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RailTec Cold Bolt Hole Expansion (CBX) Kit

The preferred method for preventing fatigue crack issues in rail bolt holes and extending their service life.

RailTec Cold Bolt Hole Expansion (CBX)

As the appointed global reseller of Fatigue Technology (FTI), we can support with RailTec Cold Bolt Hole Expansion (CBX) – a preventative process to reduce rail breakages, track-related incidents and derailments. When trains pass over the Insulated Block Joint and any fishplated rail ends, the constant stresses and forces exerted on the rail ends are concentrated at the bolt hole. The RailTec CBX process is designed to arrest crack propagation and extend the fatigue life of bolt holes. The CBX kit itself includes split sleeves, application mandrel and a mandrel checking gauge which contractors can use to apply the process to drilled holes.

The technique is superior to any other method of cold working bolt holes out there. This is because the process generates a more controllable distribution of compressive stress around a hole and through the bore, without damaging the integrity of the hole. Fatigue test data comparing as-drilled holes with cold expanded holes revealed that the cold expanded holes performed better in improving the fatigue life. 

How does the process work?

The process is accomplished by pulling a tapered mandrel, pre-fitted with a lubricated split sleeve through a hole in the rail. The disposable sleeve reduces the mandrel pull force, ensuring uniform radial expansion of the hole and allows one-sided processing.

Cold hole expansion counteracts the weaknesses of a hole by creating a compressive residual stress field around it. This effectively shields the hole from cyclic tensile stress that causes cracks to form and grow, improving the rail’s fatigue and damage tolerance.

Rails with small fatigue cracks can be reworked as part of routine maintenance on all main or branch line tracks and safely returned to services. The system can be used during the manufacture of rails, level crossings, frogs, and switches.

Key benefits include:

  • A proven system in use worldwide for over 40 years and over 30 years by Network Rail
  • Reduces track maintenance costs
  • Significantly extends inspection and maintenance cycles
  • Increases the structural integrity and safety of the line
  • Prevents the growth of micro cracks (star cracks) in holes
  • A one-sided operation that’s simple and easy to use
  • Typically improves the fatigue life of bolt holes by at least 3:1
  • Applicable to new track environments 
  • Cost-effective alternative to replacing the rail
  • Holes in existing rails can be cold hole expanded and safely returned to service, providing added protection against undetected cracks
  • Can be applied to fish plates, wheels, bridges and other structures

How we can support you with the process

If you choose to purchase our RailTec Cold Hole Expansion (CBX) kit, our qualified staff will provide you with hands-on on-site training and guidance on how to install it. We can train both national and international clients. Whoever is installing the RailTec CBX technology will need to hold the appropriate certification from FTI in order to use the system. Please contact us for more information.

Download the full technical specification

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