CEMA Error: Trough Belt to Pulley Transitions

Posted in: , on 19. Jul. 2006 - 09:07

The CEMA recommendations on transition from troughed belt to flat at pulley face are flawed. These reveal a poor understanding of basic mechanics. These recommendations have not changed since the early editions of "Belt Conveyors for Bulk Materials" (the CEMA design book) nor have they been correctly explained.

A troughed belt has a neutral axis belt line. This is the line that passes through the neutral axis of the troughed belt carcass cross-section. This line is above the belt's underside just less than 1/3 the depth of the trough, for a belt on 3-equal-roll troughing idlers. The belt tension acts along the neutral axis belt line.

Therefore:

- 1/2 Depth Transition, typical at conveyor's head end, results in an upward deflection of the neutral axis belt line. The belt is uplifted from the idlers in this area and typically the idlers are shimmed in the field to bring them into contact with the belt. CEMA offers no explanation for this phenomenon

- Full Depth Transition, typical at conveyor's tail end, results in a downward deflection of the neutral axis belt line. The belt tension, along the neutral axis beltine, exerts an exrtra load on the first troughing idler where the belt line breaks. CEMA offers no explanation or recommendation for calculating this extra load (basic statics).

If you haven't fallen asleep by now I welcome your comments. CEMA contibutors should affect revision of the transitions section of the next edition of "Belt Conveyors for Bulk Materials".

Joseph A. Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 19. Jul. 2006 - 10:28

There is a whole book that needs to be written on this subject.

Designers who get involved with the commissioning of their own plants quickly learn that the guide lines are just that... guide lines and 1/2 trough is not an good option if you follow them blindly. Also transition lengths are never quite what they should be if you read straight from the book.

Resolving problems on other plants shows this in full force where incorrect trajectories, pulley lagging wear, idler bearing failures, idler shell wear, severe belt distortion on off set idlers, skirt damage, spillage and overstressed belt edges all appear in abundance. I commend you for hitting this problem head on.

It is the old problem. Designers sit back and assume that the belt will follow any route or shape that they draw or tabulate rather than realise that the belt has right of way and will form what ever shape or any path that it logically desires.

Engicon specialises in correcting non-performing plants and low cost de-bottlenecking of systems.

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 19. Jul. 2006 - 12:58

I don't think that there is any publication that is 100% correct.

They may be a good starting point but you need to establish your own expertise from practical experience.

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 19. Jul. 2006 - 06:08

I met a man in Zambia who told me that one of my previous employers told him that they had followed the MHEA book & if the belt in Whatley Quarry was slipping then they should blame the book. They have since left the business; a move encouraged by such attitudes of the Contract Engineers.

Usually the book is near enough to make rectification viable & a book with a few wrong lines is better than no book at all.

"Designers sit back & assume the belt will go wherever...." On behalf of designers everywhere I ask you what end of the pencil did you use to write such crap?

John Gateley johngateley@hotmail.com www.the-credible-bulk.com

Cema Error: Trough Belt To Pulley Transitions

Posted on 19. Jul. 2006 - 06:34

Mr. Morgan,

I did not mean to open a can of worms. The transition guidelines are an example where the math and science are vindicated in the field. The problem is not in the math and science. It is that the CEMA recommendations don't properly recognize the implications which are accurately predicted by the math and science.

It is my experience that all field problems are a result of similarly not properly modeling and excecuting the math and science. In engineering we don't analize reality we analize a simple model of that reality. Success depends on the correctness of the model in reflecting reality.

Joseph A. Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 20. Jul. 2006 - 08:36

Hi John/Joseph,

OK I should have said SOME designers but in truth it is quite a few. The end of the pencil that I use is the same end I use to pull my hair out when I see unloaded belts with the skirts holding the belt down and no idler contact followed by massive spillage and belt distrotion when the load is applied. The ususal excuse is as you say.... the book says its ok so it must be.

These types of problem are a very sore subject with me since they are so unecessary yet are seen all to often.

Sorry if I upset you, but occassionally one needs to vent.

Engicon specialises in correcting non-performing plants and low cost de-bottlenecking of systems.

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 20. Jul. 2006 - 09:01

Joe,

Interesting that I have mentioned the same point on head pulley transition offset more than once in forum input and got no response. Maybe its when you use the "error" word you get noted.

There are caveats when the 3-roll center roll length does not equal the wings or 5 roll trough systems do not use equal roll lengths.

Another concern of the vertical pulley offset is the calculation of ore trajectory. It is significantly more complex and multi-variant that must include the change in ore loading and belt tension variations.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Cema Error: Trough Belt To Pulley Transitions

Posted on 20. Jul. 2006 - 05:44

Larry,

I too have made the point before. I just had not made it an issue.

