MXPA98003239A - Po lining system - Google Patents

Abstract

The invention relates to a powder coating system, comprising a plurality of coating units disposed substantially vertically one above the other for simultaneous powder discharge to a workpiece moving in a horizontal direction past the coating units, and further comprising a control means for detecting a powder stream flowing through the respective coating units.

Description

POWDER COATING SYSTEM The invention relates to a powder coating system cising a plurality of units that are arranged substantially vertically one above the other. In a known powder coating system the workpieces to be coated are moved inside a coating cabinet in the horizontal direction after the powder coating guns move up and down, so that all the parts of work will be exposed to dust. As a rule, a plurality of coating guns are arranged so that they meet one after the other (horizontally) in the direction of passage of the work pieces. There are historical reasons for the configurations cising several coating guns, one behind the other: The efficiency of the powder coating was not such as to allow a single coating gun to move up and down and produce a workpiece coated. A sufficiently thick coating could be achieved only with a plurality of coating guns arranged in series one behind the other. The amount of powder discharged by a single coating gun per unit time was not sufficiently constant and satisfactory homogeneity of the powder coating can consequently be obtained only by cooperation of a plurality of coating guns disposed one behind the other. Meanwhile, a great step forward was taken in the development of powder coating technology with respect to the two points mentioned above, and now the coating system is constructed where the coating guns are arranged in vertical orientation one on the other. another one so that, with the work pieces passing them horizontally, only one coating gun is "responsible" for the coating of a particular horizontal strip of the work piece. This configuration has the advantage of allowing the coating booth to be much shorter, as will be readily apparent to those skilled in the art. In this aspect, reference is made to figures 1 and 2 which will be explained in more detail below. However, the arrangement of coating guns aligned vertically gives rise to a new problem. If there is a variation in the amount of powder discharged from a coating gun, or if the coating gun fails (for example, due to plugging in the hose or powder supply nozzle) then a full horizontal strip on the workpiece It will be provided with a very thin coating or without any. Furthermore, this failure can not be made by subsequent coating guns, as would be the case if there were a horizontal succession of coating guns.

Therefore, an object of the present invention is to provide a powder coating system cising a plurality of coating units arranged vertically one above the other and it is ensured that the quality of the coating on the workpiece will not deteriorate if a coating unit gets to suffer a disturbance or failure. This object is fulfilled, according to the invention, by a powder coating system as defined in claim 1 and by a method characterized by the features of claim 15. The invention suggests a means of control that can be incorporated in the powder supply line of a coating unit or in the coating unit itself and which provides a signal as soon as the quality of the flowing powder stream falls below a desired value which could have been established from before or disappears at the same time. In the powder coating system and with the method according to the invention, the powder flow itself is controlled for each coating unit and an alarm can be released as soon as the quantity of powder discharged by a coating unit drops from the requirement or ceases to exist. The measurement signal that reflects the amount of powder or the presence of a powder stream can be generated in any of several suitable manners.

