Slewing rate refers to the rotation of an object around an axis, usually the z axis.

It all depends on whether the material is "in situ unbroken form" or loose stocked material.

Any mining machinery that digs/reclaims uses a set number of revolutions unless its controlled by a variable speed hydraulic motor such as a Staffa, KYB or other radial piston motor or for that matter a hydraulic motor controlled by a flow settting device/flow divider etc. or a variable frequency electric drive.

Bucket wheel excavators also stack at the same speed due to the conveyors drive if my memory serves my right.

A slower excavating rate/slewing rate amounts to an effiency problem "or if you think you have an efficiency problem") of how much do you want to try stuff into each individual bucket on the reclaimer and how much of the material will go into the bucket and stay there.

Overloading while reclaiming simply throws a a lot of material around and under the bucket during the reclaiming which will need to be recaptured later unless you have a grader pushing the material back to the edge to be taken again.

When the bucket wheel engages the pile it is attempting to obtain(X) the amount of the material it is scooping to throw on the belt.

The teeth on the buckets following a bucket if any are digging all the while the previous buckets are in motion digging.

When a slower slewing rate is used it is simply using a portion of a full bucket (x-) and it may or may not be fully filled while it is at work at the face of materials pile being mined or reclaimed, it also depends on the height of the pile being reclaimed as to how much of the full arc of the bucket wheel is being used to fill the buckets on the bucket wheel. It depends also on the material be taken as well.

If the face of the stock pile is shorter in height than the diameter of the bucket wheel it may not be able to fill the buckets full anyway.

The actual act of reclaiming with a spinning bucket will dig more out of the pile than the bucket can handle simply due to the teeth on the side edges of the bucket and as it lifts it allow material to fall away if it is not in the bucket. Hence the teeth on the sides of some buckets.

As the buckets are following each other on the radius of the wheel every bucket is scooping what was missed by the previous bucket and spilling for the next bucket to reclaim and this continues during the entire reclaiming cycle.

The loading of the buckets is uniform simply due to the slewing speed used and the teeth on the buckets.

The main bearings on the bucket wheel drive and hoisting cables, cable sockets, and shackles are absorbing any shock loading. The stress involved are radial stresses from the wheel assembly and any linear stress across the buckets, the bucket mounting frame, the weldments, and the shaft drive and bearings of the stacker reclaimer from the actual arc of the slewing motion.

Depending on the material and whether it is stacked loose or in the case of in situ ores to be mined "Compaction" is always an issue and the weight of materials is the same it is simply a case of "your opportunity cost" "what are you willing to give up for something else" being;

a. A faster slewing reclaim rate with more lost material falling away from the buckets but filling full buckets and carrying full weights of material at all times is dropping what material the bucket cannot reclaim to the bucket following it to the drop chute feeding the conveyor versus;

b. A slower reclaim rate with a slower slewing rate with buckets that are not quite as full, since each and every bucket is picking up what was spilled or dug by the previous bucket and lifting the reclaimed material to the drop chute to the conveyor one bucket at a time in either case anyway. Less material is left to reclaim from spill over at the slower slewing rate.

The stress load is the same at all times "on the side face and front teeth of each individual bucket" as they are doing all the work as are the rest of the buckets, the wheel and the bearings are absorbing the same side stresses at all times.

It all depends on whether you think the glass of tea is half full or half empty in basic terms.

I hope I have not muddied the football pitch to much or thrown a few too many wicked googleys.

IN short the stress level is the same as only two edges of every bucket on the bucket wheel that are digging all the time every time.

The same applies if the reclaimer is track or rail mounted with the same ability to crowd the loose pile or mined face.

I hope I did not get any of the definitions wrong-its been a while ■

Digging loads are predominantly the province of the bucket wheel drive & stress levels therein are roughly proportional to the degree of fill. Lighter buckets are easier to lift.

Slewing power is roughly the product of the boom radius, the resistance to slewing and the radial velocity. Pushing a shovel, face on, into a pile of sand will develop a resistance that depends on the shovel face area and the stiffness of the sand. The faster you push the sand aside the more power you will need but the shovel handle stress is no higher. However in the case of a bucket wheel; if you double the revs you also double the area of the aforementioned shovel within any time period. So the handle needs to be stronger.

Slew torque is limited by the slip coupling. If you wound the coupling down to a low set point you should find that slew slippage is independent of bucket fill but not independent of bucket revs.

Faster bucket wheel revs will result in higher stresses in the boom members, not least from the torsion developed across the wheel shaft bearings. Fortunately these stresses are/ought to be safely within the machine's design capacity. ■

Originally Posted by A.N.Mukherjee

Sir,

Pl.note only two buckets will be in the pile ,so the dif.slew load is negl.

It's the digging load that counts.

Regards,

A.N.M.

Surely the number of buckets involved is a function of the total number of buckets, the wheel diameter and pile size locally.

If the slewing load is negligible and only the digging load counts then a designer could reduce the CAPEX by specifying that all buckets ran completely full. From a structural stability point of view the slewing resistance influences the wheel shaft loads and the boom torsion somewhat realistically. ■

What stress are you referring to? Are you referring to the stresses on the loading, lifting and carrying or was it a spurious question relating to the cyclic twisting action off the bucket wheel drive centre axle which results in the fracturing of the drive axle flange to bucket flange mount in the disc. Every bucket wheel I have seen or been associated have all had regular testing for cracking both annularly around the centre of the disc(flange) to axle flange areas and also radially from the disc flange toward the actual buckets along the gussets welds. Higher 'Z' axis of the whole stacker/reclaimer speeds does result in higher stresses in the areas I have mention above but this does reduce when the slower but heavier bucket loading is maintained which also increases the actual loading rates. The load torque-ing off the drive centre axle flange to disc flange is more balanced around the disc and not as much twisting on the individual buckets when the 'Z' rotation speed is reduced but the bucket volume loading is increased. ■