Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 4

• R 0 = 1,370 N/mm 2 (in special cases)

• R 0 = 1,570 N/mm 2
• R 0 = 1,770 N/mm 2
• R 0 = 1,960 N/mm 2
• R 0 = 2,160 N/mm 2 (with a smaller wire diameter)

• R 0 = 2,450 N/mm 2 (with a smaller wire diameter).

The nominal strength is the minimum strength. The deviation allowed above the
nominal strength is about 300 N/mm 2 . However, the real deviation is usually much
smaller.

1.1.3 Metallic Coating

Rope wires needing to be protected against corrosion are normally zinc coated.
Zinc coating provides reliable protection against corrosion. Even if the zinc layer
is partly damaged, the steel remains protected as the electro-chemical process
results in the zinc corroding first. With zinc, the wires can be coated by hot zincing
or a galvanizing process. With hot zincing, the outer layer consists of pure zinc.
Between this layer and the steel wire there is a boundary layer of steel and zinc
compounds. With zinc galvanized wires, the whole layer of the coating, which can
be relatively thick, consists of pure zinc and has a smooth surface.
In most cases the wires are covered by hot zincing. The layer of FeZn-compounds
should be avoided or at least kept thin as they are relatively brittle which can lead to
cracks when the wire is bent. To keep the FeZn layer thin, the wires should only be
left in the zinc bath (with a temperature 440-460 C) for a short time.
During the hot zincing, the strength of the wires is somewhat reduced Wyss et al.
( 1956 ). Because of this, and also because of the rough surface resulting from the
zincing, the wires are often drawn again. This process increases the strength of the
wire again and the zinc surface is smoothed. Before drawing, the zinc layer should be
thicker than required as part of the zinc layer will be lost during the drawing process.
Blanpain ( 1964 ) found that during the re-drawing the brittle Fe-Zn layer may
tear especially if the Fe-Zn layer is relatively thick. The resulting gaps will be
entered from inside by a steel arch and are not visible from outside as they are
closed with zinc. The fatigue strength of these wires is reduced due to the sharp
edges of the gaps.
As an alternative to zinc, the wires can be coated with galfan, an eutectoide
zinc-aluminiumalloy Zn95Al5 (95 % zinc, 5 % aluminium). Nünninghoff and
Sczepanski ( 1987 ) and Nünninghoff ( 2003 ) found that this Zn-Alalloy offers better
protection against corrosion than pure zinc. The Zn95Al5 coating also has
the further advantage that the brittle Fe-Zn-layer is avoided. However, the
Zn95Al5-layer is not as resistant to wear as the pure zinc layer which means that
Zn95Al5-coated wires are not as suitable for running ropes.
In Table 1.2 , the surface-related mass of zinc coating is listed as an excerpt of
Table 1.1 of EN 10244-2 in different classes. For a very thick coating, a multiple