GB2177940A - Discharging drops or a jet of a fluid medium - Google Patents

Abstract

In a method of intermittently discharging a liquid medium, e.g. an adhesive, the medium is supplied from an inlet (46) under constant pressure to a prechamber (40). A compressed gas is supplied both to an outlet chamber (38) adjacent the pre-chamber via duct (66), annular path (70), and passage (72), and to a chamber below a diaphragm (28). The gas pressure is varied between a lower pressure enabling the medium to flow from pre-chamber (40) into the outlet chamber (38), and a higher working pressure which closes the diaphragm against the nozzle and prevents the medium from thus flowing and expels it from the outlet chamber (38) through the nozzle (32). An alternative embodiment (Figure 3 not shown) dispenses with the diaphragm but employs a liquid reservoir and an associated overflow wall. <IMAGE>

Description

SPECIFICATION A method and device for discharging drops or a jet of a fluid medium The invention relates to a method for discharging drops or a jet of a fluid medium, more particularly an adhesive, through a nozzle system to which the medium is supplied at a substantially constant presssure.

It is very difficultto discharge certain media through a nozzle system ifthey change in consistency after a certain time or under external influences, and e.g. become viscous or actually solidify. This particularly applies to numerous adhesives. The re su It is that if the discharge is interrupted owing to maintenance or the production process, the nozzle passages become blocked or the control and valve elements for controlling the discharge become stuck.

In such cases the discharge processes must either be continuous or complicated precautions must be taken to preventthe discharge devicefrom sticking while inoperative.

The object of the invention is to devise a method of the initially-mentioned kind for reliably preventing the discharge device from becoming blocked if the discharge process is interrupted.

To this end, according to the invention,the medium is supplied to a pre-chamber ofthe nozzle system, a compressed gas is supplied to an outlet chamber adjacent the pre-chamber in the flow direction, and the pressure ofthe compressed gas is varied between a wake pressure enabling the medium to flow out of the pre-chamber into the outlet chamber and a working pressure preventing the medium from flowing out and driving the medium out of the outlet chamber through the nozzle, the working pressure being higherthan the wake pressure.

By means of the inventive process, the medium can be discharged from the nozzle system without mechanically moving parts. Also, the compressed gas can continuously blow the outlet chamber and opening or the outlet duct ofthe nozzle system clear, both during the periodic interruptions in a discharge brought about by periodic changes in pressure, and during other interruptions in the discharge. In the case of a medium which e.g. sets or solidifies in air, the compressed gas can be an inert protective gas which permanently flows out of the outlet chamber and nozzle system and prevents airfrom entering it.

A compressed-gas column can easily be controlled with periodic variation in the gas pressure, even at high frequencies. In this manner, depending on the consistency of the discharged medium, the form of discharge can be varied practically at will between individual drops and a substantially continuous jet.

The time during which the gas pressure is reduced to the wake pressure will determine the amount of medium flowing out ofthe pre-chamber into the outlet chamber. During the subsequent pressure increase a pressure peak can initially be produced so as to hurl the medium in the outlet chamber through the outlet duct of the nozzle system, before the pressure falls to a retaining pressuresufficientto preventthe medium from flowing from the pre-chamber into the outlet chamber.

The invention also relates to a deviceforperforming the previously-described method and comprising a casing having at least one nozzle system and a medium inlet for connecting to the outlet duct ofthe nozzle system.

According to the invention, the device is characterised in that at least one pre-chamber and at least one outlet chamber are disposed in the flow path between the medium inlet and the outlet duct of the nozzle system, the chambers being separated by a wall having at least one overflow opening, and the outlet chamber is connected to a compressed-gas inlet in the casing, which is connectable to a com pressed-gas source at a periodically variable pres- sure. A number of pre-chambers parallel to one another can be associated with an outlet chamber.

Alternatively a number of pre-chambers can be disposed behind one another in the flow direction,to avoid uncontrolled flowing back of media into the outlet chamber.

