ISO 16625 Wire Rope Drum & Pulley Selection and Maintenance Guide
Standard Overview: ISO 16625, "Cranes — Selection and maintenance of wire rope drums and sheaves," is a guidance document issued by ISO/TC 96, the ISO technical committee for cranes. It provides systematic specifications for drum and sheave selection calculations, material requirements, rope groove dimensional tolerances, installation and maintenance practices, and discard criteria. The standard is designed to be used in conjunction with ISO 4308 Cranes — Selection of wire ropes, together ensuring the safe and reliable operation of the wire rope drive system in crane hoisting mechanisms.
Wire rope drums and sheaves are the core transmission components of a crane's hoisting mechanism. Their selection and maintenance quality directly affect wire rope service life and lifting safety. A dimensional deviation exceeding 0.5mm in the drum groove can cause rope mis-spooling and localized crushing damage; excessive wear on the sheave groove can lead to wire rope derailment and accelerated wire breaks. ISO 16625 provides a standardized technical framework for full life cycle management of these two critical components.
Drum Selection and Rope Groove Design
ISO 16625 specifies the method for determining the drum diameter D: D ≥ h₁×d (where d is the nominal wire rope diameter and h₁ is the drum diameter factor corresponding to the mechanism's work duty classification). For hoisting mechanisms rated M5, h₁=18; for M6, h₁=20; and for M7, h₁=22.4. Taking a M5 10t overhead crane as an example, with a 16mm diameter wire rope, the minimum drum diameter would be D=18×16=288mm, rounded up to a standard value of 320mm.
For the rope groove, the standard groove depth is h=0.33d~0.40d, groove pitch is p=d+(2~3)mm, and groove bottom radius is R=0.53d~0.56d. The groove inner surface roughness must be Ra≤3.2μm, and both the groove bottom and sidewalls require quenching to HRC45~50 to resist contact wear from the wire rope. The flange height on both sides of the groove must be ≥1.5d (≥1.0d when a rope spooling device is fitted) to prevent the wire rope from slipping out of the groove.
Sheave Selection and Groove Requirements
The sheave pitch diameter Dp (the diameter measured at the centerline of the wire rope) is likewise determined by Dp ≥ h₂×d. The work duty coefficient h₂ for cast sheaves is: M5=20, M6=22.4, M7=25. The sheave groove has a U-shaped cross-section with a bottom radius of R=0.525d~0.550d and a groove angle of 45°~60°. The sidewall surface roughness of the groove must be Ra≤6.3μm.
ISO 16625 classifies sheave material requirements according to the wire rope tensile strength grade: when the wire rope tensile strength is ≤1770MPa, sheaves may be made of QT500-7 ductile cast iron or ZG270-500 cast steel; when the tensile strength exceeds 1770MPa (e.g., the 1960MPa grade), the sheave groove must be medium-frequency induction hardened to HRC50~55, or alternatively made of ZG35CrMo alloy cast steel with a wear-resistant overlay welded on the groove bottom. Double-row spherical roller bearings are preferred for sheave bearings, with an H7/g6 tolerance fit to ensure smooth rotation.
Installation and Alignment Calibration
ISO 16625 requires that the parallelism deviation between the drum axis and the fixed pulley block axis be ≤0.5mm/m. The flatness of the drum bearing housing mounting surface must be ≤0.1mm/500mm, checked with a feeler gauge. The fleet angle of the wire rope on the drum (the included angle between the rope centerline and the groove centerline) must be ≤4° for bright finish drums or ≤2.5° for spiral groove drums. Exceeding these limits causes the wire rope to pinch against the groove flanges, accelerating wear and potentially causing the rope to jump out of the groove.
After sheave installation, check rotational freedom by hand — sheaves rated below M5 should rotate freely with one hand, while M6 and above should rotate easily with a lever wrench. All sheaves in a pulley block must lie in the same plane, with the flatness deviation of the groove center planes not exceeding 1/1000 of the sheave spacing. After installation, conduct a 30-minute no-load trial run to verify that the wire rope spools neatly and that no abnormal friction noise is present.
Wear Monitoring and Discard Criteria
Discard criteria for drum groove wear per ISO 16625: the drum must be replaced when groove wall thickness wear exceeds 20% of the original wall thickness; if grooves deeper than ≥1mm or wire rope indentations appear on the groove bottom, the drum may be re-machined on a lathe (provided the wall thickness after re-machining remains ≥80% of the original thickness).
