Braid trusion of hollow thermoplastic composites using expanding mandrel approach
🧬 The "Braid-trusion" Revolution: Mastering Hollow Thermoplastics
But there is a game-changer on the horizon: Braid-trusion combined with the Expanding Mandrel Approach. It’s where the high-speed structural integrity of braiding meets the continuous efficiency of pultrusion. Let’s break down why this is the future for researchers and technicians alike. 🚀
🧵 What is Braid-trusion?
Standard pultrusion mostly uses unidirectional (UD) fibers, which are great for pulling strength but weak against twisting (torsion) or bursting. Braid-trusion integrates a braiding machine directly into the pultrusion line.
By intertwining fibers at specific angles (e.g., $\pm45°$), we create a "sock" that handles multi-axial loads. When you combine this with a thermoplastic matrix (like PP, PA6, or PEEK), you get a part that isn't just strong—it’s recyclable and impact-resistant. ♻️
🎈 The Secret Sauce: The Expanding Mandrel
The biggest headache with hollow parts is the internal interface. How do you press the fibers against the outer die from the inside without the mandrel getting stuck?
The Expanding Mandrel Approach solves this beautifully:
Thermal Expansion: The mandrel is made of a material with a high Coefficient of Thermal Expansion (CTE). As it hits the heating zone, it grows, pushing the thermoplastic prepreg against the die wall. 📈
Consolidation Pressure: This "internal ballooning" creates the high pressure needed to eliminate voids and ensure the resin fully encapsulates every fiber.
Easy Release: Once the profile enters the cooling zone, the mandrel shrinks faster than the composite, creating a tiny gap that allows the finished tube to slide off effortlessly. 🧊
🧪 Research Focus: Tuning the Interface
For the researchers in the lab, the magic is in the Pressure-Temperature-Time (P-T-t) relationship.
Mandrel Material: Choosing between silicone, specialized polymers, or metallic alloys depends on your processing temperature.
Friction Coefficients: Since the mandrel is sliding while expanding, the surface coating (like PTFE) is critical to prevent fiber "bunching" or surface tearing. 🛠️
Microstructure: Researchers are using X-ray CT to prove that the expanding mandrel provides more uniform wall thickness than traditional "floating" mandrels.
🛠️ Technician’s Guide: Running the Line
If you’re the one turning the dials, braid-trusion requires a "symphony" of synchronization:
| Variable | Why it matters | Technical Tip |
| Braiding Speed | Controls the fiber angle. | Ensure the puller speed and braider RPM are electronically geared. ⚙️ |
| Take-up Tension | Prevents sagging. | High tension is key to keeping the braid tight against the mandrel before it hits the die. |
| Zone Heating | Triggers the expansion. | The "Soak Time" in the heating die must be long enough for the mandrel core to reach expansion temp. 🔥 |
Pro-Tip: Watch your Pulling Force. If it starts to oscillate, it usually means your mandrel is expanding too early or your thermoplastic melt is "freezing" before it clears the consolidation zone. 🚩
📈 Why This Matters for Industry
The move toward Braid-truded Hollow Thermoplastics is a huge win for aerospace and automotive sectors. We are seeing:
Weight Savings: Replacing heavy aluminum tubes with optimized carbon/PEEK braids.
Production Speed: Moving from batch-wise RTM (Resin Transfer Molding) to continuous 24/7 pultrusion. 🏎️💨
Sustainability: Unlike thermosets, these hollow tubes can be melted down and reformed at the end of their life cycle.
website: globalcompositeawards.com
Nomination: https://globalcompositeawards.com/award-nomination/?ecategory=Awards&rcategory=Awardee
contact: contact@globalcompositeawards.com
Comments
Post a Comment