Roots Vacuum Pump Stator Surface Hardening for Clash Mitigation
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Solution Overview
Problem
Pumps with small clearance gaps between the rotor and stator are prone to clashing due to differential thermal expansion, leading to damage, seizing, and burr generation, especially when using softer materials like aluminium for the stator.
Innovation Solution
The stator surface is treated to harden it, particularly at areas where clashing is most likely to occur, ensuring that any clashing happens between the rotor and the hardened stator surface, thereby preventing damage and seizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stator is formed of a softer material like aluminium, then the stator can accommodate thermal expansion differences, but it becomes prone to damage, gouging, and seizing when clashing occurs with the rotor
Solution Approach 1:
The stator is treated to harden only the specific surface areas where clashing is most likely to occur, while the bulk material remains soft to accommodate thermal expansion. This localized hardening through surface treatment resolves the contradiction by providing hardness where needed for clash resistance while maintaining overall softness for thermal accommodation.
Solution Approach 2:
The stator effectively becomes a composite structure with a soft bulk aluminium material and a hardened surface layer. This composite approach allows the interior material to handle thermal expansion while the exterior hardened surface resists damage and seizing during clashing events.
2Productivity
If the clearance gaps between rotor and stator are reduced to improve pumping performance, then leakage is reduced, but the risk of clashing increases due to differential thermal expansion
Solution Approach 1:
The stator surface is pre-hardened in areas where clashing is most likely to occur, creating a protective layer before any clash happens. This preliminary hardening prevents the harmful effects of clashing (gouging, burr generation, seizing) that would otherwise occur when tight clearances cause contact during thermal expansion.
3Strength
If the rotor is formed of a harder material to resist damage during clashing, then damage resistance improves, but differential thermal expansion with the stator increases
Solution Approach 1:
Instead of changing the rotor material properties, the solution extracts the hardness requirement from the rotor and applies it selectively to the stator surface. This separates the functions: the rotor maintains its original material properties for thermal compatibility, while the stator surface gains the necessary hardness through surface treatment.
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 solution effectively mitigates the risk of damage and seizing by ensuring that clashing occurs on a hardened stator surface, reducing the likelihood of burr generation and maintaining pump performance.
Implementation Method 1
said stator and rotor are configured so that any clashing that does occur occurs between the rotor and an anodised portion of the stator
Implementation Method 2
A problem associated with small clearances arises due to differential thermal expansion of the different components of the pump. This may be due to different components heating up at different speeds and by different amounts during operation of the pump and/or to different materials with different coefficients of thermal expansion being used for the different components.
Data Source
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AI summary
A multiple stage roots-type vacuum pump and method of manufacturing a pump are disclosed. The pump comprises: a rotor rotatably mounted within a stator; the stator being formed of a material that is softer than a material of the rotor. At least a portion of the surface of the stator is treated to harden the surface. The rotor and stator are configured such that clashing will preferentially occur between the rotor and the at least a portion of the stator surface that has been treated. Said stator and said rotor are configured such that axial clearance tolerances are selected to be lowest between said rotor and a higher vacuum side of one of said vacuum stages of said stator and between said rotor and a lower vacuum side of another one of said vacuum stages of said stator, such that clashes preferentially occur between the rotor and these selected sides of these stages.