What is a non-metallic fabric compensator? What is the difference between it and the metal expansion joint
Non-metallic fabric compensator, to put it bluntly, is what we often callNon-metallic expansion joints (fabric fiber expansion joints)。 Which is connected to the expansion joints made of metal bellows- -such asMetal rectangular expansion joint、Universal corrugated expansion joint— Two completely different things. The metal expansion joint relies on the bellows to expand and contract back and forth to absorb the displacement, and it has high pressure resistance but is afraid of corrosion and fatigue; The non-metallic fabric compensator relies on a flexible structure composed of multi-layer fabric bands and heat-insulating cotton, which can resist high-temperature smoke and acid-alkali corrosion, and can compensate for displacement in many directions-axial, transverse and angular absorption. It is simply a versatile person.
Think about it. Under the working conditions of power plant flue, cement production line and desulfurization system, the temperature is always five or six hundred degrees, and there are still sulfide in the medium. The metal bellows won't last long before they crack. That's when non-metallic fabric compensators come in handy. Its core strength isUnpressurized— — Or to be precise, the pressure bearing capacity is very low (generally 0.1~0.5MPa), but the displacement compensation amount is huge, and it can reach several hundred millimeters in one direction. So don't use it as a pressure-bearing part, that's the wrong object.
The skeleton of regular products: how to build fabric bands, insulation layers and flange structures
RegularRegular nonmetallic fabric compensatorIt is definitely not just wrapped up in a layer of cloth. It is divided into three layers: the outermost layer is a fabric band, generally silicone cloth, fluorine adhesive cloth or PTFE coated cloth, which is temperature-resistant and corrosion-resistant; The middle is a heat insulation layer, which is separated by ceramic fiber blanket or aluminum silicate cotton to prevent heat from being transmitted to the flange; Sometimes a layer of stainless steel wire mesh is added to the innermost layer to enhance wear resistance.
What about flange construction? The common ones are angle steel flanges or flat flanges. The spacing of bolt holes must be according to JB/T 12235-2015 standard, and the deviation of hole diameter should be controlled within ±0.5mm. Cut corners, flange thickness, bolt holes deviated, it was a matter of time before air leakage was installed. OurRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)After products and flanges are welded, they will be annealed as a whole to relieve stress, and then sandblasted to prevent corrosion. This is called the formal process.
By the way, the way the fabric loop tape is lapped is also particular. Regular manufacturers use heat sealing or sewing to reinforce, the overlap width is not less than 50mm, and the joints should be staggered, and no cross seams should appear. Otherwise, the slit will crack under high temperature, and the whole system will have to be shut down as soon as the medium springs out.
Hard indicators that can't be avoided when selecting the model: how to align the temperature, pressure and displacement
It is easiest to stumble when it comes to model selection. You have three hard indicators:Design temperature, design pressure, displacement。
Temperature:Don't just look at the temperature of the medium, but also count the radiant heat. Like 850°C inside the flue, but maybe only 200°C on the surface of the compensator-depending on the insulation thickness. Regular manufacturers will give a temperature-thickness comparison table, for example, 50mm thick ceramic fiber is used below 350℃, 100mm is used below 600℃, and then multi-layer composite is added higher. If you report the temperature directly to the sales, people can reverse the structure.
Pressure:The resistance voltage of non-metallic fabric compensator is not more than 0.5MPa, and most working conditions are 0.1~0.3MPa. If the system has positive pressure and exceeds 0.3MPa, it is recommended to install a limit rod-it is our commonexpansion joint tie rod。 The role of the tie rod is to prevent excessive expansion from causing the loop strap to tear. However, note that the tie rod nut cannot be locked when adjusting, and the displacement allowance must be reserved (the specific adjustment method can be seen in the Q&A in our stationHow to adjust the tie rod nut of expansion joint）。
Displacement Amount:This one is the easiest to underestimate. Calculate the thermal expansion of the pipeline with Δ L = α × L × Δ T, and check the linear expansion coefficient of the pipeline with α. The temperature difference Δ T is the difference between the highest ambient temperature and the working temperature. After calculating the compensation amount, don't accept it all-the displacement allowed by regular products is usually 80% of the rated value, and you have to leave a 20% safety margin. For example, if the calculation requires 100mm axial compression, choose the model that can compensate 125mm.
