This invention relates to magnetic couplings. More specifically, this invention relates to radially interfitting magnetic members for coupling rotational movement through a hermetically sealed wall or barrier.
Permanent magnet couplings in general are well known in the prior art. Typically, permanent magnet couplings comprise a pair of axially or radially opposed magnets, or sets of mangets, formed from a permanent magnet material such as alnico. One of the permanent magnets is coupled to a driving member such as a motor, and the other permanent magnet is coupled to a driven member such as a pump impeller. The magnets are magnetically coupled to each other so that rotation of the driving member causes a corresponding rotation of the driven member to obtain the desired torque output. Couplings of this type are particularly advantageous wherein a hermetic seal or barrier is interposed between the driving and driven members, such as in a motor-driven freon compressor. In these applications, the hermetic seal assures against passage or leakage of any process fluid between the driving and driven members, and thereby prolongs the operating life of the equipment. For examples of prior art magnetic couplings, including hermetic seals or barriers, see U.S. Pat. Nos. 3,877,844; 3,826,938; 3,411,450; 3,512,903; 3,378,710; 3,249,777; 3,238,883; 3,238,878; 3,195,467; 2,970,548; 2,366,562; 2,230,717 and U.S. Pat. No. 26,094.
During operation, a magnetic coupling may generate substantial quantitites of heat due to relative slippage of the magnets at excessive torque loads, induction heating effects, and the like. This is particularly true with closely aligned, radially interfitting permanent magnets rotating at relatively high speeds. Accordingly, in the prior art, magnetic couplings typically have not been used with mechanical devices rotating at relatively high speeds so as to avoid any cooling requirement. However, some attempts to cool a magnetic coupling have been made, and have comprised methods of exposing at least a portion of one of the magnets to a cooling fluid. See, for example, U.S. Pat. Nos. 3,238,883; 3,238,878; and 3,267,868. These prior art devices do not, however, provide the requisite pumping or cooling action when the coupling is used with relatively high speed machinery such as turbomachinery wherein the coupling is required to rotate at speeds of on the order of about 50,000 r.p.m. or more.
Prior art magnetic couplings have also encountered bearing design problems. That is, with low speed rotating devices, magnet-carrying shafts may be satisfactorily supported by relatively simple journal and thrust bearing structures such as sleeve bearings, ball bearings, and the like. However, as rotational speed increases, the problems of shaft stability and vibration correspondingly increase to create bearing design and cooling problems. Moreover, with increased speed, the adverse effects on the system due to incidental bearing magnetization and induction heating become substantial. However, the prior art has consistently relied upon relatively conventional bearing structures for shaft support, and not upon so-called process fluid bearings such as hydrodynamic or foil bearings. See, for example, U.S. Pat. Nos. 3,512,903; 3,378,710; 3,195,467; 3,238,878; 2,970,548 and 2,366,562. Accordingly, permanent magnet couplings have not been widely or satisfactorily used in high speed applications.
This invention overcomes the problems and disadvantages of the prior art by providing an improved permanent magnet coupling particularly for use with relatively high speed rotating machinery. In particular, the invention includes dual process fluid cooling paths for circulating process fluid to control the temperature of the coupling magnets, and high speed process fluid bearings for supporting the rotating shafts at high speeds.
USPTO Backgrounds
USPTO Backgrounds