Tests and inspections on ropeways

LATIF performs tensile tests on steel ropes to determine their maximum force; for this type of test the reference standard is UNI EN 12385-1.

For this purpose, the laboratory is equipped with two specialised testing machines: one horizontal machine with a capacity of up to 10000 kN, for a maximum sample length of 11 m and with a maximum stroke of 2 m; the other vertical machine with a capacity of up to 1200 kN, for samples with a maximum length of about 2 m. Both machines are very accurate and are class 0.5 according to ISO 7500-1.

The rope specimens are normally gripped on the testing machines by means of conical cast heads and cylindrical or fork-shaped metal lugs, which may be manufactured in accordance with standard UNI EN 13411-4 by the laboratory or by the customer himself.

LATIF is also authorised by the Ministry of Transport to check the acceptability of wire ropes intended for public transport services according to the relevant Ministerial Decree no. 1175 of 21/6/1986 with traction, bending, and torsion tests on the wires composing the ropes themselves.

Another characterisation test of the wire ropes in which the laboratory specialises is the measurement of the elastic modulus in accordance with ISO 12076 or according to the client's procedure, for which an extensometer with a 2 m length is used.

A testing machine built and installed in 2000 by the company INSTRON U.S.A. allows static and semi-dynamic tests in tension and compression with loads of up to 10 MN (1000 t).

The machine was primarily designed for tearing tests on large-diameter steel ropes, but the dimensions available for the sample and the equipment provided allow for universal use.

Technical characteristics:

• length: 21.60 m
• width: 3.30 m
• height: 2.0 m
• total weight: 105 t
• machine axis from ground: 1 m
• width for sample: 1 .40 m
• length to sample: 11 m
• cylinder stroke: 2 m
• maximum force in traction and compression: 10 MN (1000 t)
• load cell on rod head control cylinder 80 l/min 50 kW + 160 l/min 90 kW
• computerised command and control system
• equipment for tensile test on steel bars (up to 70 mm diameter)
• equipment for pull test of steel chains (up to 2 MN)
• universal plates on trolleys for mounting specific samples
• fixed trolley with motorised translation
• hydraulically opening/closing protective covers
• extensometer base length 2 m CLASS 1

Since the machine remains closed during the test, the sample area is monitored by an armoured camera swivelling from the control room, with video display and recording equipment. The video equipment makes analogue (VHS) and digital recordings on a PC, with special software that allows the film to be edited and archived on CD.

The command and control system allows the execution of classic tensile and compression tests, as well as the construction of dedicated tests that can be archived as specific test profiles.

Since the tests are carried out with the machine closed, an automated system is installed for measuring the diameter of the rope at different load levels, enabled from the control room. The system is housed underneath the machine, extendable upwards during measurements, and retracts into an armoured enclosure at the moment of tearing.

The test consists of winding the synthetic rope onto the vices of the testing machine; unwinding at the time of clamping must be avoided as much as possible, which is why the specimen is wound and centred by means of a centring ring. The final clamping is done mechanically by means of a screw. One vice remains clamped while the other is operated by an electric mechanism that causes the wire to break, and thanks to the load cell installed on the machine, the force and elongation data of the crossbar are recorded.

The reference standard is UNI EN ISO 2307 Fibre ropes

In the course of twenty years of operation, more than 3000 integrity checks have been carried out using the magneto-inductive method on ski lift ropes, for the detection of broken wires both inside and outside the rope, as well as corrosion, mechanical or atmospheric injuries. Dedicated equipment has been built.

Given the presence of external companies authorised to carry out systematic checks on the installations, the Laboratory assumed the role of verifier of the equipment used by them, performing the homologation tests indicated by the competent sector of the Ministry of Transport.

The verification instrumentation was adapted for this purpose and special test ropes were constructed, with known defects. This makes it possible to compare the response of the equipment under test with the reference equipment supplied, in order to assess its suitability for use in the field of cableways for public passenger transport.

The supplied equipment allows ropes up to a maximum diameter of 90 mm to be checked. A digital recording of the test diagrams can be made, with acquisition on a PC, for comparison with paper-writing equipment.

From the examination of several recordings over the life of the rope, together with the direct visual inspection, indications can be drawn as to whether the rope is permissible for maintenance, or whether it needs to be replaced.

Permanent-magnet detectors are manufactured for internal use, with a focus on lightness and efficiency, using the latest magnetic materials.

Diagram of magneto-inductive examination on a carrier rope taken off site, subject to special investigation.
In correspondence to each marked peak, there are 1 or 2 internal broken wires: although they do not represent a danger to the overall integrity of the rope, they denote its progressive deterioration, without external manifestations. The breaks are accompanied by diffuse corrosion, due to lack of lubrication at the time of rope construction.

The fatigue test consists of the repetition, over a large number of cycles, of high stresses in the vehicle structures, so as to reproduce in a conventional manner the technical life of the vehicle itself, i.e. the maximum period of use defined by the manufacturer or the standard. In this way, even in the absence of environmental effects, the long-term behaviour of the vehicle can be verified.

