GB1593718A

GB1593718A - Spray guns

Info

Publication number: GB1593718A
Application number: GB2606578A
Authority: GB
Original assignee: K & C Mouldings England Ltd
Current assignee: K & C Mouldings England Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-07-22

Description

(54) IMPROVEMENTS IN OR RELATING TO SPRAY GUNS (71) We, K. & C. MOULDINGS (ENGLAND) LIMITED, a British Company, of The Guild House, Water Lane, Bishops Stortford, Hertfordshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a spray gun, and in particular to a compressed air spray gun capable of spraying simultaneously two distinct liquids, such as a synthetic resin and a catalyst or hardener to cure the resin. The invention also extends to a method of spraying simultaneously two liquids with a compressed air spray gun.

When spraying synthetic resins - for instance on to glass fibre matting laid on a substrate to make a glass-fibre reinforced plastics article - it is necessary to mix at some stage the catalyst (or hardener) with the resin to promote curing of the resin.

Unless a very slow curing reaction is required, it is impractical to mix the resin and catalyst prior to spraying, because curing commences as soon as the catalyst is mixed with the resin, and the mixture rapidly becomes too polymerised to be sprayed. Consequently, there have been designed many spray guns in which the catalyst is mixed with the resin within the gun immediately prior to the resin mix issuing from the spray nozzle of the gun.

For example, the catalyst can be separately pumped for injection into the resin conduit within the gun, so that the resin/catalyst mix issues from the nozzle. This has the disadvantage that if an operator stops spraying, there is inevitably a small amount of resin mixed with catalyst in the region of the nozzle, and unless the gun is immediately cleaned, the gun will become clogged, often leading to the necessity to replace the spray nozzle.

The catalyst used with synthetic resins usually is a peroxide in an organic solvent.

This liquid is flammable and moreover must be handled with great care when compressed; the liquid becomes even more unstable when contaminated with iron, such as may happen when pumping the liquid to a spray gun. Thus another disadvantage of the known spray method for synthetic resins is that especial care must be taken with the catalyst, and even then there is still a considerable fire risk.

It is a principal aim of this invention to provide a spray gun for two liquids such as a synthetic resin and a catalyst, which gun at least mitigates or overcomes the disadvantages mentioned above of known guns for spraying resin and catalyst.

According to this invention, there is provided a spray gun for simultaneously spraying two distinct liquids, which gun has a spray nozzle defining a closable orifice for a first liquid and at least one air port juxtaposed to the orifice so that discharged air atomises liquid issuing from the orifice when open, a needle slidable axially of the closable orifice to open and close the orifice, a first liquid conduit leading to the closable orifice in the spray nozzle, and a compressed air conduit leading to the air discharge port and provided with a manually-operable air valve for simultaneous operation with the needle of the closable orifice, the needle being hollow and adapted for connection at its end remote from the spray nozzle to a second liquid conduit, the nozzle end of the needle being open, and support means for an unpressurised container for the second liquid, attached to the gun whereby when the first conduit is connected to a first liquid container, the needle is connected to a second liquid conduit and its associated supported container, compressed air is supplied to the conduit therefor and the air valve is opened withdrawing the needle to open the orifice, air issuing from the air discharge port atomises the first liquid issuing from the first liquid conduit out of the open orifice and draws the second liquid from the unpressurised supported container, through the second liquid conduit and out of the open nozzle end of the hollow needle.

The delivery of the first liquid to the spray gun will depend on the viscosity thereof. For a synthetic resin, it will usually be necessary to deliver the resin under pressure to the first liquid conduit, though if the resin is relatively mobile, the first liquid conduit may simply be connected to a container of the liquid. In this case, the liquid may be drawn out of the closable orifice, when open, by the compressed air discharged from the air port, by virtue of the Venturi effect. For a more viscous first liquid, the container thereof could be pressurised to feed the liquid to the first liquid conduit, so that the liquid issues under pressure through the orifice to be atomised by the discharged air. The first liquid could also be pumped directly to the first liquid conduit, in the case of a relatively viscous liquid.

The arrangement of the spray nozzle defining the closable orifice and air discharge port, as well as the first liquid conduit and the compressed air conduit can be somewhat similar to those employed in prior art compressed air spray guns. The air discharge port thus is preferably annular and surrounds the closable orifice for the first liquid, though additional air discharge ports may be provided to modify the spray pattern. For example, the nozzle may include a pair of wings each having an extra air discharge port, so that the resultant spray pattern is fan-shaped, rather than conical.

Known spray guns for spraying a single liquid with compressed air often have a needle which projects through a discharge orifice for the liquid, disposed in the spray nozzle, and operable to open the orifice by means of a trigger hinged to a gun body, one of the needle or the body defining the orifice having a taper. A similar arrangement may be employed for the spray gun of this invention, the needle being springbiased to the position in which the orifice is closed. The trigger may then also be coupled to the air valve of the compressed air conduit, so that the supply of compressed air to the spray nozzle may be shut off simultaneously with the closure of the orifice.

