Let's be clear first: what exactly is a high-temperature resistant non-metallic expansion joint?
"What degrees can your non-metallic expansion joint withstand?” I usually ask first, "Is your pipeline dried or wet? Is there acid corrosion?" Because the high temperature resistant non-metallic expansion joint, to put it bluntly, is the one in our product listNon-metallic expansion joint (fabric fiber expansion joint)Upgraded version of-soft connection with special fiber cloth and high temperature resistant coating combination. It is not a metal bellows, but it is more corrosion-resistant and cheaper than a metal hose, especially suitable for low-pressure and high-temperature working conditions such as flue gas and hot air. According to JB/T 12235-2015 standard, the working temperature of non-metallic expansion joints can reach above 1000℃, but this is not determined by patting the head, but depends on the specific structure: single-layer silicone cloth is 250℃ at most, and multi-layer ceramic fiber felt + PTFE coating can reach 600℃. If high silicon fiber or even quartz fiber is used, 1000℃ is not a dream.
The "secret" of high temperature resistance is hidden in material layering
You take apart a high-temperature resistant non-metallic expansion joint and find it like a thousand layer cake. The outermost layer is temperature-resistant fluorine rubber or silicone rubber coated fiberglass cloth, which is used to prevent wind and leak; The middle layer is a ceramic fiber blanket or high aluminum fiber cotton, which is truly insulated; The inner layer is usually polytetrafluoroethylene film or stainless steel wire mesh reinforced fluorine adhesive tape, which is anti-corrosion. Note that there is a pit here: in order to save money, some manufacturers use ordinary rock wool in the middle layer, which will be powdered as soon as the temperature exceeds 300℃. They are sold in our stationHigh temperature axial expansion jointAlthough it is also high temperature resistant, it is a metal bellows structure, which is completely different from non-metal. The advantage of non-metals is that they can absorb three-way displacement, especially for rectangular pipes-such as the one connected behind the smoke baffle doorRectangular non-metallic expansion jointIs specially used to deal with the thermal expansion and contraction of the flue.
Which industries can't live without it? Two typical scenarios
Let's talk about the cement industry first. The temperature of the hot flue gas from the rotary kiln is 350-450℃, and it contains a lot of dust, so the metal expansion joint is quickly worn out or corroded. At this timeMetal Corrugated Expansion Joints in Cement IndustryAlthough it works, it is expensive and troublesome to replace. The advantages of non-metallic expansion joints come out: cheap, lightweight, and quick to replace. Let's talk about the power station desulfurization system. Desulfurization tower import raw flue gas 80-160℃, outlet net flue gas with acidic droplets, do you use metal expansion joint? It sucks in a year or two. Our sideDesulfurization flue gas baffle doorEquipped with non-metallic expansion joints, liningPTFE compensatorAcid-and temperature-resistant. You may ask: Thatrubber compensatorOkay, okay? The temperature resistance of rubber usually does not exceed 100℃, so it can only be used on cold water pipes. Don't get confused.
Three parameters that are most prone to rollover in model selection
First, temperature is not the only indicator. You told me that the pipeline flue gas was 650℃. I must ask you first if there was an instant overtemperature? Because the temperature resistance limit of non-metallic expansion joints refers to the continuous working temperature, if it fluctuates frequently, the life will drop by a cliff. Second, pressure should be distinguished. Non-metallic expansion joints are mostly used for low pressure or slightly positive pressure. If it exceeds 0.1MPa, metal skeletons or tie rods should be added, such asCompound hinge transverse expansion jointThat kind of metal scheme would be more appropriate. Third, the amount of displacement compensation is not greedy. Non-metallic expansion energy saving absorbs axial, lateral, and angular displacements, but there is an upper limit in each direction. A customer next door chose a non-metallic expansion joint that was too thin to save money, and it tore directly during test run-guess what? They didn't count the cold tightness of the pipes. Therefore, before the selection, it is best to send the pipeline layout drawing, we will pressSpecific Function of Expansion Joint Guide TubeThat set of experience matches you with parameters.
Installation and maintenance: If you want to save trouble, you have to follow the rules
Many masters think that non-metallic expansion joints are soft connections, so they can be installed casually. Big mistake. First of all, the direction arrow cannot be installed backwards. The arrow refers to the flow direction of the medium. If the guide tube is installed backwards, it will be deformed by the air flow. Secondly, the tie rod nut is locked during transportation and must be loosened after installation, otherwise the expansion joint becomes a rigid connection, which is equivalent to white installation. We specifically talked about it in our FAQDo you need to remove the screw of the expansion jointThe transportation fixture is removed, not the tie rod adjustment nut. In terms of maintenance, non-metallic expansion joints are most afraid of being scratched by sharp objects-for example, the welding slag in the pipeline is not cleaned up, and the cloth layer is scratched by vibration during operation. It is recommended to check the surface every six months for bulging or leakage, and replace it if the fiber is exposed. Don't wait until air leaks before stopping work.
Metal vs Non-Metal: Which To Choose?
"Is it okay to use non-metal for vacuum pipes?" I can't just answer. Metal bellows must be used in vacuum conditions, such asDouble hinge expansion joint for air-cooled island vacuum pipelineThe sealing property of non-metals cannot withstand negative pressure. Then when to choose non-metallic? To put it bluntly, there are three: high temperature, low pressure and large pipelines. For example, the flue of power station, the tail of cement kiln and the hot air duct of iron and steel plant, these places use non-metallic expansion joints to hang metal for cost performance. However, if your pipe pressure exceeds 0.2MPa, or you need high-frequency vibration compensation, you still use it obedientlyUniversal corrugated expansion jointOrExternal pressure single axial expansion jointYeah. Remember, there is no universal expansion joint, only the most appropriate match.