The test stresses are set by the standards or derived from measurements during dynamic strain gauge tests.

A special height-adjustable structure has been built, which allows vehicles up to 6 m in height to be installed. A hydraulic cylinder (50 kN with ± 50 mm stroke) is installed on the crossbeam, which imparts vertical oscillations with adjustable amplitude, frequency and waveform (normally the sinusoidal waveform, universally adopted for such tests, is used).

Recording equipment is used to acquire the data from the various measuring points, applied in the most stressed areas.

The vehicle can be tested complete and suspended, i.e. in the real working conditions, or, if necessary, clamped to the ground, on the floor provided with anchor tracks.

Tests are also carried out on the individual suspension and supporting frame elements, after the shock-absorbing elements have been removed. The element under test is monitored at several points and the hydraulic system is calibrated to reproduce the required stresses.

It is a long and more severe test than the operational situation, but of real value in terms of transport safety. On a few occasions it has in fact led to the failure of some parts, allowing the designer and builder to intervene and recheck.

A new structure consisting of a gantry with a width of 5 m and a height of 3.4 m is equipped with three cylinders of 100 kN with ±100 mm stroke, 50 and 25 kN both with ±50 mm stroke, with the possibility of simultaneous and completely independent operation. Multiaxial forces can therefore be realised on the same sample. The various pistons can reproduce trends acquired in the field by accelerometers, strain gauges or other transducers.

At the end of each fatigue test, as required by most standards, non-destructive checks are carried out on the component in the laboratory to verify the presence of cracks or breaks due to cycling. The non-destructive tests performed by CICPND level II qualified personnel according to UNI EN 473 and ISO 9712 are: visual inspection VT, liquid penetrant PT, magnetoscopy MT and ultrasound UT.

In consideration of the importance of these elements, a specific test procedure, prepared in-house and approved by the Ministry, is foreseen to verify the performance of the vices.

This cycle of tests provides the Supervisory Authority with the elements to judge, in addition to compliance with the regulations, the technical validity of the proposed solutions and ultimately theadmissibility for use of a new vice model.

These tests are sometimes carried out on vices that have been in operation for many years, in order to verify the maintenance of efficiency.

Dimensional checks, spring tests, creep resistance tests, clamping force measurement, performance evaluation, stress relief are carried out.

Test procedures and equipment used are designed and implemented in-house, as there are no unified standards for this sector.

The most significant test is the measurement of the sliding resistance of the vice clamped on the rope, under the conditions set by the manufacturer.

By means of a hydraulic cylinder, the pull is realised and the holding force at the moment of sliding on the rope is recorded by a special load cell.

Suitable strain gauge pins are made to measure the clamping force of clamps and vices.

This is the field in which the greatest efforts have been directed over the last 10 years.

With this technique, it is possible to monitor the stresses in cableway structures both in the laboratory and on the installation in operation, under different load and speed situations.

The test is aimed at comparing the stresses predicted by the designer by means of computer models (F.E.M.) with the actual stresses, in order to verify their admissibility and general acceptance. Static tests are carried out in the laboratory, measuring the stresses at progressive vehicle loads, up to twice the nominal load. The series of tests is conducted on new vehicle models or when major modifications are made to existing vehicles.

On the basis of the results of these preliminary tests, the designer can proceed with any changes in dimensioning, before starting mass production.

After construction of the system, the dynamic tests are carried out, consisting of direct stress measurements at the most significant points of the vehicle structure and vice. The measurements are carried out, under various load and speed conditions, and along the entire route, at the passage on the line supports and at station entrances, where the most important dynamic effects occur. These tests are prescribed by the supervisory authority on all newly built detachable ropeways (4 and 6-seater chairlifts, gondolas), as well as on classic cableways and funiculars.

There has been a considerable evolution in the equipment used, both in terms of an increasing number of measurement sensors available and in terms of manageability in difficult environmental and spatial situations. A laboratory control unit can manage 48 dynamic channels.

On the plant, data acquisition systems allow the simultaneous storage of signals from 100 sensors on autonomous instruments, with subsequent transfer from Memory Card to PC and data processing on site.

Using the radio transmission system, the operator can remain at the station to monitor the test and acquire data in real time. If the line configuration does not allow this, the operator with the receiving equipment travels to the next vehicle.

The grip is subject to particular scrutiny, as it is the element that comes into contact with the station structures when the vehicle enters.

To the static stresses due to the clamping force on the rope, are added those due to impacts.

In the event of excessive stresses, the manufacturer can intervene on the construction or adjustment characteristics of the entry guides, or by modifying the vehicle with shock-absorbing elements. In this way, in addition to the technical advantage, travelling comfort is also improved, a factor particularly appreciated by users.

The recording equipment provides continuous graphs of the stresses at various points of the structure, making it possible to identify the elements on which to intervene and the effect of modifications. Measurements are carried out with the vehicle specially skidded as it enters the stations.

The large number of tests carried out in recent years, using standardised procedures, has made it possible to produce statistics, the subject of reports at international conferences.

