Spray gun

Abstract

 The subject is a spray gun (1), also called an airbrush, which has the function of nebulising the liquid substance to be applied using air at higher than atmospheric pressure. This gun is characterized in that the device (1) that regulates the flow rate of the substance to be sprayed is independent of the movement of the needle (3) that regulates the opening and closing of the substance outlet nozzle (4).

Description

[0001] The present finding concerns a spray gun, as described in the general section of claim No. 1.

[0002] As is well known, among the various systems employed in industrial processes for coating a surface with a liquid, one that is widespread involves the use of so-called "spray guns" or "airbrushes", using air at higher than atmospheric pressure for the purpose of nebulising the liquid substance to be applied.

[0003] Under current techniques, spray guns (such as, for example, those mounted on spraying machines in tanneries) operate on the principle of regulating the supply of liquid using a single needle that opens and closes the substance outlet nozzle.

[0004] A first disadvantage of this method of construction is evident when regulating the liquid flow rate .

[0005] In fact, when faced with substantial variations in the liquid flow rate, it is necessary to change both the needle and the associated nozzle with components of the appropriate size, for every variation in value of the flow rate, all requiring a certain period of downtime for the instrument and possibly the machine as well, to the obvious detriment of the machine's productivity.

[0006] In addition, in order to carry out micro-adjustments, it is necessary to alter the needle position in relation to the nozzle, so altering the profile opening of the substance outlet and, to achieve that, it is necessary to fit devices within the instrument that complicate its construction and increase the final cost.

[0007] A second disadvantage apparent in these spray guns arises from the fact that alterations to the needle position cause variations in the opening and closing times for the product outlet profile, which necessitates altering the work parameters of the machine, to adapt them to the period of time required for the needle to complete a full cycle.

[0008] The objective of the present finding is to create a spray gun or airbrush that does not have the disadvantages apparent in similar known products of this type.

[0009] This objective is achieved with a spray gun characterized in that the device for regulating the flow rate of the liquid substance to be sprayed is independent of the device that activates the operation of the needle for regulating the opening and closing of the substance outlet nozzle.

[0010] In particular, this objective is achieved with a spray gun in which the micrometric regulation of the liquid flow rate is independent of the needle and outlet nozzle sizes.

[0011] The objective is also achieved with a spray gun in which the regulation of the liquid flow rate is independent of the needle movement for opening and closing the nozzle.

[0012] Advantageously, from a constructional point of view, this objective is achieved with a spray gun characterized in that it has a liquid flow rate regulator located externally on the instrument; or more specifically, fixed on the liquid inlet opening and connected to the liquid supply tube itself.

[0013] In detail, the flow rate regulator comprises a fixed hollow casing, made as a fixed or integral part of the instrument casing, within which runs a piston-pin that determines the profile of the fluid flow.

[0014] The axial motion of the piston-pin, for the purpose of opening and closing the fluid regulator, as well as its stop limit position for regulating the flow rate of liquid entering the gun, are determined manually or by means of electro-pneumatic servomechanisms.

[0015] The invention will be better understood from a description of some of its possible embodiments (offered only by way of example and not intended to be limitative) with the help of the attached drawings, in which:

• fig. 1 (Plate I) shows a front elevation and sectional view of the spray gun referred to in this invention, in operational mode or "open";
• fig. 2 (Plate II) shows a front elevation and sectional view of the spray gun referred to in fig. 1 in rest mode or "closed".
• fig. 3 shows three different possible arrangements for the nozzle outlets;
• fig. 4 (Plate III) shows a detail of the nozzle area;
• fig. 5 shows a cross sectional view of the gun, taken on line V - V of fig. 4;
• figs. 6 & 7 (Plate IV) show an elevation and sectional view of a first embodiment of the gun's flow rate regulator as referred to in fig. 1, in open and closed modes respectively.
• figs. 8 & 9 (Plate V) show an elevation and sectional view of a second embodiment of the gun's flow rate regulator as referred to in fig. 1, in open and closed modes respectively.
• fig. 10 (Plate VI) shows a possible working arrangement for a number of the spray guns referred to in this invention.

[0016] As can be seen in fig. 1, the spray gun, marked in its entirety as item [1], comprises a casing [2], within which runs a needle [3], which engages with the nozzle outlet profile [4], to which is fixed an atomizer [5] held in place with a retaining ring [6].

