US2785088A - Electrostatic coating apparatus and method - Google Patents

Description

March 12, 1957 E. M. RANSBURG ,78

ELECTROSTATIC COATING APPARATUS AND METHOD Original Filed Nov. 23, 1951 2 Sheets-Sheet 1 1N VEN TOR.

YEDWIN M. RANSBURG B M W M F A Home y March 12, 1957 E RANSBURG 2,785,088

ELECTROSTA'FEd COATING APPARATUS AND METHOD Original Filed Nov. 23, 195] 2 Sheets-Sheet 2 5 mu? 7 E 2 58 i '10,, 5,1,1,

I Fl g. 3

INVENTOR.

EDWIN M. RANSBURG A Home] United States PatentO EEEC'I'ROSTATIG CGATENG i NIETHOD 1 Edwin M Ransburg, lntlianapolis, Inch, assignor to'Ransburg Electra-Coating Corp., a corporation of Indiana Original-application November 23, 1951, Serial No. 257,874, new Patent No. 2,728,689," dated f December 27, 1955. Divided and this application April-19,1955; SerialFNoi-SOZASS 9 Claims. (Cl; 117-93) This application relates to the spray coating .of' articles, and more particularly to the electrostatic deposition of liquid coating material on articles.-

This application is a-division of my .cope'ndingapplication, Serial No. 257,874,ffiled November 23, 1951 now Patent No. 2,728,689.

In a-majority of electrostatic coating systems, a field of electrostatic force is set up .which includes the article being-.acoated' and the atomized coating material particles in movement toward such article. In normal commercial practiceit is desirable to mount the article on a grounded conveyor and thus to make the article itself (if itis of conducting. material-) or. an electrode withinor'irnmedh atelyflbehind thearticle at ground potential; andrto pro; vide another. electrode at a-high electrical potential: with respect to ground, this electrode sometimes being the spraying, device and vsometimes being-a separate electrode near or. past which the spray passes in its-movementtoward thelarticle.

In the form of electrostatic coating apparatus where the spraying device is the electrode, it has been -found that" the' coating material can be atomized from anedge whiclrf'is maintained at high potential with respect to ground, the atomization taking placefrom-the edgefrom a. multiplic'ityof cusps, which are formed-thereon by virtue ofthe electrostaticforces present. El'ectrostaticcoating apparatus employing such an atomizing edge. are shown Mfarch 10", 1949' as Serial No. 80,753, new Patent 2,651j287ithe following applications of E. Ni. Ransburg: Serial'NoI 57,260; filed October 29, 1948, now Patent 2,558,472; Serial No. 107,687, filed July 30, 1949, HOW Patent 2,684,1656y8erial No. 143,994, filed February 13',

1-950: and other applications owned by the same assignee.

Whenanzarticle is exposed to the spray issuing from an atomizing edge in an electrostatic.coatingzsystem de position of the coating material. particles is primarilythe result of electrostatic forces and -.theiparticles asv they. are

atomizedfrom the edge-carry anelectric charge rela tivlyQPpositeY to the charge of the article and. thus. are deposited thereon with a minimum of waste. One of the problems encountered in an electrostatic coating system where atomization is achieved. from an atomizing zone suchas an atomizing edge of the type referred to above a is the'fee'd of "coating material to thezo'ne for atomization therefrom: In the'. said copending application ofE. M. Ransbutg,=filed on February 13,1950, as Serial No. 143,994, feed of'coating material to the "atomizing edge is achieved-by employing a rotating bell-shapedatomizing :5

head-,- "with the coating being fed through an orifice at the'centerof thehe'ad for flow across the interior surface of the-head to the-edge by the centrifugal force created.

However, when it is desiredto feed coating material to revolution; such" as an arcuate orlinear edge; the method an elongated atomizing'edge-Which is not a figure of 'ice of feeding coatingmaterial to such an edge by centrifugal force is impracticable.

