EP1063018A1 - Automatic spray gun with a membrane - Google Patents

Abstract

A spray gun has a needle fixed to a membrane oscillated by a pulsing device. The needle causes a product to be supplied intermittently to a spray duct. The needle may extend into a central supply channel of a spraying head.

Description

The invention relates to an automatic diaphragm gun used for spraying of products, in particular spraying of abrasive paints or enamels, water-soluble or dissolved in a solvent.

There are spray guns in which spraying the product is obtained exclusively hydrostatically, i.e. by applying pressure on the product and take it out through a nozzle at the front end of the gun. Spraying can also be achieved pneumatically, but usually a combination of the two is used, which means that the hydrostatic spraying is combined with compressed air jets which, in addition to a central spray air jet, used to adjust the shape and / or dimensions of the spray of sprayed product.

To adjust the supply of the product to the nozzle and especially to cut this brought in when the pistol is no longer actuated, conventional automatic pistols without membrane use a needle which blocks the exit of the product through the nozzle. The withdrawal of the needle to clear this outlet is controlled by means pneumatic control valves which act on the piston of a cylinder moving the needle toward the rear. When the control means are no longer actuated, a return spring acts on the cylinder in the opposite direction to move the needle to the front to close the exit.

The invention relates more particularly to automatic pistols with membrane in which the membrane is controlled by forced air so that the product, which is fed into the gun under constant pressure, sort of the nozzle by intermittent spraying.

In a known automatic diaphragm gun, the membrane is driven in an oscillating movement by pneumatic control means the pulsed shutter of the product supply comprising a supply of pulsed air which communicates with an annular chamber formed in the body of the pistol around the rod of a control piston which, when actuated by forced air, is moved backwards against the action of an elastic return means. The the piston thus performs a back-and-forth movement at the frequency of the forced air.

The front end of the piston rod rests against the diaphragm, in a central zone of the latter, in order to give it an oscillating movement. The product to be sprayed is supplied under pressure in a product receiving chamber which is immediately in front of the membrane and which towards the rear is delimited by this one. This reception room communicates through a central opening with a central product supply channel arranged in the spray head and which opens directly into the nozzle.

When the forced air control means are not actuated, and also between two successive pulses, the central opening is closed by intermittent sealing means constituted by the membrane itself which then is pressed by the end of the piston rod against the peripheral area around the opening which thus forms a seat. For this purpose, the diameter of the end of the rod piston is significantly larger than the internal diameter of the opening.

However, this seat is thus at one end of the central channel whose opposite end opens into the nozzle, which means that when the means the forced air control are no longer actuated, i.e. when the spraying is stopped, the entire volume of the central channel constitutes a residue of the product whose flow through the nozzle cannot be prevented, causing soiling.

Another disadvantage of this pistol is that the obstruction and the clearance of the opening towards the central channel during the oscillation of the membrane lack precision and do not allow the proper functioning of these means intermittent closure of the supply of the product under constant pressure to frequencies which in this technical context are considered high and which are around 4 Hz.

This membrane spray gun also has means pulsed supply of atomizing air near the nozzle spraying to improve spraying and to form the spray of the product. Looks like spray is fed independently of the pulsed output of the product using a programmable controller that feeds the spray air into a room annular formed in the spray head and which communicates with a first set of air openings or nozzles opening close to the nozzle outlet and with a second set of orifices located in a crown placed at the front end of the body gun. This arrangement allows the orifices of this second set of orifices to direct the spray air jets at a much larger angle toward the jet of the product coming out of the nozzle.

However, this independent supply of spray air requires a whole set of auxiliary circuits and in addition, the PLC which manages the supply of atomizing air requires complicated and costly adjustments, which constitutes still a very significant drawback.

A general problem that affects both spray guns to membrane than the others that work with a needle valve lies in the fact that some parts are very exposed to wear, especially when the product is a abrasive product such as paint with enamel. First of all, the nozzle, but also the membrane in the case of spray guns membrane and needle in the case of needle spray guns. All these wearing parts thus require regular replacement which must be done more or less often depending on the abrasive nature of the product. It is therefore desirable to ability to extend the life of these wearing parts and / or facilitate their use replacement.

The object of the invention is to remedy all the drawbacks mentioned above by proposing an automatic diaphragm gun which prevents contamination by discharge of a residue of the product when the gun is stopped, which operates without problem at high frequency with frank and immediate response to pulses membrane, which is provided with a simple supply of atomizing air and at least some of the wearing parts of which are designed to allow longer service life and / or easier replacement.

