Abstract:
An improved mechanical shaft seal to give a tight seal between relatively rotating machine parts and prevent the escape of particulate material into the atmosphere or into the mechanical components of the housing under adverse operating conditions. The seal provides a grease chamber that prevents solid particles from reaching the main seal by migration within the mechanical shaft seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application 60/804,873, filed Jun. 15, 2006, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     This invention relates to self-contained seals, particularly to devices and methods for providing a seal between two relatively rotatable machine parts, particularly suited for use in equipment for handling dry powdered material. 
     Manufacturing processes, such as mining and minerals, cement, or bulk powder production, require equipment that is capable of conveying, blending, mixing, or metering solids. In order to facilitate the movement of dry material through processing equipment a rotating shaft is often used, such as an agitator in the case of blending. Industries, like cement or mineral production, also force the movement of dry material that is in the form of small particles or powder by using pressurized vessels or lines. The vessels and lines used to convey raw materials must be constructed to prevent the release of particles from within a pressurized and sometimes heated system. The area around a rotating shaft is especially susceptible to the release of heated, abrasive solids. Leaks are prevented by incorporating shaft seals around the rotating shafts. 
     As those skilled in this art will appreciate, shaft seals for dry-material-handling equipment that operate under positive pressure can sometimes fail. Seals for this purpose typically have used high-pressure air lines to increase the pressure within seal housings. The increased pressure in the housing is higher than the pressure within the process equipment carrying the dust and solids; therefore, the dry material is unable to flow into the housing. Disadvantages of such pneumatic seals are increased cost (due to the need for maintenance and operation of air lines) and the risk of interrupted air supply. When air supply is interrupted, abrasive particles can escape from the system or into the housing of a seal. When such abrasive solids are introduced into shaft seal housing, they can quickly wear away rotating parts, leading to failure. The abrasive material will erode the vessel and surrounding parts. Therefore, the dry-material-handling industry requires shaft seals capable of preventing heated, abrasive solids under pressure from leaking without the use of pneumatic lines. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved mechanical shaft seal to give a tight seal between relatively rotating machine parts and prevent the escape of solid material into the atmosphere or into the mechanical components of the housing. The seal is effective in maintaining a tight seal under adverse operating conditions. 
     An advantage of the invention is that such a mechanical shaft seal is typically self-contained and avoids the need for pneumatic lines or maintenance. 
     Another advantage of the invention is that such a mechanical shaft seal is easily assembled and installed onto dry-material-handling equipment. 
     The combination of such a seal and dry-material-handling equipment is another aspect of the invention. 
     A feature of the mechanical shaft seal assembly of the present invention is a grease chamber that prevents solid particles from reaching the main seal by migration within the mechanical shaft seal. By keeping solids away from the main seal, the present mechanical shaft seal is able to maintain adequate force and prevent a breach between seal faces. The grease chamber also lubricates seal faces within the mechanical shaft seal to prevent seal faces from sticking to each other. 
     An aspect of the present invention provides a mechanical shaft seal adapted to be mounted externally such that one end thereof comprising a seal assembly is within a pressurized system containing dry material. Such a mechanical shaft seal desirably has a gland used to mount the mechanical shaft seal externally such that one end of the gland is exposed to the external atmosphere and the opposite end is mated with the sealing assembly, the gland having a bore therethrough to enable the gland to house a sealed bearing and a rotor sleeve, the rotating seal assembly also housing the rotor sleeve for rotation therein, and the rotor sleeve having a bore therethrough to enable the rotor sleeve to surround and sealingly engage a shaft for rotation therewith. 
     A more specific aspect of the invention provides a seal assembly comprising a grease housing, a lip seal, a grease chamber (a chamber having a substantial amount of grease contained therein), and a single-spring seal that prevents the migration of solid material into the rotating parts of mechanical shaft seal (which migration may result in damage due to the abrasive quality of the dry material), the grease housing and the lip seal having a bore to receive a rotor sleeve therethrough, and a stationary seat mounted around the rotor sleeve, the single-spring seal being mounted around the rotor sleeve and constrained in sealing engagement with the stationary seat, and the grease chamber bounded by the lip seal, grease housing, and rotor sleeve. 
     Other aspects, advantages and features of the invention will be apparent from the detailed description and claims presented below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features of the invention will become more apparent from the following description of an embodiment of the invention wherein reference is made to drawings. 
         FIG. 1  is a perspective view of a mechanical shaft seal of the present invention mounted on the side wall of a flap valve. 
         FIG. 2  is an exploded view of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of half of a seal assembly according to the present invention. 
         FIG. 4  is a cross-sectional view of a grease housing according to the present invention. 
         FIG. 5  is a cross-sectional view of a rotor sleeve according to the present invention. 
