CA1177241A - Shroud air generating structure for rotary head electrostatic spray coating systems - Google Patents
Shroud air generating structure for rotary head electrostatic spray coating systemsInfo
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- CA1177241A CA1177241A CA000394910A CA394910A CA1177241A CA 1177241 A CA1177241 A CA 1177241A CA 000394910 A CA000394910 A CA 000394910A CA 394910 A CA394910 A CA 394910A CA 1177241 A CA1177241 A CA 1177241A
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- air
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- passages
- chamber
- rotary head
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Abstract
SHROUD AIR GENERATING STRUCTURE FOR ROTARY HEAD
ELECTROSTATIC SPRAY COATING SYSTEMS
Abstract of the Disclosure A shroud air generating structure for rotary head electrostatic spray coating systems of the type to which a rapid rotation is imparted to a rotary spray head and a jet of coating material to be sprayed directed thereagainst for discharge from a peripheral edge of the head in a spray, is characterized by an annular manifold for receiving air therein and having a plurality of outlet passages in an annular array therearound. The passages are unevenly spaced to compensate for air pressure variations within the manifold, and provide a uniform volumetric distribution of outlet air around the manifold. A cover extends across the manifold outlet passages, and air from the passages is directed through an annular opening defined by the cover to generate a shroud of air for movement, around, across and forwardly of the rotary head. The shroud air aids in moving spray particles toward articles to be coated, while the particular shroud air structure provides a very uniform volumetric distribution of the shroud air. Also, by virtue of the cover extending across the manifold passages, the passages are not subject to clogging by spray particles.
ELECTROSTATIC SPRAY COATING SYSTEMS
Abstract of the Disclosure A shroud air generating structure for rotary head electrostatic spray coating systems of the type to which a rapid rotation is imparted to a rotary spray head and a jet of coating material to be sprayed directed thereagainst for discharge from a peripheral edge of the head in a spray, is characterized by an annular manifold for receiving air therein and having a plurality of outlet passages in an annular array therearound. The passages are unevenly spaced to compensate for air pressure variations within the manifold, and provide a uniform volumetric distribution of outlet air around the manifold. A cover extends across the manifold outlet passages, and air from the passages is directed through an annular opening defined by the cover to generate a shroud of air for movement, around, across and forwardly of the rotary head. The shroud air aids in moving spray particles toward articles to be coated, while the particular shroud air structure provides a very uniform volumetric distribution of the shroud air. Also, by virtue of the cover extending across the manifold passages, the passages are not subject to clogging by spray particles.
Description
'7~1 Background of the Invention The present invention relates to shroud air generating structures for spray coating apparatus of the type which comprises a centrifugal spra~er member or head to which a rapid rotation is imparted, and in particular to a shroud air generating structure which provides a very even and uniform volumetric distribution of air across the rotary head to aid in movement of spray particles toward articles to be coated.
Electrostatic spray coating systems have been successfully used in commerce in several different forms.
For example, systems have been used which utilize spraying or atomizing devices employing hydraulic forces or air as the atomizing mèdium. In another type of system, to which the present invention relates, atomization is accomplished by means o a centrifugal sprayer member or head to which a rapid rotation is imparted. The head has a surface against which a stream or jet of liquid to be sprayed is directed, the liquid on striking the revolving surface progressing radially outwardly thereover in a thin film under centrifugal force toward a sharp annular peripheral edge of the head, where~t it is divlded into fine particles so that it leaves the periphery in the form of a spray. For electrostatic deposition of coating material the rotàry head is made o a conductive material and connected to a high d.c.
potential, so that the spray particles on moving past the peripheral edge of the head are charged to a high electrostatic poten~ial. The resulting ionized or electrostatically charged cloud of particles is then attracted to and settles on the surfaces of articles ,. , ~ .
, 11'7'7;~41 , or ware to be coated, which àre usually maintained at ground potential.
Spray heads of such electrostatic coating apparatus have heretofore been rotated at relatively low speeds, e.g., on the order of 3,000 to 6,000 rpm. However, recent developments contemplate rotating the heads at considerably greater speeds on th order of 30,000 to 60,000 rpm, which enhances both the atomization and flow rate of coa~ing material sprayed from the head.
Obviously, at such high speeds of rotation spray particles leaving the peripheral edge of the head are flung at significant speeds generally radially of the head and parallel to ware to be coated, so that if electrostatic forces alone were relied upon to move the particles to the ware a substantial portion of the particles would not reach the ware. Consequently, the art also contemplates generating an annular shroud o air for movement around, across and forwardly of the rotary head to aid in moving electrostatically ~harged spray particles toward the ware.
