SPRAY GUN HEAD, DOUBLE SPRAY

The present invention relates to a compressed-air atomizing head for such substances as paints, enamels, varnishes etc.

Known atomizing heads comprise:

- a nozzle fed with a pressurized material to be atomized, the nozzle being fitted with a throttled conduit through which the material issues from the atomizing head to the outside, and - an air hood fed with compressed air and generating at least one pressurized external air jet able to atomize the material issuing from the nozzle through the throttled conduit.

In general these known atomizing heads assure good atomization; however they require high airflows and high pressures. Moreover, in the direction of atomization, they form a mist of the material being atomized; they are noisy and they soil rapidly at and near the throttled nozzle conduit. Also they do not lend themselves well to atomizing thixotropic materials such as water-based paints that are coming into wider use instead of the less thixotropic solvent-based paints of which the emissions should be curbed.

The objective of the present invention is to improve the known atomizing heads in order to:

- reduce the airflow and the air pressure they require for operation,

- improve their efficiency by reducing the mist of atomized material, - reduce their operating noise,

- averting nozzle soiling, and

- making easier the atomization of thixotropic materials,

but at the same time assuring excellent atomization.

For those purposes the present invention of the above relating to the above cited kind of atomizing head additionally comprises means to direct at least one internal pressurized air jet on the material to be atomized present inside the throttled conduit, the internal jet pressure being higher than that of the material to be atomized and the internal jet being appropriate to roil and atomize the material within the throttled conduit.

Accordingly, in the present invention, the material to be atomized undergoes two consecutive atomization's, namely a first atomization within the nozzle throttled conduit due to the internal jet and then a second atomization outside the nozzle by the external jet. Be it borne in mind that the second atomization is applied to a material to be atomized which already was roiled and already was at least partly atomized in the first atomization, as a result of which this second atomization shall be especially effective and shall assure excellent subsequent atomization. Moreover the roiling action in the throttled conduit allows fluidizing the thixotropic materials to be atomized and therefore raises their atomization efficiency.

In one advantageous embodiment mode of the present invention, the nozzle comprises at least one passage near the throttled conduit to set up communication between the latter and the air hood to tap the internal jet from the compressed air feeding the air hood that generates the external jet.

In a variation and regarding the general case where the atomizing head is fitted with a needle displaceable inside the nozzle to control the passage cross-section of the material within the throttled conduit, the internal jet can be guided by the needle toward the throttled conduit. The internal jet may be tapped at the overall compressed air feed to the atomizing head forming the external, atomizing air jet.

The appended Figures elucidate the implementation of the present invention. In these Figures, identical reference numerals denote similar components.

Fig. 1 is a partial section of a known atomizing head,

Fig. 2 is a view similar to that of Fig. 1 of an embodiment mode of an atomizing head of the present invention,

Fig. 3 shows an enlarged portion of the embodiment mode of Fig. 2 to elucidate its operation,

Fig. 4 is a view similar to that of Fig. 3 of an embodiment variation of the atomizing head of the present invention.

The known atomizing head 1 shown in Fig. 1 is able to atomize materials such as paints, enamels, varnishes etc. and comprises a central nozzle 2 enclosed by an air hood 3. The air hood is detachably affixed by means of a clamping collar 5 to the casing 4 of the atomizing head 1.

At its atomizing end, the nozzle 2 assumes the shape of a throttled conduit 6. A displaceable needle 7 (see double arrow 8) is configured inside the nozzle 2 and controls the flow cross-section of this throttled conduit 6, namely between total aperture and total sealing.

The pressurized material (9) to be atomized is internally fed to the nozzle 2 and is exhausted from this nozzle toward the throttled conduit 6 in the form of a jet denoted by the arrow 10.

The air hood 3 also is fed with pressurized air - the pressure of this air being higher than that of the material to be atomized - as indicated by the arrows 11 , and due to this pressurized air, the hood generates - outside the atomizing head - air jets 12 passing through orifices 13 configured around the material 10 be atomized issuing from the throttled conduit 6.

The external pressurized air jets 12 atomize the material jet 10 outside this atomizing head 1 and thereby mixing with this jet of material.

If called for, the air hood 3 also may use its pressurized air source 11 to generate pressurized transverse air jets 14, 15 that are able to shape the cross-section of the jet of material 10, which is atomized by the pressurized air jets 12.

The same components 2 through 7 and 13 as discussed above in relation to the known atomizing head 1 are also present in the atomizing head 1.1 of the present invention shown in Figs. 2 and 3.

However as regards the atomizing head 1.1 , the nozzle 2 also comprises oblique passages 16 distributed around the throttled conduit 6 and setting up communication between the latter and the air hood 3. In this manner the passages many generate internal, pressurized jets 17 tapped from the pressurized air (arrows 11) that generates the external atomizing jets 12. The pressurized material to be atomized (arrows 9) accordingly is initially roiled and atomized at least partly in the throttled conduit 6 by the internal, pressurized air jets 17 and then shall be subjected to the action of the external atomizing jets 12 outside the throttled conduit 6. The dual atomization of the material to be atomized accordingly is highly efficient.

The same components 2 through 7 and 13 as previously discussed in relation to Fig. 1 also are present in the atomizing head 1.2 of the present invention shown in Fig. 4

As regards the atomizing head 1.2, however, the needle 7 comprises a continuous duct 18 allowing at least one internal pressure jet 19 access to the throttled conduit 6. The internal pressurized jet 19 advantageously taps the overall pressurized air feed to the atomizing head 1.2, giving thereby rise to the pressurized air 11 and to the atomizing jets 12.

Accordingly, as regards the atomizing head 1.2, the material 9 to be atomized is roiled and undergoes a first and at least partial atomization in the throttled conduit 6 due to the action of the internal jet 19, and then a second atomization outside the nozzle 2 due to the external pressurized air jets 12.