High strength slow stress cracking resistant polyethylene pipe and its preparation method

Abstract

The invention discloses a high-strength and slow-speed-stress-cracking-resistance polyethylene pipe; and 95-99.9 weight parts of conventional polyethylene and 0.1-5 weight parts ultrahigh molecular polyethylene with molecular weight not smaller than 1000000 g / mol are fully mixed, and are put in a polymer pipe rotation extruding device for melting, rotating, extruding, cooling and sizing with the rotating speed of 1-24 rpm / min, the temperature of a melting section of 180-260 DEG C and the temperature of a mouth mold section of 170-220 DEG C by using any one mode of single rotation of a core rod, single rotation of a mouth mold, synchronous rotation of the core rod and the mouth mold in the same direction or synchronous rotation of the core rod and the mouth mold in opposite directions. The annular strength of the obtained pipe under the testing conditions of 80 DEG C and static hydraulic pressure is 5.69-7.28 MPa; and under the standard pressure of 120%, the damage time exceeds 1000 hours. As the relaxation time of polyethylene molecules in a molten state can be prolonged, the formation of serial crystals and the arrange directions thereof in polymer pipes are effectively controlled to form and construct orientation structures deviated from the axial direction, and the annular strength and the slow-speed stress cracking resistance of the polyethylene pipe are greatly improved.

Description

technical field [0001] The invention belongs to the technical field of polyethylene pipes and their preparation, and in particular relates to a high-strength, slow-speed stress-cracking-resistant polyethylene pipe and a preparation method thereof. Background technique [0002] Polymer pipes, especially polyethylene pipes, have excellent comprehensive properties, such as light weight, energy saving, corrosion resistance, easy installation, and low cost, and are widely used in fields such as gas transmission and water transportation. At present, my country's polymer pipe processing has formed an important national pillar industry. The average annual growth rate of consumption in the past ten years is as high as 25%. [0003] However, there are some defects in the traditional preparation process of plastic pipes: for example, weld lines are generated during the production process; the outer wall of the pipe is cooled by spraying, and the cooling rate of the inner and outer wall...

AI Technical Summary

Problems solved by technology

[0003] However, there are some defects in the traditional preparation process of plastic pipes: for example, weld lines are generated during the production process; the outer wall of the pipe is cooled by spraying, and the cooling rate of the inner and outer walls of the pipe is uneven, resulting in a large internal stress inside the PE pipe, which makes the inner wall material resistant. Slow crack growth is poor; the hoop strength of the pipe is insufficient, the axial strength of the pipe is much higher than the hoop strength of the pipe, and the hoop stress during use is more than twice the axial stress

[0009] However, it was found during the implementation process that due to the low thermal conductivity of polyethylene, when preparing polyethylene pipes, especially when preparing polyethylene pipes with larger diameters and thicker pipe walls, due to the slow cooling rate during the cooling and shaping process, the The relaxation time of polyethylene molecules is relatively fast, so that the off-axis reinforcing phase structure content formed during the rotary extrusion process does not exceed 50%, and the hoop strength of polyethylene pipes under 80°C hydrostatic conditions increases only by 20 %, and under 120% standard pressure, the rupture time does not exceed 500 hours

Images