Dear Vinay

Is this a proper ISO 5049 tripper for a stacker, or is it a simple tripper for discharging from an overhead conveyor?

For the big ones I use 20kg resistance per ton of steel plus material plus ISO load case additional loads (spillage, wind etc), plus idler and pulley resistances. Here you must assume that the pulley bearings are in poor state and about to sieze.

For the small ones everything pales into insignificance compared to the force produced via a pulley with bearings in a poor state.

Calculate for travelling upstream with all loads considered.

Regards

LSL Tekpro ■

Hi Vinay..

These little trippers do not weigh that much, and have to fight against the belt tensions with pulley bearings in poor state as I mentioned previously. This causes a huge drag force on the tripper.

So you can calculate the worst case forces involved, but it is a good thing to calculate all the vertical load components, and ensure that your tripper drive selected can provide a force equal to this load, multiplied by the coefficient of friction for steel on steel.

Cheers

LSL Tekpro ■

Aha! A virtual tripper request. ■

To the readers :

In order to calculate tripper travel drive power, one has to first calculate the travel resistance. Then power is product of resistance and travel speed, as per kW or HP formula. The travel resistance comprises of following.

1) Machine own resistance to belt motion. The belt applies equal dragging force on machine to move in direction of belt motion. This is made up of :

- Belt travel on idlers i.e. ‘conveying’ resistance on tripper

- Pulleys turning resistance

- Pulleys wrap resistance

- External scraper resistance

- Material lift resistance

- Skirt board resistance (in case of feed back)

2) Travel gradient resistance, general or localized as per track elevation tolerance

3) Cable reeling drums or power supply system resistance

4) Bunker slot sealing resistance

5) Wind resistance, particularly when open to sky

6) Resistance arising by travel wheel motion on rails. The usual tripper (which is not part of large machine like stacker or stacker-reclaimer) has wheel fixed on live shaft running in bearing blocks. These shafts not being 100% parallel or differential wear on wheel diameter results into crabbing of tripper, when fitted with cylindrical periphery wheels (simple double flange wheel without taper). This means tripper tends to steer-off rails, which is prevented by flanges. The friction between wheel flanges and rail will result into resistance to the tune of 10% of tripper weight in worst case when all flanges are rubbing. This can be avoided by about 5% taper on wheel periphery. Engineer D. E. Beckley - Australia made very useful investigation in this matter.

For tripper of large machines, the driving wheels are not on common live shaft and there such crabbing effect is negligible. The independent drives natural speed differential creates only small value side thrust, corresponding to their speed-torque graph. Again for reclaimer machines, the reclaiming operation would apply side thrust, and its effect to be accounted as applicable. Thus travel resistance due to this point is quite different, for conventional tripper and tripper of large mobile machine. This happens to be very less for tripper of mobile machines, due to independent drives.

Ishwar Mulani

Author of book : Engineering Science and Application Design for Belt Conveyors

Author of book : Belt Feeder Design and Hopper Bin Silo

Tel. No. : 0091 (0)20 2587 1916

Email : parimul@pn2.vsnl.net.in ■

Quote : "This happens to be very less for tripper of mobile machines, due to independent drives."

Unquote : Though tripper or reclaimer or stacker may have many drives, excessive load on one drive will affect other drives also.

Kindly clarify. ■

There was thread last month,or so, concerning tripper drive shaft failures on a stacker. Some handy pointers were raised, eventually fading out as structure irregularities.

"Single flanged wheels were invented by Jessop of the Butterley Company

In 1789, one William Jessop of the Butterley Iron Works in Derby, England laid a new colliery tramroad on a heavily used conventional roadway between Loughborough and Nanpantan with a novel, L-shaped iron "edge" rail."

All flanges cannot rub at the same time though. ■

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Ask Maggie Thatcher, she'll put you straight. Or then again, maybe that's beyond even her. ■