Adjustment Methods for "Flow Marks" in Flame-Retardant ABS

In injection molding production, flame-retardant ABS materials are prone to "flow marks" (commonly known as silver streaks, water ripples, or foggy spots). These defects appear as silvery white stripes, water wave patterns, or foggy marks on the product surface—they not only damage the integrity of the appearance but may also weaken the product’s mechanical properties. The core cause of this issue is that flame retardants tend to decompose during processing, releasing gases that mix into the molten material and cannot be completely discharged, eventually forming marks on the surface of the molded part. To address this pain point, targeted measures can be taken from four key dimensions: material treatment, process control, mold optimization, and equipment maintenance.

1. Material Pretreatment: Lay the Foundation for Defect Prevention

Material pretreatment is the basic step to control flow marks. Flame-retardant ABS raw materials have strong hygroscopicity; residual moisture will combine with gases from flame retardant decomposition to cause defects. Specific measures include:

• Use a dehumidifying dryer to dry the raw materials continuously at 80–90℃ for 2–4 hours, strictly controlling the moisture content of the raw materials to ≤0.02%.
• For raw materials stored in humid environments or with significant hygroscopicity, appropriately extend the drying time.
• Add 0.3%–0.5% silicone-based defoamers or flow promoters to the raw materials. This can effectively reduce the surface tension of the melt, promote gas escape, and lower the probability of flow marks.

2. Process Parameter Control: Avoid Excessive Decomposition of Flame Retardants

Precise control of process parameters is key to preventing excessive flame retardant decomposition and gas generation:

• Melt temperature: Strictly limit it to the range of 190–230℃. Too low a temperature causes uneven plasticization and increases the risk of gas entrapment; too high a temperature accelerates flame retardant decomposition.
• Injection speed: Maintain a medium speed. Excessively fast speed leads to severe shear of the molten material, causing local overheating; excessively slow speed makes the molten material cool in advance, hindering gas discharge.
• Mold temperature: Increase it to 60–80℃. This slows down the cooling rate of the melt, provides sufficient time for internal gas to escape, and improves melt fluidity.

3. Mold Structure Optimization: Improve Gas Discharge Efficiency

Optimizing the mold structure focuses on enhancing gas discharge to avoid gas entrapment in the cavity:

• Add vent grooves with a depth of 0.02–0.05mm at the parting surface, around the gate, and in complex structural areas. Alternatively, appropriately widen the fitting gap between the ejector pins and the mold plate to 0.03–0.05mm to form auxiliary vent channels.
• Optimize gate and runner design: Avoid sharp bends and narrow sections. Expand the gate size by 10%–20% and use arc transitions instead of right-angle structures. This reduces shear stress during melt flow and minimizes triggers for flame retardant decomposition.

4. Equipment Maintenance: Eliminate Secondary Pollution from Residues

Residues in the equipment can mix with new materials and cause flow marks; regular maintenance is essential:

• Dead corners in the screw and barrel easily accumulate residual materials, which gradually decompose and carbonize under long-term high temperatures.
• Clean the equipment thoroughly with PE cleaning materials or special cleaning compounds every 8–12 hours of production or when changing raw materials. Focus on cleaning key parts such as screw flights, check rings, and nozzles to ensure a clean molding environment.

Through the coordinated implementation of the above multi-dimensional measures, gas generation and entrapment during the injection molding of flame-retardant ABS can be fundamentally reduced. This effectively resolves flow mark defects and ensures the appearance quality and performance stability of the product.