Dear Ajit,

Have the Australian standards not described the specification for a proof test interval for conveyor backstops ( mandatory)?

If they have not, then they can reject any test. ■

1. I cannot share,

1a. Regarding the frequency, perhaps a FEMA is a practicable option.

2. For low speed holdbacks, I am aware of: load testing, and measurement [i.e. "strain gauge"].

I am aware of a minimum of two off low speed holdback manufacturers, that retail in Australia, that have a position regarding this matter.

Perhaps the following is off topic, however generally speaking, according to me: if holdbacks are required, the holdbacks must be low speed.

Regards,

Lyle ■

It seems like this Australian standard might have been written for Ireland.

Seriously though: it is not specific & therefore not acceptable as a standard. (Which is also the Brexiteers' view)

To test you need to bring a fully laden conveyor to rest; check the brake is on; uncouple the motor & release the brake.

If the conveyor doesn't run back then the sprag is working.

Its not rocket science: unless you want to find somewhere to bond a strain gauge into the workings & then calculate....what?

The standards recommendation to monitor wear & operation is covered in my 3rd sentence except for my ignoring 'effective' because either it slips or doesn't slip (effectively writing)

Holset used to make a gradual release holdback to release the locked in tension after a stall (NCB rules after a fatality). So please remember to make sure nobody is in a place of danger when you do your test. ■

Hello,

Once the hold-back has become part of operating installation, it will become impractical to remove it and send it to testing laboratory to authenticate its health (hold-back torque capacity). In this situation the system will remain idle till the hold-back come back again and become part of the system (installation) unless one has spare hold-back, time and take all the trouble to refit.

Easier / practical solution will be as below without all above hassle, and interference in the plant operation.

- Stop the conveyor when it is conveying at nearly 100% capacity as per belt weigher indication and also when it is convenient in context of plant operating time, and without disturbance.

- Have a marking on / at fixed stand.

- Put a piece of rope / string on belt, exactly opposite to marking on stand. This may be done after 5 minutes of stoppage.

- Now wait for say 20 / 30 minutes to see whether the belt has moved back (i.e. how far the belt along with the cord has traveled backward).

- If this is practically none, then hold-back condition is OK and it is suitable for continuation of use.

It is understood that belt has adequate idle tension as per design rule for adequate frictional grip on pulley; and belt is not shifting relative to drive pulley. To avoid such doubt, adopt following procedure:

- Make chalk marking at the pulley rim and then chalk marking on the belt edge, matching to each other.

- See that the markings have remained matching to each other during course of the earlier testing. This implies belt is not slipping on the pulley.

Make a systematic log book or record of such test as per statutory need, signed by responsible authority.

Engineers concerned with the erection - commissioning / operation can improve the aforesaid method if need be.

The suggested method is like routine testing of the car brake for its effective operation (not for maintenance and repair). Sit in the car, speed up the car and then apply brake. See whether it is stopping in applicable distance. Why to remove the brake system and then test it in laboratory or workshop and have all the hassles ?

The plant engineer can check adequacy of the existing hold-back operation, as many times as required by the standard.

Ishwar G. Mulani

Author of Book: 'Engineering Science And Application Design For Belt Conveyors'. Conveyor design basis is ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: 'Belt Feeder Design And Hopper Bin Silo'

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

I understood the question of Ajith as:

And his question is:

After explaining the possible tests for holdbacks, the question remains:

Do the Australian standards approve the proposed backstop tests?

I would say: Ask the Australian Authorities. ■

Hello,

In my earlier posting, I missed one point, which I am adding here-under:

In case the conveyor has brake (for controlled deceleration) then that brake to be deactivated (mechanically or electrically) i.e. to make its braking torque zero. This will not involve removal of the brake unit.

This implies conveyor roll-back torque is countered by hold-back only, and not jointly by hold-back and aforesaid brake.

Well, incline-up conveyor which has roll-back issue; generally will not have brake. Up-incline conveyor stops quickly on its own. However for theoretical complete information, I have added this.

Ishwar G. Mulani

Author of Book: 'Engineering Science And Application Design For Belt Conveyors'. Conveyor design basis is ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: 'Belt Feeder Design And Hopper Bin Silo'

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Here is an interesting article about testing a holdback and he talks about Australian requirements for safe guarding. As he states the best way to test is to do a controlled stop and ensuring that the conveyor does not roll back under load. Controlled stop means that EVERYONE is aware of the test and live guards are placed at a safe distance from critical areas where the material will come off the belt if the holdback has failed and the belt rolls back. These guards ensure no one comes into the affected area(s). There would be no mechanical means of testing a holdback other than this type of test. The conveyor would need to be fully loaded to test proof the holdback properly.

http://www.eurekamagazine.co.uk/desi...encies/175716/

Also make sure that at regular intervals backstops are checked for oil levels and the proper oil is always used as per the manufacturer's recommendation. Not following their recommendation can cause premature failure. ■

Thank you Mr.Gary.

The factor of safety 1.3 gives an idea about the torque limit on fixed race of hold backs could with stand.

Holdbacks are very delicate machine components, especially when they are fixed on high speed shafts, where they are normally preferred.

As Mr.Gary pointed out preventive maintenance is extremely essential for their better life. Abnormal noise, vibrations, oil leakages , poor quality of oil can be indication of expected failure of holdbacks.

Thanks and regards, ■

Just referring to a statement by the author of the article I posted earlier stating "Electric motors are not normally designed to start up fully loaded conveyor belts, or they would be over-dimensioned and inefficient in normal operation." This is unfortunately true in many installations but easily overcome by simply specifying a 200% locked rotor torque (LRT). These motors have much greater insulation and can withstand more heat during startup. Standard motors are usually around 100% to 125% LRT. Many designers only look at the HP or KW required to run a conveyor and ignore the breakaway torque required to get the conveyor going again after stopping under a full load.

Having a crew shovelling off a long conveyor would very quickly eat up the extra costs to install the correct motor in the first place. ■

Hello,

The compliance to particular standard to be done strictly as per procedure mentioned therein. The information from me is not in context of any standard. Treat this as general information.

If the commissioning engineer is first time (after erection), verifying the adequacy of the hold-back present in the drive, then he can advance such test in following steps to avoid / minimise the hazard / mishap, etc.

Start the applicable conveying system and also its feeding on the inclined conveyor to be tested. The belt loaded with material will reach curvature and then start advancing on inclined zone. Stop the conveyor when belt loaded zone has reached say 20% of lift (of conveyor). Then test the roll back situation for such loading as per the procedure mentioned by me earlier (that in this situation the conveyor is not rolling back). If it rolls back, it will reduce the magnitude of mishap to only 20%. If it does not roll back then again start the system till the loaded belt front edge reaches to say 40% of conveyor lift. Continue the procedure in steps in this manner till 100% of lift is reached. If the conveyor rolls back during any of the step, then next steps will not be there till the hold back is replaced by stronger version.

As can be seen, the aforesaid step-wise procedure reduces the hazard by 80% (i.e. roll back material problem will be only 20%).

If need be one can also choose 10% steps wherein roll back material will always remain less than 10% till the entire lift is reached.

It is probable that some engineers might be already using such / similar method.

Initially, after about one / two months use, the brand new conveyors’ conveying resistance (conveying friction coefficient) will come down to some extent. This may necessitate the testing again if need be.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis is ISO (thereby book is useful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com Website: www.conveyor.ishwarmulani.com ■