Regarding other troughing configurations, it is no different. You merely need to calculate the neutral axis. For a belt of uniform carcass properties it runs through the CG of the carcass.

On trajectory calculations I have had great success with the basic projectile equations. You must be sure to use the correct angle that approaches the pulley, lifting up at the center, dropping down (and spreading out) at the edge, interpolation in between. A couple of years ago we used a deflector and splitter to send all coal flow exceeding 1000 STPH (the capacity of the conveyor to the plant) to a stackout conveyor. Success depended on accurate prediction of the trajectory.

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Cema Error: Trough Belt To Pulley Transitions

Posted on 29. Jul. 2006 - 01:47

Mr. Morgan,

I deviate from the subject in resonding to your comment on off-set center roll idlers but this too is one of my observations.

To my knowledge CEMA (or belt manufacturers) does not link "load support" to inline versus off-set center roll idlers, but the gap at the juncture between wing and center roll is cited as cause of load support failure due to pinching. Some manufacturers have extended this to mean that if you use off-set center roll idlers, with a long center roll that overlaps the wing rolls, then you have solved your load support problem. Following this logic such off-set center roll idlers are used to justify very thin, wide belts. This is typical in grain handling. This logic is a fallacy. If the belt is too thin it will fail due to creasing at the juncture regardless of the gap.

Larry (Nordell), if you read this I welcome your comments.

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 29. Jul. 2006 - 09:30

Dear Joe,

Before I answer, can you inform us if you have made an analysis of the idler junction issue and if so, what method did you use?

As you may be aware, CDI does recommend the use of offset dilers for many overland designs and make an evaluation of the idler junction.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Cema Error: Trough Belt To Pulley Transitions

Posted on 30. Jul. 2006 - 03:41

Larry,

I have never performed a targeted analysis on this issue.

Long ago, following the indudtry wisdom that I have mentioned, I used off-set center roll idlers to justify a pretty thin belt (for the belt width) that marginally violated load support criteria. Though the belt didn't pinch in the juncture gap (as it did not exist) it ran distincly creased at the junctures and it was only a matter of time before failure (by ply delamination) would occur. We ultimately replaced the belt with one the met load support criteria.

I have since observed the creasing phenomena at at other thin belts on off-set center roll idlers.

Since that first experience I have never used the particular industry wisdom and our belts always meet load support criteria even if it means expanding the carcass thickness with additional gum between the plies.

Width of the gap at the roll juncture does indeed pose its own problem regarding load support but its elimination does not eliminate the problem. It will still be manifasted in abrupt creasing at the idler junctures.

I especially welcome the comments of the belt manufacturers on this matter.

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Offset Idler Vs In-Line

Posted on 30. Jul. 2006 - 08:25

Joe,

Thank you for being frank and honest. Design flaw investigation does contribute to better understanding and better products.

CDI promotes the use of offset idlers for six reasons:

1. Allows for the use of belt friendly transoms and eliminates/protects against the potential of idler supports cutting/ripping the belt if idlers become dislodged for various reasons.

2. Allows for the conveyor wind profile and structural supporting steel to be reduced.

3. Improves belt steering

4. Offers better load support with a proper idler configuration. Look at transition idler designs around the world. Why do they use off-set wing to center rolls and have a longer center roll that gives support for the wing compression force where the junction force and stress are at a maximum?

5. Belt performance, at the idler junction, is supperior in steel cord construction due to its longitudianally stiff cable support and compliant transverse rubber support. CDI does some fabric designs, but mainly deal with steel cord construction for overland and high lift conveyors.

6. Improves the vertical and transverse horizontal structural stiffness against modal coupling with belt flap when compared to conventional frame designs.

Some engineers experience poor performance because they are ignorant of the design details as are some manufacturers.

Today we have analytic tools to aid in evaluating such stresses and fatigue failure criteria in orthotropic construction such as belt conveyors.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Cema Error: Trough Belt To Pulley Transitions

Posted on 30. Jul. 2006 - 08:29

Joe,

More on the same though line:

What makes you believe that an in-line idler configuration would not fail in the same way since the belt load support rating would still be exceeded.

I also wonder if the nominated configuration cent roll did not support the belt properly.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Cema Error: Trough Belt To Pulley Transitions

Posted on 30. Jul. 2006 - 11:29

Larry,

You are missing my point. No where have I promoted the inline idler as superior to the off-set type (with overlapping rolls). All of the merits that you mention are true. They are not a basis for taking exception to the load support criteria as is promoted in the industry, particularly in grain handling. After you do all that you mention a belt that does not meet the load support requirements will still tend to crease at the idler junction and will be susceptable to fatigue failure.

