First, recognize what this silicone cloth in your hand is for-the core component of non-metallic expansion joint
When many people get the non-metallic compensator silicone cloth, their first reaction is "Isn't this just a cloth? Just screw it on". Tsk, if it were that simple, there would be less leaks, tears, or even shutdowns in the industrial pipeline system. This silicone cloth, to be exactNon-metallic expansion joints (fabric fiber expansion joints)The flexible body bears the heavy responsibility of absorbing the thermal displacement of the pipeline, reducing vibration and noise, and compensating the installation error. Think about it, the flue gas pipe can be extended by tens of millimeters at high temperature, and it all depends on this piece of cloth to "expand and contract". If it is not installed properly, it is not a compensator, but a breaker.
Two days ago, I met a customer, saying that their factory had changed the silicone cloth three times, and every time it cracked in less than half a year. I asked him how to install it, and he said, "Just tighten the four corners." As soon as you hear it, you know what the problem is-the wrong way of pretending, no matter how expensive the cloth is, it will be for nothing. So let's understand first: silicone cloth is not just hung casually, it needs accurate pre-stretching, symmetrical fastening, and treatment of flange surface.
2. Hardcore preparation before installation: flange surface treatment, dimension check, bolt preload estimation
First, the flange surface must be clean and flat.Old flanges often have weld slag, rust, and even residual glue from a silicone cloth. These bumps will break through the silicone cloth, and even the burr of only 0.5mm will become a stress concentration point under high temperature and pressure. Polish with an angle grinder and then check flatness with a ruler-repair welding or flange replacement if clearance exceeds 1mm. This work can't be saved. If you save it, you will dig a hole for yourself.
Second, size check.Silicone cloth has a durability limit and cannot be deadlifted when installed. Measure the inside diameter of the flange and the effective width of the silicone cloth. The standard practice is: the free length of silicone cloth should be 10~20mm shorter than the flange spacing (see the design displacement). For example, if the axial compensation amount is designed to be ±50mm, the length of silicone cloth should be about 15mm shorter than the flange spacing during installation, leaving pre-stretching space. This piece of data is usually obtained fromNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015You can find it in, don't be lazy.
Third, bolt preload estimation.Many people screw bolts all by hand feel, and as a result, they either loosen or deform the flange. Silicone cloth is generally fixed by pressure plate, and the preloading force of pressure plate bolts is recommended to be controlled at 40~60 N·m (with torque wrench). For M16 bolts, the torque value is approximately 50 N·m. If the flange is a thin-walled piece (such as the flange of a smoke baffle door), it must be lowered to 30 N·m to prevent the platen from deforming and cutting the edges of the silicone cloth. There is no standard answer for this data? Yes, ask the manufacturer for installation specifications, or refer to the product information on this siteRectangular non-metallic expansion jointThe installation instructions page.
3. Step-by-step installation practice: from the fixed end to the free end, screw the bolts diagonally to avoid accidents
All right, preparations done, start loading. Remember one principle:Fix one end first, then center it gradually, and finally tighten it diagonally.The order is wrong, and the silicone cloth is quasi-skewed.
Step 1, spread the silicone cloth onto the flange and align the bolt holes. Put the pressure plate on the free end (usually the displaced end of the pipe) first, and tighten two bolts slightly (don't tighten them, as long as they can fix the position). Then use a crowbar or manual hoist to align the flange at the fixed end (such as the equipment side) with the pressure plate, put all the bolts on this end, and screw it snugly against the pressure plate by hand.
The second step is to adjust the position of the free end. Use a flashlight to check whether the silicone cloth is centered-the gap difference between the two sides should not exceed 2mm. If there is an offset, fine tune the position of the free end flange with a crowbar. At this time, don't be lazy to smash it hard with a hammer, it will smash the silicone cloth out of wrinkles.
