scope:

This SIN shall apply to all RT60/NR60 Switches where the slide and roller baseplate fixings are Vossloh Type Screws Ss8-160. Most RT60 and all NR60 S&C is included in this, with the exceptions of:-

• RT60 with direct fix shoulders throughout, produced by Balfour Beatty are excluded.
• RT60 with VAPE screws fixing the slide baseplates, produced by Corus Cogifer are excluded.

Background and purpose

There have been a small number of incidents where Vossloh type baseplate screws have broken at slide baseplates of RT60/NR60 S&C.

Research into these failures has highlighted a significant problem with the size of screw used in this design of this S&C. The baseplates are secured with Vossloh type Ss8 screws, which have been used successfully for many years to fasten baseplates to concrete bearers. However, in some designs of RT60 (and all NR60) a different screw length was selected due to the difference in thickness of the baseplates from previous designs.

The Vossloh screw system is designed so that the insert cast into the bearer replicates the form of the screw with the parallel shank of the screw engaged within the insert (as shown on RE/PW/762 for the Vossloh Ss8-182 screw used in Vertical S&C). In some designs of RT60 and NR60 the specified screw (Ss8-160) leaves the end of the parallel shank approximately level with the top of the bearer.

In switch panels this is made worse by the use of Schwihag slide baseplates, where a thicker 10mm baseplate pad is used, this reduces the engagement by a further 5mm.

This creates the potential for fatigue failure of the screws. The risk of failure is greatest in the following conditions:-

• where the turnout is subject to freight traffic, principally in the trailing direction; and or
• where the switch rails are already known to be subject to high rates of wear, with C switches being most at risk.

The following actions are required to repair any broken screws found and replace those that are subject to fatigue failure.