In order accuratelyto control the amountflowing from the pre-chambertotheoutletchamberduring the relatively low wake pressure, advantageouslythe overflow opening is at least partly bounded by a rim comprising a sharp edge,the sharp edge being formed bytwo sides of the rim meeting atan acute angle. This embodiment is particularly useful for somewhat viscous media, in that the flow offluid breaks away immediately the gas pressure is raised, so that the amount flowing over can be exactly determined. The precise shape of the rim cross-section, however, will depend on the consistency ofthe medium.It may also be advantageous to have a rounded rim cross-section our a step instead of a sharp edge. Care must always betaken to preventthe medium from being drawn in uncontrolled manner from the pre-chamber into the outlet chamber as a result of suction bythe compressed-gas jet.

In ordertoadapttovarying delivery amounts and varying media, the flow cross-section ofthe overflow opening is adjustable. If the pre-chamber and outlet chamber are suitably disposed, the previouslydescribed embodiment also works if the overflow opening is continuously open. In another optional embodiment of the invention, the overflow opening is blockable.by at least one resilient diaphragm at least partly bounding the pre-chamber, the side of the diaphragm remote from the outlet chamber being connected to the compressed-gas inlet If the compressed gas is at the retaining pressure,the diaphragm closes the inlet ofthe outlet chamber.If on the other hand the gas pressure is reduced, the diaphragm, owing to its own elasticity and the pressure ofthe medium, moves away from the inlet of the outlet chamber so that the medium can overflow into it.

When the pressure is increased the diaphragm is again pressed against the outlet-chamber inlet, thus closing it. The diaphragm acts not only as a conveying element but also as as closure element, and is adjusted only by pressure fluctuations and not by mechanically moving parts.

Advantageously the nozzle system comprises a releasable and therefore exchangeable nozzle member comprising the outlet duct, so that differently shaped nozzles can be used for different media or the nozzles can be cleaned more easily when necessary.

Depending on the nature of the discharged medium, it may be advantageousforall surfaces coming into contact with the medium to be coated with a difficultly-wettable material, to prevent residuesfrom accumulating.

Otherfeatures and advantages of the invention will be clearfrom the other sub-claims and thefollowing description, which explains the invention with reference to embodiments in conjunction with the accompanying drawings, in which:: Figure 7 is a plan view of a first embodiment of the device according to the invention; Figure2 is a section along line li-ll in Figure 1; Figure 3 is a section corresponding to Figure 2 through a second embodiment ofthe invention; Figure4is a section along line IV-IV in Figure 3; Figure 5is a plan view of a third embodiment ofthe device according to the invention; Figure 6is a section along line VI-VI in Figure 5 and Figure 7is a pressure-time diagram showing the variation in the pressure ofthe gas during discharge ofthe medium using the device according to the invention.

Figures 1 and 2 show a square casing (general reference 10) comprising a bottom part 12 and a top part 14. Parts 12 and 14 are interconnected by screws 16andaseal 18isclamped between parts 12and 14.

Part 12 has a cylindrical recess 20 open towards the top part 14. A tubular projection 22 extending into recess 20 projects from and is integral with the side ofthe top part 1 4facing the bottom part 12; the axial length of projection 22 is such that when parts 12 and 14 are clamped together, a disc-shaped diaphragm 28 made of resilient material can be clamped between the bottom 24 of recess 20 and the axial end surface 26 ofthe tubular projection 22. An annular space 30 is formed between the peripheral wail of recess 20 and the outer peripheral wall of projection 22 and can be used to hold a heating device, e.g. an electric heating coil, if it is necessary for the discharged medium to be kept at a particular operating temperature.

Acylindrical nozzle member 32 extends into projection 22 and is screwed coaxiallywith projection 22 in a threaded bore 34 of part 14 and extends axially to nearthediaphragm 28. Nozzle member 32 has an outlet duct 36 and an outlet chamber 38 widening like a funnel from duct 36 towards the diaphragm. The shape of the outlet chambercan be adapted to the nature and quantity of discharged media. The outer diameter of nozzle member 32 is smallerthan the inner diameter of projection 22, so that an annular pre-chamber40 is formed between parts 32 and 22 and is connected to the outlet chamber 38 by an anannular gap 42.

