Granulation method and device for crosslinked polyethylene cable insulating material having voltage grade of 500 kV or more

A granulation method for a crosslinked polyethylene cable insulating material having a voltage grade of at least 500 kV, comprising a monitoring procedure and a granulation procedure, wherein the monitoring procedure comprises:

• step 1:
• controlling, by a controller, a melt extrusion system to melt an insulating material to obtain a melt;
• step 2:
• directing, by the melt extrusion system, the melt into a melt gear pump through a first branch flow channel;
• step 3:
• measuring, by a melt monitoring system, pressures at an inlet and an outlet of the melt gear pump respectively, and calculating, by the melt monitoring system, a first pressure difference ΔP1,
• Δ
• ⁢
• p
• 1
• =
• p
• 2
• -
• p
• 1
• ,
• where P1 denotes a melt pressure at the inlet of the melt gear pump, and P2 denotes a melt pressure at the outlet of the melt gear pump;
• step 4:
• adjusting a rotational speed of the melt gear pump to enable ΔP1 to approximate to 0;
• step 5:
• measuring, by the melt monitoring system, pressures at an inlet and an outlet of a capillary mold respectively, and calculating, by the melt monitoring system, a second pressure difference Δp2,
• Δ
• ⁢
• p
• 2
• =
• p
• 4
• -
• p
• 3
• ,
• where P3 denotes a melt pressure at the inlet of the capillary mold, and P4 denotes a melt pressure at the outlet of the capillary mold;
• step 6:
• obtaining a volume flow rate Q of the melt flowing into the capillary mold based on a number of steps of rotation of the melt gear pump;
• step 7:
• obtaining a shear rate {dot over (γ)}, a shear stress t, and a shear viscosity η of the melt based on the volume flow rate Q and ΔP2;
• and
• step 8:
• adjusting, by the controller, process parameters of the melt extrusion system, adjusting, by the controller, the shear viscosity η to obtain an adjusted shear viscosity η′, and causing η′ to be within a processing-suitable viscosity range of the melt;
• wherein the granulation procedure comprises:
• step 9:
• feeding, by the melt extrusion system, the melt to an orifice plate through a main flow channel;
• step 10:
• adjusting a rotational speed n of a rotary cutter in a granulation system according to η′,
• step 11:
• carrying out trial extrusion to determine a safe gap threshold δ and a pressure coefficient ε;
• step 12:
• obtaining a pressure Ph exerted by a hydraulic press onto the rotary cutter based on δ, ε, and the pressure P4 at the outlet of the capillary mold;
• and
• step 13:
• exerting, by the hydraulic press, the pressure Ph onto the rotary cutter to enable a thin melt buffer layer existing between the rotary cutter and the orifice plate, and granulating the melt.