Powder coating system incorporating improved method and apparatus for monitoring flow rate of entrained particulate flow

• US 5,739,429 A
• Filed: 04/29/1996
• Issued: 04/14/1998
• Est. Priority Date: 07/13/1995
• Status: Expired due to Fees

• Current Assignee: Nordson Corporation
• Original Assignee: Nordson Corporation
• Inventors: Askew, John R., Schmitkons, James W., Shanaberger, Jan L., Price, Richard P.
• Primary Examiner(s): Dougherty, Elizabeth L.
• Assistant Examiner(s): Noori, Max H.
• Application Number:
  US08/639,402
• Time in Patent Office: 715 Days
• Field of Search: 73/195, 73/196, 73/861.04, 73/861.63, 73/861.64, 251/24
• US Class Current: 73/196
• CPC Class Codes: B05B 12/085 responsive to flow or pressure of liquid or other fluent material to be discharged B05B1/3006, B05B1/323, B05B7/1254 take precedence
• CPC Class Codes: B05B 7/14 designed for spraying particulate materials B05B7/16 takes precedence
• CPC Class Codes: B05B 7/1454 comprising means for supplying collected oversprayed particulate material spray booth with arrangements for collecting oversprayed material B05B14/40

Abstract

A system for monitoring the flow rate of particulate material entrained within an air stream includes a feed hopper providng a source of the particulate material, and a hose for conveying the particulate material within the air stream. A pump draws the particulate material from the feed hopper and transports the particulate material with the air stream through the hose. A flow meter is associated with the hose and measures the mass flow rate of the particulate material through the hose to provide a first flow indication. A device is associated with the feed hopper and measures the change in weight of the feed hopper over a predetermined interval to provide a second flow indication. A controller corrects the first flow indication from the flow meter according to the second flow indication from the gravimetric device. The flow measurement system provides an accurate and fast responding flow meter by combining the advantages of a fast responding in-line flow meter with the accuracy of a weight measurement system.

Claims

1. A system for monitoring the flow rate of particulate material entrained within an air stream, which comprises:

a feed hopper providing a source of the particulate material;

a hose for conveying the particulate material within the air stream;

a pump for drawing the particulate material from the feed hopper and transporting the particulate material with the air stream through the hose;

a flow monitor associated with the hose for monitoring the flow of the particulate material through the hose and providing a first flow indication;

a device associated with the feed hopper for measuring the change in weight of the feed hopper over a predetermined time interval and providing a second flow indication; and

a flow indicating device having electrical inputs connected to receive the first and second flow indications from the flow monitor and the weight measuring device, respectively, the flow indicating device including a controller which corrects the first flow indication from the flow monitor according to the second flow indication from the weight measuring device to provide a corrected flow indication.

3. A system as defined in claim 1, wherein the controller includes a display for presenting a corrected flow indication.

4. A system as defined in claim 1, wherein the controller corrects the first flow indication by providing a linear adjustment to the first flow indication.

5. A system as defined in claim 1, wherein the controller corrects subsequent first flow indications from the flow monitor according to a correction factor obtained from comparing a past second flow indication with a comparable first flow indication.

6. A system as defined in claim 1, including two or more hoses for conveying the particulate material within the air stream and two or more flow monitors, each of the flow monitors being associated with one of the hoses and each providing a first flow indication.

7. A system as defined in claim 6, wherein the flow indicating device includes a controller for correcting the first flow indications from the plurality of flow monitors according to the second flow indication from the weight measuring device.

8. A system as defined in claim 1, wherein the flow monitor is a flow meter which measures the mass flow rate of the particulate material through the hose.

9. A system as defined in claim 8, wherein the flow monitor is a venturi tube flow meter.

10. A system as defined in claim 1, comprising in addition a supply hopper connected to supply batches of particulate material to the feed hopper.

11. A system as defined in claim 9, wherein the venturi tube flow meter includes an elongated, substantially straight inlet tube.

12. A system as defined in claim 11, wherein the inlet tube has a length which is at least ten times its internal diameter.

13. A system as defined in claim 9, wherein the venturi tube flow meter includes an elongated throat with pressure taps at at least two locations in the throat.

