GB2304059A - Cleaning and control of spray painting and beverage supply equipment - Google Patents

Abstract

A nozzle includes an outer casing and (solvent) collector tube 24 fitted with air inlet 20 and internal components arranged such as to create a Venturi effect 28 in the collector tube. Being substantially sealed to the device which is to be cleaned (e.g. a spray gun 10), solvent is then drawn at high speed with a turbulent swirling action through the gun, thus cleaning its internal passages (e.g. of paint product). If required, air or other gas is allowed to escape into the fluid stream at fitting 15 further enhancing cleaning efficiency. The now-contaminated solvent is emitted at high speed in a largely-unatomised so can be readily collected for later re-use. The device could also be adapted for use as an application means. A further embodiment of the device allows for its use in the cleaning of beverage supply equipment and other similar applications from high pressure hydraulic lines to fish farming.

Description

The Weaning and Control of Spraving Apparatus.

This invention relates to the cleaning of spray painting guns and similar equipment such as air brushes. In one aspect, it relates to apparatus for use in such cleaning operations. In another, it relates to a method of cleaning and control.

Most "conventional" (as opposed to "airless") spray painting guns have respective inlets for supplies of compressed gas (usually air) and liquid paint. These are mixed at the outlet of the gun and emerge as a fine spray. It is periodically necessary to clean the gun. The normal method used is simply to pass a cleaning solvent through the paint inlet by filling the paint container with solvent. The solvent is sprayed in the same manner as the paint using the compressed gas supply. This process is necessarily repeated to ensure as good a cleaning effect as is possible, and the solvent is atomised in the process. This is rather wasteful on both solvent and gas.

Furthermore the expelled solvent must be captured, since it will rarely be acceptable to spray it into fresh air. Normally a paint spray booth has a means for trapping sprayed paint, often involving mixing the spray with water treated with a chemical additive. However, the usual additives are rendered ineffectual by the admixture of significant quantities of the cleaning solvent. Thus, before the booth can be returned to spray painting, the booth contents must eventually be drained and treated chemically to remove pollutants, at some considerable expense to the operator.

In refering to British Patent No.2182266,we wish to illustrate changes in design of some spray guns which, in increasing their efficiency, have made some of the embodiments in the original patent inoperable. The figure 6 in that previous patent shows a form of air cap (item 90) which depends for its operation upon its ability to channel the compressed gas over the swept outer contours of the fluid nozzle within, such that the gas, being constrained to follow that path, then creates a partial vacuum, and a liquid sucking action, in front of the fluid opening in the fluid nozzle: see fig. 1.

below, being an enlarged sectional elevation.

The type of conventional spray painting apparatus as illustrated has long been recognised as being highly inefficient and polluting to the workplace and the environment at large in its spraying action, producing as it does a relatively poor "transfer efficiency" - i.e. the ratio of "useful" paint which lands on and adheres to the article being sprayed; to the total paint output from the gun.

In response to increasing pressures from both legislative authorities and spray gun operators, the growth of High Volume, Low Pressure (HVLP) designs of spraying equipment is resulting in increased efficiency and reduced pollution from spray painting operations.

The net result (frorn the aspect of cleaning the internal spray gun passages) however, has brought increasing difficulties. Because the amount of overspray or wasted paint, has been reduced by up to 50%, the fluid flow rate through these HVLP spray guns has also been consequently reduced by a corresponding amount.

Therefore, the even slower solvent flow rate during cleaning operations has resulted in even less efficient cleaning than was hither to the case.

For a variety of technical reasons, some of the HVLP spray guns being introduced are not designed in such a way that fluid (paint or solvent) is required to be sucked from the paint container by venturi action. The fluid is rather in these cases delivered under pressure from the paint container. Consequently, in these cases, the fluid nozzle's outer shape does not now require the "swept" outer contours shown in fig. 1 which assists in generating this venturi action. The HVLP spray head configuration is illustrated in fig. 2, being an enlarged sectional elevation.

Because of this change of design, it has not been found possible to employ the type of air cap (or removable core) referred to in Patent 2182266.

What is therefore proposed is a self contained "venturi chamber" which will, with the assistance of its own compressed gas supply, create its own high speed liquid sucking action, thereby enabling the new HVLP spray guns of this design to benefit from the same highly efficient cleaning solvent flow as was possible using the device proposed in the earlier patent.

It is also possible that the proposed device could be used in place of the alternative known cleaning nozzle disclosed in Patent 2182266 on conventional suction and gravity feed spray guns since the new unit could be designed in such a way that it would become universal for a wide range of spray gun types and models, instead of having to tailor each nozzle specifically to each style of gun.

An additional benefit from inducing a much higher speed solvent flow is that the solvent is emitted in an unatomised form, and therefore can be said to be significantly reducing the harmful solvent emissions during the cleaning cycle, since the solvent can be captured for recycling or immediate re-use.

