Pulley shaft load

Posted in: , on 21. Mar. 2007 - 07:44

Dear All,

I request your guidance on below issue...

We have a belt conveyor for transporting limestone scalping material at 280 tph...the belt speed is 1 m/s. I wanted to upgrade this belt for 400 TPH hence i changed the gear box with lesser gear ration maintaining the KW rating required for higher capacity....I would like to know whether i have to increase the diameter of drive pulley shaft corrospondingly.. Formula HP = 2*pi*N*T / 4500 indicates that the shaft need not be increased as the torque required to rotate the shaft is same..Please provide your expert comments on this.


Lyle Brown
(not verified)

Re: Pulley Shaft Load

Posted on 21. Mar. 2007 - 07:13

I am not sure I understand your issue.

Assuming you have increased you belt speed directly in proportion to the increased capacity (400/280 * 1 m/s = 1.5 m/s) through a reduced gearbox reduction (or possibly in combination with adjusted pulley diameters) the tensions in the belt should be reasonably close to the original tensions (prior to the speed increase).

If you have not increased the belt speed in direct proportion to the conveyed capacity you will probably have to do a full check (including power and tensions etc and their effect on the pulley / structure etc).

You mentioned that you maintained the power rating, however we would expect the power roughly to have increased by 150 % of the original power, so unless the original motor was oversized I am not sure this was achieved.

If you increase the size of the prime motor (motor) you will need to check the pulley (and support structure etc) is suitable for abnormal conditions (such as bogged drive etc).

Re: Pulley Shaft Load

Posted on 21. Mar. 2007 - 11:22

Hi Lyle!

Thanks for your reply....ya... I have increased the power of motor from 15 Kw to 22.5 Kw....the gearbox power rating is 24 kw...quite above the power consumed by conveyor in transporting the material....I just wanted to know if pulley is to be upgraded to avoid shaft failure when belt in operation..



Re: Pulley Shaft Load

Posted on 24. Mar. 2007 - 12:30

Dear Mr. Nadkarni

Please inform

Belt width

Pulley diameter

Shaft pulley diameter (for each pulley) at pillow blocks

Shaft construction (keyway or expansion joints?)

Shaft diameter at hubs

Pulley thickness

And it will be roughly possible to tell you if your pulleys will bear the new situation.


Alexandre Calijorne

Caltra Projetos & Consultoria

email caltrapc@yahoo.com.br

Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Re: Pulley Shaft Load

Posted on 24. Mar. 2007 - 01:21

Increasing the speed to achieve greater throughput should require only a larger motor and a change in gearbox ratio. The torque required to drive the conveyor should remain the same.

Re: Pulley Shaft Load

Posted on 25. Mar. 2007 - 03:58

Mr. Designer,

Yes, it is correct if you increased the speed at the same proportion you´ve increased the capacity.

But , for example, you could have a relative empty conveyor and could increase the speed at a lower proportion you´ve increased the capacity, gaining the desired capacity with a more loaded belt.

In this case the belt tensions and torque at the drive pulley will be higher than before, and you should verify the dimensioning of the pulleys.


Alexandre Calijorne


email caltrapc@yahoo.com.br

Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Re: Pulley Shaft Load

Posted on 25. Mar. 2007 - 09:43

Dear Shri Sujit Nadkarni,

In such situation, the general procedure is that you have to design the conveyor for revised capacity etc. Obviously in such existing installation, one tries his best to create design, which will result in minimum modifications and replacement. After making design in this manner, wherever the existing items are not suitable need to be changed.

As a general observation, if you can achieve the capacity simply by proportionate increase in speed, then forces will by large remain nearly same, and the kW will increase in proportion to the speed. There may be marginal influence on take-up. However, such conclusion will result from the method mentioned in paragraph above and pre-judgement etc. is not a good procedure.


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.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916

Re: Pulley Shaft Load

Posted on 25. Mar. 2007 - 10:09

Dear All,

I thank you all for your response and would like to add the details of conveyor as under..

1. Pulley dia : 400 mm.

2. Shell Thickness : 12 mm.

3. Dia of shaft at bearing : 90 mm.

4. Material of Shaft : EN8.

5.Bearing spacing : 1300 mm.

6. Belt width : 800mm spec NN 350/3 * 5/2 *M20 grade.

I would like to mention that the said conveyor is running ok without any problem at higher TPH...weight of material per linear meter is same as earlier before enhancing the capacity..I have raised this issue just to ensure that the shaft should not shear while the conveyor is in operation...for the safety of worker in the vicinity of conveyor...yes Mr.Mulani...I have details of conveyor design from NIRLON and I will try to redesign the same.

Thanks for participating in the forum...

Warm regards,


Re: Pulley Shaft Load

Posted on 25. Mar. 2007 - 12:31

Of course if the speed is not increased pro-rata to the increase in capacity(t/hr) the loads in the machine will be different.

While there may be small differences in loads as a result of increasing the speed, I would suggest these these will be well within the factors of safety of the components used, bearing in mind the factors used in calculations that have to be "assumed".

In materials handling the only certainty is un-certainty.

Re: Pulley Shaft Load

Posted on 28. Mar. 2007 - 04:26

Dear Mr. Nadkarni,

According my rough estimatives, you will not have problems with your pulleys.

I presumed you are using pulleys connected by keyways with the shafts.

diam. 400 - bearings 90 and at hubs the shaft has aprox. 110 mm.

Diameter between hubs estimated for 130 mm.

The shell has very low tensions.

The worst pieces at this pulleys are probably the side plates, wich are working about 80 N/mm2. ( I would prefer to work under 75 N/mm2), but it is not a great risk.

I presumed the following conditions to achieve my estimatives:

belt speed : 1,55 m/s

material weight : 72 kg/m

wrap angle : 180

gravity take up

BC 92% full

T1 operation : 2979 kg

T2 1464 kg

belt at 219 piw.

Please verify the safety factor of your reducer and couplings.

These informations are purely especulative and are valid only for the our Forum purposes..

For a safe decision, please verify all data carefully.


Alexandre Calijorne

mail caltrapc@yahoo.com.br

Alexandre Costa Calijorne Caltra Projetos & Consultoria Ltda [url]www.caltra.com.br[/url] [email]alexandre@caltra.com.br[/email] phone/fax: +55 31 2555-9097

Pulley Shaft Load

Posted on 28. Mar. 2007 - 05:29

The conveyor is a slow conveyor. The pulley diameter is adequate for handling the belt you are using for your application. You are not increasing torque load on the shaft. You have increased motor power to take care of additional power required for handling higher tonnage.

The conveyor should work properly without any problems

vinayak sathe 15, Rangavi Estate, Dabolim Airport 403801, Goa, India vinayak.sathe@gmail.com