Load support criteria is tabulated only for equal roll idlers and is based on the magnitude of the load (assuming a full belt with the material of specified density) and the angle at the juncture of the rolls. Clearly a five roll idler has better load support; reducing the angle at each juncture and the jamming load, as there are more junctures to share in the total load. Load support can be extrapolated (conservatively) for such and other trough angles and configurations or one can analyze it in detail. Such considerations don't negate the point.

Again, I hope there are some belt manufaturers reading this and I hope they will share their thoughts with all the readers of this forum.

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Idler Junction Failures

Posted on 31. Jul. 2006 - 03:52

Joe, hopefully, we can come to an agreement on belt conveyor technical issues. I press for clarity to eliminate apprehension of some owners/engineers/mfgrs. on belt carcass failures due to idler junction stress.

Logically, if you specify a belt selection below the manufacturer's recommendation, why is the idler trough configuration relevant?

Mr. Morgan generalized his disapporval of offset idlers as contributing to belt carcass failure by the comment resolving belt problems related to - "severe belt distortion with off-set idlers". You followed by implying (my interpretation) the offset rolls could be partly to blame, on a project you engineered, even though the belt was out of load support spec. Maybe you were not making such an implication.

Maybe a little clarification is in order, given that the belt will work with one idler trough configuration or type, but, maybe not the other. Here is a multiple choice:

a) will an in-line idler trough configuration yield superior belt junction fatigue to a best offset design?

b) will a properly designed offset roll assembly be superior to the in-line type?

c) don't know?

Another fact about offset idler rolls, given a longer center roll with appropriate overlap, is they support the belt surface with a greater belt contact length and therefore could have a lower peak surface pressure and yield better belt support.

Others have raised the same issue in this forum. I wonder if they have sufficient facts to lay blame on the principle of the off-set rolls?

I look forward to your further thoughts.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Cema Error: Trough Belt To Pulley Transitions

Posted on 31. Jul. 2006 - 06:07

Larry, Let me try again.

1.) I have not attempted to make one style of idler superior to the other and indeed I have acknowleged the points that you make about the off-set center roll idler.

2.) There is an industry wisdom that one can cheat on the load support requirements, when selecting a wide belt, by eliminating the roll juncture gap, using offset center roll idlers. That wisdom has been practiced in grain handling conveyors where thin wide belts are used.

3.) The point that I am making is that the industry wisdom is false. Using offset center roll idlers is not a valid basis for violating the load support criteria. Though the violating belt may not pinch in the gap it will crease notheless and be subject detrimental fatigue.

4.) Earlier in my career, pursuant to the above industry wisdom, I employed offset center-roll idlers at belts with marginal load support. This because of the expense for an expanded carcass that would meet the load support criteria. The offset center roll idlers did not solve the problem and demonstrated that they are not a valid basis for exception to the load support criteria.

5.) Since then I have adhered strictly to the load support criteria, even at substantial cost, and have used in-line idlers.

6.) This does not mean that inline idlers are better rather that the offset center roll idlers don't deliver the advantage that I was seeking and, to me, they are not worth the extra cost or the complication of the rolls inventory.

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Transitions/Load Support

Posted on 3. Aug. 2006 - 11:37

Hello All

First, I only came upon this forum recently, so I am a newby. It is the best forum I have encounterd for bulk handling and I commend whom ever started it.

Second, for the most part all commentors to this forum are very knowldegable and I have quickly gained respect for everyone here. Yes, there is venting, but for the most part it is cordual and informative with little ego being introduced. And, with out pasion, we're just animials.

Thirdly, I am not a degreed engineer, but rather a bloke who has learned to duck his head when the chain breaks merely as a result of mutliple lacerasions, even though "the book" said it will hold. In other words, school of hard knocks. So, I may not know the technical term for some of the forces and factors on this subject but I will try to convey my points as well as I can. Your indulgence is appriciated.

This thread started out inquiring of belt transition, and evolved into idler junction failure. A request for a belt manufacturer's input was put on the table, sorry, I'm the best you have so far. We're a small belt manufacture of 25 mil a year. But we've been around since 1939.

As for belt transition, Mr Santos is correct, CEMA is wrong, sort of. I agree that any book, and CEMA's manual is hardly any book, is only partaily correct. It's the application and adaptation of that base line that gets the job done. The one thing that puzzles me the most is the lack of mention here, and the a lack of requesting the information from convyor engineers, with regards to belt modulus. When considering trasitions the modulus of the belt yarn material, as well as the belt's machanical modulus inherant in the fabric weaving is rarely asked. In my 15 years with this company I've only been asked our belt's modulus perhaps 10 times. A fact I find strange. Transition is always about real estate, which is always at a premium. Whether it's yard space, or structure costs,it's a premium.

