Common Causes of Screw Breakage in Injection Molding Machines
The screw is one of the most important components in an injection molding machine. It is responsible for plasticizing, conveying, and compressing the raw material during the molding process. If the screw breaks, production may stop immediately, repair costs can increase, and damage may also affect the barrel and other machine parts.
Understanding the common causes of screw breakage can help manufacturers improve machine maintenance, reduce downtime, and prevent avoidable failures during injection molding production.
1. Poor Screw Quality
One common reason for screw breakage is poor manufacturing quality of the screw itself. If the screw material, heat treatment, or machining quality is not suitable, the component may not have enough strength, wear resistance, or fatigue resistance for long-term operation.
A low-quality screw is more likely to crack or fail under normal production stress, especially in high-load molding applications.
2. Excessive Length-to-Diameter Ratio
If the screw length-to-diameter ratio is too large, the screw may be exposed to greater bending stress and operating load during rotation. This can increase the risk of fatigue damage and structural failure over time.
For stable operation, the screw design should match the machine specification and material processing requirements.
3. Incorrect Installation and Fixing
Improper installation is another major cause of screw breakage. If the screw is not installed and secured correctly, abnormal force may occur during machine operation.
For this reason, screw installation should be carried out by qualified technicians or under proper technical guidance to ensure correct alignment and fastening.
4. Barrel Temperature Set Too Low
If the barrel temperature is set too low, the plastic melt may not soften sufficiently inside the barrel. As a result, the screw must overcome higher shear resistance during rotation.
Excessive shear force increases operating load and may contribute to screw damage or breakage during production.
5. Cold Start with High Material Viscosity
Cold-starting an injection molding machine can also create a high risk of screw failure. When the machine starts before the material inside the barrel is properly heated, the resin viscosity remains too high.
This makes screw rotation more difficult and may cause abnormal torque, especially during startup. Proper preheating is therefore important before machine operation begins.
6. Hard Impurities in Raw Materials
If the plastic raw material contains hard metal or non-metal impurities, these contaminants may damage the screw during plasticizing and conveying.
Foreign particles can cause severe wear, local stress concentration, or direct mechanical impact, which may eventually lead to screw breakage.
Conclusion
Screw breakage in injection molding machines is usually caused by poor screw quality, improper design, incorrect installation, low barrel temperature, cold startup, or impurities in raw materials. By improving equipment setup, maintenance practice, and raw material control, manufacturers can reduce the risk of screw failure and improve production reliability.