US3716024A

US3716024A - A device for spraying an electrified powdered material onto a structure

Info

Publication number: US3716024A
Application number: US00084260A
Authority: US
Inventors: G Pierson
Original assignee: Carrier SCS
Current assignee: Carrier SCS
Priority date: 1969-11-04
Filing date: 1970-10-27
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13
Also published as: BE758045A; SE372430B; DE2054242B2; DE2054242C3; ES385606A1; CA945758A; DE2054242A1; GB1316286A; FR2012801A1

Abstract

Device for spraying an electrified powdered treating or coating material onto a structure. The device comprises a cabin through which the structure is conveyed. A mixture of the powdered material and air is sprayed onto the structure by spraying means connected to metering and mixing means placed in the bottom of a bank containing the powdered material. Means are provided for recovering the powdered material which has not been deposited on the structure and returning this material to the tank.

Description

United States Patent 1 Pierson Feb. 13, 1973 [54] A DEVICE FOR SPRAYING AN ELECTRIFIED POWDERED MATERIAL ONTO A STRUCTURE [75] lnventor: Gerald Pierre Pierson, Calvados,

France [73] Assignee: Societe Carrier, societe anonyme,

Suresnes, France 22 Filed: Oct. 27, 1970 21 Appl. No.: 84,260

[30] Foreign Application Priority Data Nov. 4, 1969 France ..6937914 [52] US. Cl. ..118/630, 117/93.41, 117/102, 118/602, 118/621, 118/629 [51] Int. Cl. ..B05b 5/02, B05C 11/00 [58] Field of Search ..118/602, 621, 623, 626, 627, 118/629, 630, 631, 639, 640; 117/93.41,

[56] References Cited UNITED STATES PATENTS 3,486,921 12/1969 Wallis ..117/24 3,539,381 11/1970 Kayarian ..117/102 3,027,870 4/1962 Schirmerm ....118/504 3,396,699 8/1968 Beebe et al..... 1 18/634 3,001,719 9/1961 Sigvardsson.... ..239/15 2,794,417 6/1957 Starkey et a1... ..118/51 2,698,814 1/1955 Ransburg ....118/63O 3,434,758 3/1969 Fry ..302/61 2,706,964 4/1955 Ransburg et a1 ..118/51 3,205,853 9/1965 Wampler et a1. ..118/631 Primary Examiner-Merviri Stein Assistant ExaminerLeo Millstein Attorney-Imirie and Smiley [5 7] ABSTRACT Device for spraying an electrified powdered treating or coating material onto a structure. The device comprises a cabin through which the structure is conveyed. A mixture of the powdered material and air is sprayed onto the structure by spraying means connected to metering and mixing means placed in the bottom of a bank containing the powdered material. Means are provided for recovering the powdered material which has not been deposited on the structure and returning this material to the tank.

1 1 Claims, 6 Drawing Figures PATENTEDFEB 13 1975 SHEET 10F 4 Fiel INVENTAR GERALD P. Pl ERSON I At fs.

PATENTEDFEB 13 I975 SHEET 2 OF 4 'Irll IIIVIII 111 ruvnrron P. PIEQSON GERALD PATENTEUFEB13|973 v 3.716.024 SHEET 30F 4 Pie/1.4. Fiab.

I NVE NTo R GERALD P, PIERSoN PATENTEUFEB 13 I975 3.716(024 SHEET MOF 4 INvENToR GERA D P. PI ERSON Att'u.

DEVICE FOR SPRAYING AN ELECTRIFIED POWDERED MATERIAL ONTO A STRUCTURE in many fields, it is useful or necessary to submit component parts or various products, at some stage of their manufacture, production or realization, to a coating or surface treatment, in order to impart thereto particular appearance characteristics or well determined properties, for example, a higher resistance to oxidizing agents with which the parts or products may come in contact.

