Wire Rope Drum & Sheave Selection per ISO 16625

Proper selection of wire rope drums and sheaves directly impacts the safety and service life of the hoisting mechanism. ISO 16625 — Selection and maintenance of wire rope drums and sheaves provides a complete international framework for the selection, matching, installation, and discard of drums and sheaves. In practical engineering design, this must be combined with the D/d ratio requirements for wire rope and drum/sheave matching specified in GB/T 3811-2008 Crane Design Standard, as well as the mandatory periodic inspection provisions for hoisting mechanisms under TSG 51-2023 Crane Safety Technical Supervision Regulation. Together, these form a closed-loop management system that spans from design selection through in-service inspection.

ISO 16625 Scope and Application for Crane Drums and Sheaves

ISO 16625 — "Cranes — Selection and maintenance of wire rope drums and sheaves" — was developed by ISO/TC 96, the ISO technical committee for cranes. The latest revision was published in 2022. The standard applies to wire rope drums and sheave assemblies on all cranes with a Rated Lifting Capacity above 0.5 t, including Bridge Cranes, gantry cranes, tower cranes, Mobile Cranes, and jib cranes. It covers four key phases: selection design, installation matching, operational maintenance, and discard determination.

The standard follows a four-stage full life cycle management logic: selection — matching — maintenance — discard. In the selection phase, the D/d ratio (pitch diameter of the drum or sheave divided by the nominal wire rope diameter) serves as the primary control parameter. The matching phase centers on groove radius tolerance. The maintenance phase relies on periodic wear measurement. The discard phase applies four quantitative thresholds. In the drum design for Kelude's QZ and QD series Bridge Cranes, the engineering department strictly follows the ISO 16625 D/d ≥ 18 criterion, combined with the load combination coefficient requirements of GB/T 3811-2008, ensuring the drum fatigue life meets Work Duty M6 and above.

ISO 16625 is highly compatible with the current Chinese standard system. For drum diameter selection, Table 44 of GB/T 3811-2008 specifies minimum D/d values consistent with ISO 16625. For discard criteria, Clause C3.2 of Annex C in TSG 51-2023 directly references the ISO 16625 groove wear limits. The standard also works in tandem with ISO 4309 Wire Rope Inspection Standard — when a drum or sheave is discarded, the wire rope is typically replaced at the same time.

Six Drum Selection Criteria Under ISO 16625

Clause 5.2 of ISO 16625 defines six core drum selection criteria, listed below in order of priority:

① D/d ratio: The ratio of drum pitch diameter D to wire rope diameter d must not be less than 18 (may be reduced to 16 for Mobile Cranes with documented justification). This is a mandatory requirement that directly determines the bending fatigue life of the wire rope. For example, the Kelude QD32t Bridge Crane uses a 20 mm wire rope with a drum pitch diameter of φ400 mm, giving a D/d ratio of 20 — in full compliance.

② Groove radius: The groove radius R must be between 0.53d and 0.56d, ensuring a contact angle of 60°–90° between the rope and the groove. If R is too small, excessive compression on the rope accelerates wire breakage; if R is too large, lateral movement of the rope in the groove causes premature wear.

③ Groove pitch: The center-to-center distance between adjacent grooves P must be ≥ 1.15d to prevent cross-layer compression during multi-layer spooling. For deep-lift applications requiring multiple layers, a pitch of 1.2d or greater is recommended, along with a rope guide device.

④ Drum length: For single-layer winding, drum length L = 1.1 × (H × a / π / D + p) × P, where H is the Lifting Height, a is the Pulley Ratio, and p is the number of safety wraps (minimum 2). Multi-layer winding requires an additional 20%–30% length margin.

⑤ Shell wall thickness: The minimum wall thickness t_min must be ≥ d for cast-iron drums or ≥ 0.8d for welded steel drums, and in no case less than 12 mm. Insufficient wall thickness is the leading cause of drum cracking and deformation, accounting for approximately 38% of drum failures.

⑥ End plate flange: The end plate must extend at least 1.5d above the outermost layer of rope to prevent the rope from slipping off the drum end. For multi-layer winding, the end plate height must be calculated cumulatively based on the total number of layers — never on a single-layer basis.

Sheave Selection, Matching, and Maintenance Requirements

Clause 5.3 of ISO 16625 imposes stricter requirements for sheaves than for drums. The sheave pitch diameter-to-rope diameter ratio must be D/d ≥ 20 (may be reduced to ≥ 14 for equalizer sheaves) — approximately 11% higher than the drum requirement. Sheave grooves use a U-shaped profile with a bottom radius of R = 0.53d–0.56d, matching the drum groove. However, the groove opening width W = 1.5d–1.8d must be wider than the drum groove to accommodate the fleet angle of the rope entering and leaving the sheave.

For sheave materials, ISO 16625 recommends ductile iron QT400-18 or cast steel ZG270-500 for the sheave rim, with a surface hardness of HB170–210, followed by Quenching to HRC45–50. For frequent heavy-load applications (e.g., Metallurgical Cranes), a replaceable MC nylon or polyurethane liner in the groove is recommended to reduce wire rope wear. The liner must be replaced when worn to a thickness of less than 3 mm. Kelude uses a removable nylon liner design in its metallurgical crane Pulley Blocks, reducing replacement time to 2 hours and cutting liner cost to just 15% of a full sheave replacement.

