Railroad equipment. (Casting Market Focus).

Picture a 100-car unit train weighing 260,000 lb (13,150 tons of freight pulled by 12,000 horsepower) rapidly climbing and descending throughout the Rocky Mountains and its picturesque inclines, valleys, and peak-winding, ice-covered tracks. Throughout its journey, this train will charge through -40F mountain air to the sun-scorched heat of its final destination. The components on such a train are expected to perform at the same optimum level on every single foot of track for the 150,000 miles it will log annually--for 20 years or more. Whether you realize it or not, millions of Americans just like you are relying on these very trains to deliver the coal needed to supply the energy for your homes, businesses and daily conveniences of modern life.

Conditions this demanding leave few methods of manufacture capable of meeting such challenges while also remaining cost-effective. But, in such railroad applications where extreme properties for shock, fatigue and tensile strength, and overall toughness at minimum weight are required, casting is largely the process of choice. Take the cast steel coupler, for instance, which connects each of the 100 cars together on a Unit train. These couplers must withstand a maximum continuous force of 500,000 lb, requiring the component to meet average tensile strength requirements and ultimate strengths of 800,000 lb and 1 million lb, respectively. The combination of the casting process and material choice makes this possible.

Following is some background on casting applications within the railroad equipment industry, and in particular, some prominent steel casting components.

Workin' on the Railroad

The general classification for railroad equipment (NAICS 3365) includes those companies engaged in building or rebuilding locomotives, railroad, street and rapid transit cars and car equipment for operation on rails for both freight and passenger service.

In terms of total shipments, the railroad industry ranks as the third-largest end-use industry for all cast metal components, and represented nearly $380 million in sales last year. While virtually all cast metal groups are represented in the railroad industry in one fashion or another, cast steel dominates this sector's landscape. In a normal year, rail applications will represent one-half of all steel casting tonnage. In the decades-low year of 2002, the 270,000 tons of steel railroad castings dropped this figure to 28%. According to Steve Becker, S.W. Becker & Assoc., the four categories of steel railway castings include truck suspension parts, coupling systems, cast steel wheels and structural castings.

Meanwhile, application of cast gray and ductile iron by the rail industry last year was 7000 and 8000 tons, respectively. According to the 2002-03 Casting Source Directory CD-ROM database, more than 500 foundries in the U.S. and Canada currently supply the rail industry.

A Roller Coaster Segment

At about one-tenth the cost of trucking, rail transportation remains the most efficient way of moving material on a cost per ton basis, said Raymond Monroe, executive director, Steel Founders' Society of America. While it offers great economy and efficiency, this mode of transport also places enormous demands on rolling stock. Railroad applications are arguably the toughest job that any casting will ever face.

With steel foundries in particular so reliant upon the fortunes of the railroad industry, the cyclical demand for railroad equipment is closely monitored by the casting industry. Railroad freight car deliveries saw peaks of 76,000 and 74000 units in 1998 and 1999 (the largest totals since 1980). The increase in coal mining and shipments of grain created a larger demand for freight cars and locomotives. "Plus," said Monroe, "demand was so high in these years because industry mergers tied up traffic to the extent that there were not enough cars to service demand." Today, he said, the trend is to reduce the number of active cars to gain efficiencies.

According to Ken Kirgin, Stratecasts, Inc., the railroad sector is the most difficult of all casting markets to forecast. "No one can make any sense of the railroad industry's production scheduling, ordering and delivery policies. It's always been that way. They will build inventories and order a lot of bolsters, sideframe, coupler and wheel castings, and then freight car production can come to a screeching halt. Locomotive-type castings see the same picture, though not as dramatic as freight car components," he said.

"It's very bad for the foundries because they try to keep the capacity for the peak years while struggling to stay afloat in the near term. Compounding the poor demand is the fact that rail foundries are now facing import threats, too.

Because of the volatility in freight car demand, the demand/supply rates of steel foundries varies dramatically, from as high as 90% in some years to its current projections of 62% this year. Capacity was so high in 1999 that freight car production was actually limited by the inability to produce more wheel sets and other structural cast components, said Monroe. By 2002, freight car deliveries were down considerably, and then fell 50% in one year to 17,000 units (the lowest total in 15 years). As a result, U.S. steel casters faced 37% demand/supply rates, and steel foundries continued to be mothballed or closed.

Stratecasts estimates a 64% increase in 2003 to 28,000 cars. While this figure would be the second-lowest level in 10 years, it's still a far cry from the trying times of the mid-1980s, when four consecutive years below 20,000 units threatened not only the railroad companies but also the steel foundry industry at large. "For a good portion of the 1980s and 1990s, we never thought we'd see a 40,000 shipment year again," said Monroe.

