GB2029732A - Hot melt glue applicator - Google Patents

Abstract

A hot melt glue applicator, has a heated reservoir 10 from which glue passes along a channel 24, 25, 26, respectively in plates 15 and 16 and nozzle block 14, heated by rod 19 passing through holes 20, 21, 22. Glue passes along channel 27 to recess 28 containing gears 29, 30 constituting a gear pump. Passage of a workpiece between milled wheel 66 and back-up wheel 67 rotates wheel 66, and consequently axle 31 and gears 29, 30 of the gear pump, so that hot glue is pumped under pressure to tubes 32, 34 and thus to nozzle sockets 38, 39; the glue overcomes the pressure of spring 48 on ball 49, and issues from nozzle 47 on to the workpiece. When the workpiece ceases to rotate wheel 66, the gear pump stops, and the nozzles are closed by the spring-loaded ball valves 49 therein. Nozzle sockets 38, 39 can be blanked off as desired by plugs 40. <IMAGE>

Description

SPECIFICATION Hot melt glue applicator This invention concerns a hot melt glue applicator, that is to say a mechanical device which serves to melt glue, usually supplied in the first instance in the form of pellets, and to apply the hot glue to the surfaces of successive workpieces, which may be, for example, carton blanks made of corrugated board or like material, as said workpieces are moved successively past the applicator.

Applicators are already known in a form comprising a glue reservoir, means for heating glue in said reservoir, and having passages for receiving glue from the reservoir and feeding it to one or more nozzles each for providing a respective glue jet for application to a workpiece moved past said block, and pump means adapted to pump the glue to nozzles upon passage of each workpiece past the block.

However, the known applicator constructions suffer from a number of practical disadvantages of which probably the most important is the fact that they almost invariably drip glue, principally at their nozzles. This constant dripping of hot glue is the source of many operational problems. The glue sets upon contacting cold metal and consequently can build up in various locations on the machine.

The resultant glue accumulations can result in deflection of the workpieces passing through the applicator and consequential jamming and/or breakdown of the applicator.

An object of this invention is to provide a construction of applicator as aforesaid in which this principal difficulty is minimised or obviated, and which, in its preferred embodiment, is constructed to minimise glue leakage in other locations thereof, is versatile in that it can readily be adapted for supplying glue in different directions, and has means for deriving pump drive from workpieces moving past the nozzle block in a reliable and efficient manner.

With the above-stated object in view, the present invention provides a hot melt glue applicator comprising a glue reservoir, means for heating glue in said reservoir, a nozzle block secured to said reservoir and having passages for receiving glue from the reservoir and feeding it to one or more nozzles each for providing a respective glue jet for application to a workpiece moved past said block, and pump means adapted to pump the glue to the nozzles upon passage of each workpiece past the block, characterised in that the or each said nozzle incorporates a respective pressure-responsive valve which closes the nozzle and prevents glue passage therethrough upon pressure relaxation occurring when the pump discontinues pumping, when no workpiece is passing the block.

For ease of manufacture and economy of cost, each said nozzle conveniently comprises a hollow body through which is a passage shaped to provide a valve seat against which a ball is spring loaded. The ball, with its spring loading it against the valve seat, serves, of course, as the pressureresponsive valve which opens automatically to permit hot glue to pass upon the pump pumping the glue to the nozzle but closes substantially instantaneously upon the pump stopping.

Where only a single nozzle or single row of nozzles is provided in the nozzle block, the glue jet or jets can, of course, be directed in one direction only. To enable the glue to be directed, as desired, in one or both of two directions, the nozzle block is preferably in the form of a substantially rectangular block having, in each of two adjacent faces, a respective row of openings to which glue is pumped by the pump, at least some of the openings being fitted with respective ones of said nozzles and the rest of the said openings being blanked off with respective blanking plugs, whereby the glue jets can be directed selectively in one or both of two directions at right angles to one another.

These directions are, conveniently, respectively vertical and horizontal; the nozzle block is then preferably reversible in its disposition so that the glue jets can be directed selectively upwardly and/or horizontally, or downwardly and/or horizontally.

The pump may advantageously be a gear pump, since such a pump lends itself conveniently to being driven directly from a workpiece moving past the block, for instance by means of a double serrated wheel disposed to be engaged by the workpiece as it moves past the block.

This double serrated wheel may then be provided upon a spindle which is sealed relative to the block by an O-ring which prevents hot glue from passing from the pressure side of the pump to the drive side which is open to atmosphere.

