Vacuum Pump Rotor Geometry for High-Speed Creep Stress Reduction
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Solution Overview
Problem
Existing vacuum pumps face stress issues in the rotor cylindrical portion due to centrifugal forces, leading to creep deformation and reduced creep lifetime, which are exacerbated at high rotation speeds, and reducing speed to mitigate stress compromises exhaust performance.
Innovation Solution
Incorporating a smaller diameter portion with a tapered or chamfered design in the rotor cylindrical portion, particularly at the outlet port side, reduces stress without lowering rotation speed, using a configuration where the smaller diameter portion coincides with or starts at the extending portion and has a gradient or right-angle surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the rotation speed of the rotating body is reduced to reduce stress, then stress in the rotor cylindrical portion is reduced, but exhaust performance is deteriorated
Solution Approach 1:
The rotor cylindrical portion is designed with varying outer diameters along its axial length, creating local quality differences. The smaller diameter portion is positioned at the outlet port side while maintaining a larger diameter at the inlet port side, allowing stress reduction in critical areas without compromising overall exhaust performance. This non-uniform diameter distribution optimizes the stress profile while preserving the pump's functional efficiency.
Solution Approach 2:
The invention changes the geometric parameter of the rotor cylindrical portion by introducing a smaller diameter portion with specific dimensional relationships. The outer diameter of the smaller diameter portion is set to be less than the outer diameter of the inlet port side portion, and the axial length and positioning parameters are carefully controlled to achieve stress reduction while maintaining exhaust performance.
2Productivity
If high rotation speed is used to maintain exhaust performance, then exhaust performance is maintained, but stress in the rotor cylindrical portion increases leading to creep deformation
Solution Approach 1:
By creating local quality variations in the rotor cylindrical portion through differential diameter design, the invention reduces stress concentration in the radially inner part where creep is most likely to occur. The smaller diameter portion at the outlet port side specifically addresses the high-stress region without reducing the overall rotation speed, thereby preserving creep lifetime while maintaining exhaust performance.
Solution Approach 2:
The design preemptively addresses potential creep deformation by incorporating the smaller diameter portion during the design phase. This preliminary structural modification prevents stress from exceeding the design reference value before creep can occur, allowing the pump to operate at high rotation speeds for extended periods without degradation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces stress in the rotor cylindrical portion, preventing creep deformation and maintaining or enhancing exhaust performance by allowing higher rotation speeds.
Implementation Method 1
a centrifugal force may cause a stress in a radially inner part of the rotor cylindrical portion
Data Source
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Figure 3(a)~3(c)
AI summary
Provided are a vacuum pump capable of reducing a stress without reducing the rotation speed of a rotating cylindrical body (rotating body), and the rotating cylindrical body included in the vacuum pump. In the vacuum pump according to the present invention, in an outlet port-side lower portion of a rotor cylindrical portion (rotating cylindrical body) included in the vacuum pump, a smaller diameter portion having an outer diameter smaller than that of an inlet port-side portion of the rotor cylindrical portion is provided. More specifically, a lowermost end portion (outlet port-side end portion) of the rotor cylindrical portion is designed longer than a thread groove exhaust element (thread-groove exhaust mechanism) to provide an extending portion. In the extending portion of the rotor cylindrical portion, the smaller diameter portion having the outer diameter smaller than that of the inlet port-side portion (opposed portion) of the rotor cylindrical portion which is opposed to the thread groove exhaust element is provided. A configuration having the smaller diameter portion described above can reduce a stress generated in a radially inner part of the rotor cylindrical portion without reducing the rotation speed of the rotating body (rotor cylindrical portion).