Hello,

Pulley construction is mainly influenced by following engineering values, and its standardisation can be accordingly on the basis of the same:

1) Pulley diameter.

2) Pulley face width (belt width).

3) Total radial force acting on pulley (which reflects bending moment).

4) Peak torque.

The pulleys will have 2 categories, keyed pulley and Ringfeder mounted pulleys.

Pulleys manufacturers will have long time accumulated ready-to-use data for reasonably close situations, but they will not part with this information, because it will be ruinous to their business. That is even if they make such standardisation, they will not share with the others.

Such accumulated data is not substitute to actual design all the time, as it concern with money loss / gain (which is dominant all the time).

Pulley design is one aspect, but equally important is how perfectly the pulley is actually constructed (co-linearity of hub bores, achieved fit and tolerance between shaft-hub connection, welding quality, applicable heat treatment, etc.). Such things are practically impossible to check for constructed pulleys by the visiting inspectors, for 100% reliability. As for the plant user, it is better to have single party responsible for design-manufacture-supply for commercial safety.

Regards,

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

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: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

If you class pulleys by Light Duty, Medium Duty and Heavy Duty who decides the limits of each category? Who takes the responsibility if you install a medium duty where it should have been a heavy duty?

The best way to select pulleys is by accurately calculating the T1 and T2 tensions that will be applied on each pulley, give that information to the pulley manufacturer and make them responsible for making the pulley to the given loads that will be applied to each pulley. This is called an engineered class pulley and in my opinion it is the only way to go on most conveyor systems.

Pulley diameters must also be decided by the belt minimum bending radius. Far too many things to consider to just simply say Light, Medium or Heavy Duty. ■

Originally Posted by Gary Blenkhorn

If you class pulleys by Light Duty, Medium Duty and Heavy Duty who decides the limits of each category? Who takes the responsibility if you install a medium duty where it should have been a heavy duty?

The best way to select pulleys is by accurately calculating the T1 and T2 tensions that will be applied on each pulley, give that information to the pulley manufacturer and make them responsible for making the pulley to the given loads that will be applied to each pulley. This is called an engineered class pulley and in my opinion it is the only way to go on most conveyor systems.

Pulley diameters must also be decided by the belt minimum bending radius. Far too many things to consider to just simply say Light, Medium or Heavy Duty.

In my day I would have immediately rejected a pulley described as Light, Medium, Heavy duty or anything outside. On these forums we regularly get notices of drum failure and in every case the failure was down to design. The only answer for the better designer is to quote, and prove, 'fit for purpose' and leave it to the owners engineer and his bean counter to decide on that designer's offer.

Conveyors are a very sad case. There are rigid standards for almost every other kind of plant item but conveyors get through every time because there are only, at best, recommendations which are not enforceable. I would welcome a pulley standard but I know that it would be complex in preparation and the present conveying fraternity, in general, would be unable to apply it. The old chestnut also applies: what measurements would you use? I for one would be very reluctant to have a document with ISO units in parentheses. ■

Originally Posted by sganesh

Dear Sirs,

I am thankfully remembering the great engineers and technocrats who have standardized many other mechanical components like bolts, V Belts etc.,

Imagine bearings were not standardized, and you have to purchase the bearing on urgent basis with drawings !!!

Regards,

Even with comprehensive, complicated and expensive pulley standards it is not feasible to expect a manufacturer to always hold in stock a complete range of pulleys. It does not make manufacturing sense to carry such large stock. Furthermore any compliant manufacturer would be shooting himself in the foot. If the standard he applied was any good then there would be no need for replacement.

The Owner usually specifies a minimum spares holding which includes conveyor pulleys. If a pulley fails in service take the spare out of the store and order a replacement for that. Most operators do it that way providing the document controller hasn't thrown the baby out with the bathwater. ■

Was this a light duty, medium duty or heavy duty pulley before it failed? https://forum.bulk-online.com/showth...n-Boom-Stacker - Oh and I think it was in India.

John hit the nail on the head. The options and methods of creating pulleys are endless and far too complicated to create a simple standard. The designer needs to know that the pulley he is installing on a conveyor system will indeed work for its full expected life.

Some pulley manufacturers created a class called "Mine Duty" pulleys. Ask 10 suppliers of "Mine Duty" pulleys to give you specific particulars on the pulley and I guarantee that you will get 10 different answers. ■

Originally Posted by Gary Blenkhorn

Was this a light duty, medium duty or heavy duty pulley before it failed? https://forum.bulk-online.com/showth...n-Boom-Stacker - Oh and I think it was in India.

John hit the nail on the head. The options and methods of creating pulleys are endless and far too complicated to create a simple standard. The designer needs to know that the pulley he is installing on a conveyor system will indeed work for its full expected life.

