1. What is a non-metallic square rectangular compensator? What is the difference between it and the metal expansion joint?
The non-metallic square rectangular compensator expansion joint, to put it bluntly, is the kind of "soft connection" used in smoke and air duct systems —Rectangular non-metallic expansion jointA common form of. It is composed of a fabric fiber layer (usually a composite of silicone cloth, fluorine adhesive cloth, and ceramic fiber cloth) and a metal frame with thermal insulation cotton sandwiched in the middle, which uses the flexibility of non-metallic materials to absorb the thermal displacement and mechanical vibration of the pipe. What is the difference between it and metal expansion joint? Tsk, that's a big difference.
Metal expansion joints (like the one in our stationMetal rectangular expansion joint、Universal corrugated expansion joint) relies on the elastic deformation of stainless steel bellows, with high pressure resistance and compact structure, but its shortcomings are also obvious-the displacement is limited, especially not suitable for the working conditions of large diameter and large displacement. WhileNon-metallic square rectangular compensator expansion jointThe displacement capacity is 3~5 times that of metal parts. A typical 3000×3000 rectangular flue can easily realize the axial displacement of ±100mm and the lateral displacement of ±50mm with a non-metallic compensator. If the metal bellows achieves this order of magnitude, the cost will more than double.
2. The "special function" of square/rectangular non-metallic compensator: large displacement, temperature resistance and corrosion resistance, it can do things that metal can't do
Two days ago, I met a customer. The temperature of desulfurization flue was 180℃, and the humidity of sulfur-containing flue gas was high. The metal expansion joint was corroded and perforated in less than half a year. ChangeNon-metallic expansion joint (fabric fiber expansion joint)I haven't had any problems in two years. This is the core value of the non-metallic square rectangular compensator —Temperature and corrosion resistance。 Its fabric layer can withstand 300℃ ~1000℃ (depending on the material), and the fluororubber layer can even hold strong acids and alkali. Metal parts are like entering a meat grinder in such a harsh environment, but non-metallic materials can be easily manipulated.
Another "special function" is large displacement. The flue and air ducts of power plants and the air ducts of cement plants are always rectangular cross-sections several meters wide, with thermal expansion of tens of millimeters. The metal expansion joints either can't be so big, or the cost is ridiculously high. The non-metal compensator relies on a multi-layer fabric folding structure,A single compensator can absorb displacement of more than 100mm, and the installation space is small-by contrast, metal bellows require multiple waves in series to achieve the same displacement and at least double the length.
Also, a non-metallic square rectangular compensatorVibration and noise reductionIt works well, too. The vibration of the fan and pump is transmitted to the pipeline, and when it is separated by a non-metallic compensator, the noise immediately drops by more than ten decibels. It is itself a damping material and does not transmit vibration as easily as metal pieces. Therefore, if you encounter high-temperature flue gas, corrosive gas, large displacement and vibration isolation scenes, don't hesitate to go directly to non-metal.
3. The easiest pits to step on when selecting a model: pressure, temperature, medium-don't let the parameters fool you
What are you most afraid of when choosing a non-metallic square rectangular compensator expansion joint? According to the parameter table, the temperature can reach 600℃, but it actually leaked after three months of installation. Why? Because you only looked at the temperature, not the pressure and the medium flow rate. According toNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015The pressure-bearing capacity of the compensator is mainly determined by the metal frame and the compression structure, and the fabric layer is only sealed and temperature-resistant. However, the nominal "temperature resistance of 600℃" of many manufacturers is measured at zero pressure-whenever there is a positive pressure of 3kPa in your flue, the high-temperature gas will drill out of the gaps in the fabric, burn the thermal insulation cotton, and finally the whole compensator will be scrapped.
Let's talk about media. There are SO₂, SO₃ and HF in the desulfurization flue gas, which can not be carried by ordinary silica gel cloth, SO it must be usedPTFE-lined hoseOr a fluororubber composite layer. The dusty gas, particulate hardness and temperature on the cement production line are very high, so choose ceramic fiber cloth + anti-wear guide tube to prolong the life. There is another pit: many people think that "just use a rubber compensator when the temperature is low", but as a result, the rubber ages and becomes hard, and it cracks in three months. There is a fundamental difference between rubber and fluororubber —Rubber PTFE compensatorThe upper limit of temperature resistance is 150℃, but the life of corrosive gas far exceeds that of ordinary rubber.
So,The selection should not only look at the temperature, the pressure, flow rate, medium composition and continuous running time must be listed。 Don't take it for granted when providing parameters to manufacturers, otherwise the later maintenance cost will be enough for you to drink a pot.
