Sounds like you are installing a bum product or are not specifying appropriate engineering.

Please tell us what you mean by "not very high" and information on the details to see who/what is suspect.

Properly designed holdbacks, whether internal to the gearabox on its mid or high speed shaft, can be quite reliable. There are caveats for poor engineering and bum products.

Note, just because you have a bad experience does not mean we all do. The same can be said for low speed one-way clutch type holdbacks, and brakes used as holdbacks. All have their Achilles heals with: lubrication, speed of rotation, under loaded bearings and cams that slide and not roll, dont load share on multiple drives, brakes that do not apply on time or apply with too much vigor, etc.

There are many ways a low speed or high speed one-way clutch can be damaged in operation due to poor engineering. This forumis not the place to be pedantic on the subject.

We hope to offer advice on a point not on the encyclopedia of points.

Lawrence Nordell

www.conveyor-dynamics.com ■

I think thjat U need to conduct a root cauase anlaysis into the failures.

I would suspect that U have all the same brand of gearboxes and also by default the same type of backstops.

We have had built in issues eg:

backstops with nylon (plastic) cages whihc are prone to "melting deformation" under temp are a no n..the cages hold the cams out and the machine runs back.

also..backstops mounted on sep. layshaft on gearbox and mounted at top do not get enough lube.

I will not name suppliers of these types.

Are yr backstops rated for twice the calc. demand?

Aust. Standards require a certain SF plus recent code asks for 2 equal capacity backstops ie duplicate.

The external backstops are used for critical applications where the failure of the gearbox gearing could lead to runaway. We have had sev, cases of the gearbox breaking shafts.

U need to consider what is the root cuase first and then check out the solutions acc.

Cheers

James ■

I have had much success with Morse external backstops. In the 10 years I have been at this location we have never had a failure.

If your back stops failures are mainly internal. Check to see if the gearboxes were designed for thermal loading or mechanical loading. Thermal ratings usually require heavier reducers. If they were designed for mechanical loading only, there could be an overheating situation that will prematurely fail an internal backstop as they will not take as much heat as the reducer itself.

As others have stated a good failure analysis will get to the root cause of your problem.

Good luck,

Gary Blenkhorn ■

QUOTE: backstops with nylon (plastic) cages whihc are prone to "melting deformation" under temp are a no n..the cages hold the cams out and the machine runs back.

without actually opening a box up you would have no idea of design. most gearboxes are usually good till they go bad, they are out on the ends of hard to reach belts and out of the way places ,which makes regular maintance some what difficult. we have adopted a program to help catch these problems , it is as simple as a infra red temp gun. we take regular readings on every rotating part biweekly. this has caught several problems before it was a critical downtime issue . i didn't mean to hijack this thread with a different subject, it seems relevent maybe if you had a history of operating temps you might see a problem,,, ■

In earlier times people were using power and ratchet type hold-back and differential band brake type hold back. Present practice is to use freewheel type roller hold back or freewheel type “sprag” hold back. These hold backs can be mounted on input or intermediate shaft of gear box or can be mounted on drive pulley shaft. Hold back mounted directly on drive pulley makes it very expensive but some people use it as rotational speed and consequent wear is less. These hold backs of right design, right quality, properly selected and with proper maintenance will give satisfactory life as guaranteed by the manufacturers. The use of these holdbacks is a standard feature by the international reputed companies.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■