Update on slip and wear in multi-layer azimuth track systems

Abstract

Many antennas, such as the 100-m Green Bank Telescope, use a wheel-on-track systems in which the track segments consist of wear plates mounted on base plates. The wear plates are typically 2 to 3 inches thick and are case hardened or through hardened. The base plates are usually 3 to 4 times thicker than the wear plates and are not hardened. The wear plates are typically connected to the base plates using bolts. The base plates are supported on grout and anchored to the underlying concrete foundation. For some antennas, slip has been observed between the wear plate and base plate, and between the base plate and the grout, with the migration in the wheel rolling direction. In addition, there has been wear at the wear plate/base plate interface. This paper is an update on the evaluation of GBT track retrofit. The paper describes the use of three-dimensional non-linear finite element analyses to understand and evaluate the behavior of (1) the existing GBT wheel-on-track system with mitered joints, and (2) the various proposed modifications. The modifications include welding of the base plate joints, staggering of the wear plate joints from the base plate joints, changing thickness of the wear plate, and increasing bolt diameter and length. Parameters included in the evaluation were contact pressure, relative slip, wear at the wear plate/base plate interface, and bolt shears and moments.

Improving the service life of the 100-meter Green Bank Telescope azimuth track

“…For the new track configuration, based on the SG&H results, the hold-down bolts were moved away from the wheel path (which required a wider wear plate), the effective hold-down bolt length was increased, and the hold-down bolt preloading was increased. These two configuration changes combined to reduce the bolt stress levels sufficiently to provide a minimum bolt fatigue life of 20 years [3]. Despite the excellent analyses conducted by SG&H, two problem areas were not resolved by their efforts:…”

A Method for Damage Detecting of Large Reflector Antennas Wheel-Rail Based on Electromagnetic Ultrasonic Technology

“…The wheel-rail damage of large reflector antenna reduces its surface accuracy and directly affects the antenna pointing performance, so it is important to study the detection of damage to the wheel-rail surface. The GBT antenna in the U.S.A. was built and operated for a few years and had problems with wear on the surface of the substrate and wear plate, Anderson R et al investigated this issue, designed and manufactured a new component system, and updated the antenna component in 2007, which greatly improved the performance and service life of the azimuth orbit of the GBT antenna [13,14]; Aiming at the mechanical behavior of the inclined joint track of GBT antenna and the fretting wear of the contact interface between wearresistant plate and substrate, Juneja G et al simulated the rolling situation of the roller by using the moving load method, and analyzed the force by using the finite element method, which provided a reference for the design and transformation of the antenna wheel-rail [15]; In order to make the antenna have good pointing performance, DR Smith et al pointed out that attention must be paid to the wheel-rail design to make it have high hardness to withstand great contact pressure [16]; Guo Hongwei et al used Hertz contact theory and finite element method to analyze the stress of a radar wheel-rail type antenna mount, and did metallurgical analysis under the condition of satisfying the strength to determine the cause of cracks on the surface of the roller [17].…”

A Study on the Mechanical Characteristics and Wheel–Rail Contact Simulation of a Welded Joint for a Large Radio Telescope Azimuth Track

“…During the operation of radio telescopes, a series of problems affecting the pointing accuracy of the azimuth tracks [1], such as track wear, fatigue cracks, and impact damage to track welded joints, occur in the wheel-rail contact system. A lot of design optimizations and improvements to tracks have already been conducted [2][3][4]. For the QiTai radio telescope (QTT) studied in this paper, the joints of the azimuth track are all welded.…”