Angular displacement. If the pipe has a bend, the compensator should be able to absorb both angular and lateral displacements. At this timeCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointMore suitable, but non-metallic can also be achieved by adding a universal joint structure. We have it in our stationDouble-sealed single-axis circular baffle doorThis kind of matching piece can be used for isolation.
Easy pits in installation and maintenance-pre-stretching, guide racks, and transport storage
I met a customer two days ago and bought oursNon-metallic expansion joint (fabric fiber expansion joint)It bulged within a week of installing it. When I asked, there was no pre-stretching during installation, and the spacing between the pipe brackets was too large, so the guide frame was not installed. Doesn't this trick yourself?
Pre-stretching:When a non-metallic compensator is installed, it is usually stretched to about half its rated displacement, so that it operates with both compression and tensile allowances. The specific stretch amount will be marked on the label by the manufacturer. You can't tune it? Simple: Use the screw nut to match, slowly pull into place, and then fix the flange bolt. Note that the stretching direction should be consistent with the thermal elongation direction of the pipe.
Guide frame:Many people think that everything will be fine if the compensator is installed. In fact, guide brackets must be set on both sides of the pipeline, and the distance from the compensator is generally 6~10 times the diameter of the pipeline. The role of the guide frame is to prevent the compensator from twisting caused by the instability of the pipe. Especially for large-diameter flues, when the wind pressure blows, the pipe shakes up, and the compensator ring belt is torn in minutes.
Transportation Storage:The pit is more secluded. When regular products leave the factory, the loop belt is curled packaging, and heavy pressure is strictly prohibited. You lay it flat and stack it, and press a steel plate on it? The stress is concentrated at the crease of the ring, and it will crack on the machine. Correct practice: Place it upright to avoid direct sunlight and oil contact. If the inventory exceeds half a year, it is necessary to regularly check whether the ring belt has aged and hardened.
Don't forget to check the flange sealing surface when you finish installing and accepting it. Use a gauge to measure the spacing of bolt holes. If the error exceeds 1mm, you have to return the product. And,expansion joint guide tubeIf fitted, make sure that the direction of the guide tube is consistent with the flow direction of the medium (arrow pointing), otherwise the guide tube becomes a resistance member and accelerates wear.
Why emphasize "formality"? Hidden dangers of counterfeit and inferior products and methods to see through them at a glance
There are many small workshops in the market, which sell inferior silicone cloth as fluorine tape, and rock wool is used instead of ceramic fiber for thermal insulation cotton, and the flange thickness is halved. This kindRegular nonmetallic fabric compensatorThe "knockoff version" of, what are the consequences?
- Belt burn-through at high temperature:The temperature resistance of inferior silicone cloth is only 200℃, and the smoke will become brittle and cracked once it passes 350℃, leaking air and ash, which will cause fire in serious cases.
- Powdered collapse of insulation layer:When rock wool encounters condensed water, it will clump and lose its thermal insulation effect. The heat is transferred to the flange, resulting in thermal relaxation of the bolts and detachment of the flange.
- Flange deformation:The thin flange is deformed under the action of bolt pre-tightening force, the seal is not tight, and the air leakage rate is as high as more than 10% (the regular product is controlled within 1%).
How can you see through it at a glance? Teach you three tricks:Look at the label: The standard number of JB/T 12235-2015, design temperature, pressure, displacement, production date and inspector code are included on the regular product nameplate. No? Fake.Two-touch ring belt: The surface of fluorine tape is smooth and elastic, while the silicone cloth is hard and there are white marks on nails. If it doesn't work, burn the scraps with a lighter-the silicone cloth emits black smoke and leaves hard lumps, while the fluorine tape burns slowly and the residue is white powder.Three weighing: Compensator of the same size, the regular product is 20% ~30% heavier than the cottage product because of the high density of insulation layer. If you weigh it with your hands, there must be something wrong with it.
After all, the pipeline system costs hundreds of thousands or millions, so don't save it on the compensator, a small piece that costs tens of thousands of dollars. chooseRegular nonmetallic fabric compensatorAccording to the above indicators selection + standard installation, you don't have to worry about it for three to five years. On the contrary, the money saved is not enough for the lost work of maintenance shutdown.
(The terms and product names involved in this article refer to the published information on this site, such asNon-metallic expansion joint (fabric fiber expansion joint)、Rectangular non-metallic expansion joint、Compound hinge transverse expansion jointetc. Please consult the manufacturer according to the specific working conditions for actual selection.)