EP1104335B1 - Powder spray coating device - Google Patents

Abstract

A spray powder-coating system comprising at least one flow throttle (8, 34) in a compressed-air line of an injector (2). An electronic control unit (50) non-linearly controls the throttle as a function of setpoints.

Description

The invention relates to a powder spray coating device according to the preamble of claims 1 and 2.

Such a powder spray coating apparatus is known from US-A-5,131,350.

Furthermore, from EP 0 636 420 A3 a powder spray coating device is known, which in each case contains a pressure regulator in a conveying air line and in an additional air line. In a computer, powder flow rates (m) are plotted as a first graph axis and feed rates (FV) as a second plot axis. Furthermore, for at least one particular embodiment of the powder spray coating device, the diagram contains a curve which, for this embodiment, the optimum total air rate (GV) consisting of the conveying air and optionally added Represents additional air. At an input (52) of the computer, a powder feed rate setpoint (m-setpoint) can be set. The computer starts from this powder feed rate setpoint on the powder feed rate graph axis and calculates the associated feed rate value (FV) over the total air rate graph. Furthermore, the computer calculates the optionally required additional air rate (ZV target) from the difference between the total air rate and the delivery air rate. The calculated by the computer in this way Förderluftraten setpoints (FV target) and possibly required additional air rate setpoints (ZV target) uses the computer to control the conveying air pressure regulator and the additional air pressure regulator. Such a powder spray coating device works relatively accurately only if the delivery air actual values and the additional air actual values are also included in the control process. The regulators keep the air pressure in their air line constant. However, this only results in a constant delivery air rate, that is, per unit of time conveyed air quantity, when the flow resistance downstream of the controller in question remains constant. As the flow resistance changes, so does the amount of air delivered per unit of time. The values and curves in the diagram correspond to empirical values or values determined by tests for a specific powder conveying device. By bending an air hose, which connects the injector with a control unit, or by using different lengths of such air hoses, or by replacing the injector with other flow resistors to other injectors, changes automatically for these reasons also per unit time promoted conveying air, additional air and / or total amount of air.

These variations in the amounts of air delivered per unit time occur even if diagrams are stored in the computer for several different powder spray coating devices, because it can not be avoided that air hoses are bent or exchanged in daily operation and / or injectors are replaced, which have different flow resistances.

For a good efficiency in the powder spray coating and for a functionally and optically good powder coating surface, however, it is necessary that the powder is conveyed at a certain constant flow rate. If the conveying speed is too low, there is a risk of powder deposits in the powder hose. If the conveying speed is too high, powder particles will bounce off the object to be coated. Suitable conveying speeds for the powder are in the range between about 10 m / s and 20 m / s. For keeping constant the powder flow rate on a given Setpoint or within a certain setpoint range, however, it is necessary to keep the required for the promotion of the powder air flow rate constant.

From US-A-3 625 404 and DE-A-44 09 493 air dividers are known, which include a throttle valve in a conveying air line and a throttle valve in a supplementary air line. The two throttle valves are mechanically coupled with each other. As much as one is opened further, the other is closed further. Throttle valves have the advantage over pressure regulators that they do not keep a constant pressure according to their set opening cross section and thus their set flow resistance, but the per unit time through them flowing air. To adjust the throttles a simple control device is sufficient. A control loop with actual value measurement is not required. Throttle valves can thus be referred to as volume flow controller. The volume flow per unit time is largely independent of changes in the flow resistance in the flow path downstream of the flow restrictor, as long as this flow resistance remains relatively small relative to the resistance of the flow restrictor. In powder spray coating apparatuses, however, the flow resistances in the injector and in the powder hose, which connects the injector with a spray device, are already so great that a disadvantage of the Flow chokes noticeable. The disadvantage is that an adjusting movement on the throttle does not result in a proportional or linear adjustment of the air volume flowing through the throttle opening per unit of time. This results in using the bekannnten tandem throttles only theoretically, but not actually the required per unit time funded total air flow, flow rate and additional air flow. In order to obtain accurate values, curved surfaces would have to be experimentally determined by very complicated and time-consuming experiments, with which the walls of the throttle opening would have to be formed in order to establish a linearity between the adjustment of the throttle cross-section and the resulting changes in the air flow rates per unit time. Such forms of throttle opening cross-sections would have to be determined experimentally for each variant of the powder spray coating apparatuses having different flow resistances, and for each variant, other appropriately designed throttles would have to be used.