Tests have also been carried out using this methodology in other areas of transport and mechanical constructions in general (operating machinery, tanks, cranes, civil structures, etc.).

Strain-gauge tests are performed by qualified personnel holding CICPND level I and III licences according to ISO 9712.
Strain gauge testing of pressure and lifting equipment subjected to inspections by bodies delegated to carry out safety checks is carried out according to UNI 10659 Non-destructive testing - Testing using electrical resistance strain gauges of pressure and lifting equipment. Generalities

Below are some examples of stress analysis that the Laboratory is able to perform:

• stress analysis on cableway components;
• stress analysis on railway components;
• stress analysis on pressure vessels;
• stress analysis on lifting systems;
• stress analysis on presses.

Methodology for strain gauge tests on cableway vehicles

Strain gauge tests on components

In addition to cableway tests, the laboratory carries out tests on components required for towing vehicles or trailers. Coupling devices for motor vehicles are all parts and devices mounted on the structure, chassis and bodywork of vehicles that enable towing and towed vehicles to be connected. They also include fixed or removable parts for attaching, adjusting or operating these coupling devices.

The towing devices shall meet the following requirements

• ensure compatibility when coupling between motor vehicles and various types of trailers;
• ensure safe coupling of vehicles under all conditions of use;
• ensure safe coupling and uncoupling.

The standards lay down the construction characteristics and test methods for the towbar, towing bars and eyes. The tests are carried out according to CUNA standards or Directives 89/173/EEC, 97/24 EEC and depending on the manufacturer's choice, the test can be performed in static or dynamic mode. In the static regime, the testing machines allow testing of elements up to 10 MN, while in the dynamic regime the maximum applicable pulsating forces are up to 100 kN. Multi-axial dynamic tests can also be performed by synchronising the various hydraulic pistons of 25, 50 and 100 kN.

Drawings of some towing devices

By applying the methods indicated, mechanical tests can also be carried out in other areas, such as tow hooks, material transport vehicles, rope clamps, operating machines, chains and marine applications.

Pull-out strength of a plastic joint

A joint consisting of two pieces of high-density plastic pipe, connected by a collar, is subjected to a tensile test. The collar is locked to the tubes by electro-welding (local melting of the plastic by means of an electrical resistor embedded in the collar itself). The ends of the tubes are sealed and the assembly subjected to internal pressure. In the tensile phase, both the mechanical strength of the connection and the maintenance of the internal pressure during the test are verified. At maximum load, the plastic material begins to permanently deform, with high elongation at constant load.

Slip resistance of rope clamps

The clamps are installed in the machine, closed on a piece of the rope for which they are intended.
The nuts are tightened with controlled torque, then progressive tensile stress is applied to the end of the clamp, until creep occurs. Based on the values found, the manufacturer determines the limits of use of the equipment.

Compression test

Bales of dried municipal solid waste, wrapped in polyethylene foil, were subjected to compression testing.
On the basis of the test results, the maximum number of stacking planes of the bales could be determined.

Static and dynamic tests according to CUNA and the European Directive

Static and dynamic tests are carried out on towbars in order to verify the construction characteristics and strength of the mechanical couplings.

Dynamic measurements on the vehicle

The accelerations produced on a vehicle when passing over traffic calming devices and driving roundabouts were determined experimentally in a city environment. Various sensors were positioned to detect vertical and lateral accelerations while travelling at increasing speeds in a range between 20 and 60 km/h. This graph shows an example of an acceleration spectrum detected as the vehicle passes over speed bumps:

Measurement of the brake application time on a carrier rope or rail

The test consists of measuring the time elapsing between the brake closing command and the actual tightening of the clamps on the carrying rope or rail in the case of a funicular.

Breakage tests on wooden railings for cycle tracks

Having applied a special bracket on the upper handrail and central upright, this, orthogonally to the parapet, was connected to a hydraulic piston by means of a chain with a load cell in between. By slowly retracting the piston by means of a special hydraulic power unit, a force was applied to the parapet and simultaneously recorded the values, as a function of time, of the applied force provided by the dynamometer and the displacement provided by the wire potentiometer.

Testing the maximum working load of a continuous-loop sling

If the continuous loop sling withstands a force equivalent to 7 times the maximum working load (WLL) and if, during the test, the sheath does not break at a force equivalent to less than 2 times the maximum working load (WLL), the sample has passed the test. A test beyond this force is not required.

Tests on constituent parts of railways

Testing of components used in the construction of via ferratas. Laboratory and in situ tests on nails, connectors, ropes and dissipators according to UNI standards or client specifications.

Determination of zinc areic mass

Testing to determine the mass of zinc coating and zinc alloys on steel wires and drawn steel products with circular or other types of cross section. The mass of the coating is determined by the gravimetric method (UNI EN 10244-2).

Creep test on clamps for tensile structures or stadium roofs

In order to determine the creep force of clamps on closed ropes, the laboratory is equipped with a thrust system of up to 1000 kN that accepts Ø 120 mm ropes. The maximum torque that can be applied to the bolt is 2000 Nm.