US 2728607 A
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W. L. SMART Dec. 27, 1955 LIQUID FEEDING APPARATUS Filed June 9, 1954 INVEN TOR.
7 MW QU L S 2 U W/ m M a U H n W W duper a LIQUID FEEDING APPARATUS William L. Smart, Indianapolis, Ind, assignor to Ransburg Electra-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application June 9, 1954, Serial No. 435,463
3 Claims. (Cl. 299-63) My invention relates to apparatus for feeding liquid from a stationary member to a rotating member, particularly for feeding liquid coating material generally upwardly from a stationary tube to the atomizing edge of a rotating bell-shaped atomizer.
Numerous industrial processes require that a liquid be fed with an upward component from one stationary member to another moving member without appreciable loss or leakage of the liquid from its desired path of flow. For example, in the electrostatic spray coating of the lower surfaces of articles of manufacture it is often desired to feed liquid coating material from a stationary reservoir to a rotating conical, i. e. bell-shaped, atomizing device located generally beneath the articles for atomization therefrom and electrostatic deposition of the coating material on the articles.
It is well known that certain liquid coating materials, particularly some pigmented paints, have extremely abrasive qualities and that on exposure to air most liquid coating materials leave a gummy residue. Moreover, liquid coating materials generally contain solvents which readily attack the materials used in conventional liquid sealing devices. These qualities make the useful life of conventional sealing devices very short. Once the liquid coating material leaks past its seal, its abrasive and gummy qualities will quickly render the bearing structure and other moving parts of the rotating atomizing device unserviceable. For this reason it is desirable in feeding liquid coating material to such an atomizing hell that conventional mechanical seals and related packings be eliminated. However, excessive turbulence in the transfer of the liquid from the stationary member to the rotating bell is to be avoided as this may adversely affect the character of the atomized particles and cause uneven and undesirable coating of the articles.
An object of my invention is to provide improvements in a rotary device for the protection of the bearing structure and other movable parts. Another object is to provide means for feeding liquid without the use of conventional packings or liquid sealing devices. A further object is to provide a more eflicient means for feeding liquid coating material and the like with an upward component to the atomizing edge of a rotating bell-shaped atomizer.
I have discovered a novel liquid feeding device which comprises a rotatable hollow shaft whose axis has a vertical component and an annular-edged atomizing bell concentrically mounted for rotation on the upper end of the shaft. The atomizing bell has an inner surface which flares conically outward to an annular atomizing edge. The bell may include a generally cylindrical liquid dam mounted at its lower end concentrically within the inner surface of the bell so that the dam projects upwardly. A stationary feed tube extends concentrically through the hollow shaft and terminates at its upper end in a lipped portion whose edge surrounds and overhangs the projecting end of the liquid darn. Means are pro- "ice vided for rotating the hollow shaft, atomizing bell and liquid dam while liquid is fed through the stationary feed tube for flow over its lipped portion to the inner surface of the rotating atomizing bell.
Means for accomplishing the above stated and related objects of my invention will now be described in detail with reference to the accompanying drawing in which:
Fig. 1 is a partially broken away elevational view of an atomizing device embodying my invention for use in an electrostatic coating system; and
Fig. 2 is a detailed view of the stationary feed tube shown inFig. 1.
My invention is particularly adapted for use with a bell-shaped atomizer (herein called a bell) for spray coating but the invention may assume many different forms and the above mentioned drawings and the followdevice 10 which includes a flaring, somewhat conically shaped atomizing bell 11 mounted on one end of a generally vertical rotatable hollow shaft 12. The adjoining surfaces of bell 11 and shaft 12 are sealed by an O-ring 13 and the two are held together by a set screw 14.
, Bell 11 has an inner liquid-guiding surface with an innermost conical throat portion 11a extending outwardly from the juncture of bell 11 and shaft 12 generally toward the bells annular edge at an angle of approximately 15 to the axis of the bell and shaft. The bell and shaft may be rotated by an integral motor assembly lying within atomizer housing 15 whose details are not shown as my invention is independent of the motor or other driving means for bell 11.
Shaft 12 extends axially through housing 15. At its lower end there is affixed to housing 15 a stationary tube support 16 having an axial passageway concentric with the shaft. A hollow cylindrical tube stop 17 is positioned within the passageway in tube support 16 by a set screw 18. A stationary feed tube 20 is securely mounted concentrically within the passageway in tube support 16 with its lower end positioned against the upper annular face of tube stop 17 by means of a set screw 21. The adjoining surfaces of support 16 and tube 20 are sealed by an O-ring 22 of flexible material. A back plate 25 having an axial passageway communicating with the passageway in tube support 16 is securely mounted on the lower face of the stationary tube support. Liquid coating material to be atomized is fed from a reservoir 28 at a controlled rate by a supply tube 29 through the pasageway in back plate 25 and through tube stop 17 to the lower end of feed tube 20. Atornizing device 10 may be maintained at high electrical potential by connection to a high voltage source 30 as shown or other means known to the art employed to effect a particle-depositing potential difference between the atomized coating material and the articles. This is generally accomplished by maintaining the articles and their supports at a difference of potential from the atomizer, preferably by grounding the articles and maintaining the atomizer at high voltage as shown.
