The present invention relates to air bearings used to support rotating, turbine-driven shafts. More specifically, the invention relates to air bearings supporting rotary bell cup atomizing apparatus useful in applying coatings to substrates.
Air bearings are employed in a wide range of applications, for example, from gas turbine engines to precision machinery, to ink jet printers, and to high-speed dental drills. Air bearings have received widespread use in the robotically-controlled painting of vehicles by high-speed rotary bell cup atomizers. While the invention herein may be used in a wide variety of air bearing applications, for reasons of descriptive efficiency and expedience, the detailed principles underlying the operation of the invention and the apparatus employed will be presented with a focus on its use in rotary bell cup atomizers for applying paint to workpieces such as vehicles.
Known rotary atomizers can include a rotating bell cup applicator having a generally conical front flow surface extending between an inner, axially central paint supply orifice opening and a radially outer atomizing edge. Paint entering the bell cup through the central opening flows to the rear surface of a deflector and is disbursed radially outwardly towards the front diverging flow surface of the rotating bell cup, flowing thereover to the outer edge of the cup where it is atomized to a fine mist and applied to the workpiece.
Atomization is effected by centrifugal forces produced when the cup, mounted on a central motor shaft, is rotated at high speeds, typically at 60-80,000 RPM.
Rotary bell cup atomizers are used in liquid based paint coating operations and in powder coating operations. In such operations, electrostatic charging is applied to the atomized particles to enhance their attraction to the grounded substrate and produce a flawless finish, all of which is well known.
An early example of the use of an air bearing to support the central rotating motor shaft of an electrostatic spray painting device is found in U.S. Pat. No. 4,368,853 (1983, assigned to Toyota, K.K.). Therein, a rotary electrostatic spray painting device is disclosed comprising a rotary shaft and a spray head fixed onto the front end of the rotary shaft. Paint is fed onto the cup shaped inner wall of the spray head. The rotary shaft is supported by a single thrust air bearing and a pair of radial air bearings. The rotating motor shaft is supported by air injected through porous air bearings which enable the shaft to rotate at high rotational speeds, said to be up to 80,000 RPM, in a substantially frictionless environment. While porous air bearings are said to be useful, the reference cites no specific material of construction of any bearing.
Illustrating the diversity of applications in which air bearings find use, U.S. Pat. No. 3,969,822 discloses a porous, static pressure air bearing device for use in a dentist's handpiece. Therein, the porous, static pressure air bearing device includes a rotatable shaft for mounting thereon a cutting tool, a bearing case, an air bearing portion provided in the bearing case for supporting the rotatable shaft, and a turbine blade formed integrally with the shaft or mounted on the shaft. The air bearing portion is formed of porous material, and the reference cites sintered porous metal or ceramics, or porous synthetic resins, as suitable bearing materials. As disclosed in the '822 reference, sleeves of inverted L-shaped or L-shaped cross section are secured to the rotatable shaft such that the sleeves are in contact with the turbine blade and mounted on the outer diameter surface of the rotatable shaft. These sleeves may be formed integrally with the rotatable shaft or manufactured separately from the shaft for convenience of working. Air supplied through the air supply passage is injected against the turbine blade to rotate the rotatable shaft with the sleeves. The shaft is said to assume a high speed of rotation because it is supported by air bearings of low friction. Since the bearing portion is supported by O-rings, the damping effect provided thereby acts to absorb vibrations occurring in the rotatable shaft during its shift from an initial rotation to high-speed rotation.
U.S. Pat. No. 8,973,848 B2, commonly assigned, discloses a composite air bearing assembly supporting a turbine-driven rotatable motor shaft in a rotary bell cup atomizer. The assembly includes a composite cylindrical air bearing having alternating, bonded segmented porous carbon sections and nonporous carbon sections. The composite bearing has a sleeve installed circumferentially therearound. The sleeve has openings therein, therethrough and therearound such that the openings are adjacent the porous carbon sections and are oriented so as to be in longitudinal and circumferential registry with the porous carbon sections. Air passageways deliver supplied air into and through the sleeve openings, thence into and through the porous sections, thereby providing near-frictionless support for the rotating shaft. The assembly includes “O”-rings installed circumferentially therearound, one at each end of the assembly.
The disclosures of the '848 patent are incorporated here by reference.
A still further reference disclosing rotary bell cup atomizing apparatus and having relevance to certain features of the invention to be disclosed and claimed herein, is commonly-assigned U.S. Pat. No. 9,375,734 B1, the disclosures of which are also incorporated herein by reference.