To generate the shroud air, there is conventionally provided an annular manifold behind and around the rotary head. The manifold has a plurality of outlet passages arranged in an annular array, and air introduced into the manifold exits through the passages to form a shroud of air around the head. In an attempt to obtain a uniform layer or distribution of shroud air~
thereby to enhance uniformity of deposition of coating material on ware, the outlet passages are closely spaced and of relatively small diameter. Unfortunately, despite the close spacings and small diameters of the passages, the shroud air pattern i5 nevertheless nonuniform in that is is comprised of a plurality of discrete jets or streams of air. Also, in consequent of the small passage diameters, the same are prone to clogging by spray particles or contaminants in the air supply, which results in further nonuniformities in the shroud air pattern and the need to frequently clear the passages. For high volume production lines, this often yields a product output which is less than desirable or optimal.
Objects of the Invention An object of the present invention is to provide an improved structure for generating shroud air for a rotary head electrostatic spray coating system.
Another object of the invention is to provide a structure which generates a very unifoxm distribution of shroud air.
A further obiect of the invention is to provide such a shroud air generating structure which is not subject to blocking or clogging by spray particles or contaminants in the air supply.
Summa ~ e Invention In accordance with the present invention, there is provided in combination with a rotary head electxostatic spray coating system, of the type to which a rapid ro$ation is imparted to a rotary spray head and a jet of coating material to be sprayed directed thereagainst for discharge from a peripheral edge thereof in a spray, a structure for generating a uniform and annular layer or curtain of shroud air for movement around, across and foxwardly of the rotary head to aid eleotxostatic forces in moving spray particles toward articles to be coated. In one facet, said shroud air generating structure 4~
comprises a manifold having an air inlet for receiving air under pressure and a plurality of air outlets in an annular array for providing therethrough the curtain of shroud air. Said outlets have unequal spacings therebetween, and the spacings are such as to pro~ide a substantially uniform volumetric flow rate of air around the arcuate extent of said outlets despite variations in air pressure throughout the manifold.
In another facet, said shroud air generating structure comprises a manifold having an air inlet for receiving air under pressure and an air outlet, and in this case said air outlet is a continuous annular opening, behind the rotary head, for providing therethrough the annular curtain of shroud air.
In a preferred practice of the invention, the :
foregoing features are combined in a single structure, whi~h comprises an annular channel in a body portion -of the spray coating system behind the rotary head and coaxial tberewith. Said channel has an open side toward the head and an air inlet thereto, and a wall extends across said open side of said channel and has a plurality of passages formed therethrough.
Said passages are in an annular array, and have relatively large diameters and spacings therebetween which progressively decrease with increasing distances from said air inlet. An annular cover mounts on the body portion of the spray coating system coaxial with said annular channel, and has a radial flange which extends across and spaced from said wall to form therewith an annular chamber having a continuous annular opening coaxial with and behind the rotary head. In operation of said structure, uneven air 11'7'7;~
pressures develop throughout said channel upon intro-duction of air therein, and the uneven spacings of said passages cause a substantially uniform pressure and.volumetric distribution of air to be developed within said chamber. Consequently, air discharged through said annular opening orms a very uniform annular layer or curtain of shroud air for movement around, across and forwardly of the rotary head to aid electrostatic forces in moving spray particles toward articles to be coated.
The foregoing and other objects, advantages and - features of the invention will become apparent upon a consideration of the following detailed description, when taken in conjunction with the accompanying drawings.
Brlef Description of the Drawings Fig. 1 is a perspective view of a portion of a rotary head electrostatic spray coating system, which includes a shroud air generating structure embodying the teachings of the present invention;
Fig. 2 is a cross sectional elevation view taken substantially along the lines 2-2 of Fig. 1, and illustrates the forward portion of the rotary head electrostatic spray coating system and the arrangement of the shroud air generating structure thereon;
. Fig. 3 is a front elevation view, partly in cross section, taken substantially along the lines 3-3 of Fig. 2, and shows the arrangement of air outlet passages in an air distribution manifold of the shroud air structure, and -Fig. 4 is a c~oss sectional, fragmentary, sideelevation view ~aken substantially along the lines 4-4 of Fig. 3, illustrating the particular arrangement of a cover of the shroud air structure, which provides ~17'~41 a continuous annular outlet for a very uniformly distributed curtain of shroud air.
