GB2276103A

GB2276103A - Powder supply system for powder-lacquering welds of a container

Info

Publication number: GB2276103A
Application number: GB9403901A
Authority: GB
Inventors: Walo Steiger; Peter Kengelbacher
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-02
Filing date: 1994-03-01
Publication date: 1994-09-21
Anticipated expiration: 2014-03-01
Also published as: ITMI940225A0; IT1275406B1; GB2276103B; GB9403901D0; ITMI940225A1; DE4403022A1

Description

2276103 METHOD AND APPARATUS FOR THE APPLICATION OF POWDERED LACQUER IN A

POWDER-LACOUERING SYSTEM The invention relates to a method for the application of powdered lacquer in a powder- lacquering system, and to an apparatus for the application of powdered lacquer in a powder-lacquering system.

when container blanks are produced from tin plate, the unprotected weld seam is covered by a coating of lacquer af ter the welding process - at least on the inside of the container blanks. For some considerable time it has become usual to use powdered lacquer for this covering, such powdered lacquer being conducted initially through the welding machine and then conducted into the interior of the container blanks as they leave the welding machine and being applied there in an application device. No unsolvable problems arise as a result of supplying powdered lacquer which, as a mixture of powder and air when mixed with air in a processing system, is conducted into the application system by means of pipes, in the case of conventional container welding machines, wherein the weld seams are produced at a maximum speed of 60 m/min. Attempts have been made for some time to increase the welding speed to 100 or more metres per minute, but such an increase naturally means that a substantially greater quantity of powder per unit of time has to be supplied to the application device. This may be effected in two different ways: firstly by increasing the speed of air conveyed in the pipe system with a constant powder: air ratio, or secondly by increasing the powder content in the conveyed air. Both alternatives are not satisfactory. The first alternative necessitates that a considerable quantity of air in the application device must be removed and sucked-back. The second alternative is not easy to achieve when a large quantity is being conveyed.

In consequence, the basic object of the invention is to provide a method and an apparatus whereby the quantity of powder entering the application system can be accurately controlled.

According to the present invention there is provided a method for the application of powdered lacquer in a powder-lacquering system, wherein the powder is fluidised in a vessel and conveyed as a mixture of powder and air by an injector through a conveyor pipe to a spray head, in which the specific density (powder: air ratio) of the stream of powder and air is reduced by a supply of air before the spray head is reached.

Also according to the present invention there is provided an apparatus for the application of powdered lacquer in a powder- lacquering system, having a fluidising vessel, an injector for supplying conveyed air into a conveyor pipe, which extends from the fluidising vessel to a spray head, wherein an air supply means is disposed in the conveyor pipe at a spacing, which is smaller than the spacing from the fluidising vessel, for introducing additional air into the conveyor pipe.

By supplying additional air into the conveyor pipe at right angles or at an obtuse angle, the stream of powder and air conducted thereto and having a small quantity of air is made thinner and homogeneously mixed from the air inlet location to the application head. The quantity of powder delivered to the application head can be accurately regulated with the supplied quantity of air, and the speed at which the quantity of powder is discharged from the application head can also be set. In the event of the production of containers being interrupted, it is ensured that, with the resumption of production, a homogeneous stream of powder and air again enters the application head within a very short time, so that the delivered quantity of powder- also reaches a constant value again immediately.

The apparatus of the invention has a very simple construction and can also be subsequently incorporated in existing systems.

Because the apparatus is provided close to the application head, no measurable change in the dynamic pressure occurs at the outlet of the powder vessel, in which the powder is fluidised, as a result of air being injected into the conveyor pipe.

The invention is explained more fully with reference to illustrated embodiments. In the drawing:

Figure 1 illustrates a powder application system on a welding machine (schematically illustrated); Figure 2 is a partially fragmentary view of a powder processing vessel, the powder feed pipe and the application head; Figure 3 is a vertical sectional view through the air supply means; Figure 4 is a plan view of the air supply means; and Figure 5 is a cross-sectional view through the air supply means taken along the line IV-IV of Figure 2.

Figure 1 is a schematic view of a known seam welding machine 1 provided with the two electrode rollers 2 and 3, a number of freshly welded can blanks 4, a powder application device 5 provided with a spray head 6, an external suction device 7 and a combined processing and reprocessing system 8 as well as a known heating device 9 for fusing the powder on the seam. An electrical system for producing the high voltage for the electrostatic charging of the powder is symbolically illustrated and denoted by the reference numeral 10. The can blanks 4 are conducted on a conveyor belt 11, which travels around two guide rollers 13, and over the application head 6.

The powder passes from the powder processing system 8 to the application head 6 in a f irst pipe 15, and the excess powder, which has not been precipitated on the weld seam, and the conveyed air for the powder are sucked-back into the processing system 8 through the pipe 17. Powder particles, which may pass between two successive can blanks 4, are also conducted to the processing system 8 through a pipe 19.

