Industrial Cable Assemblies factory

How to test the flexibility of industrial cable?

Industrial cables are widely used in dynamic environments—such as robotic joints, sliding conveyors, and portable industrial devices—where repeated bending, twisting, or flexing is unavoidable. Poor flexibility can lead to insulation cracking, conductor breakage, or signal/interruption failures, directly affecting equipment reliability. Below is a step-by-step guide to testing cable flexibility, combining industry best practices and international standard requirements.

1. Pre-Test Preparation: Lay the Foundation for Accurate Results

Before starting the test, ensure consistency in sample conditions, environmental factors, and tool calibration—these directly impact result validity.

1.1 Sample Selection

• Choose samples that match the actual application specifications: Include the same conductor material (e.g., copper, tinned copper), insulation layer (e.g., PVC, silicone, polyurethane), and jacket type (if applicable) as the cables used in the field.
• Cut samples to a standardized length: Typically 1–2 meters (3–6 feet) to ensure enough length for clamping and flexing without excessive tension.
• Inspect initial condition: Check for pre-existing defects (e.g., scratches, kinks, or conductor exposed) using a magnifying glass (10–20x magnification); discard damaged samples to avoid false results.

1.2 Environmental Control

Flexibility is highly sensitive to temperature and humidity. Conduct tests in a controlled environment:

• Temperature: Maintain 23°C ± 2°C (73°F ± 4°F) (per IEC 60068-1, the international standard for environmental testing).
• Humidity: Keep relative humidity at 50% ± 10% to prevent insulation hardening (in low humidity) or softening (in high humidity).
• Avoid air flow: Drafts can cause uneven cooling or tension on the sample; test in a closed, wind-free space.

1.3 Tool Preparation

Prepare calibrated, industry-grade equipment to ensure precision:

• Flexing tester: Choose a dynamic flex tester (for repeated bending) or static flex fixture (for fixed-radius testing) that supports adjustable bending radii (critical for simulating real-world use).
• Tension gauge: To apply consistent tension (usually 0.5–2 N, depending on cable diameter) during testing—excessive tension can accelerate damage.
• Electrical continuity tester: To monitor conductor integrity in real time (e.g., detect breaks during flexing).
• Microscope or visual inspection tool: For post-test checks of insulation cracks or conductor fraying.

2. Core Testing Methods: Simulate Real-World Flex Scenarios

Industrial cables face two main flex challenges: repeated dynamic bending and long-term static flexing. Use the following methods to test both scenarios.

2.1 Dynamic Flexibility Test (Most Critical for Moving Applications)

This test simulates repeated bending (e.g., robotic arm movement) to evaluate how many cycles a cable can withstand before failure.

Step 1: Set Flex Parameters

• Bending radius: Use the radius specified in the cable’s datasheet or the actual application (e.g., 5x the cable diameter for tight spaces, 10x for broader movements). For example, a 10mm diameter cable would use a 50mm or 100mm bending radius.
• Cycle rate: 10–30 cycles per minute (to mimic typical industrial motion speeds).
• Tension: Apply constant tension (e.g., 1 N for small cables, 2 N for larger power cables) using the tension gauge to replicate the weight of the cable in use.

Step 2: Mount the Sample

• Clamp one end of the cable to the tester’s fixed bracket; attach the other end to the movable arm (which controls bending).
• Ensure the cable is aligned with the bending axis—misalignment can cause uneven stress and false failures.

Step 3: Run the Test and Monitor

• Start the tester and count cycles. Use the electrical continuity tester to check for conductor breaks in real time (a sudden loss of continuity indicates failure).
• Pause every 1,000 cycles for visual inspection: Check for insulation cracking, jacket peeling, or conductor protrusion.
• Record the failure cycle count: The number of cycles until the first sign of damage (e.g., continuity loss or insulation failure) is the key metric for dynamic flexibility.

2.2 Static Flexibility Test (For Fixed-Bend Applications)

This test evaluates a cable’s ability to maintain performance when bent at a fixed radius for an extended period (e.g., cables routed through tight machine enclosures).

Step 1: Set the Fixed Bending Radius

Use a mandrel (a cylindrical tool) with a radius matching the application (e.g., 3x the cable diameter). Wrap the cable around the mandrel tightly—ensure no gaps between the cable and mandrel.

Step 2: Apply Holding Time

Secure the cable in the bent position and hold for 24 hours (or the duration specified by the industry standard, e.g., UL 758 for appliance cables).

Step 3: Evaluate Post-Hold Performance

• Visual check: Unwrap the cable and inspect for permanent deformation (e.g., the cable cannot return to a straight shape) or insulation cracks.
• Electrical test: Measure insulation resistance (using a megohmmeter) and conductor resistance (using a multimeter). Compare results to pre-test values—significant changes (e.g., insulation resistance drop > 10%) indicate poor static flexibility.

2.3 Torsional Flexibility Test (For Rotating Applications)

For cables used in rotating equipment (e.g., spindle motors, turntables), test torsional flexibility to avoid twist-induced damage.

Step 1: Mount the Cable

Clamp one end of the cable to a fixed base; attach the other end to a torque meter (to measure twisting force).

Step 2: Apply Twists

Twist the cable at a constant rate (e.g., 1 rotation per second) to the number of cycles expected in use (e.g., 1,000 rotations). Maintain a small tension (0.5 N) to keep the cable stable.

Step 3: Check for Failure

After twisting, inspect for insulation tearing or conductor breakage. Test electrical continuity—any interruption means the cable fails torsional flexibility requirements.

3. Post-Test Analysis: Determine Pass/Fail Criteria

To validate flexibility, compare test results to three key benchmarks:

1. Industry standards: Ensure compliance with IEC 60228 (conductor standards), IEC 60332 (insulation flame resistance), or application-specific standards (e.g., ISO 10993 for medical industrial cables).
2. Datasheet claims: Verify that the failure cycle count (dynamic test) or insulation resistance (static test) meets the manufacturer’s specifications.
3. Application needs: If the cable is used in a high-cycle environment (e.g., 10,000+ bending cycles/year), ensure the test cycle count exceeds the expected annual use by 20% (for safety margin).

4. Key Tips to Avoid Common Testing Mistakes

• Do not reuse samples: A cable that has undergone flex testing may have internal damage (even if invisible) and will not provide accurate results in retests.
• Adjust parameters for material type: Silicone-insulated cables are more flexible than PVC cables—use larger bending radii for PVC to avoid over-testing.
• Calibrate tools regularly: Flex testers and tension gauges should be calibrated annually (per ISO 9001) to ensure measurement accuracy.

Industrial cable flexibility testing is not just a quality check—it is a way to prevent costly equipment downtime and safety hazards. By following these steps, you can ensure the cables you select or manufacture perform reliably in dynamic industrial environments.