Regarding wire rope lubrication

Nowadays, European-style cranes have gradually become popular products in the market. However, during customer visits, we found that many manufacturers adopt galvanized oil-free Wire Ropes. Moreover, tender documents often contain a contradictory requirement for wire rope surface condition: Galvanized, oil-free and maintenance-free wire ropes shall be used.

Galvanization is easy to understand, as it is intended for corrosion protection. But the concept of oil-free and maintenance-free… honestly, I cannot make sense of it.

Common wire surface finishes are bright finish or galvanized. Galvanized wire ropes are further classified into Grade B, AB and A, selected according to different application scenarios.

1. One point we need to clarify: unless there are special requirements, lubrication is recommended for both bright and galvanized wire ropes. Without lubrication, wire rope wear will accelerate, corrosion will occur, and service life will be reduced. This is a fundamental physical law. The following is an excerpt on wire rope lubrication from DIN 15020: “Depending on the operating conditions of the Steel Rope, it must be re-lubricated at regular intervals, particularly in its bending zones. The lubricant used must be compatible with the rope’s original lubricating medium.”
2. There are several conventional factory lubrication methods for wire ropes: A. Strand lubrication B. Rope lubrication C. Strand lubrication followed by secondary rope lubrication after closing

I will not elaborate on rope lubrication (B). At our company, all wire ropes must undergo strand lubrication (A) first. Whether secondary rope lubrication (C) after closing is required depends on the customer’s application scenario. If there is no special cleanliness requirement, strand lubrication plus secondary rope lubrication (C) is still recommended. Secondary lubrication can be divided into light oil (C-1), medium oil (C-2) and heavy oil (C-3). Customers can select different lubrication methods based on their working conditions. This may sound abstract, so several photos of actual products will help illustrate.

A Strand lubrication: Lubrication is applied when twisting single strands into rope. The grease volume is low, so there is no issue of grease stringing in winter or dripping in summer. An oil film protects individual strands. Suitable for paper mills, aluminum plants, aerospace material handling and other applications with high cleanliness requirements.

C-1 Secondary light-oil treatment: After strand lubrication, excess grease is thoroughly scraped off during rope closing. Only a small amount of lubricant remains in strand gaps. Special wire rope grease is adopted (drop point: 94°C, brittle point: -29°C, kinematic viscosity @100°C: 215 mm²/s). The oil film provides good overall protection. Suitable for most indoor general crane applications.

C-2 Secondary medium-oil treatment: After strand lubrication, grease is partially scraped during rope closing. More lubricant is retained in strand gaps to deliver sufficient lubrication protection. The same special wire rope grease is used (drop point: 94°C, brittle point: -29°C, kinematic viscosity @100°C: 215 mm²/s). It will not drip at high temperatures and reduces corrosion risks. Suitable for outdoor lifting machinery.

C-3 Secondary heavy-oil treatment: This applies to a small number of special working conditions. Some customers find it difficult to perform on-site lubrication, so this is a customized factory solution with a thicker grease layer on the surface. The same special wire rope grease is used (drop point: 94°C, brittle point: -29°C, kinematic viscosity @100°C: 215 mm²/s). Suitable for rotary drilling rigs, waste grab cranes and other working conditions.

There is another surface condition: customers want internal lubrication to guarantee rope performance while blocking external contaminants. For example, electric shovels in open-pit mines operate in heavy dust environments. Fully oil-free wire ropes cannot meet the requirements, while conventional oiled wire ropes will form oily sludge on the surface and impair performance. In such cases, fully plastic-coated wire ropes are required, as shown in the picture below.

A well-known foreign wire rope manufacturer once carried out comparative tests, which showed that the service life of oil-free wire ropes is much shorter than that of lubricated wire ropes (see the figure below). Therefore, we must actively raise objections when tender documents specify galvanized, oil-free and maintenance-free wire ropes, because this concerns operational safety.

Different application scenarios impose different requirements on wire ropes. Customized demands keep growing. Lubrication methods and grease selection for wire ropes should be tailored accordingly. Apart from surface coating processes, grease selection also deserves attention. In regions with extremely cold winters such as Northeast China, Russia and Northern Europe, grease for wire ropes must be carefully selected. Conventional wire rope grease cannot satisfy low-temperature requirements; specially formulated lubricant must be adopted to avoid hardening, otherwise wire rope performance will be affected.

For certain special working conditions, such as mine friction hoists that require increased friction, friction-increasing dedicated wire rope grease is required. For lifting machinery in key water source areas and water source protection zones with stringent ecological requirements, the Ministry of Water Resources of China mandates the use of special eco-friendly wire rope lubricant.