By the invention, the object to be achieved to provide a precisely working, but inexpensive device through which a complex and expensive device according to the type of EP -A-0 636 420 and also the inaccuracies by throttling after in the US A-5 131 350, US Pat. No. 3,625,404 and DE-A-44 09 493 are avoided.

This object is achieved according to the invention by the characterizing features of claim 1.

By the invention, throttle valves are not mechanically, but by a computer, in particular a computer, coupled together. In it, the typical values of at least one embodiment of a spray coating device are stored in the simplest manner on the basis of simple tests. In the computer or computer, the typical values of a plurality of such devices can be stored and easily retrieved for the coating operation by programs.

Fig. 1

schematisch eine Pulver-Sprühbeschichtungsvorrichtung nach der Erfindung,

Fig. 2

ein Detail der Sprühbeschichtungsvorrichtung von Fig. 1,

Fig. 3

ein Diagramm für eine Drossel mit einstellbarer Öffnungsgröße in einer Druckluftleitung, wobei auf der horizontalen Achse der Einstellbereich der Drossel als Drehwinkelgrade α und auf der vertikalen Diagrammachse die Druckluftströmungsmengen (Volumen) pro Zeiteinheit von 0 Prozent bis 100 Prozent (maximale Menge bei einem konstanten Eingangs-Luftdruck) je linear unterteilt aufgetragen sind, und in diesem Diagramm mehrere, z.B. drei, verschiedene gekrümmte Kurven A, B und C eingezeichnet sind, über welche sich für eine gewünschte Druckluft-Strömungsmenge der dazu erforderliche Einstellwert α der Drossel ergibt, wobei jede der gekrümmten Kurven A, B und C dem Strömungswiderstand einer anderen Ausführungsform eines sich stromabwärts an die Drossel anschließenden Strömungsweges entspricht und durch Versuche ermittelt wurde, und

Fig. 4

ein Diagramm, in welchem auf einer horizontalen Diagrammachse der Drehwinkel-Einstellbereich der Drossel in 0% bis 100% der Winkelgrade α linear unterteilt aufgetragen ist, wobei diese Unterteilung der horizontalen Diagrammachse gleichzeitig einem linear unterteilten Einstellbereich eines manuellen Sollwert-Eingabeelements oder linearen elektrischen Einstellwerten eines elektrischen Sollwerteinstellers entspricht, ferner auf einer vertikalen Diagrammachse Druckluft-Strömungsmengen (Volumen) pro Zeiteinheit in Form eines Prozentbereiches von 0 Prozent bis 100 Prozent aufgetragen sind, und die drei gekrümmten Kurven A, B und C für die drei Strömungswege,

von welchen jeder einen anderen Strömungswiderstand hat, eingetragen sind, und außerdem eine gerade Diagrammlinie eingezeichnet ist, so daß ein Rechner oder Computer von einem Sollwert auf der horizontalen Diagrammachse vertikal nach oben zur geraden Diagrammlinie, dann horizontal zu der betreffenden gekrümmten Kurve A, B oder C, und dann wieder vertikal nach unten zur horizontalen Diagrammachse "gehen" kann und damit dort den Winkel α in Prozent findet, auf welchen er die Drossel einstellen soll, damit sich eine Druckluft-Strömungsmenge (V) pro Zeiteinheit ergibt, welche auf der vertikalen Diagrammachse auf der Höhe liegt, auf welcher die vertikale Projektionslinie des Sollwertes die gerade Diagrammlinie kreuzt.The invention will now be described by way of example with reference to the drawings of a preferred embodiment. In the drawings show