The control means is adapted to detect a voltage stress generated by the powder stream in the powder path of a powder coating unit. To that end, for example, the propulsion nozzle of the powder transport injector or a means for supplying powder to the coating unit is made of a material that will produce tribo tension or friction stress as soon as dust particles are transported. The voltage stress depends on the amount of dust being supplied and transmitted to the wall of the dust transport path when, normally, it would pass over the earth by a line. The voltage stress can be exploited directly by providing a metal plate for the injector, a portion of metal in the powder channel of the coating unit, or a metal section in the medium that supplies the powder to the coating unit. For example, if the injector is installed in an isolated way in a plastic retainer and an instrument to measure current is inserted in the line that leads to the earth, the current tribo that flows towards the earth can be measured based on the voltage tribo generated. By measuring the current tribo a signal can be provided that indicates whether the powder is flowing or not and possibly what proportion of dust is in the powder-air stream. A threshold value can be defined so that an alarm or the like will be triggered if the current threshold falls below a predetermined value. Instead of measuring the voltage tribo or current tribo, it is possible to measure the speed of the dust stream in the dust path, the mass of dust contained in the powder stream flowing in a section of the dust path, or the dust-mass flow in the dust path. Apparatus and methods as described in DE-A-44 06 046 and DE-A-196 50 1 12 can be used for this purpose. Specific reference is made to the aforesaid patent applications and, by this reference, the apparatus and methods specified therein for measuring the speed of the powder stream, the density of the powder stream, and the powder-mass stream they are incorporated in the present application. The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates a known powder coating system; Figure 2 illustrates a powder coating system according to the invention; and Figure 3 illustrates a circuit for detecting the voltage stress of a powder coating unit. Figure 1 shows a conventional coating booth 10 of a powder coating system through which a workpiece to be coated moves in the direction of arrow 12. Normally, the workpiece (not shown) is suspended from a conveyor rail at the same time being guided through the coating booth 10. A side wall of the coating booth is formed with vertical grooves 14 through which a plurality of coating guns 16, arranged horizontally in In one row, powder is introduced into the coating booth 10 to be deposited on the workpiece. The coating guns 16 are mounted on a carriage 18 adapted to carry out reciprocal movements in the vertical direction. As the workpiece advances through the coating booth 10 in the direction of the arrow 12, the coating guns 16 move up and down the carriage 18 to thereby apply a uniform coating on the workpiece. Also shown in Fig. 1, there is a powder container 20 with the required air and powder passages and a control apparatus 22. With this known powder coating system the plurality of coating guns 16 are arranged horizontally one behind the other. the other in the direction of step 12 of the workpiece and alternate in the vertical direction in order to apply a uniform powder coating on the workpiece. The efficiency of the first coating guns was not such as to provide a sufficiently thick coating film by means of a single coating gun. further, the amount of powder expelled from a coating gun 16 per unit time was not constant enough to ensure that the resulting thickness of the coating would be uniform. A uniform and sufficient desirable thickness of the coating can be obtained only by the cooperation of a number of coating guns arranged in succession. However, the arrangement of a plurality of coating guns 16 one behind the other in the direction of passage of the workpiece necessarily caused the coating booths to become rather long. Figure 2 illustrates an example of an electrostatic powder coating system according to the invention having coating spray guns or spray guns 24 arranged vertically one above the other. In Figure 2, the same reference numerals are used as in Figure 1 to designate similar structural members that would not be described once again in this way. The coating guns 24 are mounted on a frame 26 movable in the vertical direction. In a simplified mode they can be immobile. In the powder coating system according to Figure 2, where the coating guns 24 are arranged vertically one above the other, the workpiece also moves through the coating booth 10 in the direction of the arrow 12. Now, however, the coating guns 24 each have only one horizontal "strip" of the workpiece (or a wavy line in the form of a breast - if the coating guns 24 move up and down). With this novel type of powder coating system the powder coating booth 10 can be constructed to be much shorter in the direction of passage 12 of the workpiece. However, the overall system is no longer "impervious" as it is with a plurality of spray guns one behind the other, nor the "average" of powder discharge can be achieved through a plurality of coating guns. that apply powder on the same "strip" of the work piece. For these reasons, a particularly important aspect of the powder coating system according to the present invention is to ensure that the coating guns 24 operate properly. To achieve this, a control means for detecting the flow of powder through the respective coating guns 24 is provided in accordance with the invention. One embodiment of the control means is illustrated in Figure 3. Figure 3 shows a coating gun 24 with a powder supply line 30. The powder supply line 30 in part 32 is made of a tribo generating material. friction tension or tension as soon as the dust particles are transported through line 30. This voltage stress is transmitted to the metal handle 32 and would normally be carried by a ground connection line. In accordance with the invention, however, the supply line 30 is not directly connected to ground. Instead, it is connected by means of an instrument measuring current 34 to a ground connection line 36. In an alternative embodiment, the powder transporting injector (not shown) in the powder coating gun 24 can be made from an material that generates tribo tension. In this case, the injector is mounted in an isolated manner, for example, in a retainer made of 11 speed can be especially accurate if a computer is used in addition to calculating a dust-mass flow based on the measured speed, the mass of dust per unit volume measured, and the dimensions of the dust path. The features described in the above specification, the claims, the drawing, and in the German patent applications cited DE-A-44 06 046 and DE-A-196 50 1 12 can be important, both individually and in any combination, to carry out the invention in its different modalities. plastic and connected through the instrument that measures current 34 to the line of ground connection 36. The tribo voltage depends on the amount of dust being transported. In the medium voltage, therefore, a signal is provided that indicates whether there is dust flow or not and, if so, possibly also how much more dust is being transported. A threshold value can be defined so that an alarm will be released if the voltage voltage falls below that value. The alarm indicates complete failure of a coating gun 24 or may indicate that the amount of powder discharged by at least one of the coating guns is insufficient to produce a coating of its own. In this case, the coating process can also be interrupted automatically, if desired. In an alternative embodiment (not shown) an additional coating gun mounted on the frame 26 can be provided to move vertically to the level of the faulted or decomposed coating gun to take up the task of the poor coating gun. Alternative means for controlling the flow of powder through the respective coating guns 24 are disclosed in DE-A-44 06 046 and DE-A-196 50 1 12. Those publications describe apparatus and methods which serve to measure the mass of the powder. powder per unit volume; to measure the speed of the dust-air stream; to measure the powder-mass flow during transport of the poivo-air mixture; and being suitable for use in detecting the powder stream through the powder supply line and the coating gun, respectively. Express reference is made to the description in the two mentioned patent applications. In accordance with the teaching of those particular publications in control means, it may comprise speed measuring instruments for measuring the velocities of the powder streams through the coating guns. Said speed measuring instrument comprises two measuring electrodes arranged spaced apart on the powder path to detect load variations in the dust path caused by the powder current being transported and to determine the speed of the powder stream with base in the load variations detected. The control means may also comprise measuring instruments for measuring the powder mass per unit volume in a respective section of the powder path. The mass measurement instrument comprises a microwave resonator as well as means for detecting the change in the resonant frequency and / or the microwave amplitude of the microwave resonator and for deriving the powder mass in the powder path section from the resonant frequency and / or the microwave amplitude detected. The determination of the dust current by the combined use of mass measurement instruments and

