Patent Publication Number: US-4484789-A

Title: Mercury slip rings and method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention achieves the safe use of mercury for electrical current conduction between stationary and rotating parts of an input-output structure or device prior to and during shipping of the structure, during operation, and for disassembly and repair of the structure by preventing environmental contamination of all stages. 
     2. Prior Literature 
     No literature is known which discloses the safe use of mercury slip rings but rather industry has avoided its use, because of environmental pollution, and substituted therefor coaxial air coupled cores and the like for electrical energy transfer with rotating machinery. 
     SUMMARY OF THE INVENTION 
     The invention supervises mercury confinement in its application as a slip ring type connection between rotating and stationary device components in three stages of existence. First, the mercury is confined in a closed cavity and/or capsule to permit shipping or non-use of the components, and is only intentionally liberated within the device when use is imminent. Secondly, the liberated mercury is confined to the components by employing one or more of: minimal escape paths, machined or ground contacting surfaces, pressure exerted to close the surfaces, and the use of decontaminating material in the possible escape paths. Thirdly, a separate contained supply of the decontaminant material is stored within the device, and is releasable prior to disassembly for repair or the like to neutralize the mercury so it does not harm the repairman or pollute the atmosphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the preferred mercury slip ring structure; 
     FIG. 2 shows the assembly in cross section; 
     FIG. 3 is an enlarged view showing the slip ring closure sealing the outer slip ring; and, 
     FIGS. 4 and 5 show details of the charging and capsule puncturing and sealing arrangement. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     This invention relates to the design and construction of fluid containing means (mercury slip rings) which are used to carry electricity between fixed and rotating parts of electrical machinery. 
     A primary purpose of the invention is to provide a means for sealing the input-output circuitry assembly so as to preclude air polution which results from vaporization of (eg) the mercury into the atmosphere as well as consequential loss of liquid mercury which could render the unit inoperative. 
     A further purpose is to provide a means--prior to use of the device--for encapsulating the fluid medium (mercury) within the assembly, but outside the fluid connection (slip rings) proper, to provide for easy assembly during manufacture, as well as for safe storage and shipping. 
     Another purpose is to provide means for the safe decontamination of the mercury within the assembly by combining or amalgamating the mercury with some substance, usually in granular form, to render the mercury harmless to personnel who may dismantle the unit for overhaul or salvage. Such substance may comprise fine silver particles, sulphur or other known materials. 
     The mercury slip ring assembly consists of a hollow shaft 2 to which are fixed bearings 3 and 11, inner slip rings 7 with their electric wires 7B, soldered into holes 7A, said electric wires entering the shaft 2 through holes 2A, 2B and exiting through coaxial hole 2C. Holes 2A, 2B are made in the form of slots to facilitate the task of assembly during manufacture. Also fixed to shaft 2 are the shaft insulator 9 and shaft insulator sleeves 5 which electrically insulate the shaft 2 from the inner slip rings 7 and the inner slip rings 7 from each other, and essential assembly hardware--the insulation support washers 4 and assembly nut 12. 
     In the usual case, the shaft 2 with above parts assembled thereto, rotates, and the remaining parts of the assembly are stationary. Of course, in some applications, it might be desirable to have the shaft 2 and assembled parts fixed (non-rotating) and the remaining parts rotating. 
     The usually stationary parts in the instant design include the front housing 1, the center housing 10, and the rear housing 14, between which are assembled the outer slip rings 8 and their slip ring closures 6. These stationary parts are held together by assembly screws 15 (Only one shown). The outer slip rings 8 are electrically insulated from the assembly screws 15 and from each other by the outer slip ring insulators 16, three of which are required for each outer slip ring 8, although only one for each is shown in FIGS. 1 and 2. The front housing 1, center housing 10, and rear housing 14 are all made of phenolic or other suitable insulation material, in the instant design, thereby insulating outer slip rings 8 from each other and from bearings 3, 11. 
     Electrical connections to the outer slip rings 8 are made by electric wires or straps--&#34;pigtails&#34;--(not shown) attached by connection screws 17, (FIG. 1). 
     Although the described and pictured design includes two sets of slip rings providing for two electrical connections, any number may be used as the application requires. 
     The following features contribute to making the mercury slip ring assembly effectively sealed and polution-free: 
     1. There is a close fit between the front bearing 3 and the front housing 1 to preclude vapor escape along the housing bore. 
     2. This close fit is enhanced by the wave washer 13 which serves as a thrust spring, pressing the front bearing 3 into its seat in the front housing 1. 
     3. The front bearing 3 contains double seals, typical of ball bearings. 
     4. The interference fit between the outer slip rings 8 and slip ring closures 6, as shown in FIG. 3, effectively prevents mercury leakage between these two parts. Tight assembly screws 15 maintain a close and tight contact between center housing 10 and slip ring closure 6; in turn maintaining a close and tight contact between slip ring closure 6 and outer slip ring 8. The same conditions apply, of course, to front housing 1 and its adjacent slip ring closure 6 and outer slip ring 8. 
     5. Fine machine surface finishes on the faces of the outer slip rings 8, slip ring closures 7 and housings 1, 10, 14 effectively obviates the necessity for gasketing these interfaces although gaskets such as &#34;O&#34; rings could be used if desired or necessary. 
     6. The closed end construction of the rear housing 14 eliminates an obvious potential area of leakage. Commercial manufacturing tolerances as well as heat expansion coefficients requires a thrust spring of some type. In the event it is desired to construct a mercury slip ring assembly which uses a through-shaft, the wave washer 13 could be replaced by an &#34;O&#34; ring which could provide both the thrust and sealing properties required. 