Fig. 1

schematically a powder spray coating device according to the invention,

Fig. 2

a detail of the spray coating apparatus of Fig. 1,

Fig. 3

a diagram for a throttle with adjustable opening size in a compressed air line, wherein on the horizontal axis of the adjustment of the throttle as rotation angle degrees α and on the vertical diagram axis, the compressed air flow rates (volume) per unit time of 0 Percent up to 100 percent (maximum amount at a constant inlet air pressure) are plotted per linearly divided, and in this diagram a plurality, for example three, different curved curves A, B and C are shown, over which for a desired compressed air flow rate of required adjustment value α of the throttle results, each of the curved curves A, B and C, the flow resistance of another embodiment of a downstream of the throttle adjoining the flow path and was determined by experiments, and

Fig. 4

a diagram in which is plotted on a horizontal axis diagram, the rotation angle adjustment range of the throttle in 0% to 100% of the angular degrees α linearly divided, this subdivision of the horizontal diagram axis simultaneously a linearly divided adjustment range of a manual setpoint input element or linear electrical set values of electrical setpoint adjuster, further plotted on a vertical graph axis compressed air flow rate (volume) per unit time in the form of a percentage range from 0 percent to 100 percent, and the three curved curves A, B and C for the three flow paths,

of which each has a different flow resistance, are registered, and also a straight graph line is drawn, so that a computer or computer from a target value on the horizontal graph axis vertically up to the straight graph line, then horizontally to the respective curved curve A, B or C, and then again vertically down to the horizontal diagram axis "go" and thus there is the angle α in percent, on which he should adjust the throttle, so that there is a compressed air flow rate (V) per unit time, which on the vertical Chart axis is at the height at which the vertical projection line of the setpoint crosses the straight chart line.

Fig. 1 shows an axial section of an injector 2 as a pneumatic powder feed pump. A conveying air line 4 with a throttle 8 which can be adjusted by a servomotor 6 is connected to an injector nozzle 10. An air-powder channel 12 is arranged axially opposite the injector nozzle 10. The conveying air generated on its way from the injector nozzle 10 to the air-powder channel 12 in a region 14 a negative pressure, through which powder 15 is sucked from a powder container 16 through a suction pipe 18 in the conveying air. The conveying air conveys the powder through the air-powder channel 12, a powder hose 20 and then through a manual or automatic spray gun 22 on an object to be coated 24. The spray gun 22 may comprise one or more high voltage electrodes 26 in a known manner for electrostatic charging of the coating powder. According to another embodiment, the powder hose 20 can open into a further powder container 30 and optionally be replaced by a rigid tube.

An additional air line 32 also includes a throttle 34, the opening cross-section of a further servomotor 36 is adjustable. The compressed air of the additional air line 32 arrives at a point located downstream of the injector nozzle 10 into the air-powder channel 12. According to an embodiment not shown, the additional air line 32 could open into the vacuum region 14.

The amount of powder delivered by the injector 2 is approximately directly proportional to the amount of conveying air delivered per unit time and also approximately proportional to the size of the negative pressure in the vacuum region 14. The less powder to be conveyed per unit time, the smaller the quantity of conveying air per unit time. For small quantities of powder and correspondingly small quantities of conveying air, additional air must be added to the additional air line 32, so that no powder is deposited in the powder hose 20. The total amount of air consisting of conveying air and additional air is preferably constant for the known powder spray coating equipment so large that the flow velocity in the powder hose 20 in the area between 10-15 m / s. For this reason, it is important that the total amount of air is kept constant.

The downstream ends of the conveying air line 4 and the additional air line 32 are connected to a compressed air supply line 40, which is supplied via a pressure regulator 42 from a compressed air source 44, for example the compressed air system of a company, with compressed air. In the compressed air supply line downstream of the pressure regulator 42, an adjustable throttle 46 may be arranged, which is adjustable by a servo motor 48 so that the total amount of air per unit time is kept constant.

The servomotors 6, 36 and 48 are controlled by an electronic control device 50 connected to them as a function of desired values. Actual values of the various compressed air streams do not need to be measured and taken into account for the adjustment of the throttles 6, 36 and 48, since the throttles can be set precisely in the manner described below to obtain desired compressed air flow rates per unit of time without a control device having actual value. Feedback is required.