The invention will be described further, byway of example, with reference to the accompanying drawings, in which:~ Fig. 1 is an exploded perspective view illustrating the principal components of a preferred embodiment of the hot melt glue applicator of the present invention; Fig. 2 is an enlarged perspective view, comparable with Fig. 1 but showing the parts of the nozzle block and pump of the applicator of the embodiment of Fig. 1 in the assembled condition; and Fig. 3 is an enlarged fragmentary crosssectional view illustrating the construction of one of the nozzles of the applicator of Figs. 1 and 2.

The illustrated preferred embodiment of the hot melt glue applicator of the invention comprises a glue reservoir, indicated generally by the reference numeral 10, substantially rectangular in plan and accommodating an electrical immersion heater element (not visible) and associated thermostat (also not visible) and having appropriate means, in the form of lateral lugs 1 1, 12, for enabling it to be mounted in an appropriate disposition on a cartonmaking machine or other form of apparatus requiring workpieces (such as carton blanks) to be glued.

Secured to the lower part of one sidewall of the reservoir 10 is a mounting piece 13 which serves as a mounting for a nozzle block which is indicated generally by the reference numeral 14 with a carrier plate 1 5 and a spacer 16 interposed therebetween, an end plate 17 being disposed at the end of the block 14 remote from the reservoir 10. The mounting piece 13 is bored substantially centrally at 18 to accommodate a heattransmitting rod 19 which projects out of the reservoir 10, through a hole 20 in the carrier plate 15, a registering hole 21 in the spacer 16 and a hole 22 in the nozzle block 14, and alongside this hole 18 is a supply passage 23 for hot glue to flow from the reservoir through registering apertures 24, 25 in the carrier plate 15, and the spacer 16 and into a feed passage 26 through the block 14.

The feed passage 23 connects with a channel 27 in the end face of the block 1 4 remote from the reservoir 10 which in turn communicates with a kidney-shaped recess 28 which accommodates a gear pump comprising meshing gear wheels 29 and 30, of which the gear wheel 29 is provided upon a long spindle 31 which extends through a respective bore 32 right through the block 14. The other gear wheel 30 is provided upon a short spindle 33 which is accommodated in a respective blind bore 34 in the block 14. An outlet from the gear pump comprises a passage 35 intersected by a metering valve opening 36 accommodating a valve needle 37 and leading to a pair of galleries (not visible) in the block 14, with which connect respectively a first row of nozzle apertures 38 which are upwardly directed and a second row of nozzle apertures 39 which are horizontally directed.

In the illustrated case, all of the upwardlydirected nozzle apertures 38 are fitted with respective blanking plugs 40. Three of the horizontal nozzle apertures 39 are blanked off with respective blanking plugs 40 whilst the remaining one of said apertures 39 is, as shown in Fig. 3, fitted with a nozzle which is indicated generally by the numeral 42. It will readily be understood, however, that each one of the apertures 38 and 39 may selectively be fitted with a respective blanking plug 40 or nozzle 42 as may be dictated by the manner in which glue is required to be applied to workpieces using the applicator.

As can be seen from Fig. 3, each said nozzle 42 comprises an externally-threaded tubular body 43 having a hexagonal flange 44 whereby it can be screwed into its respective nozzle aperture. A passage 45 through the body 43 is shaped to provide a valve se'at 46, and is internally threaded to accommodate a nozzle sleeve 47 serving to locate a spring 48 against a ball 49 to load the latter against the seat 46. A jet aperture 50 is provided in the outer end of the sleeve 47.

The nozzle block 14 is secured in place by a pair of bolts 51 extending through respective bolt holes 52, 53, 54 and 55 respectively in the end plate 17, the nozzle block 14, the spacer 16 and the carrier plate 15, these bolts engaging into respective fixing holes 56 in the mounting piece 13 and serving to contribute to holding the end plate 17 in position on the end of the nozzle block 14 and closing off the feed passage 26, channel 27 and recess 28 of the gear pump. A third bolt 57 extends through respective bolt holes 58, 59 and 60 and engages into its own threaded hole 61 in the mounting piece 13 to contribute to the securement of the block 14 in place, but this bolt 57 does not extend through the end plate 17.

Three studs 62 through holes 63 in the end plate 17 and engaging into respective holes 64 in the block 14 contribute to holding the end plate 17 in place.

