What Goes Round Perhaps Shouldn't
There was a very similar thread quite recently dealing with this issue.
Seatings must be correctly machined to the vendors specification to prevent premature distortion of the fit. This is true for bearings, couplings and locking bushes alike. once the seatings are correct there is still no certainty that correctly torqued locking bush bolts will not work loose eventually. In a previous thread I recommended locking wire or tab washers to secure critical fasteners like on aircraft and similar high value machinery. It saves money and maybe lives in the long run.
During my time in aircraft engine development fitting lock wire was the norm rather than an exception. However, I once was assigned a Volvo F12which had undergone a clutch refit the previous day. I ran OK until it hit a steep approach on a motorway slip road. Then Bang, Crash Wallop the trusty beast came to a rapid halt. I managed to get it onto the hard shoulder...because I'm good. It turned out that the service fitters had not wired up the screws which mounted the clutch pressure plate. So I am an advocate for wiring screws, even if I did get berthed in a very good overnight hotel while the job was fixed. So what's the point of the story? If wiring up screwed fasteners helps then you are living on borrowed time if you don't fit them. The clutch in question lasted 1 day. I don't read on the forums of any manufacturer advising locking wire or tab washers. Perhaps they think it is too much trouble, or perhaps they have a motive which I cannot grasp.
Emoticonless again ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Screw & Torque & Lube
Dear Mr. M V Saravanan,
as John here above states: Yes, the seat to a modern locking device (as BIKON is) is to be machined to device mfgr.'s specification.
Then, the bolts have to be torqued a) with correct lube & b) to correct tension & c) in the correct pattern, pls. refer to related topic https://forum.bulk-online.com/showth...tening-Pattern and others elsewhere.
If those bolts have been destroyed, you call it sheared, this might have been due to overtorqueing at assembly.
Also, the locking device must be sized correctly also in regard to bending and deformation of the shaft at the seats. Incorrect sizing would lead imo particularly to coming loose of the device and not shearing of the bolts, but others might have made other experiences.But, some photos of the damage and especially some magnified pics of the the sheared / broken surfaces would be of high interest and would give a better chance to assess the issue.
Regards
R. ■
Expense At Stop To Go Round
Hello John,
why the need for emoticons, this is quite pictorial, as alsways ;-)
"They" say, they don't need wiring or other additional means of fixation, because the bolt, torqued to correct tension, will secure itself due to local deformation and frictional forces.
As to that, jmalbrecht has lots to say to this issue, perhaps you remember. Its not that easy, at that, if not for well qualified and trained staff and correct equipment and so on.
Wiring needs at least someone able to drill small holes into the heads of the bolts ( or are there ready mades around at your place) and there's this magic word about: expense...
I do use locking washers for applications where I deem it necessary and where I can decide it, but then for bought equipment I would lose warranty if I "tamper" with the original setup.
That's a screw, that is.
So, one often has to accept mfgr.'s prescriptions, and thus to additonally clarify all imaginable (si,....) operational situations before buying the item.
Regards
R. ■
Locking Device Bolt Breakage
The most typical reasons for pulley locking device bolt breakage are:
1. Improper design of pulley, shaft, end disk configuration
2. Improper locking device that is not compatible with Item 1 above
3. Improper torque and torque pattern
Items 1 & 2 are linked. The shaft, hub and end disk deflect in such a way that it causes a rocking of the locking device due to the nature of the Bikon 4000 series design. The rocking action causes the tightening bolts to stretch. Repeated stretching pushes the bolt past yield and eventually fatigue failure. This is not a rare event with either Bikon or Rf narrow locking devices with stiff end disks/hubs, and flexible shafts. The belt width and bearing centers can be too large for the narrow locking device. A wider locking device usually corrects for this improper selection. CDI has corrected may such designs.
A second side effect is the narrow locking device will cause a stress riser at the locking device outer shoulder, which can be observed as a local depression on the shaft and at the hub ID.
Often, the designer does not have the ability to analyze such pulley flexure/displacement/permanent deformation in the pulley designs. We have repeatedly published this weakness. Our BELTSTAT code has the ability to do the proper analysis and aid in making the proper locking device selection. You must be able to do 3-D metal displacement and stress analysis of all pulley components and know how to apply the locking device expansion properties. ■
Pulley Bolt Breakage Causes
Added note to above:
The narrow BIKON 4000 series or other equivalent (Rf, Tsubaki, et al.) does not have self-locking tapers between inner and outer locking rings. The wider 1015 and 1012 have self-locking faces. Once the proper torque is applied, the locking device tapered interface locks like a self-locking incline plane (see any machinery handbook on self-releasing and self-locking tapers), then check the narrow vs. wide taper geometries. ■
Locking Assembly Screws Sheared
Pulley shell with hub moving across shaft - locking assembly screws sheared
Dear All,
In one our project sites, there was an issue at the snub pulley in conveyor of BW 1800mm. Shaft at fixed end bearing housing became loose and moved towards the floating end. On checking we found that the lock nut at fixed end was loose. Also the shell with hub had moved across the shaft from fixed end to floating end by 25mm. On checking it was found that all the fixing screws in both the locking assemblies had sheared and the shearing appearing to be old and not recent. The details are as below
Conveyor belt width - 1800mm
Material handled - Coal
Capacity - 2500TPH / 3300TPH
Pulley shaft dia at bearing - 125mm
Pulley shaft dia at locking assembly - 140mm
Size of locking assembly - 140 x 190 and make Bikon 4000 series
Bearing - 22228 CCK/W33
Bearing centers - 2450mm
Overall shaft length - 2582mm
Need help in understanding why the locking assembly screws were sheared and the shell moved across the shaft. Must the locking assembly contact surface in hub be machined or not?
regards,
M V Saravanan ■