FR2706329A1 - Pneumatic sprayer of flat spray coating product. - Google Patents

Abstract

Pneumatic sprayer for coating product with a flat jet comprising a coating product supply valve (6) delivering a paint stream characterized in that an insert (20) arranged downstream of the needle (7) of said valve transforms said vein in a hollow spray of paint. The hollow paint vein is easier to shape with the horn air, and the flat spray is achieved with minimum horn and spray pressure and air flow.

Description

"Pneumatic Flat Spray Coating Product Sprayer"

  The invention relates to a pneumatic sprayer for a flat jet coating product. Specifically, it relates to a high-volume sprayer and low-pressure spray air, usually

referred to as "H.V.L.P".

  When using a flat-blast sprayer, an essential problem is to obtain a jet having a fairly flat shape so that the sweeping movement of the sprayer allows a deposit as uniform as possible on the objects to be covered. To do this, horns are provided projecting from the front face of the spray cap: they make it possible to subject the jet of spray paint coming out of the sprayer to the action of several jets of air which

  crush. We talk about conformation of the jet.

  However, in flat-blast sprayers of the prior art, whether manual spray guns or automatic projectors, the adjustment of the air of conformation or air of horns is delicate. Indeed, if it is not powerful enough, the spray paint is not wide enough and it is necessary to print a very fast sweeping motion to the sprayer to obtain a satisfactory surface condition; this is not always possible in the case of an automatic sprayer; this is very tiring for the operator in the case of a manual sprayer. The advantages of the flat jet are then nonexistent. On the other hand, if the air of conformation is too powerful, the jet of paint is cut in two and there is no more paint in the central part of the jet: the jet obtained is no longer a flat jet but the

  combination of two more or less ovoid jets.

  The thickness of the coating obtained on the object to be covered is then irregular, which is

unacceptable.

  A conventional pneumatic sprayer uses a source of compressed air to drive the vein of

  paint into an area where it is sprayed.

  We talk about training air. A second source

  of compressed air is used for spraying, ie

  say divide into a multitude of droplets, the paint vein at the outlet of the spray orifice. We talk about spray air. Drive air and spray air may have a common source; they are then separated by

  channels inside the spray cap.

  In the particular case of H.V.L.P. flat-jet sprayers, the entrainment air also constitutes the spray air. Its pressure at the rear of the spray cap is relatively low, preferably less than 1 bar. However, to be sprayed, the paint stream must be driven and sheared by this air jet: the paint particles in the center of the vein are not subjected to the shearing action of the spray air. It is therefore sometimes necessary to increase the pressure of the spray air, which limits the advantages of the HVLP configuration, because the low pollution, the low paint losses and the high deposition efficiency obtained with a sprayer. this type come mainly from the low air pressure of

  spray and air conformation.

  US Patent 5074466 discloses a high flow and low pressure air spray gun in which the valve needle serves to make the coating product vein hollow. In this way, the hollow jet coming out of the sprayer is much easier to spray and crush by the air conformation. Indeed, in the case of a hollow vein, the ratio of the outer perimeter to the section of the paint vein is greater than that of a full vein of the same diameter. In a vein of hollow paint, the particles are on average closer to the outside of the vein and are therefore more subject to the action of external aerodynamic forces than in the case of a full vein, whether of the action of the air spray or

that of the air of conformation.

  However, this technique is only valid if the needle is placed very close to the exit of the paint channel, that is to say practically less than 5mm in the open position. Indeed, if the needle is too far from the paint outlet, the vein closes and the jet of coating product obtained is a full jet. This phenomenon will occur more or less depending on the physical characteristics of the product

  such as its viscosity and surface tension.

  The formation of the hollow vein will not be reproducible if compositions paintings

  different chemicals are used.

  In addition, the more or less hollow nature of the vein depends on the degree of opening of the valve, which is unacceptable because the efficiency of the conformation

  then also depends on the opening of the valve, that is

  ie the spray rate. The setting of such

  sprayer is particularly delicate.

  Finally, the position of the needle with respect to the seat of the valve alone conditions the profile of the vein coating product: if the needle is not exactly centered on the seat, the hollow vein obtained is not cylindrical. This dissymmetry is necessarily found in the flat jet finally obtained.

  The invention solves all of these problems.

  It relates to a pneumatic sprayer of a flat-jet coating product comprising a coating material supply valve delivering a paint stream and a spray nozzle characterized in that an insert comprising an annular channel is housed in the downstream nozzle. of the valve needle and transforms said vein into a jet

hollow of paint.

  The presence of the insert immediately before the exit of the paint channel and downstream of the valve needle ensures that the vein keeps its hollow shape until ejection of the sprayer, that is to say until it undergoes the action of the tunes of

spraying and conformation.