Since the spray gun is now effectively under remote control, it is also possible to conjecture upon a radically different design of spray gun body, devoid of the many complicated drillings and problems associated with the inherent porosity present in die-castings of which the gun bodies are frequently made.It would then be possible to radically cheapen the manufacture of the guns themselves, using the self-contained venturi chamber unit to syphon paint or other material from its container under much greater control than has hitherto been possible.

Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings in which: FIG.1 is a side elevation of a conventional suction or gravity-feed fluid nozzle showing its "swept" shape which is instrumental in creating the requisite "liquid sucking" effect referred to above.

FIG.2 is a side elevation of an HVLP suction or gravity feed fluid nozzle showing its plain truncated cone shape which does not generate any "liquid sucking" effect.

FIG.3 is a side elevation of a typical HVLP spray gun fitted with the proposed device.

FIG.4 is a sectional elevation of the outlet region of a typical HVLP spray gun fitted with the proposed device.

Description of the proposed embodiments.

In fig.3 a conventional, or HVLP spray gun has its container, 14, of liquid (solvent when cleaning is to take place) to be sprayed, connected to its fluid inlet 15.

The proposed device, 11, is connected to the guns outlet region by means of a standard retaining ring 13. A supply of compressed air is fed in (through line 12) and emerges from the device in such a manner as to create a low pressure area (by the venturi effect) which, when the spray gun trigger is depressed, will then draw liquid from the container, 14, at a much faster rate than is normally possible. This, combined with the possible (but not essential) slackening of the swivel nut at the fluid inlet, 15, which joins the spray gun, 10, to its container, 14, serves to wash all wet paint residue from the walls and other wetted surfaces within the gun's fluid passages.

These fluids are then propelled at high speed through the proposed device and, being unatomised can be readily collected by pointing the nozzle into any convenient, wide-necked container.

(It should be pointed out that line 12 is, under normal spraying conditions, more usually attached to the spray gun's compressed air inlet, 16. By means of a standard, quick detachable coupling, the change in position is easily accomplished.) It may also be necessary, should the system have a pressurised container, 14, to vent the same to atmosphere, so that the venturi device is not operating against a partial vacuum.

It is also proposed herein that in place of merely loosening the connection at 15, that it be replaced with a simple rotary or push-rod valve which during normal spraying operations remains closed, but, for cleaning only, would be opened, exposing a small hole open to the atmosphere, through which ambient air would be sucked to assist in the cleaning operation In fig. 4 is seen a cross-sectional view of the proposed venturi chamber, 11 and the head of a typical spray gun, 10. The tubular coupling, 11 is held securely in contact with the gun by means of retaining ring 13. Within the coupling are positioned two removable cores, 18 and 19 respectively called the jet and the air cap.

The jet is held in contact with the spray gun fluid nozzle 22, substantially sealing where it meets the gun peripherally 23. The air cap, 19 is trapped between the jet 18 and the internal bore of the tubular coupling, 11. The air cap 19 is dimensioned so that it embraces the air outlet passage 29 of the venturi device (the air being supplied via the line 12 and a tubular threaded connection 20) and so that the fluid outlet jet 18 projects through, and a short way beyond, the aperture 21, there being an annular space between the jet 18 and the wall of the air cap 19 that defines this aperture.

Thus, when compressed air is fed through connector 20, it builds up pressure in chamber 29 and escapes to atmosphere via the annular space 21. The venturi effect caused at 28 then partially evacuates chamberl7. (NOTE: When the whole assembly is secured onto the spray gun by retaining ring 13, the pressure built up in chamber 29 is contained and rendered harmless. There is a risk, however, that the unit may be operated off the spray gun - in which case the pressure build up in chamber 29 may cause outlet jet 18 to be ejected at high speed from the body of the assembly 11. In order to prevent this happening, a grub screw (not shown) will be fitted to the assembly in a radial orientation such that it passes through the body of the assembly and partially enters the periphery of jet 18, placing itself "in shear" and effectively capturing jet 18 in its intended position.).

When the spray gun trigger is depressed, the fluid "needle" 30 is then lifted off its seat inside the fluid nozzle 22 and the partial vacuum in chamber 17 then causes liquid (which may be solvent or other fluid material) to be sucked from its container and propelled at high speed through the internal passages of the gun. In the case of solvent, the result is a scouring action which will clean the walls of the fluid passages within the spray gun. The mixture is then propelled largely unatomised through the chamber 17 and down the barrel of the collector tube 24. This barrel would normally project into a collector container so that the residue may be allowed to settle and be reused a number of times thus greatly reducing solvent emissions from spray gun cleaning.

If at the same time, the swivel nut component 15 of the fluid connector 27 to the gun itself is loosened, then the solvent flow 25, being under less than atmospheric pressure, will draw in air bubbles 26 which will further assist the "scrubbing action" of the high speed solvent stream. It is further proposed that this artificial nut loosening could be replaced by a simple rotary or push rod valve (not shown) which would, during normal spraying operations be "closed", but for cleaning only would be "opened," thus allowing the surrounding air to be sucked into the fluid stream and assist in the cleaning action.

