A technical and commercial balancing act

Seventy-one and one-half tons (143,000 pounds) is the average static load that a freight car truck experiences in typical North American heavy-haul operation. When traveling at 80 mph, the speed limit for freight trains on class 5 track, that load generates additional dynamic force and enough stress to micro-liquefy steel at the wheel/rail interface. Whether it’s a high-speed passenger bogie, or a high-load-capacity freight car truck, recognition should be given to the manufacturers who wrestle with the operating environment, the commercial pressures, the complex regulation process, and the engineering challenges of such multifaceted and leading-edge equipment.

Operating conditions and engineering hurdles can be dramatically different across the vast territory of a typical freight truck. The different commodities (rock vs. petroleum products), the different track conditions (tangent vs. 12 degree curves), and the different wheel load conditions (8,000 pounds vs. 35,000 pounds) are just a small example of the design variables that play a very large role in the development of these systems. While these extreme conditions must be considered when developing cutting edge solutions, it is also true that the primary operational needs have not changed much and continue to focus engineering efforts toward reducing weight and lowering stresses.

General industry sentiment is that the selection of freight car components has been driven by the low cost of the initial investment; this is a short-sighted view in many cases. However, more decision makers are beginning to appreciate and consider the total cost of ownership and manufacturers are stating that they are seeing more frequent focus on the bigger picture. The total “real” cost is now a conversation and the lifetime cost to the complete system is under review. Another common sentiment is that the effort required for certification of equipment has increased significantly. Industry OEMs are attempting to benefit from economies of scale both technically and commercially by utilizing good designs across multiple platforms. One driver of this situation has been the introduction of more offshore parts manufacturers with varying levels of quality that cause the regulation and certification process to become more skeptical and arduous.

A truck is only as good as its weakest component. Some of these components do not add a large cost and are somewhat easily adapted to traditional three-piece truck designs, while others are more costly and involved.

Driving factors regarding performance, regulation, and commercial acceptance of advanced components:

• Lower energy consumption helps the rail industry compete with other forms of transportation and comply with environmental mandates, and contributes to a better environment.

• A lower stress condition results in safer operations, less track damage, and less wear on vehicles and lading. Track friendly concepts (reduction of wheel and rail wear) are also under consideration in the event that the industry moves toward track usage models that would calculate a usage fee according to the level of stress involved.

• Reducing lifecycle cost by lowering maintenance requirements saves money for car owners, operators, and consumers.

Technical advancements

The Adapter Plus® pedestal pad-liner-bearing adapter system by Amsted Rail uses a resilient polymer primary suspension pad to protect the side frame pedestal and thrust lugs from wear. It also provides for passive steering to improve wheel tread and flange life. When a car enters a curve, the patented polymer pad design deflects in combined shear and compression, storing energy as it negotiates the curve. As the car leaves the curve and enters tangent track, the stored energy is released, restoring the axle to the normal centered position.

Older all-metal adapters had the tendency to “stick” out of position due to friction, which caused excessive wheel flange contact as the axles ran out of parallel on tangent track. Passive steering elements were implemented to correct for this situation. The pads also maintain the position of each side frame so that it is centered above the bearing and more evenly distributes the load on each bearing, both of which extend bearing life. This system promotes a 25% longer expected wheel wear life and longer roller bearing life as compared to other M-976 adapters.

Side bearings have evolved dramatically in the past 30 years. A component that was once as simple as a steel block providing a solid stop has developed into one of the best dollar-for-dollar investments for improved truck stability and performance. Constant contact side bearings (CCSBs) have been around since the 1970s but much of the awareness, development, and understanding occurred after the industry embraced the benefits of long travel CCSBs in the late ’90s. CCSBs were then mandated by the AAR in 2002 on all new railcars. The primary functions of CCSBs are threefold: 1) improve curve negotiation, 2) dampen car body roll, and 3) positively affect the truck hunting threshold.

Long travel retrofit side bearings have been evolving since their introduction in 2004. Proactively addressing the pending tank car ride quality improvement mandate, engineers have developed side bearings that can be installed on a tank car fleet without having to replace an expensive component like a bolster. This application was challenging for many reasons but with advanced engineering expertise and R&D capabilities, Miner Enterprises Inc. worked with end users to address the situation. In 2014, Miner released the latest model to the family, the TCC-45-LTLP-C, which is a bolt-on application to address the need for ease of installation.

An impressive example of side bearing innovation is Miner’s TCC-IV, which was developed in response to the high performance demands of car types such as intermodal doublestack well cars. The TCC-IV has combined advancements in metallurgical processes, polymer engineering and the introduction of high performance plastics to combat fatigue and heat degradation which are present in high speed, high mileage services.

