Good comments Derek, I also welcome any good discussions on this subject.

I have had many good discussions with my boss as to which is the best way to go. Sometimes it all comes down to cost rather than best or favoured practice.

I prefer shaft mounted right angle hollow shaft gear reducers with direct coupled to the motor and shrink disc on the pulley shaft. One note of caution here you mentioned using an anti seize coating on the shaft for shaftmounts. I have seen this mistake more than once. All shrink discs need to be dry fitted to the shaft, any coatings can cause slippage. I have never had a problem getting a shrink disc off and you don't get too many worse conditions than in a salt mine.

Pro's - Easier installation, less maintenance, no belts to maintain, coupling alignment is simpler, no low speed coupling to maintain, less guarding required, less structural base. (no base at all for flange mounted motors)

Con's - Right angle is more expensive than parallel, unable to adjust speed without VFD or different reducer.

Looking forward to hearing other comments.

Gary Blenkhorn ■

We are talking about an encyclopedia here. The answers and justifications are a bit daunting for a quick hittter.

1-2. Right Angle vs. Parallel Shaft:

We design for both based on client preferences and the specific circumstances. The sizes go from 25 kW to 2500 kW/assy.

In general, right angles have advantages of reduced lateral space and Mean-Time-To-Repair (MTTR). Properly designed, right angle assys. have no alignment time other than the millwright bolt pattern fitting between reducer and pulley. THis can save many production hours.

THe right angle reducer assy and motor is precoupled and run in for vibration check at the factory. A full spare can be available. THis can typically save from 8-16 hours over the replacement of a parallel shaft with its installation and alignment to the low and high speed couplings

Furthermore, parallel shaft assys. require a flexible coupling with its meriad of conditions such as: higher level of maintenance inspeciton, lubrication, alllowable offset, angularity, et al that may cause a need to derate or oversize, required slotted keyway with shaft strength derating and general reduction of reliablility.

There are issues of sub-base loading and floundation designs.

Parallel shaft afficionados will argue that parallel shaft assys. have an inherent higher reliablility by eliminating the high speed spiral geared pinion and its overhung load and then there is the lower cost. THis is true. However, the tradoffs have to be assessed.

3. Rigid Coupling vs Hollow Shaft:

I would not reocmmend a hollow shaft reducer for the reasons stated wrt seizing. Gary may have a secret formula. Maybe he can share it.

The manufacturer cannot guaranty hollow shaft quick removal after the installation has been corroding the contacts for many years.

THere is no difficulty with the mating of motor and reducer high speed coupling and reducer pulley low speed coupling. COupling ordes are split to the mfgrs. The designated bolt pattern and tolerances are sent to motor, reducer and pulley mfgrs along with the coupling halves. This is as you suggested. Proper QC inspeciton and mounting of the right angle reducer to the motor and no-load spinning of the coupled assy.,for vibration checks, is proposed. Each mfg. fits coupling to their shaft. Obviously, the pulley final check is delayed to final installation. We have specified this on many world wide installations and have not hit a snag. Kennecott 8km overland 1987, Palabora 7100 kW incline 1988, Channar 20 km overland 1989, ....

THe reducer may be able to supply motor, couplings and reducer with swingbase, mount and spin, or add pulley and get all under one roof. You trade some dollars for assurance and delivery guarantees. Does require doubling of motor and pulley shipments.

THe hollow shaft requires bigger low speed bearings and as you suggest a lot more lateral clearance (width of reducer less LS coupling).

Rigid coupling design does not have a moment problem. THe pulley shaft does not need to be made of a larger diameter. A properly designed system cancels the overhung and bending reaction moments for normal operating conditions. You have to check the coupling design for the lesser loads.

Some rigid couplings, of the squeeze lock design, have a bad stress riser in the inner flange that can lead to premature fatigue. THis can be eliminated with a little fittle and mfgrs. compliance.

Many rigid coupling are hydraulically applied and released. SKF ships coupling is an example. The soft metal sleeve has to be replaced after each removal. The description is a little wordy and you should make the study yourself.

Enough for now. ■

I don't know of any magical method of installing hollow bore onto a shaft. We only follow manufacturers recommendations. The machining of the pulley shaft is critical to have the proper relief as I will describe below.

