Patent Application
20080247896
The present invention relates to positive-displacement fluid pumps, such as a rotary gear pumps and rotary vane pumps. In particular, the present invention relates to protective coatings for use in positive-displacement fluid pumps.
Positive-displacement fluid pumps are fluid transfer equipment employed in a variety of industrial and commercial systems for pumping fluids from one location to another. For example, positive-displacement fluid pumps may be used in aircraft to pump fuel from storage reservoirs to turbine engines during flight. Such pumps typically include rotary components (e.g., rotatable gears) that rotate within a housing to transfer the fluids. To increase pumping efficiencies, the rotary components are retained as close as reasonably possible to the housing to reduce leaks. However, this can induce abrasive or adhesive wearing of the rotary components and the housings during the course of operation.
One technique for reducing the rate of wearing includes the use of side or end plates composed of monolithic-cemented carbide or case-hardened steel. The side and end plates are correspondingly subjected to wear, thereby reducing damage to the rotary components and the housings. However, such materials can increase frictional resistance between the rotary components and the housing, which can reduce pumping efficiencies, and potentially cause metal-to-metal seizures.
Another option includes the use of side or end plates having steel or aluminum substrates coated with a leaded-bronze, sacrificial material (or the plates are solid leaded-bronze). The lead in the sacrificial material is capable of smearing around the steel substrate rather than being worn down. However, because of potential environmental and health concerns associated with the manufacture and use of lead, leaded-bronze materials are falling into disfavor. As such, there is a need for a protective coating that avoids the potential health concerns associated with lead-containing materials, but retains the positive properties of leaded-bronze materials.
The present invention relates to a positive-displacement pump that includes a housing and a rotary component disposed at least partially within the housing. The positive-displacement pump also includes a film disposed at least partially between the housing and the rotary component, where the film includes a reinforcing material and a fluoropolymer material.
Drive rotor 14 includes drive gear 30 and drive shaft 32, where drive gear 30 includes gear teeth 34 and top face 36. Gear teeth 34 are a plurality of teeth extending circumferentially around drive gear 30. Top face 36 is a top major surface of drive gear 30 that is at least partially covered with a protective film. As discussed below, the protective film reduces the amount of abrasive wearing incurred by drive chamber 22 and drive gear 30 during operation, thereby extending the operational life of pump 10. Drive shaft 32 extends axially through drive gear 30, thereby mounting drive gear 30 within drive chamber 22. Drive shaft 32 is also secured, directly or indirectly, to a motor (not shown) for rotating drive shaft 32, and correspondingly, drive gear 30.
Driven rotor 16 includes driven gear 38 and driven shaft 40, where driven gear 38 includes gear teeth 42. Gear teeth 42 are a plurality of teeth extending circumferentially around driven gear 38. Driven shaft 40 extends axially through driven gear 38, thereby mounting driven gear 38 within driven chamber 24. Driven shaft 40 is a free-rotating shaft, thereby allowing driven gear 38 to be rotated by drive gear 30.
As shown, gear teeth 34 of drive gear 30 engage gear teeth 42 of driven gear 38 at a location between entrance channel 18 and exit channel 20. This engagement desirably minimizes fluid flow directly between entrance channel 18 and exit channel 20. During operation, drive shaft 32 is rotated by the external motor, thereby rotating drive gear 30 in the direction of arrow 44. Due to the engagement between gear teeth 34 and 42, the rotation of drive gear 30 in the direction of arrow 44 correspondingly rotates driven gear 38 in the direction of arrow 46. As fluid is introduced into entrance channel 18 (represented by arrow 48), the rotation of drive gear 30 and driven gear 38 carries the fluid around drive chamber 22 and driven chamber 24, respectively. In particular, drive gear 30 carries a first portion of the fluid in a circular path around drive chamber 22, and driven gear 38 carries a second portion of the fluid in a circular path around driven chamber 24. When the first and second potions of the fluid respectively exit drive chamber 22 and driven chamber 24, the first and second portions reunite and exit housing 12 through exit channel 20 (represented by arrow 50).
