US2803496A - Atomizing apparatus - Google Patents

Description

E. M. RANSBURG 2,803,496

ATOMIZING APPARATUS I Aug. 20, 1957 Filed Nov. 21, 1951 i EDWIN M. RANSBURG Attorney United States Patent ATOMIZING APPARATUS Edwin M. Ransburg, Indianapolis, Ind., assignor to Ransburg Electra-Coating Corp., a corporation of Indiana Application November 21, 1951, Serial No. 257,621

4 Claims. (Cl. 2991) This application relates to atomizing apparatus and method, and more particularly to a unit for electrostatical- 1y atomizing and depositing liquid coating material.

For decades commercial use has been made of atomizing devices making use of fluid pressure (commonly a separate fiuid such as air) for effecting atomization of a liquid coating material and directing the spray thus formed generally in the direction of articles or surfaces to be coated, with reliance on this general direction of movement of coating material particles to cause at least some of them to deposit upon the surface being coated. Such spray coating is relatively inefiicient, however, and in recent years a form of spray coating known as electrostatic coating has been developed. In a system of this latter character, the spray discharged from an atomizing device is given an electric charge at the time the particles leave the spraying device or shortly thereafter and deposition of the coating material particles is primarily the re sult of electrostatic forces attracting the particles to the article being coated. This is accomplished by creating an electrostatic field which includes the article being coated and the charged coating material particles moving generally toward such article. Coating systems of the electrostatic type, especially those also efiecting atomization electrostatically, have proved very satisfactory and extremely efiicient commercially in coating various types of articles, particularly those of a character which were previously extremely difficult to spray coat efiiciently.

One of the most efficient electrostatic atomizing heads heretofore developed comprises a head with a circular atomizing edge, preferably the edge of a bell-shaped member which is rotated to improve the uniformity of delivery of liquid coating material in a thin film to the atomizing edge with the edge constituting the zone from which atomization takes place, an electrostatic atomizer of this type being disclosed and claimed in my copending application Serial No. 143,994 filed February 13, 1950. However, the natural pattern delivered from an electrostatic atomizing head of this type is a doughnut or annular band having a central portion which is completely or relatively void of coating material, and for this and other reasons it may be desirable to have the liquid coating material delivered to the atomizing zone through an orifice substantially coextensive with the zone and having a shape corresponding thereto, thus the coating material may be fed through an elongated narrow orifice for atomization from the atomizing zone. For example, where it is desired to have a relatively long linear pattern, it is preferable to use a relatively long linear head rather than such a bell-shaped head and to use an elongated orifice for feeding coating material thereto.

While electrostatic atomization and deposition has heretofore been effected from a relatively long straight blade, such an atomizing head has always presented problems in securing satisfactory uniform delivery of the desired liquid film entirelyalong the atomizing edge, particularly when the operation makes it desirable to use the Patented Aug. 20, 1957 head at an angle to the horizontal, the problems being greatest when the head is used vertically.

l have devised and am here disclosing and claiming a head using an elongated orifice, generally having a width of only a few thousandths of an inch and a length many times its width (as from several inches up to several feet), which if supplied with liquid coating material at relatively low pressures (as 2 or 3 pounds per square inch) may be used to feed coating material to an atomizing zone arranged vertically or at any other desired angle with Very satisfactory band patterns. The use of an orifice with a width of only a few thousandths of an inch (frequently of the order of three thousandths to five thousandths of an inch), however, has presented an extremely difiicult problem in maintenance of a clear flow path. With such an extremely narrow orifice any small bit of foreign matter in the liquid coating material is almost certain to result in clogging of a portion of the orifice; and even an extremely temporary shutdown will sometimes result in quick drying coating material forming strings or dried portions across such a narrow orifice, again obstructing flow at such points. Since the articles or surfaces being coated usually have movement relative to the head in a direction transverse to the length of the atomizing pattern, any such fixed obstruction of a portion of the orifice results in the discontinuity of the spray pattern which, in turn, results in a stripe in the coating.