The fluidising vessel 21, which is only shown by broken lines in Figure 1 and is used for the f luidising of powder 23, is shown in enlarged form in Figure 2. The base 25 of the fluidising vessel 21 is formed from porous material and permits air to be introduced into the powder column resting thereabove. Because of the introduced air, the powder 23 is "condensed" and may be conducted, like a fluid, to the application or spray head 6 through the conveyor pipe 15. An injector 27 is disposed beneath the vessel 21 to support the powder stream in the pipe 15, and additional air is injected into the "condensed" powder 23 by said injector, so that a mixture of powder and air, having an extremely large portion of powder 23, is conveyed through the pipe 15. A portion of the air injected into the vessel 21 for the fluidisation process leaves the vessel 21 together with the powder 23 through the pipe 15. once a f ilter 29 has been traversed, the remainder of the air may leave the vessel 21 or may be conducted into the processing system 8 without filtration. Powder 23 is supplied to the vessel 21 by means of a charging valve 31, which is not described more fully here.

The configuration of the spray head 6 is not the subject-matter of the invention and, in consequence, is not described more fully. However, its configuration may correspond substantially to that which is described in European Patent Specification No. 0093083.

An air supply means 33 is inserted in the pipe 15 at a distance a from the spray head 6, which spacing A is smaller than the spacing from the vessel 21. The air supply means 33 is illustrated in an enlarged form in Figures 3 to 5. The powder f eed pipe 15 is severed in the region of the air supply means 33 and reconnected by the latter, preferably without a reduction in the crosssection. Air is injected into the region between the two ends of the powder feed pipe 15 by means of two air pipes 35, which are preferably symmetrically disposed, at an obtuse angle a relative to the longitudinal axis A of the conveyor pipe 15. In the embodiment of the invention according to Figures 3 to 5, the two air pipes 35 extend into the pipe 15 at right angles to the axis A and tangentially in the region of the junction S. Instead of being introduced at right angles, the two horizontally extending arms 37 of the air pipes 35 could also assume an obtuse angle a relative to axis A (compare dash- dotted arms 37 in Figure 4).

As illustrated in Figures 3 to 5, an economical embodiment of the air supply means comprises a body 41, in which the bores 43 f or the ends of the pipe 15 are laterally provided. o- ring/seals 39 ensure a positive sealing of the pipe ends inserted in the air supply means 33. The air supply pipes 35 and 37 may comprise appropriate bores in the body of the air supply means. The air could of course also be divided into two arms 35 internally of the air supply means 33 in the body 41, so that only one single air connection would be necessary.

The mode of operation of the method, or respectively of the apparatus, is explained more fully hereinafter. The mixture of powder and air passes to the spray head 6 from the fluidising vessel 21 through the pipe 15. In addition to the already existing conveyed air, air is now supplied from two sides through the pipes 35 and 37 in the air supply means 33, which is provided upstream of the spray head 6. The two jets of air cause the flowing powder 23 to spin-round in the pipe 15 in the air supply means 33. The powder 23, flowing to the air supply means 33, generally does not fill the entire cross-section of the pipe 15, since centrifugal forces act on the powder as a result of inevitable curves in the pipe and cause the powder to slide along the pipe wall in the f orm of a crescent. After air has been supplied in the air supply means 33 and after the two jets of air, which collide withlor encounter each other in the pipe 15, from the air pipes 35 have been intensively mixed, the powder 23 is conducted to the spray head 6 with a smaller percentage of powder in the mixture of powder and air, that is to say with a smaller specific density, and also at a higher speed. The powder 23 may leave the spray head there at the desired speed, which has been adapted exactly to the welding speed, and in an appropriate quantity per unit of time.

At least the portion of the pipe 15 extending from the air supply means 33 to the spray head 6 should be configured in as rectilinear a manner as possible.

Claims

A method f or the application of powdered lacquer in a powder-lacquering system, wherein the powder is fluidised in a vessel and conveyed as a mixture of powder and air by an injector through a conveyor pipe to a spray head, in which the specific density (powder: air ratio) of the stream of powder and air is reduced by a supply of air before the spray head is reached.
2. A method as claimed in claim 1, wherein the air is supplied to the conveyor pipe through at least one pipe.
3. A method as claimed in claim 2, wherein at least one pipe extends tangentially or radially into the conveyor pipe.
4. A method as claimed in claim 3, wherein two pipes, situated opposite each other, extend into the conveyor pipe and the air in said two pipes encounter each other in the conveyor pipe.
5. A method as claimed in any of claims 1 to 4, wherein the air is supplied at right angles or at an obtuse angle (a) relative to the longitudinal axis of the conveyor pipe.
6. A method for the application of powdered lacquer in a powderlacquering system, as claimed in any preceding claim, substantially as hereinbefore described and illustrated.
7. An apparatus for the application of powdered lacquer in a powderlacquering system, having a fluidising vessel, an injector for supplying conveyed air into a conveyor pipe, which extends from the fluidising vessel to a spray head, wherein an air supply means is disposed in the conveyor pipe at a spacing, which is smaller than the spacing from the fluidising vessel, for introducing additional air into the conveyor pipe.
8. An apparatus as claimed in claim 7, wherein the air supply means is inserted in a portion of the conveyor pipe extending in a rectilinear manner.
9. An apparatus as claimed in any of claims 7 or 8, wherein at least one air pipe in the air supply means extends tangentially or radially into the cross-section of the conveyor pipe.
10. An apparatus as claimed in claim 9, wherein at least one air pipe lies at right angles or at an obtuse angle a relative to the axis of the conveyor pipe.
11. An apparatus as claimed in any of claims 7 to 10, wherein the air supply means is disposed in the spray head.
12. An apparatus for the application of powdered lacquer in a powderlacquering system, substantially as hereinbefore described with reference to the accompanying drawings.