If I understand your initial comments regarding the belt's nuetral axis belt line, I would agree IF, you are not taking into consideration the belt's modulus. If your caluclations do not take into consideration belt modulus, you are dealing with numbers based on no, or next to, no moduls. In other words, a steel belt.

Due to the material modulus of Nylon, you can drasticly reduce transition distances. You inherit many other non desireable traits however. Typical belt modulus for nylon is 12,000, less than 8,000 is common. In a Polyester warp yarn belt, the modulus of the belt is less than the modulus of the material due to crimp factors in the fabric weaving, although still greater than Nylon, with a typical polyester yarn belt yeilding a modulus of 18,000 or greater. A mechanical modulus if you will.

The "extra load" that you say isn't acounted for is, in most cases, absorbed by the modulus of the belt edges, providing the forces exerted on the belt are great enough to get into the modulus curve and the distance is not so great as to exceed the allowance for belt edge stretch. So, shimming the idlers is only required when the tension of the belt prevents the belt edge stretch from allowing the belt to come down in contact with the idlers. And thusly, not accounted for by CEMA. If the set up is perfect, you wont need to shim the idlers coming into the head pulley. However, given through put requirements, high speeds, and subsiquent increased belt tension, you have to do it in application.

Keep in mind that even the latest revison of CEMA was largely based of field data from the days of cotton carcas belts. Cotton, being a staple fiber, is a spun yarn. Even though the material modulus of cotton is quite high, the modulus of a spun cotton yarn is still quite low due to the yarns requirement to draw the knots in the fibers that make up theyarn tight before it will resist the strain. So, those "extra forces", in my humble opinion, are negligable due to the belt modulus and not a factor unless you are dealing with steel cable belt. The old rule of thumb of 2.5 times belt width for transition, is still pretty hard to beat. You cheat on it, you'll pay the price unless you have taken multiple factors into consideration and have purchased a specailty high priced belt.

As for idler junction failure, it's a multiple front. Even though there is not a gap between the idlers in an off set structure, ther is still a flex force factor. With an inline troughed idler structure, the problem is quit simple. The load pushes the belt down between the idlers, causeing the belt to be cut, or, becuase the bend is greater than the belt can handle, ply delamination. The statment of the longer bottom idler in an off set structure suporting a greater belt width is true, that in its self creates a problem. As the belt comes over the bottom roller, the load is lifted and the belt, being pushed by the load, flatens out on that roller. Then, within a very short distance and a very short time frame, the belt is lifted up and over the angled idler, which subsiquently quckly and substantually flexes the belt in that area. It flexes it longitudinally, laterally, and on a bias. So, even though you atemp to cheat on load support, you only minimize it becuase you are only replacing the pinching effect, with the suden and severe flattening and troughing of the off set idlers. In additon, the desire for the angled belt sides to slide down and creat a roll or wave in the belt at the transiton still exists, and is compounded due to the thin belt. So a thin belt still fails when it is not of substantial enough ragidity to resist destroying its self even on off set idlers.

In considering load support there are several factors. First, the distance or skim thinkness between plies. As the substraights move apart the belt becomes more rigid. A good thing when considering load suport, a bad thing when considering minimum belt width for proper troughing and minimum pulley diamiters. The reduction of skim thickness to save costs in current vanila belt constructions has resulted in a drastic increase in idler junction failure with or with out off set idler structures.

Also, the fill/weft yarn material comes into play. Plyester is much stiffer and will handle loads above what a Nylon fill yarn will. Regardless of the weft yarn material, one of the recent cost savings tricks by belt manufacturers is to reduce the number of fill/weft yarns, This reduces the crimp factor in the warp yarns which limits the belts mechanical modulus, thus creating problems with the transistion and pulley diamiter. This also reduces the nuber of yarns to resist the pinching or wrinkling effect at the idler junctions.