I have devised and am here disclosing an atomizing unit which uses such an elongated extremely narrow orifice and is provided with means for overcoming this problem of obstruction and maintaining a satisfactory coating pattern without any noticeable stripe efiect. Moreover, I have accomplished this without creating undesirable disturbances in the electrostatic field relationships between the head and the surface being coated, which would otherwise in and of themselves result in non-uniformity of deposition of the coating material.

The foregoing and other objects and features of the invention will be apparent from the following specification and the drawings, in which:

Fig. 1 is a side elevational view of an atomizing unit having an elongated extremely narrow orifice and provided with means for preventing obstruction of such orifice;

Fig. 2 is a perspective or isometric View of a portion of the head shown in Fig. 1, separated near the center to better show its construction, and enlarged with respect to Fig. 1; and

Fig. 3 is a transverse sectional view along the 1ine 3-3 of Fig. 2.

While only one specific embodiment of an atomizing unit is illustrated and will be described as an embodiment of the present invention, it will be understood that this is representative only; and it is to be understood that other embodiments may be utilized without departing from the contemplated scope of the present invention, and that no limitations are to be implied from such specific description as shall hereafter be provided. For example, the obstruction preventing features of this invention can be utilized not only in an atomizing head of the character illustrated having a straight elongated orifice, but also in an elongated orifice which is arcuate or annular as illustrated in the copending Crouse application Serial No. 13,174, filed March 5, 1948, now abandoned.

Referring now more especially to the particular embodiment of the invention illustrated in the accompanying drawing, it will be seen that the head identified in general as 19 comprises as its principal parts two side members, here identified as 11 and 12, and a top plate 13. The side members 11 and 12 are connected to the top plate in .uid outlet isthrough this elongated orifice. ing material is delivered to the chamber 17 from a suitable pump and supply source during operation of the atoma. izing unit, as through the-hose 21 illustrated. If the side" wall of a refrigerator (as a representative article) were properly spaced relationship by a suitable fastening means, as the screws 14; and are preferably clamped at each end with a suitable shim member 15 therebetween, as 'by the side screws 16. ,As may be best seen in Fig. 3,

.the side members are relatively widely spaced from each other in their upper portion to provide a chamber 17 of substantial size, and only slightly spaced from each other 7 to provide a slot or elongated orifice 18 extending from such chamber to the atomizing zone of the head pro- 'vided by the opening of this slot between the two relathe width of the flow orifice or slot 18; and suitable seals,

as the gasket means 19 and 20, insures that the only liq- Liquid coatbeing coated, for example, the head mi ht have a length of about two feet, be spaced an appropriate distance from the refrigerator as it moves along a conveyor through the coatlng zone (as ten inchesaway), and the electric field established between the head and article surface.

under the conditions just described, might be of the order of 100,000 volts. Liquid coating material delivered to .the chamber 17 would then flow out through the slot 18 moved thereto to be deposited thereon by electrostatic forces.

To insure maintenance of unobstructed flow along the entire length of the elongated orifice, I provide a wiping arrangement here shown as consisting, of a wiper member 22 adapted to extend through the slot 18, at least to the outer end thereof and preferably at least a few thousandths of an inch therebeyond, but not appreciably more and in no event should the wiper member protrude to the extent where theelectrostatic field is seriously disturbed. This wiper member 22 must, of course, be thin enough in one direction to reciprocate in the slot 18, so that if the 'slot were five thousandths of an inch wide the wiper member might be four thousandths of an inch thick,

7 as an example; but sufficient mechanical strength without pbstruction of a large portion of the orifice at the atomlzmg zone 1s provided by tapering the wiper member, as may be best seen in Fig. 2. For example, the wiper member may be of the order of one-half or three-quarters of an inch thick at its base portion, and tapering to a point 22b only a few thousandths of an inch in 'a direction parallel to the length of the orifice or slot 18. Such an arrangement provides completely satisfactory mechanical forces available, when the wiper member is reciprocated the length of the orifice, to force particles of foreign matter or other obstructions entirely out of the orifice and head or down to the Wall at one end where they will not materially disturb the coating pattern.