Bottom part 12 has a first inlet 44 for connecting to a supply pipe (not shown) for supplying the medium for discharge. Asupply duct extending from inlet 44 comprises various bores 46,48,50 in part 12 and bores 52,54,56 in part 14 and extends from the top part 14and opens into the annular pre-chamber40.

Bottom part 12 also has a second inlet 58 for connecting a compressed-gas pipe (not shown), from which two bores 60,62 lead to a flat recess 64 in the bottom surface 24 of recess 20. The recess'64 is sep arated from pre-chamber 40 by diaphragm 28. Another bore 66 in part 12 and a bore 68 in part 14form a second compressed-gasductwhich opens into an annulargroove 70 formed in nozzle member 32.

Groove 70 constitutes an annularductwhich is coaxial with the discharge duct 36 and from which at least one axially parallel bore 72 extends in nozzle member 32 and opens into the outlet chamber 38 nearthe end facing diaphragm 28.

The previously described device operates asfollows, reference also being made to the diagram in Figure 7, where the time tis plotted on the abscissa and the compressed-gas pressure P is plotted along the ordinate. After the supply line for the discharged medium and the compressed-gas line have been connected to inlets 44 and 58, compressed gas is first supplied ata pressureP20. The gas flows through bores 60,62 into recess 64 below diaphragm 28 and through bores66,68,annularduct70and bore72 into outlet chamber 38.Since the compressed gas can escape from chamber 38 through duct 36, the pressure on this side of diaphragm 28 is lowerthan in recess 64, so that diaphragm 28 is pressed upwards againstthe annular surface 74 of nozzle member 32 surrounding the outlet chamber 38, andthussepar- ateschamber38from pre-chamber40. Next, the medium for discharge is poured under pressure into pre-chamber 40 through bores 46,48,50,52,54 and 56,thesupplypressureforthemedium being adjusted relative to the compressed-gas pressure Po? so that no medium can be driven between diaphragm 28 into the outlet chamber 38.If the gas pressure is reduced to a value P1 between times t1 and t2 by a suitable control device, diaphragm 28 returns at least partly into the position shown in Figure 2,so that the medium can flow from the pre-chamber40 into the outlet chamber 38. At the time top the compressed-gas pressure is abruptly increased to a value abovethe value P0. As a result, diaphragm 28 is abruptly pressed against surface 74 of member 32, thus dis- connecting pre-chamber40 from outlet chamber 38.

Atthesametime, all the medium in-chamber 38 is driven through duct 36 by the compressed gas. This completely clears chamber 38 and duct 36 and also prevents any residues of the discharged medium from accumulating at the outlet opening of member 32. The pressure then drops from P2 back to the retaining pressure P0. This process can be periodically repeated. In the case of some media it is not necessary to raisethe pressure above the retaining pressure P0 atthetimet2. Simple square-wave control of the pressure betweenthevalues POand Pa issuf- ficient.

The following is a description of two embodiments of the inventive device operating without a diaphragm. In the embodiment in Figure 3, the casing (genera I reference 76) comprises a tubplar jacket 78 enclosing three disc-shaped parts, i.e. a bottom part 80, a middle part82 and a top part 84. Part 80 has an inlet86forconnecting a medium supply pipe and an inlet 88 for connecting a compressed-gas pipe. From inlet86, an axially parallel bore90 in the bottom part and an aligned axially parallel bore 92 in the middle part 82 iead to an annular pre-chamber 94formed in the middle part 82 and connected to bore 92 by an overflow opening 96.

From inlet 88, a bore 98 in the bottom part 80 aligned with axially parallel bores 100,102 in the middle part 82 and top part 84 respectively, and a radial bore 104 and an axially parallel bore 106 in top part 84 lead to the top or covering surface of prechamber 94.

