阅读说明：本技术 检测和诊断粉末流稳定性的方法 (Method for detecting and diagnosing powder flow stability ) 是由 R.J.莫尔兹 J.科尔梅纳莱斯 E.M.科特勒 S.赫尔墨斯罗 C.依宾尼兹 于 2018-04-26 设计创作，主要内容包括：从粉末进料器(2,111,45)输送到处理设备(3,20)(例如热喷枪)的粉末流可能具有不稳定性,该不稳定性可以使用软管背压来检测和诊断。在粉末软管管线(7,17)中,在粉末管线(7,17)与进料器(2,111,45)的连接处,结合有压力换能器,这允许以高采样率实时测量背压,以检测不稳定性并帮助诊断不稳定性的原因。诊断包括识别软管(7,17)中的周期性振荡,例如声学振荡,以及检测软管堵塞和软管破裂条件。一旦检测到,可以建议适当的纠正措施来纠正不稳定性的原因。(The powder flow delivered from the powder feeder (2,111,45) to the processing equipment (3,20) (e.g., a thermal spray gun) can have instabilities that can be detected and diagnosed using hose back pressure. In the powder hose line (7,17), at the connection of the powder line (7,17) to the feeder (2,111,45), a pressure transducer is incorporated, which allows real-time measurement of back pressure at high sampling rates to detect instability and help diagnose the cause of instability. The diagnostics include identifying periodic oscillations, such as acoustic oscillations, in the hose (7,17) and detecting hose blockage and hose rupture conditions. Once detected, appropriate corrective action can be suggested to correct the cause of the instability.)

1. A method for detecting and/or diagnosing powder transport problems, wherein powder in a carrier gas is directed from a hopper to a final processing apparatus through a powder feed hose, the method comprising:

monitoring the pressure in the powder feed hose; and

based on the monitored pressure, performing at least one of:

detecting a missing or damaged powder feed hose;

detecting the blockage of the powder feeding hose; and

feed instability is detected and diagnosed.

2. The method of claim 1, wherein the absence of powder hose back pressure indicates a missing or damaged powder feed hose.

3. The method of claim 1, wherein an increased powder feed hose back pressure indicates a blockage of the powder feed hose.

4. A method according to claims 2 and 3, wherein when the powder feed hose is neither missing or damaged nor blocked, the method further comprises calculating a standard deviation of the monitored powder feed hose pressure, wherein a standard deviation exceeding a predetermined value detects feed instability.

5. The method of claim 4, wherein the predetermined value for the standard deviation is 5% ten seconds.

6. The method of claims 4 and 5, further comprising digitizing the monitored powder feed hose pressure to calculate the standard deviation.

7. The method of claims 4-6, wherein when a feed instability is detected, the method further comprises analyzing the powder feed hose pressure to identify a periodic oscillation frequency,

wherein the identified oscillation frequency in the range of 0.4 to about 2.0Hz is indicative of acoustic oscillations in the powder feed hose,

wherein an identified oscillation frequency below 0.4Hz indicates a flow transition having a mass flow ratio of the powder to the carrier gas that exceeds a predetermined mass flow ratio, and

wherein the identified oscillation frequency above 2.0Hz is indicative of a control oscillation caused by a pressure ratio between the pressure difference in the hopper and the powder feed hose pressure being outside a predetermined pressure ratio range.

8. The method according to claim 7, characterized by at least one of the following:

wherein the acoustic oscillations can be corrected by changing the length of the powder feed hose,

wherein the predetermined mass flow ratio is 15 and the flow transition can be corrected by reducing the mass flow ratio to less than 15, and

wherein the predetermined pressure ratio ranges between 0.5 and 2.0 and the control oscillations can be corrected by changing hardware of the feeder.