In order to efiect the desired continuous movement of the wiper member along the orifice during operation of the atomizing unit, l here illustrate the wiper member 22 as mounted upon a collar 23 in turn mounted upon arotating shaft 24. The shaft is here shown as provided with two oppositely arranged helical grooves 24a and 24b; and

the "collar 23 is provided with a pin 23a extending down V c 4 tion, the drive arrangement for rotating the shaft 24 must be provided with power through an electrically insulated power source. I have found it convenient to do this by supplying compressed air through a rubber hose 25 to an air motor 26, here shown as connected through gears 27 and 28 to the shaft 24 to effect rotation thereof. The drive motor speed is preferably such as to provide a relatively rapid movement of the wiper member 22, since, within reasonable limits, the more rapidly the wiper mem-. oer moves along the slot the less tendency toward any discontinuity in the coating deposited on the surface being coated.

While I have shown and described a particular embodiment of my invention, it is to be understood that it is ca- V pable of many modifications. Changes, therefore, in the 7.

construction and arrangement may be made withoutdeparting from the spirit and scope of the invention, as disclosed in the appended claims. 7 H

I claim: p

1. An electrostatic atomizing unit comprising: a. singlefluid atomizing head having an elongated orifice adapted to have liquid flowed therethrough at relatively low pressure for electrostatic atomization therefrom, said elongated orifice having a width of only a few thousandths of an inch and a length many times its width; a cleaner member; means for mounting the cleaner member in said head with a portion movable in said elongated orifice, said portion being relatively small and not appreciably projecting therefrom; drive means for continuously reciprocating said cleaner member along said elongated orifice during atomization therefrom, and means for supplying power to said drive means with the power supplying means being of electrically insulating material.

2. An electrostatic atomizing unit comprisingz'a singlefiuid atomizing head having an elongated orifice adapted to have liquid flowed therethrough at relatively low pressure for electrostatic atomization therefrom, said elongated orifice having a width of only a few thousandths of an' inch and a length many times its width; a cleaner member; means for mounting the cleaner member with at least a portion positioned at the open end of'said elongated orifice and movable along'the length thereof; means for flowing a solid stream of said liquid through said orifice for atomization; and means for repeatedly moving said portionalong said orifice during said operation of said atomizing head.

3. An electrostatic single-fluid atomizing unit comprising: a head havingan elongated orifice adapted to have liquid flowed ther'ethrough at' relatively low pressure for electrostatic atomization therefrom, said elongated orifice having a width of only a few thousandths of an inch and a length many times its width; means for flowing a solid stream of said liquid through said orifice for atomization; a cleaner member; and means for mounting the cleaner member in said head with a portion movable along said elongated orifice','the portion movable in'said elongatediorifi'ce being small relative to'the orifice length and not appreciably projecting therefrom and having a larger and mechanically stronger portion therebehind.

4. An electrostatic charging and atomizing unit com prising: a single-fluid atomizing head having a restricted orifice adapted to have-liquid flowed therethrough for atomization from a film formed therefrom and for electricalcharging of the atomized particles, said restricted orifice having a minimum dimension of only a few thousandths of an inch; a cleaner member; means for mounting the cleaner member within'the head with at least a portion positioned adjacent the open end of said restricted orifice and movable with respect thereto; means for flowing 'a solid stream of said liquid through said forifice for atomization; and-means for moving said portion relative to said orifice forcleaning said orifice, said a i q f uf lu n i p el 1 5 6 References Cited in the file of this patent 1,367,947 Chadick Feb. 8, 1921 UNITED STATES PATENTS 1 52 3? 3: gig

, 1 11 374,290 1887 2,462,034 Zack Feb. 15, 1949 910,178 Cwmmcl 1909 5 2,473,933 Zielinski June 24, 1949 996,767 Jackson July 4, 1911

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