylic aliphatic polyurethane topcoat
It is clearly stipulated that aliphatic isocyanate, hydroxyl-containing acrylic resin and weather-resistant pigment polyurethane topcoat should be used, and its weather-resistant life can reach more than 20 years.
six
Fluorocarbon topcoat
Fluorocarbon topcoat is also called fluorine-containing polyurethane topcoat abroad. Because of its C-F bond, the bond energy is 485kJ/mol, and the bonding between atoms is strong, so it is more resistant to atmospheric exposure, acid, alkali, salt and other harmful media. Its gloss retention is far superior to polyurethane topcoat, and it is more suitable for anticorrosion coating of steel structures with landscape requirements.
7 Polyurethane coating on the upper cover plate
The top surface of the upper cover plate of the longitudinal beam, upper bearing plate beam and box beam of railway steel bridge adopts wear-resistant coating.
It consists of two layers of brown polyurethane primer (the minimum thickness of each dry film is 50μm) and four layers of gray polyurethane topcoat (the minimum thickness of each dry film is 40μm).
This coating system is characterized by good wear resistance.
8 Grey Mica Iron Epoxy Intermediate Paint
The coating has excellent adhesion and sealing properties on zinc-rich primer and zinc-sprayed and aluminum-sprayed layers of steel.
As the intermediate sealing coating of high-performance antirust paints such as epoxy zinc-rich primer and waterborne inorganic zinc-rich primer, the interlayer adhesion and protective performance of the whole coating are enhanced.
It can be matched with epoxy coating, polyurethane coating and chlorinated rubber coating, and can also be matched with alkyd coating, phenolic resin and other traditional coatings.
9 epoxy asphalt coating
It is mainly used for painting the inner surface of non-closed box beam.
Generally, four layers are coated, and the minimum thickness of each layer of dry film is 60μm m. ..
Steel bridge coating system
In order to obtain better protective effect and make the protective coating have the best corrosion resistance and durability, it is necessary to scientifically and reasonably select different coatings and formulate the coating system according to different parts and environments of steel bridges.
The following table lists the coating systems currently used for China railway steel bridges.
Table 2
Steel Bridge Painting System Painting System Painting (Paint) Name Minimum thickness of each dry film/micron total dry film minimum number of coatings/micron applicable parts 1 special red lead phenolic (alkyd) antirust primer 35270 gray aluminum powder graphite or gray micaceous alkyd topcoat used for bridge auxiliary steel structures such as bridge piers, fences and bridge inspection vehicles 352702 arc spraying aluminum layer 200 steel bridge longitudinal beams, upper deck beams and epoxy sealant 20/ Kloc-0/20 Brown Polyurethane Overlay Primer 502 100 Gray Polyurethane Overlay Topcoat 404 1603 Inorganic Zinc-rich Rust-proof Anti-skid Coating or Arc Spraying Aluminum Layer 80 180 Bolted Welding Friction Surface of Beam Connection 1004 Epoxy Asphalt Coating or Epoxy Asphalt Thick Slurry Coating 604240 Unsealed Box Girders and 38
Brown red mica iron epoxy intermediate paint 40 140 gray aluminum powder graphite alkyd topcoat 352706 special epoxy zinc-rich antirust primer
Or water-based inorganic zinc-rich antirust primer
Brown red mica iron epoxy intermediate paint
Grey acrylic aliphatic polyurethane topcoat 40280 steel beam main body is used in areas with severe corrosive environment.
40 140352707 Special epoxy zinc-rich antirust primer or water-borne inorganic zinc-rich antirust primer Brown mica iron epoxy intermediate paint fluorocarbon topcoat 40280 steel beam main body is used in areas with serious corrosive environment, strong ultraviolet radiation and landscape requirements such as acid rain and coastal areas.
40 14030: 260 Anticorrosive Coatings for Railway Steel Bridges
1
Painting of Nanjing Yangtze River Bridge The painting system currently used by Nanjing Yangtze River Bridge is the 1 system in Table 2, that is, two red lead phenolic primers and three mica alkyd topcoats.
Generally, the system needs to be maintained and painted once every (7 ~ 8) years, that is, the top coat is painted once.
2
Painting Wuhu Yangtze River Bridge The construction of Wuhu Yangtze River Bridge began on 1998. The paint coating system used is the fifth system in Table 2, namely, two layers of epoxy zinc-rich primer, 1 layer of mica iron epoxy intermediate paint and two layers of gray aluminum powder graphite alkyd topcoat.
Generally, the system needs maintenance and painting every (12 ~ 15) years.
three
Anti-corrosion coating of steel beams of Wanzhou Yangtze River Bridge is the key project of Wanzhou Yangtze River Bridge Zuyiyi Railway. The bridge is located in Wanzhou, Chongqing, with serious corrosion. Currently under construction. The coating system used is two layers of zinc-rich epoxy paint, 1 mica iron epoxy intermediate paint and two layers of fluorocarbon topcoat.
The service life of the system is expected to reach more than 30 years.
Painting of foreign steel bridges
1
Long-term protection is the main goal of rust prevention of British steel bridges coated with British steel beams, and there are also steel beams coated with decorative coatings in urban areas.
There are many steel beams in the coating system of zinc spraying, hole sealing intermediate paint and mica iron topcoat, and the anti-corrosion method and route are conservative.
