Views:112 Author:Site Editor Publish Time: 2019-10-16 Origin:Site
With the rapid development of communication modernization, more and more open-line transmissions have been replaced by new transmission methods such as cables and optical cables. There are joints in heat shrinkable cables, and the quality of joints is an important factor affecting communication quality. In addition to the non-leakage of the insulation between the wires and the joints, the contact resistance of the joints should be small, and the joints also need good protection. This article deals with the joint protection of one of the cables, that is, long-distance communication cables with plastic sheaths.
In the past, epoxy resin plastic tape or asphalt oil mixture plastic tape were used to protect the connection of long-distance communication cable with plastic sheath. Because of the complex construction technology, it is difficult to select the materials to meet the requirements of sealing and insulation in the field, and the materials used are poisonous to human body. Thermal shrinkage sheath is used instead. Pipe protection has a series of advantages, such as simple technology, convenient field construction, easy to meet the requirements of sealing and anti-corrosion, non-toxic to human body and so on.
The material for making heat shrink tubing is a kind of high polymer heat shrinkable protective material with three-dimensional mesh structure. The inner wall of the sleeve is coated with high quality hot melt sealant. When the heat shrinkable sleeve is heated to a certain temperature, the sealant melts and firmly adheres to the sheath of the cable joint to seal it, thereby preventing moisture, enhancing the connection strength, and being able to withstand a certain pressure without leaking. Because of the advantages mentioned above, the heat shrinkable sleeve can be widely used in the protection and repair of various heat shrinkable cable accessories.
At present, there are two kinds of heat shrinkable materials for the protection of communication cable joints. One is pipe material, which is like a plastic pipe. The other is sheet material. The finished product is connected into tubular shape by clamps when it is used. The selection of heat shrinkable sleeve material is generally determined according to the actual situation of the cable under construction. For example, the trunk cable is generally made of sheet material, and some of them are made of pipe material(mainly considering the high and low frequency balance needs to be started). Pipes are generally used in local telephone, regional and station cables.
When in use, the inner diameter of the heat shrinkable sleeve should be as close as possible to the outer diameter of the cable, so that the sleeve can be closely attached to the outer side of the cable after shrinking and setting. The length of the heat-shrinkable sleeve should be sufficient to protect the lead sleeve and the bare part of the cable sheath, and at least overlap the cable plastic outer sheath by 100mm.
Before the heat shrinkage encapsulation, the entire cable joint (the part to be encapsulated) should be cleaned with a clean cotton yarn, and then the casing and the solder joints should be wrapped with plastic tape to make the casing to the cable aluminum sheath. The slope of this part is gentle, avoiding the gap when the heat shrinkable sleeve shrinks here. The plastic belt is wrapped tightly, overlapping 1/2, the package is tight and not wrinkled, and the surface after wrapping is smooth.
Each heat shrinkable sleeve has a hot melt adhesive film (also called sealant). Its function is to prevent the shrinkage of heat-shrinkable sleeve, because the surface of the aluminum sheath is not smooth, the shrinkage of heat-shrinkable sleeve and the aluminum sheath can not be tightly adhered, resulting in the gas to be trapped here, which can not meet the requirements of anti-corrosion and anti-leakage. The hot-melt adhesive film should be wound around the aluminum tube at the opening of the outer sheath of the cable. When the heat shrinkable sleeve is heated When the sealing film melts, it overflows from the end. The end sealing is further strengthened to achieve airtight.
Through the construction practice of Shangfu Railway, using thermal shrinkable sleeve as cable joint protection has a series of advantages, such as convenient construction, simple technology and guaranteed quality. Especially, it overcomes the protection problem of cable joint, which is a weak link in the construction of long distance communication cable, and greatly improves the mechanical strength, gas-holding performance and chemical corrosion resistance of the cable joint. It plays an obvious role in ensuring the construction quality of cables. The Shangfu Railway has a total length of 178 km. And there are 522 joints in Shangfu Railway. In the past six months, there was no leakage or corrosion of the joints, which may affect the electrical performance. At the same time, due to the heat shrinkage and encapsulation, the construction was safe and convenient, which not only improved the construction quality of the cable, but also reduced the labor intensity and improved the construction efficiency. Compared with the outer winding protection of the plastic belt of the original asphalt engine oil mixture, the work efficiency is about 10 times.