WO1992006789A1

WO1992006789A1 - Powder coating apparatus

Info

Publication number: WO1992006789A1
Application number: PCT/AU1991/000473
Authority: WO
Inventors: Robert Joseph Pertzel; John Winsor Hannaford
Original assignee: Australian Electronic Technologies Pty Ltd
Priority date: 1990-10-22
Filing date: 1991-10-14
Publication date: 1992-04-30

Abstract

Powder coating apparatus suitable for electrostatic powder coating apparatus is provided. The powder coating apparatus has a venturi type powder pump (42) for pumping from a powder container. Manually adjustable valve means (30, 31), such as needle valves, provides relatively coarse adjustments of the air supply within normal operating limits to the venturi type powder pump. Valve means (32) also adjusts the fluidizing air supply to the container from which powder is pumped.

Description

^sPOWDER COATING APPARATUS' This invention relates to powder coating apparatus and components therefor. This invention has particular application to electrostatic powder coating apparatus. Typical electrostatic powder coating apparatus pump powder from a fluidised powder container through a hand gun for depositing onto an article to be coated. Most such apparatus utilises a venturi type powder pump to pump powder from the container of fluidised powder and the desired powder/air mix of the delivered powder is effected by introduction of a dilution air feed into the powder delivery path downstream of the powder pump.

In order to achieve the desired powder delivery from the powder pump, adjustments are provided to the powder pump air supply, the dilution air supply and the fluidising air supply to the powder container. To date such control has been provided by incorporating air pressure regulators to control the air supplies to the powder pump and the fluidising air supply. Such pressure regulators are both expensive and difficult to adjust because only very fine adjustment is provided and thus it is difficult for a user to readily gauge variations in powder supply quality with adjustment of the regulators. That is small manual adjustments of the regulators do not cause readily apparent changes in the quantity and/or ratio of the powder/air mix supplied thereby. Frequently many turns of the adjusting knobs are required before a significant change occurs in the quantity/ratio of the powder/air mix supplied.

Another disadvantage associated with the presently available powder coating machines is that a significant down-time is required -co change between different powder colours. This is mainly due to the significant amount of dismantling and reassembly required in order to clean all contaminated components of the apparatus prior to commencing with the new colour powder.

The present invention aims to alleviate the above and other disadvantages and to provide powder coating apparatus which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent. With the foregoing and other objects in view, this invention in one aspect resides broadly in powder coating apparatus having a venturi type powder pump for pumping powder from a powder container and manually adjustable valve means in the air supply line to the powder pump, said valve means providing relatively coarse adjustments of the air supply between normal operating limits.

Suitably the powder coating apparatus incorporates a dilution air inlet to the pumped powder and the dilution air supply includes manually adjustable valve means whereby relatively coarse adjustments of the air supply within normal operational limits is provided such that an operator manually adjusting the powder or dilution air supply valve means may readily observe the effect on the powder/air mix ratio and/or the quantity of the powder supply.

The adjustable valves may be of any form such as plunger or butterfly valves but preferably the adjustable valves are in the form of needle valves. Suitably the needle valves are so made and arranged that a relatively small number and preferably one turn of the needle valve will provide complete adjustment of the powder pumping means and/or the dilution air supply within normal operating limits. The needles of the needle valves suitably engage with a needle seat arranged downstream of the needle which may be formed of any suitable material such as metal if desired.

It is preferred however that the needle of the needle valve assembly be formed of a resilient material and be supported sealably adjacent its tapered end by an 0-ring which may deform to permit lateral displacement of the tapered end of the needle whereby the tapered end may self align within the complementary air passage which is adjusted by advancement or retraction of the tapered end of the needle relative thereto. It is also preferred that the air passage is formed in a resilient body or insert such that effective sealing of the air passage may be provided by advancing the needle into full engagement therewith to prevent backflow during cleaning operations and the like. In another aspect this invention resides broadly in powder supply apparatus including:- a body having an outlet passage through which powder may be supplied? a venturi inlet to said outlet passage; an inlet passage adapted for connection to a suction tube or the like supported within a powder container and through which powder may be delivered to the body and communicating with the outlet passage about the venturi inlet; an air jet passage through the body whereby a relatively high velocity air jet may be directed into said venturi inlet to cause supply of powder through said outlet passage; an air supply inlet for admitting air to the air jet passage and an adjustable needle valve associated with said air supply inlet whereby the air delivered therethrough may be adjusted. It is also preferred that the body incorporate a further air supply passage for providing dilution air to the air outlet passage and suitably the dilution air passage is associated with a further needle valve whereby the airflow therethrough may be adjusted.