14. A system as defined in claim 9, wherein the venturi tube flow meter includes pressure taps and the flow meter is connected to a supply of purge air to allow gas to be forced through the pressure taps to purge the pressure taps of accumulations of particulate material.

15. A system as defined in claim 9, wherein the venturi tube flow meter includes pressure taps and filters located in each of the pressure taps.

18. A system as defined in claim 1, wherein the pump is connected to the controller and wherein the controller uses the corrected flow indication to adjust the pump according to a set point.

19. A system as defined in claim 1, wherein the flow indicating device includes a controller which is connected to the pump and which receives the first and second flow indications, and wherein the controller uses the first and second flow indications to adjust the pump.

20. A system as defined in claim 19, comprising in addition a voltage-to-pressure transducer associated with the pump and connected to the controller to adjust pressure to the pump and thereby to adjust the output of the pump.

21. A system as defined in claim 19, including two or more hoses for conveying the particulate material within the air stream and two or more flow monitors, each of the flow monitors being associated with one of the hoses and each providing a first flow indication.

2. A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;

weighing the feed hopper at predetermined time intervals;

comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication; and

comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate, the first flow indication being provided using a venturi tube flow meter which includes pressure sensors and valving mechanisms to selectively connect the pressure sensors to atmosphere to produce a zero reading from the pressure sensors for calibration.

48. A method as defined in claim 2, wherein the first flow indication is provided using a venturi tube flow meter which includes a supply of gas at a regulated pressure, and comprising the additional step of calibrating the pressure sensors by using the valving mechanism to selectively connect the pressure sensors to the gas supply.

16. A system for monitoring the flow rate of particulate material entrained within an air stream, which comprises:

a feed hopper providing a source of the particulate material;

a hose for conveying the particulate material within the air stream;

a pump for drawing the particulate material from the feed hopper and transporting the particulate material with the air stream through the hose;

a venturi tube flow meter associated with the hose for measuring the mass flow rate of the particulate material through the hose and providing a first flow indication, the venturi tube flow meter including pressure taps and filters located in each of the pressure taps, the venturi tube flow meter including pressure sensors and valving mechanisms to selectively connect the pressure sensors to atmosphere to produce a zero reading from the pressure sensors for calibration;

a device associated with the feed hopper for measuring the change in weight of the feed hopper over a predetermined time interval and providing a second flow indication; and

a flow indicating device having electrical inputs connected to receive the first and second flow indications from the flow monitor and the weight measuring device, respectively.

17. A system as defined in claim 16, wherein the venturi tube flow meter includes a supply of gas at a regulated pressure, and wherein the valving mechanism selectively connects the pressure sensors to the gas supply for calibration of the pressure sensors.

22. A powder coating system, which comprises:

a spray gun for spraying the powder onto a workpiece;

a feed hopper providing a source of powder;

a hose for conveying the powder material within an air stream;

a pump for drawing the particulate material from the feed hopper and transporting the particulate material with the air stream from a pump output through the hose;

a flow meter associated with the hose for monitoring the flow rate of the powder through the hose and providing a first flow indication;

a device associated with the feed hopper for measuring the change in weight of the feed hopper over a predetermined interval and providing a second flow indication; and

a controller which is connected to the pump and which receives the first and second flow indications, the controller using the first and second flow indications to adjust the output of the pump.

23. A system as defined in claim 22, comprising in addition a supply hopper connected to the feed hopper, the supply hopper including a valve which when opened provides a batch of powder to the feed hopper.

24. A system as defined in claim 22, comprising in addition a voltage-to-pressure transducer associated with the pump and connected to the controller to adjust pressure to the pump and thereby to adjust the output of the pump.

25. A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

a housing block forming a venturi construction with a throat portion;

a plurality of pressure taps in the housing block;

a plurality of pressure sensors connected to the pressure taps;

a supply of gas for purging the pressure taps; and

a valving mechanism for selectively connecting the pressure taps to the gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration.

26. A venturi tube flow meter assembly as defined in claim 25, including filters located in each of the pressure taps.

28. A venturi tube flow meter assembly as defined in claim 25, comprising in addition an elongated, substantially straight inlet tube connected to the inlet of the housing block.

