Brush Seal Backing Plate Tooth Clearance Design
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Solution Overview
Problem
Brush seal assemblies in gas and steam turbines face challenges in reducing contact between the backing plate and rotary shaft during transient conditions, leading to potential mushrooming and bristle wear, while existing solutions increase cost and complexity or destabilize the seal.
Innovation Solution
A brush seal assembly with a backing plate featuring a backing tooth and tip, where the tooth clearance is less than the tip clearance, allowing the backing tooth to selectively contact the sealing surface and reposition the backing plate using a biasing member to avoid contact between the backing tip and the rotary shaft, thereby reducing wear and maintaining axial support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the fence height of the backing plate is reduced to improve pressure capability and reduce bristle wear, then the bristles have increased support and are subjected to less bending stress, but the risk of rubbing against the rotary shaft during transient conditions increases
Solution Approach 1:
The backing plate is segmented into a main body portion and a separate protruding tooth structure. The tooth extends radially toward the rotary shaft while the main body remains at a safe distance, allowing the tooth to provide necessary support without causing rubbing contact during transient conditions.
Solution Approach 2:
The backing plate has non-uniform geometry with a localized protruding tooth structure that provides targeted support in the radial direction while the rest of the backing plate maintains axial support function. This local modification allows differential functionality in different regions of the backing plate.
2Duration of action of stationary object
If the fence height is reduced to provide axial support to the bristles, then bristle wear is reduced, but the backing plate surface may mushroom or smear when rubbed by the rotating surface during transient conditions
Solution Approach 1:
The protruding tooth is extracted as a separate functional element from the main backing plate body. This tooth specifically handles the radial support function and potential contact with the rotary shaft, while the main backing plate body focuses on axial support, preventing the harmful mushrooming and smearing effects on the main surface.
Solution Approach 2:
The protruding tooth acts as a sacrificial element that can contact the rotary shaft during transient conditions without causing damage to the main backing plate surface. This beforehand cushioning protects the main backing plate from the harmful effects of rubbing contact.
3Reliability
If coatings or rubbing-facilitating materials are applied to the backing plate to prevent mushrooming, then contact tolerance is improved, but cost and complexity are increased
Solution Approach 1:
The protruding tooth is designed as a simple, inexpensive geometric feature that can be easily manufactured into the backing plate. It serves as a disposable sacrificial element that protects the main backing plate from damage without requiring expensive coatings or complex materials.
4Reliability
If the forward plate is set to a tight clearance to serve as a bump element protecting the backing plate, then backing plate contact is reduced, but a jet flow is created that destabilizes the brush seal bristles causing fluttering and wear
Solution Approach 1:
The protruding tooth serves as an intermediary element between the backing plate and the rotary shaft. It absorbs the impact and contact forces during transient conditions, protecting the main backing plate from damage without creating the destabilizing jet flow that would occur with a tight forward plate clearance.
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
The solution effectively reduces contact between the backing plate and rotary shaft, minimizing wear and maintaining axial support, while providing a cost-effective and stable sealing mechanism.
Implementation Method 1
a biasing member positioned adjacent to the backing plate and configured to exert a biasing force upon the backing plate in a direction towards the stationary position
Data Source
AI summary
A brush seal assembly is provided, including a sealing surface, a side plate, a backing plate, a plurality of bristles, and a biasing member. The backing plate is selectively located in a stationary position and has at least one backing tooth and a backing tip. The backing tooth has a tooth surface and the backing tip has a tip surface. A tooth clearance is measured between the tooth surface and the sealing surface. A tip clearance is measured between the tip surface and the sealing surface. The tooth clearance is less than the tip clearance. The bristles are located between the side plate and the backing plate. The bristles include an end portion for sealing to the sealing surface. The biasing member exerts a biasing force upon the backing plate in a direction towards the sealing surface. The backing tooth is configured for selectively contacting the sealing surface.