Another game played in the belting market is the manufacturer's allowable working tension rateing. You are buying a 3 ply 600 lb/piw belt right. But that rating involves a safty factor that is at the descretion of the belt manufacturer. So, just becuase one 3/600 belt performed well, does not mean another manufacturer's will. This is due to different fabric due to one using a 12:1 safty factor and the other manufacturer using a 7 1/2:1 safty factor. Both sold as 3/600's, but much different belts. When comparing different belts, get a yarn count, warp and fill, that will give you a good indication of the belt's ability to handle the load support. Also, ask them to document the belt's safty factor. Also, most belt is sold by a catchy name, which doesn't tell you what the belt carcass material actually is. Find out if it's an all Nylon, a Poly warp Nylon fill, or an all Poly belt. In general the Poly Warp/Nylon Fill is the most popular belt construction. EPs for our buddies not in North America. A good Polyester fabric with good crimp will allow for sufficient mecahnical belt modulus to handle your transisiton and pulley diamiters, the nylon fill yarns will give you ripe and tear resistance and much better mechanical fastener retention, and still give excelent load support providing the manufacturer is giving you at least a 10:1 safty factor. And last but not least, have them specify skim thickness (distance between plies). Most structures have the back bone to train, track, trough, and transition a high quality belt. That will be the belt sample that is stiff and thick. The flimsy belt sample is likely to have load support problems as well as the increased flex as it goes over the idlers will suck up your horse power.

Hope this helps, don't put me on ignore, just tell me I'm full of it.

Regards,

Ron Marler

Legg Co. Inc.

www.leggbelting.com

rmarler@leggco.com

Transitions/Load Support

Posted on 4. Aug. 2006 - 12:03

Hello All

First, I only came upon this forum recently, so I am a newby. It is the best forum I have encounterd for bulk handling and I commend whom ever started it.

Second, for the most part all commentors to this forum are very knowldegable and I have quickly gained respect for everyone here. Yes, there is venting, but for the most part it is cordual and informative with little ego being introduced. And, with out pasion, we're just animials.

Thirdly, I am not a degreed engineer, but rather a bloke who has learned to duck his head when the chain breaks merely as a result of mutliple lacerasions, even though "the book" said it will hold. In other words, school of hard knocks. So, I may not know the technical term for some of the forces and factors on this subject but I will try to convey my points as well as I can. Your indulgence is appriciated.

This thread started out inquiring of belt transition, and evolved into idler junction failure. A request for a belt manufacturer's input was put on the table, sorry, I'm the best you have so far. We're a small belt manufacture of 25 mil a year. But we've been around since 1939.

As for belt transition, Mr Santos is correct, CEMA is wrong, sort of. I agree that any book, and CEMA's manual is hardly any book, is only partaily correct. It's the application and adaptation of that base line that gets the job done. The one thing that puzzles me the most is the lack of mention here, and the a lack of requesting the information from convyor engineers, with regards to belt modulus. When considering trasitions the modulus of the belt yarn material, as well as the belt's machanical modulus inherant in the fabric weaving is rarely asked. In my 15 years with this company I've only been asked our belt's modulus perhaps 10 times. A fact I find strange. Transition is always about real estate, which is always at a premium. Whether it's yard space, or structure costs,it's a premium.

If I understand your initial comments regarding the belt's nuetral axis belt line, I would agree IF, you are not taking into consideration the belt's modulus. If your caluclations do not take into consideration belt modulus, you are dealing with numbers based on no, or next to, no moduls. In other words, a steel belt.

Due to the material modulus of Nylon, you can drasticly reduce transition distances. You inherit many other non desireable traits however. Typical belt modulus for nylon is 12,000, less than 8,000 is common. In a Polyester warp yarn belt, the modulus of the belt is less than the modulus of the material due to crimp factors in the fabric weaving, although still greater than Nylon, with a typical polyester yarn belt yeilding a modulus of 18,000 or greater. A mechanical modulus if you will.

The "extra load" that you say isn't acounted for is, in most cases, absorbed by the modulus of the belt edges, providing the forces exerted on the belt are great enough to get into the modulus curve and the distance is not so great as to exceed the allowance for belt edge stretch. So, shimming the idlers is only required when the tension of the belt prevents the belt edge stretch from allowing the belt to come down in contact with the idlers. And thusly, not accounted for by CEMA. If the set up is perfect, you wont need to shim the idlers coming into the head pulley. However, given through put requirements, high speeds, and subsiquent increased belt tension, you have to do it in application.

Keep in mind that even the latest revison of CEMA was largely based of field data from the days of cotton carcas belts. Cotton, being a staple fiber, is a spun yarn. Even though the material modulus of cotton is quite high, the modulus of a spun cotton yarn is still quite low due to the yarns requirement to draw the knots in the fibers that make up theyarn tight before it will resist the strain. So, those "extra forces", in my humble opinion, are negligable due to the belt modulus and not a factor unless you are dealing with steel cable belt. The old rule of thumb of 2.5 times belt width for transition, is still pretty hard to beat. You cheat on it, you'll pay the price unless you have taken multiple factors into consideration and have purchased a specailty high priced belt.

