Rongjiang Bai
5 min read
07 Apr

1. What is Injection Molding Splay? 

Splay, or silver streaks in injection molding, is a defect that affects both the visual appeal and potentially the functionality of the final piece. Tackling this issue involves an intricate understanding of the numerous factors that contribute to its occurrence. We're examining the various reasons that can cause splay through the lens of mold configuration, process settings, and material characteristics. This comprehensive review aims to equip practitioners with the necessary insights to identify and rectify the root causes of splay in the injection molding process.

2. What Causes Injection Molding Splay?

There are several causes of injection molding splay, each related to different stages and parameters of the injection molding process. The primary causes include:

  • Moisture in the Material
  • Material Contamination
  • High Melt Temperature
  • Injection Speed and Pressure
  • Poor Venting

Let's explore each cause in detail: 

3. What are the Solutions of Injection Molding Splay?

Moisture in the Material

Cause: Plastics, particularly hygroscopic materials like nylon, ABS, and polycarbonate, can absorb moisture from the air. During the injection molding process, the heat from the barrel can turn this moisture into steam, which then gets injected into the mold along with the molten plastic. The steam causes splay marks on the surface of the part as it escapes.Solution:

  • Proper Drying: Use appropriate drying equipment, such as desiccant dryers, to ensure that plastic pellets are properly dried before molding. Each type of plastic has a specific drying time and temperature, which should be strictly followed.
  • Environmental Control: Store plastic materials in a controlled environment to minimize moisture absorption before use.

Material Contamination

Cause: Contamination can occur from various sources, such as leftover materials from previous runs, dust, dirt, or foreign particles. These contaminants can interfere with the plastic's flow and create splay.Solution:

  • Cleanliness: Maintain a clean working environment and regularly clean the molding machine. Implement strict material handling procedures to prevent contamination.
  • Filtering: Use filters in the material feed system to catch any contaminants before they enter the molding machine.
MaterialMoisture Absorption RateOptimal Drying TimeOptimal Drying Temperature
NylonHigh4-6 hours80℃-90℃
ABSMedium2-4 hours70℃-80℃
PolycarbonateHigh3-5 hours100℃-120℃

High Melt Temperature

Cause: If the melt temperature is too high, the plastic material can degrade thermally, breaking down into smaller molecules and releasing gases. These gases can cause splay as they escape during the molding process.Solution:

  • Temperature Control: Regularly monitor and adjust the barrel temperature settings to the optimal range for the specific type of plastic being used. Avoid excessive temperatures that can lead to degradation.
MaterialRecommended Melt Temperature Range

Learn More About the Technical Parameters of Plastic Materials 

Injection Speed and Pressure

Cause: Incorrect injection speed and pressure settings can cause air entrapment and excessive shear stress. When the injection speed is too high, or the pressure is too low, air can be trapped in the mold cavity, causing splay.Solution:

  • Parameter Optimization: Fine-tune the injection speed and pressure settings to ensure a smooth and consistent flow of material into the mold. Use slower speeds and higher pressures if necessary to avoid trapping air.
  • Process Monitoring: Continuously monitor the injection process and make adjustments as needed to maintain optimal conditions.
ParameterOptimal RangeImpact of Deviation
Injection SpeedMedium (specific to material)High speed can cause air entrapment
Injection PressureHigh (specific to material)Low pressure can cause entrapment

Poor Venting

Cause: Insufficient venting in the mold can trap air and gases within the mold cavity. As the molten plastic fills the cavity, these trapped gases can escape through the plastic, causing splay.Solution:

  • Mold Design: Ensure that the mold has adequate venting channels to allow trapped air and gases to escape. This may involve adding or enlarging existing vents.
  • Venting Maintenance: Regularly check and clean venting channels to prevent blockages that can impede the escape of air and gases.

Many factors can contribute to injection molding splay, but a knowledgeable partner can help you avoid these issues. Ideal Pro, is an excellent choice for your upcoming plastic injection molding project. With our expertise and resources, we can effectively address Splay problems and ensure you receive high-quality injection molded parts. Contact us and get an instant quote!