Flat Belts Vs. Vee Belts

Flat belts can have lower friction losses than V-belts (something like 1.5% vs. 3%). They usually need to be higher tensioned, and this may require heavier bearings. Your 55kw is well within the practical range.

First of all let me thank all the forum engineers for their valuable contribution to my question.

Let me add here that habasit AG Switzerland in their manual. The flat drive compared to the V-Belt drive to use flat belts instead of Vee belts. I am scanning their arguments will highly appreciate if the forum engineer can come up with some result.

Picture are scanned from "Habasit AG Informa Manual(Edition October 2001 The Flat belt drive compared tothe V-Belt drive"

www.habasit.com

Thanks

Modern Flat belts are superior to Vee Belts in all aspects.

With high friction materials on the pulley side, the radial loads are considerably reduced.

People view flat belts as the old and antiquated leather belts of the past. Vee belts came to existence due to the inefficiencies of leather belts.

Habasit, Siegling and Chiorino have changed the entire equation. I have used them extensively and replaced Vee belts all the time

Modern flat belts do not need idlers and can be made virtually endless. Flat belts can work at higher surface speeds than Vee belts and are used in high power prime mover drives.

Read the data and comparisons provided by Habasit and Siegling in their catalogues and it will be an eye opener for those using Vee belts

They do not slip, Vee belts do. Check this out. In a multi Vee belt drive mark a chalk line across all the belts and then run it. In a short while you will see the chalk lines have separated.

In Europe, vee belts are hardly in use and flat belts have replaced them in most applications.

Go for it. Go for flat belts

Thank you for your valuable and technical answer to my problem.Your reply has really encouraged me to recommend the plants managers to go for Flat belts.As we are involved in energy audit our recommendation for flat belts will now carry Heavy weight.

I repeat a part of my question i.e.is there any thumb rule for the minimum rating(H.P) of the motor where we can use flat belt

I do not think there is a limit to the power being transmitted.

Siegling and Habasit will be only too glad to offer the right type of flat belt.

Unlike Vee belts, flat belts come in many different constructions. The outer layer, the type of cores and the traction surface will vary with the application. Be sure to consult them when in doubt.

The only application where I had problems was in the cross belt drives, though they claim that they have solutions for that too.

A critical aspect is the crowning of the pulleys. It has to be a curved crown, and not a vee smoothed out. People ignore this and it breaks the back of the belt. Today with CNC lathes it is not a problem to produce the crown, but in the old days of manually operated machines, making a Vee and and smoothening the sharp edge was a short cut with disastrous results.

Never ever provide side guides on the pulley. The initial alignment of the pulleys is important, whereas a Vee belt drive is more forgiving

Are you a salesman for flat belts? You seem to have baited the group with your 1st post then produced this post. "Let me add" ( to use your verbage, I'm still in the Vee camp ).

The belt slip will be more in Flat belt and hence using V belt is advisable.

This might be why someone invented "toothed belts".

Thereby achieving 'zero slip' - less friction loss - less flex loss - and reasonable side loadings on shaft bearings.

But don't let me drag you into 20th century power transmission technology.

What? Have they stopped using line shafts a well?

You Quit that Sarcasm Tony or I'll tell you to go clean your slip-rings with carbon tetrachloride and a pick axe

21st maby? S.M.

As for the belts are we talking about "V" Belts vs Flat belts (Raw Hide) or HTD Timing belts? If you are talking HTD Timing belts vs "V" belts, timing belts are the way to go.

Much more efficient than slipping V belts. Also adding an SMC to the mix would also increase your efficiency if that is your ultimate goal.

If you are talking about Flat Belts (Raw Hide), forget about efficiency and go back to the line shafts and central shafts with 0 efficiency and total slippage. It did work in the 1840's and beyond, but not in todays electric infrastructure.

I've seen old flat-belt drives with about 15 feet between pulleys, with a Mobius twist on the slack side to equalize wear on both sides of the belt. But I'm not talking about that here. I don't know the presumed losses in timing belts, but the cogs do rub on the pulleys as they engage/disengage. This creates heat and wear, just as a V-belt compresses/expands and rubs as it enter/exits the sheave groove. Flat belts still flex, but if properly tensioned they don't slip. As mentioned before, this higher tension may need beefed-up bearings.

Tornado, have you worked in a factory with Main drive lines? I have. The 2nd'ry lines slip like a bith@h in heat. You just can not get them tight enough. Man does this bring back memories. Line shafts. Oh my. Arms, hands fingers ripped off in a second. Don't miss any of that.

I wasn't really thinking of line shafts with a bunch of small floppy belts and flip sticks to switch pulley speeds, nor oldtimer rawhide stuff. But there are properly engineered flat belt drives with less loss than other types. The OP's fan is a reasonable candidate. However, retrofit is probably not as economical as original design.

At that power range you could use a flat belt without problems.

Increasing the angle of wrap will ensure that you don't incur a slippage loss.

Learning to lace a flat belt is the only part of my trade training that I haven't had to use. Not yet anyway.

If you have got the room a mobius twist is a great idea for evening out the wear. The only problem with that is you can't put any grinding paste or jeweler's rouge on the out side of the belt to make the sweetest strop you will ever have for dressing chisels, plane irons and knife blades.

BAB

Dear Sirs,

After going through all the suggestions in this regard, in continution of all the above and as per my little knowlede, I think when compared between the belt drives, the power saving factor is more in timing belts>Poly V belts>V belts>Flat belts. At present, in view of energy saving methods, it is better to choose Timing belts or otherwise poly V belts. As per the discussions had with the suppliers they informed that the life of Timimg belts and Poly V belts is more than other belt drives. We can approach to the supplier the power rating for the above belts and we can select the belts with the help of them. May be the initial cost is high for the pulleya and belts, but it will be better in the mode of energy saving. This is my opinion.

