Screw Vacuum Pump Rotor Sectioning for Precision and Backflow Control
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Solution Overview
Problem
Screw vacuum pumps require high manufacturing precision for complex pump-active geometries, particularly at the inlet area, which is costly and difficult to achieve due to wear in casting molds and challenging measurements, leading to potential defects and increased production costs.
Innovation Solution
The screw rotors have a longer first section than the closed delivery volume, allowing for reduced manufacturing precision at the inlet area without risking backflow, enabling simpler and more stable production with larger tools and reduced processing time, and improved vacuum performance at high intake pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high manufacturing precision is applied to the inlet area of the housing, then the closure of the delivery volume is precisely defined, but the manufacturing complexity and cost increase significantly
Solution Approach 1:
The screw rotor profile is divided into multiple sections with different slope characteristics. The first section has a higher slope for precise delivery volume closure, while the second section has a lower slope to prevent backflow. This segmentation allows different manufacturing precision requirements to be applied to different sections, reducing overall manufacturing complexity.
Solution Approach 2:
Different sections of the screw rotor profile are assigned different geometric characteristics tailored to their specific functional requirements. The first section uses a higher slope for precise closure at the inlet, while the second section uses a lower slope for backflow prevention further along the profile. This local differentiation optimizes performance while reducing manufacturing demands.
2Manufacturing precision
If the first section of the screw rotor is made longer than the closed delivery volume, then manufacturing precision requirements are reduced, but the overall rotor length increases
Solution Approach 1:
The screw rotor profile is segmented into multiple sections with different slope characteristics. The first section has a higher slope for precise delivery volume closure, while the second section has a lower slope to prevent backflow. This segmentation allows different manufacturing precision requirements to be applied to different sections, reducing overall manufacturing complexity.
Solution Approach 2:
The slope parameter of the screw rotor profile is changed between different sections. The first section has a higher slope value for precise closure, while the second section has a lower slope value for backflow prevention. This parameter change allows the same rotor design to meet different functional requirements without uniformly increasing length.
3Productivity
If larger tools with higher chip volume are used for profile production, then processing time is reduced, but manufacturing precision may be compromised
Solution Approach 1:
The screw rotor profile is divided into independent sections that can be manufactured separately or as a whole. The first and second sections have different geometric characteristics that can be optimized for their specific functions. This segmentation allows the use of larger, more efficient tools for each section without compromising overall precision, as each section can be manufactured to its specific tolerance requirements.
Data Source
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AI summary
Screw vacuum pump with a housing (16), two screw rotors (28, 30) arranged in the housing and meshing with each other, which, in conjunction with the housing (16), repeatedly form closed delivery volumes of the process gas and convey it towards an outlet, wherein the screw rotors (28, 30) each have at least two sections (62, 64) adjacent along the screw axis, wherein the screw rotors (28, 30) each have a first section (62) located closer to an inlet having at least substantially a constant pitch and a second section (64) having a lower pitch than the first section (62), and wherein, with respect to the screw axis, the first section (62) is longer than a section corresponding to a closed delivery volume in the first section (62).