Preferably the air outlet passage supports a removable insert through which powder is delivered through said outlet passage and said insert providing the venturi inlet and a mixing chamber from which dilution air may be supplied to the powder delivery passage within the removable insert. A further adjustable air supply may be provided for supplying fluidising air to the powder container. This may be in the form of a needle valve controlled supply or otherwise as desired.

It is also preferred that the body of the powder supply apparatus is formed of a plastics material and preferably a polyethylene material whereby the resilient needle valve seats may be constituted by the ends of the air passages adjacent the respective needles. In yet another aspect this invention resides broadly in powder coating apparatus including:- a body a venturi type powder pump in said body for pumping powder from a powder container; manually adjustable valve means in said body for adjusting the air supply to said powder pump; a dilution air supply to the pumped powder, and manually adjustable valve means in said body for adjusting the dilution air supply;

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical embodiment of the invention and wherein: FIG. 1 illustrates powder coating apparatus according to the present invention and

FIG. 2 is a sectional view of the integrated control valves and powder pump utilising the embodiment of FIG. 1.

As shown, the powder coating apparatus 10 includes a frame assembly having a base plate 11 and a central stem 12 which supports an elevated control console 13. The stem 12 extends beyond the console 13 to form a handle 14. Directly beneath the console 13 and supported by the base 11 are two powder containers 15 and 16. The front panel of the control console 13 includes an on/off control 18, a voltage control 19 and a pair of controls 20 and

21 which may be rotated to vary the quantity of the powder pumped from the associated powder gun 22 and the quantity of dilution air added to the pumped powder stream. The back panel of the control console supports a hose connection 23 for the powder gun and a fluidising air connection 24 as illustrated in Fig 2. In addition the control console 13 provides air supply connections 25 and 26 for admission of the required compressed air. A drop tube 27 connects the console to the container 15. A solenoid valve controlled by the trigger of the spray gun 22 controls supply of air to the air pump and dilution air.

The controls 18 and 19 are associated with an electronic circuit supported at one er of the console 13 and having an output lead 28 which is connected to the gun whereby a probe mounted at the tip of the gun and in the powder stream is polarised to cause adherence of the powder to the workpiece which is earthed. The other end of the console 13 supports the rectangular block which constitutes the integrated control valves and powder pump 29 illustrated diagrammatically in FIG. 2 and referred to herein as the integrated unit 29.

Referring specifically to FIG. 2 it will be seen that the integrated unit 29 comprise three adjustable valve assemblies 30, 31 and 32 which control the supply of air to the powder pump assembly 33, the dilution air inlet 34 and the fluidising air connection 24 respectively.

As illustrated, the integrated unit 29 is formed by machining or moulding a plastics block 39 of rectangular solid form and suitably polyethylene, to provide air galleries for supplying air to the respective valve assemblies. The air galleries include a first gallery 36 communicating with the plug-in air supply connection 25 and the chambers of the valve assemblies 30 and 37 , a second gallery 38 communicating with the outlet of valve 31 and the dilution air inlet 34 and a third gallery 40 communicating with the plug-in air inlet connection 26 and the fluidising air connection 24.

