Injection Machine Screw Tip Set Overview

An injection molding screw tip set is installed at the end of the screw in the injection molding machine and is responsible for ensuring the smooth operation of the injection process.

The screw tip set includes three major components:

- Screw Tip

- Seat Ring,

- Check Ring

The screw tip is responsible for directing the flow of molten plastic into the mold.

The seat ring is a component that secures the tip in place and provides a sealing point between the tip and the screw.

The check ring is the collar that leads the plastics flow and prevent it from moving back after injection, and is also called non-return valve

There are many different types of injection molding screw tip sets available on the market, each designed for specific applications and materials. Choosing the right screw tip set is important for ensuring high-quality production and reducing waste. A qualified injection molding technician can assist in selecting the best screw tip set for a particular machine and material.

What's Injection Screw Tip

In injection screw, the function of the screw head is to release the plasticized melt into the storage chamber during pre molding, and effectively seal the melt in front of the screw head during high-pressure injection to prevent backflow.

Screw heads are divided into two categories: those with and without a check ring. For those with a check ring, during pre molding, the melt in the homogenization section of the screw pushes the check ring apart and flows into the storage chamber through the gap formed with the screw head. During injection, the pressure of the melt in the screw head forms a thrust, which returns the check ring to the flow channel and blocks it, preventing backflow.

For some high viscosity materials such as PMMA, PC, AC, or materials with poor thermal stability such as PVC, in order to reduce shear action and material retention time, a check ring can be omitted. However, such injection will generate backflow and prolong the holding time.

Requirement for Screw Tip Set

① The screw head should be flexible and smooth

② The clearance between the check ring and the material barrel should be appropriate, which should prevent melt backflow and be flexible;

③ Having sufficient flow cross-section while ensuring that the end face of the check ring has a return force, allowing for quick closure during injection

④ Structurally, it should be easy to disassemble and clean

⑤ The thread direction of the screw head is opposite to that of the screw head to prevent loosening during pre molding.

Common Used Screw Tip Type

Screw tip set can be various structure depends on application field. Regular use are 

- Free-flow valve type, general purpose screw tip, can suitable basically all injection machines

- Clutch non-rotate valve type, precise metering for plastic with accurate shot weight

- Ball check valve type, excellent self-cleaning characteristics and good shutoff function

Screw Tip Set PVD Coating

Physical vapor deposition (PVD) coating is a thin film deposition technique used in the manufacturing of various products. It involves the deposition of a thin layer of a material onto a surface by the use of vacuum technology. The process is precise and controlled and involves the use of high energy particles that vaporize the coating material, which then condenses onto the surface to form a thin film. PVD coatings are used to improve the aesthetic appearance, durability, and resistance of products to wear and corrosion. PVD coatings that applies to screw tips are TiN, CrN & TiAlN normally, which can protect from corrosion and abrasion, commonly used for optical material or corrosive polymer processing.