PS Foam Extrusion mold
For PS Foam Extrusion Mold profiles with a density of 0.3–0.5 g/cm³, the mold opening needs to be lengthened with a straight section to stabilize back pressure, ensuring a smooth flow channel without dead corners and allowing for fine-tuning gaps during foaming. A multi-stage gradient shaping process is employed, with low-temperature skinning followed by foaming, combined with an adjustable structure to ensure stable density within the specified range, preventing foam collapse and solidification.
Key Design Considerations for PS Foam Extrusion Mold (Density 0.3-0.5 g/cm³)
I. Die Head (Extruder Head) Design
1. Prioritize Back Pressure, Lengthen Straight Section
Density of 0.3-0.5 g/cm³ is highly sensitive to back pressure. The straight section of the die head must be sufficiently long. It is recommended to take the straight section length as 30-50 times the average die head clearance to establish stable melt pressure. This allows the foaming agent to disperse evenly before foaming, preventing premature foaming within the PS Foam Extrusion Mold. A short straight section results in insufficient pressure, easily leading to bursting bubbles and localized collapse upon extrusion.
2. Smooth and Gradual Flow Channel Transition, Avoiding Dead Corners
The flow channel should have a streamlined, gradual transition, without steps or sharp angles. PS melt strength is generally low; if there are stagnant dead corners in the flow channel, the material will prematurely foam and carbonize, resulting in pitting, streaks, and intermittent bubble collapse. 3. PS Foam Extrusion Mold: The flow distribution of the runner should be balanced, with differentiated flow control based on thickness. Appropriate flow-blocking structures should be reserved in thin-walled areas to balance the discharge difference caused by foam expansion.
4. Allowance for Foam Expansion in the Mold Opening Gap: PS foams and expands during extrusion (extrusion expansion + expansion ratio expansion).
– Target density close to 0.3 (lighter): High expansion ratio, so the mold opening gap of the PS Foam Extrusion Mold should be smaller to allow for greater expansion space.
– Target density close to 0.5 (heavier): Low expansion ratio, so the mold opening gap can be appropriately enlarged.
A 0.2-0.5mm fine-tuning allowance should be reserved in the design, and the mold opening can be fine-tuned later by cold welding.
5. Temperature Zoning Structure: The mold head needs independent zone heating, and the mold opening area can be individually temperature-controlled. When producing a low density of 0.3, the mold opening temperature should be able to be lowered to suppress excessive foaming during extrusion; when producing 0.5, the temperature can be appropriately increased to enhance plasticization. II. The Crucial Step in Molding (0.3-0.5% Success or Failure)
The biggest difference between PS and PVC foaming: PS has lower melt strength, forming a skin first, then internal foaming; molding cannot be rushed.
1. Use a multi-stage gradient molding process (3-4 stages recommended)
– Stage 1 (Initial Molding Stage): Low vacuum, strong cooling. Quickly freeze the outer surface of the profile to form a dense skin, locking the bubbles and preventing them from bursting outwards, thus preventing bubble collapse and pinholes. The vacuum in the PS Foam Extrusion Mold should not be too high; too high a vacuum will directly suck up and break the skin.
– Stages 2-3: Gradually increase the vacuum, allowing for slow internal foaming and molding.
– Final Stage: Fine-tune dimensions, release internal stress, and reduce post-shrinkage distortion.
2. Gradual Cooling Water Channel Layout: The first stage has denser water channels, close to the cavity; gradually thinner channels follow. Avoid starting with high temperatures or rapid cooling, otherwise the skin will crack and internal foaming will be uneven.
3. Cavity shrinkage allowance is reserved according to density.
For a density of 0.3, the foaming expansion is large, so a larger magnification factor is used for the molding cavity; for 0.5, the foaming ratio is small, so a smaller magnification factor is used. The inner wall of the molding cavity is mirror-polished to reduce frictional resistance and prevent surface damage.
4. Venting must be unobstructed. The vacuum vents should be arranged reasonably, not concentrated in one place; appropriately increase micro-vents in areas with thick walls to promptly remove overflowing gas and prevent bubbling.
If you encounter any problems during production, please contact AONA EXTRUSION TOOLING. Our professional PS Foam Extrusion Mold engineers have 27 years of experience and will provide you with technical guidance at any time.
Recommendation