Detailed Description Referring now to the drawings, there is shown in Figs. 1 and 2 and indicated generally at 10 a rotary head electrostatic spray coating system which includes a shroud air generating structure, indicated generally at 12, configured in accordance with the teachings of .. . . ;
the present invention. The spray coating apparatus includes a rotatable, bell-shaped head 14 of conductive material, mounted on an output shaft 16 of a high speed air driven turbine 18. The turbine rotates the head at a high rate of speed on the order of 3Q,000 to 60,000 rpm, and is supported on an end of an arm 20 of insulating material. An opposite end o~ the arm is connected to any suitable mechanism (not shown) for moving the apparatus to positions pe~mitting proper deposition of coating material on articles, for example on articles moved past the apparatus on a conveyor.
In operation of the spray coating apparatus 10, coating material in a passage 22 passes through an orifice 24 and is directed in a stream or jet onto an interior surface 26 of a center portion 28 o the head 14. Because of rotation of the head, upon striking the surface the coating material progresses radially outwardly through a passage 30 and across an inner wall 32 of the head in a thin film under centrifugal force toward a sharp, circular, peripheral edge 34 o the head, whereat it is divided as it leaves the head into fine particles in the fo~m of a spray~ A high d.c. voltage on the order of 12Q,000 volts is connected with the head; so that spray l~t~7~41. , particles on moving past the peripheral edge a~e charged to a high electrostatic potential for attraction to articles to be coated, which are maintained at a different and usually ground potential. To this end, the insulating material support arm 20 isolates peripheral equipment from high voltages present at the spray head of the system.
--Although Lmprovements are obtained in coating .
material deposition by virtue of electrostatic attraction of the.spray particles to the ware, if electrostatic .
attraction were the sole means for moving spray particles to the ware significant portions of the particles would .
not reach the ware. This may be appreciated if it is considered .that at the ver~ high speed of rotation of the spray head 14, spra~ particles discharged from the - peripheral edge thereof travel at significant velocities in directions generally radially of the head and parallel to the ~rticles, since articles to be coated are usually positioned forwardly of the head along the axis of rotation thereof~ Thus, the direction of movement of the spray particles must be changed by up to 30 and more for the particles to reach the ware, which can hardly be accomplished with electrostatic forces alone. Con~equently, additional means is provided for aiding movement of spray particles toward the ware.
To aid movement of spray particles toware ware to be coated, the art contemplates generating a shroud or curtain of air for movement over, around and forwardly of the head and against the particles as they leave the peripheral edge of the head. Heretofore, should air genera~ing structures have included an 117'~;~41 annular manifold behind the head for receiving air under pressure, and a plurality of shroud air outlet passages in an annular array around the manifold.
In an attempt to ob~ain a uniform layer or distribution of shroud air, thereby to enhance uniformity of movement of coating material toward and deposition on articles, the outlet passages are closely spaced and of relatively small diameter. ~owever, despite the close spacings and small diameters of the passages, the shroud air pattern is nevertheless nonuniform in that is is comprised of a plurality of discrete stxeams or iets of air. Also, because of the small diameter of the passages, the same are subject to blockage by spray particles or contaminants in the air supply, which further impairs the uniformity of the shroud air pattern and therefore the uniformity of dispersion of spray particles toward articles to be coated, with the result thatprior apparatus of the general type must be frequently shut down to clear the passages.
To overcome the disadvantages of prior shroud air generating structures, and with reference also to Figs. 3 and 4, in accordance with the teachings of the present invention the improved shroud air generating structure 12 includes an annular trough, openingl channel or manifold 36 formed in a forward face of a body portion 38 of the spray coating apparatus. The manifold is of sufficient diameter to extend beyond the rearward end of the rotary head 14, and a supply (not shown) of air under pressure is connected with the manifold through an air inlet passage 40. An annular wall or air diffuser ring 42 closes a forward side of the manifold, preferably _g_ -~7'~;~41 by being press fit therein, and a plurality of 6 air outlet passages 44 are formed through the diffuser ring in an annular array.
The shroud air flows through the passages 44, and in accordance with one facet of the invention the passages are of relatively large diameter and unevenly spaced around the diffuser ring 42, the spacing being such as to provide a generally uniform volumetric distri~ution of` air discharged through the passages -~
around the arcuate extent of the ring. In this connection, it is understood that with a single air inlet to the manifold 36 from the air passage 40, movement of air through the outlet passages results in une~ual air pressures within the manifold, such that the pressure of air adjacent the inlet passage is greater than at positions remote from the inlet passage. Consequently, if the outlet passages were equally spaced around the diffuser ring, greater volumetric discharges of air would occur in proximity with the inlet passage than elsewhere, and would decrease with increasing distances from the inlet passage. However, by providing unequal spacings between the outlet passages, such that the passages remote from the inlet passage are spaced more closely together than are the passages in proximity with the inlet passage, and so that a progressively decreasing spacing between passages occurs rom a position adjacent the inlet passage to positions remote therefrom, a very volumetrically uniform discharge of air is obtained around the entire arcuate periphery o~
the di ffuser ring. At the same tLme, the relatively large diameters of the outlet passages prevents the same from becoming clogged by contaminants in the -10- , 1 1'7'~
air supply, and fewer outlet passages are requfired for a given volume flow of air.
