Lead Screw Actuators Enable World Class Rail Car Design

Christopher Nook by Christopher Nook

Globally, rail car systems build-out is projected for strong growth well into the foreseeable future. The design of rail car components has seen similar steady movement.

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Globally, rail car systems build-out is projected for strong growth well into the foreseeable future. The design of rail car components has seen similar steady movement. Enhanced design approaches, materials developments, and engineering breakthroughs all contribute to new levels of rider comfort, as well as safety, system up time, and price-performance.

In particular, engineers have brought a number of innovations to designs for two key subsystems, braking and door and/or platform barrier actuation. Both subsystems can benefit from lead screws, in large part because the many types and options of lead screws give designers a large arsenal of solutions for a broad range of design objectives.

The Challenge:

The most critical dilemma facing brake and door systems for rail cars is the need for uncompromising safety—usually a high-cost design objective—in the face of ever-present price pressures. But that’s far from the totality of challenges, which include:

  • Maintainability. Rail car operations regardless of location face unprecedented labor challenges, so the simpler and more modular the design, the better.
  • Reliability. Rail cars are unmercifully stressed in every hour of operation, whether from rushed and careless riders, ambient conditions, or rail or roadbed realities.
  • Resistance to vibration and movement. Everything from imperfect rail to out-of-round wheels adds to sway, vibration, and harshness, increasing strain on components.

Two examples illustrate the issues. First, doors should close rapidly—yet prevent entrapment during entrance or exit of tardy riders; and doors must remain closed while in motion—yet be easily opened by hand in the event of power loss or accident. Second, brakes must be positive—yet avoid skidding or undue wheel/rail wear; and they must automatically deploy in the event of power loss, operator incapacitation, or signal system demands.


The Solution:

Lead screw actuators bring a number of solutions to rail car design challenges. Electric actuation avoids the need for pneumatic or hydraulic plumbing, plus it facilitates mounting without compromise to structural members.
 Brake design benefits from lead screw actuators. Long-stroke actuation is far simpler with lead screws than with hydraulic cylinders, allowing thicker shoes for longer field life. Beam brake designs are simplified with lead screw actuation, as the beams on both sides can each be deployed evenly with its own actuator. Even application is often difficult with single-cylinder hydraulic or air systems. And lead screw mounting options enable quick change-out of actuators.

Safety-enhanced door and platform barrier designs likewise benefit from lead screw actuators. In addition to their rapid positional actuation, lead screws with efficiency greater than 50% are back-drivable. Thus, doors or platform barriers employing them can be forced open by hand in an emergency. (Relatively simple electric brake/clamp systems can prevent back-drive during normal operation.)

Reliability of lead screw actuators, while highly dependent on application circumstances and protection from ambient conditions, is enhanced by precision screw machining and nut molding, employment of wear-resistant and/or self-lubricating plastics, and ISO 9000-certified manufacturing and assembly.

Our catalog includes relevant discussions of materials and reliability calculations, including pressure-velocity (PV) and other load-dependent attributes, critical speed, temperature, and frictional and/or lubrication options. The form factor and helix angle of lead and acme screws can be varied over a wide range, making it possible to optimize components to the requirements of most applications.

These actuators are available in a wide variety of mount options that enable quick (and accurate) field replacement even by minimally-trained maintenance personnel.

Precision lead screw actuators simplify the design of safe, quiet, and reliable power-driven positioning. There’s more information about them here in our blog. See “Lead Screws vs Ball Screws: It's All about the Application”; “Questions & Answers about Lead Screws in Mechanical Design”; and “Five Key Steps for Selecting Lead Screw Motion Control Systems”.

Helix™ Parameters That Benefit You

  • Maintenance-friendly—long life expectancy combines with ease of replacement
  • Quiet
  • Powerful—linear actuators accommodate loads up to 6000N
  • Designed to enhance safety
  • Modular—our engineering approach enables versatile, customizable design to meet specific application needs.
  • Installed simply, especially compared to hydraulic and pneumatic linear actuator systems, without space-robbing hoses or pumps.
  • User friendly
  • Compact and light weight
  • Space-saving
  • Smooth in operation
  • Precisely controllable
  • Energy efficient

The Helix Advantage

Helix Linear Technologies, an ISO 9000-certified company, offers the broadest product line of any lead screw manufacturer, including a full line of rolled, milled, or ground screws and nuts, in standard and customizable sizes. The company provides the flexibility required to service the expanding and evolving customer-driven market for precision linear motion products.

Whether you need Acme, Trapezoidal, or Speedy® (high lead) threads with a precision low-backlash nut, or a state-of-the-art anti-backlash design, Helix delivers the highest quality products of exceptional value to its customers.