Rotary Machine Non-Circular Shaft Impeller Creep
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Solution Overview
Problem
In rotary machines with resinous impellers, creep deformation occurs over time, leading to reduced fastening force and unstable rotation due to the high-pressure fastening force applied by nuts, which can result in idling and increased unbalance and whirling.
Innovation Solution
A rotary machine design featuring a penetrating shaft with a non-circular portion that engages with a connecting portion on the impeller, reducing the impact of creep deformation and maintaining stable rotation by transmitting rotational force through the non-circular engagement, and additional features like alternating blade portions and separate circular and non-circular sections to enhance support and balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nut is used to fasten the resinous impeller to the turbine shaft, then the impeller can be securely attached, but creep deformation occurs over time reducing fastening force and causing unstable rotation
Solution Approach 1:
The shaft incorporates a non-circular portion (such as an oval or polygonal cross-section) that engages with a corresponding non-circular connecting portion on the impeller hub. This asymmetric geometry prevents relative rotation between the shaft and impeller, eliminating idling and ensuring stable rotation even when creep deformation occurs in the resinous material. The non-circular engagement converts the fastening mechanism from purely axial (prone to creep) to include a rotational locking component.
2Force
If high-pressure fastening force is applied to the resinous impeller, then secure attachment is achieved, but creep deformation increases over time
Solution Approach 1:
The non-circular shaft portion creates a geometric interlock that provides rotational stability without requiring excessively high fastening forces. The asymmetric engagement distributes stresses more evenly and prevents the impeller from rotating relative to the shaft, thereby reducing creep deformation caused by sustained high-pressure fastening.
3Ease of manufacture
If the shaft has a perfect circular cross-section, then manufacturing is simple, but the impeller can idle during rotation
Solution Approach 1:
The shaft is designed with a non-circular cross-section (oval, rectangular, or other asymmetric shape) in the portion that engages with the impeller. This asymmetric geometry prevents the impeller from rotating independently on the shaft, eliminating idling and ensuring positive drive engagement. The non-circular portion can be manufactured using standard machining processes, maintaining ease of manufacture while significantly improving rotational reliability.
Data Source
AI summary
Provided is a rotary machine including a rotating resinous impeller, a rotary shaft penetrating the impeller, and a fastening portion screwed to the rotary shaft, in which the rotary shaft includes a penetrating shaft portion facing an inner peripheral surface of the impeller, a tip shaft portion screwed to the fastening portion, and a fastening reception portion sandwiching the impeller between the fastening reception portion and the fastening portion, the penetrating shaft portion has a non-circular portion and an outline of a cross section of the non-circular portion orthogonal to a rotational axis deviates from a perfect circle about the rotational axis, and the impeller includes a connecting portion engaging with the non-circular portion.