Apparatus for dispensing an adhesive

Abstract: An electromagnetic dispenser (10) for dispensing is provided with a housing for guiding and concentrating the outer axial lines of flux in specific regions and then passing them through the pole and plunger. Concentrating the lines of flux in such regions provide for a more compact dispenser, thereby allowing for smaller centerline-to-centerline spacings.

Description: This invention is directed to a fluid dispenser, such as for the dispensing fluids, such as adhesives, sealants, water and caulks. More particularly, this invention is also directed to an electromagnetically actuated fluid dispenser for dispensing heated fluid materials such as, for example, hot melt adhesives. It is common in the dispensing of adhesives to use a pneumatic actuated dispenser, whereby a supply of air is used to move a plunger in reciprocal movement, such that a shutoff needle or ball connected to the plunger or armature is moved from or moved to a seat to permit or stop the dispensing of a pressurized fluid adhesive. Electromagnetic dispensers have been developed wherein the plunger is driven open by an electromagnetic field and closed by a spring biasing means. Electromagnetic dispensers, otherwise known as (electric guns), are generally larger than standard pneumatic dispenser. This increase in size does not lend electric guns or dispensers to be readily useable in multiple configurations, such as mounting a plurality of dispensers side by side to form a bank of dispensers. In many applications, such as carton sealing, it is desirous to apply a plurality of parallel beads to a substrate on fairly close centers. However, due to the larger size of electromagnetic guns it is difficult to apply closely spaced beads of material to substrates. It therefore is desirous to produce a compact electromagnetic dispenser, which is capable of operating at fast cycle rates, and is also capable of operating in a bank of dispenser so that closely spaced apart beads of material may be dispensed onto a substrate. Centerline spacing from one gun module to the next is therefore important. If the gun modules are mounted side by side, it may be very desirous to have the centerline spacing as small as possible in order to produce beads having small centerlines. As such, it is desirable that the width of the gun modules be as small as possible. US 5,375,738 discloses an electromagnetic dispenser for dispensing viscous heated fluids, such as hot melt adhesives. A fixed pole extends from a fluid chamber. The coil is located about a portion of the fixed pole and spaced from the fluid chamber to isolate the coil from the fluid flow path of the adhesive. The coil is insulated from the heat which is conducted from the adhesive as well as provided with a heat sink for dissipating heat. A plunger is mounted within the fluid chamber for reciprocal movement therein to open and close dispensing orifice in response to the field generated by coil. US 4,443,775 discloses a solenoid actuator comprising a coil surrounded externally with a magnetic frame and having a stationary core disposed therein. US patent 3,329,347 describes an electromagnetically operated apparatus for dispensing lubricants. Inside a housing there is disposed a bore in which a lubricant can be fed through a supply line. A valve needle with a conical tip co-operates with a valve seat. A stationary pole is partly surrounded by an electromagnetic coil and co-operates with a movable plunger to move the valve needle attached to the plunger back and forth. A disadvantage of this apparatus is that the valve needle must be sealed by a dynamic seal comprising O-rings which are subject to considerable wear and wear out severely during fast, high-frequency movements of the valve needle. Another disadvantage of the known apparatus is that, due to the absence of a flux guide member with a rectangular cross-section and a through bore, on the one hand, the force for moving the plunger cannot be applied by electromagnetic means as efficiently and, on the other hand, the spacing between a plurality of adjacent apparatus is much greater because the entire apparatus requires considerably more space. The spacings between a plurality of adjacent beads would thus be significantly greater. US 4,951,917 discloses an electromagnetic valving assembly for viscous fluid material. A pole piece is attached at an upstream end of a solenoid body and is in fluid communication with a source of viscous material, such as hot-melt adhesive. An armature is reciprocatingly mounted within the flow passage way. US 5,192,936 discloses a solenoid having a bobbin with a rectangular core hole, in which is mounted an armature having a rectangular cross section, and a pole piece having a rectangular cross-section. The bobbin has an upper flange and a lower flange that encloses the ends of the coil. A tubular can is seated around the bobbin. The solenoid does not bear any relation to the technical field of adhesive dispensing