For sealing the long spindle 31 relative to the block 1 4, adjacent the end of the spindle 31 remote from the gear wheel 29, where said end protrudes from the block 14, a circumferential groove (not visible) is provided to receive and accommodate an O-ring 65 of heat-resistant resilient plastics material, such as that commercially available under the Registered Trade Mark VITON, which engages resiliently with the spindle 31 and accordingly prevents escape of glue along the spindle 31. At said protruding end, a double serrated drive wheel 66 is fixed to the spindle 31 and this wheel 66 is disposed alongside a grooved back-up or guide wheel 67 rotatably mounted upon a bearing sleeve 68 secured to the carrier plate 15 by a respective bolt 69 extending through a slot 70 and engaged by a washer 71 and nut 72.It will readily be understood that the slot 70 enables the back-up or guide wheel 67 to be adjusted towards or away from the double serrated drive wheel 66 to vary the width of the nip therebetween, according to the thickness of the material of a workpiece (not shown) required to have glue applied thereto as will be described in detail shortly. An alternative slot 73 is provided for enabling the back-up or guide wheel 67 to be mounted in a corresponding alternative position. A guide plate 74, for guiding the workpiece to the nip aforesaid, is fixed to the carrier plate 15 above the back-up or guide wheel 67 by studs 75 through respective slots 76 engaging into holes 77 in the plate 15, which is provided with alternative holes 78 for correspondingly mounting the guide plate 74 when the back-up or guide wheel 67 is mounted in its alternative position by the slot 73.

The mode of operation of the applicator will readily be understood from the foregoing description. In the illustrated case, a workpiece, requiring to have a single line or stripe of glue applied thereto, is fed to the nozzle block, to move therepast, by being forwarded over the guide plate 74 to the nip between the double serrated drive wheel 66 and the back-up or guide wheel 67 whereafter it moves past the nozzle 42. This movement of the workpiece rotates the drive wheel 66 to operate the gear pump, thereby to ensure that hot glue, coming from the reservoir 10, is supplied as a jet by the nozzle 42 onto the desired region of the workpiece.The pressure of the glue from the pump deflects the ball 49 from the seat 46 to permit passage of the glue to and through the aperture 50, the ball 59 and spring 48 serving, therefore, as a pressure-responsive valve which, of course, closes against the seat 46 to shut-off the glue supply as soon as the pump stops and the pressure of the glue correspondingly relaxes. Accordingly, the glue is prevented from dripping or leaking, when there is no workpiece passing the nozzle block 14.

Of course, in the illustrated case there is only one nozzle 42 in the nozzle openings 39, but of course any selected ones of the openings 39 can be fitted with respective nozzles to provide corresponding glue jets as may be required. Also, respective nozzles 42 can be provided as may be required in the openings 38 in the place of the corresponding blanking plugs 40, in which case the back-up roller 67 and guide plate 74 will be moved to their described alternative positions. The workpieces are then moved generally in a horizontal path over the nozzle block 14 to have glue jets applied thereto in an upward direction from below.

In the illustrated case, the arrangement is such that glue jets can be obtained in the horizontal direction and/or in the upward direction. By appropriately inverting the mounting piece 13 and with it all of the components mounted thereon, one obtains the situation wherein the nozzle block 14 is inverted as compared with what is shown, so that horizontal and/or downward glue jets can be obtained. This facility enables the applicator to be set up appropriately in relation to other apparatus, e.g. machinery by which the workpieces are supplied to the applicator and/or subsequent apparatus (e.g. a packaging machine or a filling machine) for receiving the workpieces after glue application thereto.

The principle of applying hot melt glue using a direct gear drive pump is known and is used extensively in the field of packaging machinery.

However, as previously mentioned, the various forms of equipment produced to date have built-in problems particularly when they are arranged to fire downwards onto a moving surface since they cannot be instantly shut off because any non return valve present in the equipment is built into the gear pump itself. In the applicator of the invention, the non-return valve or pressure responsive valve is provided as part of and built into each nozzle 42, thus providing for the glue applicator to have instant shut-off. Each nozzle also serves as a non-drip nozzle when the hot melt glue applicator is jetting glue horizontally onto a workpiece which is moved past the glue applicator in the vertical direction; they also serve as a nondrip nozzle when the applicator is jetting in a vertical plane onto the underside of a workpiece which is passing the glue applicator in the horizontal plane.Each nozzle 42 works on the principle that when the gear pump drive wheel 66 turns by being in contact with the workpiece as this passes the block 14, the pump builds up a pressure in the hot melt glue sufficient to enable the glue to push the ball 49 from its seat 46 and compressing the spring 48. With the ball 49 off the seat 46, the glue will flow through the spring 48 and out through the aperture 50. If the drive wheel 66 ceases to make contact with the passing workpiece, the spindle 31 and hence the gear pump, stops turning. Immediately there is a drop in pressure, the spring 48 pushes the ball 49 back into its seat 46 thus stopping the flow of any further glue from the applicator. The nozzles 42 will remain closed until such times as a workpiece, moving past the block 14, again makes contact with the drive wheel 66.This instant shut-off or non-drip nozzle arrangement is particularly important and effective, since it eliminates the described difficulties attendant upon glue dripping in the known arrangements. The spindle 31 is a critical part in the gear pump in that it has one end carrying the gear wheel 29 within the recess 28 and the other end is outside the block 14 and is fitted with the drive wheel 66 which is rotated by surface contact with each workpiece as it is passed by the applicator. In simple terms each workpiece itself, as it passes by the applicator, provides the driving force for the pump to build up pressure. The position of the seal and the type of seal used on the spindle 31 is also important, the O-ring 65, positioned as described, providing a good effective seal forthe spindle 31.

