Sumitomo Examines Product Selection and Maintenance Techniques at T-Mobile Park
Introduction

In July of 1999 the Safeco Field (currently T-Mobile Park) opened its doors as the new home of the Seattle Mariners (Figure 1). At that time, this first-of-its-kind stadium designed with a retractable roof would allow the Mariners’ fans to enjoy the ball game even during inclement weather.

The retractable roof is driven by 96 Sumitomo gearboxes. After over 24 years of service, a Sumitomo gearbox was returned for overhaul. The gearbox's condition is a testament to the importance of careful selection and maintenance, as it demonstrates the exceptional durability and craftsmanship of Sumitomo gearboxes, which can provide reliable operation for many years.

This paper examines the selection process, operation, maintenance practices, and state of the gearbox after over 24 years of operation. It is demonstrated that a quality product and careful consideration of all these factors are essential for a longer service life of the gearbox. Detailed information is provided on the operation of the gearbox, as well as the maintenance practices that should be taken to ensure its longevity. Finally, the paper examines the state of the gearbox after over two decades of use and how all these factors result in lowering carbon emissions.

Product Selection

Based on Sumitomo's load classification for selection (Figure 2), a service factor (SF) of 1.4 is required for heavy shock load and intermittent duty (3 hours per day) applications. SF is calculated as the capacity of the gearbox divided by the motor power. Considering a 10 HP motor, the gearbox’s capacity should be equal or exceed 14 HP. The Sumitomo gearbox model KHFJS-D4165-R1-62 was selected as it meets all requirements. A breakdown of the application’s requirements is laid out on the following sections.

Application

The retractable roof is towed by 128 wheels powered by 96 10 HP electric motors [1] that travels through rails and wheels similar to those of a train (Figure 3). Under ideal conditions, the gearbox experiences uniform load. However, as the roof is meant to be used during inclement weather, the gearbox can experience heavy shock loads and variable loading due to wind speed.

Ambient Conditions

The gearbox installation is outdoors, which exposes the gearbox to changing weather conditions. The ambient temperature ranges from 35 to 76 °F (~2 to 24 °C), and the relative humidity is within standard limits.

Hours of Operation Per Day

The deployment time ranges from 10 to 20 minutes depending on the speed of wind and other weather conditions [1], such as built-up snow that increases both the weight of the roof and the load on the gearboxes. In a worst-case scenario, tests may be conducted to ensure proper operation of the roof, which can result in operating the roof multiple times, with an estimated maximum time of operation of three hours per day.

Output speed

To safely move the retractable roof’s structure, an output speed of 28.2 rpm was calculated, requiring a 62 ratio at 1,750 rpm input speed. Motor speed and horsepower Based on the demand torque for the application, a 10 hp motor operated at 1,750 rpm was specified.

Mounting position and output connection

The gearbox is mounted horizontally using a flange that bolts onto the structure (Figure 4). It features Sumitomo's Taper Grip Bushing (TGB), a keyless output connection that eliminates the need for precision machining of the driven shaft during installation (Figure 5).