FR2525927A1 - METHOD AND APPARATUS FOR APPLYING ELECTROSTATIC POWDER PAINT - Google Patents

Abstract

THE INVENTION RELATES TO AN APPARATUS AND A POWDER PAINT APPLICATION PROCESS. THE BODY OF THE APPLIANCE HAS A CENTRAL FLOW CHANNEL OF A MIXTURE OF AIR AND POWDER. THIS MIXTURE IS DEVIED TO THE EXTERIOR FOLLOWING A TRUNCONIC SHAPE PATH S. A SHAPING AIR CHANNEL, LOCATED IN THE BODY, DEFINES AN AIR FLOW PATH P AND CROSSES THE MIXTURE OF AIR AND OF POWDER. THE PRESSURE OF THE FORMING AIR IS ADJUSTED TO DETERMINE THE FORCE WITH WHICH THIS AIR STRIKES AGAINST THE MIXTURE OF AIR AND POWDER, THIS FORCE ALLOWING TO ADJUST THE DIMENSION OF THE BEAM SHAPED BY THE MIXTURE OF AIR AND POWDER POWDER. FIELD OF APPLICATION: ELECTROSTATIC APPLICATION OF POWDER PAINTS.

Description

1. The invention relates to a method and an apparatus for applying a

  coating powder, and it relates

  more particularly to a method and apparatus for

  electrostatic cation of powder paint.

  U.S. Patent 4,228,961 discloses an electrostatic powder paint application head in which a cleaning gas from a

  outer chamber is directed to the surface of an electro-

  of ribbon A monopolar discharge = discharge of effluents

  flows between the ribbon electrode and the needle electrode.

  The current charges the mixture of air and powder flowing through the central powder ejection port. The peripherally cleaned cleaning gas is used to maintain the ribbon electrode in a clean or powder-free state.

  thus ensuring a suitable discharge current of corona discharge.

  Cleaning air is not used to regulate or shape

the mixture of air and powder.

  U.S. Patent No. 4,235,381 discloses an electrostatic powder gun having an auxiliary supply of compressed gas. The gas is directed

  towards the nozzle and ionized so that when it is

  loaded at the end of the device, it helps the application

from the final charge to the powder.

  It is preferable, in the application of powder paint, to provide means for regulating the section of the flow of paint particles, which consequently regulates the final dimension of the beam reaching the workpiece or the workpiece. BACKGROUND OF THE INVENTION Various prior art apparatuses and methods have been used for the application of powder coatings. Powder apparatuses of the prior art, comprising means for shaping the beam formed by the ejected powder, comprise devices both

  mechanical types and air-swirl types.

  prior art mechanical forming machine comprises an outer adjusting sleeve which is normally cylindrical

  and that can be animated by an alternative movement towards the in-

  inside and outside of the powder bundle The sleeve

  deflects the powder particles forward Often the erosion

  of the sleeve and the melting of the powder on the surface

  inside the sleeve pose a serious problem.

  Another type of prior mechanical shaping device comprises a centrally located powder deflector

  mixture of powder and air and a rod connected to the deflec-

  The rod normally comes out of the back of the powder gun The beam is adjusted by moving the baffle so that the baffle is close or far away

  more of the opening of the nozzle.

  FIG. 5 of the attached drawings and described above.

  The following is an earlier air vortex shaping apparatus. A similar type air vortex structure is described in U.S. Patent No. 3,940,061. As shown in FIG. of the prior art has a central channel B for the passage of the mixture of air and powder, a diffuser C centrally disposed and a nozzle

  D The latter has several E channels for

  air chambers that communicate with a cleaning air chamber F. When the mixture of air and powder moves around the diffuser C of the gun of Figure 5, it receives compressed air swirling from the channels E air 3. swirling tangentially strikes the mixture of air and powder and gives the current of this mixture a swirling motion In this type of prior structure, when the tangential swirling air force increases, the section of the current increases downstream When the swirling air force decreases, the current section of

  air and powder mixture decreases downstream.

  U.S. Patent No. 3,964,683 discloses another electrostatic spraying apparatus of the prior art for applying a coating powder. This patent relates to a pneumatic device.

security lock.

  A powder spray gun apparatus normally in the form of a high voltage electrostatic powder spray gun. The spray gun has a remotely controlled shaping device for controlling the powder spray gun. or regulate the beam size of the mixture of air and powder coming out of the central part

from the gun nozzle.

  In a preferred embodiment of the invention, a flared diffuser is placed in the nozzle assembly of a powder gun. The latter, according to the invention, may be a hand-held gun or

  an automatic pistol The flared diffuser deviates abruptly

  outwardly the mixture of air and powder.

