The force-measuring device HZM with user approval from DB Netz AG
The HZM system is a comprehensive software package for detection and assessment of the forces measured on the point setting system with the force-measuring device
Comparison of the setting-resistance and setting-force curve of a point machine with friction coupling on stiff point/point machine (blue curve setting resistance (UMW), green curve setting force (STK)
Comparison of the setting-resistance and setting-force curve of a point machine with friction coupling on a point/point machine without failures (blue curve setting resistance (UMW), green curve setting force (STK))

Growing need for system-dependent point inspection with force-measurement

Point inspections and centrally-administered inspection databases are an important issue for mainline operators and they are also gaining significance for operators of public transport. In both areas, mainline and tram, the stress factors for route components have increased markedly in the last decades. All over Europe, mainline and tram operators are realising the necessity of performing extensive system-dependent point inspection with force-measurement on a regular basis. This entails developing customised standards for each system and optimal use of the measuring technology by trained staff.

1 Importance of point inspection

The set-up of centrally-administered inspection databases is currently a major issue for mainline operators, and an area where the Deutsche Bahn (DB) has taken on a pioneering role. DB is now attributing completely new priority to point inspection and the ensuing maintenance scope. The integrated inspection system (IIS) which they introduced is an SAP-based central database which will not only be a store of knowledge for the future, but already revealing targeted maintenance deficits. To date, this is something the tram sector has paid little attention to. HANNING & KAHL assists transport authorities by performing service tasks and providing testing and service equipment over a long time period: from commissioning to inspection and maintenance to general overhauls of individual system components. Some years ago, it already became obvious that point inspection would grow in importance for tram systems, too. On account of the much lower average speeds, transport authorities often underestimate the importance of preventive measures such as force measurements within the scope of regular inspection. While the inspection order for mainline systems can most likely not be transferred 1:1 to tram systems, this, however, does not mean that the scope in the latter system must be smaller. Thus for example grooved-rail points in under-floor arrangement with crossing road traffic constitute a long underestimated stress factor. Mainline operations are already governed by strict standardization procedures which precisely fit heavy rail conditions. Up to now, attempts have been made to transfer these standards to trams. However, as the two systems are very different, it is expedient and vital to determine a separate and standardised inspection procedure. One example is the holding forces for points. We only have actual measuring values from mainline operations, but these are much too high for tram points. In addition, transport authorities are more and more subjected to certification pressure, and documentation obligation with regard to inspection and repair data is becoming more complex. While there are still no legal specifications, testing procedures are playing a greater role. In the event of an accident, for example, it is important to be able to verify that maintenance has been performed correctly and was not the cause of the accident.

2 Changing stress factors along the route

In mainline operations, the stress factor for the route components has risen significantly in the last decades. On the one hand, on account of higher line and average speeds – in particular on regional lines – and also on account of the use of different vehicle types due to partial privatisation of operators. In the tram sector, the stress factor has even increased in square of speed in the last 20 to 30 years. One reason for this is the increase in headway – a10-minute headway has meanwhile often become a 50-second headway. However, in many cases, it is not possible to raise the maximum speed in the city. This calls for more acute acceleration and braking manoeuvres which has multiplied traction sand use in recent years causing points to silt up. DB meanwhile regulates the use of traction sand because in mainline operations, too, the protection systems are more and more prone to silting up. The vehicles themselves have also changed: vehicle lengths and train weight have doubled on average in the last 30 years. To keep axle loads bearable, the numbers of axles have also been increased. The curve radii of new lines are generally smaller in order to hold more tracks in a smaller space. While DB has the specification that the point radius must not be below 100 metres, wheel radii of 25 metres are found in tram operations. Another stress factor which should not be underestimated is low-floor technology. The rigid axles of the mainline trains oscillating in the track ensure optimum curve compensation and the wheel profile remains intact. On low-floor vehicles, on the other hand, the axles are offset and sine run is not possible due to the single wheel bearing. This leads to completely changed and unpredictable wear patterns on wheel, rail and point. In addition, natural wheel shunt is lost, and sliding contacts have to generate artificial wheel shunt. This, in turn, leads to increased maintenance. All these factors indicate that the stress factor has increased manifold in the route of tram systems. And thus the requirements for maintenance of the system have also risen: measures which were expedient 30 years ago no longer suffice; continuous measuring is becoming more and more important.