It is also proposed that by extending the length of the barrel 24, it will be possible to project paint or other fluids such as adhesives or waxes into cavities or spaces which, using existing equipment, it is not possible to reach.

This device as described above and other vacuum-inducing equipment can also relate to the cleaning of beverage supply equipment for such products as milk, beers, lagers etc.

The currently accepted method of cleaning these supply systems is by laboriously pumping them through by hand with cleaning fluids, flushing agents and then recharging them with fresh product. Current methods are widely recognised to be highly labour- intensive and inefficient, thus adversley affecting the quality of the beer, milk etc. This is due to the organic nature of the yeasts and other constituents and the importance not only of removing organic growth from the system, but also the distasteful cleaning fluids.

Commercial cleaning systems currently available all depend upon various means of PUMPING the fluids through the system in the normal way. All these systems suffer and share one major drawback in that the pressure limit on the piping, valves etc. does not permit a high speed scouring flow of liquid to clean the organic material adhering to the walls and interstices of the system.

What is proposed therefore is that the cleaning fluid be SUCKED through the system using the device described above, or using various other commercially available pieces of equipment. Sucking the cleaning fluid (or the product itself) not only can generate a high speed swirling flow, but also facilitates the ready introduction of ambient air bubbles ( or other perhaps inert gas), as will be shown, which greatly assists the cleaning action, at very little extra cost.

The introduction of such a suction-powered cleaning system to beer and lager dispensing systems will greatly assist efficient cleaning, reduce "down time" and improve the consistent quality of the products.

Some embodiments of the invention will now be described in detail with reference to the accompanying drawings in which: FIG.5 is a diagramatic representation of the proposed revised system in beverage dispensing mode.

FIG.6 is a diagramatic representation of the proposed revised system in cleaning mode.

Description of the proposed embodiments.

In Fig. 5 a conventional (or otherwise adapted) "beer engine" to use the trade name, 31 is shown attached "upstream" by supply tubing to its conventional non-return valve,32; its" FOB detector" 33; to its regular beverage container, 34; via a proposed fluid shut-off valve, 35; which in dispensing mode is of course open. The side entry to the cleaning circuit is protected by a second fluid valve, 36 which of course in dispensing mode is shut. Alternately, these two fluid valves can be combined if desired into one three-way valve.

In Fig.6 the beer engine, 31, and all equipment is shown in cleaning mode.

Valve 35 is now shut and valve 36 is open. Cleaning fluid (or possibly even the product itself) is now drawn from its unpressurised container 37 through a proposed valve 38 containing an open-to-air port (or open to another gas at ambient pressure) and via valve 36 through the circuit at high speed containing "slugs" of the gas from valve 38, cleaning the walls and interstices of the equipment of organic matter. The "beer engine" hand pump is in bypass mode, and the cleaning fluid is sucked through the system by the vacuum-creating device,39.

NOTE. This device 39 could be the previously discussed item illustrated in FIG4, where instead of meeting the spray gun peripherally at 23, would now be connected by screw-thread or quick detachable connection 42 direct to the fluid-dispensing outlet of beer engine 31.

Otherwise item 39 could be any one of a number of readily available proprietary pieces of equipment designed for similar purposes.

Item 39 would need to be powered by compressed air, either fed to it from a compressor or a compressed air bottle such as that used by deep sea divers. The cleaning fluid and gas, in an efficient swirling turbulent flow will then rapidly clean the system, and can be discharged into a suitable container 41, for disposal.

NOTE 1. The operational sequence of valves etc. can easily be controlled robotically which will improve its foolproof capability.

2. The vacuum-inducing device may also, alternatively be a vacuum chamber device previously evacuated for the purpose and maintained in that state during the sequence.

Claims (5)

1. A self-contained means of feeding compressed gas through a venturi type device to create a high vacuum-thereby inducing a turbulent swirling flow of cleaning fluid through a piped system.

2. A device as claimed in Claim 1 wherein ambient gas is allowed under a controlled means to escape into the cleaning fluid flow thereby further enhancing its cleaning efficiency by virtue of the increased turbulence produced.

3. A device as claimed in Claim 1 and 2 wherein, when used to clean spray painting (or other equipment which is cleaned with solvents). The resulting "atomisation" of those solvents is clearly reduced, thus contributed to a reduction of solvent emissions into the atmosphere.

4. A device as claimed in Claim 1, 2 and 3 wherein it can also be utilised as a spraying or application means - thereby creating a much simpler and more robust spraying or application device than is currently available.

5. A device as claimed in Claim 1, 2, 3 and 4 which, with simple adaption can be used for the cleaning of other pipework systems which handle organic foodstuffs and beverages and other products requiring a high degree of internal cleanliness of the equipment involved.