Housing 12 also includes bearings set 58 (shown in section), which is a set of journal bearings for stabilizing the rotation of drive rotor 14. As shown, bearings set 58 is disposed around drive shaft 32 at a location below drive gear 30. In an alternative embodiment, housing 12 also includes an additional bearings set (not shown) around drive shaft 32, at a location above drive gear 30.
Drive rotor 14 is desirably positioned within housing 12 such that top face 36 contacts top wall 52, and such that bottom face 54 contacts bottom surface 26. This provides seals between drive gear 30 and drive chamber 22, which minimizes fluid leakage. Driven rotor 16 also includes a similar arrangement. The seals increase the efficiency of pump 10 to transfer fluids from entrance channel 18 (shown in
Protective film 62 compositionally includes a reinforcing material interdispersed with a fluoropolymer material. While drive gear 38 rotates, protective film 62 is the portion of top face 36 that frictionally rubs against top wall 52 of drive chamber 22. As such, protective film 62 is a sacrificial layer that is slowly eroded away over extended periods of operation. However, while present, protective film 62 prevents housing 12 and drive gear 30 from directly contacting, thereby reducing the amount of abrasive wearing incurred by housing 12 and drive gear 30. Protective film 62 is particularly suitable during start-up of pump 10, where a spike in frictional force may occur because the seals between drive chamber 22 and drive gear 30 have not obtained hydrodynamic states.
The reinforcing material of protective film 62 is a wear-resistant, porous material that retains the fluoropolymer material. The fluoropolymer material reduces the friction between top wall 52 of drive chamber 22 and top major surface 60, and smears across top major surface 60 under the applied friction. As a result, the fluoropolymer material lubricates top wall 52 and top major surface 60 by material transfer in a similar manner to lead-based materials. However, the fluoropolymer material does not exhibit the potential environmental and health concerns associated with the manufacture and use of lead. As such, protective film 62 avoids the potential health concerns associated with lead-containing materials, while retaining the positive properties of leaded-bronze materials.
In an alternative embodiment, protective film 62 is secured over top wall 52 of drive chamber 22, rather than over top major surface 60. In this embodiment, protective film 62 functions in the same manner as discussed above for reducing the friction between top wall 52 and top major surface 60. Accordingly, protective film 62 may be secured to different surfaces such that protective film 62 is at least partially disposed between top wall 52 and top major surface 60.
In another alternative embodiment, protective film 64 is secured over housing surface 66 of housing 12, rather than over OD surface 56 of drive shaft 32. In this embodiment, protective film 64 functions in the same manner as discussed above for reducing the friction between OD surface 56 and housing surface 66.
Protective film 70 is compositionally the same as, and functions in the same manner as, protective film 62 (shown in
In another alternative embodiment, protective film 72 is secured over journal surface 74, rather than over OD surface 56 of drive shaft 32. In this embodiment, protective film 72 functions in the same manner as discussed above for reducing the friction between OD surface 56 and journal surface 74.
As discussed above, protective films 62, 64, 70, and 72 are each coatings that compositionally include a reinforcing material interdispersed with a fluoropolymer material. Suitable reinforcing materials for use in the composition include metal particles (e.g., aluminum, copper, tin, and alloys thereof), carbon-based fibers (e.g., carbon graphite fibers), aromatic polyamide fibers, glass particles, ceramic particles, and combinations thereof. The reinforcing material is also desirably substantially free of heavy metals (e.g., lead), thereby reducing the risk of potential environmental and health concerns. Examples of suitable concentrations of the reinforcing material in the composition range from about 50% by volume to about 95% by volume, with particularly suitable concentrations ranging from about 70% by volume to about 80% by volume.
Suitable fluoropolymer materials for use in the composition include any fluoropolymer capable of providing lubrication by material transfer, such as polytetrafluoroethylenes (PTFEs), fluorinated ethylenepropylene (FEP) copolymers, and combinations thereof. Examples of a particularly suitable fluoropolymer material includes a 50/50 (by volume) blend of a polyamide-FEP and a polyimide-PTFE. Examples of suitable concentrations of the fluoropolymer material in the composition range from about 5% by volume to about 50% by volume, with particularly suitable concentrations ranging from about 20% by volume to about 30% by volume.
