The cooling process after cross-linked polyethylene is extruded from the die head may present factors that could lead to surface quality problems in the insulated wire core:
(1) Air bubbles adhere to the cable surface. When the cable enters the water, if air bubbles are attached to its surface, small pits will appear after cooling. This is because the air bubbles trap air on the insulation surface, and the cooling rate of the part covered by the air bubbles is slower than that of the part in contact with the water. The reason for the formation of air bubbles on the cable surface is generally that the circulating water used for cooling enters the water tank at a high speed and with a rapid flow. The high-speed water flow carries air into the water, and some of the air adheres to the cable surface, forming air bubbles.
(2) Before entering the cooling water, water droplets splash onto the surface of the cable. The part in contact with the water cools and shrinks first, while the part in contact with the air is still in a high temperature state. Due to the difference in cooling speed, the surface of the insulated core becomes uneven.