3 Manufacturing procedures change the framework conditions

The framework conditions for both systems have changed as a result of new manufacturing procedures for route components. Just one example is increased point tongue inherent tension. Whereas the tongue profile used to be milled and planed from solid, today these profiles are most widely rolled for exact fit, meaning that identical tongue profiles of the same material now call for much higher bending forces. Furthermore, one repeatedly sees how important it is to record the actual dimensions, e.g. the length of the point tongues, as these can vary greatly from point to point even when of the same design. In addition, setting and holding forces of the point machines often require marginal reserves. Standards for mainline operations dictate that every drive mechanism has a setting force reserve of 20 per cent. This standard also currently applies for the tram sector but it is becoming increasingly more difficult to attain this setting-force reserve. As the points tongues are becoming shorter and shorter, in extreme cases up to 3 kN are meanwhile required per point tongue to hold the point in end position – in other words 6 kN per point in total. The setting force of the drive mechanisms is 7 kN and thus it is not only becoming more challenging to ensure 20 per cent reserve, but in emergencies manual setting is almost impossible. One can see that these factors will make regular force measurements in point systems of all designs more important in mainline and in tram operations going forward. The more measurements are performed, the clearer it will become that that new and appropriate provisions have to be found.

4 Customised measurements and inspections

There are fundamental differences between mainline and tram systems resulting in different procedures with regard to measurements and inspections. Standardised inspection stipulations must therefore cater for the concrete requirements of the two systems. One example: drive mechanisms with external locks on the tongue devices mounted beside the tracks are most common in mainline applications; in tram applications, on the other hand, drive mechanisms with internal locks installed in the middle of the tracks are more frequent. Hydraulics, electro-mechanics and electro-magnets are the force sources used. Such different conditions mean characteristically different setting force and setting-resistance curves which can have varying impact in the systems. Equally, the holding and trailing forces must be accorded different importance. The result: all operators require intensive training in order to be able to read and interpret these curves and to decide on the correct maintenance and repair measures. In order to be able to detect anomalies in these conditions before a malfunction occurs, one also needs a system-independent early-warning system which should include thorough point inspection, force, pressure and gauge measuring, and measurements in the area of the points. Problems which develop slowly can only be detected with regular, recurring measurements. This is the only way to enable early measures to be taken before a far-reaching malfunction occurs. Centrally-administered databases are a vital tool; with the data collected over the years, transport authorities can identify with which combination of different technologies and in which geographic areas the most or the least malfunctions occur. With extensive knowledge of these correlations it is possible to establish changes in the system parameters and thus set up a largely error-tolerant system. On the basis of their decades of experience, HANNING & KAHL has developed a conclusive measuring concept for the purpose, which is continuously extended and adapted as requirements change. The concept comprises a designated database and extensive measuring equipment, for example the force-measuring device HZM and different accessories. In comprehensive training workshops HANNING & KAHL staff prepare transport authority teams for the new tasks. The East-Westphalian company also offers wear assessment of the drive technology which establishes when a point machine must be overhauled. We are also working on distance-based measurement in order to ascertain when locks are really worn. Increased stress factors are an international phenomenon and thus rail operators all over Europe are recognising the urgency of the problems and the necessity of system-dependent point inspection with force measurements on a regular and wide basis. It is clear that when correctly used, the measuring technology which is available today can shorten corporate discussions before pending investments, e.g. repairs, because the measuring results clearly speak for themselves to the benefit of the service departments.