  The nozzle assembly has a shaping air ring that communicates with a cleaning compressed air supply. The shaping ring is in the form of a cylinder whose major axis is parallel.

  and normally coincides with the longitudinal axis of the channel.

  central passage of the mixture of air and gun powder

  let. Compressed air, unloaded from the air ring of mioeen form, strikes against the mixture of air and powder 4. with sufficient force to shape the beam

  Downstream In accordance with the invention, an increase

  The pressure of the air discharged from the shaping air ring increases the impact force and reduces the air in section and the corresponding area of the air and powder mixture. the pressure of the air and the force of striking increases the corresponding section of the beam. It has become apparent that this new process has, for

  result, higher transfer yields, in particular

  especially when large beams are required.

  The subject of the invention is therefore a method and apparatus for applying powder paint, allowing greater transfer efficiencies. Another object of the invention is an apparatus for the electrostatic application of a coating powder, comprising a device of implementation

  shape of the mixture of air and powder, controlled remotely.

  Another subject of the invention is an elec-

  trostatic that does not use moving mechanical elements

  to vary the size of the powder bundle.

  The invention also relates to an improved electrostatic powder apparatus in which shaping air is used during relatively short periods of time.

  frequently asked during the course of which

  the device, a small beam.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which: FIG. 1 is an elevation of a pistol

  electrostatic powder for the application of a material

  powder on a piece, corresponding to a preferred embodiment of the invention; Fig. 2 is an exploded elevation showing the main elements separated from the apparatus of Fig. 1;

  FIG. 3 is a longitudinal section through

  the apparatus of Figure 1, on an enlarged scale; 5.

  Figure 4 is a cross-sectional view of

  line 4-4 of Figure 3; and

  FIG. 5 is a longitudinal section through

  similar to that of Figure 3, showing a pistol

  the electrostatic manual of the prior art comprising a

  shaping device with air swirls.

  Figures 1 and 2 show a pistol

  manual 10 for the electrostatic application of a powder of

  clothing, such as a paint It should be noted that the gun 10 shown is only one possible embodiment of the invention The latter can be

  used in an automatic paint applicator

  rather than in the manual gun shown.

  The pistol 10 comprises a body 11 and a barrel 12 having a front section 13.

  FIGS. 2 and 3, an electrode holder 15, supporting an elec-

  trode 16, is housed in the front stretch 13 A set 18

  nozzle comprises an inner element 19 and an outer element

  20 of nozzle which are force-fitted.

  The assembly 18 has a cylindrical recess 22, which receives a diffuser 23. As can better be seen in FIG. 4, the diffuser 23 has branches 24 which bear against the wall of the cylindrical recess 22 in the position of FIG. During normal operation, the diffuser 23 does not move longitudinally

  on the longitudinal axis 27 of the barrel 12 The diffuser 23 pre-

  A flared end 28 as shown in FIG.

  3, the gun 10 comprises a cylindrical tube 29 with

  dre which fits on a cylindrical recess 30 defined by the electrode holder 15 The recess 30 terminates in a

  channel 31 to powder, presented by the nozzle 18 During the

  a mixture of air and powder is put into circulation.

  In the aligned channels, formed by the tube 29, the cylindrical recess 30 and the channel 31 when the mixture of air and powder moves along the longitudinal axis 27, the diffuser 23 and its end flared 28 deviate sharply and angularly outward

  to give it a frustoconical shape.

  The gun 10 comprises a feed circuit

  Electrical circuit, indicated generally at 33 and having a chuck resistance 34 The supply circuit 33 comprises springs 35 and 36 return that are in contact

electric with the electrode 16.

  The gun 10 according to the invention comprises a safety valve generally indicated by the numeral 40. The safety valve 40 detects the pressure of the air on the face 41. It cuts off both the powder feed and the feed. electrical energy as soon as the

  nozzle 18 loosens or separates from gun 10.

  As shown in FIG. 3, a chamber 42

  compressed air is defined by the front section 13 of the pistol

  The cleaning air supplied to this chamber has a pressure normally between 0 and 280 k Pa The nozzle 18 has an annular cavity 43 shaping or shaping which ends in an annular space

  44 containing air shaping or shaping.

  The annular space or the air ring 44 has a width

  advantageously between 0.125 and 0.65 mm, the width preferably

  in the described embodiment, being

  0.38 mm The air ring 44 for shaping extends parallel to

  Along with the longitudinal axis 27 When shaping air is discharged through the ring 44, it flows in a cylindrical path whose major axis coincides with the longitudinal axis 27 As shown on FIG. In FIG. 3, the path P of shaping air intersects the frustoconical path S, followed by the mixture of air and powder. A plane T, which is perpendicular to both

  the longitudinal axis 27 and the path P, intersects the longitudinal path

  of the mixture of air and powder, and forms an acute angle R which, in the embodiment described, is 23 However, the angle R can vary and be normally between 150 and 300, a preferred range being range

between 20 and 25.

