Lubrication - Wire Rope Lubrication

Wire Rope Lubrication

Wire ropes lubrication is typical owing to the fact that lubricant has to satisfy dual requirements of internal, as well as external lubrication, with different additive characteristics.

To understand lubrication in a wire rope, the wear and failure pattern needs to be understood

          Wear and failure.

Wear in wire ropes may be internal or external. The primary wear mode is internal and is attributed to friction between individual strands during flexing and bending around drums and sheaves. This condition is aggravated by failure of the lubricant to penetrate the rope.

 (1) Corrosion. Corrosion damage is more serious than abrasive damage and is usually caused by lack of lubrication. Corrosion often occurs internally where it is also more difficult to detect. Corrosion of wire ropes occurs when the unprotected rope is exposed to weather, to corrosive environments such as submergence in water (especially salt water), or to chemicals.

Corrosion results in decreased tensile strength, decreased shock or impact-load resistance, and loss of flexibility. Unprotected wire ropes that are used infrequently have a greater potential for rust damage due to moisture penetration. Rust may prevent relative sliding between wires, creating increased stresses when the rope is subsequently placed in service.

(2) Abrasion. During service the individual wires in the strand are subject to torsion, bending, tension and wear as a result of abrasion and friction at points of moving contact. Therefore proper lubrication is essential to reduce friction and wear between the individual wires and to ensure maximum performance.

                              Lubrication.

During operation, tension in the rope and pressure resulting from wrapping around drums forces the internal lubricant to the rope surface where it can be wiped or washed off.

Tests conducted on dry and lubricated rope operating under similar conditions provide ample evidence of the beneficial effects of lubrication. The fatigue life of a wire rope can be extended significantly (200 to 300 percent) through the application of the correct lubricant for the operating conditions.

However, under certain operating conditions lubrication may be detrimental. Unless recommended by the rope manufacturer

- Wire rope operating in extremely dirty or dusty environment should not be lubricated, unless all contaminants are removed. Abrasives may combine with the lubricant to form a grinding compound that will cause accelerated wear.

- Lubrication in wet / rainy climates tends to seal the voids where water is entrapped- resulting in corrosive wear in the core.

Heavy lubricant will provide both internal lubrication and a durable external coating to prevent corrosion and penetration of dust and abrasives.

                        Lubricant qualities.

To be effective, a wire rope lubricant should:

(a) Have a viscosity suitable to penetrate to the rope core for thorough lubrication of individual wires and strands.

(b) Lubricate the external surfaces to reduce friction between the rope and sheaves

    or drum.

(c) Form a seal to prevent loss of internal lubricant and moisture penetration.

       Should have inherently high viscosity without adding thickeners or fillers.

(d) Protect the rope against external corrosion and resist brittleness or chipping at the lowest operating temperature

(e) Be free from acids and alkalis.

(f) Have enough adhesive strength to resist washout and must not thin and drip at the highest operating temperature

(g) Have high film strength and must not cake, gum, or ball up when contaminated with dust and dirt.

(h) Not be soluble in the medium surrounding it under actual operating conditions.

(i) Not interfere with the visual inspection of the rope for broken wires or other

damage.

Typical lubricator with pressure assisted

 

core lubrication with air assisted

air assisted core lubrication

core lubrication with pressure pump

When the manufacturer’s preferred lubricant cannot be obtained, an adhesive type

Lubricant similar to that used for open gearing may be acceptable.

 When damp conditions prevail, or when severe flexing under heavy loads is encountered, a two stage lubricant application may be the most effective. Application of a lighter adhesive followed by a very heavy adhesive lubricant to seal in the oil provides the best protection.

 In certain ropes subjected to highly corrosive environments such as acids, alkalies  or salt water, providing a heavy impervious exterior lubricant coating to guard against corrosion may be more important than ensuring adequate penetration.