Efficient and Flexible Multi Spray Electrostatic System

Abstract

An efficient electrostatic spray installation that can spray a wide range of conductive materials effectively while creating very small droplets with conductivities in from about 7000 pico Siemens and greater. A compact system in which one, two or more parallel sprays can be obtained at close proximity in the order of 30 to 40 mm of each other in a compact package.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of the principle elements of the flowable material handling and supply system.

FIG. 2 is the continuation of FIG. 1 showing the individual supply lines to each of six flow distribution modules of the example. For clarity, the flow distribution modules are shown without support in a configuration of two parallel rows of three modules each.

FIG. 3 shows a typical flow distribution module with the inlet connection, a distribution channel and grooves.

FIG. 4 Shows a double spray assembly in cross section with a clamping arrangement, and the details of the principle parts.

FIG. 5 shows the connection of the high voltage cable to the charging conductive parts in a double spray assembly, with the end caps that cover the high voltage parts et each end of a spray assembly.

FIG. 6 shows a ground switch arrangement that can be used at the end of a spray assembly or at the end of a chain of several such assemblies.

FIG. 7 is a principle sketch of a double spray assembly with an enclosure, high voltage connections, or one connection and one ground switch. The target bars and catch tray arrangement is also shown.

FIG. 8 shows a compact spray assembly with four parallel sprays.

FIG. 9 shows the application of two double spray arrangements for the application of lotion to both sides of a tissue paper web in eight distinct lanes.

FIG. 10 shows the application of a shaped spray for spraying cooking oil on to a cooking tray.

FIG. 11 shows the spray assembly for spraying steel plate with a protective or lubricating oil on both sides.

FIG. 12 shows two double spray assemblies that spray on an applicator belt which transfer the sprayed material to a vertical paper web, to coat this web.

FIG. 13 shows a backstand with a belt driven parent roll of a flat wound product with two double spray assemblies that apply a spray to the two sides of the web.

DETAILED DESCRIPTION OF THE DRAWINGS AND OF THE PREFERRED EMBODIMENT

In FIG. 1, flowable material is pumped via line 1 and valve 2 into reservoir 5.

Valve 2, shown to be open in the FIG. 1, is operated by actuator 3, through a rod 4. The level in reservoir 5 is measured by one of the remote level tranducers 6.

The transducers 6 are level transmitters that operate by ultra sound, radar, infrared or other light etc, and that measure at some distance without contact to the materials that are being measured.

At the outlet of reservoir 5 is a valve 7, shown closed in FIG. 1, operated by actuator 9, through rod 8.

Reservoir 10 is electrically insulated and is filled with flowable material from tank 5 by the opening of valve 7

Reservoir 10 has a valve 11 that is operated through rod 12 by actuator 13.

As reservoir 10 is electrically insulated, rod 12 is made from an electric insulator such as Delrin.

Reservoir 10 can either be filled, or it can discharge and fill reservoir 14 through valve 11, rod 12 and actuator 13. But both operations can not occur at the same time.

Reservoir 10 functions as an electrical barrier between reservoir 14 and reservoir 5.

Reservoir 14 feeds pump 19 through line 18 and valve 15. Valve 15, shown open in FIG. 1, is operated through an insulating rod 16 by actuator 17.

Line 18 can be provided with filter arrangements, but these are not shown to simplify FIG. 1.

Also not shown are agitators that may be needed in each of the reservoirs.

If agitators are added, provisions need to be made to electrically insulate these for reservoirs 10 and 14. This can be done for instance by using agitators equipped with air motors.

Pump 19 is a multi outlet gear pump that is driven by motor 22, through gearbox 23, flexible couplings 20, and floating shaft 21. Shaft 21 is made from an insulating material.

Motor 22 is a servo or a stepping motor which can be controlled to give precise rotational speed.

The outlets of pump 19, six are shown but more or less are possible, are connected by flexible tubing 24 made of an electrical insulating material. Each tube is led through conduit 25 that is made from an electrical insulating material.

The tubing 24 are kept located in the conduit 25 by spacers 35 (one shown only), which locate the tubing but do not obstruction for flow of a gas such as air. Spacers 35 are also made from an electrically insulating material.

The reservoirs, lines, valves and pump are all mounted in an enclosure 26 that can be supplied with a hot gas, such as hot air as indicated by arrow 27, through conduit 28.

The hot gas serves to keep all parts in contact with the flowable material warm for these cases where this is required, for instance when spraying a flowable material with a melting point that is higher than normal ambient temperatures.

Line 37 and valves 36 are shown in one of lines 24 to indicate the possibility to stop one or more of the flows through lines 24, if so required, and recirculate one or more flows through reservoir 14. This can be necessary if different spray widths are required.