According to this invention, feed to an elongated edge is achieved through the use of a jet streamof coating materialwhi'ch originates from an oscillatable source and is directed by oscillation of the source across a surface for flow from such surface to the atomizing edge. Inasmuch as oscillation of the source causes the jetstream to traverse the surface just mentioned, means are provided for assuring a uniform flow of coating material -to the entirelen'gth of the atomizingedge and where the source is oscillated at a constant angular rate producing incon stant rate of linear traverse, the flow of coating. material to the source is varied in direct proportion to thespeed of traverse so as to deliver a substantially'uniform quan ti'tyof coating material to the surface for flow tothe atomizing' edge;

Another feature of the invention is the provision of a second surface positioned above and angularly inclined to the first surface, together with means for supplying coatingmaterial to the second surface for gravity flow therefromto' the edge supporting surface andthence to the atomi'zing edge. The second surface may be in the form of a bathe and the coating material may be sup plied thereto by a jet stream from an 'oscillatable source of the" type previously mentioned. By the use of the methods and apparatus disclosed herein, it is possible to supply coating materialto a feed member which feeds the coating to the atomizing edge, with the quantity of coating supplied to the feed member being. substantially uniforrn'along' the length of the feed member and supplied'from a source operable to-deliver Varying quantities of material thereto in accordance with requirements.

The above and other features of the invention will be readily apparent from the following description and drawings, in which:

Fig. 1 is a perspective view partially broken away for clarity of illustration of an apparatusembodying the invention;

Fig. 2 is a vertical section through the coating-head shown in'Fig. 1; and

Fig. 3 is a top plan-view of a modified form of coating apparatus. While two different forms-of apparatus are illustrated in the accompanying drawings and will be described hereafter as providing means for practicing the present invention, it will be understood that these are representative embodiments only- It-will also be understood that forms of spraying devices other than the particular electrostaticatomizing device shown may be utilized and that other forms'of apparatus may be employedgand 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 im'- plied from such specific description as shall now bepro vided.

Referring to Fig. 1 of the drawings, there is shown a coating head lti including an elongated wedge-shaped member 11 having an edge 12 thereon from which edge liquid coating material is atomized by electrostaticforces; The Wedge member 11 has a horizontally arranged fiat top surface 13 which is substantially coextensive with the edge 12 and over which coating materialis adapted to flow to the'ed'ge for atomization. Positioned just above the surface 13' is a batlle surface 14. As will be noted from Fig. 2, the baffle surface 14 is slightly spaced above the surface 13 and is substantially vertically arranged. A cover member 15 is formed integral with the baffle surface'ld to prevent loss of coating material during ..p eration of the device.

edge 'carrying member 11 and'the' ba'iile housing are'sup'ported upon bracket arms 16 which'in turn support a pan '17 having a drain opening 18 connected to a drain pipe 19 so that any excess of coating material which is delivered to the coating head and which is not atomized from the edge 12 may be collected and returned for disposal or for future use. The pan also prevents contamination of the surrounding area by coating material drippings. V

- An oscillatable head 20'is, rotatably mounted'on the top of a supply pipe 21 made of suitable insulating material and is provided with a nozzle 22 which is'directed toward the baflie member 14. Suitable packed bearings are provided between the head 20 andthe insulated pipe 21 so as to permit the former to oscillate relative to the latter 'without loss of coating material due to leakage. Fixedlysecured to the head2tl is'an arm 23 having a slot 24 therein which is engaged by afpin 25 carried on the end of an arm 26 secured'to a cross head .27.. The cross head 27 is'slidably mounted on a pair of rods 28 fixed in vertically spaced parallel arrangement to a supporting frame member (not shown) which also carries a pair of. sprockets 29 and 30 over which a chain 31 may travel; Secured to thechain is a pin 32 engageable in a slot 33 in the cross head 27 so that rotation of the sprocket 30, and hence movement of the chain 31, causes'the cross head 27 to reciprocate 'on the guide rods 28. Suitable insulating means,,such as the rubber belt 34, may be provided to drive the sprocket'30, the belt passing around a pulley 35 mounted on a shaft 36 connected to a speed reducing mechanism 37 and driven by a drive shaft 38 connected to an electric driving motor 39. V

Liquid coating material is delivered to the nozzle 22 under pressure by means of a pump 40 connected through a variable speed transmission'41'to the drive shaft 38 by the worm gear mechanism 42 as shown. The pump is connectedto a source of coating material (not shown) by means of a supply pipe 43 and connects to the pipe 41 by a delivery pipe 44.

