Threadlocking underpins trams reliability

In the development of its new tram model, the TMK 2200, the Croatian locomotive, tram and train builder, Končar, worked closely with Henkel’s engineering adhesive experts to select the best products for use in both assembly and maintenance.  In the process LOCTITE® products were identified that would withstand maximum dynamic loads and maintain the tram’s reliability over a potential service life of 35 years.  This is especially important as, for each tram, only 5% of repair maintenance time is allowed.

In Zagreb alone, Končar trams transport around 200 million people a year; the service is free of charge, a move introduced to reduce traffic in the city.  Naturally, passenger safety is of paramount importance and as the tram wheels need to sustain loads of up to 60 tons, each threaded component on the wheel must be securely locked in place.

Threaded assemblies generally fail through loss of bolt tension and one of the main reasons is self-loosening.  It is caused by any type of dynamic load, such as vibration or changes in temperature, insufficient clamp load or poorly fitting parts, allowing relative movement.  These load changes lead to short term frictionless situations where the bolt unwinds from the nut.  And the sum of these very small movements ultimately results in the loosening of the threaded assembly.

LOCTITE thread locking adhesives are the ideal method of addressing this problem both for automotive OEMs and those involved in maintenance and repair.  These are anaerobic adhesives which means they only cure in the absence of air.  This enables the adhesive, when applied to a bolt, to stay liquid almost indefinitely until the nut is applied.  With no air in the contact areas the adhesive then solidifies to a tough thermoset plastic. The locked assembly not only resists vibrational loosening but also prevents corrosion yet can be dismantled for maintenance, if required.

One of the main applications for LOCTITE thread lockers is a critical one, securing six studs which connect the oscillating arm onto the gearbox.  For this purpose, Končar uses LOCTITE 243, a medium strength product that has been recently upgraded to provide good bond strength even on contaminated surfaces.  It also provides higher temperature resistance and performs well on passive metals without an activator.  The same product is used for the delicate and demanding task of securing 12 radial bolts which hold the tram wheels in place.