Braking performance has been extensively evaluated over the years and the railroad industry is recognizing that braking performance can only be improved by taking a systems approach to solving problems. Brake beam designs must address the small details of adjacent component interaction and consider the components both upstream and downstream in the system. Brake beams have evolved with the needs of the industry and have addressed key aspects of braking in relation to the next component of the system. While manufacturers continue to monitor conditions in the brake shoe and wheel tread areas, they also consider the brake lever, strut pin, and side frame wear liners as critical areas of interest. Recently, diagonally opposite wear conditions on wheel flanges have been a driver in brake system research.

A significant step forward in brake beam innovation was the offering of a correction angle in the brake head to reduce uneven brake shoe wear by up to 50%. Many of the recent advancements in braking systems are focused at the interface of the brake beam with the adjacent components. As an example, consider the interface of the brake lever and strut pin in the brake lever slot. A positive stop in the strut and splined strut pin bushings (patented by Miner Enterprises) are ways to provide a consistent performing and longer lasting beam that reduces maintenance costs and keeps truck assemblies in service for longer periods of time.

Another major contributor to wear in the brake beam is a “burnt” brake head due to loose or missing brake shoes. Engineers searched for reasons that a brake shoe would be loose or missing and determined that incorrect insertion of the brake shoe key is often the primary factor. Engineers then developed features into the Miner Series 2008 brake beam with a zero interference key guide (patented) to provide improved key installation, eliminating the risk of improperly inserted keys. By addressing component interface, the new design helps protect the investment in the brake shoe and maximizes shoe life. This small detail relates to improved wheel life by working to better secure the brake shoe in the correct position relative to the wheel tread.

With more than 100 years of advancement, both Amsted Rail/ASF-Keystone® and Wabtec/Standard Car Truck/Barber design and manufacture a range of complete truck systems such as the Motion Control®, the lightest M-976 (AAR Truck Certification Standard) truck available on the market today, and the S-2-E, which boasts advanced curving and high speed stability characteristics. These advanced suspension designs improve overall performance characteristics for both empty and loaded conditions compared to earlier configurations and should be seriously considered when selecting new equipment.

The next step in truck & component advancement, both by the AAR and by truck OEMs, is focused on the safer, better performing and lower cost systems. The M-976 Standard is in the process of being updated to address loaded car hunting problems that have occurred with some currently approved trucks. The test for curved track rolling resistance is likely to be replaced in the updated standard with something thought to better reflect field performance. OEMs are also re-evaluating their current offerings in reference to these anticipated changes, and looking at modifications that will improve performance to meet the proposed new standards. The goals are to improve wheel life, improve ride quality, improve suspension component life, reduce the stress state of the rail, and improve safety.

Current certified truck offerings are a basic three-piece design consisting of a bolster and two side frames. Warp restraint is provided by the bearing adapters and the secondary suspension, without any supplemental devices. However, supplemental devices, such as frame bracing, cross links, or spring planks, might be necessary to meet the new requirements as these components would basically tie the side frames or axles together in a manner that would provide additional truck stability. Unfortunately, most of these types of performance improvements come at the price of additional weight, additional up-front cost, and additional maintenance costs even though current research is likely to result in some novel configurations of these systems. Historically, these devices have been largely rejected by the industry except in some niche markets due to the aforementioned issues. Supplemental devices have been viewed as not being worth the marginal performance improvements when compared to the traditional three-piece truck.

Prior to M-976, truck OEMs supplied different car types based on different performance requirements such as high speed stability, curving, and customer preference. Implementation of M-976 removed much of that diversity by combining performance requirements into one standard. Now, if a car will operate at 286,000 pounds gross rail load, regardless of type, that vehicle will include M-976 certified trucks. Intermodal cars, autoracks, and some utility cars will use special trucks for their unique applications, but the variations are not as prevalent as they once were. When M-976 was implemented in 2003 there were cost increases associated with the addition of improved friction wedge systems, long travel CCSBs, and primary suspension pads. Performance improvements were measurable and positive.

The current issue is whether the cost-benefit proposition has changed enough to mandate higher performance standards that might require the use of supplemental devices for rail life extension in light of increasing axle loads, more hazmat shipping, and the onset of rolling contact fatigue (RCF). Certain advanced truck features are capable of enhancing wheelset steering and railcar stability while reducing wheel/rail forces that lead to RCF, but at the cost of additional complexity, increased weight, and associated maintenance costs. The industry must also address the fact that premium products are not always embraced, since the North American Interchange System allows for component replacement with non-premium products, unless specifically required to be replaced in-kind per the AAR Field Manual.

Looking far ahead, Amsted has developed an Advanced Swing Motion® truck, in conjunction with Amtrak, that incorporates hydraulic suspension elements in lieu of conventional friction damping. This has further enabled stability and carbody force control at speeds exceeding 100 mph. This design would allow for safer transport of premium or hazardous goods and potentially offers a solution for higher speed freight operations. While this technology acceptance may be further in the future, it highlights how advancements are far from limited. The industry is now considering the cost of technology implementation and maintenance against the potential benefits of wheel/rail life extension and a safer, faster, more productive freight network.