The object of the invention is an automatic diaphragm gun for the spraying a product such as paint fed under constant pressure into the gun, comprising means for pulsed spraying of the product comprising an oscillation membrane associated with intermittent sealing means of the supply of the product to a nozzle, and means for controlling said means of pulsed spraying of the product, characterized in that said sealing means have a needle secured to the membrane and passing through it so as to be connected to a pulsation control device.

• le pointeau est fixé à la membrane par des moyens de serrage disposés de part et d'autre de la membrane;
• les moyens de serrage sont constitués par des brides solidaires du pointeau et disposées de part et d'autre de la membrane afin de la serrer entre elles;
• l'extrémité avant du pointeau s'étend dans un canal central aménagé dans une tête de pulvérisation, et le pointeau peut venir en appui contre un siège aménagé dans le canal central immédiatement derrière la buse;
• dans un pistolet du genre comportant des moyens d'alimentation pulsée en air de pulvérisation débouchant à proximité de la buse de pulvérisation, et des moyens de commande desdits moyens d'alimentation pulsée en air de pulvérisation, lesdits moyens de commande desdits moyens de pulvérisation pulsée du produit comprennent également lesdits moyens de commande desdits moyens en alimentation pulsée de l'air de pulvérisation;
• l'extrémité du pointeau est constituée d'un embout interchangeable;
• l'embout du pointeau est en résine de synthèse;
• du côté en contact avec le produit, la membrane est revêtue d'une couche en polytétrafluoréthylène.

According to other characteristics of the invention:

• the needle is fixed to the membrane by clamping means arranged on either side of the membrane;
• the clamping means are constituted by flanges integral with the needle and arranged on either side of the membrane in order to clamp it between them;
• the front end of the needle extends into a central channel arranged in a spray head, and the needle can come to bear against a seat arranged in the central channel immediately behind the nozzle;
• in a pistol of the kind comprising means for pulsating supply of spraying air opening in the vicinity of the spray nozzle, and means for controlling said means for supplying pulsed air with spraying, said means for controlling said means for pulsating spraying of the product also comprise said means for controlling said means in pulsed supply of spraying air;
• the end of the needle consists of an interchangeable tip;
• the needle tip is made of synthetic resin;
• on the side in contact with the product, the membrane is coated with a layer of polytetrafluoroethylene.

• La figure 1 est une vue schématique en coupe longitudinale d'un pistolet de pulvérisation à membrane selon l'invention, vu dans sa position d'arrêt correspondant à sa position entre deux pulsations successives des moyens de commande de la pulvérisation pulsée du produit,
• La figure 2 est une vue schématique en coupe longitudinale du pistolet de la figure 1, lorsqu'il se trouve dans sa position de pulvérisation dans laquelle aussi bien la pulvérisation pulsée du produit que l'alimentation pulsée de l'air de pulvérisation sont actionnées.

The invention will now be described in more detail using a nonlimiting example of an embodiment of the pistol according to the invention with reference to the accompanying drawings in which:

• FIG. 1 is a schematic view in longitudinal section of a membrane spray gun according to the invention, seen in its stop position corresponding to its position between two successive pulses of the means for controlling the pulsed spraying of the product,
• FIG. 2 is a schematic view in longitudinal section of the gun of FIG. 1, when it is in its spraying position in which both the pulsed spraying of the product and the pulsed supply of spraying air are actuated.

The automatic pistol shown in the drawings is a pistol membrane of the type in which the spraying of the product is obtained by pulsed spraying of the product fed into the gun under constant pressure, in combination with a pulsed supply of atomizing air which, in addition to spraying adjusts the shape and / or dimensions of the product spray sprayed. The process of spraying and adjusting the spray of product sprayed by compressed air jets is well known and, not being part of the invention, it does not will therefore not be described in detail.

The gun comprises a body 1 which, preferably, is made of light metal. This body is at its front and rear ends extended by a cylindrical protuberance front 2 and rear protrusion 3 respectively, which are threaded outwardly. The front projection carries a spray head 4 and the rear protuberance carries a cap 5 inside which are housed means control of intermittent output of the product to be sprayed.