Thankyou for giving the oppertinuity to express my self.

No.

The belt is just a transfer of motion. For the record put my vote in for the Vee Groove. They have a a better surface area without moving the belt further away from the bearing adding to bearing load.

I doubt you'll see any tangible difference in energy savings regardless of the belt type. The load is where you want to look for improvement, that's what's consuming most of your energy.

I would think that the selection of the belt would have to consider the starting torque of the fan since many fans depending on the blade design have starting torque well in excess of what's required at normal operation and not just be related to the motor HP. Flat belts can get quite wide to avoid slipping when there is a high starting torque which is why I would stick with the v-belts. As mention before there is the question of the size(width) of the pulley and the adverse affect on the shaft output end bearings from the cantilevered load. throw in a high starting torque and you could end up with shorter bearing life. The increased energy may way be a lesser cost than bearing replacement or motor damage from bearing failure.

If u see the torque vs speed curve of the fan most of them have low starting torque.The problem is the Inertia which motor has to accelerate.

If u see the torque vs speed curve of the fan most of them have low starting torque.The problem is the Inertia which motor has to accelerate.

See below:

Motor Starting Torque

The motor starting torque for a belt driven fan can be expressed as:

I_m = 1.1 I_f (n_f / n_m)² (1)

where

I_m = moment of inertia that the motor must be capable of turning at the motor shaft (lb_m ft², kg m²)

I_f = moment of inertia of the fan wheel (lb_m ft², kg m²)

n_f = fan speed (rpm, min^-1)

n_m = motor speed (rpm, min^-1)

For direct drive fan I_m always exceeds I_f.

It would seem from the above that inertia is part of the starting torque.

First of all why we want to inverse the history at all. Flat belts were in efficient and needs more area for transmission of same power, thats why "V" belts were invented which are efficient both in slip and power loss.

Timing or toothed belts can give further better efficiency but for 55 kw I am not sure toothed belt will be available or not.

For power saving you have to think of direct drive type of thing through gear box or use variable frequency drive to achieve the required power saving and good efficiency.

Going by the voting in this thread, it looks like it's a flat belt verses 'V' belt sales promotion.

Where flat belts don't 'compare', is in the presence of any lubricant or when alignment alters with torque variations. (e.g.sound isolated components, or flex in a sub-frame)

What is not being compared (for some reason) is flat belts with poly-V and/or toothed belts.

"Timing belts need the least tension of all belts, and are among the most efficient. They can bear up to 200 hp (150 kW) at speeds of 16,000 ft/min" (Wiki)

Lubricants are not a problem, nor are alignment variations, given flanges.

A poly-V belt is a flat belt with greater friction area per unit width, and superior alignment stability.

Of interest; "A further advantage of the polygroove belt, and the reason they have become so popular, stems from the ability to be run over pulleys on the ungrooved back of the belt ...... a polygroove belt may be wrapped around a pulley on its back tightly enough to change its direction, or even to provide a light driving force".

Note, the back of a poly-v is akin to a 'flat belt'. So the reason it says "light driving force" is because the required belt tension is less and the friction area is a fraction, compared to the V side.

As many above have commented, when suggesting other than 'flat belt' - it is no-doubt because of experience with alignment, environment and bearing life.

I don't see any above, bar one, that are 'against' flat belts, when used appropriately.

I have several machines where they are 'the choice' and a number where 'other belts' are better. And where I do use gang V-belts, I buy a matched set, which negates most of the problems illustrated in the comparison above.

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So let's have a look at the other issues affecting selection of belts.

(from Wiki)

Belt friction Main article: Belt friction

Belt drives depend on friction to operate but, if the friction is excessive, there will be waste of energy and rapid wear of the belt. Factors which affect belt friction include belt tension, contact angle and the materials from which the belt and pulleys are made.

[edit] Belt tension

Power transmission is a function of belt tension. However, also increasing with tension is stress (load) on the belt and bearings. The ideal belt is that of the lowest tension which does not slip in high loads. Belt tensions should also be adjusted to belt type, size, speed, and pulley diameters. Belt tension is determined by measuring the force to deflect the belt a given distance per inch of pulley. Timing belts need only adequate tension to keep the belt in contact with the pulley.

[edit] Belt wear

Fatigue, more so than abrasion, is the culprit for most belt problems. This wear is caused by stress from rolling around the pulleys. High belt tension; excessive slippage; adverse environmental conditions; and belt overloads caused by shock, vibration, or belt slapping all contribute to belt fatigue.

hi,

In our Plant, we converted all flat belts into v - belt drives and you know what we got savings in maintenance costs of about 25 - 30%.

Using V - belt reduced initial torque required by the motor to rotate the machine, aside from that, V- belt is more likely to have longer operating life due to its design and increase rotor or Pedestal bearings operating life

trust me v - belts is much better than Flat belt.

of course toothed belts are far better than v - belt also, so its up to you.

Mike

I use timing belts for most applications as they are the best for most of "My" applications. When it is not a good fit I use Dyna Grip V belts that do a great job and I also use the back side as well. I've had bad results with flat belts in past years.

One of the things I did notice on the flat belt web site was the 1:1 ratio. In cases like this I directly coupled the motor to the driven part and used the best coupling for that application. I moved away from spider couplings 30 years ago. Most of my applications are 2.8:1 or higher. Flat belts are out of the question.