Pre-chamber 94 is open towards the top part 84 and surrounds an attachment 108 extending from the bottom of chamber 94 and comprising a first largerdiameter portion ll0andanaxiallyadjacentsmaller- diameter portion 112, which extends into a recess 1 in part 84. A cylindrical nozzle member 120 having an outlet duct 122 is screwed into an axial threaded bore 116, the inner end of which merges into a hemispherical outlet chamber 118.

Inlet openings 126 of axially parallel ducts 128 are formed in an annularsurface 124 at right angles to the axis and connecting the outer surfaces of port ionsll0andll2.Openingsl26extendtotheunder- side of part 82 and thence through radial connecting ducts 130 and are connected to an inlet opening 132 ofthe outletchamber 118 (see also Figure4).

The annular pre-chamber94is surrounded by another annular chamber 134 adapted to receive a heating winding (or a cooling device) for heat-treating the medium to be discharged. The compressed gas flowing through bore 100 can also be pre-heated. An an nularinsulating layerl36ofheat-insulatingmaterial is also disposed at the outer peripheral surface ofthe central part 82.

The previously-described device operates asfollows, also with reference to the pressure-time diagram in Figure 7.

The surface of the medium to be discharged is at the height indicated by the broken line, as long as the retaining pressure P0 prevails. At this pressurethe compressed gas prevents the fluid from flowing from bore 92 through the overflow opening 86 on the one hand orfrom pre-chamber94intotheinletopen- ings 124 on the other hand. The compressed gas also flows through bores 128,130 and outlet chamber 118 and outlet duct 122 to atmosphere.If the pressure is reduced to the value P1 attimet1,the material fordis- charging flows out of bore 92 through opening 96 into pre-chamber 94 and thence through inlets 126, ducts 128 and 130 into the outlet chamber 118, the overflowing amount being determined by the iength ofthetimet2-t1. Atthetimet2,the pressure ofthe compressed gas is increased to P2. This abruptly stops the medium from flowing from duct 92 into pre-chamber94 and thence into the outletchamber 118. At the same time, the medium between openings 126 and duct 122 is driven out by the compressed gas. The pressure then drops back to the retaining pressure P0.This makes it easier to meterthe medium, since a sharp edge 138,140 respectively is formed atthe overflow opening 96 andthe inletopenings 126 respectively and ensures that the flow of medium is cut off or breaks down. The embodiment in Figures 3 and 4 is mainly designed for ejecting material upwards out ofthe nozzle. Notwithstanding, thedescribed device can also operate if inclined to the horizontal.

In the embodiment shown in Figures Sand 6, the casing (general reference 142) comprises a flattop part 144and aflatbottom part 146 interconnected by threaded bolts 148. The top part 144 has an inlet 150 into which the connecting mem ber 152 of a com- pressed-gas hose is screwed. A coaxial bore 154 extends from inlet 150 to the bottom part 146, which is formed with a bore 156 in ine with bore 154. A nozzle member 158 is disposed in the end portion of bore 156 remote from the top part 144.

A bore 162 extends axially parallel to and along side bores 154 and 156 and is connected thereto by an overflow opening 160. The bottom rim of opening 160, i.e. remotefrom top part 144, has a sharp edge 164formed bythewall of bore 156and a side 166 rising obliquely from bore 162 to the sharp edge 164.

Aclosure member 168 is closablyguided in thetop part of bore 162 and is axially adjustable by a screw threadedboltl70andhasaclosuretongue 172.The height of the gap between edge 164 and tongue 172 can be adjusted by moving the closure member 168.

The underside of tongue 172 has a baffle surface 174, the inclination and shape of which can be varied in accordance with the amount and consistency of the conveyed medium.

The bottom end of bore 162 forms a pre-chamber l76connected by bores 178,180 and 182toan inlet 184 in the top part 144for connecting a supply pipe for the medium to be discharged.

The device shown in Figures 5 and 6 operates in the same manner as the embodiment in Figures 2 and 3.