The electronic control device 50 contains at least one computer or computer. It also includes a manual setpoint adjuster 52. The setpoint adjuster 52 has a manual adjustment element 54 in the form of a pushbutton, slider or a rotary knob, wherein in the present Case is assumed that it is a knob. The manual adjustment member 54 is adjustable relative to a linearly divided scale 56 over a rotation angle of for example 180 °. These 180 ° are linearly divided on the horizontal diagram axis of FIG. 3 or linearly divided in FIG. 4 on the horizontal diagram axis in 0% to 100%.

The scale 56 may be labeled with angular degrees or percentages or compressed air flow rates per unit time or amounts of powder per unit time or their percentages.

In the electrical control device 50, a total air setpoint for the per unit time funded total amount of air consisting of conveying air of the conveying air line 4 and additional air of the additional air line 32 is stored. To control the throttle 34 of the additional air line 32, the control device 50 needs only a set value for the per unit time promoted conveying air quantity of the conveying air line 4 to be input to the setpoint adjuster 52. The control device 50 then calculates the difference value from the total air setpoint value minus the conveying air setpoint value and uses this as setpoint value for setting the additional air throttle 34.

The control device 50 can according to the embodiment shown here for all three throttles 8, 34 and 46 or even for only one or two of these throttles be used. Each of these chokes 8, 34 and 46 can be controlled by the control device 50 according to the diagram of Fig. 3 or the diagram of Fig. 4, without an actual value measurement and an actual value feedback for a control is required. Representative of all throttles, the control of the conveying air throttle 8 will be described below.

According to one embodiment of the invention, a diagram according to FIG. 3 is stored in the control device 50 of FIG. 1 for each throttle 8, 34 and 46. On the horizontal diagram axis, the setting rotational angle of the respective throttle 8 or 34 and 46 are linearly plotted. The vertical graph axis plots linearly in percent percentages from zero percent to 100 percent of the compressed air flow rates per unit time that can be conveyed through the restrictor at a given constant input air pressure. In the diagram of FIG. 3 projection lines 60, 61, 62 and 63 are entered for the curve A, for example for the volume percentages 20, 30, 80 and 90 of the vertical diagram axis, through which the corresponding setting angles α for the relevant throttle 8, 34 or 46 result. The type and size of the curvature of the curve A is dependent on the flow resistance of the flow path, which downstream of the respective throttle 8 or 34 and 46, respectively. This means that for each flow path, the downstream of the respective throttle 8 or 34 or 46 has a different resistance, a corresponding curve in the control device 50 must be stored. As an example of two further embodiments, the two further differently curved curves B and C are shown in FIG.

For the adjustment of the conveying air of the conveying air line 4 through the throttle 8 is applied to the setpoint adjuster 52 in linear distribution either also in percent or in a specific unit linearly the relevant conveying air flow rate per unit time. Since these values are directly proportional to the amount of powder delivered per unit of time, the percentages can also be regarded as a corresponding quantity of powder or the scale can be labeled with powder delivery rates per unit time.

The set point for the throttle 34 of the additional air line 32, the controller 50 is calculated by calculating the difference value from the total air flow rate per unit time minus the delivery air flow rate per unit time. 3 corresponding diagram of the additional air throttle 34 are also curved diagram lines similar to the curves A, B and C used, the curvature of the flow resistance of the flow path downstream of the additional air throttle 34 is dependent. Since the additional air has much less influence on the coating quality than the conveying air, the additional air of the additional air line 32 could be controlled instead of by a throttle 34 by a pressure regulator, which but would be more expensive. Also in the supply line 40, the throttle 46 can be controlled in the same manner according to a diagram of FIG. 3, this throttle 46 could be omitted, since the controller 50 from the sum of conveying air and additional air calculate the total amount of air and thereby through the throttles 8 and 34 of the conveying air line 4 and the additional air line 32 can keep the total air rate constant.

As the projection lines 60, 61, 62 and 63 of Fig. 3 show, the throttle adjustment change values α are not proportional to the compressed air amount change values. For example, for 10% change in the amount of compressed air in the range of 20% to 30%, a much smaller change in the setting angle α of the throttle is required than in the upper percentage range, for example between 80% and 90%, which is marked by hatched boxes 64 and 65.