The product is fed under constant pressure through a pipe 6 in a product supply chamber 7 fitted in the front part of the gun and having a generally frustoconical shape with the smaller diameter end emerging directly into a central channel 8 of the spray head 4 which connects the chamber supplying product 7 to a spray nozzle 9. The means allowing obtaining pulsed spraying of the product have a membrane 10 disposed at the larger diameter end of the frustoconical supply chamber 7.

The periphery of the membrane 10 is fixed by clamping between a front part 1 'and a rear part 1 "of the body 1. These two parts 1' and 1" are assembled by screwing and must be separated for the change of the membrane 10 following wear caused by the product on the front of the membrane. The membrane is in a material such as nitrile. The face exposed to this wear is according to the invention coated with a polytetrafluoroethylene (PTFE) layer, which substantially increases the service life of the membrane.

For pulsed spraying of the product at the nozzle, the membrane 10 is according to the invention oscillating mounted by means of a needle 11 extending in a through central bore 12 of the second part 1 "of the body 1 and which is connected to control means imparting a back-and-forth movement at this needle. The needle 11 crosses the membrane 10 through a central hole (not shown) thereof and is made integral with the latter by clamping means consisting of flanges 13, 14 integral with the needle and arranged on either side of the membrane 10 so to clamp it between them.

The front end of the needle may, as shown in Figure 1, come in support against a seat 15 immediately behind the nozzle in order to constitute together means of intermittently shutting off the supply of the product under pressure into the nozzle. The product passes from the product inlet chamber 7 to the nozzle 9 through a annular spacing defined between the internal wall of the central channel 8 and the external face of the needle. The space behind the membrane 10 in the product inlet chamber is vented through a conduit 16.

The needle 11 is guided in a guide sleeve 17 placed inside the central bore 12 and provided with seals 18.

The nozzle 9 thus constitutes with the needle 11 and the membrane 10 means of pulsed spraying of the product controlled by control means tires comprising a forced air supply pipe 19 connected to a duct 20 which opens into an annular chamber 21 formed around a piston rod 22 extending into the central bore 12 to be connected to its piston 23 which is guided in the cap 5.

The forced air arriving through the pipe 19 is supplied to the annular chamber 21 so as to push the piston 23 against the effect of a return spring 24 bearing on one side against the piston and on the other side against an internal wall of the cap 5. We obtain a reciprocating movement of the piston 23 and therefore also the needle 11 which drives the membrane 10 in an oscillating movement.

Figure 1 shows the advanced position of the needle between two pulses of the control air admitted into the annular chamber 21 through the air duct 20, this position also corresponding to the needle position when the gun is stopped. In the latter case, there is no product leakage through the nozzle 9, since the end of the needle is in abutment against the seat 15 immediately behind the nozzle.

When the piston 23 is pushed back by a pulsation of control air towards the rear, compressing the spring 24, to the retracted position shown in the figure 2, the end of the needle 11 leaves its seat 15 to free access to the nozzle of spraying 9 for the product under pressure which passes from the inlet chamber of produces 7 at the nozzle by the annular spacing defined between the internal wall of the channel central and the external face of the needle. At the same time, the central area of the membrane 10 is pulled back to fill the inlet chamber as much as possible product 7.

Between two pulses of control air, the device returns to the position shown in Figure 1 by a displacement of the piston 23 forwards, under the effect of the action of the return spring 24, thereby moving the needle 11 forwards in driving the membrane through the central area of it and this until the needle rests against its seat 15 in order to close the access of the product to the nozzle.

To improve spraying and better form the product stream sprayed out of the spray nozzle 9, the gun is also provided with means for pulsed supply of atomizing air opening near the spray nozzle 9. These spray air supply means have a compressed air hose 25 connected to an air duct 26 opening in a generally circular air inlet chamber 27 arranged around the needle 11 in the rear part 1 "of the body 1 of the pistol. This inlet chamber air 27 is, via another air duct whose opening is indicated in the figures and which extends in the rear and front parts of the body 1, connected to a external circular chamber 29 arranged in the spray head 4. This external chamber 29 is in communication with an internal circular chamber 30 and the two chambers are in a manner known per se connected to the atmosphere by holes opening to the front face of the spray head 4.

The orifices 31 of the external chamber 29 are arranged in a ring 32 arranged on the front face of the spray head 4, coaxially with the outlet of the nozzle 9. These orifices 31 form inside the crown 32 air jets directed slightly outwards and converging towards the product jet.

The orifices 33 of the internal chamber 30 form near the outlet of the product of the spray nozzle 9 of the air jets directed outwards and divergent to laterally delimit the jet of product.