As long as the retaining pressure P0 prevails,thesur faceofthe mediumfordischargein pre-chamberl76 remains at the level ofthe broken line in Figure 6. If the gas pressure is reduced attimet1,the medium flows outof pre-chamber 176 over edge 164 into a space 186 forming the outlet chamber abovethe nozzle system 158 and, during the subsequent increase in pressure, is expelled by the compressed gas through the nozzle outlet duct 188, and theflow of medium from pre-chamber 176 is simultaneously interrupted. This device is mainly designed for discharging a medium on to a surface underneath the nozzle.

Acommonfeature of all three embodiments isthat the medium is metered and discharged simply by periodically varying the pressure of the compressed gas, and the respective outlet chamber and the respective nozzle outlet duct are always blown clear by the compressed gas. Consequently, when discharged ing adhesives which very easily form a skin or immediately set when exposed to air, the discharge of medium can be interrupted without it being subsequently necessaryto replace or clean the nozzle system because it has become blocked.

Claims (12)

1. A methodfordischarging drops or a jetof a fluid medium, more particularly an adhesive, through a nozzle system to which the medium is supplied at a substantially constant pressure, characterised inthatthe medium is supplied to a pre chamberofthe nozzle system, a compressed gas is supplied to an outlet chamber adjacent the prechamber in the flow direction, and the pressure ofthe compressed gas is varied between a wake pressure enabling the medium to flow out of the pre-chamber into the outlet chamber and a working pressure preventing the medium from flowing out and driving the medium out of the outlet chamberthrough the nozzle, the working pressure being higherthan the wake pressure.

2. A method according to Claim 1, characterised in that during the intervals when the medium is not being discharged, the nozzle system is blown clear bythe compressed gas.

3. A device for discharging drops or a jet of a fluid medium, more particularly an adhesive, comprising a casing having at least one nozzle system and an inletforthe medium connectable to the outlet duct of the nozzle system, characterised in that at least one pre-chamber and at least one outlet chamber are disposed in the flow path between the medium inlet and the outlet duct ofthe nozzle system,the chambers being separated by a wall having at least one overflow opening, and the outlet chamber is connected to a compressed-gas inlet in the casing, which is con nectable to a compressed-gas source at a periodically variable pressure.

4. A device according to Claim 3, characterised in thatthe overflow opening is at least partly bounded by a rim comprising a sharp edge, the sharp edge being formed by two sides of the rim meeting atan acute angle.

5. A device according to Claim 3 or4, char- acterised in that a supply duct connecting the prechamberto the medium inlet opens above the prechamber bottom through an overflowthreshold into the pre-chamber,the distance between the overflow threshold and the pre-chamber bottom being at least equal to the distance between the overflow opening and the pre-chamber bottom.

6. A device according to any of Claims 3 to 5, characterised in that the flow cross-section and/or the geometrical shape of the overflow opening is adjustable.

7. A device according to Claim 3, characterised in thatthe overflow opening is blockable by at least one resilient diaphragm at least partly bounding the prechamber, the side of the diaphragm remote from the outlet chamber being connected to the compressedgas inlet.

8. A device according to any of Claims 3 to 7, characterised in thatthe pre-chamber is constructed as an annular space surrounding an attachment containing the nozzle system and the outlet chamber.

9. A device according to Claim 8, characterised in thatthe attachment comprises a first portion adjacent the pre-chamber bottom and a second and smaller-diameter portion remote from the pre-chamber bottom,the overflow opening being formed in a transition surface joining the two portions.

10. A device according to Claim 8, characterised in that the attachment extends from the top ofthe pre-chamberto near the pre-chamber bottom and its surfacefacingthepre-chamberbottom is formed with the inletforthe outlet chamber, the bottom of the pre-chamber being at least partly formed bythe resilient diaphragm.

11. A device according to any of Claims 3 to 10, characterised in that the nozzle system comprises a releasably disposed nozzle member comprising the outlet duct.

12. A device according to any of Claims3to 11, characterised in that a heating device for heating at least the pre-chamber is disposed in the casing.