The body 39 is also provided with a cylindrical chamber 41 opening to the underside thereof and into which the drop tube 27 may be plugged. The upper end of the cylindrical chamber 41 extends about the inner end of a venturi tube 42 which pushes sealably into the inner end of an externally protruding plug-in insert 43 which constitutes the outlet connection to the powder delivery hose for the powder gun 22. The insert 43 includes a shoulder 44 which locates it within the body 39, pair of external 0-ring seals 45 and an intermediate waisted portion 46 which communicates with the bore of the insert 43 through passageways 48. The venturi tube 42 is also provided with a pair of external O-rings 50 which engage sealably within the bore of the insert 43 and a reduced diameter end portion 51 which extends forwardly of the 0-ring seals 50 and beyond the waisted portion 46 so that the dilution air can be supplied to the pumped powder in the annular chamber between the extension portion 51 and the bore of the insert 43 prior to mixing with the pumped powder. The venturi tube 42 is preferably made of teflon and the insert 43 is suitably made from delrin. A small diameter jet passage 52 extends from the tapered valve seat 53 of the first valve assembly 30 into the cylindrical chamber 41 arranged oppositely and concentrically aligned with the bore of the venturi tube 42. The latter suitably has a cylindrical bore diameter of six point three five millimetres [6.35mm] and the jet passage 52 has a bore of one point six millimetres [1.6mm] and the arrangement is such that a jet of high velocity air passing through the jet passage 52 passes into the chamfered end of the cylindrical venturi bore causing a pressure reduction in the cylindrical chamber 41 and powder to be pumped up through the drop tube 27 and through the insert 43 for supply to the hand gun 22 through the associated hose.

A needle assembly 58 controls the flow of air through the valve seat 53 of the valve assembly 30 whereby it may be used to control the flow of powder pumped to the hand gun 22. A similar needle assembly 59 controls flow of air through the valve seat 60 communicating with the gallery 38 which supplies dilution air to the waisted portion 46 of the insert 43.

Each needle assembly 58, 59 is formed from a plastics material or metal,if desired, and threadedly engages with a respective insert 61 screwed into the body 39. An 0-ring seal 62 supports the leading end of each needle valve sealably within the inner end of the respective passage 63 v.ithin which the needle assembly 58, 59 is supported such that their tapered ends may be moved to and from the respective valve seat 53, 60 by rotation of the respective finger knob 64. The combination of the plastics needle supported at its leading end by a resilient O-ring enables misalignment between the tapered ends and the respective valve seats to be accommodated by both deflection of the valve member and the resilient O-ring seal/support. Thus wider manufacturing tolerances are permitted without detraction of the performance of the apparatus. Furthermore, the threaded shank of each needle valve is such that one turn of the finger knob 64 will permit adjustment of the flow rate of air through the passage 52 sufficient to vary the rate of delivery of powder to the gun 22 of between 0 to 30 kg per hour, at an air supply of 50 psi at the inlet 37 which is supplied by an external air regulator. A similar adjustment is provided for the dilution air.

Such coarse adjustment permits the cause and effect relationship between adjustment of the valves and quantity/ratio of powder/air mix supplied from the gun 22 to be readily apparent to an operator. Thus it permits an operator to readily achieve the desired quantity ratio of powder/air mix sprayed from the gun 22. In this respect it is considered that the proportion of the diameter of the jet passage 52 to the cylindrical venturi passage 53 in the range of 0.2 to 0.3 achieves optimum efficiency.

The fluidising air is controlled by a screw-in valve member 70 which is self threaded through a passage in the block 39 such that it may be advanced or retracted across the side passage 71 through which air is passed to the outlet 24. The self threading of the valve member 70 effects a seal between the needle and the block 39 such that further sealing measures are not necessary. The outer end of the valve member 70 is slotted to permit screwdriver adjustment thereof. Normally the valve member 70 is set for the more common types of powders and is only adjusted to suit different type powders as required.

Barbed plugs are utilise to lock gallery ends as illustrated.

From the above it will be seen that the integrated unit 29 provides a powder pump and fluidising air supply which is simple to manufacture, easy to operate and of small size whereby powder coating apparatus may be provided in a small compact assembly and without a plurality external pressure regulators which are expensive and vulnerable to damage. Furthermore, the procedure for cleaning of the equipment between colour changes is simplified as fewer connections have to be disconnected, cleaned and re-connected.