Line 29 is an insulated electrically conductive wire that connects the pump, normally made of stainless steel or similar material, to the contact 30 in tube 31. Tube 31 is made of an electrical insulator.

Actuator 33 can move contact 32 to touch contact 30, to electrically ground pump 19 when this is required, through the ground wire 34.

This system provides for heating of the flowable material as well as complete electrical insulation of the flow handling system.

The electrical insulation is a requirement for spraying higher conductivity materials, as otherwise the high voltage would be lost through the flowable material supply system.

Using lower conductivity materials, this system does not provide a path to ground and therefore there is less demand on the electrical power supply to maintain the voltage high.

The pump will however accumulate charge and grounding will be needed for safety reasons when the pump or reservoir 14 needs to be accessed by personnel.

FIG. 2 shows the continuation of lines 24 in conduit 38 into enclosure 39.

The hot gas or air that is blown through conduit 38 warms the six flow distribution modules 40 that are shown schematically and without support in this isometric view.

Tubes 24 are connected to the flow distribution modules by the use of fittings 41, which are made of an electrical insulating material such as Delrin, Kynar or the like.

FIG. 3 shows a flow distribution module 40, with threaded inlet 55. The module is made from an electrically insulating material. Inlet 55 is connected to groove 54 which distributes the flowable material over the width of the module. As this is a module for spraying downwards, the inlet is located below the level of the groove 54. For upwards spraying this would be the other way around.

An O-ring groove 53 assembled with an O-ring, provides a seal to the vertical member in the assembly.

Grooves 56 provide a path for the flowable liquid in the direction of the electrostatic field. Opposite grooves 56 is a conductive charging strip. The grooves are shown only in the left hand portion of the face of the flow distribution module, but of course occupy the full area between the O-ring grooves. The shape of the grooves can be triangular, rounded, rectangular or a combination of these shapes. A triangular shape is shown in FIG. 3.

In FIG. 4, the flow distribution modules 40 are shown assembled with member 54 and charging strips 59. Nonconductive foil or sheet 57 is placed above the conductive strip 59, and non-conductive foil or sheet 60 is placed below the module. The last can be sharpened to a point as this helps to concentrate the electrical field and more ligaments can be formed. Or it can be very thin and is therefore sharp by it shelf.

O-ring 57 provides a seal with vertical member 54.

Member 53 is bolted to vertical member 54. All bolts shown are made from a non-conductive material. (fibre reinforced glass or the like).

Horizontal members 52 and vertical members 55 form a clamp arrangement.

This clamp arrangement can be positioned in various positions along the length of the spray assembly to accommodate the dimensions of flow distribution modules 40.

Bolts 56 exert a force on flow distribution modules 40 that keep these modules in place.

FIG. 5 shows the arrangement at the end of a spray assembly where a high voltage cable provides the high voltage to the charging strips 59. Cable 62 is led through tube 66 made from an electrical insulator. The contact 63 at the end of the cable pushes against resistor 64 which in turn contacts through-bolt 65. The throughbolt 65 holds charging strips 59 in place. It is typically made from stainless steel and is the only electrical conductor used in the assembly apart from the charging strip 59.

A clamp arrangement 55 is used as for the flow distribution modules to keep two end caps 61 in place using bolts 56. End caps 61 are provided with a depression to accommodate the head and nut of the through bolt. End caps 61 do not have Oring grooves. The insulator 58 goes around the conductive strip 59 at both ends of the spray assembly on member 54, thereby insulating conductive strips 59 at either end of the assembly.

FIG. 6 shows a ground switch that is used to remove the high voltage from the charging strips when the electrostatic spray is stopped. Plastic non conducting rod 67 is equipped with a contact 68 to a wire (not shown) that is connected to ground. Pipe 66 is made of a non conducting plastic material and guides rod 67.

Grounding of the charging strips 59 is accomplished by moving rod 67 down and touch through-bolt 65 with contact 68.

FIG. 7 shows an assembly with multiple flow distribution modules 40 and clamps 52, in an enclosure 39. Tubes or pipes 66 are shown at either end of the assembly for the high voltage connections and or a ground switch.

The electrostatic field of each spray is directed to the target bars 50 that are located above a drip pan 51. The drip pan 51 can be given any convenient shape to conveniently collect flowable material, as it is separate and located further away from the charging strips than are the target bars 50. Further indicated are flow distribution modules 40, vertical member 54, and horizontal member 53.