Kirgin expects orders for freight cars to continue at an average rate of nearly 45,000 per year in the next decade with a series of strong years ahead (Fig. 1). Combined with increased locomotive business and the expansion of transit systems, this growth has meant an increase in steel casting demand. Though car builders are searching for ways to reduce weight, the solutions appear to be more along the lines of highly engineered steel castings than of material substitutions.

Another trend affecting castings is the integration of railroad freight cars with conventional shipping (intermodal). This has resulted in additional connector-type applications for steel castings.

Suspension Systems

One of the most common casting applications is the truck (also called a bogie) suspension system. The major casting components in the truck assembly are the bolster, side frame and wheels (Fig. 2). Casting is regarded as the method of choice for domestic truck frames.

In comparing the methods of manufacturing these suspension systems, Scott Duncan, vice president, Meridian Rail, said, "Fabrications have a low strength-to-weight ratio with respect to castings, and have a higher variable production cost. For mass-produced suspension systems, an all-cast design is more favorable. It allows the product shape, strength and weight to be fully optimized. Furthermore, due to the volume of units sold and the lower variable costs of production, all-cast suspensions offer the most value."

American Steel Foundries notes that these castings are designed and tested to assure they will last for the life of the car, and beyond, which is usually several million miles.

European companies such as Thyssen who have used U.S. test facilities have found that their fabricated trucks cannot survive the load requirements needed to operate on the U.S. rail lines.

In discussing some of the innovations in truck production, Tim Zimmer, vice president, Atchison Casting Corp., described the change in design paradigms, and the role of the 21st century casting. The heavier-was-better mindset featured cast-solid undercarriages and even the addition of cement ballasts, he said. When locomotive manufacturers looked to gain fuel economies, the wall sections of the truck were candidates for redesign, he recalled.

"Over the past few decades, conventional wisdom and technology have joined to realize that tractive effort is not a function of mass alone," said Zimmer. Working jointly with locomotive-manufacturer EMD, the combination of classical analysis with modern design tools helped achieve thin wall castings with a highly tractive effort. The three-axle, high-traction truck that resulted (Fig. 3) achieved both significant weight savings (contributing upward of 25%) and superior tractive effort.

The Rotary Coupler

Another noteworthy casting application is the rotary coupler (Fig. 4), which is used in the rotary-style dump car on unit trains. This style of car, which allows the unloading of a car without decoupling, eliminated the previously time- and labor-intensive process of manually opening and closing the hopper doors.

The rotary dump car's success is predicated on the rotary coupler, which consists of six main cast steel parts: the rotary shank coupler, the rotary connector, the rotary yoke that holds the connector, the front support for the yoke, a connector pin and pin support. Forces acting on the coupler are extremely complex and include train resistance (friction, air), grade resistance (lifting the weight in an ascending grade) and curve resistance (friction between the wheel flange and rail on curves) as well as the trailing tons represented by the other cars.

With the rotary dump system, a train is moved progressively through a dumping station that can handle two cars at once. The car is clamped in the station and simply turned upside down. The rotary coupler's assembly allows the complete 180[degrees] rotation of a car to the inverted position and back with total safety and reliability. The system allows the complete unloading of a car in 1-2 min. Alternative metalforming methods are incapable of performing this unique application.

High Yield, Manufacturability

Castings produced for the railroad industry generally fare very well because of the railroad equipment manufacturers' heavy reliance on its casting suppliers to provide nearly all of the design and, in some cases, testing services. This translates into high-performance components that are more easily manufacturable with a high casting yield.

As opposed to receiving a predetermined design and "making it work" on its production arrangement, the steel railroad foundry's upfront role in design allows it to realize yields as much as 45% higher. According to Monroe, this is because the foundry can make the casting process so robust that, on some jobs, the risers can practically empty out into the casting. Added Becker: "Because foundries often design the castings themselves, they can get a high level of functionality and design flexibility to make the part not only serviceable, but also very manufacturable. On side frame and bolster castings, yields of 90% can be typical."

Increasing Challenges

The demands of railroad equipment are ever-changing. The movement toward the use of two 6000-hp AC locomotive engines instead of three 4000-hp locomotive sets to provide better fuel economy and operating costs is changing the casting requirements. The average age of freight cars is also placing greater importance on durability, up to 29.4 years now from 14.9 two decades ago. By marrying proven casting know-how with today's modeling and engineering tools, castings are providing real advantages to the railroad industry.

This article was updated from one that originally appeared in Engineered Casting Solutions.

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