To produce the coating or surface treatments, there are mostly employed liquid products having a variable fraction of solvent, the nature and the quantity of which depend on the natural or forced drying processes employed. The surfaces of parts are usually treated or coated by means ofa brush or a roller, or by spraying or dipping.

ln any case, more or less complex but always expen sive treating installations must be designed to prevent, as far as possible, the emanation of products which are generally poisonous'to the personnel in charge of the supervision, maintenance or feeding of material to said installations.

Moreover, notwithstanding the fact that methods such as spraying or dipping have been considerably improved, these methods always entail an excessive consumption of treating or coating product, which is subsequently very difficult to recover.

Further, when the parts must be transferred to a drying or a baking enclosure, it will be understood that it is extremely important to take every precaution to avoid the sticking of particles, dust or other foreign elements in suspension in the environment to the still-wet coatings.

Consequently, it is generally necessary to create transfer passages or tunnels which are usually kept at a relative pressure with respect to the surroundings while the treating enclosure with which they communicate has a relative depression prevailing therein so as to avoid the emanation of poisonous products. Consequently, the devices are complex and expensive and the cost is practically always out of proportion to the treating possibilities or the importance of the parts or structures to be treated.

An object of the present invention is to remedy the above-mentioned drawbacks by providing a new device for coating or treating the surfaces of structures or parts whereby it is possible to reduce to a minimum the quantity of treating product utilized, and preclude risks of evaporationor emanation of this product even when the parts under treatment must be transferred from the spraying device to a cooling, drying or baking enclosure.

The invention provides a device for spraying electrified powdered material for coating or treating the surface of parts or structures comprising a cabin having an interior kept at a pressure lower than the surrounding pressure, some sides of the cabin having lock-chambers for the passage of a conveyor for moving the parts or products, wherein'the parts are made to pass in front of at least one spray distributor for spraying an airpowder mixture, the particles of said mixture being subjected to an electrostatic charge different from the charge of the parts, the effective part of the distributor being provided with an element dividing up the airpowder mixture flowing therein, the distributor being in communication with an adjustable metering and mixting means which is supplied with compressed air and disposed in a supply tank containing the powdered material and connected to the lower part of said cabin by devices for the recovery of excess powdered material projected.

Various other characteristics of the invention are revealed by the following detailed description.

Embodiments of the invention are shown by way of example in the accompanying drawings, in which:

FIG. lis a diagrammatic sectional perspective view, partly in section, of the device of the invention HQ 2 is a partial, perspective, enlarged view, partly in section of one of the elements of the device FIG. 3 is a section on a reduced scale of a modification of the device of FIG. 1

FIG. 4 is a sectional view of a modification of the element of FIG. 2;

FIG. 5 is a side elevational view of another modification of the element of FIG. 2

FIG. 6 is a perspective view, partly cut-away, illustrating another embodiment of one of the components of the device.

In FIG. 1, the device comprises a cabin 1 having two opposite openings 2 made in the same way as air lockchambers. The openings 2 allow a path of movement 3 to extend through the cabin, the path comprising a conveyor extending from a loading station, through the cabin l and leading to a natural or forced drying enclosure.

The cabin 1 is provided at its base with a container 4 containing a supply 5 of powdered product of small grain size, the maximum or optimum level of the product being diagrammatically shown in dash-dot line. The container 4 includes a flat bottom 6 joined to two panels 7 upwardly diverging from the bottom 6 to corresponding lateral sides of the cabin to constitute product recovering or collecting means. The container 4 supports, by means of fixed cross-bars 8, a metering and mixing means 9 made of a tubular element 10, similar to the tapered part of a venturi, the small section end 11 thereof being spaced from the bottom 6. The large section portion 12 of the tubular element 10 is combined with a pivotable shutter 13 whereby the section of the tubular element 10 can be regulated. The shutter 13 is connected to a control rod 14 provided with a control handle 15.