apparatus. EP 0 719 592 shows a nozzle apparatus for dispensing adhesive material. A flushing liquid such as water can be introduced into a nozzle channel, in order that adhesive is flushed out of the channel before solidification of the adhesive. SUMMARY OF THE INVENTION It is an object of the invention, according to one embodiment of the invention, to provide an electromagnetic dispenser which does not require dynamic seals. This may be accomplished, for example, by providing a movable plunger which is located in a fluid chamber or bore in which the movement of the distal end of the plunger from the valve seat, does not extend beyond the fluid chamber or bore in the retracted position. Eliminating the dynamic seal eliminates a wear part which may fail. It is also an object of the invention according to one embodiment of the invention, to provide an electromagnetic dispenser which has improved performance characteristics. It is also an object of the invention to provide an electrical gun which is capable of closely mounting a plurality of gun modules in side-by-side relationship to provide improved bead-to-bead spacing. It is an advantage of this invention that improved centerline-to-centerline spacings between gun modules may be obtained by focusing or directing the lines of magnetic flux more towards the front and the back of the module's outer housing, which allows for a reduction in the width of the module. Some of these and other objects and advantages may be accomplished according to one embodiment by an apparatus for dispensing an adhesive material comprising the features of claim 1. Still further, some of these and other objects and advantages may be accomplished according to an embodiment of the invention by a method of dispensing an adhesive material comprising the features of claim 10. DESCRIPTION OF THE DRAWINGS The following is a brief description of the drawings in which like parts may bear like reference numerals and in which: FIG. 1 is a perspective view of a dispenser or gun including a gun module in accordance with one embodiment of this invention; FIG. 2 is a perspective view of a dispenser or gun including three gun modules in accordance with another embodiment of this invention; FIG. 3 is an elevational cross-sectional view of the gun modules of FIGS. 1 and 2; FIG. 4 is a partial exploded view of the gun modules of FIGS. 1 and 2; FIG. 5 is a cross-sectional view of the magnetic circuit of FIG. 6 taken substantially along line 5-5; FIG. 6 is an elementary magnetic circuit of the gun module; FIG. 7 is a cross-sectional view of the magnetic circuit taken substantially along line 7-7; FIG. 8 is a cross-sectional view of an alternate embodiment of a housing or flux guide member; FIG. 9 is a cross-sectional view of an alternate embodiment of a housing or flux guide member; and FIG. 10 is an end view of the plunger 50. DEFINITIONS The following definitions are applicable to this specification, including the claims, wherein; "Axial" and "Axially" are used herein to refer to lines or directions that are generally parallel to the axis of reciprocal motion of the plunger of the dispenser. "Inner" means directions toward the axis of motion of the plunger and "Outer" means away from the axis of motion of the plunger. "Radial" and "Radially" are used to mean directions radially toward or away from the axis of motion of the plunger. DETAILED DESCRIPTION OF THE INVENTION For the purpose of the present discussion, the method and apparatus of this invention is described in connection with the dispensing of an adhesive, including hot melt polymeric materials used in adhesive applications. Hot melt materials are those materials which are normally solid at room or ambient temperature but, when heated, are converted to a liquid state. It should be understood that the methods and apparatus of this invention are believed to be equally applicable for use in connection with the dispensing of other heated fluid materials, such as waxes, as well as those adhesives which are normally a liquid at room or ambient temperature and therefore do not require heating and are sometimes referred to as cold glue. Now, with reference to FIG. 1, there is illustrated a dispenser or gun, shown generally by reference numeral 10. The dispenser 10 includes a dispenser body, otherwise known as a gun module or valve 12, according to one embodiment of this invention, mounted to a service block 14, otherwise known as a manifold. The service block 14 has an inlet 16, capable of being coupled to an adhesive supply source (not shown) as well as internal fluid passages and an outlet for supplying the adhesive to the module 12 and further contains heaters and temperature sensors, coupled to control circuitry via conduits 18, to maintain the temperature of the hot melt adhesive within the dispenser 10. The dispenser module 12 may be mounted to the service block 14 by mounting screws 20. The module 12 receives the adhesive from the service block and in turn dispenses