Nordson Corporation

Donald R Hastings

Martin J Harjar

John Sharpless

John A Hendricks

Gerald W Crum

James L Kennon

Lawrence J Macartney

Don R Scarbrough

Alvin A Rood

Edward A Williams

Glen A Herstek

John C Dunn

George H Morin

Bruce J Banning

A method and apparatus for spraying liquid coating material containing supercritical fluid or liquified gas as a diluent comprises a spray gun having internal passages which transmit the liquid coating material under high pressure from an inlet to a nozzle at the tip of the gun and then to an outlet so that the liquid coating material can be continuously recirculated. A relatively short flow discharge path is formed between the internal passages in the spray gun and the nozzle to avoid the formation of an area of ambient or reduced pressure so that the supercritical fluid or liquified gas is substantially maintained in solution in the liquid coating until it is discharged from the gun. A pressure regulator is provided to maintain a substantially constant pressure drop across the inlet and outlet of the gun to induce flow of liquid coating material through the gun, and to permit several guns to be connected in series without creating a substantial pressure drop therebetween.

Method and apparatus for spraying a liquid coating containing

An electrostatic spray system including a spray device having an electrode for electrostatically charging coating particles emitted from the spray device toward an article to be coated, a high voltage electrostatic supply, and a high voltage insulated electrical cable interconnecting the electrostatic supply and the spray device electrode. The high voltage cable includes a fibrous resistive core, preferably fabricated from silicon carbide fibers, a fiber-restraining layer of insulative thread tightly wrapped spirally around the entirety of the core to prevent fiber ends from projecting outwardly from the core, an outer dielectric sheath, and an intermediate sheath sandwiched between the spirally wound inner fiber-restraining layer and the outer dielectric sheath and having a resistivity lying between that of the inner resistive fiber core and the outer dielectric sheath. The intermediate sheath provides uniform voltage stress distribution in the region surrounding the resistive core, thereby avoiding internal corona sites which cause degradation of the outer dielectric sheath, which might otherwise occur due to the very small diameter of the resistive core coupled with the very high operating voltages used in electrostatic spray coating operations. The intermediate sheath also avoids high voltage stresses at the ends of stray resistive fibers projecting through the spirally wound layer, which might otherwise occur due to the extremely small diameter of the projecting fibers.

Flexible voltage cable for electrostatic spray gun

A tool for removing the nozzle assembly of a coating spray gun. The tool has an inner wall surface of a configuration congruent with an outer surface of the spray assembly. The inner wall thereof defines a cavity which is closed at one end thereof such that the tool, when placed over the nozzle assembly, encloses the nozzle and protects the user from spray injection. Preferably, the outer surface of the tool is knurled to facilitate use.

Spray nozzle and removal tool

An electrostatic spray system including a spray device having a coating-charging electrode, a source of high voltage electrostatic potential, and a resistive path for safely transmitting high voltage between the electrode and the electrostatic supply. The resistive high voltage transmission path is composed of plural parallel-connected continuous silicon carbide fibers.

Electrostatic spray coating system

A method of substantially eliminating corona discharge at the high-value resistor of an electrostatic spray gun comprises the steps of inserting an insulating tube within a bore formed in the gun barrel, positioning a high-value resistor in the insulating tube, filling a portion of the insulating tube with a slug of dielectric material such as grease and then inserting a high voltage cable into the insulating tube so as to force the grease ahead of the cable. The grease encapsulates the resistor and flows into the space between the insulating tube and bore in the gun barrel to eliminate the presence of air around the resistor so as to prevent corona discharge.

Method of reducing corona discharge in an electrostatic spray gun

An air atomizing nozzle assembly for electrostatic spray guns is disclosed. The nozzle assembly is made of plastic parts and includes an air cap having a central bore which surrounds a fluid nozzle tip. The nozzle has a nut formed on its forward end to facilitate threading of the rearward end of the nozzle tip into a threaded bore of the gun body. Formed on the front part of the nozzle, either as a part of the nut or a cylindrical surface adjacent the nut, is an accurately machined surface engageable in press fit relationship with a mating accurately machined bore of the air cap. These mating press fit surfaces center the bore of the air cap relative to the nozzle tip so as to leave an annular, evenly dimensioned air flow passage surrounding the nozzle tip and defined between the nozzle tip and the bore of the air cap. The air cap is retained in a one-piece resilient retaining ring by snapping the air cap into an annular lip of the retaining ring. The retaining ring is then threaded onto the gun body to secure the nozzle assembly onto the gun body.

Air atomizing nozzle assembly

An air atomizing nozzle assembly for spray coating systems such as an electrostatic spray gun is disclosed. The nozzle assembly includes an air cap having a central bore which surrounds a fluid tip nozzle. The bore has a plurality of uniformly dimensioned axially aligned gas flow passages evenly spaced about its circumference and a plurality of radially inwardly extending ribs therebetween. The ribs engage the outside surface of the fluid tip nozzle to positively align its center axis on the axis of the central bore. The air cap and nozzle tip thus cooperate to form a plurality of uniform gas flow passages around the nozzle thereby producing a finely atomized uniform spray pattern of coating material emitted from the fluid tip. In a preferred embodiment of the invention, the gas flow passages and ribs are formed in a metal element inserted in a center bore in the air cap. The metal element is so dimensioned that the ribs make a press fit with the fluid tip to positively align it. The air cap is retained in a one-piece resilient retaining ring by snapping the air cap into position over an annular lip of the ring. The air cap and retaining ring form a seal which prevents control air from escaping to the atmosphere.