Means are provided for maintaining the assembly, including the wedge member 11 and the bafiie housing, at high potential with respect to ground, and for this purpose there is provided'a high voltage supply 46 having one terminal connected by the line 47 to the coating head and having its other terminal connected by'the line 48 to ground. r

connected by a shaft 55 to the drive motor and thus to tation of the shaft causes rotation of the drive member 53 and hence oscillation of the head 20'. With this arrangement, however, the rate of angular motion of the head 20' is more nearly constant so that the lineal speed of the jet stream against the battle 14' is inconstant, it being most rapid near the extremities and slowest at the center of the baflle. Thus if the supply of coating material to the nozzle 22' were constant, an unequal quantity of coating material would be supplied across the baffle 14'. An unequal supply of coating material to the baflle would result in an unequal feed to the atomizing edge. Such inequality in feed results in uneven, coating application on an article being coated To avoid uneven coating due to unequal feed or other factors in the coating operation, means are provided for varying the flow of coating material through the nozzle 22'. For this purpose a variable displacement pump 56 is provided for supplying coating material to the nozzle 22', together with means for varying the displacement of the pump during the coating operation to produce a' flow of coating material to the nozzle 22' which varies directly proportionally to the linear speed of the jet stream across thebafile member 14.

.To this end the pump 56 includes a cylinder 57 having a piston 58 reciprocable therein with the piston being fixed to a connecting rod mechanism including a piston rod 59 and a connecting rod 60 pivotally connected at one end to the rod 59 and at the other end 63 and 64.

. Operation of the motor'39 delivers coating material under pressure to the nozzle 22 for ejection therefrom as a jet stream 45 against the battle member 14. Simultarie'ously, -'the motor causes reciprocation of the cross head 27 and hence oscillation of the head 20 to cause the jet stream to traverse the bafile plate. The pin and slot connection 24 and 25 produces oscillat ion' of the head 20 at a variable rate, the oscillation being fastest as the, jet stream traverses the center portion ofthe baffle 14 and slowest as it traversesthe end portions. Thefapparatus is so arranged as to producea substantiallyconstant'line ar speed of traverse'of the jetistream across the bafile to deliver a substantially uniform quantityof coating material along the extent of the baflle. Coating material supplied to the baffle flows by gravity to the surface 13 and thence to the edge 12 for atomization therefrom.

The modification shown in Fig. 3 is similar to the apparatus shown in Figs. 1 and 2 except for the means for oscillating the head 20 and the means for supplying coating material under pressure to the nozzle 22' carried thereby. For this reason only those portions of the device shown in Fig. 3 which difier from the corresponding portions of theidevice of Fig. 1 will be described in detail. 7 v M vSecured to. the oscillatable head 20' is a gear segment 5% provided with teeth meshingwith a sccond rotatable gear segment 51, which latter segment is connected by an.arm.52 to a drive member in the form of a rotatable gear 53. The gear 53 is driven by a suitable worm 54 1 Delivery to the nozzle 22' is through a flexible supply line 65 made of insulating material connected to a passage 66 connecting in turn to a pair of fluid passages 67 and 68, each opening into the interior of the cylinder 51 and each pr ovided with flap valves'69 and 70. During upward movement of the piston 58 the lessened pressure beneath the piston closes the flap valve 69 while opening the flap valve 63 to permit coating material to flow into the cylinder beneath the piston. Simultaneously, the 'increased fluid pressure .above the piston closes the flap valve 64 while opening the flap valve 70 to permit coating material under pressure to pass through the passages 68 and 66 and into the delivery line 65 for ejection from the nozzle 22'. Because of the connecting rod arrangement 59 and 60, the speed of travel of the piston 58 is variable, being at its maximum at the point illustrated in the drawings at which time the linear speed of the jet stream 45 across the bafile is also at its maximum. The piston 58 travels at its minimum speed when its connecting I rod mechanism is at approximately dead center at which time, however, the jet stream is traveling at its minimum linear speed inasmuch as it is then traversing the central portion of the baflie plate. Thus the delivery of the pump is varied in order to meet the requirements of proper feed to the atomizing edge. 7 V