9. The method according to claims 7 and 8, wherein when the analysis of the powder feed hose pressure does not identify a periodic oscillation frequency, the method further comprises:

determining whether the mass flow ratio of the powder to the carrier gas exceeds the predetermined mass flow ratio;

determining whether a pressure ratio between the pressure differential in the hopper and the powder feed hose pressure is outside of the predetermined pressure ratio range;

one of the following:

determining whether a pressure differential in the hopper is at an upper end or a lower end of an operating window; and

determining whether one of the disc speed or the screw speed is at an upper end or a lower end of the operating range;

determining whether the feeder is damaged; and

determining whether the powder is at least one of wet, contaminated, and has poor flow characteristics.

10. The method of claims 7-9, wherein the analysis of the powder feed hose pressure comprises performing a Fast Fourier Transform (FFT) frequency analysis.

11. A system for detecting and/or diagnosing powder transport problems, comprising:

a powder feed hose through which powder is conveyed;

a pressure transducer arranged to detect a pressure within the powder feed hose; and

a feeder diagnostic device coupled to the pressure transducer for monitoring pressure within the powder feed hose for performing at least one of the following operations:

detecting a missing or damaged powder feed hose;

detecting a hose blockage; and

feed instability is detected and diagnosed.

12. The system of claim 11, further comprising: a feeder arranged to dose the powder into the powder feed hose; and a final processing device to which the powder is delivered through the powder feed hose.

13. The system of claims 11 and 12, wherein the pressure transducer is external to the feeder.

14. The system of claims 11-13, wherein the pressure transducer is arranged to detect powder feed hose pressure at any point along the powder delivery path between the feeder and the final processing device.

15. The system of claims 11-14, wherein the pressure transducer is arranged to detect a powder feed hose pressure between the feeder and half the length of the powder feed hose.

16. The system of claims 11-15, wherein the feeder comprises a hopper, and the pressure transducer is disposed at an outlet of one of the feeder and the hopper.

17. The system of claims 11-16, wherein the feeder diagnostic device is external to the feeder.

18. The system of claims 11-17, wherein the pressure transducer is integrated in the feeder.

19. The system of claims 11-18, wherein the feeder diagnostic device is integrated into the feeder.

20. The system of claims 11-19, wherein the feeder diagnostic device is adapted to analyze the powder feed hose pressure to identify a periodic oscillation frequency.

Background

Powder feeding using a conveying hose is typically accomplished using in-flight transport in which particles are entrained in a carrier gas stream to deliver the powder to final processing equipment, such as spray guns. Flow instability can occur for a variety of reasons, resulting in powder flow fluctuations that can affect the effectiveness of the spray.

Lasers have been used to measure optical transmission through the powder stream. However, this approach has several disadvantages:

1. the hose carrying the powder flow must be changed to provide a suitable location, preferably near the processing equipment or end use, where the laser can shine through the powder flow. This change itself can introduce instability by creating discontinuities in the flow.

2. The signal attenuation of the laser light transmission is high, and although this provides excellent sensitivity, the signal may quickly become saturated under high flow conditions, thereby preventing proper diagnosis. This is particularly true where the mass flow ratio of powder to carrier gas is high, in which case the powder flow may completely block laser light transmission.

3. The addition of a laser adds considerable cost to the processing equipment and also adds complexity to the already complex system in which precise feeding and control of the powder flow is necessary.

The two main types of powder feeders are the jet and volumetric types. Both types can feed various powders ranging in size from about 150 μm to less than 5 μm and in powder density from about 3g/cc up to 15 g/cc. In addition, these feeders can feed powders at a wide range of feed rates from about 1g/min up to 300 g/min. These powder feeders may be used in industrial applications such as pharmaceutical, food processing, thermal spraying, and other suitable industries.

Many powder feeders incorporate a pressure transducer, such as an Oerlikon Metco 9MP-CL, in the powder line at the powder feeder outlet. The transducer is used to define a hose pressure feedback which is in turn used to calculate the hopper differential pressure required to control the feed rate in the jet feeder using a gravity device. In some types of powder feeders, hose back pressure may also be used as a safety check to isolate the powder hopper under sudden or unexpected high back pressure conditions. This signal is also displayed on the powder feeder as a strictly filtered signal, which is updated about once per second. Heretofore, no feeder has attempted to use a pressure signal to determine whether the powder flow in the hose is stable.