Packaging material required to be glued is very often of corrugated board which is composed of a flat sheet of liner material, a corrugated fluate material and a flat sheet of facer material. The back-up roller 67 serves to press such corrugated board against the serrated drive wheel 66 causing the wheel 66 to dig into the board surface. As the corrugated board is drawn past the hot melt glue applicator the serrated wheel 66 is made to revolve, thus providing the main driving force for the glue applicator gear pump. If the drive wheel 66 were provided with only a single narrow-faced serrated edge the wheel could run into a valley in the corrugated fluting medium, so that the serrated wheel might then have too little surface friction to drive the gear pump efficiently. This problem is overcome with the illustrated double helical serrated wheel 66.This double helical serrated wheel 66 has two narrow contact faces spaced a sufficient distance apart to ensure, that at any one time, one edge surface or the other of the wheel will be running on a ridge or peak of the corrugated board fluting medium. The double helical serrated wheel is therefore a further important feature of the preferred embodiment of the applicator of the invention.

The edges of the serrated wheel 66 of the applicator should either be sufficiently sharp so as to dig into the surface of the material to be glued or alternatively should have a covering with sufficiently high coefficient of friction so as to be driven by the material to be glued, since, of course, the glue applicator is suitable for applying hot melt glue to a variety of surfaces such as corrugated board, solid board, carton board, plastics, rubber, laminates, cloth and foil combination materials.Accordingly, if desired the drive wheel 66 can be of different form from what is described and may be of mild steel, high carbon steel or steel with hard tipped surfaces; or it may be of standard roller form with a surface of mild steel, or carbon steel in plain or knurled finish, or it may be a plain roller with covering in rubber, in neoprene, nylon, Formica (Registered Trade Mark), aluminium or combination materials, again with a plain or knurled finish.

The construction of the nozzle block 1 4 in the described embodiment of the applicator is of particular importance. There are, in the illustrated case, two sets of nozzle apertures 38 and 39, disposed at 900 to each other and each having four apertures. The number of such apertures can vary from one to ten depending on how many glue outlets are required on the applicator, and each aperture will be fitted with a respective blanking plug 40 if no glue is required from that particular outlet or a respective non-drip nozzle 42 if it is required that glue should be supplied through the particular aperture. Under normal running conditions one complete.set of the nozzle apertures will be blanked off and only the other set of apertures, at 900, or some of them will be used.

The reason for having two sets of the outlet apertures at 900 to each other is, as previously mentioned, to allow the glue applicator to be set up to supply glue as desired either through the horizontal apertures 39 onto the surfaces of workpieces passing in a vertical plane past the glue applicator, or through the vertical apertures 38 onto the undersides of workpieces passing in a horizontal plane past the glue applicator.

An advantageous feature is the positioning of the hole 18 for the heat-transmitting rod 18 and the glue supply passage 23 with their axes on a common horizontal plane. Because of this, the nozzle block 1 4 can be released, turned through 1 800 and reassembled to the reservoir 10 in an upside-down disposition compared with its illustrated position, using an appropriately modified end plate 17 and spacer 16, so that the applicator is then set up for supplying glue either downwards through the nozzle apertures 38 onto workpieces passing the glue applicator in a horizontal plane, or horizontally through the nozzle apertures 39 onto workpieces passing in a vertical plane past the applicator.The provision of the sets of nozzle apertures at 900 to each other and the provision of the hole 18 and glue supply passage with their axes on a common horizontal plane accordingly give substantial advantages.

