Big industrial fans are often used in shopping malls, supermarkets, stadiums, factory workshops, and other places. However, people who have purchased industrial fans for sale in person may find that industrial fans are still different. For example, the blades of some giant industrial fans are bent, etc. Some of them don't have deformation problems. Then, why do industrial fan blades have deformation problems? How to avoid and prevent the deformation of the fan blade during production or self-welding? Next, I will introduce the reasons for the deformation of the large industrial fan blades and preventive measures. I hope it will be helpful to you.
Ⅰ. Causes of deformation of large industrial fan blades
At present, the giant industrial fans blades on the market are mainly made of aluminum alloy. This is because aluminum alloy materials have low density and high strength, high thermal conductivity, strong corrosion-resistance, and good physical and mechanical properties. However, improper selection of welding method and welding process parameters will cause severe mechanical deformation of the blade due to excessive concentration of force after welding. Possibly welding seam pores, slag inclusion, and incomplete penetration, etc., and it may result in metal cracks or the loose texture, which seriously affects product quality and performance. Next, we will specifically analyze several reasons for the deformation of the fan blade:
1. Easily oxidized
In the air, aluminum is easy to combine with oxidation to produce a dense aluminum oxide film (thickness of about 0.1-0.2mm) with a high melting point (about 2050°C), which greatly exceeds the melting point of aluminum and aluminum alloys (about 600°C) about). The density of aluminum oxide is 3.95-4.10g/cm, which is about 1.4 times that of aluminum. The surface layer of the aluminum oxide film is easy to absorb moisture. When welding, it will hinder the fusion of basic metals, easily form pores, slag inclusion, and lack of fusion, resulting in performance degradation.
2. Prone to pores
The main factor that produces pores during the welding of aluminum and aluminum alloys is hydrogen. Since liquid aluminum can dissolve a large amount of hydrogen, but solid aluminum basically does not dissolve hydrogen, when the temperature of the molten pool is rapidly cooled and solidified, hydrogen is too late to escape, so that pores are formed in the weld. Hydrogen holes are currently difficult to completely eliminate. There are many sources of hydrogen, such as hydrogen in the arc welding atmosphere, aluminum plates, and the surface of the welding wire adsorb moisture in the air.
3. Prone to deformation during welding
The linear expansion coefficient and crystal shrinkage rate of aluminum are about twice larger than that of steel, which is easy to generate relatively large internal stress of welding deformation, and the structure with greater rigidity will accelerate the formation of thermal cracks.
4. Evaporation and burning of alloying elements
The aluminum alloy contains elements with low boiling points (such as magnesium, zinc, manganese, etc.). Under the action of a high-temperature arc, it is easy to evaporate and burn, which will change the chemical composition of the weld metal and reduce the performance of the weld.
5. Low-temperature strength and plasticity
At high temperatures, the strength and plasticity of aluminum are very low, which destroys the formation of the weld metal, and sometimes causes the weld metal to collapse and weld through. These are caused by the softer texture of aluminum. To avoid these situations, you need to control the temperature during the welding process to avoid deformation or weld penetration caused by excessive temperature.
Ⅱ. Preventive measures for fan blade deformation
1. Prepare for welding
Use chemical and mechanical methods to strictly clean the surface oxide film on both sides of the weld groove. Chemical cleaning is to clean the surface of the workpiece with edible alkali or acid. This method can remove both the oxide film and the oil. Mechanical cleaning can be done with pneumatic and electric milling cutters, scrapers, files, and other tools. For thinner oxide films, a 0.25mm copper wire brush can be used to polish and remove the oxide films. Welding is performed immediately after cleaning. If the storage time exceeds 4 hours, it must be cleaned again.
2. Determine assembly gap and tack welding pitch
During the welding process, the aluminum plate is heated and expanded, which reduces the gap between the weld grooves. If the assembly gap before welding is left too small, the grooves of the two plates will overlap during the welding process and increase the unevenness of the plate surface and deformation after welding. If the matching gap is too large, it will be difficult to weld and may burn through. A certain tack welding gap can ensure the required tack welding gap. Choosing a suitable assembly gap and tack welding gap is an effective measure to reduce deformation.
3. Choose the right welding equipment
There are many types of welding products on the market, and AC TIG welding (ie TIG welding) is usually recommended. It is a welding method that uses the arc heat generated between the tungsten electrode and the workpiece to melt the base material and fill the welding wire under the protection of argon. When the welding machine is working, the polarity of the alternating current changes periodically. In each cycle, the half-wave is DC positive and the half-wave is DC reverse.
4. Choose the right welding method
The welding method parameters are usually selected by the left welding method, and the welding torch and the workpiece will form a 60° angle. When the welding thickness is 15mm, use the right welding method, and the welding torch will form a 90° angle with the workpiece. When the welding wall thickness is more than 3mm, open the V-shaped groove, the included angle is 60°～70°, the gap should not be greater than 1mm, and the multi-layer welding method is used to complete. When the wall thickness is below 1.5mm, no grooves, no gaps, and no filler wires are added. When welding and fixing pipe butt joints, if the pipe diameter is 200mm and the wall thickness is 6mm, it is advisable to use a tungsten electrode with a diameter of 3~4mm, a welding current of 220~240A, and a filler wire with a diameter of 4mm. Use 1~ 2 layers are welded.
Source: Gaxiaofan Press Department
Publication Date: 12/8/2020
