These are standards. There is no right or wrong. If you accept that the standard compiles information from the industry and classifies the information with some relevant knowledge of the application, then you accept how to use it.

Neither CEMA or ISO can be classified as accurate. You could ask why smaller or larger is better, when they differ. You could ask what is the impact, if you knew why. Case in point: larger roll reduces the pressure at the interface of belt and idler. Is this: a) better, b) at what cost, c)can other advantages be realized such as:

1) reduced power,

2) increased idler spacing,

3) improved idler life or

4)improved belt cover wear

5) lower noise

6) and so on.

Standards do not design, they advise. You must understand all the peripheral implications to make a best choice. ■

Originally Posted by nordell

Standards do not design, they advise. You must understand all the peripheral implications to make a best choice.

Very well put! I'll remember that phrase for future use.

Reading some posts I get the impression that these days too many think that adherence to the "right" standard, or "right" reference book or "right" piece of software is the only qualification needed to produce the "right" machine for the job. ■

Hi there..

I gave up CEMA in the 80's and reverted to ISO.

This is mainly because I found it more user friendly when I launched into the realms of dynamic calculations.

Since then I have had excellent result with ISO based calcs.

Cheers

LSL Tekpro ■

Hello,

As a new one on conveyors subject i was wondering about this.

Mr. Spriggs has a very good point. ISO definitely looks more user-friendly. As a starter i chose to hang on to it. However, IMHO, CEMA is more detailed and makes me feel "more accurate".

Mr. Nordell's post was also enlightening for me. I also loved this quote:

I have it more clear in my mind, which standart to choose. Thanks. ■

Dear Afsaneh,'

Please specify the number of ISO and edition that you use for selecting diameter of idler?

Iso xxx ?

Best regards ■

Dear Lyle Brown,

Thanks for your post. Please be informed that ISO1537 is about general dimensions of idlers.

Which part of ISO is about selecting diameter of idlers in designing?

CEMA, CHAPTER 5, is about idlers and explains procedure of selecting idlers.

According to CEMA selection of proper idler diameter & size of bearing and shaft is based on the type of service, operating condition, load carried and belt speed. What about ISO? Are there such requirements in ISO? Does ISO guide or advise you to select proper idler?

Thanks & Best regards ■

Take your pick ---

http://www.iso.org/iso/isocatalogue...CS2=40&ICS3=10

http://www.iso.org/iso/isocatalogue...CS2=40&ICS3=20 ■

Dear designer,

From the ISO Ocean! that you showed me only iso5048 and iso1537 are related to my question.

As I mentioned in previous post iso1537 is about general dimension of idlers (geometry).

In ISO5048 (5.1.3 artificial friction coefficient) there are some information about idler diameter influence on friction factor and not more.

If you have studied these ISO standards, kindly give me a more accurate address or reference that I couldn’t find by review all of them.

Thank you and Best regards, ■

So you have found the problem with some ISO standards, rather than one large one you have many small ones!

Maybe the following

ISO 5048:1989

ISO 2109:1975

ISO 1537:1975 ■

Gentlemen,

Kindly refer to the CEMA website where it clearly states that the CEMA recommendation is just that. It is not in itself a Standard and has no legal standing. While some CEMA Standards do carry an American Standard authentication the Handbook itself does not. Accordingly if you use CEMA, as we generally understand it, in a conveyor design then, good as it is, you have no legal support in litigation, i.e. you proceed at risk. That's the sort of thing that makes lawyers rich. ISO will always take precedence outside North America or thereabouts. ■

Originally Posted by afsaneh782003

Hi, All

In belt conveyor design field which standard is more accurate ISO or CEMA ?

for example I have two choice for diameter of idler 1- according to ISO : 89 mm

2- according to CEMA : 4" I dont know which one is more accurate .

thanks

Afsaneh

There is no hard and fast rule. In fact, you need to go with the idler manufacturer's recommendation on size as ultimately they are the ones manufacturing the product and who guarantee their product.

Don't get caught up with pumping in what you might consider highly accurate data to spit out "better" result. All the way along you are dealing with approximations and generalisations. The bulk density you use is only an approximation. The material characteristics are only approximate. The motor speed is approximate. The starting characteristics are typical unless you get certified motor curves. Even here, what happens when the motor is replaced?

Many years ago I had to review a belt conveyor program that supposedly gave you a graphic demonstration of how the belt tension built up on a long conveyor. It even went to showing how long it took for the tail to start moving on start up. But then, they used the approximation factor for working out the loading inefficiency when loading on an incline rather than actually calculating the correct profile, and this was made worse when they did not calculate the skirt friction correctly as a result. Let's put it this way, it looked nice.

Remember, the accuracy of your output can only ever be as accurate as your least accurate input. There is no substitute for design experience. There is no quick fix when it comes to engineering design. Know what you are doing and don't believe everything you see. Question everything. ■

There is no accurate Standard. How can a Standard be used when it can be off by 50%? ■

Originally Posted by waiwhite

There is no hard and fast rule. In fact, you need to go with the idler manufacturer's recommendation on size as ultimately they are the ones manufacturing the product and who guarantee their product.

Don't get caught up with pumping in what you might consider highly accurate data to spit out "better" result. All the way along you are dealing with approximations and generalisations. The bulk density you use is only an approximation. The material characteristics are only approximate. The motor speed is approximate. The starting characteristics are typical unless you get certified motor curves. Even here, what happens when the motor is replaced?

Many years ago I had to review a belt conveyor program that supposedly gave you a graphic demonstration of how the belt tension built up on a long conveyor. It even went to showing how long it took for the tail to start moving on start up. But then, they used the approximation factor for working out the loading inefficiency when loading on an incline rather than actually calculating the correct profile, and this was made worse when they did not calculate the skirt friction correctly as a result. Let's put it this way, it looked nice.

Remember, the accuracy of your output can only ever be as accurate as your least accurate input. There is no substitute for design experience. There is no quick fix when it comes to engineering design. Know what you are doing and don't believe everything you see. Question everything.

Thanks very much for that: it was just what we needed. ■

Dear all,

After all posts, I should ask my question again

Please specify the number of ISO and edition that you use for selecting diameter of idler? ISO XXX? Which part? I read all related ISO STD and didn’t find it!!!

Before that kindly read all above posts.

Best regards ■

No. You read through the posts again. Contributors expalin stuff and some people do not seem to want to grasp what goes down.■

As said earlier, various standards provide basic guidelines / information on various subjects. The designer is to make right choice to suit the application.

Regarding idler diameter, one primary consideration is that it should not result into excessive rpm. Now, the limiting value of rpm will depend upon the quality of make. As an example, when referred, to some party I recommend 400 rpm, to some 500 rpm and there are also companies who make so good an idler that they use up to 700 rpm.

The other issue about the choice of idler diameter are quite complex like material bulk density, idler spacing, i.e. belt pressure on idler, the belt sag value, and the influence on the conveying coefficient of the belt conveyor.

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

Email: parimul@pn2.vsnl.net.in ■

Some manufacturers can produce idler rolls that can exceed 900 rpm. Special knowledge of lubricants, balance, sympethetic vibrations of belt, rollers, support compliances, and TIR are required.

This goes beyond the design notes in this forum. ■

The standards show the way, but the designer must select real values. This is essential for a correct design. ■

Just download a copy of the Rulmeca Handbook; and read it. Loadsa fun.■