The needle employed in the spray gun of this invention preferably is open axially, though the needle could be provided with one or more radial openings at the nozzle end thereof, either in addition to or instead of an axial opening. Advantageously, the needle has an extension at its end nearer the spray nozzle, which extension projects forwardly from the nozzle and is hollow with an axial opening, so that the second liquid issuing from the axial opening of the needle is delivered into the atomised spray of resin issuing from the closable orifice.

In this way, the second liquid easily may intermingle with the resin, the mixing process being completed as the sprayed liquids contact a surface.

The end of the needle remote from the nozzle conveniently is formed so as to allow a flexible plastics tube to be fitted thereover, the bore of the tube communicating with the interior of the hollow needle, to allow the second liquid to be delivered to the nozzle end of the needle.

The needle need not however be open axially at the end thereof remote from the nozzle, and instead a pipe connector could be provided communicating with the interior of the needle through a radial passage in the needle.

The gun body includes support means to support an unpressurised container for the second liquid, there being a second liquid conduit connected to the needle and projecting to the bottom of a supported container to allow liquid to be drawn therefrom. Conveniently, the container is made of a transparent plastics material, such as polyethylene, so that an operator may see how much second liquid is present in the container.

It is often advantageous to vary the amount of catalyst supplied to a given amount of resin, for instance to adjust the rate of curing, or for different types of resin. In the spray gun of this invention, the amount of second liquid sprayed with the first liquid may be controlled by selection of the size of the opening of the hollow needle at the nozzle end thereof.

Thus a range of needles may be provided, having different opening sizes, and the needle used is selected depending on the amount per cent of second liquid to be sprayed with the first liquid.

According to another aspect of this invention, there is provided a method of spraying two liquids simultaneously with a compressed air spray gun, in which method compressed air is discharged from an air port in a spray nozzle of the gun, a first liquid issuing from a first liquid conduit out of a closable orifice in the spray nozzle and juxtaposed to the air port is atomised by the discharged air, and a second liquid is drawn only by the discharged air out of an opening in a hollow needle projecting through the closable orifice, the first liquid conduit and the hollow needle respectively communicating with reservoirs for the first and second liquids, the latter being unpressurised, and the hollow needle being movable axially to open and close the closable orifice.

It will be appreciated that in the method of this invention, the second liquid is not compressed or otherwise pumped to the hollow needle, the liquid simply being drawn by the Venturi effect out of the open end of the needle. Thus, the danger of fire or explosion is greatly reduced when the spray gun is used to spray resin and catalyst simultaneously. Moreover, should spraying be stopped, there is no resin/ catalyst mix within the gun to start curing, and the likelihood of clogging of the gun is greatly reduced, if not eliminated altogether.

By way of example only, one specific embodiment of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a diagrammatic side view, partially in section, of a spray gun constructed in accordance with this invention; and Figure 2 is an end view of the spray nozzle of the gun of Figure 1.

The embodiment of spray gun of this invention and shown in the drawings comprises a body 10 which includes a spray nozzle 11 and has a handle portion 12. A trigger 13 is pivoted by a bolt 14 to an upper part of the body 10, to depend downwardly in front of the handle portion 12. A compressed air conduit 15 extends through the handle portion 12, the conduit having an internally-threaded counterbore 16 at the lower end of the handle portion for the attachment of a flexible compressed air hose (not shown). A compressed air valve 17 is built into the handle portion 12, the spool of the valve 17 having an operating rod 18 projecting forwardly into engagement with a surface of the trigger 13, for operation thereby. When the valve 17 is opened, compressed air may flow through a further compressed air conduit 19 to the spray nozzle 11.

The spray nozzle 11 has a central circular orifice 20 communicating with a first liquid conduit 21 formed in the gun body.

The liquid conduit 21 tapers inwardly to the orifice 20, and thus internally is of generally conical shape. A needle 22 extends axially through the orifice 20, the major part 23 of the needle in the region of the spray nozzle having a diameter slightly greater than the orifice diameter, so that when urged fully to the left (in Figure 1) the major part 23 of the needle wholly obstructs the orifice, thereby closing the orifice to the passage of liquid therethrough. A gland seal 24 surrounds the major part 23 of the needle in a portion of the body 10 opposed to the spray nozzle, the needle extending rearwardly through an aperture in the trigger 13 and then through a bore 25 in an upper part of the body. An abutment 26 is mounted on the needle for engagement by the trigger 13 so that the needle is moved to the right (in Figure 1) simultaneously with the operation of the compressed air valve 17 on depressing the trigger. A threaded adjuster 27 is engaged in screw threads formed in the bore 25, a compression spring 28 surrounding the needle 22 and engaging opposed faces of the abutment 26 and the adjuster 27 to bias the needle 22 to a position in which the orifice 20 is closed by the needle.