[0017] Openings "H" an "K" are formed in the casing [2], providing for the intake respectively of nebulising air, conveyed via a duct [7] to the nozzle [4] and of pressurised air which, when working, is used both to elevate the piston [8] so as to open inlet "H" and to raise the needle [3] so as to open the nozzle [4].

[0018] Conversely, as can be seen in fig. 2, when the gun is inactive and once the flow of pressurised air into opening "K" is interrupted, opening "H" is closed by the piston [8], which is lowered by the thrust action of the spring [9].

[0019] The lowering of the piston enables the needle [3] to move downwards, under the thrust action of the spring [10], resulting in the openings [12] in the nozzle [4] being closed by means of the corresponding pins [11].

[0020] The first innovative feature of the invention provides for the flow rate of the liquid to be sprayed to be determined by means of a flow rate regulator, marked in its entirety as item [20], located externally on the casing [2] and communicating with the nozzle [4] via channel [13] formed in the above casing and connected externally to the liquid inlet tube "L".

[0021] As can be seen in figures 6 to 9, the flow rate regulator [20] comprises a casing [21] equipped with a piston-pin [22] capable of running axially between the opening and closing positions of the channel [13] and vice versa.

[0022] The reciprocating movement of the piston-pin [22] occurs by means of the thrust action of the pressurised air "PL" on the piston [23] (opening phase) and, when the above airflow ceases, through the reverse thrust of the spring [24], retained by hub [25] which is fixed to the casing [21] (closing phase).

[0023] The liquid flow rate from the tube "L" to the channel [13] is determined, at the operating stage, by the position of the piston-pin [22], which stops against the spindle [26] screwed onto the hub [25].

[0024] As can be seen in fig. 6, in a first embodiment of the finding the micrometric regulation of the stop limit of the spindle [26] is manually achieved through the rotation of the sleeve [27] fixed to the above spindle that is screwed onto the hub and unscrewed from it.

[0025] Advantageously, to show the operator the angular rotation value of the outer sleeve [27] and thence the flow rate value of the liquid entering the gun, part of the hub [25] is provided with longitudinal ribbing [28] and a click-pin [29], fixed to the sleeve, which engages with this ribbing.

[0026] In this way, as the outer sleeve rotates, each rib triggers the click-pin, this being observed by the operator or read from appropriate markings incised on the external surface of the sleeve [27]; the operator is therefore able to appreciate the extent of the sleeve's angular rotation and hence the movement of the piston-pin [22] or rather, the extent to which the liquid flow tube is open or blocked.

[0027] As can be seen in fig. 8, a second form of micrometric regulation of the stop limit of the spindle [26] is automatically achieved through the equilibrium between the thrust action of pressurised air flow "PF" on the piston [30], fixed to the above spindle and the reverse thrust of the spring [31] contained within the outer sleeve [27].

[0028] Conversely, as can be seen in figs. 7 and 9, the closure of the flow rate regulator [20] occurs when the flow of air "PL" ceases and the compressed spring [24] then pushes the piston-pin completely into its housing.

[0029] The second innovative feature of the finding concerns the facility, on each spray gun, to regulate the flow rate of nebulising air that is input through opening "H" and goes on to create the spray cone of the atomizer [5].

[0030] As can be seen in fig. 4, the regulation of air flow occurs by means of the partial constriction of the through holes [14] in the fixed disc [15] by rotating the ring [16] and its holes [17], so that, as can be seen in fig. 5, the usable air flow profile, "S" equates to the free area resulting from the partial overlap of each pair of holes [14 / 17].

[0031] The angular rotation of the ring [16], for regulating the overlap of the two through holes [14 / 17], is achieved by means of a threaded connection consisting of a grub screw [18] which is screwed into the casing and engages with a threaded section formed in the ring [16].

[0032] In order that the instrument can be adapted to the properties of the liquid to be sprayed, the invention features further improvements in construction, such as:

• an annular shape for the tube [7], terminating, at the upper end thereof where it engages with the piston [8], in an essentially spherical configuration, all to assist the free flow of nebulising air;
• various configurations for the openings [12], for example: circle [4.1], lozenge [4.2] and segmented circle [4.3] shapes;
• operation without use of the needle [3].

[0033] Finally, the invention allows for a single flow rate regulator [20] to supply two or more spray guns [1.1, 1.2 & 1.3] simultaneously and regulate their liquid substance flow rate.

[0034] There are obviously additional embodiments possible apart from that described, according to the type of instrument to be supplied, the types of fluid to be handled and mechanical components used, without, however, departing from the scope of the claims set out below.