Claims (3)

1. CLAIMS 1. - Dust coating system, comprising a plurality of coating units (24) arranged substantially vertically one above the other for simultaneous powder discharge to a workpiece that moves with a horizontal component after the coating units and which further comprises a control means (32, 34) for detecting a powder stream flowing through the respective coating units (24).
2. 2. The powder coating system according to claim 1, further characterized by a powder path consisting of a powder supply line (30) leading to the coating unit (24) and a conveying means of powder is associated with each coating unit (24), and that the control means includes a plurality of detector devices (34), each coupled to a respective powder path of a coating unit.
3. 3. The powder coating system according to one of the preceding claims, further characterized in that the control means (34) emits a signal when the powder current through at least one coating unit (24) does not reaches a desired value given. A. The powder coating system according to one of the preceding claims, further characterized in that the control means (32, 34) detects tribo tensions generated by the powder streams flowing through the coating units (24). ) or the dust conveyor is isolated and connected to earth by means of a current measuring instrument (34). 5. The powder coating system according to one of the preceding claims, further characterized in that the powder path or part of the powder path of each coating unit (24) or the powder conveying means is isolated and connected. to earth by means of a current measuring instrument (34). 6. The powder coating system according to one of the preceding claims, further characterized in that the control means comprises speed measuring instruments for measuring the flow velocity of the powder streams passing through the units of the powder. coating (24). 7. = The powder coating system according to claim 6, further characterized in that the speed measuring instrument comprises two measuring electrodes arranged spaced apart on the powder path to detect load variations in the dust path caused by the powder current being transported and to determine the speed of the powder stream based on the detected load variations. 8. The powder coating system according to one of claims 2 to 7, further characterized in that the control means comprises measuring instruments for measuring the mass of powder per unit volume in a respective section of the powder path. 9. The powder coating system according to one of claim 8, further characterized in that the mass measurement instrument comprises a microwave resonator as well as means for detecting a change in the resonant frequency and / or the microwave amplitude. of the microwave resonator and to derive the powder mass in the powder path section from the resonant frequency and / or microwave amplitude detected. 1 - The powder coating system according to claim 8 or 9, further characterized in that the control means comprises a computer to calculate a dust-mass stream based on the measured speed, the mass of powder by volume of measured unit, and the dimensions of the dust path. eleven . The powder coating system according to one of the preceding claims, further characterized in that the plurality of coating units (24) arranged substantially vertically one above the other are motionless and the workpiece is guided by passing them in a horizontal direction. 12. - The powder coating system according to one of claims 1 to 10, further characterized in that the plurality of coating units (24) arranged substantially vertically one above the other are movable together in vertical direction and the workpiece it is guided by passing them horizontally. 13. The powder coating system according to one of the preceding claims, further characterized by an additional coating unit which is movable in the vertical direction and can replace another coating unit for which an insufficient powder stream is detected. 14. The coating system according to one of claims 1 to 13, further characterized by a device for stopping the operations of the powder coating system by detecting an insufficient powder stream of a coating unit. 15. A method for controlling the powder coating system, comprising a plurality of coating units (24) arranged substantially vertically one above the other and discharging powder substantially simultaneously to a workpiece, wherein the part of working moves past the coating units, a stream of powder flowing through the respective coating units is controlled, and a signal is emitted when the powder stream through at least one coating unit does not reach a desired value given.