低烟无卤控制电缆--电缆用塑料基本性能的含义

Meaning of basic properties of plastics for cables

Author：hlyb Add Time：2016-05-07 16:33:37

Meaning of basic properties of plastics for cables source: China cable online Author: time: September 23, 2011 editor: Liu Yongguang 1 Volume resistance coefficient plastic has leakage current passing through under the action of electric field. The resistance of leakage current passing through plastic is called volume resistance. The resistance of current passing through every 1cm3 of plastic is the volume resistance coefficient V, with the unit of ohmmeter and the unit symbol of m。

Meaning of basic properties of plastics for cables

1. Volume resistance coefficient

Plastic has leakage current passing through under the action of electric field. The resistance of leakage current passing through plastic is called volume resistance. The resistance of current passing through every 1cm3 of plastic is the volume resistance coefficient ρ v. The unit is Ohm meter and the unit symbol is Ω m。 The higher the volume resistance coefficient, the better the insulation performance.

2. Breakdown field strength

When the voltage applied to the plastic reaches a certain limit, the plastic loses its insulation performance and is broken down. The voltage applied at the moment of breakdown is called the breakdown voltage of the plastic. The ratio of the breakdown voltage to the thickness of the plastic is called the breakdown field strength e, and the unit symbol is kV / mm.

3. Dielectric constant

It is an indicator of the polarity of plastics. Dielectric constant ε The smaller, the smaller the polarization intensity of plastic under the action of electric field, and the smaller its dielectric loss.

4. Dielectric loss tangent

Under the action of alternating electric field, the level consumed in plastics is called dielectric loss. It is often expressed as the tangent of the dielectric loss angle TG δ To show. Dielectric loss tangent TG δ The smaller the dielectric loss, the better the electrical insulation performance of the plastic. When used under high frequency and high pressure, the Tg of plastics is required δ The value is not more than a few thousandths or ten thousandths; Tg of plastic at low voltage and general insulation δ The value is not more than a few percent.

5. Corona resistance

Under the condition of high voltage, corona is caused by the discharge on the insulating surface. When it attacks the insulator, the polymer is cracked due to ion impact, electron attack, ozone attack and local heat, which worsens its electrical insulation and physical and mechanical properties. The ability of plastics to resist corona and maintain its service performance is called corona resistance.

6. Tensile strength and elongation

Apply static tensile load to the plastic sample on the material tensile testing machine and stretch it at a certain speed until the sample breaks. At this time, the tensile force on the unit section of the sample is called the tensile strength of the plastic. The percentage of the increase in length when the specimen breaks is called the elongation of the plastic.

7. Density

At a certain temperature (usually 20oC), the mass per unit volume of plastic sample is called the density of plastic.

8. Heat deformation resistance

The high temperature at which the plastic can still maintain good physical and mechanical properties under heating conditions is the heat deformation resistance of the plastic. It is usually expressed by the temperature at which the plastic deforms to the specified value under a certain load when it is heated at a constant speed.

9. Melt index

The number of grams of molten resin extruded from a certain hole within 10 minutes under a certain temperature and pressure is called the melt index, which is expressed in MI and the unit is g / min.

10. Cold resistance

The ability of plastics to maintain certain physical and mechanical properties at low temperature is called the cold resistance of plastics. It is usually expressed by the following cold resistant temperature.

1) Low temperature embrittlement temperature: that is, the temperature at which 50% of the samples are damaged under specific impact load at low temperature.

2) Low temperature folding temperature: that is, the temperature at which the plastic sample will break but not break when it is bent for 180o.

3) Low temperature impact compression temperature: that is, the temperature at which the plastic sample is impacted and compressed by a hammer with a certain energy and speed at a low temperature to make its fracture rate reach 50%.

11. Flame resistance

Flame resistance refers to the ability of plastics to resist flame combustion. Generally, plastics will burn after contacting the flame. After removing the flame, the delayed combustion situation varies with different types of plastics, so the flame resistance is also different.

12. Heat aging resistance

In the process of processing and using plastics, the properties of plastics become worse due to heating. This phenomenon is called thermal aging. The ability of plastics to resist thermal aging is called thermal aging resistance. The heat aging resistance of plastics is measured by carrying out accelerated thermal aging test at high temperature and measuring the retention rate of plastic properties (mechanical or electrical properties) after aging.

13. Weather resistance

When plastic is used under atmospheric conditions, it is affected by severe natural conditions such as sunlight, rain, wind and air pollution. The deterioration of plastic performance is called atmospheric aging. The ability of plastics to resist atmospheric aging is called the weather resistance of plastics.

14. Oil resistance and solvent resistance

When plastics come into contact with mineral oil or various solvents, the ability to resist oil or solvents is called the oil resistance or solvent resistance of plastics. It can be measured by measuring the absorption rate, volume change rate or retention rate of tensile strength and elongation of the sample immersed in oil or solvent at a certain temperature for a certain time.

15. Water resistance and moisture resistance

The ability of plastics to resist the infiltration of water or humid gas under water immersion or humid conditions is called the water resistance or moisture resistance of plastics. After the plastic absorbs water or moisture, it will reduce the insulation resistance and breakdown field strength, increase the dielectric loss, and change the appearance, weight and mechanical properties of the plastic. Therefore, it is required that plastics should have good water resistance and moisture resistance. For plastics for wires and cables, the main consideration is to ensure that the electrical insulation performance of plastics meets the use requirements after immersion or moisture absorption. The water absorption of plastics can be expressed by the water absorption, water absorption or water absorption weight per unit area. The moisture permeability of plastics is expressed by moisture permeability coefficient and vapor permeability.

16. Environmental stress cracking resistance

Some crystalline plastics crack during storage and use due to the existence of internal stress during processing and contact with chemicals during use, which is called environmental stress cracking. The ability of plastics to resist environmental stress cracking is called environmental stress cracking resistance. It can be measured by the number and proportion of plastic bending samples with groove marks on the surface, placing them in surfactant and observing the cracking samples within the specified time.

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Meaning of basic properties of plastics for cables