For the structure th~s far described, it is apparent that the air patt~rn would be improved over tha~ provided by prior structures, in that there would be a uniform volumetric outlet of air around the arcuate extent of the annular array of outlet passages, but tha~ the air pattern would nevertheless be comprised of a plurality of discrete streams of -~
air. Accoxdingly, to generate a very uniform and continuous annular layer or curtain of shroud air for movement across and forwardly of the rotary head 14, in accordance with a further feature of the invention an annular shroud air cover~46 is threaded onto thP forward end of the body portion 38. The diffuser ring 42 is generally L-shaped, and a forwardly .extending leg thereof defines an outer, annular, peripheral surface 4~. The cover has a radially inwardly extending flange or wall 50, and when the cover is on the ~ody portion a radially extending annular chamber 52 is formed be~ween the wall and portions of the forward faces of the body portion and diffuser ring, and an annular and axially extending shroud air outlet passage 54 is defined between an innermost end or edge of the wall and the peripheral surface 48 of the diffuser ring. Also, when the cover is mounted on the body por~ion an annular seal is formed between the cover and body portion along a sealing surface 56 of the cover, thereby preventing unwanted leakage of shroud air from the chamber 52~
11~7'~
It may now be appreciated that the invention provides an improved structure for generating a very uniform annular layer or curtain of shroud air around, across and forwardly of the rotary head 14. To this end, the uneven spacings between the outlet passages 44 in the diffuser ring 42 provide within the chamber 52 a very uniform volumetric and pressure distribution of air, despite variations in the pressure .
.,.. . , :~
of air within the manifold 36. At the same time, the annular outlet passage 54 is continuously open around its circumference, so that with the uniform volumetric .and pressure distri~ution of air within the chamber, the shroud alr pattern issuing through the passage is very uniform and is not comprised of discrete streams of air. Consequently, the shroud air pattern imparts a very uniform movement of spray particles toward ware to be coated, so that significant improvements are obtained in deposition of coating material on the ware. In addition, because of their relatively large diameters, not only are fewer passages 44 required for a given volume flow of air, which decreases manufacturing costs of the structure, but the passages are also not prone to blockage by contaminants in the air supply. Further, since the wall 50 of the cover extends across the passages, the passages are also shielded against deposition therein o~ spray particles.
While embodiments o the invention have been described in detail, it is understood that various modifications and other embodiments thereof may be deviced by one skilled in the art without departing fxom the sp~rit and scope of the invention, as defined in the appended claims.
-12- J .
Electrostatic spray coating systems have been successfully used in commerce in several different forms.
For example, systems have been used which utilize spraying or atomizing devices employing hydraulic forces or air as the atomizing mèdium. In another type of system, to which the present invention relates, atomization is accomplished by means o a centrifugal sprayer member or head to which a rapid rotation is imparted. The head has a surface against which a stream or jet of liquid to be sprayed is directed, the liquid on striking the revolving surface progressing radially outwardly thereover in a thin film under centrifugal force toward a sharp annular peripheral edge of the head, where~t it is divlded into fine particles so that it leaves the periphery in the form of a spray. For electrostatic deposition of coating material the rotàry head is made o a conductive material and connected to a high d.c.
potential, so that the spray particles on moving past the peripheral edge of the head are charged to a high electrostatic poten~ial. The resulting ionized or electrostatically charged cloud of particles is then attracted to and settles on the surfaces of articles ,. , ~ .
, 11'7'7;~41 , or ware to be coated, which àre usually maintained at ground potential.
Spray heads of such electrostatic coating apparatus have heretofore been rotated at relatively low speeds, e.g., on the order of 3,000 to 6,000 rpm. However, recent developments contemplate rotating the heads at considerably greater speeds on th order of 30,000 to 60,000 rpm, which enhances both the atomization and flow rate of coa~ing material sprayed from the head.