         FIG. 6  is a cross-sectional view of a gland according to the present invention. 
         FIG. 7  is a perspective view of an alternative embodiment of a mechanical shaft seal of the present invention mounted on the side wall of a flap valve. 
         FIG. 8  illustrates a multiple valve configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  and  FIG. 2 , a mechanical shaft seal embodying the present invention is adapted to be externally and sealingly mounted onto dry-material-handling equipment, such as onto a flap valve (e.g. an Airlock® valve sold by Plattco Corporation (Plattsburgh, N.Y.)), or a flap valve, or a diverter valve or other valve maintaining a pressure differential between two environments. Applications for a mechanical shaft seal of the invention include, but are not limited to, installation around an entry point of a mixer or packer. 
     Gland  13  for the mechanical shaft seal  19  is exposed to the outside atmosphere and secured to end cap  37 , e.g. by fastening bolts  39  through apertures  36 . End cap  37  is then attached to the side wall of flap valve  38 . Shaft  20  extends from within flap valve  38  and through end cap  37  and mechanical shaft seal  19 . A bore through the center axis of the mechanical shaft seal  19  is large enough to accept a rotating shaft  20  and prevents the release of dry material between the mechanical shaft seal  19  and the end cap  37 , as well as preventing leaks between the rotating shaft  20  and the bore. No pneumatic lines are required in order to prevent dry material from escaping from the inside of the flap valve. 
     Referring to  FIG. 3 , a mechanical shaft seal  19  is comprised of a seal assembly  40 , a rotor sleeve  3 , and gland  13 . The seal assembly  40  is comprised of grease housing  14 , lip seal  17 , grease chamber  18 , and a single-spring seal  1 . The seal assembly  40  is secured to the rotor sleeve  3  via at least one snap ring  6 . “Single-spring seal” is defined as a mechanical seal that is capable of rotating with a shaft while maintaining a seal with a stationary seat to prevent the migration of material along the length of the shaft. The seal assembly  40  is exposed to dry material under pressure. The gland  13  is mounted externally and exposed to the atmosphere. Extending along the axis of symmetry of mechanical shaft seal  19  is the rotor sleeve  3  and a rotatable shaft  20 . The seal assembly  40  prevents the release of dry material into rotor chamber  21 . 
     The ledge  22  provides a seat for a lip seal  17 . The lip seal  17  is preferably made of a fluoroelastomer. Lip seal  17  creates a seal between the inner wall of grease housing  14  and the outer wall of the proximal end of portion  29  of rotor sleeve  3 . The ledge  30  provides a step for a stationary seat  2 . The stationary seat  2  is preferably made of tungsten carbide or silicon carbide. Stationary seat packing  4  is located in between stationary seat  2 , ledge  30 , and the inner wall of portion  25  of gland  13 . Stationary seat packing  4  secures stationary seat  2  also provides a seal between the seal assembly  40  and chamber  21 . Stationary seat packing  4  secures stationary seat  2  against spring seal  1  and provides a seal between chamber  18  and rotor chamber  21 . The stationary seat packing  4  is preferably made of a fluoroelastomer. A rotating single-spring seal  1  disposed around portion  29  of rotor sleeve  3  presses against stationary seat  2 . The single-spring seal  1  is preferably comprised of “316” stainless steel, Viton® (DuPont), and carbon. An annular groove around the outer wall of the proximal end of portion  29  of rotor sleeve  3  holds a snap ring  6  that secures the rotating single-spring seal  1  against stationary seat  2 . The snap ring  6  is preferably made of “302” stainless steel. A back-up ring  5  is disposed around rotor sleeve  3  between snap ring  6  and single-spring seal  1 . The back-up ring  5  is preferably made of “316” stainless steel. Snap ring  6  and back-up ring  5  set the operating length of single-spring seal  1 . Chamber  18  houses snap ring  6 , back-up ring  5 , and single-spring seal  1 . Chamber  18 , which is bounded by the lip seal  17 , the inner wall of grease housing  14 , stationary seat  2 , and the outer wall of portion  29  of rotor sleeve  3 , is packed with grease. 
     Fluoroelastomer O-rings useful in the present invention include those of fluorocarbon rubber (FKM) such as Viton® (DuPont). Grease useful in the present invention includes grease conforming to NLGI 2 (National Lubricating Grease Institute grade 2, corresponding to a worked penetration value of 265-295, using the standard NLGI penetration test apparatus, as is known in the art), which are lubricants exhibiting high viscosity and that are resistant to breakdown. Preferably, the lubricants are Almagard® lubricants, e.g. Almagard 3752 NLGI 2 (Lubrication Engineers, Inc., Fort Worth, Tex.). 
