Service Environment of Heat Shrinkable Tube and Heat Shrinkable Material

The following three different types of environments must be fully considered when developing heat shrinkable materials for specific terminations and connections: 1. Not affected by climate; 2. Affected by climate; 3. Underground connections.

1. It's not affected by the climate: used for indoor heat shrinkable power cable termination and the connection, because of the influence of the climate can be neglected, so the application is simple, only when the design consideration of insulation, flame retardant problem without considering the influence of other factors, because the radiation crosslinking of polymer alloys superior comprehensive performance is enough to safe use.

2. Outdoor application: Heat shrinkable material is used for outdoor cable terminating, which involves very complex environmental problems. The design formula should be considered comprehensively. After prolonged outdoor exposure, does it have one or more of the following adverse effects:

Polymer due to oxidation and pollutants on the surface of the aggregation of molecular change and degeneration, so that the physical properties and electrical properties of a significant decline;

Whether the addition of various additives will exude or phase;

Whether the addition of various fillers will affect the performance of the substrate;

In fact, the study of environmental influences will mainly include the following relevant factors and their effects on polymers.

Climate: sunshine, rain and weather conditions.

Erosion: natural sand, dust, salt and other industrial ash, waste gas.

Mechanical effects: Caused by the thermal expansion and contraction of different materials, as well as external factors such as wind, snow, ice, etc. Obviously, these conditions vary greatly from place to place, so the formulation design is based on the most severe climatic conditions in a particular region. The following factors are most likely to cause significant changes in polymer properties:

Ultraviolet rays in sunlight, chlorine in the atmosphere, moisture, rain, dew, ice, etc. Ultraviolet light in the sun and oxygen in the atmosphere can make the polymer gradually decompose, water can dissolve the pollutants in the surface water film, thus reducing the electrical properties of the polymer, water can also dissolve some additives, thus causing embrittlement or the reduction of antioxidant capacity;

Gas pollution: common gas pollution for ozone, sulfide, nitrogen oxides, they are mainly factories, chimneys and cars directly discharged, many pollutants in the atmosphere and ultraviolet rays exist at the same time, can make many polymers strong catalytic decomposition;

Solid pollution: salt containing polymer surface leakage, resulting in carbon marks, electrical erosion, some strong acid and alkaline and organic solvent pollutants will cause chemical erosion.

Thermo-mechanical effect: cable terminal shunt is often in the environment of high temperature and low temperature mutation, in this environment, the moving stress and strain will make the material surface for ultraviolet decomposition of small seam open and close, so that the material here than elsewhere faster damage; The cable is always at a high temperature in normal operation, so the material needs to have a high temperature resistance grade to adapt.

Through unremitting efforts and scientific development, heat shrinkable materials also have the following properties:

Carbon trace resistance: In the pollution of the atmosphere environment, most of the organic polymer are not applicable to high voltage, under the condition of high pressure, water or mist, hail, salted, particles, ionic contamination etc. Will cause a small amount of leakage, insulation surface leakage current may last a few seconds, the temperature rise, causing moisture evaporation, dry zone formation, Sparks and surface discharges also increase in temperature as they pass through the dry zone, which causes the polymer to decompose and form a conductive carbon channel; Once formed, carbonaceous channels often spread quickly like vines, eventually destroying the insulation. In order to develop carbon trace resistance materials, the selected materials must meet the requirements of low corrosion rate, toughness, gas resistance, at the same time, no carbon trace during use and continuous use temperature of -55℃~+105℃.

Hydrophobic and hydrophobic migration: rubber and plastic alloy substrate molecule chain outside with a layer of nonpolar organic groups, for water solubility, and the water is not mutually close, difficult to absorb moisture, when it contacts with water droplets formed different separation of small water droplets, condensed wet surface, not only at the same time also has the hydrophobic mobility, the large area of dust or impurity heap on heat shrinkable materials On the surface, the hydrophobicity of the material migrates to the dirty surface after about 10 hours to make the dirty surface also hydrophobic.

3. Underground applications

Underground wiring not like outdoor environment requirements, but underground application materials required have excellent mechanical strength, wear resistance and good waterproof performance, therefore, the product in the pipe inner surface coated with a suitable sealant to meet the application requirements, underground sealant for a thermal shrinkage of adhesive, another for the sticky adhesive, heating installation and electricity flow or melt when they make accessories The cable is bonded as a whole and has significant mechanical strength after cooling, which can resist quite high external pressure. In addition, an iron shell protection cylinder is designed at the underground connection to increase its mechanical strength, wear resistance and water resistance.