Obviously, at such high speeds of rotation spray particles leaving the peripheral edge of the head are flung at significant speeds generally radially of the head and parallel to ware to be coated, so that if electrostatic forces alone were relied upon to move the particles to the ware a substantial portion of the particles would not reach the ware. Consequently, the art also contemplates generating an annular shroud o air for movement around, across and forwardly of the rotary head to aid in moving electrostatically ~harged spray particles toward the ware.
To generate the shroud air, there is conventionally provided an annular manifold behind and around the rotary head. The manifold has a plurality of outlet passages arranged in an annular array, and air introduced into the manifold exits through the passages to form a shroud of air around the head. In an attempt to obtain a uniform layer or distribution of shroud air~
thereby to enhance uniformity of deposition of coating material on ware, the outlet passages are closely spaced and of relatively small diameter. Unfortunately, despite the close spacings and small diameters of the passages, the shroud air pattern i5 nevertheless nonuniform in that is is comprised of a plurality of discrete jets or streams of air. Also, in consequent of the small passage diameters, the same are prone to clogging by spray particles or contaminants in the air supply, which results in further nonuniformities in the shroud air pattern and the need to frequently clear the passages. For high volume production lines, this often yields a product output which is less than desirable or optimal.
Objects of the Invention An object of the present invention is to provide an improved structure for generating shroud air for a rotary head electrostatic spray coating system.
Another object of the invention is to provide a structure which generates a very unifoxm distribution of shroud air.
A further obiect of the invention is to provide such a shroud air generating structure which is not subject to blocking or clogging by spray particles or contaminants in the air supply.
Summa ~ e Invention In accordance with the present invention, there is provided in combination with a rotary head electxostatic spray coating system, of the type to which a rapid ro$ation is imparted to a rotary spray head and a jet of coating material to be sprayed directed thereagainst for discharge from a peripheral edge thereof in a spray, a structure for generating a uniform and annular layer or curtain of shroud air for movement around, across and foxwardly of the rotary head to aid eleotxostatic forces in moving spray particles toward articles to be coated. In one facet, said shroud air generating structure 4~
comprises a manifold having an air inlet for receiving air under pressure and a plurality of air outlets in an annular array for providing therethrough the curtain of shroud air. Said outlets have unequal spacings therebetween, and the spacings are such as to pro~ide a substantially uniform volumetric flow rate of air around the arcuate extent of said outlets despite variations in air pressure throughout the manifold.
In another facet, said shroud air generating structure comprises a manifold having an air inlet for receiving air under pressure and an air outlet, and in this case said air outlet is a continuous annular opening, behind the rotary head, for providing therethrough the annular curtain of shroud air.
In a preferred practice of the invention, the :
foregoing features are combined in a single structure, whi~h comprises an annular channel in a body portion -of the spray coating system behind the rotary head and coaxial tberewith. Said channel has an open side toward the head and an air inlet thereto, and a wall extends across said open side of said channel and has a plurality of passages formed therethrough.
Said passages are in an annular array, and have relatively large diameters and spacings therebetween which progressively decrease with increasing distances from said air inlet. An annular cover mounts on the body portion of the spray coating system coaxial with said annular channel, and has a radial flange which extends across and spaced from said wall to form therewith an annular chamber having a continuous annular opening coaxial with and behind the rotary head. In operation of said structure, uneven air 11'7'7;~
pressures develop throughout said channel upon intro-duction of air therein, and the uneven spacings of said passages cause a substantially uniform pressure and.volumetric distribution of air to be developed within said chamber. Consequently, air discharged through said annular opening orms a very uniform annular layer or curtain of shroud air for movement around, across and forwardly of the rotary head to aid electrostatic forces in moving spray particles toward articles to be coated.
The foregoing and other objects, advantages and - features of the invention will become apparent upon a consideration of the following detailed description, when taken in conjunction with the accompanying drawings.
Brlef Description of the Drawings Fig. 1 is a perspective view of a portion of a rotary head electrostatic spray coating system, which includes a shroud air generating structure embodying the teachings of the present invention;
Fig. 2 is a cross sectional elevation view taken substantially along the lines 2-2 of Fig. 1, and illustrates the forward portion of the rotary head electrostatic spray coating system and the arrangement of the shroud air generating structure thereon;
. Fig. 3 is a front elevation view, partly in cross section, taken substantially along the lines 3-3 of Fig. 2, and shows the arrangement of air outlet passages in an air distribution manifold of the shroud air structure, and -Fig. 4 is a c~oss sectional, fragmentary, sideelevation view ~aken substantially along the lines 4-4 of Fig. 3, illustrating the particular arrangement of a cover of the shroud air structure, which provides ~17'~41 a continuous annular outlet for a very uniformly distributed curtain of shroud air.
