# Description of main test indexes of Teflon pipe PTFE products

1. The coefficient of linear expansion indicates the degree of expansion or contraction of the material. It refers to the expansion rate of PTFE plastic products when the temperature rises 1 ℃ under a certain pressure, expressed as the linear expansion coefficient relative to the unit length. The coefficient is one of the important indexes to understand the change degree of the size of PTFE products with the increase of temperature. The linear expansion coefficient formula is α = L / (L * t), where l is the change of object length under the given temperature change t, and l is the initial length. The linear expansion coefficient of PTFE is about 10-12 × 10-5 / ((ambient temperature 25-250 ℃), i.e. (0.01-0.012)%. The coefficient of linear expansion of polytetrafluoroethylene is 10-20 times that of iron, which is larger than that of most plastics.

2. Thermal conductivity: also known as thermal conductivity, it reflects the thermal conductivity of the material. It is defined as two parallel planes with an area of 1 square meter and a distance of 1 meter, which are perpendicular to the heat conduction direction inside the object. If the temperature difference between two planes is 1K, the heat transfer from one plane to another in one second is defined as the heat transfer rate of the material in watt-mi-1.kai-1 (w.m-1. K-1). The research on the insulation performance of the target product is the reference index for product design.

3. The fracture tensile strain refers to the tensile strain corresponding to the tensile fracture stress when the yield failure of PTFE product occurs under the action of tensile load. It is the ratio of the difference between the sample length and the original length when the plastic rake appears. It is expressed as a percentage (%).

4. Tensile strength: in the tensile test, the critical value of transition from uniform plastic deformation to local concentrated plastic deformation represents the resistance of the material to uniform plastic deformation, which is also the plastic under static tension. This unit is MPa.

5. Elongation at break: refers to the increase of index distance (i.e. change rate of length) starting from the original unit length, and the ratio of the difference between the fracture length and the original length to the original length, expressed in percentage (%).

6. Breakdown voltage: the breakdown voltage of the sample is the highest voltage before breakdown. That is to say, at this voltage, the sample will not decompose. Breakdown is usually caused by partial discharge in the gas or liquid medium around the sample and electrode, which destroys the sample at the edge of the small electrode (or two equal diameter electrodes).

7. Electrical strength: it refers to the breakdown parameter of equipment insulation under a certain rated voltage, and indicates the insulation degree of the product under voltage. Under certain conditions, the ratio of breakdown voltage to sample thickness is the electrical strength of the product.

8. Withstand voltage refers to the voltage of the sample before breakdown when the power frequency AC voltage rises.

9. The ratio of the mass of a substance to its volume, that is, the mass of a substance per unit volume, is called the density of the substance. The polytetrafluoroethylene (PTFE) plastic products of kg / m3 or 1g / cm3 (1.0 × 103kg / m3) were tested by immersion, pycnometer and titration.

10. Nominal fracture strain refers to the tensile strain corresponding to the fracture stress when the tensile specimen does not yield or continues to crack, which is expressed in dimensionless ratio or percentage.

11. The change rate of longitudinal dimension refers to the percentage of the difference between the length of the treated sample and the original dimension when the pipe with a certain length is cut off and put into the oven for 3 hours (2602c) and taken out for 4 hours at room temperature in 232 hours.

12. Dielectric strength is a measure of the electrical strength of a material as an insulator. It is defined as the maximum voltage per unit thickness at the time of sample breakdown, that is, the ratio of breakdown voltage to sample thickness. The breakdown voltage shall be measured in accordance with GB / t1408.1-2006, and the dielectric strength shall be measured in kV / mm (k). V/mm).