The gun body 10 has an internallythreaded boss 29 depending downwardly behind the spray nozzle 11, the bore within the boss forming an extension of the first liquid conduit 21. A flexible hose (not shown) for the first liquid is connectible to the threads in the boss 29.

The needle 22 has an extension 30 at its forward end, which extension is of smaller diameter than the major part 23 of the needle and projects forwardly beyond the spray nozzle 11. The needle 22 is hollow for its entire length, there being an axial opening at the end of the extension 30 and a further axial opening at the opposite end of the needle beyond the adjuster 27. That opposite end of the needle is formed with an end section 31 of reduced diameter on which is fitted a flexible plastics material pipe 32. A bracket 33 is bolted to the body 10 and supports a clear polyethylene container 34 having a metal pipe 35 projecting to the bottom of the container, the plastics pipe 32 being connected to the metal pipe 35 immediately above the container.

The spray nozzle 11 includes a cap 36 having a central aperture 37 retained on the body 10 by means of a ring nut 38.

The aperture is arranged to surround the part of the nozzle defining the orifice 20, so as to form an annular air discharge port surrounding both the orifice 20 and the needle 22. The further compressed air conduit 19 leads to the space between the body 10 and the cap 36, so that the air may leave the gun through the annular air discharge port.

In use, the counterbore 16 of the gun described above is connected to a flexible compressed air hose at a pressure of from 40 to 60 p.s.i. A flexible hose for synthetic resin is connected to the threaded boss 29, the other end of the hose being connected to a pipe dipping in a tank or drum of the resin. The compressed air source is also connected to the container for the resin, so as to apply top-pressure to the resin and thus to drive the resin along the hose into the first liquid conduit 21. The container 34 is filled with a liquid resin catalyst, such as methyl ethyl ketone peroxide. When the trigger is depressed, the air valve 17 is opened and air issues through the annular air discharge port in the cap 36. At the same time, the needle is withdrawn partially from the orifice 20 to open the first liquid conduit, allowing the pressurised resin to issue through the orifice; the compressed air then atomises the resin into a very fine spray. Moreover, the issuing compressed air also draws the liquid resin catalyst from the container 34, through the flexible pipe 32, through the hollow needle, and out of the axial opening in the extension 30 of the needle, by virtue of the Venturi effect. The catalyst is thus also atomised to be dispersed into a fine spray in the spray of the resin. When the sprayed resin and catalyst contact a surface, the mixing is completed and curing of the resin can take place.

It will be appreciated that in the gun of this invention, the catalyst is not compressed or otherwise pumped, and this makes a significant contribution to safety.

Because no mixing of resin and catalyst takes place within the gun itself, any resin remaining in the gun will not commence to cure should spraying be stopped. Thus it is not necessary immediately to flush the gun with solvents once spraying is stopped.

The amount of catalyst available for spraying is visible through the transparent walls of the container 34, and thus it is most unlikely that an operator inadvertently will spray resin without catalyst -- which relatively easily can happen with the known spray guns having a separate pumping arrangement for catalyst. Moreover, with the gun of ths invention, the amount of catalyst supplied into the spray of resin is controlled by the diameter of the axial opening in the needle extension 30, and by selecting a needle with an appropriate opening diameter, a required amount of catalyst can be dispensed. The changing of needles is of course relatively easy, merely requiring withdrawal of the adjuster 27 whereafter the needle can be pulled out of the bore 25, and substituted by another needle.

WHAT WE CLAIM IS: 1. A compressed air spray gun for simultaneously spraying two distinct liquids, which gun has a spray nozzle defining a closable orifice for a first liquid and at least one air port juxtaposed to the orifice so that discharged air atomises liquid issuing from the orifice when open, a needle slidable axially of the closable orifice to open and close the orifice, a first liquid conduit leading to the closable orifice in the spray nozzle, and a compressed air conduit leading to the air discharge port and provided with a manuallyoperable air valve for simultaneous operation with the needle of the closable orifice, the needle being hollow and adapted for connection at its end remote from the spray nozzle to a second liquid conduit, the nozzle end of the needle being open, and support means for an unpressurised container for the second liquid, attached to the gun whereby when the first conduit is connected to a first liquid container, the needle is connected to a second liquid conduit and its associated supported container, compressed air is supplied to the conduit therefor and the air valve is opened withdrawing the needle to open the orifice, air issuing from the air discharge port atomises the first liquid issuing from the first liquid conduit out of the open orifice and draws the second liquid from the unpressurised supported container, through the second liquid conduit and out of the open nozzle end of the hollow needle.