The protective films (e.g., protective films 62, 64, 70, and 72) may each be formed by depositing one or more layers of the reinforcing material onto the appropriate surface (e.g., top major surface 60). The reinforcing material may be deposited in a variety of manners, such as with a powder deposition system. The coated component is then soaked in a mixture containing the fluoropolymer material (e.g., a dispersion, emulsion, and/or a suspension of the fluoropolymer material in a carrier fluid). During the soaking process, the mixture migrates into and fills the porous regions of the reinforcing material. The soaking process is desirably performed under a vacuum or reduced pressure to remove entrained gases from the porous regions of the reinforcing material. After a suitable duration for filling the porous regions (e.g., 1-3 hours), the coated component is then dried to form a protective film (e.g., protective film 62) on a corresponding surface (e.g., top major surface 60).
The film thicknesses of protective films 62, 64, 70, and 72 may vary depending on design criteria required to provide suitable seals. Examples of suitable film thicknesses for each of protective films 62, 64, 70, and 72 range from about 5 micrometers to about 1,000 micrometers, with particularly suitable film thicknesses ranging from about 10 micrometers to about 100 micrometers.
After formation, protective films 62, 64, 70, and 72 may also undergo one or more post-processing techniques, such as smoothing, radiation exposure, vacuum aging, and combinations thereof. Smoothing processes are suitable for providing uniform thicknesses of a given protective film, and for obtaining a desired film thickness. Radiation exposure and vacuum aging are beneficial for improving the physical properties of the fluoropolymer material. The heat generated by the radiation exposure and vacuum aging cause portions of the fluoropolymer material to at least partially cross link, thereby increasing the durability of the protective films.
Radiation exposure involves exposing the protective film to actinic radiation for a suitable duration. Examples of suitable types of actinic radiation for the radiation exposure include those having wavelengths ranging from gamma-rays to ultraviolet (UV) wavelengths (e.g., gamma, x-ray, and UV), electron beam radiation, and combinations thereof. Suitable durations for the radiation exposure generally depend on the wavelength and the power or power density of the actinic radiation being utilized. Examples of suitable durations for the radiation exposure range from about 1 second to about 100 minutes, with particularly suitable durations ranging from about 1 second to about 60 seconds.
Vacuum aging involves exposing the protective film to one or more elevated temperatures under a vacuum or reduced pressure to minimize the exposure to oxygen. Suitable temperatures for vacuum aging generally depend on the polymeric composition of the protective film. Examples of suitable temperatures for vacuum aging range from about 65° C. (about 150° F.) to about 260° C. (about 500° F.), with particularly suitable temperatures ranging from about 100° C. (about 210° F.) to about 250° C. (about 480° F.). Suitable durations for the vacuum aging range from about 10 minutes to about 9 hours, with particularly suitable durations ranging from about 1 hour to about 5 hours.
In one embodiment, the protective films (e.g., protective films 62, 64, 70, and 72) undergo a radiation exposure process at an elevated temperature and under vacuum or reduced pressure. This increases the physical properties of the fluoropolymer material while also minimizing the exposure of the protective films to oxidizing environments. After the post-processing, the components containing the protective films (e.g., drive gear 30) may be assembled to form pump 10 (shown in
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, while the above-discussed protective films (e.g., protective films 62, 64, 70, and 72) are used with drive chamber 22 and/or drive rotor 14, similar protective films may be used with the corresponding components of driven chamber 24 and/or driven rotor 16. Additionally, while pump 10 is illustrated as an external-gear positive displacement pump, the present invention is also suitable for use with positive displacement pumps of other designs, such as internal-gear positive displacement pumps. Moreover, while drive gear 30 and driven gear 38 are depicted as intermeshing spur gears, the present invention is also suitable for use with gear pumps that contain other types of gears (e.g., helical and herringbone-type gears).