The substantially middle portion of tube 10 communicates with a pressurized air injecting pipe 16. The tubular element 10 communicates with a tube 17 diametrically opposed to the pipe 16 and leading to a spray distributor 18 which extends vertically inside the cabin 1. Depending on the shape of the parts or structures to be treated, the spray distributor 18 can be rectilinear, bent or have some other shape. The distributor 18 is maintained parallel with the wall alongside which it extends by spacer member 19.

The wall of the distributor 18 has throughout the effective length thereof an axially extending slot 20 through which extends a strip 21 preferably of insulating material and extending transversely across substantially the whole of the inside section of the distributor 18. This strip 21 has notches 22 and 23 on the two wide faces of the strip, said notches having a constant spacing, but being disposed in alternating staggered relation on the two faces of the strip. The

notches

22 and 23 can have a uniform shape throughout the width of the strip 21 or can taper from the edge 24 of the strip facing the inside of the cabin l to nothing on the corresponding wide faces of the strip. The strip 21 is preferably interchangeable to allow a modification of the spraying characteristics of the distributor 18 in accordance with the nature of powdered product 5 and the work to be performed. The strip 21 extends between two fixed or adjustable supports 25, mounted on the distributor 18 to hold a metallic wire 26 taut in front of the edge 24 of the strip 21. The wire 26 is connected to two conductors 27 and 38 leading from a high-frequency electric power generator 29.

The above-described device operates in the following way After filling the container 4 with a powdered product, the compressed air supplied by the pipe 16 passes through the metering and mixing means 9 before reaching the tube 17. The suction which is created inside the tubular element 10, the magnitude of which can be regulated by controlling the position of the shutter 13, draws inadditional air and the powdered product which is drawn along at a constant flow in the tube 17. The latter constitutes a chamber for both metering and homogeneizing the mixture of air and powdered product caused to flow through the distributor 18, the volume of which ensures the expansion of the mixture.

Inside the spray distributor 18, the air-powered product mixture flows through the

notches

22 and 23 and is divided into as many spray jets thereby ensuring a continuous and distributed or spread spraying of the mixture. Said mixture necessarily passes through the ionizing field created by the stretched metallic currentcarrying wire 26. Beyond the ionizing field, the particles of powdered product which are subjected to an electrostatic charge are sprayed or projected onto the parts which are conveyed through the cabin 1. When the distributor 18 is relatively high, the mixture must be brought to sufficient pressure to ensure that the upper part of the distributor 18 is suitably fed with the airpowdered product mixture. To prevent the pressure causing formation of excessively strong spraying jets which would detach the particles sprayed onto the parts, the upper end of the distributor 18 is provided with a relief flap 18, which returns the excess mixture to the cabin.

To prevent the excess powdered product escaping to the exterior of the cabin,. in spite of lock-chambers 2, the cabin 1 is connected by a pipe 30 to a source of suction which ensures that the pressure inside the cabin is lower than the surrounding pressure. The result is that the excess product is drawn out of the cabin and recovered through a cyclone (not shown) and recycled to the container 4. The pipe 30 is provided in the upper part of cabin 1 so as to limit the amount of the excess product drawn out, the major part thereof falling to the lower part of the cabin 1, where it is collected by the recovering means 7 and directed toward the supply tank.

The parts or structures which are made to travel through the cabin l have, of course, an electrostatic charge which is different from the charge of the sprayed particles of the powdered product so that the parts are automatically covered with an adhering coat. Said coat is then submitted, out of the spraying zone or possibly outside the cabin 1, to a fixing treatment so as to obtain an homogeneous, dense and resistant coating.

With this arrangement of the spraying device, there is no risk of emanation, evaporation or spraying of the treating or coating product outside the cabin, and the consumption of said product is limited to the quantity required to ensure a complete and even coating of the parts which can be conveyed, with no loss or flow of the product, to a station outside the cabin 1 to receive the fixing treatment.