Disclosure of Invention

In an embodiment, the powder flow delivered from the powder feeder to the processing equipment (i.e., the hot spray gun) may have instability that can be detected and diagnosed using hose back pressure. The incorporation of a pressure transducer in the powder hose line, for example at the connection of the powder line to the feeder, allows the back pressure to be measured in real time at a high sampling rate to detect instability and help diagnose the cause of instability. Diagnostics include identifying periodic oscillations, such as acoustic oscillations, in the hose, and detecting hose blockage and hose rupture conditions. Once detected, appropriate corrective action may be suggested, recommended, and/or taken to correct the cause of the instability.

Embodiments are therefore directed to devices and methods for detecting powder flow fluctuations and detecting and diagnosing instabilities as they occur. Preferably, these devices and methods do not require additional instrumentation.

Embodiments of the present invention relate to methods for detecting and/or diagnosing powder transport problems. Powder entrained in the carrier gas is directed from the hopper to the final processing apparatus by a powder feed hose, and the method comprises monitoring the pressure in the powder feed hose and performing at least one of the following operations based on the monitored pressure: detecting a missing or damaged powder feed hose; detecting the blockage of the powder feeding hose; and detecting and diagnosing feed instability.

According to an embodiment, a lack of powder hose back pressure may indicate a missing or damaged powder feed hose. Furthermore, increasing the powder feed hose back pressure under steady state flow conditions may indicate a powder feed hose blockage. In an embodiment, when the powder feed hose is neither missing or damaged nor blocked, the method may further comprise calculating a standard deviation of the monitored powder feed hose pressure, wherein the standard deviation exceeds a predetermined value to detect feed instability. The predetermined value for the standard deviation may be 5% for ten seconds. In an embodiment, the method may further comprise digitizing the monitored powder feed hose pressure to calculate a standard deviation.

According to an embodiment of the invention, when feed instability is detected, the method may further comprise analyzing the powder feed hose pressure to identify the periodic oscillation frequency. An identified oscillation frequency in the range between 0.4 to about 2.0Hz indicates acoustic oscillations in the powder feed hose, an identified oscillation frequency below 0.4Hz indicates flow transitions with a mass flow ratio of powder to carrier gas exceeding a predetermined mass flow ratio, and an identified oscillation frequency above 2.0Hz indicates control oscillations caused by a pressure ratio between the pressure difference in the hopper and the powder feed hose pressure being outside the predetermined pressure ratio range. Further, there is at least one of the following: the acoustic oscillations may be correctable by changing the length of the powder feed hose; the predetermined mass flow ratio may be 15, and the flow transition may be correctable by reducing the mass flow ratio to less than 15; and the predetermined pressure ratio range may be between 0.5 and 2.0, and the controlling oscillation may be correctable by changing the hardware of the feeder such that the pressure ratio is greater than 0.5 and less than 2.0. Furthermore, when the analysis of the powder feed hose pressure does not identify the periodic oscillation frequency, the method may further comprise: determining whether the mass flow ratio of powder to carrier gas exceeds a predetermined mass flow ratio; determining whether a pressure ratio between the pressure differential in the hopper and the powder feed hose pressure is outside a predetermined pressure ratio range; at least one of the following: determining whether the pressure differential in the hopper is at the upper or lower end of the operating window, and determining whether one of the disc speed or the screw speed is at the upper or lower end of the operating range; determining whether the feeder is damaged; and determining whether the powder is at least one of wet, contaminated, and has poor flow characteristics.

In an embodiment, the analysis of the powder feed hose pressure may include performing a Fast Fourier Transform (FFT) frequency analysis or similar numerical method to convert the time-based pressure signal to the frequency domain.

Embodiments of the present invention relate to systems for detecting and/or diagnosing powder transport problems. The system includes a powder feed hose through which powder is delivered; a pressure transducer arranged to detect a pressure within the powder feed hose; and a feeder diagnostic device coupled to the pressure transducer for monitoring pressure within the powder feed hose for performing at least one of: detecting a missing or damaged powder feed hose; detecting a hose blockage; and detecting and diagnosing feed instability.