Step 3: Twist the bolts diagonally. This is too critical. Assume that there are 16 bolt holes in one circle of the flange, first screw the four points 1, 9, 5 and 13, and hit the torque to 30 N·m; Screw again 3, 11, 7, 15, again 30 N·m; Then fill all the bolts in sequence, and finally add to the target torque uniformly. Why do you want this? Because if you twist it one by one along a circle, the silicone cloth will be "squeezed" aside, and wavy wrinkles appear. During operation, these wrinkles are stress concentration zones and will quickly wear out.
And guess what? Many on-site workers directly twisted the electric wrench from 1 to 16 in order to get fast. It took five minutes to get it done. The consequence is: after three months, the silicone cloth cracks at the edge of the bolt hole, and they will blame the poor quality of the product-in fact, the fault lies in the installation technique.
4. The installation and rollover sites we saw in those years: over-stretching, deflection and unilateral compression
After working for more than ten years, I can write a book about the rollover cases I have seen. Pick three typical ones and say:
1. Over-stretching.There is a rotary kiln flue in a cement plant. When the silicone cloth is installed, it is pulled too tightly, so it is directly used as a "bandage". As a result, the pipe was elongated after heating up, and the silicone cloth had no margin, which was torn at the edge of the platen. Correct practice: Let the silicone cloth be in a "slightly loose" state when installing, retaining at least 10mm of axial relaxation. Criteria of judgment? Press the middle of the silicone cloth with your hand, and it is normal to easily press 5~10mm.
2. Deflection.A brother who was doing a desulfurization project loaded the silicone cloth 8mm crooked. As soon as the transverse displacement of the pipeline occurs during operation, the silicone cloth bears tension on one side, and the side collapses directly after three months. How to solve it? After installation, check the flange alignment with a laser measuring instrument. If the deviation exceeds 3mm, it must be adjusted.
3. One-sided compression.In order to catch up with the construction deadline, some sites only screwed half of the bolts of the flange, thinking "test it first, and make up if it leaks". As a result, as soon as the fan is turned on, the negative pressure sucks in the silicone cloth on the unfastened side and tears it in half directly. Therefore, every bolt must be in place during assembly, and no one can leak.
How many of these pits have you stepped on? Don't think it's all the fault of a novice. I've seen twenty-year-old masters still make it. In the final analysis, the silicone cloth is treated as an "ordinary gasket".
5. Don't rush to go after installation: pressure test, displacement check, and how to make silicone cloth use for two more years
The bolts are screwed, not the end. There are three more barriers to pass:
First, test the pressure.For pipelines under pressure (such as the non-metallic section next to the corrugated expansion joint used in the power station industry), perform a hydraulic test with 1.25 times of the design pressure, hold the pressure for 30 minutes, and observe that there is no leakage at the flange connection. If it is a negative pressure pipe (such as the flue before and after the smoke baffle door), check all bolt holes and joints with soapy water, no air bubbles.
Second, displacement check.Mark several reference points on the silicone cloth (for example, draw an alignment line between the cloth surface and the edge of the flange with a marker), then simulate the temperature rise and fall under the working condition, and measure the actual displacement with a caliper. If the measured displacement exceeds 80% of the design value, it means that the installation reserve is not enough, and it must be readjusted.
Third, the SAO operation to extend the life.Want to make silicone cloth last two more years? A few tips:
- Applying a temperature-resistant and waterproof coating (such as silicone rubber varnish) on the outer surface of silicone cloth can greatly slow down the aging.
- If it is outdoor installation, add stainless steel protective cover to prevent direct UV rays.
- Check the torque of the platen bolts periodically-thermal cycling causes attenuation of the preload force, re-tighten every six months.
After all, how to install non-metallic compensator silicone cloth? There is no standard answer to this question, but there is a standard process. If you follow the above five steps, you won't make a mistake. If you want to save trouble and pretend blindly, then this piece of cloth will only last half a year if it dies, and the money for shutting down the machine and changing the cloth will be enough to buy several sets of good ones. This account, you can settle it yourself.