A DEVICE FOR DETECTING A FLOW OF POWDER PARTICLES

Abstract: The present invention relates to a device for detecting a flow of powder particles, particularly paint particles, said flow being arranged to flow in a transportation line (3, 6) between a reservoir (1) holding powder particles (2) and at least one powder spray gun (7) of the kind wherein an electrical field charges the particles. A portion (9) of the transportation line (3, 6) is provided on its interior face with an electrostatically friction-charging material and a signal-carrying line (10) interconnects a unit (11) for measuring electrical signals and the electrostatically friction-charging material in said portion (9). Finally, said unit (11) is provided with a third line (12) to close the circuit between said unit and said material in said portion (9). When the powder particles (2) are made to flow through the transportation line (3, 6), a charge is generated as a result of the friction arising upon contact between the particles and the friction-charging material in portion (9). This charge produces an electrical signal, which is detected by the measuring unit (11).

Description: A DEVICE FOR DETECTING A FLOW OF POWDER PARTICLES Technical Field The present invention relates to a device for detecting a flow of powder particles, particularly paint particles, said flow being arranged to flow in a transportation line between a reservoir holding powder particles and at least one powder spray gun of the kind wherein an electrical field charges the particles. Technical Background Electrostatic powder coating processes for application of paint-powder particles use spray guns of a kind wherein an electric field charges the paint-powder particles, for instance guns known as corona guns. The powder particles are supplied to the gun from a powder reservoir by way of transportation lines. In industrial applications large-dimension systems are often used wherein a plurality of guns and transportation lines, for instance in the number of 15, are arranged in parallel. Problems arise when for some reason or other the paint-powder particle flow is obstructed in the transportation line and the particles are prevented from reaching the gun. As a result, an insufficient amount of paint powder will reach the product to be coated. When several guns are used simultaneously it is difficult to discern visually that a certain part of the product is coated to an insufficient degree with the powder for an acceptable layer of paint to be obtained in the subsequent heat treatment in an oven. Consequently, the fault is not corrected until the defect, i.e. the unsatisfactorily painted products, are discovered in the subsequent quality control step. Likewise, it is difficult to discern in which one of the guns that the obstruction occurs. For this reason it is often necessary to examine large parts of the transportation line system to find the fault. Fault-localising and discarding are, however, time-consuming and expensive. Summary of the Invention The object of the present invention is to provide a simple and reliable device for detection of a flow of powder particles that may be used to monitor large transportation-line systems. This object is achieved in accordance with the present invention in a device of the kind defined in the introduction, which device is characterised in that a portion of the transportation line is provided on its interior face with an electrostatically friction-charging material, that a signal-carrying line interconnects a unit for measuring electrical signals and the electrostatically friction-charging material in said portion, and that said unit is provided with a third line to close the circuit between said unit and said material in said portion. The electrostatically friction-chargiπ:: material on the interior face of said transportation lir.e portion is of such a nature that it is electrostatically charged by the friction arising upon contact between the powder par- tides of a flow streaming through the line and the material. The magnitude of the charge of the material is then measured by said unit for measuring electrical signals. In this manner the device in accordance with the invention provides a tool for detection of v/hether or not a particle flow is moving through the transportation line, since the measuring unit shows response only when particles flow through said portion of the transportation line . The third line preferably is connected to earth. In accordance with one embodiment of the invention all of said transportation-line portion is manufactured from an electrostatically friction-charging material. The powder flow can be generated by means of a pump that is connected to the transportation line. Preferably, the electrostatically friction-charging portion of the line could be provided adjacent to the pump. It goes without saying that this portion of the line could be located upstream or downstream from the pump in the direction of travel of the powder flow. It could likewise be located inside the pump itself. In large systems where several powder guns are ar- ranged for simultaneous operation one detecting device in accordance with the invention may be arranged in each one of the transportation lines leading to the respective spray guns. The signals from each one of the measuring units of the respective detecting devices may be supplied to a control panel for system monitoring. Owing to this monitoring feature any flow obstruction in any one transportation line thus may be immediately detected and localised. Consequently, the fault may be remedied before it has led to production disturbances, and the fault- localising time is reduced since the control panel will show in precisely which transportation line the fault is to be found. In addition, the device in accordance with the invention is inexpensive and easy to install, in new as well as in existing transportation-line systems. Brief Description of the Drawings The drawing figure illustrates one embodiment of a device in accordance with the invention. Description of a Preferred Embodiment One embodiment of the device will be described in the following with reference to the drawing figure. A receptacle 1 holding paint-powder particles 2 is connected to a spray gun of the kind known as a corona gun 7, designed to discharge a powder, via a transportation line 3, 6. A pump 4 is located along the transporta- tion line 3, 6, at a point between the receptacle 1 and the gun 7. A portion 9 of the transportation line 3, 6 consists of an electrostatically friction-charging material. In the present case, the portion 9 is located adjacent to the pump 4. Via a signal-carrying line 10, the portion 9 is connected to an electrical-signal measuring unit. In the present case, the unit is a amperemeter 11. A third line 12 connects the amperemeter 11 to earth. When the powder particles 2 are made to flow through the transportation line 3, 6, by means of the pump 4, the friction generated upon contact between the powder particles 2 and the friction-charging material in portion 9 produces a charge in that portion 9. This charge gen- erates a current, which via the signal-carrying line 10 may be read from the amperemeter 11. The earthed line 12 is necessary to close the circuit to ensure that the amperemeter 11 continuously shows the current signal values . If the flow of powder particles 2 in the transportation line 3, 6 were to be throttled or obstructed at any point on its travel from the receptacle 1 to the friction-charging material portion 9, no electric charge is generated in portion 9 and consequently the ampere- meter 11 shows no response. As will be appreciated the above embodiment may be modified in various ways within the scope of protection of the invention as the latter is defined in the appended claims. For instance, only the inner face of the line portion 9 may be coated with an electrostatically friction-charging material. The amperemeter 11 could be replaced by other types of electrical-signal measuring devices, such as a voltage meter. It goes without saying that the device may be used to detect a flow of powder particles of another kind than paint-powder particles. The gun 7 may be positively or negatively polarised and the line 12 should always be connected to earth.