In an embodiment, the system may further comprise a feeder arranged to dose powder into the powder feeding hose, and a final processing device to which the powder is delivered through the powder feeding hose.

According to an embodiment, the pressure transducer may be external to the feeder. In particular, the pressure transducer may be arranged to detect the powder feed hose pressure at any point along the powder transport path between the feeder and the final treatment device, or the pressure transducer may be arranged to detect the powder feed hose pressure between the feeder and half the length of the powder feed hose. Further, the feeder may comprise a hopper, and the pressure transducer may be arranged at an outlet of one of the feeder and the hopper. In an embodiment, the feeder diagnostic device may be external to the feeder. In an embodiment, the pressure transducer may be integrated in the feeder. Furthermore, the feeder diagnostic device may be integrated into the feeder.

According to further embodiments of the invention, the feeder diagnostic device may be adapted to analyze the powder feed hose pressure in order to identify the periodic oscillation frequency.

Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.

Drawings

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 shows a flow chart of an exemplary method of powder hose diagnostics;

FIG. 2 shows a block diagram of a known fluidic powder feeder;

FIG. 3 shows a block diagram of a known positive displacement powder feeder;

figure 4 shows a block diagram of a known gravity powder feeder;

FIG. 5 graphically depicts various measurements of instability in a powder hose;

FIG. 6 graphically depicts upstream pressure measurements of acoustic oscillations in a powder hose;

FIG. 7 shows an exemplary test stand for measuring a powder hose with a pressure transducer and a laser transducer;

FIG. 8 graphically depicts a comparison of upstream pressure before and after corrective action is taken to account for acoustic oscillations in the powder hose; and

FIG. 9 graphically depicts upstream hose pressure stability versus pressure ratio calculated as the standard deviation of the hose pressure.

Detailed Description

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Figure 2 shows a functional block diagram of a jet-type powder feeder of known type. The carrier gas flow 1 is supplied by a carrier gas source (not shown) through a hose 7, the hose 7 passing through a bottom portion of the pressurized hopper 4 to transport the powder 6 from the feeder 2 to the processing device 3, e.g. a spray gun. Powder 6 in the hopper 4 is drawn into the hose 7 through the aperture 5 and entrained by the flowing carrier gas stream 1 to the processing apparatus 3. The powder feed rate of the powder 6 through the hose 7 is determined or determined by the pressure difference between the pressure of the pressurized hopper 4 and the pressure of the hose 7. The hopper 4 includes an agitator 9 or mechanical agitator (not shown), such as a blender, driven by a gas vibrator 8 to fluidize the powder 6 in the bottom portion of the hopper 4 to facilitate flow of the powder 6 into the carrier gas stream 1 for delivery through the hose 7.

Figure 3 shows a functional block diagram of a disc or volumetric powder feeder of known type. A powder hopper 14 containing powder 6 supplies powder 6 through an outlet at the bottom of the hopper 14 into a groove 15 of the rotating disc 12. The disk 12 rotates in direction 22 to transport powder 19 from hopper 14 to hose 17. As the powder 19 is conveyed towards the hose 17, a carrier gas flow 11 supplied from a carrier gas source (not shown) is directed into the recess 15, so that the powder flow 13, i.e. the powder 19 entrained in the carrier gas flow 11, is directed to the powder hose 7 and transported to a processing device 20, such as a spray gun. Hopper 14 includes an agitator 16 or mechanical agitator (not shown), such as a blender, driven by a gas vibrator 18 to fluidize powder 19 in the bottom portion of hopper 1 to facilitate flow of powder 19 into grooves 15 of rotating disk 12. The rotational speed of the disc 12 may be about 10-30rpm, which determines the powder feed rate.

Known jet and volumetric powder feeders may be provided with a weight controller. Fig. 4 shows a functional block diagram of an exemplary known arrangement of a jet powder feeder with a weight controller. The hopper 41 may be arranged on a bracket 43 attached to a weigh scale 42, the weigh scale 42 being mounted to a stationary base 44 of a feeder 45. The powder feed rate is directly controlled by the weight loss measured by the weigh scale 42 and is used to adjust the hopper pressure (jet) or the disc speed (volumetric) to achieve the desired powder feed rate.