FIG. 3 shows that the spraying device may have more than one spray distributor when opposed surfaces of parts have to be coated or treated. According to FIG. 3, the container 4 supports two metering and mixing means 9a,9b, placed in a staggered manner. The means 9a,9b, communicate with individual pipes 16a,16b supplying compressed air and also communicate with two tubes 17a,17b leading to two spray distributors 18a,18b. The wires 26a,26b of said distributors can be supplied with current by two different generators or by a generator 31 having two outputs. The shutters 13a,13b are connected to control rods l4a,l4b preferably accessible simultaneously from one of the sides of cabin l. The two spray distributors 18a,l8b can have a similar or different shape, depending on the characteristics of the exposed surfaces of the parts to be treated.

FIG. 4 shows a modification in which the spray'distributor 18 is composed of a tubular element 32 made of an insulating material and defining an axial slot 33. The tubular element 32 contains a dividing component 34 shaped like a comb having teeth 35 which have different lengths but ends aligned in a plane parallel to the plane of the opposed longitudinal edge of the component 34. The latter is placed in the slot 33 in such manner that the shorter teeth are located adjacent the base of tubular element 32. The purpose of this arrangement is to ensure that the jets of the mixture passing through the slot 33 have a substantially uniform concentration all along the distributor 18. Indeed, the spaced 36 between the teeth ensure a deviation of the product into the slot 33 which progressively increases with increase in the length of the teeth 35 and this compensates for the reduction in the concentration of the air-powder mixture as it rises in the distributor 18. This allows the same quantity of powder to be sprayed throughout the height of the spray sheet formed by the aligned jets.

If the dividing component 34 is made of an insulating material, the wire 16 has to be connected to the high frequency electric power generator 29. However, the component 34 can be made of an electrically conductive material and connected to the generator 29 by conductors 37 and 38. The component 34 may have a width which is different from the section of the distributor 18 so as to dispose the ends of the teeth 35 on either side of the slot 33.

A further modification is represented in FIG. 5 according to which the dividing component is composed of a strip or a filament 39 having corrugations 40 whose magnitudes increase from the end 41 located in the lower part of the distributor 18. The corrugations 40 are so designed as to have a configuration whose transverse extent is equivalent to that of the spaces 36 between teeth 35 so that they perform the same function when the filament of the strip 39 is disposed in the distributor 18 in such manner that the aligned crests of the corrugations 40 are at least partly engaged within the axial slot 33. The strip or filament 39 can be made of insulating material when the electrostatic field is produced by the wire 26 or of an electrically conductive material in which case it is directly connected to conductors 37 and 38.

FIG. 6 shows another embodiment of the means for supplying and subsequently recovering the powdered product. According to this embodiment, cabin l includes a plane bottom 42 under which is hung, through elastic sealing elements 43 such as flat gaskets, a

hopper 44 constituting the recovering or recycling means for the excess powdered product. The bottom of hopper 44 is extended by a nozzle or other tubular element 45 the interior of which is provided with a removable filtering cartridge 46. The above-described recovering means is connected to a vibrator 47 of any suitable type. The nozzle is connected through a flexible sleeve 48 to a tubular shaft 49 projecting from above a container or tank 50. A horizontal metering and mixing means 51 extends through the tank 50 and is connected, on one hand, to the tube 17 and, on the other hand, to the air-injection pipe 16. The means 51 can be directly constituted by the end portion of the tube 17 into which the pipe 16 partly extends. Preferably, the means 51 is constituted by a sleeve slidably mounted on the tube 17 so that by the adjustment of the axial position of the sleeve through a manual control, it is possible to vary the proportion of the drawn-in powdered product without modifying the volume of the carrier fluid supplied by the pipe 16.

The metering and mixing means 51 is placed above a porous element 52 dividing the tank. into a lower chamber 53 and an upper chamber 54. The chamber 53 communicates with a pipe 55 supplying air at low pressure, whilst the chamber 54 contains the powdered product, it being filled with the product through an inspection hole 56. The chamber 54 also includes a float 57, operating a switch 58 controlling the electric current 59 supplied to the vibrator.

