Fracture Mechanisms in PTFE Paste Extrusion at High Reduction Ratios

Reduction ratio refers to the ratio of the cross-sectional area of the extrusion billet to the cross-sectional area of the finished product, which is a key process index characterizing the deformation degree of PTFE paste extrusion. High reduction ratio extrusion is widely used in the production of ultra-thin-walled PTFE tubing, fine-bore capillary tubes and micro-precision profiles, which can realize ultra-fine molding and high molecular orientation of products. However, excessive reduction ratio will cause extreme shear deformation and stress concentration of PTFE paste in the die, inducing various fracture defects of extruded products. Studying the fracture mechanisms under high reduction ratios is of great significance for optimizing high-precision extrusion processes and avoiding product failure PTFE TUBE.

The primary fracture mechanism under high reduction ratios is shear-induced structural fracture. When the reduction ratio exceeds the optimal process range, the PTFE paste undergoes extreme shear compression in the narrow die flow channel, and the instantaneous shear force far exceeds the bearing limit of the paste structural bonding force. The uniform particle stacking structure inside the paste is destroyed, local particle separation and layer separation occur, forming micro-cracks and layered fracture defects inside the extruded blank. This shear fracture is the main cause of longitudinal cracking and layered peeling of high-reduction-ratio extruded products, which seriously reduces the structural integrity and mechanical strength of products.

Flow instability fracture is another typical failure mechanism in high reduction ratio extrusion. Under large deformation conditions, the flow velocity gradient of PTFE paste in the die increases sharply, and the laminar flow state is transformed into turbulent flow state, resulting in disordered material flow and local flow interruption. The uneven flow velocity leads to inconsistent material molding speed, forming periodic transverse fracture and wave-shaped surface defects on the product surface. In severe cases, continuous material fracture and discontinuous extrusion will occur, resulting in batch product scrapping. This flow-induced fracture is closely related to the excessive shear rate caused by high reduction ratio and rapid ram speed PTFE SHEET.

Residual stress-induced delayed fracture often occurs in high reduction ratio extruded products. After high-deformation extrusion, the product accumulates a large amount of internal residual stress due to severe molecular orientation and structural compression. In the subsequent drying, sintering and placement process, the residual stress is gradually released, resulting in structural shrinkage, deformation and micro-fracture of the product. This delayed fracture is hidden and difficult to find in the extrusion stage, but it will cause product failure in the subsequent processing and service process, affecting the batch yield and product reliability.

In order to suppress fracture defects under high reduction ratios, targeted process optimization strategies are adopted in industrial production. First, appropriately increase the lubricant content to improve paste fluidity, reduce shear friction and structural damage. Second, adopt low-speed stable extrusion to reduce instantaneous shear rate and maintain laminar flow state. Third, optimize the die flow channel structure to realize gradual deformation and avoid sudden excessive compression. In addition, extend the static maintenance time of extruded blanks to release residual stress in advance and eliminate delayed fracture hidden dangers. By comprehensively regulating process parameters and die structure, the fracture problem of high reduction ratio PTFE paste extrusion can be effectively solved, realizing stable production of high-precision and high-quality micro PTFE extrusion products.