Redesign of Hydraulic Press Knock-out Assembly

Photo of John Bergman, William Loose-Mitchell, Hector Loya (Team Lead), Vincent Mo
Students: John Bergman, William Loose-Mitchell, Hector Loya (Team Lead), Vincent Mo

Sponsor: Wyman-Gordon

Date: Fall 2012

Requirements:
The adaptor must hold the knock-out rod steadily in place and must withstand the loading caused by the knock-out press. The hydraulic press pushes the knock-out rod upwards with a variable loading of 300 tons in compression 350 times per day, 1000 tons in compression three times per week, and 300 tons in tension once per week. The interface of the knock-out rod and adaptor is around 200°F. The downtime of any redesign must be less than the current downtime of twenty-four hours every two and a half months. The main constraint is that the hydraulic press as a whole cannot be changed. in particular, the knock-out rod length and outer diameter cannot be changed. Its diameter must be 6 in and its length must remain 63 in. Wyman-Gordon has a hydraulic impact wrench capable of producing 30,000 ft-lbs of torque, which is the maximum torque that can be applied to the assembly. Lastly, there is a locking pin through the adaptor that keeps the adaptor from becoming loose from the hydraulic ram. This pin location must maintain the radius of three and a quarter inches from the center of the adaptor.

Problem:
Wyman Gordon operates a 29K ton hydraulic press system to forge turbine components. The system suffers failure every 2.5 months on the knock-out rod stud. The knock-out press operates with variable loading with a maximum load of up to 1000 tons. The failure occurs at the interface between the knock-out rod and the adaptor. The current solution is to remove the slide platform, disassemble the bushing from the base platform, and replace the failed adaptor. This process requires approximately 12-24 hours down time and results in lost profit. The team is to apply stress/fatigue analysis, determine the failure causes, and develop at least one workable maintenance plan for the current operation. The team will also redesign the knock-out assembly to reduce lost profits.

Solution:
The rod is currently failing in such a short time because it is becoming unscrewed during operation. After becoming unscrewed and during maximum compression loading, the threaded stud of the rod yields across the diameter. This extreme stress causes microscopic yielding which in turn leads to a crack, and eventually failure. To correct this problem, we suggest that Wyman-Gordon manufacture the bottom adaptor, knock-out rod, and top adaptor according to our drawing specifications: 4 in thread stud for the knock-out rod, hex headed knock-out rod, and 4 in rod adapter added to the assembly. Preloading the knock-out rod to 9000 ft-lbs and the addition of Loctite 2422 will increase the life of the assembly to a theoretical 29 months.

Images related to the project:

Photo related to Redesign of Hydraulic Press Knock-out Assembly project
Photo related to Redesign of Hydraulic Press Knock-out Assembly project
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