  Several holes 46, spaced circumferentially

  are defined by the inner element 19 of the nozzle

  18 and communicate with the forming air cavity 43.

  The other ends of the holes 46 communicate with a chamber

  The air cavity 43 communicates with the compressed air chamber 42 by means of channels, one of which is indicated by dashed lines at 48. Therefore, the air cavity 43 communicates fully with the chamber. compressed air 42 by

  the holes 46, the annular chamber 47 and the channels 48.

  When using an automatic device, the pressure of

  air in the air chamber 42 and thus in the

  43 air conditioning is controlled remotely.

  There is no need to manually adjust a rod or

  manually adjust the longitudinal position of a

  deflector mechanism to shape the air mixture and

powder coming out of the gun.

  In the embodiment described, the pres-.

  air in the chamber 42 and in the cavity 43 is

  set to a manometric value of between 0 and 280 kPa.

  When the mixture of air and powder passes into the tube 29

  powder and is deflected outwards in a truncated form.

  following the path S, the shaping air is discharged from the annular space 44 in the cylindrical path P The shaping air cuts off the frustoconical path S and strikes against the mixture of air and powder The striking force causes the mixture of air and powder giving it the shape of beams of which

  the section decreases when the air pressure increases.

  If the air pressure decreases, the size of the downstream beams increases, the maximum dimension being obtained

  when the air pressure becomes zero.

  It has been found that transfer efficiencies or efficiencies, especially in the case of large beams,

8 2525927

  are significantly increased by the process and apparatus

according to the invention.

  The transfer efficiency is the ratio of the amount of powder arriving on the workpiece to the amount of powder passing through the spray apparatus. The following test results, although not covering all

  apparatuses of the prior art or all of the operating parameters

  tion, indicate that at the largest beam section, at which many industrial operations

  application of powder paint are made, the appa-

  according to the invention (shown in Figure 3 and identified by the name "De Vilbiss FL") has a yield of

significantly higher transfer.

  The device of the type De Vilbiss Standard EHP-504

  is a device of the prior art which uses a tourbil-

  air for beam shaping This unit

is shown in Figure 5.

  The apparatus "N" uses diffusers replacing Qa

  with different diameters to adjust the size

beam.

  The apparatus "G" uses a diffuser that can be moved along the longitudinal axis of the nozzle to make

vary the size of the beam.

  During operation, the electrode 16 Yield Beam Flow Pistol tried for effective di transfer maximum flow De Vilbiss FL 91% 48,26 cm 200 g / min From Vilbiss Standard 81% 39,37 cm 200 g / min

ERP-504

  N 84% 48.26 cm 200 g / min G 78% 40.64 cm 200 g / min 9. of the apparatus according to the invention electrostatically charged

  the particles discharged from the gun 10.

  It goes without saying that many modifications can be made to the method and apparatus described and shown, without departing from the scope of the invention. 10.

Claims (6)

  1 Method for applying a constitutional paint   powder particles, characterized in that it consists of   to move a mixture of air and powder along a longitudinal axis (27), angularly deflecting outwards the mixture of air and powder to give it a substantially frustoconical shape, and causing the intersection of the frustoconical mixture of air and powder by a current of air   forming a cylindrical path (P), this work   a cylindrical jet having its major axis coinciding with the longitudinal axis, the shaping air stream having sufficient force to strike against the air mixture and   powder and shape the outer peripheral part   higher, so that the beam produced downstream is regulated at a predetermined dimension.   2 Method according to claim 1, characterized in that it consists in adjusting the force of the air stream shaping-when cutting the mixture of air and powder to vary the beam formed downstream of the mixture air and powder.   3 Process according to claim 2, characterized in that it also consists in charging electrostatically powder particles.   4 Process according to claim 3, characterized   in that a plane (T), which is perpendicular to the longitudinal axis   tudinal and the cylindrical path, cut the mixture of air and powder, put in a frustoconical shape, to form with him an acute angle (R).   Method according to Claim 3, characterized in that the pressure of the air flow   shaped can vary between 0 and 280 k Pa.   Process according to Claim 4, characterized   in that the acute angle is between 200 and 250.   Apparatus for electrostatically applying powder paint, characterized in that it comprises a body 11 (11) which has a longitudinal air and powder circulation channel having a longitudinal central axis (27), a diffuser ( 23) placed on this central axis, in the immediate vicinity of the discharge end of the air and powder circulation channel, the diffuser forming an angular path (S) which communicates with the air and powder channel, the   body also having a cylindrical channel of circular   cleaning air which discharges air along a path (P) parallel to the central axis, this path followed by   air intersecting said angular path, so that the air of net   the invention can strike against the mixture of air and powder, along said angular path, in order to shape this mixture to a predetermined size, means (16) being   for electrostatically charging the powder.