4. Installation and maintenance: pull rod, guide tube, transport screw-small details determine big life
Many engineers regard non-metallic square rectangular compensators as "soft cloth joints", plug them into the flange and screw the bolts. And the result? It either pulls and cracks after a few days of operation, or it leaks and smokes. Here are a few key details, if you don't follow it, you will get a 50% discount on your lifespan.
First,Transport screw must be removed。 Non-metallic compensators are shipped with several temporary screws or angles welded inside to prevent transport deformation. When installed in place, these screws, if not removed, will limit the normal expansion and contraction of the compensator, which is equivalent to turning the compensator into a rigid connection-as soon as the pipe expands, all the force acts on the fabric, and it will tear in a few weeks. See the question and answer "Does the screw of the expansion joint need to be removed?" The answer is clear: it must be removed.
Second,The installation direction of the guide tube cannot be reversed。 Non-metallic compensators are typically equipped withguide tube(The function is to direct the high-speed airflow to the center and avoid direct washing of the fabric layer). The direction of the arrow of the guide tube must follow the flow direction of the medium. If it is installed backwards, the air flow directly impacts the fabric, and the life of the guide tube will drop sharply. Refer to the article "Specific Function of Expansion Joint Guide Tube", the guide tube can also reduce fluid resistance and vibration.
Third,The tie rod nut should be adjusted to the proper position。 Large tie rod non-metallic compensators usually come with tie rod nuts for pre-tensioning or limiting maximum displacement. Before installation, the nut spacing should be adjusted according to the design drawings to ensure that the compensator is in the "cold pre-stretched" state-so that the displacement can be centered and absorbed in the hot state. Twisting the nut indiscriminately can cause the compensator to deflect or the tie rod to break under force during operation. If you don't understand, you can flip through the question and answer "How to adjust the expansion joint tie rod nut".
Also, pay attention to flange surface flatness. The non-metal compensator is tightly sealed by the flange. If the pipe flange is welded and deformed, the bolt is tightened, and the fabric will be pressed out of dents, which will quickly leak air. It is recommended to check the flatness of the flange with a level ruler before installation. If it exceeds 2mm, it must be polished or sealed.
5. Industry practice: from desulfurization flue to cement air duct, how do non-metals work with metals
In practical projects, the non-metallic square rectangular compensator rarely works alone, it often followsMetal corrugated expansion joint、Flue gas baffle door、Electric plug-in insulation doorUse it in conjunction. Let me talk about two typical scenarios.
Scenario 1: Desulfurization flue of power plant
The temperature of the flue at the inlet and outlet of the desulfurization tower is 120℃ ~180℃, and the flue gas contains a large amount of water vapor, SO₂ and Cl⁻¹. The mainstream scheme is to useRectangular non-metallic expansion jointAbsorb thermal expansion, for use in straight pipe sectionsMetal rectangular expansion jointBear internal pressure, addrubber compensatorVibration isolation. Non-metallic compensators are responsible for "large displacement + corrosion resistance", metal parts are responsible for "pressure keeping", and rubber parts are responsible for "vibration isolation"-each performs its own duties. In addition, installation at the flue entranceDesulfurization flue gas baffle doorAnd cooperate with the non-metal compensator to isolate the medium during maintenance to avoid poisoning by maintenance personnel.
Scenario 2: Air duct of cement production line
The exhaust gas temperature of cement kiln tail is as high as 400℃ ~600℃, containing dust hard particles. Here, the non-metallic compensator must be reinforced by ceramic fiber cloth + stainless steel wire mesh, and an anti-wear guide tube must be added inside. The pipeline connection in the high-temperature section is usuallyHigh temperature axial expansion joint(metal) to bear the axial displacement, while the non-metal compensator is placed at the fan inlet or turn to absorb the multi-directional displacement. Special reminder: In the cement industry,Metal Corrugated Expansion Joints in Cement IndustryAndNon-metallic expansion jointOften alternately arranged-metal parts are pressure-resistant, and non-metal parts are temperature-resistant and corrosion-resistant. Only when the two complement each other can they support the safe operation of the whole set of pipelines.
Non-metallic square rectangular compensatorWithManual plug-in insulation doorPaired, used in dust collector inlet and outlet. First cut the non-metallic compensator and remove it, and then close the plug-in door, so that the compensator can be quickly replaced without shutting down the whole production line-this trick is very practical in power plants and steel mills.
In short, the non-metallic square rectangular compensator expansion joint is not omnipotent, but it is the most cost-effective "flexible joint" in the smoke and air duct system with high temperature, corrosion, large displacement and large diameter. Give all the parameters when selecting, and don't be lazy when installing, so it can carry it for ten years with peace of mind. If you're still worried, look through our stationNon-metallic expansion joint (fabric fiber expansion joint)The specific parameters are checked against the national standard JB/T 12235-2015, and I feel more confident.