There are other methods of feeding and/or dosing the powder into the carrier gas stream, including rotating screws, and such rotating screws may be used in embodiments without departing from the spirit and scope of the present invention.

The processing equipment provided by known powder feeders may include spray guns, which may include, but are not limited to, powder coating sprayers, thermal spray guns, and powder dispensers.

In known powder feeders, instabilities in the powder flow may occur, wherein acoustic oscillations, hose blockage and/or hose rupture/disconnection conditions occur. It is therefore desirable to detect the occurrence of such instabilities, to ensure consistent quality of the final product, and in the worst case, to prevent damage to the feed system. It is also desirable to diagnose the detected instability so that corrective action can be taken to eliminate the instability from the feed system. In detecting the occurrence of instabilities in the powder flow, active monitoring of hose pressure feedback can be used to diagnose whether:

1. the powder hose is accidentally disconnected or broken during operation. In this case, the actively monitored hose pressure will not be present or will not be recorded with a sufficiently high value indicating the presence of a properly functioning powder hose. Thus, the first diagnosis is to determine a hose break by the lack of hose back pressure.

2. The powder hose gradually becomes clogged or clogged. In this case, the pressure in the powder hose increases during steady-state operation, i.e. with a constant carrier flow and powder flow. Thus, the second diagnosis is to determine a hose blockage by an increase in hose back pressure.

3. There is instability during feeding or transport. In this case, the standard deviation of the hose back pressure exceeds a certain preset value. Further, by analyzing the type or pattern of instability, the cause of the instability can be determined, as well as corrective measures to reduce or eliminate the instability. Such corrective action may be an automatic or manual action, such as changing hardware settings and/or changing operating parameters. Of course, other corrective actions may be taken to reduce or eliminate the instability without departing from the spirit and scope of the embodiments. The diagnosis is described in the flow chart shown in fig. 1, where the pressure of the powder hose is determined 101. In this regard, a pressure transducer, such as omega PX209-015G10V, sense SPT25-10-0100A, may be arranged to read the powder hose pressure. If the transducer does not produce digital data, the analog data from the transducer may be converted to digital data. At 102, the standard deviation in powder hose pressure is calculated to detect instability. At 103, a frequency analysis of the powder hose pressure is performed to further aid the diagnosis. Finally, at 104, the cause of the instability is diagnosed based on the frequency and operating conditions.

In order to perform a full range of flow stability diagnostics, i.e. as shown in the flow chart of fig. 1, the hose pressure feedback needs to be scanned at a sufficiently high sampling rate, see 101. While sampling rates greater than 100 may be used, for example up to and greater than 100,000 samples per second, it has been found that using sampling rates greater than 50 samples per second generally does not provide additional information for diagnosis. Thus, the sampling rate may be as low as 10 samples per second, preferably 10 to 100,000 samples per second, more preferably 10 to 1000 samples per second, even more preferably 10 to 100 samples per second.

The standard deviation of the pressure values of the powder hoses is calculated as indicated at 102 in fig. 1. If the calculated standard deviation exceeds a preset value, for example in the range of 1% -10% in a time interval of 1-30 seconds, and preferably in the range of 3% -7% in a time interval of 5-20 seconds, and most preferably 5% in a time interval of 10 seconds, the powder hose is considered to have an instability, the cause of which can be diagnosed at 104. The powder hose pressure value is fed into a frequency analysis program, such as a Fast Fourier Transform (FFT), to identify any periodic oscillation frequency. From the frequency analysis, the following causes of instability can be diagnosed:

1. periodic oscillations in the frequency range between 0.4 to about 2.0Hz are generally indicative of acoustic oscillations in the powder hose. Under certain conditions, these oscillations can be substantial (see, e.g., fig. 6, where the pressure variation is 38% or about 1.44psi (99.3 mbar)) of the total pressure, and can exceed 50% of the total pressure, e.g., 100 mbar (1.45 psi). Since the mass flow of the powder oscillates in synchronism with the pressure oscillations, the amplitude of these oscillations in the spray plume of the treatment device is large and can therefore be easily observed.