Some pulley manufacturers created a class called "Mine Duty" pulleys. Ask 10 suppliers of "Mine Duty" pulleys to give you specific particulars on the pulley and I guarantee that you will get 10 different answers.

========================================================================

Mechanical Power Transmission Association (MPTA) published the standards for most pulleys supplied to items below 200 mm diameter. They produced a table of sizes: belt width, belt tensions, pulley diameters, belt wrap angles, et. al. I thought CEMA endorsed the MPTA table. Maybe CEMA has changed. Mainly used for crowned rim pulleys.

This standard is not for engineered class pulleys, which are still individually engineered according to tri-axial stress fatigue properties and yield/endurance limits. However, the engineered class does not have guidelines among suppliers. Some use FEA, some use classical mechanics procedures based on fatigue mechanics, some use formulae developed from Timoshenko's 1935-1941 text including Theory of Elasticity, et. al.

Later Dr. Helmut Lange and others advanced the theory further after 1963 using Fourier Loading techniques and fatigue analysis methods.

Conveyor Dynamics, Inc. (CDI) and maybe others have commercialized the pulley stress & fatigue analysis codes into computer programs that can provide accurate analysis of most pulley assemblies & their components. This is a short hand method for those not gifted in FEA. An early version was trade named PSTRESS. ■

".... some use formulae developed from Timoshenko's 1935-1941 text including Theory of Elasticity, et. al."

Bejabers there now. Tim O'Shenko was a favorite mystic of mine at university and I owe him for the 95% pass in my final year theory of structures exam. Regretfully I have lost my copy of Roark, Formulas for Stress and Strain and will soon have to buy a new copy. Although Roark is heavier to lug around I prefer it to ANSYS simply because I can get the result from Roark faster than it takes me to build an ANSYS model after I have had to resize the meshes and elements a few times. Maybe its just me and my age but when proprietary software openly admits that there is an inbuilt percentage error before I start and then starts messing me about with model input data I am encouraged to eventually resort to the textbook.

I was considering slatted pulleys and later on spiral pulleys for one of my jobs recently. Although they didn't get much headway in the end I was surprised to realise that they should be a lot cheaper to make than our conventional stuff. I suspect that these specials get priced out of consideration very quickly and many manufacturers have lost out on a quick buck in the process. What says the panel? ■

Dear Mr. S. Ganesh,

It is possible to standardize your pulley dimensions and sizes. However, you will end up paying a lot more for your pulleys than you do now.

Some major influences on the pulley design that you do not include in your list are the wrap angle and bearing centers.

By not having standard pulleys, the pulley manufactures can "optimize" the pulley design to the particular tensions, wrap angles, torques, bearing centers, diameter, face width etc. This can lead to 10's of thousands of dollars in savings on an individual project. How well the manufacture can optimize their design usually determines who ends up with the order.

In each continent and country there are standard practices regarding face width and diameter.

In 1960 and again in 1982 CEMA defined standard diameters, widths and load ratings for what are known as "CEMA Class Pulleys". These load ratings vary with the diameter and the wrap angle of the belt. However, this standard has not kept pace with advances in reduced ply belt design which allow for smaller pulley diameters.

As an example where the current attempts to standardize have real life limits for even lighter duty pulleys:

Consider a 48" wide 600 PIW belt. (A very typical fabric belt.)

At 48" wide the belt tension could be as high as 800 * 600 = 48,000 lbs.

For 81-100% of rated tension the recommended minimum diameter is 24 inches. Table 7.41, pg 306. of the 7th edition.

From Table 1 of the CEMA Standard B105.1 Welded Steel Conveyor Pulleys for a 24 inch diameter pulley the maximum rated load is 345 PIW for 180 degree wrap angle. 150 PIW for a 90 deg wrap.

So, if you selected the diameter of the pulley based on the minimum pulley diameter needed for the belt as per CEMA (most people do this) and bought that diameter CEMA class pulley (in this case 24 inches) the conveyor tensions would be expecting a pulley rated for 800 PIW while the pulley is only designed for 345 PIW, at best. It could be as low as 150 PIW for a 90 degree bend pulley application. Clearly this pulley will fail in a short period of time. To use a "standard" CEMA pulley you would need to purchase at least a 48" diameter pulley. I expect, this will cost you more than a non-standard, properly designed, 24 in diameter pulley.

Using this example and checking other belt ratings, load percentages and pulley ratings there are very few (if any) combinations where you can select the minimum pulley diameter required for the belt and successfully use a CEMA class pulley at that same diameter.

My impression is that this mismatch between the belt requirements and standard pulleys has led to the wide spread use and acceptance of "Mine Duty" pulleys. However, as Gary Blenkhorn correctly pointed out : "Ask 10 suppliers of "Mine Duty" pulleys to give you specific particulars on the pulley and I guarantee that you will get 10 different answers."