The device of FIG. 6 operates in the following manner:

First, when starting the device, the lower chamber 53 of the tank 50 is supplied with air after having previously filled the chamber 54 with a suitable quantity of powdered product. The air delivered by pipe 55 passes through the porous element 52 and ensures that the powdered product is put in suspension in the air. Thus, the behavior of the product can be likened to that of a fluid or liquid having a practically stable level. The float 57 is consequently kept in its upper position and the switch 58 cuts off the supply to the vibrator 47. The pipe 16 is supplied with the air as described above so as to supply the air-powdered product mixture to the spray distributors, the metering'and mixing means 51 being adjusted if required.

As, in the previously describe embodiment, the excess powdered product falls by gravity onto the bottom 42 and the hopper 44 while being kept at the level of this recovering or recycling element by the presence of i the filtering cartridge 46. When the consumption of the powdered product causes the level of tank 50 to drop below the point ensuring a good operation of the metering and mixing means 51, the float 57 is urged downwardly and closes the switch 58 which allows power to be supplied to the vibrator 47.

The vibrations of the vibrator 47 are transmitted to the recovering means which causes the excess powdered product to fall into the tank 50 and thus reestablishes the optimum level of the product in the tank.

It must be understood that the recycling of the excess product which is collected by the recovering means and also possibly by a cyclone placed in the suction pipe 30, must be compensated from time to time by a complementary filling of the tank 50 when the level of the charge of product in this tank does not permit optimum operation of the metering and mixing means 51.

It was mentioned hereinbefore that, for the purpose of preventing the presence of excessively strong jets in the lower part of the distributor 18, a pressure relief flap l8, is provided. Another solution consists in the provision of a baffle-plate in an adjustable position in front of the slot 20 to ensure the deviation of a variable fraction of each jet as it issues from the distributor. The distributor can also be advantageously inclined so as to prevent droppings from the upper jets causing an increased concentration of product in the lower jets.

lclaim:

1. A device for spraying an electrified powdered coating or treating material onto the surface of a structure, comprising a cabin having opposed walls, means for conveying and supporting said structure in a path in the cabin, means defining apertures in said opposed walls for the passage of said conveying and supporting means and said structure, means for maintaining the interior of the cabin at a pressure lower than a pressure prevailing outside the cabin, spray distributing means located in the cabin for spraying onto said structure supported in said path a mixture of air and said powdered material, means for creating a difference of electrostatic charge between said powdered material of said mixture and said structure, the spray distributing means comprising at least one hollow element, spray outlet means in form of a longitudinally extending slot in the hollow element, means for'dividing said mixture issuing from said outlet means into a plurality of spray jets, said dividing means comprising an element which extends from within the hollow element into said slot and defining, with said outlet means, orifices producing jets of said mixture, a powdered material tank adjacent a lower part of the cabin, adjustable means for metering the amount of powdered material taken from the tank and mixing the material with air,-said adjustable means for metering and mixing the powdered material comprising means defining a cavity having an inlet disposed in the tank for receiving the powdered material in the tank, a compressed air supply pipe for connection to a source of air under pressure for supplying air to said cavity and means for putting said cavity in communication with the hollow element of the spray distributing means, and means for recovering excess powdered material which has not become deposited on said structure, said recovering means being capable of guiding back said excess powdered material into the tank.

2. A device as claimed in claim 1, wherein said means for putting said cavity in communication with the hollow element comprises a tube for homogenizing said mixture.

3. A device as claimed in claim 1, wherein the spray outlet means comprise means defining an elongate opening in the hollow element and the dividing means comprise a strip located in said opening and having two opposed faces and notches in said opposed faces, the notches in each of said opposed faces being spaced equal distances apart from each other and the notches of one of said opposed faces being in staggered relation to the notches of the other of said opposed faces, said notches defining with said opening outlets producing said spray jets.