Claims

1. SPRAY GUN, also called airbrush, with the function of nebulising the liquid substance to be applied using air at higher than atmospheric pressure,
   said gun being characterized in that
the device for regulating the flow rate of the substance to be sprayed is independent of the movement of the needle that regulates the opening and closing of the substance outlet nozzle.

2. SPRAY GUN, as described in claim No. 1, characterized in that the micrometric regulation of the flow rate of the substance to be sprayed is independent of the needle and outlet nozzle sizes.

3. SPRAY GUN, as described in claim No. 2, characterized in that the regulation of the flow rate of the substance to be sprayed is independent of the needle movement for opening and closing the nozzle.

4. SPRAY GUN, as described in claim No. 1, characterized in that the device that regulates the flow rate of the substance to be sprayed is automatically controlled, using the same flow of air [PL / K] that activates the needle control device.

5. SPRAY GUN, as described in one or more of the preceding claims, of the type that comprises a casing [2], within which runs the needle [3], which engages in the flow profile of the nozzle [4], onto which is fixed the atomizer [5], held in place by the retaining ring [6], on the casing [2] with openings [H] and [K] formed to allow for the inlet, respectively, of nebulising air, conveyed via the tube [7] to the nozzle [4] and pressurised air which, when working, is used both to elevate the piston [8] so as to open inlet "H" and to raise the needle [3] so as to open the nozzle [4], said gun being characterized in that it provides for the flow rate of the liquid to be sprayed to be determined by means of a flow rate regulator [20] located externally on the casing [2] and communicating with the nozzle [4] via channel [13] formed in the above casing and connected externally to the liquid inlet tube [L].

6. SPRAY GUN, as described in claim No. 7, characterized in that the flow rate regulator [20] comprises a casing [21], fixed to the casing [2] of the gun, a piston-pin [22] acting as a shutter for the channel [13], capable of running axially between the opening and closing positions of the channel and vice versa and where the reciprocating movement of the piston-pin [22] occurs by means of the thrust action of the pressurised air [PL] on the piston [23] in the opening phase and, when the above airflow ceases, through the reverse thrust of the spring [24], retained by hub [25] which is fixed to the casing [21] in the closing phase and where the liquid flow rate from the tube [L] to the channel [13] is determined, at the operating stage, by the position of the piston-pin [22], which stops against the spindle [26].

7. SPRAY GUN, as described in claim No. 5, characterized in that the micrometric regulation of the stop limit of the spindle [26] is achieved through the rotation of the outer sleeve [27], fixed to the above spindle, which is screwed onto the hub [25] and where part of the hub [25] is provided with longitudinal ribbing [28] and a click-pin [29], fixed to the sleeve, which engages with this ribbing.

8. SPRAY GUN, as described in claim No. 5, characterized in that the micrometric regulation of the stop limit of the spindle [26] is achieved automatically through the equilibrium between the thrust action of pressurised air flow [PF] on the piston [30], fixed to the above spindle and the reverse thrust of a spring [31] contained within the outer sleeve [27].

9. SPRAY GUN, as described in one or more of the preceding claims, characterized in that the regulation of air flow occurs by means of the partial constriction of the through holes [14] in the fixed disc [15] by rotating the ring [16] provided with holes [17], so that the usable air flow profile, [S] equates to the free area resulting from the partial overlap of each pair of holes [14 / 17].

10. SPRAY GUN, as described in claim No. 9, characterized in that the angular rotation of the ring [16], for regulating the overlap of the two through holes [14 / 17], is achieved by means of a threaded connection consisting of a grub screw [18] which is screwed into the casing [2] and engages with a threaded section [19] formed in the ring [16].

11. SPRAY GUN, as described in one or more of the preceding claims, characterized in that the tube [7] has an annular shape, terminating, at the upper end [7.1] where it engages with the piston [8], in an essentially spherical configuration.

12. SPRAY GUN, as described in one or more of the preceding claims, characterized in that the openings [12] are, for example, in the form of circles [4.1], lozenges [4.2] or a segmented circle [4.3].

13. SPRAY GUN, as described in one or more of the preceding claims, characterized in that it is able to operate without using the needle [3].

14. SPRAY GUN, as described in one or more of the preceding claims, characterized in that it is supplied by the same flow rate regulator [10] that simultaneously supplies two or more spray guns [1.1, 1.2 & 1.3] and regulates their liquid substance flow rate.

Drawing