Shaft mounting with hollow bore is by far my personal preference. We use shrink disc style external to the reducer (no key). This allows for a relief for most of the shaft length through the reducer. The only contact directly to the shaft is on the pulley bearing side (which requires an O'ring to keep dirt out of the relief area.) and directly at the shrink disc area. Anti seize compounds can be used on the pulley bearing side of the reducer but the shrink disc side must be dry fitted.

Because the shrink disc has an initial clearance fit over the shaft and if proper torquing sequenses are followed during the installation there is no problen in getting the reducer off the shaft. (At least we have never had a problem) I have on occasion had a siezed shrink disc which had to be cut off to remove the reducer but I have never had a reducer seized on the shaft. I have more problems with external back stops seizung than i do with shrink discs. (but that is another discussion in itself)

This is only based on my experience with drives up to 600 HP. Maybe this style is not recommended with higher horsepower drive such as those used on overland conveyors. Maybe Larry can enlighten us on this.

I have attached a sheet showing a typical shrink disc installation such as I have described.

Gary

Attachments

shrinkdisc (JPG)

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Gents

May be we need a comment on the generic rules of thumb

This would cover more than just belts.

For my 2 bobs worth

LOW SPEED couplings

Shaft mounted gets away from the low speed couplings - alignment/maintenance and also pulley alignment issues - it has my vote

Hollow shaft and external shrink discs were the answer to keyed designs. Over 80-100 mm diameter, they can be prone to fretting welding onto the shaft if not properly fitted (short cuts by the contractor). Torque flucuations can casue fretting and welding on the pulley side as well......so U can have 2 issues with getting the gearbox off!!. Even with inner bronze bushes and lube on the pulley side does not fix this. We have had to cut shafts and broken gearbox casings...creates another issue to deal with!!!

Hollow shaft and keyed designs are OK but need good tolerances and fits for torque flucuating applications.

Hollow shaft design require room for removal of the end of the shaft - need to be aware of in low width installations such as stockpile feed conveyor galleries etc.

Shaft mounted with rigid couplings seem to be a good answer - I have seen some but no experince. The gearbox will be more expensive to make, the pulley side coupling will need a torque transmission method to the shaft eg keyed/shrink or compressive device. They get away from the issues on the hollow shaft/shrink disc setup.

DESIGN APPLICATION

Torque flucuations/shock loading needs to be considered for connection type eg keys/shrink discs etc

SMALL DRIVES

Small drives (<30kW) >>> shaft mounted, hollow shaft with either taper grip or shrink disc or keyed (personal preferences) with torque arm. Parallel or right angled OK

GEARBOX TYPE

Right angle drives are the common and accepted drive but if U need one in a real hurry, they will take longer to procure.

HIGH SPEED couplings

V belts - use for <30kW only...there are a maintenance issue and usually break on night shift. The pulley sizes are usally selected as small as possible and use cogged belts > pulley wear as well. V belts can make for wrong conveyor design ei speed up/slow down ie corrective for a mistake elsewhere eg "lumpy feed" from reclaimers causing belt overload/spillage.

Fluid Couplings - try to get them mounted on the motor shaft to avoid bending on the gearbox input shaft. Be aware of heat effect on the internal coupling rubbers that is transmitted from the gearbox shaft

Flange mounted motors are OK but consider store holding and common frame types on site. Some motors are not IEE standard, hence, will need LP adapters if U wish to hold only these type of motors - which have a bearing inside with no greasing facility. I have heard from the supplieir of these non IEE flange mounted motors that IEE flange motors can fret them selves into the gearbox - but this could be their pitch.

Flange mounted motors may get away from the seal issues with the gearbox HS shaft - seems to be commoj with the more compact (and hotter running) gearbox of these days.

We generally (for larger drive) have foot mounted motor/gearbox with base frame - can have lifting lugs postioned for balanced lifts.

TORQUE ARMS

I like the rubber bushing types to provide some shock absorbtion but for higher force applications, this is not possible and either the simple pin/bush designs are used. Need to consider lateral movement in the design eg pulley alignment changes etc

Cheers

James ■

Derek,

The only places that I have seen foot mounted parallel shaft gearboxes in on screw conveyors - have the room and also support system for it....I have also seen shaft mounted right angle and parallel drives as well for the same.