The control means of these air supply means of spraying are for the pulsed supply of air included in the means of control of the pulsed product spraying means. According to the invention, the needle 11 also forms a valve allowing the pulsed supply of air from spray. For this purpose, the needle comprises a valve body 34 constituted by a cylindrical part of larger diameter which at its rear end is connected to the piston rod 22 and which at its front end has a first shoulder beveled 35 intended to cooperate with a second beveled shoulder 36 complementary to the first and arranged inside the central channel 8 immediately in front of the inlet chamber 27 of the compressed air. This second shoulder constitutes a seat for the valve body 34.

In the position shown in Figure 1, which corresponds to a position of the device between successive pulsations of the pulsed control air and at a stopped position, the valve composed of the first and second shoulders 35, 36 makes function of sealing means preventing the supply of atomizing air towards the spray head 4.

Under the effect of a pulse printed on the piston 23 which moves the needle 11 backwards, the valve body 34 leaves the seat 36 to allow free passage of air spray to the spray head. This opening and closing cycle of the valve repeats for each pulse.

In order to obtain a slight delay in the opening of the needle 11 relative to opening the valve 34 so that the supply of spray air begins just before the intermittent release of the product, a second return spring 37 is disposed inside the cap 5 to control the movement of the needle. This second return spring 37 bears on one side on the rear end of the needle and on the other side on the cap 5 to urge the front end of the needle against seat 15 thereof. There is a slight axial clearance between the piston 23 and the rear end of the needle 11, which means that at the start of a pulsation of the control air, the needle opens with a slight delay compared to the valve 34 and when the pulsation ends, the needle 11 closes slightly before valve 34.

Thanks to the invention, a membrane spray gun is thus obtained. in which we no longer need a separate controller to manage the air supply spraying and it is possible to apply an operating frequency without problem high with frank and immediate response.

In order to improve the wear resistance of the most exposed parts, the invention proposes several solutions.

Thus, the membrane which usually is made of nitrile, can advantageously be coated with a layer of polytetrafluoroethylene, which considerably increases the service life of this part.

In order to avoid having to dismantle the whole pistol to carry out the change of the whole needle, the end of it is according to the invention consisting of an interchangeable tip which is simply fixed by screwing. For change this nozzle, just remove the spray head to access it. Through elsewhere, to improve the wear resistance of this tip, it can advantageously be made of a synthetic resin suitable for the product to be sprayed.

Thanks to the fact that the nozzle is closed by a needle whose end of closure is immediately behind the nozzle, there is no longer any risk of leakage of product by opening the nozzle when the gun is stopped.

Other variants are of course possible without departing from the scope of the invention.

Claims (8)

Automatic diaphragm gun for spraying such a product than paint fed at constant pressure into the spray gun, including means for pulsed spraying (10, 11) of the product comprising a membrane oscillation (10) associated with intermittent shutter means (11) of the supply of the product towards a nozzle (9), and control means (19, 22, 23) of said means for pulsed spraying of the product, characterized in that said means shutter comprise a needle (11) integral with the membrane (10) and passing through the latter so as to be connected to a pulsation control member (22). Gun according to claim 1, characterized in that the needle (11) is fixed to the membrane (10) by clamping means (13, 14) arranged on the side and on the other side of the membrane. Gun according to claim 2, characterized in that the means for clamping consist of flanges (13, 14) integral with the needle (11) and arranged on either side of the membrane (10) in order to clamp it between them. Gun according to any one of the preceding claims, characterized in that the front end of the needle (11) extends in a central channel (8) fitted in a spray head (4), and in that the needle can come in support against a seat (15) arranged in the central channel (8) immediately behind the spray nozzle (9). Gun according to any one of the preceding claims, of the kind comprising means for pulsed supply of atomizing air (25 to 33) opening near the spray nozzle 9, and control means (11, 23, 34, 35, 36) of said means for pulsed supply of atomizing air, characterized in that said control means (11, 23, 34, 35, 36) of said means for pulsed spraying of the product also comprise said means for control (11, 23) of said means for pulsed supply of spraying air. Gun according to any one of the preceding claims, characterized in that the end of the needle (11) consists of an interchangeable tip (38). Gun according to claim 6, characterized in that the end piece (38) of the needle (11) is made of synthetic resin. Gun according to any one of the preceding claims, characterized in that on the side in contact with the product, the membrane (10) is coated with a layer made of polytetrafluoroethylene.

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