1. What exactly are non-metallic expansion joints? Why do you have to customize?
Non-metallic expansion joints, to put it bluntly, are flexible joints that rely on fabric fibers, rubber or fluoroplastics to absorb the thermal displacement of pipes. You've probably seen it in power station flues, cement plant air ducts or even desulfurization tower outlets — those gray-black, soft cloth loops. Its core function is the same as the metal expansion joint, which is to compensate the thermal expansion and contraction of pipelines, but its advantages lie in corrosion resistance, good vibration reduction, relatively low price, and can absorb multi-directional displacement.
Then why can't you buy the standard product directly? Alas, the problem lies in "non-standard". The pipe diameter ranges from DN100 to DN6000, and the working temperature ranges from-40℃ to 1200℃. The medium may be sulfur-containing flue gas, corrosive acid mist or high-temperature dust. Which standard part can take all in this kind of working condition? Therefore, it must be customized: according to your pipe diameter, temperature, pressure and medium characteristics, match the corrosion protection grade of the ring belt material, flange thickness, guide tube material and even mounting bolts.
Take a practical example. Last year, there was a cement factory customer. The original general-purpose rubber compensator cracked in three months. The reason is that the flue gas temperature at the kiln tail is above 350℃ for a long time, while the temperature resistance limit of ordinary rubber is 150℃. Later, it was replaced with a customized high-temperature non-metallic expansion joint (fabric fiber + silicone coating), which was used for more than a year and still leveraged. What's this called? Call money to be spent wisely.
2. Core parameters that must be found before customization: temperature, pressure, medium and displacement
When you go to the manufacturer and say "I want a non-metallic expansion joint", the manufacturer manager will definitely ask four numbers: How high is the temperature? How stressful? What's the medium? How much displacement? Don't be bothered, these four things are indispensable.
TemperatureIs the worst thing. The belt material can't withstand high temperatures, and no matter how good the structure is, it is useless. Neoprene or EPDM below 100°C; Silicone rubber below 250°C; fluororubber or polytetrafluoroethylene for use below 400°C; If it exceeds 400℃, you have to rely on ceramic fiber cloth + stainless steel wire mesh. In our product information,Non-metallic expansion joint (fabric fiber expansion joint)The series covers the range from-40℃ to 1000℃, but which coating to choose must be determined by the actual working temperature.
pressureGenerally not high, non-metallic expansion joints are usually used in micro positive pressure or negative pressure pipes (within 0.1MPa). However, if the system has pulsed pressure or instantaneous overpressure, it must be additionally reinforced. We have encountered cases where the pressure fluctuated in the flue at the inlet of the desulfurization tower due to the surge of the fan, and the manufacturer did not provide the peak pressure data, resulting in the ring belt being burst.
MediumDetermines the corrosion resistance grade of the contact material. The flue gas contains SO₂ and NO, SO you have to consider fluororubber or PTFE lining; There are many hard particles of dust, so wear-resistant layer must be added on the outside. This site'sRubber PTFE compensatorIs specially designed for strong corrosive media. There is also the moisture content of the medium-the condensed acid in the wet flue will corrode the metal flange. At this time, you may wish to choose stainless steel flange or add anti-corrosion coating as a whole.
displacementIncluding axial, transverse and angular displacements, it is preferable to give the maximum value in the three-dimensional direction. Many drawings only mark the axial compensation amount and ignore the lateral displacement. As a result, the ring belt is torn askew after installation. Remember: the displacement is not just the value, but also the direction. The manufacturer will design the wave height and the number of layers according to the total displacement.
3. Key points of selection in different industry scenarios-power station, cement, desulfurization, flue duct
The same rice raises hundreds of people, and the same non-metallic expansion joint varies greatly in the selection of different industries.