FIG. 8 shows an arrangement with four parallel sprays. There are two vertical members 69 in this assembly. Each of the vertical members has a charging strip arrangement on both sides, as previously described. The flow distribution modules 40 that are located on the outside are the same as described earlier. Flow distribution modules 70 are special for this multi spray assembly as they have grooves 56 at both sides. Furthermore these modules are supplied with flowable material from using threaded hole 71 and clearance holes 72. In this sandwich construction, vertical members 69 are either precisely positioned, or they are allowed to be movable to some degree, so that the clamp arrangement will achieve proper sealing for all the flow distribution modules.

EXAMPLES

The following examples are presented as illustrative of some aspects of the present invention and should not be construed so as to limit the scope of the present invention.

FIG. 9 shows an application whereby a tissue paper web 73 is sprayed with a high melting point lotion on both sides of the web.

The paper tissue substrate is sprayed using a gapped spray 74 which is obtained by having grooves in the equivalent areas of the flow distribution modules, and by having the target bars 50 shaped with raised parts to attract and direct the spray where it is required.

The lotion and the spraying equipment is kept at a temperature of 45 degrees Celsius, by blowing hot air under the enclosures 39. The lotion contains mineral oil, waxes to raise the melting point, as well as a conductivity agent, besides other ingredients. The last can be ingredients that are beneficial to the human skin and ingredients that enhance the feel of the tissue paper.

The spray is gapped and the unsprayed areas is where the multiply tissue paper is subsequently bonded together by mechanical means. The ply bonding of multiply tissue paper is more difficult when lotion is applied, so it is an advantage not to apply lotion in these areas, besides reducing cost.

FIG. 10 shows the spraying of a shaped baking tray with cooking oil. The tray is made of metal and forms the grounded target for the cooking oil spray. Vertical member 54 is shaped to follow the contour of the baking tray. The spray distribution modules on both sides of spray distribution module 40 are angled on one side to accommodate the contour to be sprayed.

End caps 61 are cut away to fit under horizontal member 53.

FIG. 11 shows the coating of a steel sheet with oil for lubrication and corrosion protection.

This is a traditional application for electrostatic spraying. One assembly is for spraying upwards and one is for spraying downwards on to the steel sheet 84, which is also the grounded target for each spray. In this application, typically low add on rates are required, so one spray in each assembly will be used at the time and the other parallel spray will be kept on stand by.

FIG. 12 shows the spraying of an applicator belt 82 which in turn applies flowable material to a vertical web. The advantage of using an applicator belt or roll is that the electrostatic spray application is separated from the application to the substrate. This may in some cases be desirable, for instance if coating by contact is preferred over direct spraying. In this case the spraying can be vertically downward and the web to be coated can be running vertically down as well. Doctor blades 83 are provided to clean the applicator belt from any material that may be dislodged from web 73.

The left hand assembly is positioned slightly lower so that the web is forced to change direction slightly and gentle contact is provided with both applicator belts 82.

FIG. 13 shows two electrostatic sprays in a cantilevered arrangement. The spray arrangement is positioned directly behind a parent roll 86 that is surface driven by a drive belt arrangement 88. The web 90 passes through spray assembly 94 and is sprayed on one side, then it passes through spray assembly 96 and is sprayed on the other side. A web path as indicated by dotted line 92 can be used in case no spray treatment is required.

The cantilever spray arrangement 98 is mounted on rollers 100 and can be moved over rails 102. The web 90 can be threaded with the cantilever spray arrangement in retracted position. Once threaded, the spray arrangement 98 can be positioned over web 90.

The skilled person will appreciate that numerous modifications and variations of the present invention are possible, having regard to the above description and that the scope of the present invention should be understood in terms of the claims as follows and not limited to any specific detail of structure or operation as described or shown in the present specification or drawings.

Claims

1. An electrostatic spray system installation comprising members and flow distribution modules made from non conductive materials that are held in contact with each other, in which a conductive surface that is part of a member and that faces a flow distribution module is maintained at a voltage of a minimum of 20,000 volts, wherein each of the flow distribution modules is supplied by a controlled flow of a flowable material, and wherein the flow distribution modules can be given different dimensions and can be positioned to give various spray configurations.

2. An electrostatic spray system as claimed in claim 1 wherein the flow distribution modules are positioned at two sides of a member, or several rows of one or more parallel flow distribution modules are positioned in between parallel members, and in which flow distribution modules can in addition be positioned on the outside surfaces of the members.

3. A system as claimed in claim 1 wherein a number of flow distribution modules are assembled to obtain a required spray length, in which different flowable materials are submitted to the flow distribution modules, in which the flow distribution modules have different dimensions, in which different flow rates are used for one or more flow distribution modules.

4. A system as claimed in claim 1, comprising one or more target bars to define an electrostatic field or fields, in which the target bars are separate from a catch tray, and which may be formed to have high and low parts, to create distinctive electrical fields.

