kief99
Mechanical
- Nov 23, 2009
- 4
Hi hope anyone can help
I have encountered a problem during the commission of a back to back test rig for industrial gearboxes. The test rig is of mechanical type so the driveline is looped by means of two transfer boxes connected by a long tube, actually two tubes. The operating speed of rotation of these is 1600RPM.
The design of the tubes is such that is made out of a standard tube lenght 4.2m OD 216mm an ID196mm. There are solid hubs welded at the ends which step down the OD and are supported in two pilllow block bearings. The tubes are connected to the tranfer boxes and between each other using gear couplings.
The problem that we have is the vibrations are high on the bearing supports. We have increased the support rigidity with some sucess but not yet acceptable levels. One of the tubes was balanced at high speed up to 1000 RPM but was vibrating at 1300 RPM, And from the balancing machine data, vibrations increase with speed and unbalance also changes with speed. It seems that we are approching first order vibration as the phase of the unbalance force at the meassuring points are almost in phase.
Can anyone with experince sugget an approach to solve the problem?
Some of the options have been
To add a bearing on the middle of the tube restricting from whirling .i.e having the torque tube on three bearings.
To reduce the torque tube length and have three instead of two.
Try to balance the torque tube at operating speed of 1600RPM but would need to balnce it on the test rig as the balancing machine will not reach that speed.
Also other related questions: if the torque tube is balanced under operating speed and no load. when the load is applied the twist from end to end can be up to 0.7 degrees. Would this have a significant effect on the balance.
We suspect that the manufacturing tolerances of the tube section would make it very hard to balance since the tube is behaving as a flexible rotor.
If any one can suggest what would be the best approach to solve the problem or share some knowledge, would appreciate your input.
Thank you
I have encountered a problem during the commission of a back to back test rig for industrial gearboxes. The test rig is of mechanical type so the driveline is looped by means of two transfer boxes connected by a long tube, actually two tubes. The operating speed of rotation of these is 1600RPM.
The design of the tubes is such that is made out of a standard tube lenght 4.2m OD 216mm an ID196mm. There are solid hubs welded at the ends which step down the OD and are supported in two pilllow block bearings. The tubes are connected to the tranfer boxes and between each other using gear couplings.
The problem that we have is the vibrations are high on the bearing supports. We have increased the support rigidity with some sucess but not yet acceptable levels. One of the tubes was balanced at high speed up to 1000 RPM but was vibrating at 1300 RPM, And from the balancing machine data, vibrations increase with speed and unbalance also changes with speed. It seems that we are approching first order vibration as the phase of the unbalance force at the meassuring points are almost in phase.
Can anyone with experince sugget an approach to solve the problem?
Some of the options have been
To add a bearing on the middle of the tube restricting from whirling .i.e having the torque tube on three bearings.
To reduce the torque tube length and have three instead of two.
Try to balance the torque tube at operating speed of 1600RPM but would need to balnce it on the test rig as the balancing machine will not reach that speed.
Also other related questions: if the torque tube is balanced under operating speed and no load. when the load is applied the twist from end to end can be up to 0.7 degrees. Would this have a significant effect on the balance.
We suspect that the manufacturing tolerances of the tube section would make it very hard to balance since the tube is behaving as a flexible rotor.
If any one can suggest what would be the best approach to solve the problem or share some knowledge, would appreciate your input.
Thank you