The connecting rod 52 may be of insulating material and the entire assembly supported upon insulated supports so that the atomizing edge, its wedge-shaped support and ithe bafiie housing may be maintained at a high potential with respect to ground and for this latter purpose there is provided a high'voltage supply 71 having one terminal connected by the line 72 to the edge supporting member and having itsother terminal grounded as indicated at. 73. While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of m any modifications. ,Changes, therefore, in the constutq na d r em nt m y mad W thout .l Pi -l'fill from the spirit and scope of the invention as defined in the appended claims.

I claim:

-l The method of feeding coating material to an elongated substantially horiz ontally arranged atomizing edge of an extended substantially horizontal surface which comprises directing a jet stream of coating material from an oscillatable source against a second surface-angularly inclined to and positioned above the first surface while oscillating said source to traverse the second surface with said jet stream and correlating the discharge rate of the source with the linear speed of the jet stream in traversing the second surface to supply a substantially uniform quantity of coating material thereto for gravity flow to the first surface.

2. The method of feeding coating material to an elongated substantially horizontally arranged atomizing edge of an extended substantially horizontal surface which comprises directing a jet of coating material from an oscillatable source against a second surface angularly inclined to and positioned above the first surface while oscillating said source at a substantially constant angular rate to traverse the second surface with said jet stream at an inconstant linear rate and supplying coating material under pressure to said source for discharge therefrom at an inconstant rate correlated with the linear traverse rate of the jet stream to supply a substantially uniform quantity of coating material to said second surface for gravity flow to the first surface.

3. In a method of feeding coating material to an atomizing zone in an electrostatic coating system by a pressure producing means wherein articles to be coated are moved at a substantially constant speed in spaced relationship past the atomizing zone, the steps which comprise varying the displacement of the pressure producing means during the coating operation in accordance with variations in a variable factor in said coating operation to produce a desired distribution of coating on an article.

4. In an electrostatic coating apparatus, in combination with a single fluid atomizer having an atomizing zone, feed means comprising means providing a coating material supporting and conducting surface positioned adjacent the zone for feeding coating material therto, a variable displacement pump for supplying coating material to the last named means, and means for varying the rate of displacement of the pump in accordance with varying requirements of said atomizer for coating material.

5. An electrostatic coating apparatus comprising an atomizing edge, a surface substantially coextensive with the edge and positioned immediately adjacent thereto, means for supplying coating material to said surface for flow to the edge for atomization therefrom including a variable displacement pump, means for varying the rate of displacement of the pump, and means for operating the displacement rate varying means during the coating operation including a member movable in response to varying feed requirements of said surface to produce a desired even distribution of coating material on an article.

6. Electrostatic coating apparatus of the character described comprising a member having an extended substantially horizontal upper surface terminating in an elongated atomizing edge, a substantially vertical baffle above and extending along said surface in spaced relation thereto, an oscillatable nozzle positioned adjacent but spaced from the bafile, means for supplying coating material under pressure to said nozzle for ejection therefrom as a jet stream against the baflle, means for oscillating the nozzle at a substantially constant angular rate about an axis substantially normal to the major extent of the baffie to cause traverse of the bathe by the jet stream at an inconstant linear rate, means connected to the oscillating means for varying the quantity of coating material supplied to the nozzle in direct proportion to said linear rate to supply a substantially uniform quantity of coating material 'to portions of the bafiie, a supply having one terminalconnected to said edjgej'to make said edge one electrode of an electrostatic field of suificient strength to electrostatically atomize coating material from 'said edge and to disperse the atomized particles and deposit them :on an article.

