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Hollow Switch Ties (HST®) Rotary Assist

voestalpine Nortrak’s Rotary Assist was originally developed to complement Nortrak’s Hollow Switch Ties System. At the time of its development, competing systems were large, bulky, inefficient and ineffective.

After evaluating requirements for a rear switch throw assist the following guidelines were established.

  • Must be very stiff mechanically.
  • Simple adjustment with common hand tools in maintainers kit.
  • Light weight components to eliminate the need for installation lifting equipment.
  • Common industrial sub-components permitting local replacement.
  • Useable in all existing applications including both wood and concrete ties.

To meet these requirements Nortrak produces a light weight, mechanically efficient rear assist mechanism that has proven to be effective and cost competitive. The Rotary Assist couples to the front Throw Rod of the turnouts and through a system of bellcranks and torsion shafts transmits a force to one of the rear switch rods in the turnout assuring that the switch lie fully against the stock rail along the length of the switch. The Rotary Assist generally uses two torsion shafts connected end to end using a slip joint to compensate for changes in distance between the Throw Rod and rear switch rod due to installation variance, temperature, dynamic loads or tie spacing making it ideal for retrofits. Lost motion adjustment at the rear rod is obtained by using a very simple arrangement of a threaded rod, jam nuts and a bronze bearing block assuring simple adjustment and long life. 

Sub-components of the Rotary Assist have been chosen to use commonly available Power Transmission component at all location possible. For example the rotary bearings are common conveyor belt pillow block bearings. The torsional shafts are designed to use common components used in farm equipment Power Take Off (PTO) shafts and truck drivelines.

These components when installed into Nortrak’s Rotary Assist combine to produce a robust, dependable mechanism to assure that the switch is fully in position before the passage of vehicles.