How Lead Screws Enable World-Class Rail Car Design

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

In particular, engineers have brought several innovations to designs for two critical subsystems, braking and door and 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. Regardless of location, rail car operations 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 tardy riders' entrance or exit; 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 several solutions to rail car design challenges. Electric actuation avoids the need for pneumatic or hydraulic plumbing and facilitates mounting without compromising structural members.

Brake design benefits from lead screw actuators. Long-stroke actuation is far simpler with lead screws than 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 their actuator. Even application is often tricky 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 regular operation.)

The 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 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 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 many mount options, enabling 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. 

Design Parameters That Benefit You

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

The Helix Linear Technologies 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 to service the expanding and evolving customer-driven market for precision linear motion products.

Whether you need Acme, Trapezoidal, or high-lead threads with a precision low-backlash nut or a state-of-the-art anti-backlash design, Helix Linear Technologies delivers the highest-quality linear motion products for the transportation industry.