Finally, the design of a pulley is a lot more complicated than a bolt, a beam or even a bearing.

Best regards,

Andrew Hustrulid ■

Originally Posted by ahustrulid

Dear Mr. S. Ganesh,

It is possible to standardize your pulley dimensions and sizes. However, you will end up paying a lot more for your pulleys than you do now.

Some major influences on the pulley design that you do not include in your list are the wrap angle and bearing centers.

By not having standard pulleys, the pulley manufactures can "optimize" the pulley design to the particular tensions, wrap angles, torques, bearing centers, diameter, face width etc. This can lead to 10's of thousands of dollars in savings on an individual project. How well the manufacture can optimize their design usually determines who ends up with the order.

In each continent and country there are standard practices regarding face width and diameter.

In 1960 and again in 1982 CEMA defined standard diameters, widths and load ratings for what are known as "CEMA Class Pulleys". These load ratings vary with the diameter and the wrap angle of the belt. However, this standard has not kept pace with advances in reduced ply belt design which allow for smaller pulley diameters.

As an example where the current attempts to standardize have real life limits for even lighter duty pulleys:

Consider a 48" wide 600 PIW belt. (A very typical fabric belt.)

At 48" wide the belt tension could be as high as 800 * 600 = 48,000 lbs.

For 81-100% of rated tension the recommended minimum diameter is 24 inches. Table 7.41, pg 306. of the 7th edition.

From Table 1 of the CEMA Standard B105.1 Welded Steel Conveyor Pulleys for a 24 inch diameter pulley the maximum rated load is 345 PIW for 180 degree wrap angle. 150 PIW for a 90 deg wrap.

So, if you selected the diameter of the pulley based on the minimum pulley diameter needed for the belt as per CEMA (most people do this) and bought that diameter CEMA class pulley (in this case 24 inches) the conveyor tensions would be expecting a pulley rated for 800 PIW while the pulley is only designed for 345 PIW, at best. It could be as low as 150 PIW for a 90 degree bend pulley application. Clearly this pulley will fail in a short period of time. To use a "standard" CEMA pulley you would need to purchase at least a 48" diameter pulley. I expect, this will cost you more than a non-standard, properly designed, 24 in diameter pulley.

Using this example and checking other belt ratings, load percentages and pulley ratings there are very few (if any) combinations where you can select the minimum pulley diameter required for the belt and successfully use a CEMA class pulley at that same diameter.

My impression is that this mismatch between the belt requirements and standard pulleys has led to the wide spread use and acceptance of "Mine Duty" pulleys. However, as Gary Blenkhorn correctly pointed out : "Ask 10 suppliers of "Mine Duty" pulleys to give you specific particulars on the pulley and I guarantee that you will get 10 different answers."

Finally, the design of a pulley is a lot more complicated than a bolt, a beam or even a bearing.

Best regards,

Andrew Hustrulid

===============================================================

I am not sure of your point Andrew. I would like to interject another point in the selection process of pulley dimensions. Typically, the belt sets the pulley diameter for both fabric and steel cord types. Each belt manufacturer may elect certain types of carcass construction (internal stress limits) and ply count to meet the tension rating and nominated belt width based on speed and capacity. The pulley diameter, belt width & shell width, belt tensions, wrap angle, belt construction, and bearing centers generally set the pulley forces (metal stresses), that in turn set rim thickness, shaft size, hub size and end disk construction as per tri-axial fatigue stress levels.

Many early designs were tabulated by the Mechanical Power Transmission Association (MPTA) in close proximity to a small range of belt tensions, shaft sizes for nominated belt widths, diameter, et. al. Although their stress and fatigue levels of accuracy can be questioned today, they did provide a reasonable service to aid designers in finding an appropriate design for many years.

Today, we do have more accurate tools and manufacturing techniques to refine those designs and those that exceed the MPTA limits. I do disagree with your assessment of 10 suppliers will yield 10 different designs. I can, as you can, pick 10 that will fulfill your forecast. That does not bode well for good design practice. I can deliver, maybe 10, that will give reasonably close design dimensions, given belt width, tensions, wrap angle,... based on either classical stress-strain mechanics or via FEA, based on fundamental standards of stress analysis.

I do not think it is prudent to confuse the less knowledgeable that there is no control of modern methods that won't yield appropriate commonality of pulley designs. I hate double negatives, but, sometimes they are useful.

I would like to know that you still have another point to make and that I may misrepresent your intentions. ■

Hi Larry,

I don't think our views are too different. Let me try and clarify.

The initial question was about standard pulleys.

My observations over the years is that engineers look at pulleys from two different vantage points a) the belt or b) the pulley design. (They should look at both!)