Detailed Description Referring now to the drawings, there is shown in Figs. 1 and 2 and indicated generally at 10 a rotary head electrostatic spray coating system which includes a shroud air generating structure, indicated generally at 12, configured in accordance with the teachings of .. . . ;
the present invention. The spray coating apparatus includes a rotatable, bell-shaped head 14 of conductive material, mounted on an output shaft 16 of a high speed air driven turbine 18. The turbine rotates the head at a high rate of speed on the order of 3Q,000 to 60,000 rpm, and is supported on an end of an arm 20 of insulating material. An opposite end o~ the arm is connected to any suitable mechanism (not shown) for moving the apparatus to positions pe~mitting proper deposition of coating material on articles, for example on articles moved past the apparatus on a conveyor.
In operation of the spray coating apparatus 10, coating material in a passage 22 passes through an orifice 24 and is directed in a stream or jet onto an interior surface 26 of a center portion 28 o the head 14. Because of rotation of the head, upon striking the surface the coating material progresses radially outwardly through a passage 30 and across an inner wall 32 of the head in a thin film under centrifugal force toward a sharp, circular, peripheral edge 34 o the head, whereat it is divided as it leaves the head into fine particles in the fo~m of a spray~ A high d.c. voltage on the order of 12Q,000 volts is connected with the head; so that spray l~t~7~41. , particles on moving past the peripheral edge a~e charged to a high electrostatic potential for attraction to articles to be coated, which are maintained at a different and usually ground potential. To this end, the insulating material support arm 20 isolates peripheral equipment from high voltages present at the spray head of the system.
--Although Lmprovements are obtained in coating .
material deposition by virtue of electrostatic attraction of the.spray particles to the ware, if electrostatic .
attraction were the sole means for moving spray particles to the ware significant portions of the particles would .
not reach the ware. This may be appreciated if it is considered .that at the ver~ high speed of rotation of the spray head 14, spra~ particles discharged from the - peripheral edge thereof travel at significant velocities in directions generally radially of the head and parallel to the ~rticles, since articles to be coated are usually positioned forwardly of the head along the axis of rotation thereof~ Thus, the direction of movement of the spray particles must be changed by up to 30 and more for the particles to reach the ware, which can hardly be accomplished with electrostatic forces alone. Con~equently, additional means is provided for aiding movement of spray particles toward the ware.
To aid movement of spray particles toware ware to be coated, the art contemplates generating a shroud or curtain of air for movement over, around and forwardly of the head and against the particles as they leave the peripheral edge of the head. Heretofore, should air genera~ing structures have included an 117'~;~41 annular manifold behind the head for receiving air under pressure, and a plurality of shroud air outlet passages in an annular array around the manifold.
In an attempt to ob~ain a uniform layer or distribution of shroud air, thereby to enhance uniformity of movement of coating material toward and deposition on articles, the outlet passages are closely spaced and of relatively small diameter. ~owever, despite the close spacings and small diameters of the passages, the shroud air pattern is nevertheless nonuniform in that is is comprised of a plurality of discrete stxeams or iets of air. Also, because of the small diameter of the passages, the same are subject to blockage by spray particles or contaminants in the air supply, which further impairs the uniformity of the shroud air pattern and therefore the uniformity of dispersion of spray particles toward articles to be coated, with the result thatprior apparatus of the general type must be frequently shut down to clear the passages.
To overcome the disadvantages of prior shroud air generating structures, and with reference also to Figs. 3 and 4, in accordance with the teachings of the present invention the improved shroud air generating structure 12 includes an annular trough, openingl channel or manifold 36 formed in a forward face of a body portion 38 of the spray coating apparatus. The manifold is of sufficient diameter to extend beyond the rearward end of the rotary head 14, and a supply (not shown) of air under pressure is connected with the manifold through an air inlet passage 40. An annular wall or air diffuser ring 42 closes a forward side of the manifold, preferably _g_ -~7'~;~41 by being press fit therein, and a plurality of 6 air outlet passages 44 are formed through the diffuser ring in an annular array.