27. A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

a housing block forming a venturi construction with a throat portion;

a plurality of pressure taps in the housing block;

a plurality of pressure sensors connected to the pressure taps;

a first supply of gas for purging the pressure taps;

a second supply of gas at a regulated pressure; and

a valving mechanism for selectively connecting the pressure taps to the first gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration, the valving mechanism selectively connecting the pressure sensor to the second supply for calibration of the pressure sensors.

29. A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

a housing block having an inlet and an outlet, the block forming a venturi construction with a throat portion;

an elongated, substantially straight inlet tube connected to the inlet of the block;

a plurality of pressure taps in the housing block, two of the taps being located in the throat portion; and

a plurality of pressure sensors connected to the pressure taps.

30. A venturi tube flow meter assembly as defined in claim 29, wherein the inlet tube has a length which is at least ten times its internal diameter.

31. A venturi tube flow meter assembly as defined in claim 29, comprising in addition

a supply of gas for purging the pressure taps;

and

a valving mechanism for selectively connecting the pressure taps to the gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration.

32. A venturi tube flow meter assembly as defined in claim 31, including filters located in each of the pressure taps.

33. A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

a housing block having an inlet and an outlet, the block forming a venturi construction with a throat portion;

an elongated, substantially straight inlet tube connected to the inlet of the block;

a plurality of pressure taps in the housing block, two of the taps being located in the throat portion; and

a plurality of pressure sensors connected to the pressure taps;

a first supply of gas for purging the pressure taps;

a second supply of gas at a regulated pressure; and

a valving mechanism for selectively connecting the pressure taps to the first gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration, the valving mechanism selectively connecting the pressure sensor to the second supply for calibration of the pressure sensors.

34. A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;

weighing the feed hopper at predetermined time intervals;

comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication;

comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate.

35. A method as defined in claim 34, comprising the additional step of continuing to monitor the flow rate in the hose using an in-line flow meter to provide a first flow indication and applying the correction factor previously obtained to the first flow indication to obtain a corrected flow rate.

36. A method as defined in claim 34 for monitoring flow of particulate material from a feed hopper through two or more hoses to two or more dispensers, wherein the monitoring step is performed by using two or more in-line flow meters, each associated with one of the hoses, to provide a plurality of first flow indications, and wherein the plurality of first flow indications is used in association with the change of weight of the feed hopper to apportion the flow between the hoses.

37. A method as defined in claim 34, comprising the additional step of periodically supplying batches of particulate material to the feed hopper from a supply hopper connected to the feed hopper.

38. A method as defined in claim 37, wherein the second flow indication is obtained from previous second flow indications when a batch of particulate material is supplied from the supply hopper to the feed hopper.

39. A method as defined in claim 34, including using a display to present a corrected flow indication.

40. A method as defined in claim 34, wherein the correction factor is applied to the first flow indication to provide a linear adjustment to the first flow indication.

42. A method as defined in claim 34, wherein the first flow indication is provided using a venturi tube flow meter.

43. A method as defined in claim 42, wherein the first flow indication is provided using a venturi tube flow meter with an elongated, substantially straight inlet tube.

44. A method as defined in claim 43, wherein the first flow indication is provided using a venturi tube flow meter with an inlet tube which has a length which is at least ten times its internal diameter.

45. A method as defined in claim 34, wherein the first flow indication is provided using a venturi tube flow meter having an elongated throat with pressure taps at at least two locations in the throat.

46. A method as defined in claim 34, wherein first flow indication is provided using a venturi tube flow meter which includes pressure taps, and wherein the flow meter is connected to a supply of purge air, and comprising the additional step of forcing the gas through the pressure taps to purge the pressure taps of accumulations of particulate material.

47. A method as defined in claim 34, wherein the first flow indication is provided using a venturi tube flow meter which includes pressure taps and filters located in each of the pressure taps.

49. A method as defined in claim 34, comprising the additional steps of using a pump to transport the particulate material with the air stream through the hose and using the corrected flow rate to adjust the pump according to a set point.

50. A method as defined in claim 49, comprising the additional step of using a voltage-to-pressure transducer associated with the pump to adjust pressure to the pump and thereby to adjust the output of the pump.

41. A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;

weighing the feed hopper at predetermined time intervals;

comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication;

comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate; and

correcting subsequent first flow indications from the flow monitor according to a correction factor obtained from comparing a past second flow indication with a comparable first flow indication.