In the further embodiment according to the invention according to the diagram of FIG. 4, in addition to the curved diagram lines A, B and C, a straight diagram line D is entered, which as well as the curved diagram characteristics A, B and C were determined by tests and in the control device 50 is stored in hardware or in software. The straight graph line D in effect represents a "linearization" of the non-linear dependence of the air flow rate per unit time on the setting of the throttle. On the horizontal graph axis, the adjustment range of the manual Set point adjustment element 54 linearly plotted from 0% to 100% of adjustment angles α. This division also applies to the adjustment range of the respective throttle. If electric adjustment values are used by a higher-level control device instead of a manual adjustment element 54, then the same applies to the horizontal diagram axis, for example for clock signals or for other types of electrical current and / or voltage. When using electric stepper motors as servomotors 6 or 36 or 48, it is expedient to use clock pulses. These electrical variants are also applicable to a diagram according to FIG. 3. On the vertical diagram axis of FIG. 4, the air flow rate per unit time is plotted in 0% to 100% or in actual units of value for the relevant type of air. The diagram of Fig. 4 is described here as an example of the conveying air throttle 8, however, similar diagrams are also stored for the optional additional air throttle 34 and possibly existing supply air throttle 46 in the control device 50. Their set values arranged on the horizontal diagram axis are obtained in the same way as described above.

As shown in FIG. 4, dashed projection lines 66, 67 and 68 for the curved diagram line A, at the setpoint adjuster 52, a linear value can be set manually or electrically, which is proportional to a value of the vertical diagram axis. Of this value the horizontal axis of the diagram, the control device 50 corresponding to the projection line 66 vertically upwards to the straight line D, then according to the projection line 67 horizontally to the curved diagram line A, and then according to the projection line 68 back down again vertically to the horizontal diagram axis to the there specified value, which is the value at which the throttle 8 must be adjusted by its servo motor 6 from the controller 50 so as to give a conveying air amount per unit time, which is set at the setpoint adjuster 52.

Claims (10)