The illustrated configuration of the glue reservoir 10 is also advantageous. It is made, for example, of cast aluminium and has the two lugs 11, 12 across its width for support, and the mounting piece 13 which serves for the mounting of the block 14 and associated components. The two lugs 11, 12 can be machined to give foot mounting with support in each corner of the reservoir 10 or alternatively they can be machined parallel to the side faces to enable the reservoir 10 to be trunnion mounted. With trunnion mounting, it is possible to incline the complete applicator and hence the block 14 as may be desired or convenient in relation to the direction of approach of workpieces to be glued.

There may be, in the reservoir 10, a number of cast fingers (not visible) which help to distribute heat evenly through the glue, which may be initially in the form of pellets. The symmetrical shape of the reservoir, and the machined location of the glue supply passage 23 allow the same casting to be used for a right hand glue applicator assembly or a left hand glue applicator assembly, as may be desired, by providing, in the bottom of the reservoir, two outlet positions one of which is blanked off and the other of which is used to supply glue to the nozzle block 14. To change from a left hand applicator to a right hand applicator one of the bottom ports is fitted with a full depth plug while the other part is fitted with a half depth plug which allows the flow of glue into the required passages.To change over from a left hand glue applicator to a right hand glue applicator the respective plugs are changed over.

To control the volume of glue that is ejected by the operative nozzle or nozzles recycling capillary (not visible) is drilled into the block 14 to allow glue to pass from the exit side of the gear pump recess 28 back to the inlet side of said recess. The valve needle 37 has a tapered end which projects into the recycle passage. Setting of the needle 37 allows adjustment of the amount of glue recycling through the pump, with the remainder passing to the outlet nozzles.

A drain outlet (not shown) having a capping plug 77 may be provided for permitting draining of glue from the passages in the nozzle block 14.

The illustrated form of the carrier plate 15 is of practical significance. As already described, this plate 15 has therethrough the slots 70 and 73 which extend respectively in the vertical direction and the horizontal direction, and serve for the fitting of the back-up or guide wheel 67 which ensures that workpieces, being glued, engage with the drive wheel 66. The slots enables the back up wheel 67 to be adjusted in or out to accommodate different thickness of material to be glued. If the workpieces to be glued are travelling past the glue applicator in the horizontal plane, the back up wheel 67 is positioned in the vertical slot 73. If the workpieces are passing the glue applicator in the vertical plane the back up wheel 67 is fitted in the horizontal slot 70. The guide plate 74 is, of course, correspondingly positioned when the back-up wheel is changed over.

Claims (9)

1. A hot melt glue applicator comprising a glue reservoir, means for heating glue in said reservoir, a nozzle block secured to said reservoir and having passages for receiving glue from the reservoir and feeding it to one or more nozzles each for providing a respective glue jet for application to a workpiece moved past said block, and pump means adapted to pump the glue to the nozzles upon passage of each workpiece past the block, characterised inthatthe or each said nozzle incorporates a respective pressure-responsive valve which closes the nozzle and prevents glue passage therethrough upon pressure relaxation occurring when the pump discontinues pumping, when no workpiece is passing the block.

2. A hot melt glue applicator as claimed in claim 1 wherein each said nozzle comprises a hollow body through which is a passage shaped to provide a valve seat against which a ball is spring loaded.

3. A hot melt glue applicator as claimed in claim 1 or 2 wherein the nozzle block is a substantially rectangular block having, in each of two adjacent faces, a respective row of openings to which glue is pumped by the pump, at least some of the openings being fitted with respective ones of said nozzles and the rest of the said openings being blanked off with respective blanking plugs, whereby the glue jets can be directed selectively in one or both of two directions at right angles to one another.

4. A hot melt glue applicator as claimed in claim 3 wherein the said directions are respectively vertical and horizontal.

5. A hot melt glue applicator as claimed in claim 4 wherein the nozzle block is reversible in its disposition so that the glue jets can be directed selectively upwardly and/or horizontally, or downwardly and/or horizontally.

6. A hot melt glue applicator as claimed in any preceding claim wherein the pump is a gear pump adapted to be driven by a workpiece moving past the block.

7. A hot melt glue applicator as claimed in claim 6 wherein drive means for the gear pump comprises a double serrated wheel disposed to be engaged by the workpiece as it moves past the block.

8. A hot melt glue applicator as claimed in claim 7 wherein the double serrated wheel of the gear pump is provided upon a spindle which is sealed relative to the block by an O-ring which prevents hot glue from passing from the pressure side of the pump to the drive side which is open to atmosphere.

9. A hot melt glue applicator substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.