Compressor Scroll Corner Stress via Offset Cavitation Peening
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Solution Overview
Problem
Scrolls for compressors experience stress concentration at the corner portion where the end plate and wall portion are joined, leading to fatigue and potential cracks, which existing methods like shot peening are not effectively addressing due to the unique spiral shape of the scroll.
Innovation Solution
A method and device utilizing water jet peening with cavitation bubbles generated underwater, where the center of the bubbles is offset from the spiral shape's center, allowing the bubbles to impinge on corner portions, thereby imparting compressive residual stress and preventing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is used to impart compressive residual stress, then fatigue strength is improved, but the method is not suitable for scrolls because steel balls cannot hit the target region at the corner portion where the end plate and wall portion are joined
Solution Approach 1:
The patent replaces the mechanical shot peening system (steel balls) with a fluid-based cavitation bubble system. The cavitation bubbles generated by water jet can reach and impinge on the corner portion where the end plate and wall portion are joined, which is inaccessible to steel balls due to the scroll's unique spiral shape and stepped portions.
Solution Approach 2:
The patent uses hydraulic cavitation bubbles generated by underwater water jet instead of mechanical shot peening. The fluid nature of cavitation bubbles allows them to penetrate and impinge on difficult-to-reach areas of the scroll, including the corner portion between the end plate and wall portion, while still imparting compressive residual stress to improve fatigue strength.
2Manufacturing precision
If cavitation bubbles are used to reach smaller regions, then the target region at the corner portion can be treated, but the unique shape of the scroll with wall portion on end plate makes it difficult for cavitation bubbles to impinge on the target region
Solution Approach 1:
The patent introduces asymmetry in the water jet application by offsetting the center of the cavitation bubbles from the center of the spiral shape of the wall portion on the end plate. This asymmetric positioning allows the cavitation bubbles to be directed toward the specific corner portion where the end plate and wall portion are joined, overcoming the obstacles created by the scroll's asymmetric spiral shape and stepped portions.
Solution Approach 2:
The patent applies local quality by concentrating the cavitation bubble impingement specifically on the corner portion where the end plate and wall portion are joined, rather than uniformly treating the entire scroll surface. This localized approach ensures that the target region receives sufficient compressive residual stress while the unique spiral shape and stepped portions do not prevent treatment.
3Reliability
If the center of cavitation bubbles is offset from the center of the spiral shape, then cavitation bubbles can impinge on corner portions, but the step portion and stepped portion must be positioned at the outer peripheral portion of the cavitation bubbles
Solution Approach 1:
The patent employs asymmetry by offsetting the cavitation bubble center from the spiral shape center, which enables the bubbles to reach the corner portion for effective crack prevention. The positioning requirement that step portions be at the outer peripheral portion of the cavitation bubbles creates a specific asymmetric configuration that ensures both reliability and manufacturability.
Solution Approach 2:
The patent changes the positioning parameters of the water jet system to offset the cavitation bubble center from the spiral center. This parameter adjustment, combined with positioning the step portions at the outer peripheral region of the cavitation bubbles, creates optimal conditions for imparting compressive residual stress to prevent cracks while accounting for the scroll's unique geometry.
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
Effectively imparts compressive residual stress to the target regions of the scroll, enhancing fatigue strength and preventing cracks, thus reducing the risk of accidents caused by cracks.
Implementation Method 1
water jet peening by jetting cavitation bubbles generated underwater by a water jet
Implementation Method 2
jetting cavitation bubbles generated underwater by a water jet
Implementation Method 3
The impact force generated by the collapse of the cavitation bubbles imparts compressive residual stress to the metallic material
Data Source
AI summary
A method for manufacturing a compressor scroll that appropriately impinges cavitation bubbles on target regions of a scroll. The method includes the step of water jet peening by jetting cavitation bubbles generated underwater by a water jet at a first side of an end plate (13A) of the scroll (13), with a center (P1, P2, P3) of the cavitation bubbles being offset from a center (O) of the spiral shape of a wall portion (13B) on the end plate (13A) and the step portion (13Aa) and the stepped portion (13Ba) positioned at an outer peripheral portion of the cavitation bubbles (C).