From the cited prior art, it will be seen that air bearings constructed of various combinations of porous and non-porous materials (having orifices), sleeves, and “O”-rings are disclosed in the known atomizer prior art. However, the air bearing assembly disclosed and claimed herein, which provides its inherent and significant advantages over prior bearings, all to be described in detail hereinbelow, is nowhere disclosed in the known prior art.
Rotary bell cup atomizing apparatus driven by a turbine mounted on a rotatable motor shaft supported within an air bearing assembly is provided. The apparatus is contained within a housing and includes an external air supply for supplying air to drive the turbine and channeling air to the air bearing assembly. The air bearing assembly includes a cylindrical main air bearing supporting the motor shaft through which main bearing the motor shaft extends, a proximal, annular, disk-shaped thrust bearing supporting the turbine axially disposed proximally with respect to the turbine, through which thrust bearing the motor shaft extends, a distal, annular, disk-shaped thrust bearing supporting the turbine axially disposed distally with respect to the turbine, through which thrust bearing the motor shaft extends. The apparatus includes air gaps formed between all bearings and all in-operation rotating surfaces of the atomizing apparatus. The apparatus includes a vibration-damping “O”-ring positioned proximally adjacent the proximal thrust bearing through which the motor shaft extends, and a vibration-damping “O”-ring positioned distally adjacent the distal thrust bearing through which the motor shaft extends, and also includes “O”-rings installed circumferentially around the cylindrical main air bearing, one at the proximal end and one at the distal end of the main bearing. All bearings include air passageways extending through all bearings for supplying air from the external air supply through all bearings into all air gaps between all bearings and all in-operation rotating surfaces of the atomizing apparatus.
In operation, air supplied to the apparatus is delivered through the air passageways and into all air gaps, thereby driving the rotatable turbine and motor shaft such that all rotating surfaces of the atomizing apparatus are supported in air and the “O”-rings provide both axial and radial 3-dimensional vibration damping of the turbine and motor shaft during rotation.
In specific embodiments, the “O”-rings are composed of an elastomer, and a perfluoroelastomer is a preferred material. The main bearing may be constructed of nonporous carbon, porous carbon, or a composite of nonporous and porous carbon.
In a preferred embodiment, the main bearing is a composite bearing having alternating, segmented porous carbon sections and nonporous carbon sections bonded together. Thrust bearings of porous carbon and nonporous carbon are preferred. Composite thrust bearings may be constructed of suitable materials, including metals such as aluminum and carbon components, both nonporous carbon and porous carbon.
The apparatus may have at least one sleeve installed externally and circumferentially about the main bearing, the sleeve having openings formed therein, therethrough and therearound such that the openings are adjacent the porous carbon sections and are oriented so as to be in longitudinal and circumferential registry with the adjacent porous carbon sections. This apparatus may include “O”-rings installed externally and circumferentially about the at least one sleeve, one at the proximal end and one at the distal end thereof, all as more specifically described in U.S. Pat. No. 8,973,848 B2, which has been incorporated herein by reference.
The at least one sleeve may be constructed of a suitable metal such as stainless steel, a ferrous metal or a non-ferrous metal.
The atomizing apparatus may include a base plate and at least two inlet ports to the apparatus for supplying air to drive the turbine, wherein the at least two inlet ports are connected, respectively, to two air channels leading through the base plate, the two air channels converging within the base plate and opening into a single drive air outlet from the base plate, the single base plate drive air outlet mating at the base of the turbine assembly with a single drive air inlet into a flow distribution intermediate plate, which intermediate plate houses the blades of the turbine, wherein the intermediate plate has a channel therein and therearound extending from the single drive air inlet partially and substantially in a direction circumferentially around the intermediate plate, and through which intermediate plate channel the drive air is directed bi-directionally to the turbine blades, all as described in U.S. Pat. No. 9,375,734 B1, included here by reference.
In a still further embodiment, the apparatus includes a base plate and at least two drive air inlet ports connected, respectively, to two parallel drive air inlet channels leading into a flow distribution intermediate plate through which drive air is directed to the turbine blades.
In its broadest form, the invention provides an air bearing assembly supporting a turbine driven motor shaft, the assembly including a cylindrical main air bearing, preferably of carbon, supporting the motor shaft, a proximal, annular disk-shaped thrust bearing and a distal, annular disk-shaped thrust bearing, both preferably of carbon, and both supporting the turbine, and including vibration damping “O”-rings disposed adjacent all bearings to provide, universal 3-dimensional vibration damping of all rotating components.
