To properly repair the wire and cable, it is important to analyze the cause of the wire and cable failure. Causes of wire and cable failures are generally as follows:
Insulation aging deterioration
Wire and cable insulation is subject to thermal, chemical, and mechanical effects that are accompanied by electrical effects, so that the insulating medium undergoes physical and chemical changes that degrade the insulation level of the medium. Insulation is damp. Intermediate joints or terminal heads cause insulation and dampness due to poor sealing of the structure or poor installation quality; defects such as blisters or cracks are left in the manufacture of lead-bundle cables, which can also make the cables damp.
2 cable overheating
There are many reasons for overheating the cable. The internal cause is local heating of the air gap inside the cable insulation, which in turn causes the insulation to char. External factors are cables installed in dense cable areas, cable tunnels, etc. Cables that are put in dry pipes and cables that are close to the pipes can cause accelerated insulation damage due to cable overload or poor heat dissipation.
3. Mechanical damage
Mainly refers to the cable damage caused by external forces. This is mainly due to mechanical action such as vibration of the vehicle and deformation of the cable. Deformation of the cable results in excessive bending, damage to the inner insulation or an air gap inside the insulation.
4. Cover corrosion
Due to the electrolysis or chemical effects of lead corrosion of the cable, due to the different nature and degree of corrosion, the lead package has red, yellow, orange and yellowish compounds or pores resembling sponges.
5. Overvoltage causes breakdown
Atmospheric overvoltage and internal overvoltage cause the insulation of the cable to exceed the allowable stress and cause breakdown. Moreover, analysis of actual faults indicates that many outdoor terminal head faults are caused by atmospheric over-voltage.
6. Design of intermediate joints and terminal heads and manufacturing process problems
When stripping semiconductors, damaged internal insulation or insulating surfaces have particles, dust, and other impurities; poor sealing of the cable heads, causing moisture inside the insulation, resulting in moisture insulation; cable joint process is not standard, sealing is not standardized, resulting in grounding; production environment humidity is large Causes the insulation integrity of the production site (cable head); the grounding of the cable is incorrect, causing the ground wire to form a current or break.
Wire and cable maintenance measures
After analyzing the causes of wire and cable faults, the wire and cable maintenance strategy can be formulated in light of the actual situation.
For the production process of the intermediate joints and the terminal heads, it is possible to strengthen the test of the attachments of the cable entry heads and strictly check on the basis of the implementation of the relevant regulations. Carefully operate the semiconductor layers of the jackets and insulating shields to thoroughly polish and clean the insulation surfaces. Prevent foreign particles from remaining on the insulation; the humidity of the installation environment is kept below 70%.
A series of clear provisions are made for the installation of cables: the armor layer and the copper shield must be grounded separately and their cross-section is not less than 25mm2; the single-core cable must be grounded at one end of the power receiving end, and the three-core cable must be grounded at both ends. The tin of the cable is tinned.
In order to prevent the cable from being damaged due to external forces, the force part can be protected by pipe protection and fixed. The middle joint is protected from the outside, and the joints are fixed on both sides. During the construction process, the thread nose is not twisted and deformed by external forces. If necessary, To handle twisting, measures should be taken to make the surface flat; when a construction team near the cable is under construction, it is necessary to increase the number of striking signs, and if necessary, send a reminder to the construction personnel.
Cut joints: Before cutting, first check the joint for water and moisture. If it exists, you cannot cut the joint with the blowtorch, because the blowtorch heats the moisture from both sides of the joint to the inside of the cable, preferably with a hammer and The trowel cuts the casing; if there is no moisture and moisture, the torch can be used to open the lead sleeve, remove the lead set dirt, scrape the rust spot, wipe off the solder slag, remove from the cable connection, and prepare it for reuse.
Remove moisture: available baking method. It is a torch or charcoal fire to drive off the moisture. This method can only be used with a small amount of moisture. When the paper-insulated core wire is exposed to heavy moisture, the method of pouring the wax can be used, and hot wax can be used to remove the moisture. Blended with 60% ash and 40% medium Vaseline and heated to 130-140°C. When pouring wax, control it at 120-130°C. Pour wax from the lead bushes on both sides of the cable and cut 10-15cm at the cable lead sleeve. At the beginning, the cast was gradually removed from the incision and the wax at the incision was allowed to condense and then poured into the center of the joint until no air bubbles and sounds of impregnation were present on the core.
Common wire and cable maintenance methods
After analyzing the causes of wire and cable faults and determining the wire and cable maintenance strategy, it is necessary to select appropriate wire and cable maintenance methods to repair the wires and cables.
The commonly used wire and cable maintenance methods are as follows:
1. Electric iron repair - simple operation, but the appearance is not good, the middle part of the repair part of the repair contact is not true.
2. Plastic welding torch repair - need to have a certain technology, a good appearance, the operation to avoid the gun too close to the cable, the temperature is too high will affect the plastic deformation effect. The plastic used before the repair should be repaired in advance, and the plastic and cable should be fully adhered in time, and the hard-paper or cable sheathing should be used to avoid fingerprints or other fingerprints.
3. Torch repair - strong technical, time-consuming, use a large area repair, but the quality, appearance is excellent. When repairing, the torch shall be heated with a smooth iron sheet (2-3 cm wide and 2-3 mm thick), and the plastic shall be glued to the replacement part with a hot iron sheet. Use iron tablets and iron it up repeatedly until it looks good. During the repair process, the iron pieces will continue to cool and require constant heating, and sandpaper will also be required to sand away the plastic residue from the iron pieces.
4. In the event of cable pleats, discounts (dead bends), do not force the bend back to avoid damaging the insulation. Can be soaked with boiled water until the cable is softened and slowly corrected. The action should be gentle and ensure that the cable is fully softened during calibration. It can be done several times depending on the situation.
5 color insulation (such as BV, RVV, etc.) is best to use the expected welding gun, the temperature should be appropriate, and try to complete at once, so as not to change the expected material.
6. No matter what method is used for repair, use a rocker test to ensure that the insulation is intact.
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