Electrostatic spray assembly

An electrostatic spraying assembly is provided. The spraying assembly includes a housing having a fluid inlet passage that is connectable to a fluid source and communicates with a plurality of discharge passageways each of which extends through the housing to a downstream end at a discharge end of the housing. The housing has a one piece construction and is made of an electrically insulative material. The spraying assembly also includes an electrode assembly. The electrode assembly includes a plurality of elongate electrode elements each of which is disposed in a respective one of the discharge passageways in the housing and an electrode header. The electrode header is electrically connectable to a voltage source and each of the electrode elements is electrically connectable to the electrode header.

FIELD OF THE INVENTION

The present invention relates generally to spray nozzle assemblies, and more particularly, to electrostatic spray nozzle assemblies that electrostatically charge fluids discharging from spray nozzles to facilitate liquid particle breakdown and distribution.

BACKGROUND OF THE INVENTION

Electrostatic spray nozzle assemblies are utilized for applying oil and other coating and lubricating fluids in various manufacturing processes. Electrostatic spray nozzle assemblies, such as shown in U.S. Pat. No. 4,749,125, discharge a plurality of fluid flow streams which are electrostatically charged and atomized by means of a high voltage electrode with the assistance of a grounded induction bar for disposition onto items to be sprayed or coated, typically as they are conveyed past the spraying apparatus.

Heretofore, such electrostatic assembly spray nozzle assemblies have suffered from various operating and maintenance problems. For example, imprecise manufacture and assembly of such spray nozzles and charging electrodes can result in high voltage leakage that can significantly affect the operating efficiency of the spray operation. Fluid leakage problems also can adversely affect the spray distribution and lead to waste of costly spray liquids.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrostatic spray nozzle assembly that is adapted for more efficient and reliable spraying of oils and other lubricating and coating fluids.

Another object is to provide an electrostatic spray nozzle assembly which includes electrostatic charging electrodes that are adapted for more precise manufacture and mounting within the nozzle assembly, and hence more efficient operation with reduced power consumption and increased life expectancy.

A further object is to provide an electrostatic spray nozzle assembly of the foregoing type which is operable for electrostatically charging a plurality of fluid flow streams for more uniformly coating or lubricating of items that are sprayed.

Still another object is to provide an electrostatic spray nozzle assembly of the above kind which is adapted for more effectively atomizing the fluid flow streams so as to produce a uniform fine particle distribution onto items being sprayed.

Still another object is to provide an electrostatic spray nozzle assembly that can have relatively large fluid passages that resist clogging and are easy to clean.

Still another object is to provide an electrostatic spray nozzle assembly that requires a relatively low voltage at the nozzle tip thereby improving safety and reducing the tendency of sparking.

Yet another object is to provide such an electrostatic spray nozzle assembly which is relative simple in construction and lends itself to economical manufacture.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now more particularly to the drawings, there is shown inFIGS. 1 and 2an illustrative electrostatic spraying assembly10embodying the present invention, which is adapted for directing an elongated spray of oil or other lubricating or coating fluid on items conveyed below the spray assembly10. The illustrative spray nozzle assembly10basically comprises an elongated housing11supported in adjacent relation to a fluid supply pipe12, an electrode assembly14for charging fluid passing through and directed from a lower discharge end13of the housing11, and an induction bar15disposed in parallel spaced relation to the discharge end of the housing11for enhancing liquid particle breakdown. The housing11in this case is supported by the fluid supply pipe12by means of a plurality of transversely directed conduit sections16that communicate between the fluid supply pipe12and fluid inlet ports16ain a side of the housing.

In accordance with an important aspect of the invention, the electrode assembly comprises a metallic block or header as well as a plurality of electrode elements in the form of pins each disposed within a respective fluid passageway communicating with the fluid inlet ports of the housing for charging fluid as it passes along the length of the pins and is discharged from the spray nozzle assembly. To this end, in the illustrated embodiment, the electrode14comprises a plurality of electrode pins14awhich are disposed in a longitudinally spaced array from a common header or strip14b(see, e.g.,FIGS. 2 and 3). Each electrode pin14a,which in this instance is generally vertically oriented, is concentrically disposed in a respective fluid passageway26in the housing11(shown without the pins inFIG. 4) that is sized larger than the pin14asuch that an annular fluid flow passage is defined between the pin and the housing passage. The electrode14is made of a highly conductive metal material with the electrode pins14apreferably being press fit within respective apertures within the electrode header14b.The electrode header strip14bin this case is disposed within a fluid inlet passage in the form of an elongated, longitudinal flow channel18of the housing11having a greater transverse width than the strip14b(see, e.g.,FIG. 2) for defining a longitudinal fluid flow passage communicating between the fluid inlet ports16aof the housing and the annular fluid passages about the electrode pins14a.

