With the development of industry now, everyone should be very familiar with color-coated rolls. Because of its characteristics, it is widely used. In order to better use the equipment, let's understand the reasons for the aging of color-coated rolls.
The prerequisite for the aging or photochemical reaction of the color-coated coil is that the surface composition of the color-coated coil can absorb radiation. When the radiation absorbed by the molecular structure is greater than the bond energy of the molecular structure, the coating can be dissolved, because the less the wavelength of the light source, the contained The more kinetic energy. The brittleness of color-coated rolls in air pollution is the kinetic energy of natural light in the ultraviolet band, which is higher than the bond energy of molecular structures. As the polyurethane coating ages, the substrate itself is gradually missing, and the surface of the coating gradually becomes smooth and loses light. The loss of this matrix leaves a more stable color paste, which is left in the form of a non-sticky powder for the surface layer of the polyurethane coating. This process is called delamination. The aging resistance of thin-coated polyester steel coils varies greatly, and the aging resistance of thin-coated color plates is weak.
The above is about the reasons for the aging of color coated rolls. Any product can only achieve good results according to the correct operation method, and avoid problems causing unnecessary trouble. If you don't understand, you can call for consultation.
Color-coated board roof is a new type of panel, which is considered to be the most ideal material for modern buildings and has a relatively long life. There are many precautions for installing color-coated board roofs as bottom plates. Professional construction masters are required to install. Aluminum-magnesium-manganese roofing panels are made of aluminum-magnesium-manganese plates. This type of material will not corrode even if it is used for a long time. Under normal conditions, it can be used for forty years, so as not to affect the future use effect. The specific installation precautions are as follows:
Before installation, it is necessary to clean up the contamination of the color-coated board roof to avoid corrosion of the panel. In addition, pay attention to the flatness of the panel during installation, and there should be no bending and deformation. The color-coated board roof overlaps a wave crest, so it has been recognized by many users. The entire system of aluminum-magnesium-manganese roof panels adopts a mechanized seaming mode, so that water leakage can be avoided, and it has a good elimination system, especially in heavy rain weather, which can drain water in time. It can avoid the huge pressure caused by the extrusion of water, and can prevent the deformation of the project. This will be firmer and will not leak water. It is best to be anchored reliably, the installation should be kept flat, and there should be no gaps between the plates.
Color-coated board roofing and floor installation need to be from high to low, and the design of the lightning protection system is familiar. The roof panel can be used as an air-termination device alone without the need for lightning protection belts. It can also be used in conjunction with avoidance belts or lightning rods to form a safe multiple lightning protection system; the installation method from the middle part to the edge, the overlap method is from low to high. After the floor installation starting line is installed, select self-tapping screws to confine both ends, and then install the second board. It is necessary to install the second color-coated board roof to make a mark, check whether the board has deviations, and need to meet the design requirements, if it cannot meet the needs, adjust it, and then fully tighten it. After installation, pay attention to check whether there are any omissions. If the tightening is not enough, there will be rain leakage, so be careful.
Hot-dip galvanized coils have gradually become the mainstream variety in steel coil applications because of their excellent corrosion resistance and good cost performance. At the same time, because of the characteristics of the hot-dip galvanized coil product, it can be used directly in the bare or can be subsequently painted. The complex usage scenarios and the individual requirements of different applications also make users pay more attention to the surface quality of hot-dip galvanized coils.
Understanding the quality defects and countermeasures of hot-dip galvanized coil products will help us better communicate with users and improve trade quality.
一 The zinc layer peels off (the oxide is attached)
Morphology: The galvanized layer is easy to peel off (large or small pieces). The substrate surface under peeling is oxidized, which is black, blue or black and blue. Generally, the plating layer will form pinholes and the surface morphology of the plating layer before peeling occurs. Visual abnormalities (spangles protruding in a three-dimensional shape, the surface is particularly bright... etc.); when the production line stops for a short time due to some reasons, such as poor atmosphere control of the non-oxidizing furnace, peelable oxide scale is formed on the steel surface This part of the zinc pool is blown off by the air knife to form exposed black spots. In addition to the surface of the zinc pool being blown off, some of the scale may also be suspended in the zinc bath, which often takes a long time. Take it all out.
Causes: can be divided into furnace area and non-furnace area factors
furnace area factor:
-Incorrect air/gas combustion ratio and flow control lead to inappropriate CO and O2 content in the furnace atmosphere
- The furnace temperature is too low or not matched with the plate temperature, and the plate temperature is too low
- The dew point is too high, that is, the water content (H2O) is too high
- Sudden change of plate temperature causes excessive changes in furnace temperature, which is related to the thickness, roughness, surface condition of the substrate, etc.