or applies the adhesive 22 to a substrate. While the dispenser or gun 10 of FIG. 1 utilizes only one gun module 12, a gun may utilize multiple gun modules. For example, with reference to FIG. 2, there is illustrated a gun, shown generally by reference numeral 10'. The gun 10' includes three gun modules 12A, 12B, and 12C, each identical to gun module 12 of FIG. 1, mounted to a manifold 14' in side-by-side relationship for dispensing 3 streams or beads of adhesive onto a substrate. Now with reference to additional FIGS. 3, 4, and 10 the gun module 12 of FIGS. 1 and 2 will be more fully described. Gun module 12 includes an inlet port 24 for receiving the liquid material from the manifold or service block 14, 14'. An O-ring 26 is mounted within a groove about the inlet port 24, for sealing and preventing the leakage of material therefrom. The inlet port communicates with a passage 28 to a fluid chamber 30. The fluid chamber 30 is coupled to discharge outlet 32 for dispensing the adhesive material therefrom. Inlet 24, passageway 28, and outlet 32 are all disposed in valve seat body 34. Valve seat body 34 includes a threaded step bore 36. The outer periphery of the valve seat body 34 adjacent to the discharge outlet 32 may include threads 38 for mating with and attaching a nozzle (not shown). Preferably, valve seat body 34 is comprised of brass for those applications employing a heated material, such as hot melt or other thermoplastic materials. This is to provide good heat transfer from the heated manifold 14, 14' in order to maintain the desired temperature of the fluid contained within the gun body 12 prior to dispensing through discharge outlet 32. In the dispensing of other materials, such as cold glue, because of corrosion, the valve seat body may be manufactured from some other non-magnetic material that is more corrosion resistant. Mounted within valve seat body 34 is a sleeve member 40. Sleeve member 40 includes a bore 41 therein and further including an end 40a which threadably engages the threads 38 of stepped bore 36 of the valve seat body 34. End 40a further includes a groove for receiving an O-ring 42. Sleeve member 40 should be a non-magnetic material and may be manufactured from a type 303 stainless steel. Sleeve member 40 at its distal end from the valve seat body 34 receives a pole piece 44. Pole piece 44 is manufactured from a ferromagnetic material or other soft magnetic material. The pole 44 is attached to the sleeve member 40. This may be accomplished by knurling a portion 46 of the pole 44 retained by or within the sleeve member 40 as a pressed fit. The attachment of the pole piece to the sleeve is further accomplished by brazing, such as by forming a brazed ring 48. Unlike the sleeve member, pole piece 44 is of a magnetic material, such as a heat treated magnetic stainless steel, such as 430 FR stainless steel. For certain less corrosive fluids, it is preferred to use a stainless steel having a low chrome content, such as those wherein the chrome content is about 12%. An electromagnetic coil assembly 56 is located around the sleeve 40 and is enclosed by housing 58. The coil assembly should not be attached to the sleeve member, as the sleeve/pole piece needs to be able to be rotated as will be discussed further. The electromagnetic coil assembly generates an electromagnetic field when it is subjected to a source of electrical power (not shown). The electromagnetic coil assembly 56 includes a coil 60 comprising a plurality of windings wrapped around a bobbin or spool 62. The windings of the coil 60 may be encased in a potting layer of epoxy. The spool 62 is located about the sleeve 40 such that a portion of the pole piece 44 is located within the bore area of the spool. Located at either end of housing 58 are end caps 64. Each end cap 64 is press fitted flush into the housing 58. The end caps and the housing are comprised of a magnetic material, such as magnetic iron, such as a silicone iron alloy, with a 2½% silicone content or some other ferromagnetic material or soft magnetic material. Preferably the housing is manufactured from the same materials as the end caps. The spool 62 may include an axially extending portion 66 to provide a spacing between the spool from the end caps 64. Preferably, the resulting space between the spool and the end caps is filled with a highly thermally conductive adhesive for bonding the spool assembly with the end caps and the housing 58. Electrical leads 68 pass through an aperture 70 in the housing 58 coupled to a source of electrical power, such as carried by the service manifold 14. The distal end 72 of pole piece 44 includes the plurality of threads 74 about its periphery, as well as a slot 76. The threads 74 engage a lock washer 78 and a retaining nut 80 for retaining the housing 58 in engagement with the pole 44 and the valve seat body 34. Pole piece 44, sleeve 40, and valve seat body 34 together form the fluid chamber 30. Located within the fluid chamber 30 is a plunger or armature 