Originally authored by Mr. Len Hensel, BSME, MS-PDD Wheel Engineer
The five-piece rim design has been the standard for construction and mining wheels for well over 60 years. In general, the functional design has remained the same with adaptations for changes the tire construction (radial tires) and new tire sizes. The tire capacities have grown over this time as well. The adaptations have allowed the rims to maintain their durability expectations.
However, extreme applications such as steel slab haulers have push the durability envelope beyond what the rims can sustain for long term life. In extreme service conditions, five piece rim/wheel designs, can exhibit fast wearing of mating surfaces and rim cracking due to the higher loads and application speeds. Characteristics of radial tire constructions have added to field issues of the rims. Wheel engineers evaluated the failure modes with slap hauler rims and observed the following characteristics:
Wheel engineers looked at the observed issues and implemented several incremental design changes to address the problem. Some of these changes have been:
The results of the modifications were:
While the service life was improved, it was not sufficient to achieve a service life that was acceptable to end users. Since the traditional changes did not yield a sufficient improvement, a new solution was needed. It was decided that an integrated design which tied the side flange to the back section would be tested in this machine application.
One-piece fixed flange designs are not new to off-road applications. They have been used in rim and wheel designs for over 100 years in smaller diameter applications. Typical applications have been tube type track rims, motor graders and small front-end loaders. In the last 15 years, one piece back sections have been used in wheel designs on medium size loaders and some special application 33” machines.
A fixed flange design will:
A series of FEA (Finite Element Analysis) simulation models were run to verify that the fixed flange design would have sufficient strength to carry the loads of extreme service applications. Three load conditions were also used to evaluate the fixed flange design.
Load Case 1 – 66,000 lbs. (30,000 Kg) @ 110 psi. (7.6 bar)
Load Case 2 – 132,000 lbs. (59,900Kg) @ 110 psi. (7.6 bar) (Impact load)
Load Case 3 – 110,000 lbs. (49,900 Kg) @135 psi (9.3 bar) (Extreme Service Loading)
The conclusion of the FEA simulation models was that the new fixed flange design is very robust and will adequately carry the extreme service loads imposed by radial tires.
The predicted deflections of the FEA simulations were evaluated to determine the effects of the fixed flange back design compared to the baseline model which was the typical 5 piece design. The results show that the deflections of the new fixed flange back is 30% lower than the baseline model at the standard load condition. The reduced deflection of the fixed flange back demonstrates the improved stiffness of the section. This will have a positive impact on the tire and lower tire bead area.
The conclusion of the computer modeling was that the new “fixed flange design” rim design is very robust and will handle the loads and stresses imposed by radial tires. The deflections of the computer models were evaluated to determine the effects of the one-piece design.
The new fixed flange design has placed into a controlled field trial at a steel mill to verify the results in a real world environment. The fixed flange was specified to be made from a seamless rolled ring to eliminate are issues from a seam weld. A HSLA (High Strength Low Alloy) grade material with exceptional characteristics was specified to ensure that the component would have exceptional fatigue life. The component was fully machined to the final profile to create the best possible fit with the tire. Rim knurling was also specified to further contribute to reducing tire indexing. Full penetration circumferential weld joints were specified to facility inspection and verification that the welds were free from internal defects
Slab hauler applications are typically severely loaded (100,000 Lbs./45,360 Kg per tire) as compared to the typical haulage truck. This application was specifically selected as a field test because of the high load nature of the equipment and the high air pressures that are used (typically 135 PSI / 930 kPa). The cracking mode of the five piece assemblies is comparable to the mode seen in typical haulage applications at quarries and small mining operations.
Because of the high load environment, the cracking modes in the slab hauler application occur much earlier in the life of the part than would be expected in an average haulage application. The typical life of the rim in the slab hauler application, depending on which five-piece design is used, “varies from 800 hours up to about 3,000 hours”. After this, replacement of rim base components is required. A high cost for the end user. It is important to note that the slab hauler application is operating “well outside the norm” for a 27.00 R 49 tire application. These loads encountered would not be approved for the standard high-speed (30 Mph/50 KPH) applications.