     Additionally, it was found helpful to provide minimal clearances between the shaft insulator 9 and center housing 10, and between the shaft insulator sleeves 5 and the outer slip ring 8 or slip ring closure 6. These small clearances proved effective in keeping the mercury, at least while in the liquid state, within the slip ring wells. The shaft insulator 9 and the shaft insulator sleeves 5 have slots 2A and 2B which provide for passage of the electrical wires from the inner slip rings 7 into and through the shaft 2. These slots do not extend to the outer diameters of said parts, and therefore there is no access for the mercury to the shaft 2. 
     A mercury charging port is drilled radially from the outside circumference of each outer slip ring 8 (FIGS. 1 and 4) into the mercury well 10A. After charging with a pre-measured quantity of mercury, the charging ports are closed with screws 18 similar to connection screws 17. 
     Turning now to the secondary and tertiary purposes: FIGS. 4 and 5 show a means to provide for encapsulating the mercury within center housing 10 with further, a means to release at will, the mercury from the capsule 19 thereby allowing it to flow into the slip ring well when it is desired to place the mercury slip ring assembly into service. 
     Center housing 10 and rear housing 14 may be provided with cavities 10A and 14A, (FIG. 1), respectively. Intersecting these cavities are screw threads and conical valve seats 10B, (FIG. 4) and 10C, with corresponding parts for rear housing 14, not illustrated. As will be explained, these screw threads and valve seats are optionally fitted with conically pointed capsule puncturing and cavity sealing screws 18. The valve seats lead to ports, such as 10D, (FIG. 4), which engage ports 8A drilled into the outer slip rings 8. 
     Should it be desired, front housing 1 may be constructed similarly to the center housing 10 and rear housing 14 in regard to the cavity, valve seat and port, provided the relative dimensions of the parts permit. 
     At the time of assembly, a soft, pliable, plastic capsule 19, (FIG. 4), containing the required quantity of mercury is placed within the cavities such as 10A. It is important that these capsules 19 contain some air or other suitable gas (es). 
     When it is desired to place the mercury slip ring assembly into service, the capsule puncturing and cavity sealing screws 18 are driven into the housings 10, 14. The sharp points of the screws 18 penetrate the upper surface of the capsules 19. Because the capsules 19 containing some air as mentioned supra, the capsules 19 are permitted to deform under the pressure of the screws 18, and therefore no mercury is expelled around the points of the screws 18 when the capsules 19 are punctured. 
     The screws 18 are driven further until they also puncture the lower portion of the capsule 19. Then the screws 18 are partially withdrawn, allowing the mercury to flow through the ports 10D, 8A into the wells of the outer slip rings 8. 
     After allowing sufficient time for all the mercury to flow into the wells of the outer slip rings 8, the screws 18 are fully driven into the housings 10, 14 until the conical points of the screws 18 fully engage the conical valve seats, such as, 10C, thereby sealing the mercury within the slip ring assembly. Of course, the screws 18 must be positioned uppermost during this operation, in order that gravity may do its work and cause the mercury to flow downward into the wells of the outer slip rings 8. 
     It can be readily seen that because of the relative sizes of the housings 10, 14 and their cavities 10A, 14A, several cavities can be provided within each housing 10, 14. If desired, a second cavity 10A, 14A with valve seats 10C, 14C and ports 10D, 14D can be made within each housing 10, 14. These would engage additional valve seats 10C, etc. which are provided with conically pointed screws similar to or identical to the capsule puncturing and cavity sealing screws 18. 
     The above mentioned additional features may provide means to accomplish the tertiary purpose, because conventional mercury vapor assemblies cannot be safely repaired; and if opened, toxic mercury vapor escapes into the atmosphere. The present invention includes a detoxification material cavity or capsule receiving region for communication with the sealed mercury vapor region to decontaminate the mercury vapor upon intentional release of the detoxifying material into said communication. 
     This chemical material will neutralize the mercury, to prevent vapor escape, and may comprise zinc or sulphur powder, as well as other well known materials suited to this purpose (ie) which will amalgamate with mercury. 
     During assembly, the secondary cavity may be provided with a sealing screw 18 which is fully driven so as to close off the cavity, such as 10A, from the slip ring well. Some substance, granular iron as an example, which would combine or amalgamate with the mercury is placed within the cavity. If and when it is desired to render the mercury harmless, the secondary cavity sealing screw 18 is withdrawn a few turns from its valve seat. The mercury slip ring assembly is positioned so that the sealing screw and cavity are downward. Mercury then flows into the cavity where it combines with the amalgamating substance, thereby rendering the mercury harmless. 
     A variation on the above is to provide the secondary cavity containing the amalgamating substance with no valve seat 10C, 14C or sealing screw 18, but instead provide a port 10D, 14D significantly smaller than the granular substance. In this case, the amalgamating substance combines with any mercury vapor present, thereby rendering it harmless. 
     Of course, mercury slip ring assemblies can be constructed with any or all of the abovedescribed features for mercury charging and mercury removal and/or amalgamating. 
     The amalgamating material is located at the outer edges of any possible escape routes for the mercury such that it is decontaminated only if it is likely to reach the environment. Such locations are between the housing members 10 and 14 of FIG. 3, toward the outer periphery thereof; along the right hand edges of bearing 3, along both edges of outer slip rings 8, past bearing 11, and along assembly screws 15.