Detailed Description
High Tensile + Grab — Two Demands, One Cable
A grab crane subjects its cable to two independent mechanical loads simultaneously:
- Hoist tension: The cable must support the combined weight of the grab assembly (bucket, hydraulic cylinders, rigging) plus its own suspended weight over the lift height. On a large ship unloader with a 20-ton grab at 40 m lift, the cable supports approximately 25 tonnes total.
- Grab cycling stress: Every 30–90 seconds, the grab bucket opens and closes. This rapid cyclic motion creates internal core movement, generates heat from conductor friction, and subjects the cable jacket to repeated flex at the grab head connection point.
Dual Motor Power — 7+ Cores Minimum
The grab crane cable must power two independent motor groups:
| Core | Function | Typical Cross-Section |
|---|---|---|
| U1, V1, W1 | Hoist motor (lift/lower) | 25–95 mm² each |
| U2, V2, W2 | Grab motor (open/close) | 10–35 mm² each |
| PE | Protective earth | 16–50 mm² |
| Control 1–4 | Limit switches, position sensors | 0.75–1.5 mm² each |
The PET fleece separation layer between the power core group and the control core group is essential. During grab cycling, the power conductors move and flex — without a physical separator, this movement abrades the thin-walled control cores, leading to premature signal failure even though the power conductors are intact.
Class 6 vs Class 5 — Why the Finer Stranding Matters
Class 5 (fine-stranded) copper is standard for most reeling cables. Class 6 (extra-fine-stranded) uses approximately 30% more individual wire strands per conductor of the same cross-section. This matters for grab cables because:
- Higher bend frequency: 40–120 bend cycles per hour (vs 10–20 for standard hoist). Class 6's finer wires experience lower individual strain per bend
- Smaller bend radius: D/d 12:1 with Class 6 vs 15:1 with Class 5 for equivalent service life
- Reduced internal friction: The larger number of thinner wires reduces inter-strand friction during bending, generating less heat
Why Choose Yichi High Tensile Grab Reeling?
- Oversized tensile core calculated: We calculate the steel wire cross-section for your grab weight, lift height, and cable length — not a catalog standard
- Class 6 copper standard: Finer stranding for the high-frequency bend cycles of grab operation
- PET fleece inter-layer separation: Prevents the #1 control core failure mode in grab cables — power-to-control core abrasion
- Marine configuration: Stainless steel tensile core + marine PUR jacket + DNV GL certification — for shipboard and floating crane installations
- Combined cycle testing: Our rated life is based on simultaneous hoist + grab open/close cycling, not separate tests extrapolated