POM (Polyoxymethylene), also known as acetal or polyacetal, is a high - performance engineering plastic widely used in various industries due to its excellent mechanical properties, such as high stiffness, strength, and good dimensional stability. As a POM plastic part supplier, I have encountered numerous cases of molding defects in POM plastic parts during the production process. In this blog, I will discuss the common molding defects of POM plastic parts and the corresponding solutions.
Common Molding Defects of POM Plastic Parts
1. Shrinkage
Shrinkage is one of the most common defects in POM plastic parts. POM has a relatively high shrinkage rate, typically ranging from 1.5% - 3.5%. This shrinkage can lead to dimensional inaccuracies in the final parts, which may affect their functionality and assembly. Shrinkage occurs because the plastic material contracts as it cools and solidifies after injection molding.
2. Warping
Warping refers to the distortion of the plastic part from its intended shape. In POM parts, warping can be caused by uneven cooling, non - uniform shrinkage, or internal stresses during the molding process. For example, if the cooling rate is different in different areas of the part, some regions will shrink more than others, leading to warping.
3. Burn Marks
Burn marks appear as dark or charred areas on the surface of the POM plastic parts. They are usually caused by excessive heat during the molding process. This can happen when the melt temperature is too high, the injection speed is too fast, or there is poor ventilation in the mold cavity. The high - temperature decomposition of POM can result in these burn marks, which not only affect the appearance of the parts but also reduce their mechanical properties.
4. Short Shots
Short shots occur when the molten plastic does not completely fill the mold cavity. This can be due to insufficient injection pressure, low melt temperature, or a blocked gate or runner system. In POM molding, short shots can be especially problematic because POM has a relatively high viscosity, and it requires sufficient pressure and temperature to flow smoothly into all parts of the mold.
5. Silver Streaks
Silver streaks are thin, silver - colored lines that appear on the surface of the POM parts. They are often caused by the presence of moisture in the plastic material. POM is hygroscopic, which means it can absorb moisture from the environment. When the moist POM is heated during the molding process, the water turns into steam, creating these silver streaks on the part surface.
Solutions to Molding Defects
1. Shrinkage
- Mold Design Optimization: Design the mold with appropriate wall thickness and rib structures. A uniform wall thickness helps to ensure even cooling and shrinkage. Additionally, adding ribs can increase the stiffness of the part and reduce the overall shrinkage effect.
- Process Parameter Adjustment: Increase the injection pressure and holding pressure. Higher pressures can help to pack more plastic material into the mold cavity, compensating for the shrinkage during cooling. Also, adjust the cooling time to ensure that the part cools slowly and uniformly.
2. Warping
- Improve Cooling System: Optimize the cooling channels in the mold to ensure uniform cooling. This can be achieved by using a balanced cooling layout, such as a baffle or spiral cooling channel design. By maintaining a consistent cooling rate across the part, the risk of warping can be significantly reduced.
- Stress Relief Treatment: After molding, perform stress relief treatment on the parts. This can involve annealing the parts at a specific temperature for a certain period to reduce internal stresses and minimize warping.
3. Burn Marks
- Lower Melt Temperature: Reduce the barrel temperature during the injection molding process. Make sure to keep the melt temperature within the recommended range for POM. Additionally, slow down the injection speed to prevent excessive friction and heat generation.
- Improve Ventilation: Ensure that the mold has proper ventilation. Adding vents to the mold cavity can help to release the gas generated during the molding process, preventing the accumulation of heat and the formation of burn marks.
4. Short Shots
- Increase Injection Pressure and Speed: Raise the injection pressure to ensure that the molten plastic can flow through the runner system and fill the mold cavity completely. Adjust the injection speed to a suitable level to maintain a continuous flow of plastic.
- Check and Clean the Mold: Inspect the gate and runner system for any blockages. Clean the mold regularly to remove any debris or plastic residues that may impede the flow of the molten plastic.
5. Silver Streaks
- Drying the Plastic Material: Dry the POM pellets thoroughly before molding. Use a desiccant dryer to remove moisture from the plastic. The recommended drying conditions for POM are usually around 80 - 100°C for 2 - 4 hours.
- Maintain a Clean Molding Environment: Keep the molding area clean and dry to prevent the re - absorption of moisture by the plastic material.
Our Product Advantages and Related Links
As a POM plastic part supplier, we have rich experience in dealing with these molding defects. We use advanced molding technology and strict quality control systems to ensure the high - quality of our POM plastic parts. Our products are widely used in various fields, such as automotive, electronics, and machinery.
In addition to POM plastic parts, we also offer other high - quality plastic products, such as Injection Molded ABS Horizontal Motor Housing, High Pressure Micro ABS Plastic Accessories Inject, and Injection Molding Pmma Machining Parts. These products are also manufactured with high precision and excellent performance.
Contact Us for Purchase and Negotiation
If you are interested in our POM plastic parts or other plastic products, please feel free to contact us for purchase and negotiation. We are committed to providing you with the best products and services. We can customize products according to your specific requirements, ensuring that they meet your needs perfectly.
References
- "Injection Molding Handbook" by Rosato, D. V., & Rosato, D. V.
- "Plastics Materials and Processing" by James F. Carley.
- Technical documents from POM resin manufacturers.