As for idler junction failure, it's a multiple front. Even though there is not a gap between the idlers in an off set structure, ther is still a flex force factor. With an inline troughed idler structure, the problem is quit simple. The load pushes the belt down between the idlers, causeing the belt to be cut, or, becuase the bend is greater than the belt can handle, ply delamination. The statment of the longer bottom idler in an off set structure suporting a greater belt width is true, that in its self creates a problem. As the belt comes over the bottom roller, the load is lifted and the belt, being pushed by the load, flatens out on that roller. Then, within a very short distance and a very short time frame, the belt is lifted up and over the angled idler, which subsiquently quckly and substantually flexes the belt in that area. It flexes it longitudinally, laterally, and on a bias. So, even though you atemp to cheat on load support, you only minimize it becuase you are only replacing the pinching effect, with the suden and severe flattening and troughing of the off set idlers. In additon, the desire for the angled belt sides to slide down and creat a roll or wave in the belt at the transiton still exists, and is compounded due to the thin belt. So a thin belt still fails when it is not of substantial enough ragidity to resist destroying its self even on off set idlers.

In considering load support there are several factors. First, the distance or skim thinkness between plies. As the substraights move apart the belt becomes more rigid. A good thing when considering load suport, a bad thing when considering minimum belt width for proper troughing and minimum pulley diamiters. The reduction of skim thickness to save costs in current vanila belt constructions has resulted in a drastic increase in idler junction failure with or with out off set idler structures.

Also, the fill/weft yarn material comes into play. Plyester is much stiffer and will handle loads above what a Nylon fill yarn will. Regardless of the weft yarn material, one of the recent cost savings tricks by belt manufacturers is to reduce the number of fill/weft yarns, This reduces the crimp factor in the warp yarns which limits the belts mechanical modulus, thus creating problems with the transistion and pulley diamiter. This also reduces the nuber of yarns to resist the pinching or wrinkling effect at the idler junctions.

Another game played in the belting market is the manufacturer's allowable working tension rateing. You are buying a 3 ply 600 lb/piw belt right. But that rating involves a safty factor that is at the descretion of the belt manufacturer. So, just becuase one 3/600 belt performed well, does not mean another manufacturer's will. This is due to different fabric due to one using a 12:1 safty factor and the other manufacturer using a 7 1/2:1 safty factor. Both sold as 3/600's, but much different belts. When comparing different belts, get a yarn count, warp and fill, that will give you a good indication of the belt's ability to handle the load support. Also, ask them to document the belt's safty factor. Also, most belt is sold by a catchy name, which doesn't tell you what the belt carcass material actually is. Find out if it's an all Nylon, a Poly warp Nylon fill, or an all Poly belt. In general the Poly Warp/Nylon Fill is the most popular belt construction. EPs for our buddies not in North America. A good Polyester fabric with good crimp will allow for sufficient mecahnical belt modulus to handle your transisiton and pulley diamiters, the nylon fill yarns will give you ripe and tear resistance and much better mechanical fastener retention, and still give excelent load support providing the manufacturer is giving you at least a 10:1 safty factor. And last but not least, have them specify skim thickness (distance between plies). Most structures have the back bone to train, track, trough, and transition a high quality belt. That will be the belt sample that is stiff and thick. The flimsy belt sample is likely to have load support problems as well as the increased flex as it goes over the idlers will suck up your horse power.

Hope this helps, don't put me on ignore, just tell me I'm full of it.

Regards,

Ron Marler

Legg Co. Inc.

www.leggbelting.com

rmarler@leggco.com

Cema Error: Trough Belt To Pulley Transitions

Posted on 4. Aug. 2006 - 10:37

Mr. Marler,

Thank you for sharing your impressive knowledge. I hope the following comments will be of interest:

1.) All that you say, about modulus and construction and how these affects proper transion, is true. My point was much simpler. my comments would apply to a rope. If the troughed belt's neutral axis (the rope in tension) is deflected upward it will tend to lift. If it is deflected downward it will bear down on the idler or group of idlers over which it is deflected.

2.) Thank you for your fine comments on belt modulus. We are the exception. We track modulus very closely and specify it stringently. We build sandwich belt high angle conveyors, particularly the DSI Snake Sandwich system where troughed belts are carried over and under alternating convex curves. Radius of curvature constraints are of extreme importance. We use nylon by nylon belts and we specify the modulus (per ISO 9856) not to exceed value. We are always looking for low modulus belting and because of the benefits we are happy to accomodate the larger stretch.

3.) The ambiguous belt working rating is typical in North America. The rest of the world designates the breaking strength, a better clearer approach that allows the user to choose and know the safety factor for the application.

Just my two cents.

