Patent Application
20130319728
The subject matter disclosed herein relates to an apparatus and method to insulate a rotatable shaft and, more particularly, to an apparatus and method to insulate bearings from shaft currents by insulating a rotating shaft for variable frequency drive (VFD) applications.
A variable-frequency drive (VFD) system is a system for controlling rotational speed of an alternating current (AC) electric motor by controlling a frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive and may be known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. VFD systems are used in a wide number of applications to control pumps, fans, hoists, conveyors and other machinery.
In VFD applications, however, a problem exists in that shaft currents induced along rotatable shafts may cause bearing pitting in the shaft bearings. To prevent this from happening, the bearings may be insulated with ceramic coatings. Such insulated bearings are relatively expensive and their use can require higher lead time for procurement.
According to one aspect of the invention, an apparatus to insulate a rotatable shaft is provided. The apparatus includes a sleeve disposable about the rotatable shaft and including an exterior surface on which a bearing seat is mountable, a first insulation part interposable between an axial surface of the mountable bearing seat and a corresponding axial surface of the rotatable shaft and a second insulation part interposable between a radial surface of the sleeve and a corresponding radial surface of the rotatable shaft.
According to another aspect of the invention, an apparatus to insulate a bearing seat from a rotatable shaft is provided. The apparatus includes a base insulation part interposable between an axial surface of the mountable bearing seat and a corresponding axial surface of the rotatable shaft and a composite insulation part including reinforcing structures interposable between a radial surface of the bearing seat and a corresponding radial surface of the rotatable shaft.
According to yet another aspect of the invention, a method of insulating a bearing seat from a rotatable shaft is provided. The method includes mounting the bearing seat about the rotatable shaft and interposing first and second insulation parts between an axial surface of the mounted bearing seat and a corresponding axial surface of the rotatable shaft and between a radial surface of the mounted bearing seat and a corresponding radial surface of the rotatable shaft, respectively.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
With reference to
A shoulder of the rotatable shaft 11 includes an axial surface 111 proximate to an end of the drive element 13. An exterior surface of the rotatable shaft 11 includes a radial surface 112. When assembled together, the bearing components 12 may be seatably disposed adjacent to the axial surface 111 and about the radial surface 112. The bearing components 12 include an outer ring 121, a bearing seat 122 and ball bearings 123. The ball bearings 123 are radially and axially secured between the outer ring 121 and the bearing seat 122. The bearing seat 122 is formed to define a bore 124 through which the rotatable shaft 11 is extendable and includes an axial surface 1221 and a radial surface 1222.
The axial surface 1221 is configured to face in an axial direction and to axially oppose the axial surface 111 of the rotatable shaft 11. The radial surface 1222 is configured to face radially inwardly and to radially oppose the radial surface 112 of the rotatable shaft 11.
The apparatus 10 includes a sleeve 20, a first insulation part 30 and a second insulation part 40. The sleeve 20 may be formed of steel or a similar metal or metallic alloy and is disposable in shrunk fit form about a portion of the radial surface 112 of the rotatable shaft 11. The sleeve 20 includes a machinable exterior surface 21 on which the bearing seat 122 is mountable. The first insulation part 30 is interposable between at least a portion of the axial surface 1221 of the bearing seat 122 and a corresponding portion of the axial surface 111 of the rotatable shaft 11. The second insulation part 40 is interposable between an inner diameter of the sleeve 20 and a corresponding portion of the radial surface 112 of the rotatable shaft 11.
The first and second insulation parts 30 and 40 may be formed of different or substantially similar materials provided the materials are electrically insulating. For example, the first and second insulation parts 30 and 40 may be formed of one or more of insulation tape and/or paper.
In accordance with embodiments, the first insulation part 30 may be provided as a ring member 31 that is formed of electrically insulating material. The ring member 31 may be thicker along a radial dimension thereof than along an axial dimension thereof, which is relatively narrow. In this way, the ring member 31 may have a washer-shape with opposite faces and a bore 310 defined through the ring member 31 from one face to the other. Thus, as shown in
The second insulation part 40 may include one of insulation tape and insulation paper and may have a substantially cylindrical shape. Where the second insulation part 40 is substantially cylindrical, the second insulation part 40 is interposable between a substantially cylindrical portion of an inner diameter of the sleeve 20 and a corresponding substantially cylindrical portion of the radial surface 112 of the rotatable shaft 11. The second insulation part 40 may include a plurality of sleeve member portions 41. For example, the second insulation part 40 may include two sleeve member portions 41 of electrically insulating materials that each extends about halfway around the rotatable shaft 11. When these two (or more) sleeve member portions 41 are positioned in a circumferential end-to-end configuration, an entire circumference of the rotatable shaft 11 may be surrounded by the second insulation part 40.
Still referring to
Once the sleeve 20 is shrunk fit, the exterior surface 21 thereof may be machined to substantially match a topography of the radial surface 1222 of the bearing seat 122. This may be accomplished by any suitable machining process or processes. At this point, the bearing seat 122 may be mounted onto the machined exterior surface 21 of the sleeve 20 such that the axial surface 1221 of the mounted bearing seat 122 is disposed against the first insulation part 30, which is itself disposed against the axial surface 111 of the rotatable shaft 11.
With reference to
The composite insulation part 400 may be formed by disposing the insulation band 401 with glass fibers provided therein about the rotatable shaft 11 such that the glass fibers become at least partially warped. The insulation band is then cured by, for example, baking processes, to harden the glass fibers into the reinforcing structures 402. At this point, an exterior surface 403 of the composite insulation part 400 may be machined to substantially match a topography of the radial surface 1222 of the bearing seat 122. This may be accomplished by any suitable machining process or processes. The bearing seat 122 may then be mounted onto the machined exterior surface 403 of the composite insulation part 400 such that the axial surface 1221 of the mounted bearing seat 122 is disposed against the first insulation part 30, which is itself disposed against the axial surface 111 of the rotatable shaft 11.
In accordance with the description provided above, the bearing components 12 are insulated from shaft current. The insulation is cost effective as compared to other insulation methods, such as the use of ceramic bearings.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
