Find out one thing first
Circular expansion joints are all over the street, so why have they to be square (or rectangular)? Square metal expansion joints are mainly used in scenes with square cross sections such as flue gas pipes, air ducts and dust removal equipment, such as desulfurization flues of power plants and kiln head/kiln tail pipes in cement industry. The biggest difference between it and circular expansion joint is that the four corners of rectangular section are stress concentration areas, and the bearing capacity and displacement compensation characteristics are completely different. Therefore, customization is not just about reporting the length and width. If one key parameter is missed, it may crack in two months after installation.
The first step of customization: smash the size and working condition data to the manufacturer
The length × width of a rectangular section is the most basic, but there is a series behind it: compensation amount (what are the axial, transverse and angular directions?) pressure level (negative or positive pressure? How many kPa?) temperature range (what is the highest ℃? Is there an instantaneous peak?) media composition (are there corrosive gases? Is the dust content high?) These data are indispensable. For example, in the same flue of a power station, the temperature and corrosiveness before and after desulfurization are very different, and the material and wall thickness of the corrugated pipe used are completely different. Think about it, before desulfurization, the flue gas temperature can reach above 160℃, and it also contains a lot of SO₂; After desulfurization, the temperature drops to about 50℃, but the humidity is high and sulfurous acid remains. If you report the same set of parameters, the manufacturer designed it before desulfurization, and it may corrode faster after desulfurization-reverse rollover.
Material selection is where there are the most "pits" for customization
The main body of corrugated pipe is generally made of stainless steel 304 or 316L, but when it encounters high temperature (> 400℃), it has to be replaced with heat-resistant alloy, such as Incoloy 800. The end pipe and flange are usually made of the same material as the pipe. Carbon steel Q235B is the cheapest, but don't forget to consider the lining for corrosion protection. Do you want to add the deflector? It can reduce the scouring of the bellows by the medium, and is especially suitable for dust-containing air flow; If you don't add it, the cost will be low, but the life may be compromised. In addition, if the medium is highly corrosive, you can also add PTFE lining on the inside of the bellows-note that we havePTFE-lined hoseAndPTFE compensator, ideas can be used for reference. Two days ago, I met a cement factory customer. The picture was cheap and the dust content was not mentioned. As a result, the deflector was not made, and the bellows wore out for half a year-was this tuition paid unjustly?
Structural design is the link that reflects the level of manufacturers
The number of waves, the number of layers is single or multi-layer, and how to determine the wave height and wave pitch-these directly affect the compensation ability and fatigue life. For square sections, the four corners usually need arc transition to reduce stress concentration, and the arc radius is calculated according to wall thickness and compensation. If you need to absorb lateral displacement, you can design it as a duplex structure or add hinges (such as our stationCompound hinge transverse expansion jointIt has reference value). The tie rod is also a common configuration. Its function is to constrain the axial displacement of the bellows and avoid excessive stretching-but how to adjust the tie rod nut? Don't put it backwards, otherwise it will be useless. We specifically talked about it in the FAQ of our siteHow to adjust the tie rod nut of expansion jointLater, you go and flip through it. There is another overlooked point in the structure of large-size square expansion joints: segmented manufacturing or integral molding? If it exceeds a certain size (such as 6m ×3m), transportation is limited, and it has to be segmented and then welded on site. Then the weld position and welding process have to be finalized with the manufacturer in advance.
Don't ignore the connection method and installation details
Flanged connections are the most common, but confirm the flange standards (GB/T 9119, HG/T 20592, etc.) and the sealing surface form (protruding surface, tongue and groove surface, etc.). In the case of a welded connection, the groove form and welding process should be determined in advance. Large-size square expansion joints are easy to deform when transported and hoisted, so temporary supports are often set before leaving the factory, and they can only be removed after being installed in place. Pre-stretching/pre-compression is also a technical task-the cold tightness is calculated according to the actual installation temperature, and a difference of one degree may affect the displacement of several millimeters. It has been mentioned in the FAQ of this siteCorrect installation method of expansion joint of large tie rodThe truth is universal. And guess what? Some installation teams try to save trouble and screw the tie rod nut to death directly. The expansion joint is equivalent to welding a rigid part to death, and it is compensated for a fart. Alas, this has not happened once or twice.
Finally, let's be honest
Customized square metal expansion joint is not picking cabbage, don't just compare the price. The reliable process is: send the working condition list to the manufacturer → the manufacturer makes the preliminary plan and drawings → you confirm the key parameters → look at the samples or past cases → do the pressure test and displacement test before leaving the factory. Our station has various industry-specific expansion joints, such asCorrugated expansion joint for power plant industry、Metal Corrugated Expansion Joints in Cement Industry、Desulfurization flue gas baffle doorWait, if you are not sure about the selection, directly ask the manufacturer about the product information of these corresponding scenarios, which is the most efficient. Remember, the core of how to customize the square metal expansion joint is not whether the manufacturer can do it, but whether you have told the data thoroughly. Only when the data is said thoroughly can the manufacturer match you with the correct material, wavenumber, guide tube and tie rod configuration. Otherwise, it is either over budget or unusable.