In the accompanying figures:
Rotary bell cup atomizing apparatus driven by a turbine mounted on a rotatable motor shaft supported within an air bearing assembly is provided. The air bearing assembly includes a cylindrical main air bearing supporting the motor shaft, a proximal, annular, disk-shaped thrust bearing and a distal, annular, disk-shaped thrust bearing supporting the turbine, and including vibration-damping “O”-rings positioned adjacent the bearings. In operation, air supplied to the apparatus drives the turbine and supports the turbine and motor shaft such that all rotating surfaces of the atomizing apparatus are supported in air, and universal, 3-dimensional vibration damping, both axial and radial, of all rotating components is provided.
A detailed description of the invention and preferred embodiments is best provided with reference to the accompanying drawings, wherein
Compressed drive air to drive turbine 47 is channeled through inlet port(s) 40 and internally to and through channel 24. Bearing air is supplied through line 18 into and through air passageways/channels 28 through bearing housing 14 to cylindrical main bearing assembly 30 and to proximal thrust bearing 56 and distal thrust bearing 54, the details of the air passageways and channels to be described below. Proximal thrust bearing axial vibration-damping “O”-ring 50 is positioned proximally adjacent proximal thrust bearing 56 and distal thrust bearing axial vibration-damping “O”-ring 52 is positioned distally adjacent distal thrust bearing 54, all as depicted in
Also indicated in
Sleeve 33 has circumferential openings 36 therethrough and therearound as shown, which openings are positioned such that, on installation, and overwrapping the adjacent composite bearing assembly 30, openings 36 are aligned over each of their respective porous adjacent carbon segments 34 of the bearing assembly 30.
Drive air entering the apparatus is guided internally through channel 24, to drive turbine 47, and bearing air is channeled to and through air passageways 28, within bearing housing 14, all as depicted in
For completeness of the detail shown in
Bearing air entering the apparatus through inlet 18 is channeled as shown to and through main bearing assembly 30 and proximal and distal axial bearings 70 and 72, into the narrow gaps 35, 74 and 76 which support the rotating turbine 47 and motor shaft 44 in operation.
In operation, in the illustration of
Main air bearing assembly 30 is described above in detail for illustrative purposes, but other constructions, known in the art and supportable within the bearing assembly of the invention, are also within the scope of the present invention. For example, the main bearing components may be of nonporous carbon, of porous carbon, and of a composite of segments of porous and nonporous carbon as presented above and disclosed in U.S. Pat. No. 8,973,848 B2, and of other suitable materials known in the art.
Air gap 35 is shown in more detail in a magnified view to be described below.
The optional reinforcing sleeve 33 over the main bearing assembly 30 may be of stainless steel, other metals including aluminum, and other suitable ferrous and nonferrous metals. As indicated, the sleeve 33 has openings 36 therethrough and therearound, all in registry with the passageways 34 through bearing component 31.
The main cylindrical air bearing assembly 30 has “O-”-rings 48 and 46 installed proximate each end, one, 48, at the proximal end and one, 46, at the distal end thereof as shown.
Proximate the outer periphery of the proximal annular disk shaped thrust bearing 56, a proximal, axial vibration damping “O”-ring 50 is positioned as shown adjacent the proximal face of the bearing 56. And proximate the outer periphery of the distal annular thrust bearing 54, a distal, axial vibration damping “O”-ring 52 is positioned as shown adjacent the distal face of the bearing 54.
In operation of the atomizing apparatus, these “O”-rings 50 and 52 effectively dampen axial vibrations of the turbine 47 and motor shaft 44.
The vibration damping “O”-rings 46, 48, 50 and 52 described above are preferably elastomeric, most preferably being of a perfluoroelastomer.
Included in
Functional, joint-sealing “O”-rings, unnumbered, are shown in
Proximal thrust bearing 56 is not similarly shown, being essentially a mirror-image of bearing 54.
In all of
Also shown in
A second preferred embodiment for introducing drive air into the atomizing apparatus includes the configuration shown in
While the invention has been disclosed herein in connection with certain embodiments and detailed descriptions, it will be clear to one skilled in the art that modifications or variations of such details can be made without deviating from the gist of this invention, and such modifications or variations are considered to be within the scope of the claims hereinbelow.
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