Parallel shaft boxes are also used in large mill drive with centre drive and also can be piggy backed with right angle high speed redcuers eg apron feeder duty with electro-mech drives.

We have over 750 drives on site - each new project creates issues with drives - new models, spares holding etc etc. U would not want to keep spares of each drive. Gearboxes (in general) do not break if looked after, motors do fail over time. Our plant does not have any line redundancy and it goes well.

I have been on both sides of the fence, and can see the issues and points acc.

Cheers

James ■

Hello Derek

I prefer the following:

Right angle....less space

Shaft mounted....easy to install

Keyed, warm a bit and slide-on rigid low speed coupling on pulley...always perfectly aligned

Locking element in other half of coupling on the gearbox...easy to rotate, torque and align properly

No hollow shaft over 45kW... too heavy gets stuck

Bellow 45kW you can use what you like

Incidentally, if you shaft mount the drive with the motor pointing towards the tail pulley and put the torque arm in the right place, then the drive reaction force on the pulley is upwards and the overhanging load disappears.

Regards to you

LSL Tekpro ■

Follow the KISS (keep it simple stupid) principle. This extends to the drive arrangement and other equipment that affects the drives (such as take-up arrangement, etc).

- Minimize the number of pulleys to perform the function.

- Minimize remoteness (from the belt line) of the equipment, both drive and take-up.

- Minimize the number of drive units

- Where multiple drives are appropriate then modularize to minimize spares.

- Minimize structural ambiguity (this favors shaft mounted drives over base mounted with flex coupling)

Just some thoughts.

Joe Dos Santos ■

Hi Derek..

"Keyed, warm a bit and slide-on rigid low speed coupling on pulley...always perfectly aligned

Locking element in other half of coupling on the gearbox...easy to rotate, torque and align properly"

(Sorry I wrote this lot in a bit of a rush so let me explain)..

In practice it is not easy to torque up the locking element in a rigid low speed coupling, and get it to run straight and true.

This is why so many shaft mounted drives jiggle around with each rotation of the pulley, and don't keep still.

Also, if you try and remove a low speed coupling, and re-torque it, you will battle your backside off trying to align the thing. This is especially so on a pulley as you cannot rotate it with the belt on, and you are only supposed to torque them once anyway.

To overcome this on the pulley side, I now simply use a bored out and keyed low speed rigid coupling. Since the bore is machined, it will always run 100% straight and true. I use a gas ring to heat the coupling up a bit and with the aid of a pair of asbestos type gloves and a come-along, I simply slide it on.

On the gearbox side, this coupling can always be aligned in the workshop. I have no problem rotating it whilst aligning by simply rotating the high speed input.

I will probably in future however go for keyed and bored here as well, as it is fool proof, simple and far cheaper too.

"Incidentally, if you shaft mount the drive with the motor pointing towards the tail pulley and put the torque arm in the right place, then the drive reaction force on the pulley is upwards and the overhanging load disappears."

Don't tell me you are short of space too! I thought it was INDIA which is short of space.

Anyway, all I am saying is that it is good practice to put the drive on with the motor pointing towards the pulley whenever possible

Regards to you

LSL Tekpro ■

Dear Graham.

You seem to have a strong preference for keyed shafts. Have you had a bad dream about hydraulically clamped ship's couplings or shrink disks?

I do note you disuss a internal clamping device but not either external clamp or friction clamp with hydraulic stretch. These will not have the wobble or precession you experience.

Larger shaft and keyways raise strength integrity issues. We have been very sucessfull in applying hydraulically applied and removed low speed coupling halves.

There are some stress riser concerns with the shrink disk design. However wobble is not an issue. ■

Hi Larry..

Believe it or not, I have spent at least 12 of my many (sheltered) years working on site, and as you may or may not have gathered, I actually quite enjoy getting my hands dirty, and have aligned countless drives and conveyors myself.

It is therefore not at all by way of a dream that I have likes and dislikes for certain things.

Internal locking elements have significantly contributed to my grey hairs.

