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To design rope drives in lifts, it is in many
cases still indispensable to this day to
conduct experimental investigations into
sample ropes, for example to determine
elongation behaviour in the longitudinal
rope direction. Since its establishment,
the Institute of Mechanical Handling and
Logistics (IFT) of the University of
Stuttgart has been engaged in research in
the field of rope technology.
I
n many modern lifts, ropes as lifting gear are
a decisive factor for the service life and main-
tenance intensity of the entire system. The
rope not only has to be wear-resistant, but also
reliably indicate its wear condition and above all
the replacement state of wear. The replacement
state of wear of the rope – i.e. permanent da-
mage – has been reached when the system still
operates safely, but an unsafe condition could
be reached in the near future.
Spontaneous damage to the rope can for ex-
ample also occur due to external mechanical
factors – this frequently occurs in the area of
crane construction. By contrast, ropes in lifts
usually wear out on account of over-rolling of
the discs. What is important in this regard is clear
and reliable indication of the so-called replace-
ment state of wear, the time of rope replacement.
Furthermore, an excessively high modulus of
elasticity (e-modulus) can stretch the rope under
the load of the car too much and as a result trig-
ger a very uncomfortable sinking of the car upon
entry and regulation problems in the travel drive.
A change in the modulus of elasticity and as a re-
sult in the rope elongation behaviour during the
rope’s service lift can be even more problematic.
Apart from the service life of the lifting gear, the
modulus of elasticity is an important parameter
for lift ropes and should be determined according
to application.
The IFT (see box) regularly conducts expe-
riments on the institute’s own traction testing
machinery to measure the modulus of elasti-
city. There is no linear progression in the rope
stress-rope strain curve for the rope’s strength.
Consequently, it is very important during the
measurement to take into account the use of the
rope and the associated rope forces that occur.
For example, for the rope tensile forces, safety
factors between 14 and 25 for the lifting gear are
normally used. At the IFT, three measuring rigs
are available for strain measurement of the rope
for various force ranges, installed in two tensile
testing machines (for example, in Fig. 1). Measure-
ments can either be conducted by a parallel rod
clamped on the rope at two measuring points
or by two rope displacement pickups evaluated
in parallel (shown in Fig. 1). The result of the
measurement is a stress-strain diagram (Fig. 2).
Normally, the secant modulus of elasticity
according to Feyrer [1] is determined in the ex-
periment (yellow in Fig. 2). For this purpose, the
rope is extended between the minimum and ma-
ximum rope loads occurring in the operation of
the rope, that is to say, run to the upper and lower
limit load several times in succession. After this,
the tenth extension cycle for example is evalua-
ted – the rope extension is determined from the
measurement log while running past the two
observation limits.
In addition to the secant modulus, the tangent
modulus (shown red in Fig. 2) can also be deter-
mined from the intersections of the elongation
curves with the observation limits. In each case,
the difference between loading and load reduc-
tion is important, since as a result of inner fricti-
on in the rope, the elasticity behaviour can in part
differ markedly depending on the direction.
⇤
STEFAN HECHT
The author is a qualified engineer and head of the
research group Destructive Rope Testing of the Insti-
tute of Materials Handling and Logistics (IFT) of the
University of Stuttgart.
[1] Feyrer, K., Wehking, K.-H.: Drahtseile – Bemessung,
Betrieb, Sicherheit, Springer Verlag, Berlin, 2018
Abb. 1: Messaufbau zur Bestimmung des Seil-Elastizitätsmoduls
Fig. 1: Measuring rig to determine the rope modulus of elasticity
WHAT IS THE IFT?
Since its establishment in 1927, the Institute of
Mechanical Handling and Logistics (IFT) of the Uni-
versity of Stuttgart has been engaged in research
in the field of rope technology. The rope technology
department concentrates on wire ropes, fibre ropes,
personal protective equipment, cableway techno-
logy and rope use. It provides studies to determine
rope service life in continuous bending fatigue
and extension experiments, static and dynamic
experiments, drawing up damage expert opinions,
safety and risk analyses, cableway technology and
destructive and non-destructive rope testing. Fur-
thermore, the IFT advises industrial companies as
well as the operators of installations and buildings
on the specific use of ropes. The department is re-
cognised worldwide as a testing and expert opinion
authority. The over 1300 m² experiment hall at the
IFT, the rope laboratory, is equipped with testing
machinery and installations for rope testing, in part
developed at the laboratory itself.
WAS IST DAS IFT?
Das Institut für Fördertechnik und Logistik (IFT) der
Universität Stuttgart befasst sich seit der Grün-
dung im Jahr 1927 mit der Forschung im Bereich der
Seiltechnologie. Die Schwerpunkte der Abteilung
Seiltechnologie sind die Bereiche Drahtseil, Faser-
seil, Persönliche Schutzausrüstung, Seilbahntech-
nik und Seilanwendung. Es bietet Untersuchungen
zur Ermittlung der Seillebensdauer in Dauerbiege-
und Schwellversuchen, statische und dynamische
Prüfungen, die Erstellung von Schadensgutachten,
Sicherheits- und Risikoanalysen, die Seilbahn-
technik sowie zerstörende und zerstörungsfreie
Seilprüfungen. Außerdem berät das IFT Industrie
unternehmen sowie Betreiber von Anlagen und
Bauwerken bei der spezifischen Anwendung von
Seilen. Die Abteilung ist weltweit als Prüf- und
Gutachterinstanz anerkannt. Für Seilprüfungen ist
die über 1300 m² große Versuchshalle am IFT, das
Seillabor, mit zum großen Teil eigenentwickelten
Prüfmaschinen und -einrichtungen ausgestattet.
Foto: © IFT