1. Powder spray-coating device comprising an injector (2) in the form of a pneumatic feed pump, at least one compressed air line for supplying compressed air to the injector, a flow restrictor (8, 34, 36) in at least one of the compressed air lines of which there is at least one, an electronic control installation (50) having a computer for adjusting the aperture cross-section of the flow restrictor (8, 34, 36) as a function of specified data, characterised in that in the control installation (50), at least for the flow resistance of one embodiment of the flow path adjoining downstream from the flow restrictor, the relationship between the setting of the flow restrictor aperture and desired values for the stream of compressed air controlled by this flow restrictor is stored in a diagram and the control installation (50) controls a servomotor (6, 36, 48) of the flow restrictor (8, 34, 46) as a function of this diagram and by this means, in the event of changes to the set desired value, brings about a change in the compressed air flow rate per unit time proportional thereto, that in the control installation (50) the compressed air flow rates per unit time are plotted on one axis of the diagram and the desired value settings of a desired value setter (52) required for this purpose are plotted on another axis of the diagram, and that in the diagram of the control installation, for each embodiment of the flow path adjoining downstream from the flow restrictor (8, 34, 46) a specific curved characteristic curve which is a function of the flow resistance of this flow path is stored, by means of which the control installation sets non-linearly the servomotor (6, 36, 48) of the flow restrictor (8, 34, 46) for each set desired value of the compressed air flow rate and in doing so generates an actual value of the flow rate per unit time which is proportionately dependent on the set desired value.
2. Powder spray-coating device comprising an injector (2) in the form of a pneumatic feed pump, at least one compressed air line for supplying compressed air to the injector, a flow restrictor (8, 34, 36) in at least one of the compressed air lines of which there is at least one, an electronic control installation (50) having a computer for adjusting the aperture cross-section of the flow restrictor (8, 34, 36) as a function of specified data, characterised in that in the control installation (50), at least for the flow resistance of one embodiment of the flow path adjoining downstream from the flow restrictor, the relationship between the setting of the flow restrictor aperture and desired values for the stream of compressed air controlled by this flow restrictor is stored in a diagram and the control installation (50) controls a servomotor (6, 36, 48) of the flow restrictor (8, 34, 46) as a function of this diagram and by this means in the event of changes to the set desired value brings about a change in the compressed air flow rate per unit time proportional thereto, that in the diagram of the control installation (50) compressed air flow rates per unit time are plotted linearly on one axis of the diagram and diaphragm opening cross-sections are plotted linearly on another axis of the diagram; that for at least one embodiment of a flow path adjoining downstream from the flow restrictor (8, 34, 46) a curved characteristic curve (A, B, C) is plotted in the diagram, which curve reproduces the actual relationship between, the compressed air flow rate and the diaphragm opening cross-sections, wherein for each required throughput flow rate the setting of the diaphragm opening cross-section needed therefor is obtained from the curved characteristic curve; that a straight characteristic line (D) is plotted in the diagram, which line corresponds to a theoretical, in reality non-existent linear relationship between the compressed air flow rate per unit time and the settings of the diaphragm opening cross-section; that the control installation (50) has a desired value input (52) for the input of linearly variable desired values and is constructed to take in each case an opening cross-section on the axis of the diaphragm opening cross-section diagram corresponding to the desired value and to reflect it back onto the axis of the diaphragm opening cross-section diagram via the straight characteristic line (D) and the curved characteristic curve (A, B, C) and then to set the diaphragm cross-section by controlling the servomotor (6, 36, 48) in accordance with the new diaphragm opening cross-sectional value so determined.
3. Powder spray-coating device according to claim 1 or 2, characterised in that in the control installation (50), for at least two embodiments of a flow path adjoining downstream from the flow restrictor, which each have a different flow resistance, the values for said relationship are stored in the diagram.
4. Powder spray-coating device according to any of claims 1 to 3, characterised in that the at least single compressed air line (4) containing the flow restrictor (8) is connected to an injector nozzle (10) of the injector (2) and that the flow restrictor (8) is arranged in such a way that through it can flow only the compressed air conveyed as so-called transport air through the injector nozzle (10).
5. Powder spray-coating device according to any of claims 1 to 4, characterised in that the at least single compressed air line (4) containing the flow restrictor (34) is connected to an air-powder channel (12) of the injector (2) extending downstream from the injector nozzle (10) and that the flow restrictor (34) is arranged in such a way that through it can flow only the compressed air conveyed as so-called secondary air into the air-powder channel (12) without flowing through the injector nozzle (10).
6. Powder spray-coating device according to claim 4, characterised in that another (32) of the compressed air lines is connected as the secondary air line to an air-powder channel (12) of the injector (2) which extends downstream from the injector nozzle (10), that this secondary air line (32) has a flow restrictor (34), that in the control installation (50) at least one total air desired value for the sum of the transport air (8) and secondary air (32) is stored or is storable, and that the control installation (50) has means for arriving at the difference value of the total air desired value minus a transport air desired value and for setting the secondary air on the flow restrictor (34) of the secondary air line (32) in accordance with this difference value as the desired value for the secondary air.
7. Powder spray-coating device according to claim 6, characterised in that in the control installation (50), for at least one embodiment of the flow path adjoining the flow restrictor (34) of the secondary line (32) and exhibiting a certain flow resistance, values,for the secondary air flow rates per unit time and experimentally determined settings of this flow restrictor (34) needed for this purpose are stored, and that the flow restrictor (34) is settable by the control installation (50) to the value whose associated secondary air flow rate corresponds to said difference value, wherein said difference value is the desired value for the secondary air flow rate.
8. Powder spray-coating device according to any of claims 6 and 7, characterised in that the control installation (50) has a desired value transmitter input (52) on which transport air desired values are inputtable.
9. Powder spray-coating device according to claim 8, characterised in that the desired value transmitter input has a manual setting element.
10. Powder spray-coating device according to claim 8, characterised in that on the desired value transmitter input (52) the desired value is inputtable by means of electric signals.

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