Find out one thing first: what is the relationship between non-metallic expansion joints, rubber compensators and fabric fiber expansion joints?
"Are your non-metallic expansion joints and rubber compensators different things?" To be honest, this question is not your fault, because the name is too messy in the industry. You just have to remember one sentence:Non-metallic expansion joints are family names, and rubber compensators and fabric fiber expansion joints are its two common forms.
Just take it apart and look at the structure. The main body of non-metallic expansion joint is composed of flexible band, flange, guide tube and heat insulation layer, among which the most critical layer in flexible band is rubber. As for the fabric fiber expansion joint, in addition to rubber, there are also high-temperature resistant layers such as glass fiber and aluminum silicate wool in its loop. Therefore, you can think of the rubber compensator as a non-metallic expansion joint with "rubber playing the leading role" and the fabric fiber expansion joint as a version of "rubber + fiber composite" going into battle together. Not three things, but different ratios on a line.
Rubber in this structure, to put it bluntly, is the part responsible for "deformation". The displacement caused by thermal expansion and contraction of pipelines, equipment vibration and installation error is all catched by it softly. Metal parts are responsible for supporting the skeleton, and rubber is responsible for doing soft work.
Why are plumbing designers willing to compensate with rubber?
Comparing metal expansion joints with rubber, many people's first reaction is that metal is strong. Yes, metal pressure and temperature resistance are its strengths, but in terms of shock absorption, noise reduction and multi-dimensional displacement compensation, the advantages of rubber are incomparable to those of metal.
Take an example. The vibration of the flue gas pipe and the fan outlet, if you use a metal bellows, the vibration will be transmitted all the way down the pipe wall, and the noise is so loud that people can't stay in the workshop. Replace with a rubber compensator, the damping characteristics of rubber can directly eat a large part of high-frequency vibration, and the noise can be reduced by more than ten decibels. More importantly, rubber can absorb axial, transverse and angular displacements at the same time, while most metal expansion joints can only focus on one direction. If you want multi-directional compensation, you have to add hinges and tie rods, which have complicated structures and occupy space.
Of course, rubber is not a panacea. Its hard boundary is very clear: the temperature generally does not exceed 200℃ (special rubber such as fluororubber can reach about 230℃), and the pressure is usually in the range of 0.1~0.5MPa. The medium must avoid strongly oxidizing and corrosive things. If you use it to remove high-temperature steam or strong acid, you are simply letting it die.
Rubber is not as simple as a piece of skin: cord fabric, fluororubber, EPDM, what are each tubes?
Many customers think that the rubber compensator is a circle bent by a thick rubber skin, which is a big misunderstanding. In fact, in a flexible band, there are several layers of rubber layer alone, and there is a layer of cord cloth sandwiched in the middle-the kind of cord cloth in tires, which is used to increase strength and prevent the rubber from being burst by air pressure.
The rubber material of the outer layer determines what medium the product can carry and how long it can live. Ethylene propylene monomer (EPDM) is a general main force, which is resistant to aging, ozone, dilute acid and alkali, and basically chooses it in flue gas, dust and water vapor environments. Fluororubber (FKM) is a life-saving brand in the environment of organic solvents and strong acids and alkali. Its price is several times more expensive, but its life is much longer. Two days ago, I encountered the purchase of a chemical plant, and took a rubber compensator to take the benzene-containing waste gas. As a result, it cracked in three months. Later, it was replaced with fluorine rubber ring belt, and it was still the same as new after more than two years of use. If you choose the wrong material, you will have to double the cost saved.
The four most easily overlooked parameters in model selection: displacement, pressure, temperature, medium
These four parameters, each has a pit.
displacement amountIt's not that bigger is better. Some people buy rubber compensators to specially pick models with large compensation, thinking that it is safe to leave a margin. However, once the compensation amount is large, the ring belt has to be made softer and thinner, and the pressure resistance will decrease. In order to make up for the 10mm displacement, the result is a high pressure circle with a bulge. What is the picture?
pressureThe same is true, not the thicker the better. When the thickness of the band increases, the flexibility decreases, and the displacement that should be absorbed can not be absorbed. Moreover, the pressure selection depends on whether it is positive or negative pressure. Negative pressure pipeline is the easiest to be ignored, and the working conditions of the exhaust fan outlet and inlet are completely different. Excessive negative pressure can deflate the rubber ring belt.
TemperatureAndMediumTo look at it together. The temperature of many flue gas pipes is not high, but they contain sulfide and acidic condensate. At this time, it is not enough to choose EPDM just by looking at the temperature. You have to consider whether the medium will condense and corrode on the rubber surface. We generally recommend that customers write all the media components, even if the concentration is not high, and don't just write the word "smoke" to fool things.
Common pits in installation and operation and maintenance: Is the rubber compensator finished when installed?
If you fail to install this level, there will be all the trouble behind.
Let's start with the limit screw. Non-metallic expansion joints usually come out of the factory with several limit screws, which are used to prevent the ring belt from being overstretched or compressed during transportation and installation. Once installed,Limit screw must be loosened or removedOtherwise, the expansion joint can't move at all, which is equivalent to installing an iron knot. Many customers forget this, and the tube tears the loop strap directly when it is hot. We have sold this for so many years, and we have encountered at least a dozen cases.
Let's talk about flange noodles. The rubber band is pressed tightly by the flange. If the flange surface is deformed, burred or sandwiched with welding slag, the rubber will be damaged when pressed. Before installation, be sure to clean and smooth the flange surface. It is best to compress it evenly with a flat washer. Don't screw a bolt to the end, but twist it symmetrically several times.
Finally, partial clothing is strictly forbidden. The so-called partial installation is to intentionally install the ring belt diagonally in order to compensate for the pipeline installation error. This will cause the uneven stress of the rubber layer, one place is too tight and the other place is too wrinkled, and the service life is directly reduced in half. If the pipe is not aligned, it is a problem with the pipe. First adjust the pipe and then install the expansion joint.
As for rubber aging, there are three judgment criteria: surface cracking, hardening and loss of elasticity, or layered peeling. Don't wait until it leaks before replacing it. At that time, the nearby equipment may have been corroded by smoke.
What is the difference between rubber non-metallic expansion joint and rubber PTFE compensator?
The two products in the station have similar names, but their uses are completely different.
Rubber PTFE compensator, the core is polytetrafluoroethylene (PTFE) lining, and rubber is reinforced in the outer layer. PTFE material is resistant to almost all strong acids and alkali, with extremely low friction coefficient and will not be polluted by media. Therefore, it specializes in dealing with highly corrosive media, such as concentrated sulfuric acid, hydrochloric acid and acetic acid. The rubber non-metallic expansion joint is made of pure rubber or rubber composite fabric band. Its corrosion resistance depends on the chemical inertness of the rubber itself. It is okay to deal with milder smoke, dust and water vapor, but it will be blinded when it encounters strong acid.
How to choose? Remember one thing:The medium is strongly corrosive, and the rubber PTFE compensator is selected; The medium is flue gas, dust, weak acid and alkali, and the non-metallic expansion joint (rubber compensator) is selected。 In addition, the temperature range of rubber PTFE compensator is also limited by PTFE, which generally does not exceed 150℃, while the rubber fabric composite band can be made higher after adding heat insulation layer. If you take PTFE to take away the high-temperature smoke, the PTFE layer will soften and deform; If you take the rubber to remove concentrated sulfuric acid, the rubber will be scrapped in a few days.
So don't let them fight each other on the shelves, they're supposed to take care of their own stalls.