Stainless Steel Coil Tube for Laparoscopic / Endoscopic Working Channels

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, spring-wound tubing product specifically designed for use as a working channel in laparoscopic and endoscopic surgical instruments. This product serves as the critical structural backbone within minimally invasive surgical tools, providing a flexible yet rigid conduit through which optical fibers, irrigation lines, and surgical instruments are transmitted to the operative site within the body cavity.

Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is engineered to meet the demanding requirements of modern surgical endoscopy, balancing three fundamental performance parameters: sterilization tolerance, instrument passability, and mechanical flexibility. These attributes collectively ensure reliable clinical performance across repeated use cycles in high-volume surgical environments.

2. Material & Properties

2.1 Base Material Specification

The coil tube is fabricated from austenitic stainless steel in two primary grades:

2.2 Key Mechanical Properties

Property 304 Grade 316L Grade Test Standard
Tensile Strength (Rm) ≥ 515 MPa ≥ 485 MPa ASTM A270
Yield Strength (Rp0.2) ≥ 205 MPa ≥ 170 MPa ASTM A270
Elongation (A50mm) ≥ 40% ≥ 40% ASTM A270
Hardness (HV) ≤ 210 ≤ 210 ASTM A270
Corrosion Resistance (3% NaCl, 24h) No pitting No pitting ASTM G48
Magnetic Permeability ≤ 1.05 (at 1000 A/m) ≤ 1.05 (at 1000 A/m) ASTM A968

2.3 Sterilization Compatibility

The 316L grade coil tube has been validated for repeated exposure to the following sterilization modalities without measurable degradation of mechanical integrity or surface quality:

3. Technical Specifications

Parameter Specification Tolerance
Wire Diameter (d) 0.3 – 2.0 mm ±0.02 mm
Coil Inner Diameter (ID) 2.0 – 12.0 mm ±0.1 mm
Coil Outer Diameter (OD) 2.6 – 14.0 mm ±0.15 mm
Helix Pitch (P) 0.8 – 3.0 mm ±0.05 mm
Number of Turns 10 – 500 (customizable) ±1 turn
Effective Length (L) 100 – 3000 mm ±2 mm
Surface Roughness (Ra, inner bore of parent tube) ≤ 0.4 μm —
Surface Roughness (Ra, coil wire surface) ≤ 0.8 μm —
Concentricity ≤ 0.1 mm —
Compressive Load (axial, at 50% compression) 1.5 – 15 N (diameter-dependent) ±10%
Spring Rate (k) 0.05 – 0.8 N/mm ±10%
Maximum Bending Radius ≥ 3× coil OD —
Operating Temperature Range −40°C to +150°C —
Standard Length per Roll 5000 – 10000 mm (coil form) —

4. Manufacturing Process

4.1 Precision Welded Tube Fabrication

The parent tube from which the coil wire is drawn is manufactured via Automatic Orbital TIG Welding (AOT) or Precision Laser Welding processes. This ensures a seamless-like weld integrity with weld bead height deviation of ≤ 5 μm, critical for maintaining uniform inner bore geometry.

4.2 Process Flow

  1. Raw Material Inspection — Incoming 304/316L stainless steel strip or bar undergoes spectroscopic verification (PMI — Positive Material Identification) for chemical composition compliance per ASTM A270.
  2. Precision Tube Forming — Cold-rolled and precision-welded tube is produced with tight dimensional tolerances (±0.05 mm on OD).
  3. Weld Seam Grinding / Polishing — Internal and external weld beads are mechanically or electrochemically removed to achieve a smooth, uniform bore surface (Ra ≤ 0.4 μm).
  4. Wire Drawing — The precision tube is drawn down to the required wire diameter through multi-die reduction, maintaining concentricity and roundness.
  5. Coil Winding (Spring Forming) — The wire is wound onto a precision mandrel using CNC-controlled coil winding machines. Helix geometry (pitch, number of turns, diameter) is controlled to ±0.05 mm accuracy.
  6. Stress Relief Annealing — Post-winding annealing at 1050–1150°C in a protective atmosphere (H₂ or vacuum) eliminates residual stresses while preserving the austenitic microstructure and non-magnetic properties.
  7. Surface Finishing — Electropolishing or mechanical polishing to achieve the specified surface roughness (Ra ≤ 0.8 μm for coil wire surface).
  8. Dimensional & Performance Verification — Comprehensive inspection including inner wall smoothness verification, spring rate testing, compression set measurement, and visual/microscopic surface examination.
  9. Packaging — Delivered in coil (reel) form, protected with anti-corrosion packaging suitable for medical device OEM integration.

4.3 Inner Wall Smoothness Verification

A critical quality gate in the manufacturing process is the inner wall smoothness verification of the parent precision welded tube. This is performed using:

5. Applications

5.1 Primary Application Domain: Surgical Endoscopy

The coil tube serves as the flexible structural backbone within the following minimally invasive surgical instruments:

5.2 Secondary Applications

6. Quality Certifications & Compliance

Standard / Certification Scope
ISO 13485:2016 Medical Device Quality Management System
ISO 9001:2015 General Quality Management System
ISO 14971:2019 Risk Management for Medical Devices
ASTM A270 / A270M Material specification for austenitic stainless steel seamless and welded tube
ASTM F899 Standard specification for wrought 18-8 chromium-nickel stainless steel (304) used for medical devices
ASTM F138 Standard specification for wrought 18-8-3 chromium-nickel-molybdenum stainless steel (316L) used for medical devices
ISO 10993-1/5/7/10/12 Biological evaluation of medical devices (general, chemical characterization, ethylene oxide residuals, sterilization, implantation)
EN ISO 14179-1 Sterilization of health care products — Requirements for supplier's documentation
RoHS 2011/65/EU Restriction of Hazardous Substances compliance
REACH (EC) No 1907/2006 Chemical substance registration compliance

7. Unique Selling Points

Triple Performance Guarantee: The integration of sterilization tolerance, instrument passability, and mechanical flexibility in a single coil tube component addresses the core engineering challenge of endoscopic working channel design — achieving controlled compliance without sacrificing lumen integrity.