     Portion  25  of gland  13  and annular collar  27  form an annulus that provides a seat for a sealed bearing  8  disposed around portion  28  of rotor sleeve  3  that bears against portion  26  of gland  13 . In order to prevent sealed bearing  8  from moving axially that would result in potential leakage of dry material, sealed bearing  8  is press fit onto portion  28 . An annular groove in the outer wall of portion  28  holds a snap ring  7  and an annular groove in the inner wall of portion  26  holds a snap ring  12 . Snap rings  7  and  12  secure the sealed bearing  8  against portion  25  of the gland  13 . Snap rings  7  and  12  are preferably made of “302” stainless steel. 
     A plurality of set screws  15  extend radially through the male coupling  23  and female coupling  24  to secure the grease housing  14  to the gland  13 . The set screws  15  are preferably made of hardened steel. An annular groove in the male coupling  23  is adjacent to the set screw and holds the grease housing O-ring  16 . The grease housing O-ring  16  is preferably made of a fluoroelastomer. A circumferential groove adjacent to the female coupling  24  holds the gland O-ring  11 . The gland O-ring  11  is preferably made of a fluoroelastomer. 
     Referring to  FIG. 4 , grease housing  14  is cylindrical with a proximal end  36  exposed to the pressurized dry material and a distal end  33 . The grease housing  14  is preferably made of “304” stainless steel. Grease housing  14  has a short ledge portion  22  that extends inwards radially at the proximal end  36  of the grease housing  14 . Grease housing  14  also has a male coupling  23  integrally connected at the distal end  33  of the grease housing  14 . 
     Referring to  FIG. 5 , rotor sleeve  3  has a proximal end  34  exposed to the dry material and a distal end  31  exposed to the atmosphere. Rotor sleeve  3  is preferably made of “304” stainless steel. Rotor sleeve  3  includes three main portions: an elongated barrel portion  29  located at proximal end  34 , a short barrel portion  28  located at the distal end  31 , and an annular collar  27  located between portions  28  and  29 . Rotor sleeve  3  has a bore extending axially therethrough, sized to accommodate shaft  20 . A plurality of set screws  10  extend radially through the distal end  31  of portion  28 . The set screws  10  are preferably made of alloy steel. An annular groove adjacent to the set screws  10  in the inner wall of the rotor sleeve  3  holds the sleeve O-ring  9 . The sleeve O-ring  9  is preferably made of a fluoroelastomer. 
     Referring to  FIG. 6 , gland  13  has a proximal end  35  which connects to grease housing  14  ( FIG. 4 ) and a distal end  32  exposed to the atmosphere. The gland  13  is preferably made of “304” stainless steel. The gland  13  includes an axially directed portion  26  and a radially directed portion  25  thus giving a segment of such gland, as seen in cross-section, a generally L-shaped appearance. Portion  25  has a short ledge portion  30  that extends inwards radially into the rotor chamber  21 . Gland  13  has a bore extending axially therethrough sized to accommodate the rotor sleeve  3  and a plurality of circumferentially-spaced apertures  36  through portion  26 . The proximal end  35  of gland  13  has a female coupling  24 . 
     Referring to  FIG. 7  and  FIG. 8 , an alternative embodiment of a flap valve  60  that uses mechanical shaft seal  19  is shown. In this embodiment, flap valve  60  has opening  62  to receive material. Shaft  20  is mechanically linked to a flap (not shown) that is movable to either restrict or allow the flow of material within flap valve  60 . Shaft  20  is mechanically linked to lever  64 , which is mechanically linked to air cylinder  72  via cylinder shaft  68 . Pneumatic supply lines ( 74 A and  74 B) are fed by a compressed air system (not shown). In operation the air cylinder is activated and deactivated to control the flow of material through the valve as desired. 
       FIG. 8  illustrates a flap valve system  80 . In embodiment shown, multiple flap valves (here, indicated as  60 A and  60 B) are arranged in a vertical manner as shown. The multiple valve configuration allows for more precise control of the flow of the material. Preferably, the flap valves are configured to have opposite phases. That is, when flap valve  60 A is “open” and allowing material to pass through it, valve  60 B is closed, and material accumulates in valve  60 B, but can not exit since valve  60 B is closed. Then in the next cycle, valve  60 A is closed, and valve  60 B is open, allowing only the material that had been previously deposited in valve  60 B to pass through. The opposite phase relationship can be implemented via a pneumatic control system (not shown) that opens and closes flap valves  60 A and  60 B with the desired timing sequence. In one embodiment, the multiple valve configuration comprises two flap valves. However, it is possible to use more than two valves without departing from the scope of the present invention. 
     Although the present invention has been described in connection with a specified embodiment thereof, many other modifications, corrections and applications are apparent to those skilled in the art. Therefore, the scope of the present invention is not limited to the embodiment described herein.