Conclusions of the jamming tests

From these four figures jamming can be detected from the motor torque and motor speed values. When the motor torque starts to rise but motor speed is dropping, it can be concluded that there is active jamming situation going on. Which means that by simply observing motor parameters from the frequency converter can be detected a jamming situation. Static motor speed with frequency converter rarely differs more than +/- 3% of the motor speed reference (+/- 0.3% with DTC frequency converters), which means that limit for motor speed drop can be set in 95% of the reference speed [ABB 2011]. Motor torque limit is a bit trickier but can be set as 40% of the nominal torque but depends on how sensitive the jamming detection needs to be.

Vibration tests and measurements

Vibration tests were done by using acceleration sensor in two distinct direction: Axial and radial. Both times they were attached close to motor. Motor side was chosen, because it was impossible to get acceleration sensor to the other side of the screw conveyor. It would have been filled with granulite. Tests were then done with two angles, 20 degrees and 40 degrees.

The third variable was screw conveyor state. It was driven as full, in other words it was as full as granulite as it takes in normal circumstances. But it was also driven as empty, as in there were no material inside.

Figure 5-19 In this figure is shown how spectrum shifts when motor speed increases. These measure-ments were done with empty, 20 degrees, axial settings, but they are applicable for other settings too. As can be seen, when motor speed increases, vibration increases too.

In figure 5-19 is shown how vibration spectrum shifts with the motor speed. As can be seen, the spectrum shifts to higher vibrations with the increased motor speed. Same phenomenon can be seen with different settings, such as setting inclination to 40 degrees, changing screw conveyor state from empty to full (as in, transfer material while taking up measurements), or switching to radial placement of the acceleration sensor. Motor speed will increase vibra-tion regardless of other settings.

Figure 5-20 In this figure is shown how changing of degree effects on vibration. Left side are 20 degrees measurement with different motor speed and on the right 40 degrees measurement with corresponding motor speeds. As can be seen, comparing 20 degrees to 40 degrees doesn’t have considerable effects on vibration. Spectrum doesn’t shift.

In figure 5-20 is shown how changing inclination effects on vibration. As can be seen, there are no considerable changes on spectrum when comparing the results. In the 100 rpm meas-urements we can observe slightly more vibration in the 20 degrees case compared to 40 degrees case. But other than that, there can’t be observed radical changes. Results are appli-cable even when screw conveyor state is changed from empty to full or acceleration sensor placement is changed from axial to radial.

Figure 5-21 In this figure are shown measurement results when comparing empty and full screw con-veyor. On the left side are measurement results in empty state with different motor speeds, and on the right side are measurement results for full case with corresponding motor speeds. As can be seen, when screw conveyor is empty, it vibrates lot more.

In figure 5-21 are shown measurement results when screw conveyor state is changed from empty to full. As can be seen, screw vibrates a lot more when it is empty compared to when it is full. This is due to damping effects of the material when screw is full. The results are applicable even when inclination is changed from 20 degrees to 40 degrees or acceleration sensor placement is changed from axial to radial.

Figure 5-22 In this figure are shown measurement results for the axial and radial acceleration placement.

On the left side are axial results with different motor speeds, and on the right side are measurement results for the radial settings with corresponding motor speeds. As can be seen, radial placement is more prone to vibrations than axial placement.

In figure 5-22 are shown measurement results for the axial and radial acceleration sensor placements. As can be seen, for every motor speed, radial placement shows more vibrations than in the axial. This means that vibrations are stronger in radial direction in the screw than in axial direction. The measurement results are applicable even when inclination is changed from 20 degrees to 40 degrees or screw conveyor state is changed from empty to full.

Furthermore, it is possible to calculate relative vibration of the screw with regard to specific parameter(s). In tables 5-1 to 5-4 are shown calculated averages from the multiple sets for the both AC and DC component with different parameters. From these four tables it can be further noticed how much does parameter changes effect on vibration. All the values in tables are scaled to 10^-3 mm/s^s rather than 1 mm/s^s used in figures. As can be seen from the tables, inclination of the screw conveyor does not have much effect on the vibration results.

DC-component of the vibration measurements

Table 5-1 In this table is shown 20-degree angle DC-component measurement results with different mo-tor speeds with regards to empty/full and radial/axial states. Note that scale is changed from mm/s² used in figures to 10^-3mm/s^s used in table.

As can be seen from table 5-1, motor speed increases the DC-component of the vibration regardless what other parameters are in 20-degree situation. Motor speed increases vibra-tions up to 17 times more. Radial direction vibravibra-tions are about two times higher than axial direction vibration. Vibration intensity with regards of empty or full state depends greatly on the used speed, but empty screw conveyor vibrates anywhere from two to six times more than full screw conveyor.

Table 5-2 In this table is shown 20-degree AC-component measurement results with different motor speeds with regards to empty/full and radial/axial states. Note that scale is changed from mm/s² used in figures to 10^-3mm/s^s used in table.

As can be seen from table 5-2, motor speed increases the AC-component of the vibration regardless what other parameters are in 20-degree situation. Motor speed increases AC-com-ponent up to 24 times. Radial direction vibrations are about two times higher than axial direction vibrations. Like with DC-component, vibration intensity with regards of empty or full state depends greatly on the used speed, but empty screw conveyor vibrates anywhere from two to seven times more than full screw conveyor. When compared with table 5-1 to table 5-2, we can see that AC-component is about two to three times higher than DC-com-ponent.

DC-component of the vibration measurements

Table 5-3 In this table is shown 40-degree DC-component measurement results with different motor speeds with regards to empty/full and radial/axial states. Note that scale is changed from mm/s² used in figures to 10^-3mm/s^s used in table.

As can be seen from table 5-3, motor speed increases the DC-component of the vibration regardless what other parameters are in 40-degree situation. Motor speed increases vibra-tions up to 23 times more. Radial direction vibravibra-tions are from about equal to two times higher than axial direction vibration. Vibration intensity with regards of empty or full state depends greatly on the used speed, but empty screw conveyor vibrates anywhere from two to five times more than full screw conveyor.

AC-component of the vibration measurements

Table 5-4 In this table is shown 40-degree AC-component measurement results with different motor speeds with regards to empty/full and radial/axial states. Note that scale is changed from mm/s² used in figures to 10^-3mm/s^s used in table.

As can be seen from table 5-4, motor speed increases the AC-component of the vibration regardless what other parameters are in 40-degree situation. Motor speed increases AC-com-ponent up to 34 times. Radial direction vibrations are about two times higher than axial direction vibrations. Like with DC-component, vibration intensity with regards of empty or full state depends greatly on the used speed, but empty screw conveyor vibrates anywhere from two to six times more than full screw conveyor. When compared with table 5-3 to table 5-4, we can see that AC-component is about two to three times higher than DC-component.