2. Periodic oscillations in the frequency range less than 0.4Hz generally indicate flow transitions resulting from a high mass flow ratio of the powder flow to the carrier gas flow, for example at a mass flow ratio equal to or greater than 10, preferably at a mass flow ratio equal to or greater than 12, most preferably at a mass flow ratio equal to or greater than 15. Through this diagnosis, the mass flow ratio of the powder flow to the carrier gas flow exceeding the high mass flow ratio can be calculated to identify the cause of the instability.

3. Periodic oscillations in the frequency range above 2.0Hz are generally indicative of control oscillations caused by pressure imbalances of the jet feeder. With this diagnosis, the pressure ratio between the hopper differential pressure and the hose pressure can be calculated to be below 0.5 or above 2.0 (where it is understood that the pressure ratio is stable between 0.5 and 2.0) to identify the cause of instability. Since the volumetric feeder maintains the same pressure between the hopper and the powder hose, such pressure imbalance does not occur in the volumetric feeder.

If no significant periodic frequency is detected in the frequency analysis, there may be a number of problems from which the cause can be determined using the process of elimination of the conditions described below.

1. This may be the cause of instability if the mass flow ratio of powder to carrier gas is a high mass flow ratio, for example 10-20, preferably 12-18, most preferably equal to or greater than 15. The diagnostics are applicable to fluidic and positive displacement feeders. Furthermore, in case it is found that the high mass flow ratio is the cause of instability, corrective measures can be taken to reduce the mass flow ratio of powder to carrier gas to less than the defined high mass flow ratio.

2. If the pressure ratio between the hopper pressure differential and the powder hose pressure is less than 0.5 or greater than 2.0, then a pressure imbalance between the hopper pressure differential and the powder hose pressure may be the cause of instability. This only applies to jet feeders, since positive displacement feeders keep these pressures the same. In the event that such a pressure imbalance is found, corrective action may be taken to change the feeder hardware, such as hose diameter, powder pick-up hole diameter, etc., to change the pressure ratio until it is within limits.

3. If the hopper pressure differential is at the low end (e.g., 10% or less) or at the top end (e.g., 90% or more) of the target operating window of the jet powder feeder, this may indicate the cause of instability in the jet feeder. For example, assuming a target operating window of 1-15psi (0.069-1.034 bar), when the hopper pressure differential is within the low end (e.g., 1-2.4psi (0.069-0.166 bar)) or within the top end (e.g., 13.6-15psi (0.038-1.034 bar)), this may indicate the cause of instability in the jet feeder. In a volumetric feeder, this may be the cause of instability if the disc or screw speed is at the top (e.g. 90% or higher) or at the low end (e.g. 10% or lower) of the normal operating range of the volumetric powder feeder. Thus, for example, assuming a normal operating range of 1-30rpm, this may be a cause of instability when the disk or screw speed is within the low end (e.g., 1-3.9rpm) or high end (e.g., 27.1-30 rpm).

4. If none of the above conditions are met, the cause of instability may be the powder itself, e.g., moisture, contamination, poor flow characteristics such as electrostatic adsorption, or feed equipment damage (e.g., regulator instability, internal leakage, etc.). In this case, corrective action may be taken to perform a leak check of the feeder, recalibrate the feeder, and try another batch of powder, preferably in that order, but not necessarily.

When multiple instabilities are detected, the largest instability, such as the largest amplitude frequency identified in the frequency analysis, is diagnosed for correction. Each identified instability is then subsequently diagnosed, for example, in order of decreasing frequency amplitude.

