The Lab-Scale Breakthrough: RobotDigg’s Desktop Wire Coating Line for PEEK & Fluoropolymers

In the world of wire and cable manufacturing, working with "super polymers" like PEEK (Polyether Ether Ketone) and Fluoropolymers (FEP, PFA, and widely referred to as PTFE) typically requires massive industrial lines and significant material waste.

The RobotDigg Desktop Wire Coating Experimental Line (often based on the SJ25 or SJ35 extruder platforms) has emerged as a niche solution for R&D labs and small-batch manufacturers. It allows for the extrusion of these difficult, high-temperature materials on a desktop scale, bridging the gap between theoretical material science and physical wire prototyping.

1. The Core Equipment: SJ25 & SJ35 Platforms

Unlike standard PVC wire lines, the RobotDigg experimental line is built around modularity and high-temperature capability.

• The Extruder (SJ25/SJ35):

  • Size: The "25" and "35" refer to the screw diameter (25mm or 35mm). This small size is critical for expensive materials like PEEK (which can cost $100+/kg) because it minimizes the "residence volume"—the amount of material lost inside the barrel during startup and shutdown.

  • High-Temperature Config: Standard extruders max out at ~300°C. For PEEK and Fluoropolymers, RobotDigg modifies these units with high-wattage heater bands, specialized thermocouples, and hardened steel barrels (often Nitrided 38CrMoAl) to sustain processing temperatures of 380°C to 420°C.

• The Crosshead (The "Heart"):

  • The line uses a precision micro-crosshead. This tooling splits the molten polymer flow to coat the wire.

  • Self-Centering vs. Adjustable: For lab use, the line typically features an adjustable centering mechanism. This allows operators to manually tune the concentricity (wall thickness uniformity), which is vital when running experimental batches where flow rates might fluctuate.

2. Experience with PEEK (Polyether Ether Ketone)

Processing PEEK is notoriously difficult due to its high melting point (~343°C) and rapid crystallization. The RobotDigg line addresses the specific challenges of PEEK coating:

• Thermal Management: PEEK requires a stable melt temperature (approx. 380°C–400°C). If the temp is too low, the motor stalls (high torque load); if too high, the material degrades and produces black specks. The RobotDigg experimental line allows for precise zone-by-zone temperature control to maintain this window.

• Pre-Heating: A critical "experience" factor with PEEK is conductor preparation. The line includes a wire pre-heater. If molten PEEK hits a cold copper wire, it freezes instantly ("quenches"), leading to poor adhesion and internal stress cracking. The pre-heater ensures the wire is hot enough to bond with the PEEK.

• Cooling Gradient: PEEK must be cooled carefully to control its crystallinity. The experimental line’s water trough allows for warm-water cooling (or air gaps) to prevent the insulation from becoming brittle due to shock cooling.

3. Experience with Fluoropolymers (PTFE/FEP/PFA)

Clarification: While often labeled broadly as "PTFE extrusion," true PTFE (Polytetrafluoroethylene) is not melt-processable and requires Ram Extrusion (pushing a paste). The RobotDigg screw extrusion line is designed for melt-processable fluoropolymers such as:

• FEP (Fluorinated Ethylene Propylene)

• PFA (Perfluoroalkoxy)

• ETFE (Ethylene Tetrafluoroethylene)

Key Processing Features:

• Corrosion Resistance: Fluoropolymers release corrosive hydrofluoric acid gas when melted. The RobotDigg screws and barrels for these applications must be made of corrosion-resistant alloys (like Hastelloy or specialized bimetallic liners) to prevent the machine from being eaten away from the inside.

• Draw Down Ratio (DDR): Fluoropolymers are often extruded as a "tube" larger than the wire and then pulled down tight (Tubing Tooling). The RobotDigg line’s Capstan and Take-up units are synchronized to allow for high "draw down," enabling the production of extremely thin, lightweight insulation layers common in medical and aerospace wires.

4. Why Use a "Desktop" Line?

The primary driver for using this specific equipment is Cost of Failure.

• Industrial Line: Testing a new PEEK grade on a standard industrial extruder might require 50kg of material just to purge the screw. That is ~$5,000+ of waste.

• RobotDigg Experimental Line: Can run tests with as little as 1–2kg of material. This makes it a standard choice for university labs, medical device prototyping (e.g., catheter guide wires), and specialized electronics cabling.

5. Summary of Capabilities

Conclusion:

The RobotDigg plastic wire coating experimental line represents a "democratization" of high-performance wire manufacturing. By shrinking the industrial process to a desktop footprint, it allows engineers to gain experience with temperamental materials like PEEK and Fluoropolymers without the prohibitive costs of full-scale production trials.