APPLICATION TECHNOLOGY
The use of lockbolts in rail track applications
The safety critical nature of rail track applications such as switches and crossings, arc rail suppression and cold hole expansion lends itself perfectly to the use of a range of lockbolts, or as they are commonly known, multigroove locking pins (MGLPs).
I
nvolved in the rail industry for over 40 years and currently with Huck fasteners and tooling solutions in use on a number of applications in rail track Alcoa Fastening Systems explains more.
How lockbolts work Lockbolts provide greater vibration resistance than common nuts and bolts and can withstand the vibration of rail tracks without working loose. Lockbolting technology works on a different principle to regular bolting, where instead of a threaded nut, a cylindrical ‘collar’ is used that has a smooth inside bore. The collar is placed over a pin with locking grooves that either follow the form of annular grooves or a special form helical thread. During installation this collar is ‘swaged’, permanently deforming the collar material into the locking grooves of the pin. This joining process offers a number of significant advantages
over regular bolting. Firstly, the joint is maintenance free as once the collar is swaged, it will not work loose under vibration. This offers significant savings in labour costs by not having to re-torque bolts periodically in order to ensure joint integrity as well as safety benefits, in that the joint is guaranteed to maintain clamp and not become compromised over time. Additionally the installation process is fully controlled by the
tool, the operator only starts the installation. The installation tool is designed in such a way that a perfect installation is achieved every time. Operators need training in the safe use of the tool only. The tooling solutions offer additional benefits for the end-user.
Firstly a much quicker installation time compared with conventional bolts, typically a Huck C50L product will install in just 55 seconds. The tooling has the additional capability of performing cold hole expansion with a simple and effective mandrel. Huck offer two main types of C50L family products for the rail
sector, the C50LR lockbolt and the C50LH lockstud, both fully approved. The C50LR offers easy and quick installation in applications where clearance is not an issue where as the C50LH is used where access is an issue from one side. The installation sequence for Huck C50LR lockbolts is shown
in Figure 1. In an installed lockbolt there is near full contact between
the pin’s annular groves and collar material, whereas with a conventional nut and bolt there is significantly less surface contact. It is this extra contact that leads to the superior vibration resistance of the lockbolt.
Switch and crossing applications Typical switch and crossing (S&C) applications include:
Crossings: 1. FB checked block joint. 2. FB CWR tight joint. 3. Non-raised checkrail blocks. 4. Vee splice. 5. All vee blocks. 6. Wing rail blocks (limited access).
Switches: 1. Stockrail bolts. 2. Distance block (CHOG). 3. Back heel block.
The initial installation costs of lockbolts are little more than
the traditional types of bolt used on track, but the subsequent elimination of maintenance makes the whole life cost very attractive. In new S&C (switch and crossing) work, these fasteners eliminate forged blocks or cast washers and can save money overall. Significant savings are possible in other cases, for example
broken stockrail bolt replacement. Experience has shown that on most sites bolts can be replaced with Huck fasteners without the need for track possessions. If a section of switches and crossings is systematically
converted to Huck fasteners then savings will emerge from the following benefits:
• A reduction in costly checking and maintenance by patrolmen. • Patrol staff will be less exposed to risk; by reduction of bolt tightening work in the four foot more patrolling can be done from the cess.
• S&C secured with lockbolts will not develop the wear and tear typical of bolted units. There will be less need for fettling, crossing welding and other attention, and component life will be extended even when retrofitted to old layouts.
• Major concentrations of S&C offer great potential, whether in running lines or sidings. On other routes where CWR (Continuous Welded Rail) is standard many of the issues associated with using threaded, maintenance prone fasteners can be eliminated.
122 Fastener + Fixing Magazine • Issue 72 November 2011
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