2. A compressed air spray gun as claimed in claim 1, wherein the needle is open axially at the spray nozzle end thereof.

3. A compressed air spray gun as claimed in claim 2, wherein the needle has an extension at its end nearer the spray nozzle, which extension projects forwardly from the spray nozzle and is hollow with an axial opening at its forward end.

4. A compressed air spray gun as claimed in any of the preceding claims, wherein the spray gun comprises a gun body having a trigger hinged thereto and arranged on operation simultaneously to move the hollow needle against a springbias to open the closable orifice and to open the air valve of the compressed air conduit.

5. A compressed air spray gun as claimed in any of the preceding claims, wherein support means supports an unpressurised container for the second liquid and a second liquid conduit extends from the hollow needle to the supported container.

6. A compressed air spray gun as claimed in claim 5, wherein the container for the second liquid is made of a transparent plastics material.

7. A compressed air spray gun as claimed in any of the preceding claims, wherein the air discharge port is annular and surrounds the closable orifice.

8. A compressed air spray gun as claimed in any of the preceding claims, wherein means are provided for delivery of the first liquid under pressure to the first liquid conduit therefor.

9. A compressed air spray gun substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

10. A method of spraying two liquids simultaneously with a compressed air spray gun, in which method compressed air is discharged from an air port in a spray nozzle of the gun, a first liquid issuing from a first liquid conduit out of a closable orifice in the spray nozzle and juxtaposed to the air port is atomised by the discharged air, and a second liquid is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the issuing compressed air also draws the liquid resin catalyst from the container 34, through the flexible pipe 32, through the hollow needle, and out of the axial opening in the extension 30 of the needle, by virtue of the Venturi effect. The catalyst is thus also atomised to be dispersed into a fine spray in the spray of the resin. When the sprayed resin and catalyst contact a surface, the mixing is completed and curing of the resin can take place. It will be appreciated that in the gun of this invention, the catalyst is not compressed or otherwise pumped, and this makes a significant contribution to safety. Because no mixing of resin and catalyst takes place within the gun itself, any resin remaining in the gun will not commence to cure should spraying be stopped. Thus it is not necessary immediately to flush the gun with solvents once spraying is stopped. The amount of catalyst available for spraying is visible through the transparent walls of the container 34, and thus it is most unlikely that an operator inadvertently will spray resin without catalyst -- which relatively easily can happen with the known spray guns having a separate pumping arrangement for catalyst. Moreover, with the gun of ths invention, the amount of catalyst supplied into the spray of resin is controlled by the diameter of the axial opening in the needle extension 30, and by selecting a needle with an appropriate opening diameter, a required amount of catalyst can be dispensed. The changing of needles is of course relatively easy, merely requiring withdrawal of the adjuster 27 whereafter the needle can be pulled out of the bore 25, and substituted by another needle. WHAT WE CLAIM IS:

1. A compressed air spray gun for simultaneously spraying two distinct liquids, which gun has a spray nozzle defining a closable orifice for a first liquid and at least one air port juxtaposed to the orifice so that discharged air atomises liquid issuing from the orifice when open, a needle slidable axially of the closable orifice to open and close the orifice, a first liquid conduit leading to the closable orifice in the spray nozzle, and a compressed air conduit leading to the air discharge port and provided with a manuallyoperable air valve for simultaneous operation with the needle of the closable orifice, the needle being hollow and adapted for connection at its end remote from the spray nozzle to a second liquid conduit, the nozzle end of the needle being open, and support means for an unpressurised container for the second liquid, attached to the gun whereby when the first conduit is connected to a first liquid container, the needle is connected to a second liquid conduit and its associated supported container, compressed air is supplied to the conduit therefor and the air valve is opened withdrawing the needle to open the orifice, air issuing from the air discharge port atomises the first liquid issuing from the first liquid conduit out of the open orifice and draws the second liquid from the unpressurised supported container, through the second liquid conduit and out of the open nozzle end of the hollow needle.

drawn only by the discharged air out of an opening in a hollow needle projecting through the closable orifice, the first liquid conduit and the hollow needle respectively communicating with reservoirs for the first and second liquids, the latter being unpressurised, and the hollow needle being movable axially to open and close the closable orifice.

11. A method as claimed in claim 10, wherein the first liquid is drawn out of the closable orifice, when open, by the action of the air discharged from the air port.

12. A method as claimed in claim 10, wherein the first liquid is pumped to the first liquid conduit in the gun so as to be expelled under pressure out of the closable orifice, when open.

13. A method as claimed in any of claims 10 to 12, in which the relative proportions of the first and second liquids is adjusted by selecting a hollow needle having an opening dimensioned to give the required proportions.

14. A method as claimed in any of claims 10 to 13, in which the first liquid comprises a synthetic resin and the second liquid comprises a catalyst therefor.

15. A method of spraying two liquids simultaneously with a compressed air spray gun and substantially as hereinbefore described with reference to the accompanying drawings.