Going Round In Circles.
In paragraph 1 you gave a very comprehensive situation of your bucket wheel operation, finishing with commendation of the fluid coupling behaviour. As you say, bucket rpm varies and the variation is permitted by the fluid coupling. Why would you want to change? Why do you need to monitor the bucket wheel rpm? You cannot have constant speed. Only excessive power will enable you to approach nearly constant speed....which is what bucket wheel manufacturers are in business to provide. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Replacing Bucket Wheel Drive Fluid Coupling
Thank you Mr.John Gateley,
Are all reclaimers bucket wheels fixed with fluid couplings only ? There are hydraulic motors also used for such applications.
Such arrangements may allow the speed variations at the bucket wheel, due to various site conditions.
By monitoring speed of bucket wheel, we may ensure the bucket wheels are operated within the desired conditions, thus protecting bucket wheel and related mechanicals.
Again within bucket wheel system itself, there could be chances that the power transmission may be failed , like, fluid coupling's fuse plug is blown away, gearbox internal damages, shrink-disc slippage etc.,
As far as I know, the site conditions majorly decide the power requirement of reclaimer bucket wheel system.
Regards, ■
Re: Replacing Bucket Wheel Drive Fluid Coupling
Dear Experts,
We had replaced bearings in two reclaimers. In both reclaimers, scrollings were found at bucket wheel shaft gripping area by the shrink disc. That means, relative motion had happened between the bucket wheel and its driving shaft. Shrink-disc suppliers claim that the shrink disc arrangements are maintenance free. "Fit and forget". No periodic retightenings are advised in the manual of OEM also. The bearings were replaced after 4 to 5 years of operation.
Operators never felt about this slippage during operation. After noticing the scrolling marks, we provided Zero Speed Mechanism on the bucket wheel. But even now slippage is seen. It is very minimum. 20 mm slippage was visible, after one week. That means, slippage is happening in microns, which could not be traced by operator or Zero speed switch.
I feel that there should be a fool proof arrangement to avoid this slippage and very good monitoring system to ensure this.
Have you ever faced such problem and eliminated the slippage? Kindly post your opinion.
Regards, ■
No Slip No Way
Dear Mr. Sganesh,
in conjunction with the original theme of the thread i assume, that the drive train consists of an electric motor + fluid cplg + gearbox mounted onto the bucket wheel shaft. The bucket wheel then is fixed onto the shaft by a shrink disc arrangement.
Under such circumstances, the shrink disc arrangement should not slip. If it does so, it might be not sufficiently strong to withstand the operating loads imparted, even if the fluid coupling cushions the torque alterations. However, as the bucket wheel is most probably located between the two bearings, local bending deformation of the bucket wheel shaft must be considered in the design of the shrink disc arr-gmt. Such deformation might lead to loosening of the tight seat. Once the shrink disc arr. starts to slip, in my exp. it will continue to do so even until the whole seat gives way and fixation is lost.
Redesign (if considered) might take two ways at least:
a) stronger shrink disc arrangement considering local bending deformation and a healthy safety margin
b) mechanical principle of fixation by bolting onto a flanged bucket wheel shaft
Regards
R. ■
Really Well Shafted
Your problem is probably faulty machining of the shaft. Makers have often ignored the machining specification because they supplied a built up assembly and no outsider would find out until it was too late. I've come across this practice in oil and gas work as well. Rougher seatings exhibit troughs and crests. With use the crests get deformed and the fit deteriorates. You can retighten the bushes, without telling the OE supplier. Eventually the seating will wear down again until the limit mentioned by Roland is reached.
A similar situation might have occurred with your bearings which last for 4 years. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Replacing Bucket Wheel Drive Fluid Coupling
Thank you Mr.Ronald Heilmann & Mr.John Gateley.
In our reclaimers , the bucket wheel shaft is supported by 02 plummerblocks. In one end, gearbox is fixed & at another end bucket wheel is fixed.
When I browsed few shrink-disc manufacturers web sites, I understood that too smooth or too rough surface finish are not recommonded. I agree with your statements on the importance of the tolerances at the seating area and the serious consequence, if the shaft starts slipping.
Is there any method to stop the reclaimer, if the bucket wheel starts slipping ? What are the preventive or alarm systems implemented reclaimers to raise alarm & to take immediate actions ? Seeking experts advice, whoever had come across this problem.
Regards, ■
Replacing Bucket Wheel Drive Fluid Coupling
Replacing fluid coupling in bucket wheel drive by suitable flexible coupling
Dear experts,
We have a fluid coupling between motor and gearbox, in one of our reclaimers. I think that the slippage between pump and turbine vane may not be constant in the fluid coupling. The slippage may vary according to the material density, depth of scoop, individual bucket's condition, moisture of material, ability to dig in individual materials, operator's skill etc.,. But we did not face any problem in the fluid coupling so far.
Unlike conveyors, there is no monitoring system, to ensure the constant RPM of bucket wheel., i.e., constant power transmission from motor to bucket wheel. We are planning to install ZSS ( Zero Speed Switch or Speed OK switches) proximity switch
at the bucket wheel to ensure constant RPM of bucket wheel. But having doubts on its reliability.
Is it necessary to have fluid coupling in reclaimer bucket wheel drive system? Can it be replaced by any other flexible coupling, to eliminate the slippage in the high speed coupling. This can help me to monitor the bucket wheel RPM more effectively.
Kindly post your valuable opinions.
Thanks & Regards, ■