Claims: CLAIMS 1. A device for detecting a flow of powder particles, particularly paint particles, said flow being arranged to flow in a transportation line (3, 6) from a reservoir (1) holding powder particles (2) to at least one powder spray gun (7) of the kind wherein an electrical field charges the particles, c h a r a c t e r i s e d in that a portion (9) of the transporta- tion line (3, 6) is provided on its interior face with an electrostatically friction-charging material, that a signal-carrying line (10) interconnects a unit (11) for measuring electrical signals and the electrostatically friction-charging material in said portion (9), and that said unit (11) is provided with a third line (12) to close the circuit between said unit (11) and said material in said portion (9) . 2. A device as claimed in claim 1, c h a r a c t e r i s e d in that the third line 12) is connected to earth. 3. A device as claimed in claim l or 2, c h a r a ct e r i s e d in that said portion (9) is made from an electrostatically friction-charging material. 4. A device as claimed in any one of the preceding claims, c h a r a c t e r i s e d by a pump (4) located along the transportation line (3, 6) . 5. A device as claimed in claim 4, c h a r a c t e r i s e d in that said portion (9) is located adjacent to the pump (4) 6. A device as claimed in claim 4, c h a r a c t e r i s e d in that said portion (9) of the transportation line (3, 6) is located between the pump (4) and the spray gun (7) . 7. A device as claimed in claim 4, c h a r a c - t e r i s e d in that said portion (9) of the transportation line (3, 6) is located between the reservoir (1) and the pump (4). 8. A device as claimed in claim 4, c h a r a c ¬ t e r i s e d in that said portion (9) of the transportation line (3, 6) is located inside the purr.p (4) AMENDED CLAIMS [received by the International Bureau on 05 May 1999 (05.05.99); original claimsl-8 replaced by new claims 1-6 (1 page)] 1. A device for detecting a flow of powder particles, particularly paint particles, said flow being arranged to flow in a transportation line (3, 6) from a reservoir (1) holding powder particles (2) to at least one powder spray gun (7) of the kind wherein an electrical field charges the particles, characterized in that a portion (9) of the transportation line (3, 6) is provided on its interior face with an electrostatically friction-charging material, that a signal- carrying line (10) interconnects a unit (11) for measuring electrical signals and the electrostatically friction-charging material in said portion (9) , and that said unit (11) is provided with a third line (12) to close the circuit between said unit (11) and said material in said portion (9) , whereby a pump (4) is located along the transportation line (3, 6) and whereby said portion (9) is located adjacent to the pump (4) . 2. A device as claimed in claim 1, characterized in that said portion (9) of the transportation line (3, 6) is located inside the pump (4) . 3. A device as claimed in claim 1 or 2 , charact erized in that the third line 12) is connected to earth. 4. A device as claimed in any of the claims 1 - 3, characterized in that said portion (9) is made from an electrostatically friction-charging material. 5. A device as claimed in any of the claims 1 - 4, characterized in that said portion (9) of the transportation line (3, 6) is located between the pump (4) and the spray gun (7) . 6. A device as claimed in any of the claims 1 - 5, characterized in that said portion (9) of the transportation line (3, 6) is located between the reservoir (1) and the pump (4) .

Inventors: SIMONSSON LARS, SIMONSSON, LARS
Applicants: NORDSON CORP, SIMONSSON LARS, NORDSON CORPORATION, SIMONSSON, LARS
Application year: 1998
Main classification: B05B5
IPC codes: B05B5, B05B7, B05B12, G01F1