Embodiments of the method are applicable to any powder feeder that uses in-flight delivery (i.e., entraining powder in a carrier gas) to transport particles to final processing equipment, including but not limited to:

gravity feeder

Positive displacement feeder

Jet type feeder

In order to perform and test the method according to embodiments described in the present application, the test bench is configured to measure the conditions inside the powder hose. Fig. 7 shows a block diagram of a test stand apparatus. The powder feed hose 70 was measured in three different ways:

1. a laser 71, such as Keyence IB-05 with a Keyence IB-1000 control module, is arranged towards the powder outlet end of the powder hose 70 to measure the light transmission through the powder flowing in the powder hose 70 together with the carrier gas. It was found that fluctuations in the powder flow would result in fluctuations in the light transmission through the powder in the hose.

2. A pressure transducer 72, such as omega dyne PX209-015G10V, is mounted in the three-way in the hose located towards the powder outlet end of the powder hose 70 to measure the pressure at the downstream end of the powder hose 70 near the processing apparatus, i.e. the downstream pressure. It was found that fluctuations in powder flow resulted in downstream pressure fluctuations.

3. A pressure transducer 73, such as omega (R) PX209-015G10V, is mounted in the hose in a tee positioned towards the powder inlet end of the powder hose 70 to measure the pressure at the upstream end of the hose, i.e. the upstream pressure. It has been found that fluctuations in powder flow will result in pressure fluctuations. Furthermore, since some known powder feeders (e.g., Oerlikon Metco9MP) include a pressure transducer to define a hose pressure feedback for calculating the hopper pressure differential, such a pressure transducer may additionally be used to measure the upstream pressure, according to embodiments. Furthermore, in powder feeders without such pressure transducers, it has been found that positioning the pressure transducer at the outlet of the hopper or at the inlet of the hose provides advantageous results.

In an exemplary embodiment, a powder feeder, such as a jet-type powder feeder, for example, an Oerlikon Metco 9MP-CL, Oerlikon Metco9MP, or 5MPE or older generation model (e.g., Oerlikon Metco 4MP or 9MP-DJ), is configured to feed powder (e.g., chromium oxide powder having a particle size of-45 +22 μm) via a carrier gas (e.g., argon flowing at 6 standard liters per minute (nlpm)) through a powder hose 70, which powder hose 70 may be, for example, a standard 9 foot long diameter 3/16 "powder hose. It should be noted that any powder size/particle size suitable for use with the selected powder feeder may be used without departing from the spirit and scope of the embodiments. Also, any size hose suitable for the selected feeder and the characteristics of the powder, etc. may be used without departing from the spirit and scope of the embodiments. With this bench set-up, it was found that feed instability was induced in the powder hose at a feed parameter of 40g/min, and the resulting laser light transmission values in the hose 70 as well as the upstream and downstream pressures were measured. To analyze the results of the above measurements of the powder feeder, the laser transducer 71 and pressure transducers 72, 73 may be coupled to a data acquisition module 75, such as a National instruments ni USB-6009, to read the output of the transducers and forward the acquired digital data to a data processing system 76, such as a computer, which includes a memory device for storing, for example, a set of instructions for receiving and plotting light transmission values and pressures over time from the acquired data.

Fig. 5 shows the results of measurements made in the test stand of fig. 7. In particular, it was found that in this test the laser signal amplitude exceeded 50% of the total light block (light block), indicating that the attenuation using the laser was very high, although the powder feed rate was not very high or unstable. Therefore, in the case of a very unstable flow rate or a high powder supply rate, the laser signal in the laser transducer 71 may be easily saturated and thus not usable for diagnosing the feed system. It was found that the downstream pressure signal amplitude from the pressure transducer 72 was very low, which made detection of flow instability difficult. The upstream pressure signal amplitude from the pressure transducer 73 produces sufficient signal amplitude to enable detection while still allowing the pressure transducer sufficient range to avoid signal saturation. The differential pressure calculated as the difference between the hopper pressure and the hose pressure is also plotted and found to be low.