In recent decades, protective coating methods such as zinc yellow antirust paint or zinc-rich paint, mica iron intermediate paint and various topcoats have been adopted.
They believe that ordinary standard paint can be used in general environment, zinc spray or zinc-rich paint can be used in harsh environment, and then protective topcoat can be applied.
On the inner side of the box beam, solvent-free heavy-duty anticorrosive paint is used for protection because of the difficulty in maintenance and the large amount of condensed water.
In terms of maintenance, it should be recoated once every six years to prevent the original coating from deep aging and damage.
2
American steel bridges are all painted with American steel beam paint for rust prevention, but also for long-term protection, and there are also decorative protective paint steel beams.
Zinc-rich paint is often used as primer, coated with polyethylene, polyurethane and other coatings. Red lead antirust paint and zinc chromate antirust primer are also commonly used.
They attach importance to initial disassembly and thorough rust removal, and think that zinc-rich paint is used as primer, and the topcoat is durable and multi-coated, with a service life of more than 20 years.
They summed up several conclusions: a. Steel beams should be sandblasted for rust removal in harsh environment, and the roughness should be appropriate; B. The required dry film thickness of the coating is related to the performance of the coating; C. The primer should avoid excessive fillers; D. Oily paint and alkyd antirust paint have good performance in general environment. E. Zinc-rich paint has good performance in harsh environment, but the effect varies with the variety and its supporting topcoat; F, primer and topcoat collocation is very important, should pay attention to when construction.
three
Steel bridges are coated with steel beams for protection and decoration. First, red lead antirust paint and alkyd topcoat were used. Zinc-rich coatings, chlorinated rubber coatings and polyurethane coatings were used in 1970s and 1980s. In recent years, super weather-resistant fluorocarbon coatings have also been used as protective materials for steel beams.
As we have entered an aging society, the maintenance cost and difficulty of steel structures are increasing, so we attach great importance to the research and application of long-life coatings and coating systems, and use the life-cycle cost analysis method to select and evaluate coatings and coating systems.
development trends
With the development of high-speed and electrification of railway, the requirements for maintenance and overhaul of steel bridges are higher, and it is impossible to carry out construction work on bridges as often as before, which requires the development of painting systems with better anti-corrosion performance and longer service life. Steel bridges are only painted once and twice in the whole use process, and at the same time, water-based coatings and environmentally friendly coatings with little environmental pollution are developed.
1
High-performance coatings, such as fluorocarbon coatings cured at room temperature, have extraordinary weather resistance, outstanding salt spray resistance, excellent chemical resistance, good contamination resistance and corrosion resistance.
There is still a certain gap between domestic fluorocarbon coatings and foreign products in main performance, so we should strengthen the research and development of fluorocarbon coatings, especially fluorocarbon resin, and produce real fluorocarbon coatings.
2
With the continuous improvement of living standards, people's awareness of environmental protection is also increasing. It is an inevitable trend to use waterborne coatings for steel bridge painting.
Water-borne inorganic zinc-rich paint has been widely used as a pre-coating primer for steel structures in China, and also as a supporting primer for steel bridges in China. However, there are still some problems in use, such as high brittleness and poor compatibility with other coatings, which need further improvement and research.
three
The surface of steel bridge with composite protective material is arc sprayed with metal, and then coated with topcoat.
Metal spraying protection began in 19 10, and has a history of more than 90 years.
In 1930s, zinc spraying paint was widely used abroad, and then aluminum spraying paint was used to protect railways and highway bridges, various hydraulic steel structures, hydropower station equipment, petrochemical equipment and ships.
It has been used in China for 50 years since 1950s.
Practice has proved that metal spraying is a long-term applicable anti-corrosion method.
After more than 90 years of development, metal spraying can not only spray zinc and aluminum, but also spray aluminum alloy, aluminum magnesium alloy and aluminum rare earth alloy. Spraying technology has gradually developed from flame spraying to arc spraying and even high-speed arc spraying.
In recent years, arc spraying metal recoating topcoat has been applied to ports, docks and bridges in China, such as Yuehai trestle bridge project.
four
Protective materials for railway reinforced concrete bridges At present, the design life of railway reinforced concrete bridges is the same as that of steel bridges, which is 100 years. In addition, the existing concrete bridges on this line have also suffered from different degrees of corrosion and other damage.
Therefore, it needs to be repaired or protected, and one of the main protective measures is to develop protective coatings and formulate corresponding construction techniques.
The following table is the reference table of coating varieties used at home and abroad 1.
Commonly used steel bridge coatings at home and abroad
In the national primer, the topcoat is China Hongdan antirust paint, zinc-rich primer micaceous alkyd topcoat, gray aluminum graphite alkyd topcoat, polyurethane topcoat, fluorocarbon topcoat and other German Hongdan alkyd primer and oily Hongdan paint.
Mica aluminum alkyd topcoat British zinc yellow phenolic primer, zinc-rich primer
Mica phenolic topcoat, mica polyurethane topcoat, French red lead primer
Cloud iron topcoat American zinc-rich primer leveling topcoat, epoxy paint aluminum powder phenolic topcoat, aluminum powder polyethylene topcoat, polyurethane topcoat zinc-rich primer, oily red lead primer, zinc-rich primer cloud iron epoxy paint polyurethane topcoat, chlorinated rubber topcoat, alcohol ester topcoat and fluorocarbon topcoat.