Talking about Wire Ropes for European Overhead Cranes

We started selling imported Wire Ropes back in 2007. At that time, imported brands dominated the domestic market for European-style overhead cranes and electric hoists, such as Konecranes, DEMAG, Abus, SWF and so on. Most of the original-equipment wire ropes were 8-strand compacted wire ropes. Later, many domestic manufacturers began producing European cranes. Whether for wire rope electric hoists or European hoisting winches, they followed the lead of imported brands and adopted 8-strand rope products.

I. Features of European Overhead Cranes

European cranes adopt lightweight, compact designs with low dead weight and small wheel load, more delicate compared with traditional cranes. Their drums and pulleys also have relatively smaller diameters. They operate smoothly, most equipped with frequency conversion control, delivering low impact during start and stop, and high positioning accuracy. They emphasize high reliability, long service life, low failure rate, less downtime for maintenance, low full life-cycle cost and long service life of spare parts.

These characteristics of European cranes — lightweight design, small drum size and long service life — determine that they must use wire ropes with higher breaking strength, smaller diameter, smoother operation and longer service life.

II. Why Crane Manufacturers Prefer 8-Strand Compacted Wire Ropes

1. Refer to the schematic diagrams of common 6-strand line-contact wire ropes and 8-strand line-contact wire ropes.
   
   

Compared with 6-strand wire ropes of the same diameter, 8-strand wire ropes have a more rounded outer surface. Thanks to their larger outer surface area, they exert lower pressure on pulleys and drums, delivering better wear resistance, higher flexibility and superior fatigue resistance.

6-strand rope advantages: Simple structure, mature production process, low cost, widely available and easy to source. 6-strand rope disadvantages: High axial rigidity, inferior flexibility to 8-strand ropes, higher pressure on the grooves of drums and pulleys, moderate wear resistance.

8-strand rope advantages: Rounder outer profile, better flexibility, improved bending fatigue performance, lower pressure on drums and pulleys, superior wear resistance. 8-strand rope disadvantages: Higher price. Its manufacturing process is more demanding than 6-strand rope, placing higher requirements on manufacturers.

European cranes are generally sold at a higher price than conventional cranes, with extremely strict requirements for wire ropes. The higher cost of 8-strand rope versus 6-strand rope is not a primary concern. Crane manufacturers require not only 8-strand construction but also higher breaking load. For this reason, most select 8-strand compacted wire ropes. Common constructions include: 8×K19S-IWRC, 8×K26WS-IWRC, 8×K36WS-IWRC. To achieve higher breaking strength, grades are mostly 1960 MPa and 2160 MPa.

Compacted wire ropes have much better overall performance than line-contact ropes.

Compacted strand wire ropes are produced by pressing round strands made of round Steel Wires through a forming die. During compaction, deformation of the steel wires brings the following benefits:

1. Increased metallic cross-sectional area of the strand → higher breaking load
2. Larger contact area between steel wires, narrower gaps between strands, and more uniform internal stress
3. Smoother outer surface → lower pressure applied to the grooves of drums and pulleys
4. Improved lateral stability of strands under side loads
5. Better compaction and higher modulus of elasticity

The larger metallic cross-section of compacted strand wire ropes enables higher load capacity. Meanwhile, higher strand strength and expanded contact surface allow compacted strand ropes to operate under heavy lateral pressure and severe wear conditions.

This product performs well. But for European crane builders: show me your best option, hold nothing back. We only want the top tier.

To meet the stringent requirements of European crane manufacturers, wire rope makers further upgraded the product: plastic-coated independent Wire Rope Core (EPIWRC)

Advantages:

1. Improved structural stability of the wire rope
2. Enhanced performance under a wider range of fleet angles
3. Absorption of dynamic loads
4. Prevention of internal rope corrosion caused by contaminants and corrosive substances
5. Reduced friction between inner and outer strands
6. Prevention of distortion of the wire rope geometry
7. The steel core is fully encapsulated by plastic coating, with complete internal lubrication
8. Importantly, the cost increase is modest, only about CNY 1,000–1,300 per ton. It offers a good return on investment.

Here are several real photos for comparison of 6/7/8-strand compacted wire ropes with plastic-coated steel core. From left to right: same diameter 6×K36WS-EPIWRC, 7×K31WS-EPIWRC, 8×K26WS-EPIWRC. When it comes to outer roundness, the 8-strand version is undoubtedly the best.

Summary of wire rope selection for European overhead cranes:

1. 6-strand line-contact rope: Low breaking load, thick rope body that hinders compact layout, poor wear resistance → Rejected
2. 8-strand line-contact rope: Much rounder exterior, good appearance, yet insufficient breaking load → Put aside
3. 8-strand compacted (surface-contact) rope with independent wire rope core (IWRC): Smooth rounded surface, stable structure, high breaking strength. Fully meets requirements → Selected
4. 8-strand compacted rope with plastic-coated independent wire rope core (EPIWRC): The previous option is good, yet our standard keeps rising. When such a high-performance wire rope is available, this becomes the preferred choice.

Finally, a brief note on parallel-wire rope core (PWRC). To pursue ultimate breaking load, technical teams of European crane manufacturers sometimes choose PWRC wire ropes. Please refer to the design drawing for comparison.

Independent wire rope core (IWRC) or plastic-coated independent wire rope core (EPIWRC), as the name suggests, is itself a separate wire rope, with common constructions like 7×7, 7×13, 7×19, featuring excellent stability.

Compared with IWRC / EPIWRC, PWRC contains many more filler wires inside. The increased number of internal wires creates a larger metallic cross-sectional area, which raises the minimum breaking load of the whole rope. However, the larger metallic area also brings relatively lower flexibility, and imposes stricter requirements on the rope fleet angle of equipment.

When a wire rope enters a sheave at an angle, it first touches the sheave rim, slides down along the rim and finally seats into the rope groove. During this process, even under tension, the wire rope will twist and slide, changing the lay length of outer strands (shortening or lengthening). Greater fleet angle leads to more severe twisting. To minimize wire rope torsion, the recommended maximum fleet angle is 2.5° for IWRC ropes, while for PWRC ropes the fleet angle should not exceed 1.5°.

PWRC wire ropes place very high demands on wire rope manufacturers in terms of design and fabrication technology. Only a small number of domestic factories can produce qualified PWRC ropes, because being able to manufacture it and making it reliable are two different things. I will not judge which is better between IWRC and PWRC. The best solution is one with good workmanship that matches the customer’s application.