The benefits of plastic in wire rope have been clearly demonstrated. The performance of wire rope improves when the empty spaces between the metallic strands are filled with plastic.
Core impregnated rope, as the name suggests, has the core of the rope covered by a sheath of plastic that flows out between the outer strands. Taking the use of plastic one step further results in a fully plastified, or plastic full impregnated, wire rope – or PFI, as it is known. The key feature of PFI is that all the gaps between the strands are fully filled with plastic, with no increase in rope diameter. PFI has been designed with compacted strands to get the benefit of compaction to increase fatigue performance.
The introduction of a plastic impregnated core on compacted eight strands was designed to reduce wear between the inner strands and to protect the core from corrosive or abrasive external agents. PFI follows this technical improvement by adding further benefits:
• it reduces wear on the sheaves
• it retains lubricant inside the rope and gives total protection against corrosion
• it increases the fatigue life up to three times compared to conventional six strand non-compacted rope
• it keeps the rope clean and needs no maintenance
• its fluorescent colour adds to safety
• it improves structural stability of the rope against external forces that would damage the geometry of other ropes
• it increases the life of sheaves and drums because of its rounder shape.
The PFI rope concept is designed to prevent the hard abrasion, corrosion and fatigue conditions on the lifting applications where a six or eight strand rope is normally used. This is where the superior performance of PFI ropes has been particularly demonstrated compared to any other type of design.
The plastic used is polypropylene with special flowing features to allow a good rope impregnation. The extrusion technology is also special and the production line must be equipped with high technology machinery to allow an excellent impregnation of the plastic from the outside of the rope to inside. There are only a few wire rope manufactures in Europe with the capacity to produce PFI rope.
PFI rope can withstand a temperature range of between -30°C and 70°C without any plastic damage. It is ultraviolet protected so the bright fluorescent colour will remain during the rope’s operating life. Plastic over the strand crowns will disappear very quickly after the first few hours of operation but the plastic between the strands will remain throughout the rope’s service life.
PFI rope has better lubrication retention because 90% of the rope grease is encapsulated by the plastic during the extrusion process. This contributes to the increase in the life of the rope. No grease is noticeable on the outside of the rope – it is clean. Sheaves should be greased as usual, and it is advised that the drum be polished before using compacted PFI ropes to take maximum advantage of the rope’s benefits.
A visual inspection for broken wires can be carried out as normal after a few operating cycles when the crown of the outer wires have become visible. There is no way of knowing what is happening inside the rope, but this is a general problem with the use of plastic cores, be they PFI or any sheathed core rope.
However, the clear endurance benefits on this kind of wire rope are making them very popular nowadays in cranes and other applications where rope life and safety are especially important. This solution is certain to become a standard option in the selection of high performance wire ropes in the very near future. Tycsa has been making compacted eight strand rope with a plastic impregnated core for five years and has three years experience producing plastic full impregnated wire rope, and every day it is getting better performances in hoisting and luffing wire ropes.
