Motor Grounding Seal with Conductive Insert

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Solution Overview

Problem

Existing shaft sealing devices for rotating equipment, particularly in electrical motors with variable frequency drives, fail to effectively prevent contamination and premature bearing failure due to shaft voltage-induced electrostatic discharge, which causes pitting and fluting in bearings.

Innovation Solution

A bearing isolator assembly with a receptor groove in the stator for a conductive insert, preferably made of bronze, that directs and transmits accumulated bearing current to ground, preventing contamination and reducing electrostatic discharge through a low impedance path.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conductive insert is added to the bearing isolator assembly, then shaft voltage and electrostatic discharge are reduced, but device complexity increases

Engineering Contradiction:

Improvebearing lifeVSAvoidseal assembly structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The conductive insert is nested within the bearing isolator assembly, specifically positioned in the receptor groove of the stator. This nesting approach allows the grounding function to be integrated into the existing seal structure without requiring a completely separate system, thereby reducing overall device complexity while still providing shaft voltage protection.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The conductive insert acts as an intermediary element between the bearing isolator and ground. It provides a dedicated low-impedance path for shaft voltage to discharge to ground, mediating the electrostatic discharge problem without requiring direct modification of the bearing isolator's primary sealing function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the bearing isolator encompasses the stator within the rotor, then lubricant retention and contamination prevention are improved, but manufacturing complexity increases

Engineering Contradiction:

Improvelubricant retentionVSAvoidassembly construction

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The bearing isolator assembly is segmented into distinct functional components: the rotor portion, the stator portion with receptor groove, and the conductive insert. This segmentation allows each component to be manufactured separately using standard processes, then assembled together, reducing overall manufacturing complexity while achieving the encompassing configuration for improved lubricant retention.

Inventive Principle:

Principle #1Segmentation

3Productivity

If variable frequency drive control is used to regulate motor speed, then productivity is improved, but bearing current and electrostatic discharge increase

Engineering Contradiction:

Improvemotor speed controlVSAvoidshaft voltage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The invention converts the harmful shaft voltage generated by VFD operation into a beneficial grounding current. By providing the conductive insert with a low-impedance path to ground, the harmful electrostatic discharge that would normally damage bearings is redirected through the conductive insert, protecting the bearing while allowing continued VFD operation for improved productivity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Substantially reduces shaft voltage and attendant electrostatic discharge, extending bearing life by preventing premature failure and maintaining lubricant retention while protecting the conductive insert from environmental exposure.

Implementation Method 1

a bearing isolator for directing electrostatic charge to ground while retaining lubrication solution and repelling contamination

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

shaft voltage-induced electrostatic discharge, which causes pitting and fluting in bearings

Methodology Applied

Scientific EffectElectrostatic discharge: Electrostatic Discharge

Implementation Method 3

The rotor and stator are magnetically coupled together such that the rotor encompasses the stator within the rotor

Methodology Applied

Scientific EffectMagnetic repulsion: Ion Repulsion/Attraction

Data Source

PatentUS10270320B1Motor grounding seal

Publication Date: 2019.04.23 INPRO SEAL LLC

AI summary

A shaft seal assembly is disclosed having a stator including a main body and axial and radial projections therefrom. The rotor may be radially extended to encompass the axial and radial projections from said stator. A passageway formed between the radial projection of stator and rotor results in an axial passageway having its opening facing rearwardly from the rotor and away from the source of impinging coolant and/or contaminant. A concentric circumferential receptor groove in the stator facing the housing allows insertion of a conductive insert for transmission of electrostatic charge away from the shaft through the shaft seal assembly to the housing and ground. The receptor groove is opposite the axial passageway and provides for both a substantially lower contaminant environment and improved engagement with the conductive insert.