The shroud air flows through the passages 44, and in accordance with one facet of the invention the passages are of relatively large diameter and unevenly spaced around the diffuser ring 42, the spacing being such as to provide a generally uniform volumetric distri~ution of` air discharged through the passages -~
around the arcuate extent of the ring. In this connection, it is understood that with a single air inlet to the manifold 36 from the air passage 40, movement of air through the outlet passages results in une~ual air pressures within the manifold, such that the pressure of air adjacent the inlet passage is greater than at positions remote from the inlet passage. Consequently, if the outlet passages were equally spaced around the diffuser ring, greater volumetric discharges of air would occur in proximity with the inlet passage than elsewhere, and would decrease with increasing distances from the inlet passage. However, by providing unequal spacings between the outlet passages, such that the passages remote from the inlet passage are spaced more closely together than are the passages in proximity with the inlet passage, and so that a progressively decreasing spacing between passages occurs rom a position adjacent the inlet passage to positions remote therefrom, a very volumetrically uniform discharge of air is obtained around the entire arcuate periphery o~
the di ffuser ring. At the same tLme, the relatively large diameters of the outlet passages prevents the same from becoming clogged by contaminants in the -10- , 1 1'7'~
air supply, and fewer outlet passages are requfired for a given volume flow of air.
For the structure th~s far described, it is apparent that the air patt~rn would be improved over tha~ provided by prior structures, in that there would be a uniform volumetric outlet of air around the arcuate extent of the annular array of outlet passages, but tha~ the air pattern would nevertheless be comprised of a plurality of discrete streams of -~
air. Accoxdingly, to generate a very uniform and continuous annular layer or curtain of shroud air for movement across and forwardly of the rotary head 14, in accordance with a further feature of the invention an annular shroud air cover~46 is threaded onto thP forward end of the body portion 38. The diffuser ring 42 is generally L-shaped, and a forwardly .extending leg thereof defines an outer, annular, peripheral surface 4~. The cover has a radially inwardly extending flange or wall 50, and when the cover is on the ~ody portion a radially extending annular chamber 52 is formed be~ween the wall and portions of the forward faces of the body portion and diffuser ring, and an annular and axially extending shroud air outlet passage 54 is defined between an innermost end or edge of the wall and the peripheral surface 48 of the diffuser ring. Also, when the cover is mounted on the body por~ion an annular seal is formed between the cover and body portion along a sealing surface 56 of the cover, thereby preventing unwanted leakage of shroud air from the chamber 52~
11~7'~
It may now be appreciated that the invention provides an improved structure for generating a very uniform annular layer or curtain of shroud air around, across and forwardly of the rotary head 14. To this end, the uneven spacings between the outlet passages 44 in the diffuser ring 42 provide within the chamber 52 a very uniform volumetric and pressure distribution of air, despite variations in the pressure .
.,.. . , :~
of air within the manifold 36. At the same time, the annular outlet passage 54 is continuously open around its circumference, so that with the uniform volumetric .and pressure distri~ution of air within the chamber, the shroud alr pattern issuing through the passage is very uniform and is not comprised of discrete streams of air. Consequently, the shroud air pattern imparts a very uniform movement of spray particles toward ware to be coated, so that significant improvements are obtained in deposition of coating material on the ware. In addition, because of their relatively large diameters, not only are fewer passages 44 required for a given volume flow of air, which decreases manufacturing costs of the structure, but the passages are also not prone to blockage by contaminants in the air supply. Further, since the wall 50 of the cover extends across the passages, the passages are also shielded against deposition therein o~ spray particles.
While embodiments o the invention have been described in detail, it is understood that various modifications and other embodiments thereof may be deviced by one skilled in the art without departing fxom the sp~rit and scope of the invention, as defined in the appended claims.
-12- J .
Claims (7)
1. In combination with a rotary head electrostatic spray coating system of the type to which a rapid rotation is imparted to a rotary spray head and a jet of coating material to be sprayed is directed thereagainst for discharge from a peripheral edge of the head in a spray, a shroud air generating structure comprising an annular manifold having an air inlet for receiving air under pressure and a plurality of air outlet passages in an annular array behind and around said rotary head, said air outlet passages having unequal spacings therebetween which progressively decrease with increasing distances of said passages from said air inlet to provide a substantially uniform volumetric flow rate of air around the arcuate extent of said annular array of air outlet passages, and a cover for said manifold, said cover extending around said air outlet passages and forming with said manifold a chamber for receiving air discharged through said passages, said cover defining with said manifold a continuous annular opening from said chamber around and behind said rotary head for passage therethrough of shroud air from said chamber for movement in a very uniform annular curtain around, across and forward of said rotary head.
2. The combination as in claim 1, wherein said manifold comprises an annular channel in a surface of a body portion of said spray coating system behind said rotary head, an annular diffuser ring closes said channel, said air outlet passages are formed through said diffuser ring, said air inlet communicates with said channel, and said cover is mountable on a body portion of said spray coating system behind said rotary head, said cover having a generally radial annular wall extending across and spaced from said outlet passages and defining said chamber with said manifold, an inner edge of said wall being spaced from said manifold and forming therewith said continuous annular opening.