The details of stationary feed tube 20 are shown in Fig. 2 with the upper liquid discharging portion of the tube shown in cross section. In order to properly feed liquid coating material to the inner surface 11a of the bell the upper end of stationary feed tube 20 is lip-like. This upper lipped portion of the tube terminates in a preferably sharp knife-like annular edge 20a generally concentric with the axis of the tube. The outer liquid guiding surface 20b of the feed tube over which liquid flows to be discharged onto inner surface 11a of the bell is generally cylindrical and parallel with the axis of the tube. Edge cu should be suiiiciently spaced from surface 11a to perit the formation of discrete liquid droplets whichwill not bridge the gap between tube edge 20a and surface 11a; and with most commercial coating materials the edge should be'spaced not less than 0.125 inch from the inner surface of the bell.
To prevent liquid coating material from reaching the bearing structure of atomizer a generally cylindrical sleeve or liquid dam 32 may be pressed or otherwise mounted in thethroat of bell 11. It is to be understood-that darn 32 may be an integral part of the hell but for ease of construction aseparate cylindrical member securely fitted into the bell has been found more convenient. Liquid dam 32, is preferably concentric with the bell and-extends upwardly into-the central passageway formed by bell surface lla so thatthe uppermost end of the, damis surrounded by surface 20b of the feed tube. Thus edge 200 should lie in a plane lower than-the uppermost end of dami32.
Liquid discharged from feed tube 20 onto the inner surface of rotating bell 11 will spread into a thin film which will move upwardly to the annular atomizing edge of. the bell under the influence of centrifugal force. Any liquid which might tend to flow downwardly toward shaft 12 will be stopped by liquid dam 32. "The dam serves'the' further function of preventing liquid on the inner surface of the bell from running downwardly toward the bearing structure when the bell is not rotating or when the centrifugal force is not sufiicient to move the liquid coating material in an upwardly direction.
One commonly used atomizing device which embodies my invention includes a rotating hollow shaft having an inner diameter of approximately 0.75 inch and a bell in which surface 11:: makes an angle of approximately 15 withthe axis of the bell and shaft. Various coating operations employing this device require liquid to be fed to surface 11a of the bell at rates of from 15 to 900 cubic centimeters per minute. The bell may be rotated at speeds of from several hundred to several thousand revolutions per minute.
"The inner diameter of feed tube is approximately 0.25 inch. Liquid discharge edge 20a is of knife-like sharpness and has a diameter of approximately 1.125 inches. Edge 20a lies approximately 0.75 inch below the uppermost portion of the feed tube and is spaced 0.15 inch from surface 11a. Cylindrical surface 20b is substantially parallel tothe axis of the feed tube. Liquid dam 32 is approximately 1.25 inches in length and extends within the space bounded by tube surface 20b a distance of approximately 0.5 inch.
Although atomizer 10 is shown in Fig. l in a vertical position, it may be operated with its axis substantially inclined. Liquid can be properly fed to the bell so long as the axis of the atomizer has a vertical component.
1. -A device for feedingflliquid comprising a rotatable hollow shaft whose axis has a vertical component; a bellshaped atomizer mounted for rotation on the upper end of said shaft, said atomizer having an interior surface portion flaring conically at a substantial angle to the axis of said shaft and atomizer; a cylindrical liquid dam mounted at its lower end concentrically within the interior surface portion of said atomizer with the upper end of said 7 cylindrical dam projectingupwardly from said interior surface portion; astationary feed tube extending concentrically through said shaft and terminating in an, upper lip-like portion having an annular liquid discharge edge or knife-like sharpness concentric with said interior sur' face portion of the atomizer andencircling the upper end of said cylindrical dam, said edge being spaced from said interior surface portion a distance greater than a drop of the liquid can bridge; means for rotating said shaft and atomizer; and means for feeding liquid upwardly through said feed tube andover its upper lip-like portion to the inner surface of said rotating atomizer.
2. Apparatus as set forth in claim 1 wherein the interior surface portion of the atomizer lying adjacent the upper portion of 'the feed tube is conical and forms an angle of 15 to the axis of the shaft and'atomizer.
3. A device for feeding liquid comprising a generally vertical rotatable hollow shaft; an atomizing bell concentrically mounted for rotation on the upper end of said shaft, ,said bell having an inner surface portion flaring conically at an angle to the axis of said shaft of approximately l5; a cylindrical liquid darn mounted at one of its endswithin the inner surface portion of said bell concentrically with the axis of said bell with the other endof said cylindrical dam projecting upwardly from saidinner surface portion; a stationary feed tube extending concentrically through said hollow shaft and terminating in an upper lipped portion having a knife-like liquid discharge edge overhanging the projecting edge of said liquid dam; said edge being spaced more than .125 inch from the inner surface portion of'the bell; means for rotating said shaft, bell and dam; and means for feeding liquid to said feed tube for flow therethrough and over said liquid discharge edge to the inner surface of therotatingbell.
References Cited in-the file of this patent UNITED STATES PATENTS