I agree that "Typically, the belt sets the pulley diameter for both fabric and steel cord types." My comments are only directed at mid and lower tension fabric belt <= 800 PIW because this is the range covered by standard CEMA class pulleys. My reference, Table 7.41, pg 306. of the 7th edition of the CEMA publication "Belt Conveyors for Bulk Materials", presents minimum pulley diameters for a range of fabric belt strengths and constructions. It should be at least equal, if not slightly more conservative, than what is published by the belt manufactures. The content of this chapter is prepared with, and essentially by, the belt manufactures.

Yes, the initial CEMA standard published back in the 1960's were published by the MPTA. Over the years this has changed into the current ANSI/CEMA Standard B105.1 as is documented in the Foreward of the standard. The current load rating table,Table 1, was expanded in 1982/1983. I also agree that "they did provide a reasonable service to aid designers in finding an appropriate design for many years." Belt constructions and splicing has improved over the last 30+ years, allowing smaller pulley diameters. Conveyor belt technology, and the market, has shifted from 4, 5, 6, 7+ ply belting to 1, 2, 3, and 4 ply belting. Except for imports from outside North America, I rarely see a 5 ply or higher fabric belt construction in the US. The load ratings for standard CEMA class pulleys have not kept up with these market changes, so they are much less relevant.

I'm not raising a question about how pulleys are designed. I completely agree that the technologies for designing pulleys have advanced significantly since Sitzwohl, Smoltzi, Lange, Timoshenko and many others. I also agree that different manufactures can come up with different designs that meet the application requirements.

The point that Gary made, that I agree with, was regarding "Mine Duty" class pulleys commonly used in the United States. There is no standard load rating for these classes of pulleys so the load rating is left up to each manufacturer. Some example comments regarding "Mine Duty" pulleys from major pulley manufactures in the US.

• Mine Duty 1.5 - Roughly 1.5X service factor of CEMA standard
• Mine Duty 2.0 - Roughly 2.0X service factor of CEMA standard
• Super Duty - Exceeds 2.0X service factor of CEMA standard
• http://www.vangorp.biz/products/mineduty.html
• "Pre-Engineered" Conservative construction - more that 2.0 overload capacity
• Minimum 150% end disc strength over Heavy Duty
• Minimum 300% rim strength over Heavy Duty
• Extra capacity for rim wrap factor
• Extra rim thickness for abrasion
• 3/8" thru 1" Rims
• 1", 1-1/4" and Heavier End Discs
• 3/8" Center Plates

The capacity of a "mine duty pulley" from supplier A is different than a "mine duty pulley" from supplier B.

I am not stating that there is no control of modern methods. (Note the double negatives.) Using modern pulley design methods and tools engineers can reach similar designs that will meet the application requirements. Variations will mainly be around the locking assembly choice, the end disk design / thickness, allowable stress limits, and the cost.

I am stating that people need to be knowledgeable and aware when using CEMA standard pulleys.

When selecting the pulley diameter from the minimum requirements of the fabric belting (which I have found most people do), one then needs to take a close look at the load capacity of the standard CEMA pulley for that diameter. In doing so, the majority of time, you will find that the standard CEMA pulley is underrated and you will need to either a) select a much larger pulley diameter if you want to use a "standard" pulley or b) use a non standard pulley.

Andrew Hustrulid

Originally Posted by nordell

===============================================================

I am not sure of your point Andrew. I would like to interject another point in the selection process of pulley dimensions. Typically, the belt sets the pulley diameter for both fabric and steel cord types. Each belt manufacturer may elect certain types of carcass construction (internal stress limits) and ply count to meet the tension rating and nominated belt width based on speed and capacity. The pulley diameter, belt width & shell width, belt tensions, wrap angle, belt construction, and bearing centers generally set the pulley forces (metal stresses), that in turn set rim thickness, shaft size, hub size and end disk construction as per tri-axial fatigue stress levels.

Many early designs were tabulated by the Mechanical Power Transmission Association (MPTA) in close proximity to a small range of belt tensions, shaft sizes for nominated belt widths, diameter, et. al. Although their stress and fatigue levels of accuracy can be questioned today, they did provide a reasonable service to aid designers in finding an appropriate design for many years.

Today, we do have more accurate tools and manufacturing techniques to refine those designs and those that exceed the MPTA limits. I do disagree with your assessment of 10 suppliers will yield 10 different designs. I can, as you can, pick 10 that will fulfill your forecast. That does not bode well for good design practice. I can deliver, maybe 10, that will give reasonably close design dimensions, given belt width, tensions, wrap angle,... based on either classical stress-strain mechanics or via FEA, based on fundamental standards of stress analysis.

I do not think it is prudent to confuse the less knowledgeable that there is no control of modern methods that won't yield appropriate commonality of pulley designs. I hate double negatives, but, sometimes they are useful.

I would like to know that you still have another point to make and that I may misrepresent your intentions.

■