For enclosing the upper end of the elongated flow channel18, the housing11has a cover19which is secured to the upper end of the housing11by appropriate fastening bolts with a sealing gasket21interposed there between. The header strip14bof each electrode assembly14is retained in position within the flow channel18by bolts20which extend through the cover19, and each electrode header strip14bis connected to a high voltage line through a conventional banana coupling22(seeFIG. 2).

In keeping with the invention, the electrode pins14aeach terminate with a gradually tapered pointed end14cwhich maximizes charging and ultimate liquid particle breakdown upon discharge from the spray assembly. While the theory of operation is not entirely understood, it is believed that the sharp points14cof the pins14aaccumulate the electrical charge pursuant to a theory known as the Gauss theorem. The enhanced electrical charging of the fluid as it is directed along the pins14aand discharged past the sharp pointed ends14cfurther optimizes atomization and charging the fluid particles, which by virtue of their repelling nature, are more uniformly directed onto the items to be coated or lubricated. Hence, the pointed ends of the electrode pins14aenhance the generation of smaller-sized fluid droplets, which is particularly important in airless electrostatic spraying systems.

The electrode pins14apreferably each protrude outwardly of the discharge end of the housing11a predetermined distance “x,” such as about ¼ inch (seeFIG. 2). It has unexpectedly been found that the protruding electrode pin arrangement maximizes liquid flow rate through the spray nozzle assembly. Again, although the theory of operation is not entirely understood, it is believed that the greater surface area of pins over which the liquid travels facilitates liquid flow and discharge from the spray nozzle assembly. The increased contact with the electrode pins further enhances charging of the liquid and ultimate atomization. The housing11in this case is formed with a plurality of generally frustoconical exit points (see, e.g.,FIGS. 2 and 7) through which the electrode pins14aconcentrically protrude for reducing the effect of surface tension on the liquid as it discharges from the housing about the electrode pins.

In carrying out a further important feature of the invention, the electrode receiving body of the housing11has a one-piece block construction which facilitates precision concentric mounting of the electrode pins14awithin the housing passageways and which prevents fluid and high voltage leakage. The illustrated housing11includes a one-piece body25(see, e.g.,FIG. 4) preferably machined from plastic stock, with the pin receiving flow passageways26being drilled in the body and the longitudinal channel18being milled. It will be understood by one skilled in art that by virtue of such one-piece housing block construction, there are no parting planes associated with the liquid flow passageways26typical of multi-part housings, nor fasteners for retaining a multi-part housing body in assembled condition at such parting planes. The resulting improved dimensional tolerances enhance even charging of the fluid as it travels along the perimeters of the elongated electrode pins14a.As a result of the novel electrode design and arrangement, the electric spray nozzle assembly of the present invention has been found to have significantly improved operating efficiency over prior art spray devices of such type. For effecting spray performance comparable to such prior art spray devices, the subject electrostatic spray nozzle assembly has been found to be operable at 30 to 50 percent lower voltage requirements.

In the embodiment ofFIGS. 1 and 2, it will be seen that the spray nozzle housing11includes three housing bodies25supported in a longitudinal array, each having a respective electrode assembly14comprising a header14band a plurality of pins14a,and a respective cover19. The fluid inlet port16aof each electrode body25is coupled to the fluid supply pipe12by a respective conduit section16. For purposes of illustration, the electrode assemblies are shown in partial section inFIG. 2to depict the electrode pin arrangement.FIGS. 6-9disclose a similar electrostatic spray nozzle assembly, but utilizing a single housing body25, cover19, and electrode assembly14.

In carrying out a further feature of the invention, the induction bar15is mounted for selective positioning relative to the downstream ends of the electrode pins14afor maximizing the effect of the electrical field therebetween on the discharging liquid, and hence, maximizing liquid particle breakdown. As shown inFIG. 1, the induction bar15, in this case, is supported by elongated arms30fixed in depending angled relation to opposite ends of the housing11. The induction rod15is selectively positionable within elongated slots31formed in the supporting arms30for effecting the desired spray characteristics.

