NR TWI 2G029 ISSUE 2 PDF

Introduction

Cold expansion is a process that reduces substantially the risk of cracking at fishbolt holes.

Cold expansion improves the fatigue resistance of fishbolt holes in:

• Flat-bottom and bullhead-rail

• EN13674 Normal Grade steel

• EN13674 Standard Grade steel

• Heat-treated pearlitic grades, including head-hardened rails

Premium Steel rail (High Performance, or HP Rail) can be cold expanded, but difficulty might be encountered in drilling and expanding the fishbolt holes due to the increased hardness of the web.

In the process described here, cold expansion is achieved by pulling a tapered mandrel through a rail hole; the rail hole and the tapered mandrel are separated by a thin, dry-lubricated, stainless steel split sleeve. The split sleeve is a vital part of the process as it guarantees that the metal around the rail hole is forced radially outwards by the mandrel, rather than pulled through with it, so that the material around the hole is placed in compression when the mandrel is removed.