The Gear Works Completes Testing of New Gearboxes for the Ballard Bridge
Friday, August 14th, 2009
Since 1918 the Ballard Bridge has served as a major link to N.W. Seattle by providing access for 52,000 vehicles a day over the Lake Washington Ship Canal. During the year, the bridge will open approximately 5,200 times for boat traffic.
The Gear Works has successfully completed the design, manufacture and testing of the first 2 gearboxes for the Ballard Bridge Rehabilitation Project in Seattle. When the Seattle Transportation Department decided to replace the mechanical drives on the 83 year old bascule bridge, they developed an extensive gearbox procurement specification that required the capability and expertise of a full service gear manufacturer.
All parallel shaft gear components were case-hardened and ground within AGMA Q-12 tolerances on our Gleason-Pfauter P1600B gear tooth grinding machine.
Within weeks of receiving the competitively bid contract, the Gear Works engineers were collaborating with the contractor and city officials on all aspects of the new gearbox design. The project requires a total of four custom gearboxes and output pinions, one pair for the north draw span and the other pair for the south span. The new drives will be electronically linked which will replace an antiquated assembly of interconnected cross-shafts, differentials and open gear trains.
The gearboxes were assembled back to back on an 18″ thick concrete foundation to allow for rigid load test positioning. All gear contact patterns and bearing settings were checked and recorded.
Our Scope of Work Included:
- Field measurements of each existing gear rack to ascertain the point of tightest mesh with the new output pinions. This required the use of a unique portable composite tester specially built for the project.
- Complete design of left and right hand gearbox assemblies including all shop drawings, to extensive engineering specifications and AGMA gear rating standards. The gears were required to have a strength rating to survive 300% of full motor torque, and the bearings were rated at a design life of 40,000 hours.
- Precision manufacture of the fabricated housings and gearing components, plus complete assembly of the 22,500 lb. gearbox. To achieve an 85% gear mesh contact requirement, the case hardened main reduction gears were ground to AGMA Q-12 tolerances.
- Manufacture and assembly of 5″ pitch output pinions. Each 2300 lb. pinion was custom cut to match the wear pattern and backlash requirements of each mating draw span rack.
- Shop load testing at 200% of full motor torque. Using our gearbox test bed, incremental loads were applied by having the gearboxes, mounted back to back, drive a generator connected to the electrical grid.
A 200% load test was applied to the gearboxes by using an electrical regenerative method. Over 2,500,000 lb./in. of torque was applied to the low speed shafts in both directions. Temporary anchors secured the assemblies to the test bed foundation.
- Gearbox Ratio: 286:1
- Gearbox and pinion weight: 22,500 lbs.
- Full rated motor power: 60 H.P.
- Gearbox rating including S.F.: 90 H.P.
- Output pinion speed: 3 RPM
- Gearbox test torque: 2,548,000 lb./in.
- Gearbox oil capacity: 90 gal.
When your gearbox needs a lift, test The Gear Works!