3. In combination with a rotary head electrostatic spray coating system of the type to which a rapid rotation is imparted to a rotary spray head and a jet of coating material to be sprayed is directed thereagainst for discharge from a peripheral edge thereof in a spray, a shroud air generating structure comprising an annular manifold having an air inlet thereto for receiving air under pressure and an air outlet therefrom, said air outlet being a continuous annular opening behind said rotary head for providing therethrough an annular curtain of shroud air for movement around, across and forwardly of said rotary head to aid electrostatic forces in moving spray particles toward articles to be coated, wherein said manifold includes a first annular chamber having said air inlet thereto, a second annular chamber axially aligned with said first chamber and having said annular outlet therefrom, and a wall between said first and second chambers, said wall having a plurality of air distribution passages formed therethrough between said first and second chambers for passage of air from said first chamber to said second, said first chamber developing uneven air pressures therein upon the introduction of air therein and said air distribution passages having unequal spacings therebetween which progressively decrease with increasing distances of said air distribution passages from said air inlet to provide a uniform pressure and volumetric distribution of air in said second chamber and thereby to provide a very uniform volumetric flow rate of shroud air through said annular air outlet.
4. The combination as in claim 3, wherein said wall comprises an air distribution ring on a side of said first chamber, and including a cover over said air distribution ring and forming therewith said second chamber and said annular outlet.
5. The combination as in claim 4, wherein said first chamber is formed in a forward body portion of said spray coating system behind said rotary head thereof and said cover mounts on said forward body portion and has a wall extending generally radially of said first chamber and defining with said air distribution ring said second chamber and said annular air outlet therefrom.
6. In combination with a rotary head electrostatic spray coating system of the type to which a rapid rotation is imparted to a rotary spray head and a jet of coating material to be sprayed is directed thereagainst for discharge from a peripheral edge thereof in a spray, a structure for generating a uniform and annular layer or curtain of shroud air for movement around, across and forwardly of said rotary head to aid electrostatic forces in moving spray particles toward articles to be coated, said shroud air generating structure comprising an annular channel formed in a body portion of said spray coating system behind said rotary head, coaxial therewith and having an open side toward said head and an air inlet thereto for entrance of air under pressure into said channel; a wall extending across said open side of said channel and having a plurality of passages formed therethrough in an annular array, said passages having relatively large diameters and spacings therebetween which progressively decrease with increasing distances from said air inlet; and an annular cover mounted on said body portion of said spray coating system coaxial with said annular channel, said cover having a radial flange which extends across and spaced from said wall and forms therewith an annular chamber having a continuous annular opening coaxial with and behind said rotary head, said channel developing uneven air pressures therein upon introduction of air therein and said spacings of said air passages in said wall developing a substantially uniform pressure and volumetric distribution of air within said chamber for discharge through said annular opening, whereby air discharged through said annular opening forms a substantially uniform annular layer or curtain of shroud air for movement around, across and forward of said rotary head to aid electrostatic forces in moving spray particles toward articles to be coated.
7. The combination as in claim 6, wherein said wall comprises an annular air distribution ring mounted in said open side of said channel, said air distribution ring being generally L-shaped and having a first leg extending radially of said annular channel and a second leg extending coaxial therewith, said air passages being formed in said first leg and said cover flange extending across and spaced from said first leg to form said chamber therewith and having an innermost edge spaced from said second leg to form said annular opening therewith.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US22836481A | 1981-01-26 | 1981-01-26 | |
| US228,364 | 1981-01-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1177241A true CA1177241A (en) | 1984-11-06 |
Family
ID=22856876
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394910A Expired CA1177241A (en) | 1981-01-26 | 1982-01-26 | Shroud air generating structure for rotary head electrostatic spray coating systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1177241A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106417217A (en) * | 2016-12-06 | 2017-02-22 | 福建省罗源创鲜农业科技有限公司 | Insecticide spraying system for edible fungi |
-
1982
- 1982-01-26 CA CA000394910A patent/CA1177241A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106417217A (en) * | 2016-12-06 | 2017-02-22 | 福建省罗源创鲜农业科技有限公司 | Insecticide spraying system for edible fungi |
| CN106417217B (en) * | 2016-12-06 | 2022-10-18 | 福建省罗源创鲜农业科技有限公司 | Domestic fungus insecticidal spraying system |
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