For cleaning the needle assemblies 58 and 59 are fully closed j sealing against the resilient material from which the block is formed- The insert 43 together with the venturi tube 42 are withdrawn and cleaned and the drop tube 27 is released permitting air blast cleaning of the galleries without contamination upstream of the needle valves. After cleaning the parts are readily re-assembled ready for use.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is defined in the appended claims.

Claims

THE CLAIMS DEFINING THIS INVENTION ARE AS FOLLOWS:-

1. Powder coating apparatus having a venturi type powder pump for pumping powder from a powder container and manually adjustable valve means in the air supply line to the powder pump, said valve means providing relatively coarse adjustments of the air supply within normal operating limits.

2. Powάar coating apparatus including:- a body a venturi type powder pump in said body for pumping powder from a powder container; manually adjustable valve means in said body for adjusting the air supply to said powder pump; a dilution air supply to the pumped powder, and manually adjustable valve means in said body for adjusting the dilution air supply;

3. Powder coating apparatus as claimed in claim 1 or claim 2 and including a dilution air supply to the pumped powder, wherein said dilution air supply includes manually adjustable valve means providing relatively coarse adjustments of said dilution air supply between normal operating limits.

4. Powder coating apparatus as claimed in any of the preceding claims and including a further adjustable air supply for supplying fluidising air to the container from which powder is to be pumped and said adjustable fluidising air supply includes manually adjustable valve means providing relatively coarse adjustments of said fluidising air supply between normal operating limits.

5. Powder coating apparatus as claimed in any of the preceding claims, wherein said manually adjustable valve means is a needle valve assembly.

6. Powder coating apparatus as claimed in claim 5, wherein said needle valve includes an adjusting knob or lever which may be rotated between one half to two turns to achieve adjustment between normal operating limits.

7. Powder coating apparatus as claimed in claim 5 or claim 6, wherein the or each said needle valve includes a tapered needle which engages with a needle seat downstream of the needle.

8. Powder coating apparatus as claimed in any one of claims 5 to 7, wherein the needle of the or each needle valve assembly is formed of a resilient material and is supported sealably adjacent its tapered end by an O-ring which may deform to permit lateral displacement of the tapered end of said needle.

9. Powder coating apparatus as claimed in one of the preceding claims, wherein the or each said valve means are formed in a common resilient plastics body.

10. Powder coating apparatus as claimed in any one of the preceding claims, wherein said venturi type pump includes a venturi throat and spaced therefrom and in substantially axial alignment therewith an air jet passage having a circular bore less than two millimetres diameter.

11. Powder coating apparatus as claimed in claim 10, wherein said bore is approximately one point six millimetres diameter and said venturi throat is approximately six point three five millimetres diameter.

12. Powder supplying apparatus including:- a body having an outlet passage through which powder may be supplied; a venturi inlet to said outlet passage; an inlet passage adapted for connection to an inlet tube or the like supported within a powder container and through which powder may be delivered to said body and communicating with said outlet passage about said venturi inlet; an air jet passage extending through said body whereby a relatively high velocity air jet may be directed into said venturi inlet to cause supply of powder through said outlet passage; an air supply inlet for admitting air to said air jet passage, and an adjustable needle valve associated with said air supply inlat whereby the air delivered therethrough may be adjusted.

13. Powder supplying apparatus as claimed in claim 12, including a further air supply passage for providing dilution air to said air outlet passage and a further needle valve assembly for adjusting supply of air through said further air supply passage.

14. Powder supplying apparatus as claimed in claim 12 or claim 13 wherein said air outlet passage supports a removable insert through which powder is delivered through said outlet passage, said insert forming said venturi inlet and a mixing chamber from which dilution air may be supplied to the powder delivery passage.

15. Powder coating apparatus as claimed in claim 2, including a further adjustable air supply in said body for supplying fluidising air to the container from which powder is to be pumped.

16. Powder coating apparatus as claimed in claim 15, wherein the or each said manually adjustable valve means is a needle valve assembly.

17. Powder coating apparatus as claimed in any one of the preceding claims, wherein said body is a plastics body.

18. Powder coating apparatus substantially as hereinbefore described with reference to any one of the accompanying drawings.