When the pump is aligned, the dial indicator returns to 0 degrees, but the value does not return to zero?
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Brother, I am a new field installation engineer of mobile equipment. I recently found a very confusing question.: When performing an alignment check on a centrifugal pump, a dial indicator is mounted on the motor shaft with the pointer pointing toward the pump shaft. During the alignment check process, the axial and radial alignment errors were both within 0.05mm. However, the strange thing is that every time the dial indicator rotates back to the starting point of 0 degrees, the value is always not zero, within +/-0.04mm, and is either positive or negative. And no matter whether the dial indicator is mounted on the pump body itself or on the motor, as long as the pointer of the dial points to the pump shaft or the shaft coupling, there will be this problem. I think generally speaking, as long as there is no problem with the pump itself, the dial indicator reading should be zero every time when it returns to zero during alignment. This pump is a new pump. The DE end is equipped with two SKF 31316-J1/QCL thrust bearings, and the NDE end is an SKF 6215/C3 sliding bearing. I suspected the problem was with the bearings, but I couldn't figure it out. Could any expert please give me some advice? Thank you very much!
From time to time, the watch is not set properly and it is not tight enough.； Can you check the table to see if there is any problem?
If it does not return to zero, it means that the number of the meter is inaccurate. Recheck the installation table for flutter ； Re-change the block table for debugging ； Recheck the amount of coupling shaking when turning.
First of all, thank you for the answers on the 2nd and 3rd floors! When we perform on-site alignment, we will set up a dial indicator in the radial direction and two indicators in the axial direction (end face), so that we can observe the axial movement of the pump shaft caused by the rotating shaft during alignment. But maybe it’s because I’m still young. In all the alignments I’ve seen, the dial indicator usually returns to zero. This is because my understanding is that after the shaft rotates once, no matter whether the shaft or coupling is out of round, the pointer will remain at the original position. In other words, my understanding is that this phenomenon is also caused by the bearing? I have changed the dial indicator several times, but the reading is still the same. ； The meter is mounted on the pump shaft (not on the coupling), but the result is still the same. Does it mean it has nothing to do with the coupling? In addition, turn the pump and motor shafts 1 turn and 2 turns at the same time. . . After n turns, the meter value does not return to zero each time and the readings are either positive or negative. Does this mean that the pump shaft moves up and down when rotating due to bearing problems? Welcome everyone to communicate and discuss, thank you!
If the watch has been replaced and everything is fine, then the problem will not lie with it. You can check to see if the bearings and couplings are loose or if you are turning the coupling too fast. That's my understanding. See if it works
If three gauges are used for alignment, the two axial blocks may not necessarily return to zero because there is axial movement. Installing two blocks will eliminate the movement. The radial direction should theoretically return to zero, but there will be an error in actual operation, but it should not be too large. If it is too large, you can check whether the watch frame is not rigid enough. In addition, the two axles should rotate slowly at the same time when turning.
Find the essentials: 1. When finding the alignment, the upper, lower, left and right points must be determined (clock position 12, 6, 3, 9), the car should be turned at the same time, and the 12 o'clock position must be accurate. The meter cannot be tilted and should be kept vertically. 2. Determine whether the runout of the outer circle of the coupling end face is out of tolerance. 3. The stiffness and stability of the alignment shelf should be good. 4. Consider the temperature difference factor and find the correct temperature change. 5. If the alignment error is too large, it will affect the alignment measurement. 6 The influence of oil film should also be considered.
Is the watch stand original or homemade? Use a small watch. It does not need to return to zero in the axial direction but must return in the radial direction. If it does not return, the positions of the watch stand, watch and the four points on the watch must be accurate.
If three gauges are used for alignment, the two axial blocks may not necessarily return to zero because there is axial movement. Installing two blocks will eliminate the movement. The radial direction should theoretically return to zero, but there will be an error in actual operation, but it should not be too large. If it is too large, you can check whether the watch frame is not rigid enough. In addition, the two axles should rotate slowly at the same time when turning. Before formal alignment, several zero-return tests must be carried out to eliminate factors that do not return to zero.
Generally, it is a problem with the fixation of the watch frame, or there is a problem with the watch. The situation we encounter in practice is a problem with the watch frame.
All the Hai brothers upstairs have said a lot, I will add a few more: The radial direction is required to return to zero, but it is also necessary to check a1+a3=a2+a4. If it meets the above regulations, the measured data is real.
Thank you everyone upstairs for your enthusiastic help! After communicating with the original manufacturer in the past few days, the answer I got is as follows:: Generally, the thrust bearing of a pump is designed as a thrust ball bearing. However, because this pump requires a large fluid load according to the process requirements, the thrust bearing manufacturer of this pump specifically chose a thrust taper roller bearing. However, for this kind of roller bearing, when the pump is turned by hand when there is no load, the pump shaft will move axially during the turning process (a * al clearance), will cause the inclined roller of its roller thrust bearing to move slightly up and down. In this way, when the pump is aligned and the dial indicator returns to the origin, its reading will not be zero. The above is the original reply, everyone is welcome to communicate with us!
gain knowledge, learn* Yes, thank you! It is recommended to have more high-level discussions like this in the future
I do not completely agree with the manufacturer's opinion. The bearing clearance will not cause an error of +/-0.04mm. It is recommended that if you suspect the influence of the bearing, always lean the rotor against one end (working surface) during alignment and check. If it returns to zero, it is the influence of the bearing. Otherwise, other aspects should be further checked. (see 8th floor)
Do not change the position of the needle. Before turning, make a mark on the position of the needle on the coupling (for example, with a marker pen). In addition, the position of the needle must be smooth. At each turning position, it must be ensured that the position of the hands does not change. In addition, when turning, turn slowly according to the direction of the pump and do not turn back and forth to reduce the impact of bearing clearance.
Do not use a magnetic watch base, it must be fixed.