50, which is slidably mounted for reciprocal motion. The plunger is also manufactured of a ferromagnetic material or other soft magnetic material. The plunger 50 has a valve needle 52, such as a ball, located at one end of the plunger 50 for mating with a seat 54, located within the valve seat body 34, in the closed position. Seat 54 may be a carbide seat brazed into valve seat body 34. The plunger 50 is stepped having a first portion 82 having a diameter which closely approximates that of the diameter of the bore 41 of the sleeve member. This helps to keep the plunger properly aligned as it slides back and forth. While a close fit provides for good guiding of the plunger, it does not provide a good flow path for the material. Therefore, in order to help the fluid material to flow past the first portion 82 includes bypass channels 83 extending axially along the outer periphery. Causing the fluid to flow past the plunger in this manner helps to prevent dead spots from occurring in the flow of the adhesive through the dispenser, as well as helping to reduce the force required to move the plunger back and forth. With dead spots, the fluid may begin to oxidize to produce undesirable particles or chunks, commonly know as char. Preferably, the bypass channels have a semi-circular cross-section. Having a semi-circular cross-section provides for better magnetic efficiency and improved fluid flow over a straight sided slot. The first portion 82 of the plunger 50 further includes a stepped bore 84 having a spring 86 retained therein for engaging the plunger 50 and the pole piece 44. The spring 86 provides a biasing force for urging the ball 52 into engagement with the seat 54 to prevent the flow of material from the discharge outlet 32. When dispensing, the face 88 of the first portion 82 of the plunger 50 will be adjacent to and/or in contact with the end 90 of the fixed pole 44. Fluid material trapped between face 88 of the plunger 50 and the end 90 of the pole 44 will contribute to an increase in the force required to begin to move the plunger to the closed position and/or will cause the closing response time to increase. This phenomenon is similar to the increase in force that is required to separate two pieces of glass which have a drop of fluid placed in between them. As used herein, this phenomenon will be referred to as squeeze film lubrication. It has been previously known to provide a raised annular ring to the face of the plunger in order to minimize the contact area between the plunger and the fixed pole in order to reduce the effect of squeeze film lubrication. See, for example, U.S. Pat. No. 4,951,917 to Faulkner, U.S. Pat. No. 5,375,738 to Walsh, et al.. It is preferred in this embodiment to utilize 4 portions 87 or segments of an annular ring as oppose to a complete ring, each segment being equally spaced about the pole face of the plunger. Not only does this reduce the squeeze film lubrication force, but also provides a means for reducing the residual magnetism within the plunger. This is accomplished by reducing the cross-sectional area in contact between the pole face of the pole and the face of the plunger. Furthermore, in order to further help reduce the effect of squeeze film lubrication, it has been found to be beneficial to provide a means for introducing a flow of fluid between the pole 44 and the plunger 50 to provide vacuum relief. This may be accomplished by providing angled flow channels 92 for intersecting with the stepped bore 84 and which open into the fluid chamber 30. As the plunger 50 begins to move toward the closed position fluid is directed into the openings of fluid channel 92, into stepped bore 84, and eventually into the area formed between the fixed pole 44 and the face 88 of the plunger 50. The introduction of fluid into this area from bore 84 reduces the vacuum like attraction force between the pole and the plunger as the plunger is being driven to the closed position. To help further, the face 88 may be provided with a radial channel 85 intersecting with the through bore 84. Preferably radial channel 85 has a semi-circular cross-section. Furthermore, the flow path 84, 92 helps in decreasing the response time necessary to move the plunger to the open position. As the plunger moves from the closed to the open position, there is fluid between the face 88 of the plunger and the pole piece 44 which must be displaced. The head, acting much like a piston will displace fluid through the bypass channels 83, as well as through flow channels 84 and 92, and into the fluid chamber 30. In that it is desirous to keep the heat generated by the coil to a minimum, reducing the magnitude of the current passing through the coil will, therefore, help reduce the amount of heat generated by the coil. Once the plunger has moved to its full open position, the magnitude of the current passing through the coil may be reduced to a lower hold in current. In other words, current may be sent to the coil in order to generate an