WAYSIDE WHEEL INSPECTION HISTORY
Broken wheels due to internal cracks are of major concern to railways from both a safety and economic perspective. A broken wheel can lead to a derailment or damage up to several miles of track before it is noticed and remedial action taken.
In 1999 the American Association of Railroads (AAR) initiated a research program to detect cracks in railroad freight car wheels using ultrasonic testing methods. Under the direction of the AAR Railway Technology Working Committee, the Transportation Technology Center (TTCI) in Pueblo, Colorado began research and development for this project.
In June 2005, TTCI was authorized to partner with Dapco to deploy an Automated Cracked Wheel Detection (ACWD) system utilizing Dapco’s proprietary product line. In the spring of 2006, a system was deployed and commissioned for inspection of all wheels on one side of a train. In April 2007, the installation at TTCI was featured on the History Channel TV Program, Modern Marvels.
In 2008, Dapco was contracted by the Union Pacific Railroad to install an Ultrasonic Cracked Wheel Detector at the Bailey Yard in North Platte, NE. The Union Pacific Cracked Wheel Detector represents the latest evolution of the Dapco Wheel System Technology. This groundbreaking system includes many design modifications, new features and increased functionality since the installation of the prototype system at the Transportation Technology Center (TTCI) in early 2006.
The commissioning of the Union Pacific Cracked Wheel Detector represents a milestone in the railroad industry. This is the first wayside wheel inspection system that can directly mitigate the risk and costs associated with internal wheel defects. In July 2009, the Union Pacific Cracked Wheel Detector was featured in Fast Company Magazine.
HOW DOES IT WORK?
The Dapco Wayside Cracked Wheel Detection System uses a conventional ultrasonic approach to dynamically inspect railway wheels at train speeds of up to 5mph (8km/h). The main function of the patented Dapco Wayside Ultrasonic Cracked Wheel Detector is to verify the integrity of the rail wheel by ultrasonically inspecting the wheels to determine the presence of internal defects. The system provides real-time assessment and reporting of flaw type, size, and location in and across the tread and rim of the wheel.
The system consists of four inspection stations per rail with up-to eight transducers housed in each inspection station. Each inspection station is mounted on a set of travelling robotics. Each inspection station will inspect one wheel in a four wheel sequence. For example, if inspection station#1 inspects the first wheel in a train formation, then it will inspect the 5th, 9th etc. Similarly the remaining three inspection stations will test their relative sequential number.
Fig 1: Illustration of Wheel Inspection Station Sequencing
As the inspection elements are put in place, the Ultrasound is coupled into the surface of the rail wheel from underneath via a fine water mist. The Wheels are inspected ultrasonically and after the inspection is complete the station will lower the inspection elements and return them to their home position to stand ready for the next assigned wheel.
The system utilizes flange-bearing track which exposes the tread of the wheel for ultrasonic inspection. The inspection probes are engaged to the tread surface of the wheel from underneath and fine mist of water is used to couple the ultrasound into the steel as the train and the wheel travels at speeds of up to 8km/h.
Fig 2: Illustration of Flange Bearing Track
Photo courtesy of Union Pacific Railroad