  Thanks to this insert, the hollow character of the vein is obtained independently of the adjustment of the flow rate of the coating product and its physical characteristics. The centering of the needle on the seat of the valve does not condition the symmetry of the coating product vein. Finally, in the case of an electrostatic sprayer, the relatively large electrical capacity that is the metal needle can be housed deep enough in the body of the sprayer to avoid any risk of spark. It is easy to transform a known flat jet sprayer to benefit from the invention. It suffices to house the insert characterizing the invention in the nozzle of the sprayer instead of the conventional injector which is removable from the front of the sprayer. The invention will be better understood and other advantages thereof will appear more clearly in the light

  of the following description of a mode of

  embodiment of a pneumatic sprayer of a flat-jet coating product in accordance with its principle given solely by way of example and with reference to the appended drawings in which: FIG. 1 is a schematic sectional view of a pneumatic sprayer according to FIG. 2 is a view on a larger scale of the sprayer insert of FIG. 1 and FIG. 3 is an enlarged view of a

  variant of the sprayer insert of FIG.

  The sprayer 1 of FIG. 1 is of the HVLP type, it comprises a paint inlet channel 2 fed by a pipe 3 penetrating into the sprayer through the butt 4. The trigger 5 makes it possible to control a valve 6 whose needle 7 rests on a seat 8 near the spray orifice 9 formed in a spray nozzle 10. An air supply duct 11 also enters the butt 4. It allows to feed through ducts 12 and 12 the sprayer 1 air drive and spray on the one hand and air horn or conformation on the other. The horns 13a and 13b comprise conforming air outlet openings 14a, 15a, 14b and 15b directed towards the vein of paint coming out of the sprayer through the orifice 8. These horns are part of a spray cap 16 kept in position. place on the nozzle 10

by a tightening nut 17.

  Downstream of the seat 8 of the paint supply valve is disposed an insert 20, for example of plastic material, transforming the paint stream into a hollow paint stream. This insert is housed in

  the nozzle 10 near the spray orifice.

  It is actually the terminal part of the

paint in the nozzle 10.

  The insert 20 is visible in FIG. 2. It comprises four input channels 21 regularly distributed on the side of the seat 8 and the needle 7 of the paint supply valve and an annular outlet channel 22 constituting the orifice of FIG. spray. The

  channels 21 and channel 22 are in communication.

  In the case of an electrostatic type sprayer, the insert 20 comprises an axial bore 25 in which is housed a charging electrode 26 supplied in a manner known per se from

  of a high voltage generator not shown.

  The electrode 26 protrudes from the insert 20 over a length L sufficient so that it loads the paint stream both by contact and by

Corona discharge.

  The operation is as follows: after passing through the pipe 3 and the pipe 2, the paint passes between the needle 7 and the seat 8 of the supply valve. It is then divided into four threads by the four conduits 21, which are joined in the channel 22 to form a single jet which is kept hollow to the spray orifice 9 through the central inner portion 27. The presence of the central portion 27 to the end of the insert 20 prevents the paint stream from becoming a hollow vein before the air spray begins to shear and drive it and before the air conformation do not start crushing it. It is then possible to use a spray air and a conformation air at a relatively low pressure for

  drag and flatten this vein of paint.

  If the charging electrode 26 is long enough, the crushing begins at the end thereof and it is in direct contact with the paint stream, which leads to a load on contact. Otherwise the electrode loads the Corona discharge paint vein because its end is near the vein

  painting during spraying.

  The variant of Figure 3 relates to an insert 120 including a modification of the geometry of the central portion 27 of Figure 2: it is referenced 127. It has one end

  frustoconical 128 which deflects the vein of paint.

  The paint therefore has a radial component of speed when it meets the spray air which

  is substantially parallel to the axis of the insert 120.

  In this way, the penetration of air into the paint stream is further facilitated and the pressure of the spray air can be kept to a minimum. In the case of an electrostatic sprayer, the insert may also be metallic or a conductive material. The electrode 26 is then removed and the coating product is charged by contact during its passage in the channels 21 and 22 and / or Corona discharge on the edges of the insert 20 or 120. This insert can also be made in ceramic, which ensures a longer life due to the hardness of this material.

  The description was made with reference to a

  manual sprayer but the invention also obviously relates to an automatic sprayer. Likewise, the invention applies equally to an electrostatic or purely pneumatic pneumatic sprayer, with a large flow rate and low air pressure.

spray or conventional.

Claims (6)

  1) Pneumatic sprayer for a flat-jet coating product comprising a coating product supply valve (6) delivering a paint stream and a spray nozzle (10) characterized in that an insert (20, 120) comprising a channel annular (22) is housed in said nozzle downstream of the needle (7) of said valve and transforms said vein into a hollow stream of paint. 2) Sprayer according to claim 1 characterized in that said sprayer is of the type with high flow rate and low air pressure spraying.   3) Sprayer according to one of the claims   characterized in that the insert (20, 120) has a plurality of inlet channels (21) on the needle (7) side of the valve (6), said channels being in   communication with the annular channel (22).   4) Sprayer according to one of the claims   previous characterized in that the hollow vein of paint is sprayed at the outlet of the insert and then shaped flat jet by jets of air from horns (13a, 13b).    Sprayer according to one of the claims   characterized in that the hollow vein of paint has a radial component velocity at the outlet of the insert (120).   6) Sprayer according to one of claims 3 or   characterized in that the central inner portion (127) has a frustoconical end (128) forming deflector.   7) Sprayer according to one of the claims   characterized in that the insert (20) has an axial bore (25) in which is housed a charging electrode (26).   8) Sprayer according to claim 7 characterized in that the electrode (26) protrudes from the insert (20) of a length (L) sufficient to be   in contact with the crushed paint vein.