For sheave bearings, ISO 16625 requires a calculated bearing life of L_10h ≥ 5,000 hours (Work Duty M5) or ≥ 10,000 hours (Work Duty M6 and above). Bearing Clearance C3 is the recommended precision grade. During installation, axial play of the sheave must not exceed 0.3 mm. Routine sheave maintenance includes monthly checks of bearing operating temperature (normal ≤ 80°C), grease condition (lithium grease replenished every 500 hours), and groove wear measurement (annual ultrasonic thickness gauge inspection).

Four Discard Criteria Explained

Clause 7 of ISO 16625 defines four discard criteria for drums and sheaves. All use quantitative thresholds rather than qualitative judgment, ensuring consistent and reproducible inspection results:

① Groove wear discard (§7.3.1): The drum or sheave must be discarded when groove bottom wear exceeds 15% of the original groove depth. Measurement is performed using a dedicated groove profile gauge at four equally spaced points around the circumference (0°, 90°, 180°, 270°), taking the maximum value. Once wear exceeds the limit, the contact area between the rope and groove bottom decreases, contact stress rises sharply, and the wire rope breakage rate increases by 3–5 times.

② Rim/shell crack discard (§7.4.2): Discard is required when any crack exceeds 5 mm in length or 10% of wall thickness in depth, regardless of direction. Magnetic Particle Inspection (MPI) or penetrant testing is the preferred detection method — visual inspection alone is not acceptable. Cracks in the weld heat-affected zone of welded drums are particularly dangerous. Repair welding is prohibited: residual welding stresses accelerate crack propagation, and a repaired drum typically achieves less than 30% of its original service life.

③ Shell wall thinning discard (§7.5.1): Discard is required when wall thickness reduction exceeds 20% of the original wall thickness. Measurement uses an ultrasonic thickness gauge at three cross-sections along the drum length (front, middle, rear), taking four readings per section and recording the minimum value. Thinning typically concentrates in the rope winding zone (the middle 60% of drum length); the non-working zones at both ends may be allowed up to 25% reduction.

④ Bearing clearance discard (§7.6.1): The sheave bearing must be replaced when radial clearance exceeds 0.5 mm (bore diameter ≤ 100 mm) or 0.7 mm (bore diameter > 100 mm). Measurement uses a dial indicator to check radial runout of the sheave hub relative to the shaft, with a radial load applied to eliminate play. Axial play exceeding 0.3 mm also triggers bearing replacement.

Drum and Sheave Matching Verification and Inspection Intervals

Clause 6 of ISO 16625 requires systematic matching verification between the drum and sheaves to ensure groove radius, fleet angle, and winding configuration are mutually compatible. The fleet angle of the wire rope relative to the groove is the core parameter: the fleet angle at the drum end must not exceed 3° (plain drum) or 1.5° (grooved drum), and at the sheave end must not exceed 2.5°. Excessive fleet angles cause severe friction between the rope and the groove sidewall, accelerating single-side groove wear by 5–8 times and producing concentrated wire breaks on the rope surface.

Regarding inspection intervals, ISO 16625 defines three levels based on operating conditions: daily checks (each shift) verify smooth rope travel in the groove and detect abnormal noise; monthly inspections measure groove wear and record trend curves; annual inspections cover all four discard criteria and produce a formal inspection report. Kelude's after-sales team provides customers with a "Drum and Sheave Full Life Cycle Management File" — each inspection record is entered into a cloud-based system that automatically generates wear trend prediction curves, providing 3–6 months of advance warning before the discard window.

For cranes operating in harsh environments (temperature > 60°C, humidity > 85% RH, dust concentration > 100 mg/m³), ISO 16625 recommends shortening monthly inspections to biweekly and annual inspections to semiannual. For special applications such as metallurgy, Casting, and Port operations, additional infrared thermography (quarterly) and vibration spectrum analysis (semiannual) are recommended to supplement conventional visual and dimensional inspections.

Drum and Pulley Parameter Comparison

Scrap Determination Standard Clause Comparison Table

8. ISO 16625 Key Data Indicators at a Glance

9. 📖 Further Reading

The following articles cover crane wire rope, drum, and hoisting mechanism standards and selection guidelines. We recommend exploring them for deeper insight:

📖 GB/T 3811 Crane Design Standard: Selection methodology for 9 load combinations and work duty classifications from A1 to A8 — the domestic design basis for drum and sheave D/d ratios.

📖 ISO 16625 Wire Rope Drums and Sheaves — Selection, Maintenance and Usage Guide: A complete interpretation of the standard covered in this article.

📖 How to Select Crane Wire Rope? Fiber Core vs. Steel Core vs. Rotation-Resistant — 4 Parameter Comparisons and 5 Scrap Criteria — A companion guide to wire rope selection and retirement standards.

📖 How to Select a Crane Reducer? Hardened Tooth Flank, Planetary, and Cycloidal — 4 Parameter Comparisons and Selection Calculations — Reference for hoisting mechanism drivetrain selection.

📖 How to Tell If Coupling Elastomers Have Aged? 6 Detection Methods and Replacement Intervals — Maintenance reference for hoisting mechanism transmission components.

10. Frequently Asked Questions