electromagnetic field which quickly drives the plunger from the closed to the open position. However, once in the full open position, the amount of current required to maintain the plunger at that position is less than it takes to drive it from the closed to the open position. There are several different driving methods which can attain this result. For example, U.S. Pat. No. 4,453,652 (Controlled Current Solenoid Driver Circuit), describes a method of reducing the current flow through a coil once the plunger has moved to its fully extended position. Other current driving schemes could also be used which help reduce the power requirements of the coil. OPERATION OF THE GUN MODULE Upon energization of the coil 60, the generated magnetic field will induce an electromagnetic field which will cause the plunger or armature 50 to be attracted to pole piece 44. This force will be sufficient to overcome the force of the spring 86 thereby drawing the face 88 of the plunger 44 towards the end 90 of pole 44. This in turn causes the ball 52 to be spaced from the seat 54 thereby causing a fluid flow path from the fluid chamber 30 to the discharge outlet 32. This allows the adhesive to be dispensed from the outlet 32. When the coil is de-energized, the field collapses and the plunger 50 will be moved back to the closed position by the spring 86. The electromagnetic field generated however, is not symmetrical throughout the axial length of the gun module. For example, with reference to FIGS. 5 through 7, the magnetic circuitry of the gun module is represented schematically. When the coil is energized, the electromagnetic field or lines of flux, shown generally by reference EM passes through pole piece 44, plunger 50, the end caps 64, and the corners 58a, b, c, d of the housing 58a. In the end cap regions, rather than the field radiating symmetrically from pole piece 44 or the armature 50, lines of flux are bent or concentrated into the corner regions of the housing. It is preferable that little or no flux passes through the regions between the corners of the housing 58. Therefore, in cross-section, the lines of flux are not distributed uniformly about the housing 58, but rather, are distributed un-uniformly and concentrated in discrete areas. The housing 58, provides a member for guiding the lines of flux of the electromagnetic field between the end caps. In general, the lines of flux in the comers of the housing or guide member 58 will pass axially from one end of the housing to the other and will be parallel to those passing through the pole and plunger. In traditional electric guns, the outer core or housing is cylindrical. However, by utilizing the same cross-sectional area but re-configurating it into a rectangle or other geometric shape, such as for example a trapezoid, allows for a smaller centerline spacing between the modules. This allows for a smaller spacing between streams of material to be applied to the substrate. While the housing is illustrated as having a rectangular cross-section, it is foreseeable to utilize shapes that are substantially rectangular and still obtain the benefit of reduced spacing. For example, with reference to the FIG. 8 corner regions 58a-d of the housing could be rounded while still having substantially flat sides 100a-d, therebetween. Alternatively, the flat sides could each be somewhat curved. For example, with respect to FIG. 9, the outer periphery 102 of the housing may have a configuration that is substantially that of an ellipse or substantially oblong. The thickness X of an end cap 64 is a function of the internal surface area of the bore 94 of the end cap. The internal surface area of the bore 94 of an end cap should be equal to the cross-sectional area of the housing 58. The fitting of the gap G between the pole 46 and the armature 50 is preferably 0,254 mm ± 0,0254 mm (.010" ± .001). However, the stroke of the plunger 50 can be adjusted by inserting a screw driver into the slot 76 of pole piece 46. Rotating pole piece 46 causes sleeve member 40 to be adjusted by rotating on the threads of the valve seat body 34. In fitting the gap G, it is preferred to tighten the pole/sleeve assembly 44/40 until it has bottomed out in the valve seat body 34. The housing 58, including the coil assembly 56 is then placed over the sleeve. Preferably, the body 58 has a locating pin which matches up with a corresponding hole the valve seat body 34. Once in place, the lock washer and nut are then tightened. Preferably, a nozzle gauge is then attached to the valve seat body by screwing it onto the threads 38. With the sleeve/pole bottomed out, the plunger 58 should not move. Using the screw driver in slot 76 of the pole piece, the pole piece may be rotated until the gauge indicates that the proper gap setting has been obtained. At which point in time the nut 80 may be tightened completely and the gap, i.e. the movement of the ball from the seat as recorded by the gauge provides a spring force against the ball, can be verified.

