Injection molding machine screw nozzle

I. Main Components
Nozzle:
Open nozzles are common, offering the advantage of low pressure loss, but are prone to "drooling" when processing resins with high temperatures or low viscosities.
For resins prone to drooling, valve nozzles, such as spring-loaded and slider-loaded nozzles, can be used to prevent drooling by closing the valve when the mold is opened.
Screw:
The screw is the core component of the injection unit, responsible for pushing the plastic material forward and heating it to a molten state.
The screw is typically divided into a feed section, a compression section (conveying section), and a metering section. The feed section primarily transports the raw resin and preheats it. The heat for melting the resin in the compression section is primarily shear heat from the screw. The relative motion between the screw and barrel pushes the resin toward the metering section. The metering section delivers a quantitative amount of the plasticized plastic from the compression section to the front end of the screw.
Screw performance parameters include compression ratio and aspect ratio. A higher compression ratio improves mixing uniformity but reduces discharge volume. A higher aspect ratio improves plasticization but increases manufacturing and assembly complexity. Check Ring (Valve):
The outer diameter of the check ring is the same as the inner diameter of the barrel, but its inner diameter is larger than the corresponding diameter of the screw, allowing it to move freely forward and backward within a certain range.
During the injection phase, the screw shoulder limits the check ring's backward movement. When the screw moves forward, the check ring merges with the screw shoulder, blocking the resin's backward flow path.
During the plasticizing phase, the molten resin pushes the check ring away from the screw shoulder, moving forward until it contacts the screw head, where it stops.

Screw Head:
The screw head is designed with a tapered shape to reduce melt injection resistance and prevent molten resin from stagnating at the front of the screw.

Barrel:
The barrel is a critical component of the plasticizing process, housing the screw and surrounding an electric heating coil.
The barrel heats the resin and maintains its viscosity, while also withstanding combined stresses and thermal stresses.
The clearance between the barrel and the screw must be properly controlled to avoid problems such as reduced plasticizing capacity and increased friction. II. Working Principle
Feeding: Plastic raw material (usually granular plastic) is placed into the injection molding machine's hopper. The hopper is located at the top of the injection unit, and the raw material is fed into the heating zone by gravity or a screw conveyor system.
Melting: In the injection molding machine's heating zone, the plastic granules are heated by the temperature control system and gradually melt into a fluid molten state. Heating coils use electrical or oil heating to raise the temperature of the plastic granules to a suitable range (typically between 170°C and 330°C, depending on the type of plastic used).
Injection: Once the plastic is completely melted, the injection screw rapidly pushes the molten plastic toward the injection nozzle and into the mold cavity through the nozzle. This process must be completed extremely quickly to ensure that the molten plastic fills the entire mold and quickly forms the product. Injection pressure is typically high, typically reaching several hundred megapascals (MPa).
III. Importance
The performance of the injection unit directly impacts the production efficiency, product quality, and energy consumption of the injection molding machine. A high-quality injection unit ensures that the plastic raw material is evenly heated and quickly injected into the mold, resulting in a high-quality product. At the same time, reasonable injection pressure and speed settings can also help reduce energy consumption and extend equipment life.