4. A device as claimed in claim 1, wherein the spray outlet means comprise means defining an upwardly extending elongate opening in the hollow element and the dividing means comprise an upwardly extending strip located in said opening and having a plurality of transversely extending teeth which define a plurality of gaps which progressively increase in length from one gap to another in the direction upwardly of the strip, said teeth having outer ends substantially parallel with said elongate opening.

5. A device as claimed in claim 1, wherein the spray outlet means comprise means defining an upwardly extending elongate opening in the hollow element and the dividing means comprise an elongate member having transversely extending loop portions defining transverse corrugations which progressevely increase in transverse extent from one corrugation to another in the direction upwardly of the member, said corrugations having outer end portions substantially parallel with said elongate openings.

6. A device as claimed in claim 1, wherein the means for creating a difference of electrostatic charge comprise a wire extending in front of the spray outlet means and a high-frequency current generator connected to said wire.

7. A device as claimed in claim 1, wherein the means for creating a difference of electrostatic charge comprise said means for dividing said mixture which is in the form of an electrically conductive element extending in the spray outlet means and a high-frequency current generator connected to the conductive element.

8. A device as claimed in claim 1, wherein the metering and mixing means comprise a tube having a small lower inlet portion adjacent and in spaced relation to a bottom wall of the tank and a large upper outlet end portion, an adjustable shutter associated with the tube for variably closing the outlet end portion, the tube defining said cavity and said cavity communicating with the hollow element in a region intermediate said end portions of the tube.

9. A device as claimed in claim 1, wherein the tank is disposed below the cabin and a passageway connects the tank to the recovering means which are vibratory.

10. A device as claimed in claim 9, wherein the recovering means comprise a hopper located at the base of the cabin, resiliently yieldable means connecting the hopper to a lower part of the cabin and allowing vibration of the hopper relative to the cabin, and vibrating means associated with the hopper for vibratin the ho er, said assa ewa bein flexible.

fil. A d ice as cl imef in clii- 1m 1 further comprising a porous wall dividing the tank into an upper chamber for containing said powdered material and a lower chamber, a pipe for connection to a low-pressure air supply connected to the lower chamber for fluidifying the powdered material in the upper chamber via said porous wall, float means in the upper chamber responsive to the level of the powdered material in the upper chamber and associated with the vibrating means to control operation of the vibrating means in accordance with the level of the powdered material in the upper chamber.

Claims

1. A device for spraying an electrified powdered coating or treating material onto the surface of a structure, comprising a cabin having opposed walls, means for conveying and supporting said structure in a path in the cabin, means defining apertures in said opposed walls for the passage of said conveying and supporting means and said structure, means for maintaining the interior of the cabin at a pressure lower than a pressure prevailing outside the cabin, spray distributing means located in the cabin for spraying onto said structure supported in said path a mixture of air and said powdered material, means for Creating a difference of electrostatic charge between said powdered material of said mixture and said structure, the spray distributing means comprising at least one hollow element, spray outlet means in form of a longitudinally extending slot in the hollow element, means for dividing said mixture issuing from said outlet means into a plurality of spray jets, said dividing means comprising an element which extends from within the hollow element into said slot and defining, with said outlet means, orifices producing jets of said mixture, a powdered material tank adjacent a lower part of the cabin, adjustable means for metering the amount of powdered material taken from the tank and mixing the material with air, said adjustable means for metering and mixing the powdered material comprising means defining a cavity having an inlet disposed in the tank for receiving the powdered material in the tank, a compressed air supply pipe for connection to a source of air under pressure for supplying air to said cavity and means for putting said cavity in communication with the hollow element of the spray distributing means, and means for recovering excess powdered material which has not become deposited on said structure, said recovering means being capable of guiding back said excess powdered material into the tank.

10. A device as claimed in claim 9, wherein the recovering means comprise a hopper located at the base of the cabin, resiliently yieldable means connecting the hopper to a lower part of the cabin and allowing vibration of the hopper relative to the cabin, and vibrating means associated with the hopper for vibrating the hopper, said passageway being flexible.