Why do cable troughs need expansion joints-thermal expansion and contraction are not that simple
Many people think that the cable tray is just an iron slot for wiring. How much impact can thermal expansion and contraction have? Two days ago, I met a customer. The 200-meter-long metal trough in the factory building directly bent the bracket in the straight section in the high temperature in summer, and the cable was squeezed so that the outer skin was wrinkled. And guess what? They didn't have expansion joints at all. The expansion coefficient of metal wire trough is the same as that of ordinary steel, and the elongation is about 0.12mm per 10℃ per meter. Two hundred meters of wire trough, the temperature difference is 50℃, and the cumulative displacement exceeds 120mm. This amount is not digested by the little clearance of the bolt hole. What's more troublesome is that the cable tray is often fixed on the steel structure, and the steel structure itself is also deformed by heat. The two systems are superimposed, and the displacement is more than doubled. So,Metal trough expansion jointIt's not the icing on the cake, it's just needed-especially in places with large temperature differences and long wire trough spans.
Core Structure of Metal Wire Channel Expansion Joint: Matching of Rectangular Section and Corrugated Element
Unlike a circular tube expansion joint, the wire trough has a rectangular cross section, so the compensation element must be made rectangular. We have a product libraryMetal rectangular expansion jointStructurally, it is a rectangular flange plus bellows. But here is a gateway: the corrugated components are not necessarily all-metal bellows, and in some cases, nonmetallic fabric fibers are matched, such asRectangular non-metallic expansion joint。 All-metal scheme is generally usedUniversal corrugated expansion jointChanging rectangular, high temperature resistance and long life; The non-metallic scheme has good corrosion resistance and flexibility, but poor pressure bearing capacity. Which one to choose? Depends on the working conditions. For example, if there is water and corrosive gas in the cable tunnel, the non-metallic expansion joint is more suitable; If it is a high-temperature workshop (steel rolling, power plant), metal rectangular expansion joints must be installed. The core component is bellows, and the wall thickness, wave pitch and number of layers determine the compensation ability and fatigue life. In addition, the guide tube is rarely used in the expansion joint of the metal wire trough, because the medium in the wire trough is air and cable, and it is not washed by high-speed airflow, so it mainly plays a role in preventing foreign objects from entering.
Three elements of type selection: displacement, diameter size and working temperature
In fact, the selection is not complicated, and three parameters are stuck: the first is the displacement. You have to calculate the axial expansion and contraction of the wire trough at the maximum temperature difference. The calculation formula is simple: Δ L = α × L × Δ T. α takes 1.2×10⁻⁵/°C. Calculate, for example, 50mm, then choose the expansion joint with a compensation amount of more than 60mm and leave a margin. The second is the diameter size. With the outer dimensions of the wire trough, the length × width should be consistent, otherwise the flange can't be installed. Note that the wire trough has a cover plate, and the flange connection of the expansion joint should consider whether the cover plate can be opened and closed normally. The third is the operating temperature. Conventional polyurethane sealing ring can only reach 120℃, and silica gel can reach 250℃. If it exceeds 300℃, it has to be sealed with pure metal bellows and high-temperature packing. On our stationHigh temperature axial expansion jointIt is for this, using stainless steel 304 or 316L, with a temperature resistance of up to 600℃. After the three parameters are determined, the model number will basically come out.
Installation Guide for Pit Avoidance: Cooperative Arrangement of Fixed Bracket, Guide Bracket and Expansion Joint
The expansion joint is directly welded on the bracket as an ordinary wire trough section, which is equivalent to wasting the expansion function. The correct thing to do is to divide the compensation segments. Each section of wire trough is provided with a fixed bracket, a guide bracket, and an expansion joint is arranged in the middle. The fixed bracket should lock the wire trough and not let it run; The guide bracket only constrains vertical and lateral displacement, allowing free sliding in the axial direction. Leave at least 500mm straight sections at both ends of the expansion joint for convenient adjustment. How to adjust the tie rod? The tie rod nut is generally pre-tightened when the product leaves the factory to limit the deformation during transportation. After installation in place, the tie rod nut should be loosened to the specified stroke, otherwise the bellows can't move, so it will be installed in vain. For details, please refer to ourHow to adjust the tie rod nut of expansion jointThe Q&A. In additionLarge tie rod expansion jointSuitable for large-span wire troughs, the pull rod can withstand the blind plate force to prevent the bellows from being crushed. Another point: when there are many cables in the trough, the installation position of the expansion joint should avoid the place where the bending radius of the cable is too small, and don't let the cable bend at the bellows.
Daily maintenance and fault judgment: What to do about loose tie rod and corrugation leakage
Say two of the most common glitches. The first is that the tie rod is loose. Over time, vibration or thermal cycling will cause the tie rod nut to fall back. The consequence is that the expansion joint loses its limit, the bellows is excessively compressed or stretched, and the life is plummeted. It is recommended to check the maintenance frequency once every six months, pull the pull rod with a hand, and screw it in place if it feels loose. Be careful not to screw to death, and leave a gap according to the design stroke. The second is ripple leakage. It doesn't matter if the metal bellows has cracks or corrosion perforations, and the internal pressure medium (air) leaks, but if corrosive gas enters the corrugated layers, it will accelerate the damage. How to judge leakage: Listen to the sound (chichi) or apply soapy water to see the bubbles. After discovering a leak, if it is a non-load-bearing part, it can be temporarily bypassed with a metal hose? No, the trough is rigid and can't be bypassed. Can only be replaced with new parts. Therefore, daily maintenance should be rust-proof, especially at welds. There is also the problem of the deflector tube falling off-although the deflector tube is rarely used for the trough expansion joint, if it is used, it will fall off and jam the bellows. If you hear an abnormal noise, you should disassemble it for inspection. In fact, these minor problems are in place, and an expansion joint will last for ten years without any problem. We haveService life of expansion jointDetailed instructions, you can flip through if you are interested.