Discard criteria for sheave grooves: the sheave must be replaced when groove bottom wear exceeds 25% of the wire rope diameter (e.g., with a Φ16mm wire rope, a groove bottom wear depth of 4mm means the sheave is due for replacement); when sidewall wear reaches 30% of the original thickness; or when cracks or chipping appear on the wheel flange — replacement is required immediately regardless of the extent.
Lubrication and Routine Maintenance
During operation, the drum groove and sheave groove are self-lubricated by the grease on the wire rope surface. ISO 16625 recommends lubricating the wire rope every 200 operating hours or at least once per month (whichever comes first), using a wire rope-specific grease free of acidic and resinous components (NLGI 2 consistency). Sheave bearings should be regreased with lithium-based grease every 500 operating hours; if bearing temperature exceeds 70℃, the lubrication interval must be shortened.
Routine inspection items: visually check that the wire rope spools neatly on the drum, look for abnormal bright wear marks on the grooves, verify that sheaves rotate freely without abnormal noise, and confirm that bearing end cover bolts are tight. Measure groove wear quarterly using a vernier caliper or profile gauge, and maintain records for trend analysis.
| Work Duty / Classification | Drumh₁ | Pulleyh₂ | Rope Diameter16mm D | Rope Diameter20mm D |
|---|---|---|---|---|
| M5 | 18 | 20 | ≥288320 | ≥360400 |
| M6 | 20 | 22.4 | ≥320355 | ≥448450 |
| M7 | 22.4 | 25 | ≥358400 | ≥500500 |
FAQ
Q: Why is the wire rope not spooling evenly on the drum?
A: There are four main causes: ① The wire rope fleet angle exceeds the 2.5° limit specified in ISO 16625 — reposition the deflector sheave or add a rope guide; ② The rope groove machining accuracy is insufficient, with groove pitch tolerance beyond the ±0.3 mm range — re-cut the grooves on a lathe; ③ Insufficient initial preload — when installing a new rope, wind 3–5 turns under a tension equal to 10%–15% of the working load; ④ Wire rope rotation (inherent to rotation-resistant rope) — switch to a rotation-resistant wire rope or fit a free-rotating swivel at the rope end to release torque.
Q: What are the early signs of sheave bearing failure?
A: Early warning signs include: ① Abnormal noise or a periodic "clicking" sound from the sheave when running unloaded; ② Bearing cap temperature noticeably higher than that of other sheaves (temperature differential > 15°C); ③ A feeling of drag or uneven resistance when rotating the sheave by hand; ④ Periodic runout at the sheave rim (radialRunout > 0.5 mm). If any of these signs appear, stop the machine immediately and check the bearing condition using a vibration analyzer or stethoscope. Replace the bearing if necessary to prevent the wire rope from chafing against a seized sheave, which could lead to rope breakage.
Q: Can drum grooves be repaired on site?
A: Yes, but with limitations. If the groove has worn to a depth of less than 2 mm, it can be smoothed out on site using an angle grinder, and the groove profile should then be checked with a template gauge. If groove wear exceeds 2 mm but the remaining wall thickness is still greater than 80% of the original, the drum must be removed and sent to the Machining Workshop for re-cutting of the grooves on a large lathe. If re-cutting reduces the wall thickness by more than 20%, or if the enlarged groove diameter causes the drum diameter factor h₁ to fall below the requirement for the mechanism's Work Duty classification, the drum must be replaced. Field welding of drum grooves is not permitted under ISO 16625 — the heat input alters the surface hardness of the groove and introduces the risk of micro-cracks.
Q: How do I choose between cast and rolled sheaves?
A: Cast sheaves (made of QT500-7 ductile cast iron or ZG270-500 cast steel) are suitable for small to medium diameters (≤800 mm) and normal lifting capacities. They offer lower manufacturing costs, and the groove profile is ensured by the casting die. Rolled sheaves (formed by spin-forming Q345B steel plate) have uniform wall thickness, are lighter in weight, and are ideal for high-volume standardized production — but their groove dimensional accuracy is slightly lower than that of cast sheaves. ISO 16625 recommends prioritizing cast steel sheaves with medium-frequency induction hardening of the groove for applications rated at M6 and above, or where the wire rope diameter exceeds 20 mm, to extend groove service life.