Power station industry: Rectangular non-metallic expansion joints are commonly used in the boiler smoke and air system with large pipe diameter (more than 3 meters at every turn), high temperature (300-500℃) and low pressure. The key is to look at the temperature resistance level of the ring belt and the material of the guide tube. This site'sCorrugated expansion joint for power station industryAlthough there are metal solutions, the rectangular sections of the flue are almost all non-metallic-because rectangular metal expansion joints are expensive, stress concentrated and not as flexible as fabric structures. In addition, it is sometimes necessary to use metal expansion joints and non-metallic expansion joints in power stations, such as high-temperature axial expansion joints for boiler outlets and non-metallic expansion joints for tail flues.
Cement industry: The biggest headache is high-temperature dust and alkali corrosion. The outlet temperature of the kiln tail preheater can reach 900-1100℃, which can not be carried by ordinary fabrics. At this time, we have to use a multi-layer composite structure: the innermost layer of high-temperature resistant ceramic fiber, the middle layer of heat insulation, and the outer layer of airtight layer (fluororubber). This site'sMetal Corrugated Expansion Joints in Cement IndustryIt is usually used in mill pipes, and non-metallic ones are used at the connection between cyclones and air ducts. Note: The accumulation of cement dust will increase the self-weight of the expansion joint, so the supporting structure should be considered when designing.
Desulfurization industry: The wet flue environment can be called "chemical hell"-sulfuric acid condensate droplets with a temperature of 60-80℃, saturated humidity and a pH value of 2-3. Fluororubber or polytetrafluoroethylene is the preferred material for the ring belt, and the flange must be corrosion resistant. OurDesulfurization flue gas baffle doorAndPTFE compensatorIt's for this scenario. Note when selecting: The expansion joint should leave drainage holes to avoid acid accumulation and corrosion of the bottom. In addition, the desulfurization system usually has a large number of flange connections, and the length of non-metallic expansion joints should not be too long, otherwise it is easy to twist during installation.
Smoke duct (universal): This is the most common scenario, the temperature is not high (
4. Customize the process and the door chosen by the manufacturer, as well as several common pits
Provide parameters → manufacturer's design drawing → confirmation → production. But the pits here are deeper than the other.
Pit 1: "Cutting corners" of ring belt materials。 Some manufacturers report fluororubber composite fabric, but the actual use is low-priced neoprene rubber with a layer of surface treatment. The identification method is very simple: it is required to provide the material physical property table (experimental data of temperature resistance and medium resistance), or take the sample for high-temperature aging test. OurNon-metallic expansion joint (fabric fiber expansion joint)The product page is attached with detailed material description, welcome to compare.
Pit 2: Insufficient flange thickness。 The flanges of non-metallic expansion joints are usually welded from angle or flat steel and need to withstand the pre-tightening force of mounting bolts. In order to save costs, some manufacturers thin the flange thickness, resulting in deformation and air leakage after installation. Standard practice: 6mm flat steel below DN300, 8mm for DN300-DN1000, and 10mm or thicker over DN1000. If you find that the quotation is significantly lower than that of your peers, there is a high probability that it has been manipulated here.
Pit 3: Ignore the guide tube。 The function of the guide tube (also called the liner tube) is to protect the ring belt from being directly washed by the medium, and at the same time guide the airflow to reduce turbulence. Many bargains directly omit the deflector, or use ordinary carbon steel plates (rust-worn for a few years). The manufacturer is required to specify the material (stainless steel 304/316L or weather-resistant steel) and thickness of the guide tube in the scheme. Regarding the specific function of the deflector, this site has a special question and answer, you can go and flip through it.
Then how to choose the manufacturer? Three hard indicators: ① Have the certificate of the national standard JB/T 12235-2015 for non-metallic expansion joints; ② The factory has press forming equipment and tensile tester. Don't just look at the price. There are too many examples of the first purchase being attracted by the low price and finally reworking to fill the leak.
Non-metal compensator expansion joint manufacturer customizationIn this matter, seven points depend on material selection and three points depend on installation. No matter how well the manufacturer does, the torque of screwing bolts is uneven during installation, the fixing bolts of the guide tube are missed, and the transportation limit device is not left... there are still problems. Therefore, after getting the product, let the manufacturer provide the installation instructions, and don't save one step.
What other specific work conditions do you want to talk about? Welcome to dump the parameters directly, and we will help you screen them.