Based on these results, the inventors have found that upstream pressure information read by transducer 73 provides the most advantageous results in detecting and measuring powder flow instabilities in the feed system. Thus, detection and diagnosis of instabilities in the powder hose 70 may be performed using data acquired from the pressure transducer 73 at the outlet of the hopper 74/inlet of the hose 70. To analyze the results, the pressure transducer 73 is coupled to a data acquisition module 75, such as National Instruments NI USB-6009, to read the output of the pressure transducer and forward the acquired digital data to a data processing system 76, such as a computer or PLC, that includes: a storage device for storing, for example, a set of instructions for performing a frequency analysis, such as an FFT, on the acquired data; and a processor for receiving and processing the set of instructions to generate and provide a frequency analysis of the acquired data. Additionally, the memory device or a separate memory device may store another set of instructions that may be processed by the processor to monitor and maintain the pressure differential in the hopper 74. A display readable by a user may receive the results of the frequency analysis. The processor may also send corrective actions to the display for the user to take to mitigate the calculated instability in the powder hose 70. The display may be incorporated into the data processing system 76 or may be a separate display configured to receive data to be displayed from the data processing system 76 via wired or wireless transmission.

Analysis of other results from the test rig showed that the instability had a periodic frequency of about 0.65 Hz. Furthermore, it was found that this periodic instability is a result of acoustic resonance in the powder hose 70, which is one of the main causes of powder flow instability. Further analysis of the bench results confirmed that the acoustic properties of the oscillations follow general acoustic theory. FIG. 6 shows an exemplary graph of oscillations caused by elevated carrier gas flows (e.g., from 6nlpm to 10nlpm) at the same powder flow rate of 40 g/min. Here, the resulting oscillation frequency is almost exactly 1.0 Hz. Additional tests have also shown that the frequency of these acoustic oscillations ranges from about 0.4Hz up to 2.0 Hz. Various corrective measures have been taken to address the acoustic oscillations and it has been found that the resonance can be greatly reduced or eliminated by merely changing the length of the powder hose. By way of example, fig. 8 shows the upstream pressure in a 9 foot long hose through which the powder is delivered, which is a periodic oscillation signal of about 1Hz with an amplitude of about 1.5psi (103 mbar), while when changing to a 15 foot long hose, the periodic oscillation is reduced by almost an order of magnitude, while the frequency drops to about 0.4 Hz.

In other tests, for example, for various powders ranging in density from 3g/cc to as high as 15g/cc, it was found that a mass flow ratio of powder to carrier gas of more than 15 resulted in an unstable flow of all the powders, although some powders showed an unstable flow at a mass flow ratio as low as 10, all tested powders became unstable once the mass flow ratio reached 15 this simulation of the powder flow through the powder hose also supports the discovery of the inventors based on calculations and experimental work done at the munich university (Niederreiter, 2005), i.e., starting instability at approximately the same mass flow ratio (see g. niedereerreiter reiter, "unterschung pfropwentstensting, pfropfenstablit ä ei der pneschumatisen dichtstromef ö rdermg", Doktor-inder gener chemistigme, university pfropnhansche, pfrophenschen, ö rd, and 3683, if it is found that the powder flow rate had to be clearly changed in a manner to prevent the powder flow in a manner that it would have been found to be likely to continue to be blocked in a manner, and to prevent the powder flow when this was also disclosed herein, and if the flow rate was not changed in a consistent manner, the powder was found to be detected in a consistent with this way, the test, the invention, where no.

In other tests, many different powders were fed through the exemplary jet powder feeder of the bench under different flow conditions of carrier gas and powder flow, using an unoptimized feed hardware setup, such as Metco 601 aluminum polyester mixture, Amdry 9951 CoNiCrAlY, and Amdry 6415 chromium oxide. Thus, some test conditions are caused by a pressure imbalance between the hopper pressure differential and the hose pressure. Further, in this test, no acoustic oscillation was generated, and the mass flow ratio of the powder to the carrier gas was kept below 15.

The results of this test are plotted and shown in fig. 9. It can be seen from the figure that the powder flow is stable in all cases when the pressure ratio is between about 0.5 and 2.0, the standard deviation of the hose pressure is below 5% over a 10 second period.

By monitoring and analyzing the powder hose pressure in real time, the inventors have found that instabilities related to the powder flow can be detected, diagnosed and corrected for. Furthermore, the method may form the basis for a way of providing self-diagnosis and self-optimization of the powder feeder.

It should be noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.