Claims: An apparatus for dispensing an adhesive comprising: a housing (58) defining a bore (84) therein, said bore (84) having a first and a second end; an inlet (24) for coupling the bore (84) to a source of adhesive; a pole (44), extending from the first end of the bore (84) such that a portion of an external surface (88) of the pole (44) is in fluid communication with the adhesive, a coil (60) for generating an electromagnetic field, disposed about a portion of a pole (44) and the bore; a discharge opening (32) coupled to the second end of the bore; a plunger (50), having first and second ends, disposed within the bore (84) and mounted for reciprocal movement between a closed position and an open position, wherein in said open position, adhesive is dispensed from the discharge opening (32), and in said closed position, adhesive is prevented from being dispensed from the discharge opening (32); a pair of magnetic end caps (64) located in each end of the housing (58), one located at either end of the coil (60); wherein the end caps are circular, having a through bore (84) therethrough; a flux guide member, which is provided by the housing (58) having a rectangular cross section and having a through bore (84), and which is coupled between the end caps for non-uniformly guiding lines of flux of the electromagnetic field between the end caps, and wherein one end cap distributes the flux between the pole piece and the flux guide member, while the other distributes the flux between the plunger (50) and the flux guide member such that the plunger (50) is moved to the open position. The apparatus of claim 1, wherein the pole (44) is adjustable for adjusting a gap between the pole (44) and the plunger (50). The apparatus of claim 1, wherein the plunger (50) has a stepped outer diameter, having a first portion (82) of a first diameter and a second portion of a reduced diameter, the first portion (82) containing a through bore (84) therein and angled flow channels (92) for intersecting with the bore (84) and which open into a fluid chamber (30). The apparatus of claim 3, wherein the through bore (84) of the plunger (50) has substantially a Y-shaped cross-section, the bore (84) extending from an end of the first portion. The apparatus of claim 1, wherein said first portion (82) further containing a plurality of axially extending channels about the outer periphery and wherein the first portion (82) of the plunger (50) further carrying a radial channel (85) on a face (88) opposite the pole (44) and said radial channel (85) intersecting with the through bore (84) of the plunger (50). The apparatus of claim 5, wherein the axially extending channels and the radial channels (85), each have a semi-circular cross-section. The apparatus of claim 1-6, wherein the flux guide member is rectangular, having a through bore (84) therethrough. The apparatus of claim 1, wherein the pole (44) is solid, thereby preventing the flow of adhesive therethrough. The apparatus of claim 1, wherein the first portion (82) of the plunger (50) further carrying a radial channel (85) on a face (88) opposite the pole (44) and said radial channel (85) intersecting with the through bore (84) of the plunger (50). A method of dispensing a liquid material comprising the steps of: directing a flow of said material through a bore (84) containing a plunger (50) slidably mounted and contained therein; directing the flow of said material about a portion of a electromagnetic pole (44) extending from said bore; generating an electromagnetic field; causing the electromagnetic field to pass axially through the pole (44) and said plunger (50); and further directing the field in concentrated axial areas, parallel to that passing through said pole (44) and plunger (50); wherein the field is concentrated into comers of a geometrically shaped housing (58) having a rectangular cross section and a through bore (84); wherein the electromagnetic field effectuates movement of the plunger (50) from a closed to an open position such that the liquid material is directed past the plunger (50) and discharged from the discharge orifice. The method of claim 10, wherein a pair of magnetic end caps(64) located in each end of the housing (58), one located at either end of the coil (60); wherein the end caps are circular, having a through bore (84) therethrough; a flux guide member, which is provided by the housing (58) having a rectangular cross section and having a through bore (84), and which is coupled between the end caps for non-uniformly guiding lines of flux of the electromagnetic field between the end caps, and wherein one end cap distributes the flux between the pole piece and the flux guide member, while the other distributes the flux between the plunger (50) and the flux guide member such that the plunger (50) is moved to the open position; such that the lines of flux are distributed un-uniformly in cross section and concentrated in discrete areas of the housing (58).

Inventors: CHASTINE CHRISTOPHER R, FORT WESLEY C, HASSLER WILLIAM L, ULRICH HOWARD E, CHASTINE, CHRISTOPHER R., FORT, WESLEY C., HASSLER, WILLIAM L., ULRICH, HOWARD E.
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1998
Main classification: B05C11
IPC codes: B05C17, B05C5, B05D7, B05B1