Nozzle assembly for spray coating systems

An airless electrostatic spray gun for atomizing and electrostatically depositing liquid coating materials onto substrates. The gun is characterized by a low capacitance which enables the electrode of the gun to be shorted to a grounded object without the resulting spark having sufficient energy content to ignite the surrounding atmosphere.

Low capacitance airless spray apparatus

A continuous coater of the type having a conveyor extending through a coating booth where paint or other material is sprayed onto the products as they are conveyed through the booth. The booth has an air flow control vestibule located adjacent the entrance and exit ports. Each vestibule is connected to an air flow exhaust system and is so configured that it is operative to draw air almost exclusively from outside the booth into the exhaust system so that there is a minimum of input air to the exhaust system from within the booth. The incoming air from outside the booth effectively forms a flow barrier to the egress of sprayed material and/or solvent to the atmosphere through the vestibule entrance and exit ports. Preferably, there is located in each vestibule means for creating an air curtain which functions to minimize the egress of paint or solvent from the coater cabinet and to provide a more nearly saturated atmosphere inside the cabinet.

Continuous coater

An improved electrostatic spray gun is disclosed including an electrically conductive metal handle assembly, an electrically insulative barrel assembly, and an electrically insulative nozzle assembly terminating at its forward end in a small diameter discharge orifice through which the coating material is ejected. An ionizing electrode protrudes from the discharge orifice. The flow of material through the barrel and the nozzle assembly is controlled by a trigger actuated needle and seat valve assembly close to the discharge orifice and in axial alignment with an annular fluid flow passageway in the barrel portion of the gun. A high value resistor is disposed in the barrel portion of the gun and a second lower value resistor is disposed inside the needle valve immediately upstream of the ionizing electrode. The elements of the improved electrostatic spray gun cooperate to provide clean and safe operation.

Electrostatic spray gun

An improved electrostatic spray gun, particularly of the hand-held type, is disclosed including an electrically insulative barrel and nozzle assembly, an electrically insulative air valve module mounted to the rear of the barrel assembly and externally thereof, and an electrically conductive metal handle assembly enclosing the rear end of the barrel and the air valve module. A charging electrode protrudes from the discharge orifice of the nozzle assembly. The flow of air through the barrel and nozzle assembly is controlled by a trigger which actuates the air valve. Actuation of the air valve in turn controls a needle and seat valve assembly close to the discharge orifice of the nozzle assembly to control the flow of coating material through the gun. A resistor is disposed inside the needle valve immediately upstream of the charging electrode. The elements of the electrostatic spray gun of this invention cooperate to provide a simple, lightweight, balanced gun having a high degree of reliability and repairability and clean and safe operation.

An air atomizing nozzle assembly for electrostatic spray guns is disclosed. The nozzle assembly includes an air cap having a central bore which surrounds a fluid tip nozzle. The bore has a plurality of axially aligned holes evenly spaced about its circumference and intersecting the edge thereof thereby defining a plurality of uniformly dimensioned, circumferentially spaced axial gas flow passages with spaced, radially extending ribs therebetween. The ribs between the holes engage the outside diameter of the nozzle to align its center axis on the axis of the central bore. The air cap and nozzle tip thus cooperate to form a plurality of uniform gas flow passages around the nozzle thereby producing a uniform atomizing air flow pattern around the nozzle. The air cap is retained in a one-piece resilient retaining ring by snapping the air cap into position over an annular lip of the ring. The air cap and retaining ring form a seal which prevents control air from escaping to the atmosphere.

Nozzle assembly for electrostatic spray guns

An electrostatic spray coating gun for applying coating materials which have high to moderately high electrical conductivity is disclosed. The gun has an improved high voltage electrical system, improved hydraulic seals, and is adaptable to apply porcelain enamel coatings in slurry form. The gun has a flexible and resilient electrode in the form of an elongated coil spring. This form of electrode substantially eliminates the likelihood of scratching or puncturing the skin of an operator or repairman, and allows the electrode to return to its proper orientation after being bumped, while exhibiting proper paint charging characteristics for use in electrostatic spray coating. The electrode is positioned forward of a flat-fan spray nozzle and is displaced from the axis of the spray by means of an extension assembly which can be angularly displaced about the axis of the spray. The gun further incorporates improved packingless bellows sealing between an opening into the coating conduit in the barrel of the gun and a control rod for a needle valve in the conduit. Novel static seals allow the use of a bellows in the form of a non-machined extruded fluorinated hydrocarbon commonly known as TFE Teflon. The packingless seals, properly designed flow passages, the position of the charging electrode, and wear resistant material at the nozzle tip and needle valve allow the gun to be used not only for the electrostatic spraying of the common electrically conductive coating materials, but also for abrasive coating materials, such as glazes, in slurry form.

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Elyria, OH, United States of America

Donald R Hastings