Balancing Of Idlers
Sir,
Even during the manufacturing stage, since the idlers will be life sealed with grease, there will be a definite movement of grease (of certain mass)inside the bearing housing. On such a condition, how is it possible to balance the idlers precisely.
Further as per your comment on a different thread (Balancing of Idlers), I presume that balancing of Idlers will be required only when the Idlers rotate at speeds greater than 700 RPM. Can you please explain as to how it is done?
Regards ■
Balancing Idlers
Grease cannot make a difference. The roll spins at 600-800 rpm. Differential grease mass and small radius of gyration pails in comparison to errors on the shell during tube mfg or roll assy. Shell influence is about 7 times as sensitive as bearing race for the same mass. Just calculate the amount you need to make a difference at the bearing race diameter and grease mass. The grease becomes highly deformable with little structural integrity during operation.
Talk to the idler manufactures that build rolls for high speed operation - Precismeca (Germany), Prok(Australia), Melco (RSA), Continental (USA). You need a dynamic balance machine to locate the axis and mass to be added. The added mass is welded to the end disk. This can get tricky do to the stress field. Each have their way. See David Thompson's paper, at Perth 1999 IIR Conference, Australia where he told of Alcoa's experience with balancing and machining idlers on high speed conveyors >7m/s. He may have made further publications I believe as Alcoa was investigating 9 m/s.
Lawrence Nordell
Conveyor Dynamics, Inc.
1111 West Holly St
Bellingham, WA 98225 USA
ph 360/671-2200
fx 360/671-8450
email: nordell@conveyor-dynamics.com
www.conveyor-dynamics.com ■
Second Comment
It seems the interest is in post installation balance detection. I dont believe it to be practical or having ever been practiced.
However, noise frequency analysis has been implemented. This is a consideration for long overland conveyors such as the Channar 20 km overland. Noise spectra analysis was used to monitor and trend variations in idler bearing sonic patterns. This is not to be confused with imbalanced force excitation. The idler emits a particular noise pattern asociated with bearing race integrity. As the race begins to spaul, prior to entering the failure mode, the rolling element generates a frequency that is detected and equated to balls/rpm/race. A frequency analyzer (FFT) can be tuned or calibrated to automatically record unacceptable levels that initiate maintenance. For Channar, noise monitoring receiver and recorder equipment was mounted on a pickup.
LK Nordell ■