Reinventing the (fifth) wheel
Laser alloying provides next generation of truck components
Building on a strong tradition as an innovator in the large truck component market, the Holland Group (Holland, MI) has developed a fifth wheel that, unlike its forbearers, requires no lubrication. Working with development and manufacturing partner Surface Treatment Technologies Inc. (ST2; Baltimore, MD) and using laser processing technology developed at the University of Tennessee Space Institute (UTSI; Tullahoma, TN) and licensed from The University of Tennessee Research Corporation, Holland is now marketing and delivering the No-Lube fifth wheel to customers. Key to the product is the kingpin lock set, which is produced using UTSI's patented Laser Induced Surface Improvement (LISI) process. Several years of process development and manufacturing prove out have resulted in a revolutionary product that will not only provide significant benefit to Holland customers but also help keep the environment clean.
Historically, grease and other lubricants are used to minimize wear and to provide smooth operation of the various locking components typical in a heavy vehicle coupler, or "fifth wheel," as well as the interface between the top plate surface of the fifth wheel and the mating upper coupler bolster plate on the trailer. Greaseless solutions have been in development for several years due to concerns relative to the cost in materials and labor to maintain these lubricated surfaces, detrimental environmental consequences (on every standard tractor, almost 45 pounds of "excess" grease is potentially distributed on roadways every year), and customer dissatisfaction associated with handling and cleaning.
Holland has previously marketed, with good success, a Low-Lube line of fifth wheel components engineered for reduced lubrication requirements. This success spurred the investigation of cost-effective, high-performance wear surfaces as potential candidates for a No-Lube fifth wheel product that would provide an advantage in maintenance costs as well as being more environmentally friendly.
Figure 1. Kingpin lock jaws as installed in fifth wheel—(L) bottom view and (R) top view.
One of the most difficult surface interactions in such an application is that between the kingpin and the kingpin locks (see Figure 1). The fifth wheel lock mechanism interacts substantially with the trailer-mounted kingpin in normal vehicle operations, where it must be able to rotate about a generally vertical axis while being held by the lockjaws in the fifth wheel. Forces due to braking, acceleration, maneuvering and so on are necessarily exchanged between the lock and kingpin while the kingpin rotates. This gives rise to sliding loaded contact between the two parts—a wear condition that traditionally requires lubrication for proper operation. A coating system to replace the lubricant must be designed to minimize wear on both the lock and the kingpin, because the fifth wheel will be used to couple with trailers having standard kingpins. Thus, the coating on the lock must protect the lock from wear without inducing excessive wear in the kingpin. The coating also needs to provide lubricity and prevent galling between these two components. In addition, the coating process cannot reduce the life of the lock forging. This balanced approach to coating design is challenging and limits the materials that can be used. One must also consider the large impact forces that occur during tractor-trailer coupling. Therefore, application requirements defined for the No-Lube product line included the following: over-the-highway application; no adverse effect on system performance or lifetime durability; typical coupling (10,000 cycles, single incidents up to 5 mph impact); environmental exposure (salt, temp extremes, cleaners and solvents, road debris); and economical viability.
Focusing on the fifth wheel component, Holland selected approximately 30 surface process candidates for extended laboratory testing. Selection criteria included dry sliding wear performance, impact resistance, expected mating surface wear, cost and manufacturability. Among the candidates were various electro- and plasma-deposited surfaces as well as laser alloyed (LISI) surfaces. During this exploratory effort, Holland worked closely with ST2 and UTSI to obtain LISI components best suited for the laboratory testing.
LISI surfaces are produced by applying a precursor mixture to a surface and using a laser to incorporate or alloy precursor materials into the substrate. As indicated in this magazine (ILS, September 1999), LISI surfaces offer advantages in processing rate, cost and control of surface properties—all of which are important for the fifth wheel application.