Non-furnace area factors:
- poor cleaning
-Poor water quality in the washing section
A) Prevent air leakage in the furnace area
B) Prevent leakage of cooling water systems in the furnace area
C) Carefully and appropriately control non-oxidizing furnace atmosphere CO%: 3-5 %; furnace temperature> 1200 ℃
D) Properly control alkali washing conditions: free alkali, alkali ratio, alkali washing temperature
E) When the water quality is poor, add a bypass soft, pure water manual valve
F) When H2 does not react well with the steel plate, the plate temperature can be increased to promote the reduction rate or slow down to increase the reaction time
二 Zinc layer peeling off (surface carbon)
Form: The coating is easy to peel off, the surface is accompanied by black powder, and the substrate may sometimes be blue. The black powder may be oxide or carbon (C) powder, so you need to do experiments or experience To observe and judge (mostly appear at the head and tail).
- Improper control of furnace atmosphere (CO% is too high)
A) Properly control furnace atmosphere: CO%: 2 – 3%
三 Excessive zinc dross accumulation on the surface
form: one is block (slag of oxidized peeling flakes); the other is granular (intermetallic compound), which can be divided into two types-top scum and bottom slag. These slags will cause the surface of the steel plate to be rough (distributed on the entire surface of the steel plate or on both sides of the steel plate). In severe cases, it is easy to form warped edges after winding.
- The temperature of the zinc pool changes too much, especially when the zinc ingot is immersed too quickly, it will easily cause the surrounding temperature to change
- AL content is too high, if the Al content is too low, it is easy to generate bottom slag, so the Al content should be controlled within 0.18 – 0.22%
-Oxide peeling due to shutdown defects or other factors
- Defects on the surface of the substrate can easily cause dross adhesion
A) Try to keep the zinc pool temperature stable. (Because Fe and Al are easy to dissolve in high temperature, but it is easy to precipitate at low temperature and produce zinc dross)
B) When adding large zinc ingots, slowly dip into the zinc bath
C) Do not remove the scum on the surface of the zinc bath too often, just move it to the side and remove it at regular intervals (such as 1 hour)
D) When adding small zinc ingots, don’t put them in one place, but distribute them evenly
E) Try to remove the oxide scale from the zinc bath to prevent sinking to the bottom or suspended in the zinc bath
F) Properly adjust the air knife and its pressure and angle
Analyze the development of color-coated sheets in my country
1. Sufficient supply of resources. Affected by the shortage of substrates, the actual output of domestic color-coated plates has not increased much. At present, substrates are abundant, and the price of color-coated plates has not stopped falling. Therefore, some domestic manufacturers with potential production capacity are still waiting and watching. In general, even if import factors are not taken into consideration, domestic color-coated sheet resources are relatively sufficient at present. Of course, in the next step, major steel mills will respond to the call of the China Iron and Steel Association to adjust product structure and reduce production capacity in order to stabilize the market. Therefore, the domestic color-coated sheet market (especially high-end products), there will be no imbalance between supply and demand in the short term.
2. Affected by the hot-dip galvanized sheet market, the color-coated sheet market and the hot-dip galvanized sheet market are strongly correlated, and the two will maintain a certain market price difference. The current hot-dip galvanized sheet price has not stopped falling, so As its downstream product, the price of coated board is difficult to stop falling. In the next step, when the prices of hot-dip galvanized sheet and even its upstream products, cold and hot-rolled coils, will stabilize, it will be an important signal for the color-coated sheet market to turn around.
3. The demand is still growing. This year, my country's economy will continue to maintain steady and rapid growth, the domestic market for steel demand is still in a period of growth, and the Olympic project, the revitalization of the northeast and the west, and the construction of urban infrastructure and key industrial projects will continue to increase the demand for color coated sheets.
On the continuous unit, cold-rolled strip steel and galvanized strip steel (electro-galvanized and hot-dip galvanized) are used as substrates, and the surface is pretreated (degreased and learned), and one or more layers of liquid are applied by roller coating. Coating, the plate after baking and cooling is the coated steel plate. Since the coating can have various colors, it is customary to call the coated steel sheet a color coated steel sheet.
The color-coated plate uses cold-rolled strip steel and galvanized strip steel (electro-galvanized and hot-dip galvanized) as the substrate on the continuous unit. After surface pretreatment (degreasing and chemical treatment), it is coated with one layer or Multi-layer liquid paint, the plate obtained after baking and cooling is the coated steel plate. There are back (primer) paint and top (front) paint coatings in China. Generally, the domestic one has one back paint and two top paints, and the foreign business has two top paints and back paints. Since the coating can have various colors, it is customary to call the coated steel sheet a color coated steel sheet.