Hot-cut plastic pelletizing machine for cable sheathing

Purpose

Granulators are widely used in industries such as chemicals, petrochemicals, pharmaceuticals, food processing, building materials, mining and metallurgy, environmental protection, textile dyeing, ceramics, rubber, and plastics. They are forming machines capable of producing materials into specific shapes. Based on their structure and operating principles, they can be further classified into different types. Energy efficiency in pelletizing machines can be divided into two components: the drive system and the heating system. The power required by a pelletizer is directly proportional to the extrusion rate and increases exponentially with screen size. In a cold‑cut pelletizing system, pellets are cut from the solidified polymer at the end of the processing stage; in contrast, in a hot‑cut pelletizing system, pellets are cut as the molten polymer exits the die, with subsequent cooling of the pellets downstream.

Basic Information

The main unit of a plastic pelletizing machine is an extruder, which consists of an extrusion system, a drive system, and a heating–cooling system. Vigorously develop renewable resources. ,Turning waste into treasure.

1. Extrusion system The extrusion system comprises a hopper and a die head. Within this system, the plastic is plasticized into a uniform melt and, under the pressure generated during the process, is continuously forced through the die head by the screw.

⑴ Screw: It is the most critical component of an extruder, directly determining the machine’s application scope and production capacity, and is manufactured from high-strength, corrosion-resistant alloy steel.

(2) Barrel: It is a metal cylinder, typically made of heat‑resistant, high‑pressure‑strength, wear‑resistant, and corrosion‑resistant alloy steel, or of a composite steel pipe with an alloy‑steel liner. The barrel works in conjunction with the screw to crush, soften, melt, plasticize, degas, and compact the plastic, while continuously and uniformly feeding the molten material into the molding system. Generally, the length of the barrel is approximately times its diameter. 15 to 30 times, with the principle of ensuring the plastic is adequately heated and thoroughly plasticized.

(3) Hopper: The bottom of the hopper is equipped with a shut-off device for adjusting and stopping the material flow, while the side of the hopper features a sight glass and a calibrated metering device.

(4) The Head and Die: The die head consists of an alloy‑steel inner sleeve and a carbon‑steel outer jacket, with a forming die mounted inside. Its function is to convert the rotational motion of the plastic melt into a parallel linear motion, guide it smoothly and uniformly into the die sleeve, and impart the necessary molding pressure. Within the barrel, the plastic is plasticized and compacted; it then passes through a porous filter plate along a defined flow path, enters the die neck, and flows into the die‑forming cavity. The core and sleeve are properly matched to create an annular gap whose cross‑section continuously decreases, causing the molten plastic to form a continuous, dense tubular sheath around the core wire. To ensure an optimal flow path within the die head and eliminate dead zones where plastic might accumulate, a分流套筒 (flow‑diverting sleeve) is often installed. Additionally, to mitigate pressure fluctuations during extrusion, a pressure‑equalizing ring may be provided. The die head is also equipped with mechanisms for die alignment and adjustment, facilitating precise centering of the core and sleeve. 2. Drive System The drive system is responsible for driving the screw and providing the torque and rotational speed required during the extrusion process; it typically consists of an electric motor, a reducer, and bearings.

3. Heating and cooling unit Heating and cooling are essential conditions for the plastic extrusion process to proceed.

⑴ In 2013, extruders typically employed electric heating, which is categorized into resistance heating and induction heating. Heating elements were installed in various sections of the machine, including the barrel, the die neck, and the die head. The heating system raises the temperature of the plastic within the external heating cylinder, bringing it to the level required for the specific processing operation.

(2) The cooling system is designed to maintain the plastic within the temperature range required by the processing conditions. Specifically, it removes excess heat generated by shear friction during screw rotation, thereby preventing overheating that could lead to plastic degradation, scorching, or difficulties in shaping. Barrel cooling is categorized into water cooling and air cooling; typically, small and medium-sized extruders employ Air cooling is generally more suitable, while larger units typically employ water cooling or a combination of both. For screw chillers, central water cooling is the preferred method, aimed at increasing the solid‑material conveyance rate, stabilizing the extrudate output, and enhancing product quality. However, cooling at the hopper serves two purposes: first, to improve the transport of solid material and prevent plastic pellets from becoming sticky and clogging the feed port due to temperature rise; second, to ensure the proper operation of the drive system.