The base laboratory testing included dry sliding wear to measure wear resistance and compatibility with the kingpin, cyclic environmental exposure to determine response to truck environment and coupling sled impact to identify sensitivity of the coatings to impact damage. Several candidates stood out, most notably LISI and several of the plasma-based coatings. These were chosen for track testing of prototype components.
The ultimate benchmark as far as testing a possible No-Lube fifth wheel solution was considered to be the accelerated durability test normally conducted at Bosch Automotive Proving Ground (BAPG), which Holland has successfully utilized for product durability testing. The two-loop, 1.8-mile long course includes cobblestones, inverted chatter bumps, undulating road, resonance bumps and gravel road as well as turns and braking. Testing has shown that 12,000 track miles accumulates wear and durability damage equivalent to approximately 600,000 over-the-highway miles.
Two track tests of a No-Lube fifth wheel were completed at BAPG, spanning all four seasons and including combinations of environmental conditions similar to that expected in service (hot; dry and dusty; rain and mud; and snow, ice and salt). The fifth wheel assembly was run without any secondary lubrication (grease) applied, that is, "dry," for the duration of each test. The system was inspected every 1000 track miles or whenever the test personnel suspected a possible issue had arisen.
Figure 2. Detachment of surface on plasma-coated lock after partial track testing.
The selected plasma coatings either wore much more aggressively than predicted by the laboratory wear tests creating galling of the kingpin or tended to delaminate and detach (see Figure 2). None of the plasma coatings completed the 12,000-mile cycle.
Figure 3. LISI lock after track testing.
The first set of LISI prototype locks completed a partial Test Track cycle with excellent results. Mating kingpin wear performance was also very good. UTSI and ST2 had continued to improve on the process for the fifth wheel application, and a second track test was conducted with the second-generation LISI prototype lock. Figure 3 shows one of the LISI lockjaws after 12,000 grease-free accelerated durability miles at BAPG. Still clearly visible are the characteristic raster marks of the LISI coating and some smoothing of the surface toward the rear of the lock. No evidence of severe adhesive galling on the locks or kingpin occurred, as was seen with the other surface treatments.
After these positive results, Holland worked with ST2 and UTSI to develop a path to a manufactured product, starting with hundreds of units per month and anticipating market growth with increasing customer awareness. Holland elected to pursue an aggressive launch schedule that provided limited time for transitioning the prototype development into production. Within a year, Holland, ST2 and UTSI had worked to develop processing conditions for manufacturing multiple locksets, and they developed an automated precursor application for repeatable, high throughput processing. The precursor layer thickness and laser processing parameters (speed and power) were selected to form a LISI layer with specified surface roughness and hardness that give optimum wear resistance for the lock and the kingpin (see Figure 4).
Figure 4. As-processed No-Lube right and left lock.
Qualification procedures, documentation, quality assurance and acceptance guidelines and procedures and other items necessary to meet the November 2002 launch were also developed for the LISI locks. Additional development and manufacturing prototype tests were conducted parallel to the process documentation process to ensure product compliance with defined performance metrics. Finally, internal parts identification, user installation and usage documents, and external marketing materials were developed for the No-Lube components. The flexibility of the LISI process was useful in fine tuning properties such as surface finish and dimensions to the design and manufacturing requirements.
No-Lube fifth wheels are currently available on the market and include an industry-leading, six-year, 600,000-mile Performance Guarantee. Initial feedback has been positive, and the development team is currently re-evaluating future production needs and discussing other possible future LISI applications.
Steve Dupay is director of research and development with The Holland Group Inc (Holland, MI), Tim Langan is president of Surface Treatment Technologies (Baltimore, MD) and John A. Hopkins is vice president for marketing with University of Tennessee Research Corporation (Knoxville, TN). Additional information on the No-Lube fifth wheel can be found on Holland's web site www.thehollandgroupinc.com. Information on ST2 capabilities can be found at www.stt-inc.com, and additional information about UTSI's research can be found at www.utsi.edu.