' 7. Electrostatic coating apparatus of the character described comprising a member having an extended; substantially horizontal upper surface terminating-in an-elongated atomizing edge, asubstantially vertical bathe above and extending along said surface in spaced relation thereto, an oscillatable nozzle positioned adjacent but spaced from the baffle, a pump for supplying coating material under pressure to said nozzle for ejection therefrom as a jet stream against the bafiie, means for oscillating the nozzle at a substantially constant angular rate about an axis substantially normal to the major axis of the baflie to cause traverse of the bafiie by the jet stream at an inconstant linear rate, and means for varying the quantity of coating material supplied to the nozzle in direct proportion to said linear rate to supply a substantially uniform quantity of coating material to all portions of the bafile, said last named means including a rotatable drive member, a gear secured to the nozzle, a second gear meshing with the first named gear, a drive rod pivotally connected to the second gear and to the drive member to oscillate the second gear to cause traverse of the bafille by the jet stream at a rate which varies between minimum and maximum with each degrees rotation of the drive member, an actuating member secured to the drive member and adapted to vary the displacement of the pump directly proportionally to said linear rate to supply a substantially uniform quantity of coating material to all portions of the bafile, a power supply having one terminal connected to said edge to make said edge one electrode of an electrostatic field of sufiicient strength to electrostatically atomize coating material from said edge and to disperse the atomized particles and deposit them on an article.

8. Electrostatic coating apparatus of the character described comprising a member having an extended substantially horizontal upper surface terminating in an elongated atomizing edge, a substantially vertical bafiie above and extending along said surface in spaced relation thereto, an oscillatable nozzle positioned adjacent but spaced from the baffle, a pump for supplying coating material under pressure to said nozzle for ejection therefrom as a jet stream against the bathe, means for oscillating the nozzle at a substantially constant angular rate about an axis substantially normal to the major axis of the bafile to cause traverse of the bafile by the jet stream at an inconstant linear rate, and means for varying the quantity of coating material supplied to the nozzle in direct proportion to said linear rate to supply a substantially uniform quantity of coating material to all portions of the baflie, said last named means including a rotatable drive member, a gear secured to the nozzle, a second gear meshing with the first named gear, a drive rod pivotally connected to the second gear and to the drive member to oscillate the second gear to cause traverse of the baffle by the jet stream at a rate which varies between minimum and maximum with each 180 degrees rotation of the drive member, said pump including a piston and cylinder device for pumping coating material to said nozzle, a connecting rod mechanism connected to the piston and being connected to the drive member to reciprocate the piston at a rate which varies between minimum and maximum with each 180 degrees of rotation of the drive member, with the connecting rod mechanism being secured to the drive member at a point correlating maximum flow from the pump with the maximum traverse rate of the jet stream, a power supply having one terminal connected to said edge to make said edge one electrode of an electrostatic field of sufiicient strength to electrostatically apespes atomize coating material from said edge and to disperse the atomized particles and deposit them on an article.

; 9.'In an electrostatic coating apparatus, in combination with a single fluid atomizer having an atomizing zone, feed means comprising a feed device positioned adjacent the zone for feeding coating material thereto, a variable displacement pump for supplying coating ma- .terial under pressure to said feed device, and means for varying the rate at which coating material is supplied in accordance with varying requirements of said feed device for coating material.

' 8 RefelrencesCited inthe file of thisxpatent UNITED STATES PATENTS Juers Dec. ,8, Brackett a .1 June y15, Bramsen June 24, Ran sburg July 3, Huebner July 31, Paa sche Sept. 16,

u hi g my 21,

Claims (1)

1. THE METHOD OF FEEDING COATING MATERIAL TO AN ELONGATED SUBSTANTIALLY HORIZONTALLY ARRANGED ATOMIZING EDGE OF AN EXTENDED SUBSTANTIALLY HORIZONTAL SURFACE WHICH COMPRISES DIRECTLY JET STREAM OF COATING MATERIAL FROM AN OSCILLATABLE SOURCE AGAINST A SECOND SURFACE ANGULARLY INCLINED TO AND POSITIONED ABOVE THE FIRST SURFACE WHILE OSCOLLATING SAID SOURCE TO TRAVERSE THE SECOND SURFACE WITH SAID JET STREAM AND CORRELATING THE DISCHARGE RATE OF THE SOURCE WITH THE LINEAR SPEED OF THE JET STREAM IN TRAVERSING THE SECOND SURFACE TO SUPPLY A SUBSTANTIALLY UNIFORMED QUANTITY OF COATING MATERIAL THERETO FOR GRAVITY FLOW TO THE FIRST SURFACE.

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