In operation of the spray nozzle assembly10, it will be seen that oil or other lubricating or coating fluid may be supplied through the liquid supply pipe15and communicate with housing inlet ports16athrough the conduit sections16. The fluid entering the housing inlet ports will communicate through the longitudinal flow channel18to and through the depending flow passageways26in surrounding relation along the length of the electrode pins14a,being charged along the entire length of travel. Upon discharge from the housing11, the pointed ends14cof the electrode pins14aenhance charging of the discharging fluid, such that upon entering the electrical field23(seeFIG. 1, for example) between the electrode pins14aand the induction bar15, the liquid is dispersed into fine particle spray with the repelling charges of the particles effecting substantially uniform distribution onto items passing below the spray nozzle assembly10to be coated.

While in the embodiment illustrated inFIGS. 1-9, fluid is electrically charged by passage about the electrode pins14a,alternatively, as depicted inFIGS. 10 and 11, fluid may be directed through the electrode itself. To this end, the electrode can include a plurality of electrode tubes32having flow passages extending therethrough. With theFIGS. 10 and 11arrangement, fluid may be directed through the flow passages in the electrode tubes32and discharged from flow openings at their terminal ends32a. As the fluid passes through the electrode tubes32, it is charged such that when the fluid exits the tubes and enters the electrical field between the terminal ends32aof the tubes and the induction bar15, the fluid is dispersed into a fine particle spray. The use of the electrode tubes32provides relatively large flow passages that are more resistant to clogging and are easier to clean. Moreover, according to a further aspect of the invention, to enhance safety, the electrode tubes32can be arranged such that each tube terminates a small distance S (FIG. 11) from the electrode block or header14binside the longitudinal fluid inlet channel18of the housing. As a result of this arrangement, the electrode tubes32are not in direct electrical contact with the electrode block or header. With this arrangement, the electrode tubes32will not be charged at a high electrical potential that could pose a safety hazard. Instead, the electrode tubes are charged inductively due to their proximity to the electrode header14b. The inductive charging of the electrode tubes32will provide sufficient charging to provide the desired level of added charge to the fluid passing through the tubes32. Accordingly, safety of the spray operation is increased without significant degradation in spray performance.

Referring now more particularly toFIG. 12of the drawings, there is shown an alternative embodiment of the spray nozzle assembly35in accordance with the invention, which utilizes a single electrode pin36. The spray nozzle assembly35again includes a one-piece housing body38, in this case having gun shape with an upstream cylindrical end portion and a downstream frustoconical end portion. The housing body38, which again can be machined from plastic stock material, has longitudinal passageway39which includes a relatively small diameter downstream passageway section39awithin which the electrode pin36is concentrically mounted for defining an annular liquid flow passage similar to that described previously. The longitudinal passageway39includes an enlarged diameter passageway section39bwhich communicates with a radial inlet port40to which a fluid supply conduit41is connected. The passageway39further includes an enlarged counter bore section39cat the upstream end of the body38within which a high voltage line42connects with an upstream end of the electrode pin36through a banana coupling44. The electrode pin36in this case has an enlarged threaded steam portion45to facilitate coupling with the high voltage supply line.

In carrying out a further feature of the invention, the electrode pin36in this case is selectively positionable within the passageway section39afor the desired spray and liquid flow rate to be generated by the spray nozzle assembly. To this end, a washer configured shim48having a selectively determined longitudinal width “w” is interposed between the high voltage coupling and a downstream end wall of the enlarged counter bore section39cfor selectively locating the electrode pin36within the passageway39a,and hence, selectively establishing the distance “x” the electrode pin36extends beyond the downstream end of the housing body38. It will be seen that a thicker shim48will lead to reduced exposed needle surface at the tip of the nozzle body38, and hence decrease the flow rate. Thinner shims48will enable a greater exposed needle surface area at the tip of the nozzle body and hence, increase the flow rate. In this manner, an optimum flow rate can be readily established through selection of desired shim width.

From the foregoing, it can be seen that the electrostatic spray nozzle assembly of the present invention is adapted for a more efficient and reliable spraying of oils and other lubricating and coating fluids. The spray nozzle assembly includes electrostatic charging electrodes that are adapted for more precision manufacture and mounting within the nozzle housing, and hence, more efficient operation with reduced power consumption and increased life expectancy. The spray nozzle assembly further is effective for more effectively optimizing fluid flow streams for uniform fine particle distribution onto the sprayed items.