The true test of any design is how it will perform in the real world, in a real operation where the environment has all the application variables that are not fully represented in the computer simulations. Several sets of wheels were placed in service on slab haulers. The rims were inspected are 3,000 hours & 5,000 hours of operation.
The results were phenomenal. At 3,000 hours the parts still had a like new look to them. While the flange area shows that the paint has been removed because of movement of the lower bead area of the tire. The bead seat surface of the rim shows very little wear which suggests that the tire bead has a more stable surface (less deflection)
A NDT (Non-Destructive Testing) examination of the rear radius of the fixed flange did not show any evidence of early fatigue crack initiation. At 5,000 hours, the fixed flange design parts did not have any indications of fatigue cracks.
This picture shows the condition of a fixed flange design after 5,000 hours of operation.
An unexpected benefit that was derived from the new fixed flange design was a significant improvement in tire indexing and lower bead area durability. This improvement was observed by the end user. This can be translated into to better equipment up time and a reduction of their tire costs.
The new 49” four-piece design has achieved its intended design objectives and more:
1. Fretting has been eliminated on the back flange area of the rim.
2. There has been minimal impact to the weight added to the total rim assembly weight (100 lbs. /45kg).
3. Improved stability of the tire bead area.
4. Virtually no tire slippage.
5. Minimal metal erosion under the bead of the tire.
6. Extended life to the rim and reduced down time because of broken rim components
7. Ability to handle the new 80 series radial tires.
8. Improved tire life in the slab hauler application. (Normal casing life on five piece designs was 2,500 to 3,500 hours. With the four-piece rim casing life has been extended to 4,500 hours to 5,000 hours.)
All of the above benefits have resulted in reduced maintenance cost and increased tire utilization. The net result is reduced equipment operational cost, which in turn contributes to improved profitability for the steel mill.
The original design improvements and testing were done in 2000 and 2001. Since that time, many rims have been put in service on slab haulers in Canada and the U.S. All the rims have been subject to periodic NDT inspection processes at factory authorized inspection and repair facilities. Critical areas are inspected and necessary repairs done to repair or replace defective rim parts such as gutter sections, center sections and rim locators.
The scheduled inspections and repairs on an as needed basis have extended these rims service life well beyond anyone’s expectations for the rim design resulting is a very low cost of ownership and extended service life. A win-win deal for companies that own these rim products and the companies responsible for servicing them.
For more information about this product design and how it can work for you, contact Keith Heeres at the phone number at the top of this page.
Mr. Len Hensel, BSME, MS-PDD
Len has over 39 years of industry experience in providing wheel system solutions for the mining, construction and agricultural applications. He has worked extensively with the entire major off road equipment manufacturers and off road tire (OTR) companies to provide designs that meet the needs of new applications, pushing the envelope for greater load capacity and durability. He has worked in leadership positions in off the road wheel industry new product development, application engineering, new design validation, research and development projects, and quality assurance. He is a member of the Society of Automotive Engineers (SAE), participated in development of international standards (ISO) related to off the road wheels, and a past member of the Tire and Rim Association (TRA) representing the rim and wheel industry manufacturers.
Contact: [email protected]
If you operate, maintain or manage a Cat 769C, 769D, 770, 770G, 771D, or 772G off-highway truck and you need new or replacement scallop disc wheels, give me a call.
Cat part number 143-2138 wheels are built using a unique scallop disc wheel design. Due to the operating conditions these trucks work in, the wheels do get damaged and do wear out.
The wheel shown on the right is a new replacement Cat PN 143-2138 wheel assembly complete with all the wheel components.
The Cat Rim Group PN 143-2138 which when purchased includes all the component parts.
Cat Rim Group includes all the component parts.
A common problem associated with Cat scallop wheels are broken scallops in the disc. Scallops get broken as a result of issues such as failure to maintain proper wheel nut torque causing the wheels to run loose, metal fatigue and stress, and just general wear and tear. The good news is we can help with that!
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