What is a large size non-metallic compensator? Let's break the name into three pieces
Don't be fooled by the phrase "large-size non-metallic compensator". When disassembled, it is a straightforward industrial part: the compensator is the expansion joint, and its function is to absorb the displacement caused by thermal expansion and contraction of the pipeline; Non-metal means that the main body of the ring belt does not need metal bellows, but uses flexible materials such as fabric, rubber and fluoroplastics instead; Large size refers to a rectangle or circle with a large cross section-a side length of one or two meters or even larger, which is specially fitted to air ducts and flues. You go to our station "non-metallic expansion joint (fabric fiber expansion joint)" and "rectangular non-metallic expansion joint", which are typical representatives. To put it bluntly, it is a flexible connection that can be telescoped, specializing in serving large-diameter pipes.
Why can non-metals get bigger, but metals can't?
The metal expansion joint depends on the deformation of the bellows to absorb the displacement, but think about it, when the diameter exceeds one or two meters, how much does the wall thickness of the bellows have to be added? The difficulty and cost of processing are soaring up like a rocket, and the materials are easy to become unstable-yesterday, I heard from a friend in a steel mill that they tried a 3-meter diameter metal bellows, and it bulged within two months of installation. There is no such problem with non-metallic belts: silicone cloth, fluororubber and glass fiber cloth. These materials can be stacked into a large format of dozens of square meters, and it is no problem to do it on the spot. More importantly, it is corrosion resistance. The sulfur-containing flue gas in the desulfurization flue of power stations, the metal bellows will erode in a few months, and it is common for non-metals to last for three to five years. And guess what? Some foreign appliance plants use the non-metallic compensator in our station, and the ring belt is changed only once every ten years, which saves a lot of downtime losses.
There are three layers of structure: ring belt, frame and heat insulation. Don't think about complicated
The internals of large-sized non-metallic compensators are far less intimidating than the name. The ring belt is the core, and a layer of sealing film is sandwiched between the multi-layer fiber cloth, just like wearing a leakproof jacket for the pipeline; The frame is welded with metal angle steel or steel plate and is subjected to system pressure; The insulation layer is tucked between the loop belt and the frame to prevent the high temperature from spreading outside. Some working conditions require a guide tube to adjust the direction of airflow-the specific function of the guide tube of the expansion joint, as we talked about in the question and answer, is to reduce vortex erosion. The "rectangular non-metallic expansion joint" in our station is designed according to this logic. By the way, the national standard JB/T 12235-2015 specifically stipulates the strength and sealing requirements of these components. When you buy a product, if the other party doesn't even dare to mention the national standard, just pass.
The three most headache numbers in model selection: temperature, pressure and displacement
When making technical selection, customers like to ask these three parameters. Let's talk about the temperature first: the conventional silicone ring is fine to 250℃, and the fluororubber layer can carry it above 300℃, but don't exceed 400℃. After this thread, the fabric begins to carbonize, and the whole ring belt will be wasted. Stress? Large-size non-metallic compensators are generally used in low-pressure air duct systems, and the design pressure does not exceed 0.1MPa. If it is really high-pressure working condition, obediently choose metal expansion joints. What about the amount of displacement? Axial ± 100mm and horizontal ± 50mm are easy to do, depending on the number of circle layers and wrinkle design. Two days ago, a customer set the parameters of metal expansion joints. Tsk, it was completely confused-metal deforms elastically by bellows, and non-metal slides by fabric folds. The calculation formulas are different, and chaos will cause big problems.
Practical application scenarios are very concentrated: desulfurization in power plants, blast in steel plants, and cement kiln tail
You can see the shadow of large-size non-metallic compensators in any pipeline with large temperature fluctuation, strong medium corrosion and oversized cross section. Desulfurization flue of thermal power plant, blast furnace blast of iron and steel plant, kiln head and tail of cement plant, and waste gas pipeline of chemical plant-it is almost standard in these occasions. Moreover, it is often used in conjunction with baffle doors: for example, the "desulfurization flue gas baffle door" and "circular baffle door (double seal)" of our station are responsible for cutting off the airflow, and the compensator absorbs the thermal strain of the pipeline, which is indispensable. Rectangular air ducts must use rectangular non-metallic expansion joints, and circular air ducts can be rounded. Remember one sentence when installing: the ring belt cannot be twisted, the bolts must be symmetrically tightened, and the insulation layer should not be compacted-compaction will affect expansion and contraction.
Maintenance is simple enough to surprise you
Routine maintenance is to check whether there are aging cracks on the surface of the ring belt and whether the frame bolts are loose. Found a partial breakage? Treat it temporarily with special repair tape, but in severe cases, you have to change the tape as a whole. Don't worry about the money-a non-metallic compensator costs only 1/3 of the price of the same caliber metal, and it can be changed as fast as hell: loosen the bolts, pull out the old ring belt, stick in the new one, and tighten it again, and two or three people can do it in a day. You have to ask about longevity? Depending on the working conditions: the indoor clean air duct is 8-10 years, and the outdoor corroded smoke is 3-5 years, but compared with the 1-2 years of metal bellows, is it much stronger?