External locking elements lost favour as well, not only for me, but I notice generally here in South Africa, as they sit between the coupling half and the pulley bearing and are extremely difficult to work on, and there is normally no room to get a torque wrench in.

As for getting the damn things off... many more grey hairs and scarred knuckles, and even a few choice expletives.

I get your point about stress raisers, but compared to the simplicity and perfect alignment of a bored and keyed coupling, I really do like them.

I will try and dream about hydraulically clamped ship's couplings tonight. (But only if I can actually stop dreaming about Meg Ryan)

Regards to you Larry

LSL Tekpro ■

we manufacture shaft mounted speed reducers

we have tried to sell shaft mounts with stailess 420 grade hubs but have found a market resistance due to higher costs

maybe the guys in pirchase want to buy a cheaper gearbox rather than protect the conveyor shaft a few years down the line !!!

We then developed the keyless taper clamp bubs where in the taper clamps are made in SS 420 grade steel

the gearbox hub does not sieze with the conveyor shaft !!!!

href="http://www.involutetools.com" target="blank">www.involutetools.com

Attachments

smgu-s7 (JPG)

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Dear Mr. Bishop,

Generally for stationary conveyors where drive unit is mounted in transfer house, one opts for either parallel shaft helical gear box or bevel helical type right angle gear box, the choice happens to be due to economy in the available space. The parallel shaft gearbox requires bigger size of transfer house. If the transfer house is of lesser height, its more price due to enlarged dimension may still keep it economical compared to using right angle gearbox. The right angle gearbox would require lesser cross section of transfer house. If there is space limitation or if the transfer house is very tall then using bevel helical gearbox would be economical / essential. The economy is to be considered in totality i.e. gearbox price plus structural; cost of the house and the civil cost.

Please note that if there is no any specific technical need then, the decision is always by the economy in overall arrangement or preference of the buyer.

Generally one would opt for foot mounted type gearbox. However if there is a limitation in space then in case of bevel helical gearbox, one will tend to use shaft mounted arrangement.

Shaft mounted bevel helical gear box is found to be more suitable for conveyor on mobile machine as they are compact. They are also preferred on shiftable conveyors due to compact nature and chances of misalignment occurring due to distortion of structure is not there.

Regards,

Ishwar G Mulani.

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

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 ■

I agree with I G Mulani. The drive system selection as with all engineering endeavors should, once all constraints are considered, reduce to economics. Back in the day, one of my professors defined an engineer as one who could do for one dollar what any fool could do for five.

In reality it doesn't always reduce to economics. Customer bias often defeats the best (most economical) solution. I cite one prominent example. In the mid 1980's we engineered the well published high angle conveyor for Majdanpek Mine in Yugoslavia. This 4000 t/h copper ore, 93.5 m lift system featured 2000mm belts and 3x450=1350 kW drives. The modular head end drives, one at the top belt, two at the bottom belt, were at the end of the cantilevered truss. Right angle, shaft mounted drives, each with a torque link to a cross beam, offered the simplest most economical solution. Our customer did not trust shaft mounted or right-angle units and insisted base mounted parallel shaft drives. To meet LS coupling deflection limitations we mounted the drive pulley and drive(s) on a common rigid drive frame that could then deflect structurally as a unit.

In the case of the bottom belt drive this arrangement looked like the wings of an airplane. At the top belt drive one of the wings was missing.

This solution resulted in more than US Dollars $ 50,000.00 premium over the simpler right angle shaft mounted drive solution.

Joe Dos Santos ■

Involute

For hollow shaft mounted boxes, which are for the lower KW ratings (=<45KW), I have got away with having a fairly sloppy tollerance on keyed shafts.

This makes them easy to slide on, and they don't sieze onto the shaft through the slight movement starting and stopping. (No need for stainless steel hubs, or locking elements).

The box can then float a bit between a shoulder on the shaft, and the locating disc bolted onto the end of the shaft, though they don't seem to move noticeably in practice.

Incidentally, I reckon that in the last 30 years or so, I have installed parallel non-shaft mounted boxes on only 3 conveyors out of hundreds of others.

Cheers

LSL Tekpro ■