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]

Neutral Axis

Posted on 7. Aug. 2006 - 04:54

Hello Mr. Dos Santos,

First, I appoligize for adressing you as Mr. Santos.

1. If you have a single rope, representing the bottom of the belt, ie. the bottom troughing idler line, then I would agree. And yes, tensions and forces on the belt would do as you say. When comeing off the tail pulley the belt wants to ride up as it is being raised by the edges as it approaches the troughed idlers. Like wise on the head pulley, the edges want to raise the center of the belt. But this is true the entire length of the conveyor. The middle wants to ride up. When designing the belt it must be flexible enough to lay down on the bottom iders so that it will track empty, but yet not so flexible that you have idler junction failure.

2. The only industries that have ever encountered of belt modulus were, a. Sandwich conveyor applications, b. Telescoping or fold over conveyors, c. The odd OEM that's pushing the transition limit and knows it becuase they desinged a conveyor, installed it, and trashed the belt in 3 months, so back to the drawing board.

3. By the book, you are correct in your assesment of the North American AWT system vs: the European/Internationl standards for belt tension, however; don't kid yourself, there are plenty of games played in the internationl rating game. One of our foreign fabric suppliers has, as do the others I've talked to, 5-6 different EP200 rated fabrics,(to pick an example) all of which will meet some standard for that break. So why 5 of them, becuase different belt mfg. are in different markets, some only worring about price.

Depending on whether their rating is based on a single end break, grab, or ravel test, will give you considerable varience in it's actual break. In additon, you can sell a belt that is merely a culmination of the fabric lab break test of the fabric multiplied by the number of plies. So, if the fabric is rated using a single end break test, you multiply that times the SPECIFIED number of ends, and that will give you the rating, be it inches or meters. So, if the spec is 18-20 yarns per inch, that's one variable in the belt's actual break becuase perhaps the 3 rolls that made the 3 ply belt all were 18 ends per inch. But, it's an EP600/3 right?

Also, typical Polyesters in the market will degrade approximately 15-20% in the cure process, depending on the compound reaction and the cure temp/preasure. But, belt will be rated as, since there is 3 plies of EP200, an EP600, and that belt is absolutely on the market right now, being sold as an EP600 even though it WILL NOT break at that.

Some mfgrs. will cure rubber on both sides of the fabric, realizing the degradation in break strength. So, the EP200 fabric now becomes EP170(15% strength loss). So now, that mfgr sells it as a 3 ply EP500, and that belt is on the market now. The best tests, we believe, is to cure a 3 Ply sample. The belt will not relize it's full break strength in a multi ply belt due to unequal ply tension, can't avoid it totally.

So, as you can see, there is plenty of smoke and mirrors, even in the International market. I do believe that the international standard is better than the US standard of AWT, but still the games are played. So, ask the belt mfg how they come about their belt tension rating. Just because our guy got caught juicing for a bike race, don't think we're the only culture/society that will take you to the cleaners. But I'm sure you already know that.

And before you say it, yes, there are standards that call out exactly how to test a belt to derive the appropriate EP rating for the actual BELT, down to the number of plies. But people don't ask that, with most not knowing those standards if they heard them. A dude comes in, says it's an EP600/3, and no body asks how that rating was derived. Or they ask, and the dude says, Oh,,, that's ISO-451-KP-78 (2002), and the poor purchasing agent don't now what he's hearing, sounds official, he's sold. Happens every day.

Thanks for the reply Mr. Dos Santos, very stimulating conversation.

Regards,

Ron Marler

Legg Co. Inc.

www.leggbelting.com

rmarler@leggco.com

Neutral Axis

Posted on 7. Aug. 2006 - 05:22

Hello Mr. Dos Santos,

First, I appoligize for adressing you as Mr. Santos.

1. If you have a single rope, representing the bottom of the belt, ie. the bottom troughing idler line, then I would agree. And yes, tensions and forces on the belt would do as you say. When comeing off the tail pulley the belt wants to ride up as it is being raised by the edges as it approaches the troughed idlers. Like wise on the head pulley, the edges want to raise the center of the belt. But this is true the entire length of the conveyor. The middle wants to ride up. When designing the belt it must be flexible enough to lay down on the bottom iders so that it will track empty, but yet not so flexible that you have idler junction failure.

2. The only industries that have ever encountered of belt modulus were, a. Sandwich conveyor applications, b. Telescoping or fold over conveyors, c. The odd OEM that's pushing the transition limit and knows it becuase they desinged a conveyor, installed it, and trashed the belt in 3 months, so back to the drawing board.

