Wire Rope Lubrication
As pointed out previously, a wire rope is a machine. Each time a wire rope bends over a sheave, or straightens from a slack position, many wires move against each other. Lubrication is necessary to help prevent wear caused by this movement. Lubrication also helps prevent deterioration of wire rope due to rust and corrosion. (Note: Corroded rope is dangerous since there is no way of determining its remaining strength).
Most wire ropes are lubricated during manufacture, but the lubricant doesn't last the life of the rope. The lubricant is squeezed out of the rope as it runs over sheaves under tension, washed off by rain, and if it is a dry film it will flake, etc.. Wire rope must be periodically lubricated with a durable long lasting product.
No set rule can be given for lubrication frequency. This will depend on the conditions the rope is operating under and the characteristics of the chosen lubricant and method of lubrication. A rope operating in wet conditions would need lubrication more often than one operating under dry conditions to prevent rust and corrosion.
Lubricants used for wire rope lubrication should have the following properties:
- Can deteriorate the rope and be threatening to the environment as well.
They must contain no acids or alkalis.
- Certain lubes marketed with linseed oil base have a low water wash resistance unless completely dry prior to being placed in the water.
They must have enough adhesive strength to stay on the rope.
- Thinner lubes are able to accomplish this at the expense of fluid film support between the strands. More suited to static ropes not working wire ropes.
They must be able to penetrate between the wires and strands.
- With the advent of pressure lubricators, thicker viscosity's can be applied and penetrate as far as their thinner counter parts giving a working wire rope much more fluid film support between the inner wires greatly reducing friction and abrasion.
They must have high fluid film strength.
- Corrosion inhibitors should be present in addition to the abrasion fighting characteristics.
They must resist oxidation.
- The pliability of a lubricant allows the lube to spread through out the rope as it flexes. If a spot in the rope is rubbed thin of lube, the remaining lube will re-distribute itself to cover that which has been rubbed thin. This is very important in moving, load carrying wire rope. Some lubricant suppliers are providing products which dry on the rope. These products are very weak against abrasion present in working wire ropes. Flaking can occur. These kind of lubricants are more in line with static applications such as guy wires.
They must remain pliable.
