Motor Grounding Seal

Abstract

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application is a continuation-in-part and claims priority from U.S. patent application Ser. No. 12 / 401,331 filed on Mar. 10, 2009 which application was a continuation of and claimed priority from U.S. patent application Ser. No. 11 / 378,208 filed on Mar. 17, 2006, which claimed the benefit of U.S. provisional App. No. 60 / 693,548, filed Jun. 25, 2005, all of which are incorporated herein in their entireties.FIELD OF THE INVENTION[0002]The present invention relates to an improved bearing isolator sealing device, and more particularly, to a bearing isolator for directing electrostatic charge to ground while retaining lubrication solution and repelling contamination such as water, dust, dirt, sand and paper stock from the bearing environment and away from the shaft grounding ring, within the bearing cavity of a hub assembly such as an electrical motor bearing for engagement with a rotatable shaft.STATEMENT REGARDING FEDERALLY SPONS...

AI Technical Summary

Benefits of technology

[0011]An objective of the motor grounding seal is to provide an improvement to seals or bearing isolators to prevent leakage of lubricant and entry of contaminants by encompassing the stator within the rotor to create an axially directed interface at the radial extremity of the rotor. It is also an objective of the present invention to disclose and claim a seal or bearing isolator for rotating equipment that retains lubricants, prevents contamination and conducts and transmits and directs accumulated bearing current to ground.

[0013]It has been found that a bearing isolator assembly having a rotor and stator manufactured from bronze has improved charge dissipation qualities. The preferred bronze metallurgy is that meeting specification 932 (also referred to as 932000 or “bearing bronze”). This bronze is preferred for bearings and bearing isolators because it has excellent load capacity and antifriction qualities. This bearing bronze alloy also has good machining characteristics and resists many chemicals. It is believed that the specified bronze offers increased shaft voltage collection properties comparable to the ubiquitous lighting rod due to the relatively low electrical resistivity (85.9 ohms-cmil / ft@68 F or 14.29 micro-ohm-cm@20 C) and high electrical conductivity (12% IACS@68 F or 0.07 MegaSiemens / cm@20 C) of the material selected.

Problems solved by technology

Adequate maintenance of rotating equipment is difficult to obtain because of extreme equipment duty cycles, the lessening of service factors, design, and the lack of spare rotating equipment in most processing plants.

Lip seals or other contacting shaft seals can quickly wear to failure and are also known to permit excessive amounts of moisture and other contaminants to immigrate into the oil reservoir of the operating equipment before seal failure had exposed the interface between the rotor and the stator to the contaminants or lubricants at the radial extremity of the seal.

The problem of seal wear and damage as applied to electrical motors using variable frequency drives is compounded because of the very nature of the control of electricity connected to variable frequency drive (VFD) controlled motors.

There are many causes of bearing current including voltage pulse overshoot in the VFD, non-symmetry of the motor's magnetic circuit, supply imbalances, and transient conditions, among other causes.

This random and frequent discharging has an electric discharge machining (EDM) effect, causing pitting of the bearing's rolling elements and raceways.

Eventually, the deterioration will lead to complete bearing failure.3 See www.Greenheck.com

Most external applications add to costs, complexity, and exposure to external environmental factors.

However, installing insulated bearings does not eliminate the shaft voltage, which will still find the lowest impedance path to ground.

Thus, insulated bearings are not effective if the impedance path is through the driven load.

Therefore, the prior art does not teach an internal, low wearing method or apparatus to efficaciously ground shaft voltage and avoid electric discharge machining of bearings leading to premature bearing failure.

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