3. By the book, you are correct in your assesment of the North American AWT system vs: the European/Internationl standards for belt tension, however; don't kid yourself, there are plenty of games played in the internationl rating game. One of our foreign fabric suppliers has, as do the others I've talked to, 5-6 different EP200 rated fabrics,(to pick an example) all of which will meet some standard for that break. So why 5 of them, becuase different belt mfg. are in different markets, some only worring about price.

Depending on whether their rating is based on a single end break, grab, or ravel test, will give you considerable varience in it's actual break. In additon, you can sell a belt that is merely a culmination of the fabric lab break test of the fabric multiplied by the number of plies. So, if the fabric is rated using a single end break test, you multiply that times the SPECIFIED number of ends, and that will give you the rating, be it inches or meters. So, if the spec is 18-20 yarns per inch, that's one variable in the belt's actual break becuase perhaps the 3 rolls that made the 3 ply belt all were 18 ends per inch. But, it's an EP600/3 right?

Also, typical Polyesters in the market will degrade approximately 15-20% in the cure process, depending on the compound reaction and the cure temp/preasure. But, belt will be rated as, since there is 3 plies of EP200, an EP600, and that belt is absolutely on the market right now, being sold as an EP600 even though it WILL NOT break at that.

Some mfgrs. will cure rubber on both sides of the fabric, realizing the degradation in break strength. So, the EP200 fabric now becomes EP170(15% strength loss). So now, that mfgr sells it as a 3 ply EP500, and that belt is on the market now. The best tests, we believe, is to cure a 3 Ply sample. The belt will not relize it's full break strength in a multi ply belt due to unequal ply tension, can't avoid it totally.

So, as you can see, there is plenty of smoke and mirrors, even in the International market. I do believe that the international standard is better than the US standard of AWT, but still the games are played. So, ask the belt mfg how they come about their belt tension rating. Just because our guy got caught juicing for a bike race, don't think we're the only culture/society that will take you to the cleaners. But I'm sure you already know that.

And before you say it, yes, there are standards that call out exactly how to test a belt to derive the appropriate EP rating for the actual BELT, down to the number of plies. But people don't ask that, with most not knowing those standards if they heard them. A dude comes in, says it's an EP600/3, and no body asks how that rating was derived. Or they ask, and the dude says, Oh,,, that's ISO-451-KP-78 (2002), and the poor purchasing agent don't now what he's hearing, sounds official, he's sold. Happens every day.

Thanks for the reply Mr. Dos Santos, very stimulating conversation.

Regards,

Ron Marler

Legg Co. Inc.

www.leggbelting.com

rmarler@leggco.com

Sorry For Double Post

Posted on 7. Aug. 2006 - 05:40

I'm sorry for the double posts, not sure what the deal is.

Cema Error: Trough Belt To Pulley Transitions

Posted on 7. Aug. 2006 - 06:51

Mr. Marler,

Thanks for the additional comments.

1.) Let me try to further simplify the neutral axis belt line issue. What you mention, that as the wings bear down the center will tend to lift. Indeed this is a belt that is naturally flat being forced into a trough and depending on troughablility it will resist being troughed. If the belt is perfectly troughable (no resistance to troughing) or the transition distance is very long, or the belt remains flat, there remains a neutral axis belt line that is subject to uplift, or imposes downawrd deflection loads, according to belt line (neutral axis) geometry and belt line tension. CEMA offers no comment on this where they recommend full depth transitions (resulting in bearing loads) and half depth transitions (resulting in net uplift of the belt line). In the latter case, depending on the tension, shimming may be required far back from the transition area just to bring the idlers up to proper contact with the belt's underside. CEMA does address these belt Line deflection forces and uplifts elsewhere they just don't seem to recognize the same implications at the transitions. Maybe it is because this issue is so clouded by the other significant forces that you mention.

I welcome others weighing in on this.

2.) Regarding ratings, my point is that rating based on breaking strength removes the ambiguity. To get the same in North America you need two values rather than one; working rating and the safety factor against break (for that rating). We also track what I call specific modulus, the value Bm/Tbrk. We protect ourselves against fraud; requiring testing of the actual belt (after manufacture) including Bm per ISO 9856, tension and stretch at breaking. Additionally we require a cut of the actual belt, long enough to allow us to obtain that testing independently in case of dispute.

As before thanks for your comments, they demonstrate your deep understanding of the beling industry. What is your work history that has resulted in such a deep understanding in this field?

Joe Dos Santos

Dos Santos International 531 Roselane St NW Suite 810 Marietta, GA 30060 USA Tel: 1 770 423 9895 Fax 1 866 473 2252 Email: jds@ dossantosintl.com Web Site: [url]www.dossantosintl.com[/url]