5. A system as claimed in claim 1 wherein the electrostatic field follows a contour in a flat or curved plane, by shaping the main vertical member and flow distribution modules and by having a similar contour in the target bars.

6. A system as claimed in claim 1, wherein the flow distribution module contains a distribution groove that is connected to a number of smaller grooves parallel and in the direction of the electrostatic field, and that are distributed over the width of a flow distribution module.

7. A system as claimed in claim 1, comprising a flowable material supply system that is electrically insulated, that can operate continuously, and that supplies the flow distribution modules with controlled flows.

8. A system as claimed in claim 1 wherein the flowable material supply system is heated by a hot gas or liquid.

9. A system as claimed in claim 1 wherein the members and flow distribution modules are heated by a hot gas or liquid.

10. A system as claimed in claim 1 wherein the conductive charge imparting parts are thin, and covered by flow distribution modules.

11. A system as claimed in claim 1 wherein the drip proof stop of the spray action is obtained by the control of the flow to the flow distribution modules in two directions, to provide temporary reverse suction of flow.

12. A system as claimed in claim 11 wherein the drip proof stop of the spray is obtained by combining temporary suction of the flow to a flow distribution modules with the quick removal of the high voltage from the charging strip by means of a ground switch.

13. A system as claimed in claim 1 wherein the drip proof stop is further facilitated by the location of the inlet of each distribution module below the feed line of the grooves that are aligned with the electrostatic field, ensuring the minimum of flowable material to be available for dripping.

14. A system as claimed in claim 1 wherein a precise stacked metering pump, driven by a precisely controlled motor, supplies a number of flow distribution modules over the length of a spray assembly.

15. A system as claimed in claim 1 wherein the outlet lines of the precise stacked metering pump are provided with valves so that individual flow distribution modules can be supplied with flowable material or be disconnected from the supply, by diverting the flow from the outlet lines back to the feed tank.

16. A system as claimed in claim 1 wherein the flowable material is sprayed on a belt or roll which subsequently transfers this material to a web of material to be coated with the flowable material.

17. A system as claimed in claim 16 wherein the web comprises two sides and the two sides of the web are coated by using two spray assemblies which spray downwards and through which the web is guided by rollers in an S configuration.

18. A system as claimed in claim 17 wherein the two sides of the web are coated by using two spray assemblies which spray downwards and through which the web is guided by rollers in an C configuration.

19. A system as claimed in claim 1 wherein the flowable material is heated when being sprayed, but then subsequently cooled with a cold gas such as cold air to provide a lower temperature of the flowable material when it reaches the target.

20. A system as claimed in claim 1 wherein the spray system with flow distribution modules is illuminated in the area on the lips where ligament flow occurs during spraying, and a video camera is used to count the ligaments.

21. A system as claimed in claim 1 wherein grounding switches are provided as a means to removes the high voltage quickly from the charged parts.

22. A system as claimed in claim 1 wherein said system is automated and controlled by a computer system.

23. A system as claimed in claim 1 wherein said system is preceded by a dust removal device such as a web cleaner, or a separate electrostatic device for dust removal.

24. A system as claimed in claim 1 wherein atomization by a gas such as air is incorporated.

25. A system as claimed in claim 1 wherein mechanical energy is used to affect the spray characteristics.

26. An electrostatic flow distribution and charging system, for the spraying of a flowable material by distribution and charging to a suitable high voltage and the spraying of the material by a multiplicity of parallel ligamental streams, wherein said system comprises: an assembly of one or more insulated non-conductive flow distribution modules, said modules comprising grooves, a conductive surface with electrical connection to such surface, whereby the flowable material is electrically insulated in said system except for said conductive surface and electrical connection, means for application of an electrostatic field, one or more target bars to define the electrostatic field, and one or more catch trays, each groove being aligned with the direction of the electrostatic field, whereby:the flowable material is sprayed with minimum loss from electrical currents through said assembly, the flow of material being distributed and guided through said grooves in the non-conductive flow distribution modules and over the electrically conductive part of said assembly substantially parallel with the electrostatic field, the application of the electrostatic field providing a positive force or pressure to move the material that is sprayed, through said grooves, the flow through each groove in a flow distribution module being substantially equal or independent of specific geometry of groove or module, to hydrodynamically distribute the flowable material to be sprayed over a length of a distribution module, while the flow to each distribution module is controlled separately so that long, multiple and shaped spray assemblies can be made with a precise distribution of flow, while different flowable materials can be used in sections of the spray assembly, and wherein the target bars that define the electro static field are separate from any catch trays and shaped to create different spray patterns.