Re: Fatigue In Steel Cord Conveyor Belts
Does not directly address your enquiry, though there is literature of the torque vrs tension (construction) performance of ropes availiable (CASAR have various publications and various mine winders papers etc).
Regards,
Lyle ■
Re: Fatigue In Steel Cord Conveyor Belts
I have been in the industry a very long time and the way you describe these issues is new to me. Transverse breakages in steel cord belts at the edge is more likely to be caused by a poor transition or poor tracking (belt then hits structure) than any other causes. Sure build up if it is very bad can also cause breakages but material entrapment around the pulleys is a more likely cause. Further if build up is an issue before a belt cable breaks tracking should be an issue and so you should detect a problem through drift limit switches. The steel cables in a belt have some limited elasticity plus the rubber can elongate and displace the cables so build up on the surface of an idler or pulley has to be significant.
As to vibration, harmonics causing an issue. I have never encountered this breaking a belt cable. It can cause serious issues with the conveyor structure and this is why we calculate this and allow for it with the way we space idlers. I once saw an extreme case of a harmonic where the steel cord belt would build up into a wave motion that at its peak was over 500mm high, no cable breaks but some damaged idlers.
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Re: Fatigue In Steel Cord Conveyor Belts
Sidd, forgot the other part of the question re what happens as a splice goes over a drum. If it is a drive drum then there is a significant tension change around the pulley face and this does result in the belt and the splice for that matter changing its length slightly in this area. The cables however are never in compression, this only occurs if there is negative tension and by design this must be avoided
Cheers
Colin Benjamin ■
Torque Spike When Splice Wraps Around Drive Pulley
I am not sure I understand the question regarding longitudinal and transverse cracks.
I will try an explanation we have offered on this forum in the past regarding irregular pulley/belt geometry that cause torque spikes on drive pulleys.
First, understand the difference in pulley/belt geometry that may cause such a spike. Given a drive motor electrical slip can be between 0.5 -1.0 % slip or 7.5 to 15 rpm drop from 1500 RPM synchronous speed. How much geometric change constitutes 0.5-1.0 % on a 1000 mm diameter drive pulley? This is about 5 to 10 mm for a 100% deviation in motor torque. Can the belt splice or pulley lagging create a geometric difference of this magnitude? If there are two drives that have a sum difference between pulleys of this magnitude? Can material build-up cause such a difference?
The answer is yes. Sometimes this torque spike will occur but not be noticed by the operator due to poor instrument response. Sometimes an inverter set-up is incorrectly applied that can pertrubate the problem. These power spikes have been known to break the belt from pulley build-up. We do measure the drive torque with sufficient accuracy to see these spikes. You must record the event in a low millisecond data recorder along with the torque strain-gage system.
I do not get: 1. vibration causing cracks or 2. the belt cord twist phenomenon from foreign build-up on drive pulley. You mention polymer (elastomer) fatigue, but, are discussing steel cord fatigue.
I have not seen the edge vibration causing elastomer fatigue. I may happen. To create such an occurence don't you need to produce sufficient force to induce this level of fatigue? Failure of the polymer is usually a shear oscillation. We also see a local polymer failure under the steel cord helix high point at the idler to belt cover interface. This is an abrasive failure caused by the belt local sliding longitudinally and transversely. Again, I do not read these points in your request. These are not cracks (tensile failures), but, abrasive losses. ■
Clarification Of Some Of My Initial Queries
Hi again,
I would like to thank everyone for their input. Collectively it has helped make things clearer. I will re phrase some of the points i put forth with a bit more detail and then ask my questions again
1) I understand belt edge vibration, unless under extreme circumstances, cannot cause belt fatigue. However the point I read in literature states that this vibration can cause dynamic stresses. It also states that this factor is load dependent and therefore variable which helps add weight to the point that vibration alone cannot lead to cracking.
2) Pulley buildup is time related and all of you have mentioned this being the case.
Mr Nordell, sorry for the confusion. I am discussing elastomer fatigue of a steel cord conveyor belt rather than damage to the steel cords themselves.
Anyway let me try and summarize my questions in a more concise manner. they are numbered for experts' convenience -
1) If rip detection is such an issue on conveyors, why have so many people implemented methods to detect rip(do not get me wrong, I am aware that this is super important) rather than prevent rip. Mr Nordell, I understand from one of your earlier replies chute design is the single most effective method to reduce rip risk. However the belt going around the drive drum creating a spike in torque is most certainly bound to propagate the transverse and longitudinal rips over time. Is there no way to continuously monitor or maintain this at a certain value that can prolong the belt life?
2) I notice a popular method to detect longitudinal rip is to measure sum of distances of belt edges from two sensors places at opposite edges of the belt. This doubles up as a belt tracking system. Transverse cracks cannot be identified with this system. Has specific technology been developed to detect transverse cracking? Other than sensor loops please.
3) Is there any way to monitor vibration profiles of segments of the conveyor system? For example, a) conveyor belt experiences different modes of vibration b) vibration of shaft connected to the drive drum(this is where strain gages are usually attached for torque measurements)
Thank you again to everyone who has contributed their opinions.
-Sidd ■
Re: Fatigue In Steel Cord Conveyor Belts
I think you are on the wrong track, rip propogation in the longitudinal direction needs a source that will exert significant shear force after initially penetrating the belt carcass. Remove it and the rip basically stops, it is no longer propogated to any significant degree by other dynamic forces in the belt.
Transverse rips are as I said before not related to vibrations. Elastomer degradation over time is more likely an issue of weathering or poor compounding than any dynamic in the belt as most good rubber compounds can elongate 2-300%. In some belt systems there is the potential to create tension spikes that can cause catastrophic problems but this is a different subject all together.
I think if you want to go further you need to reference the material you are referring to. Transfer chute designs are the key to eliminating most longitudinal rips but there are other causes. For instance scrapers, major spillage, poor belt tracking or failed idlers so not only do we need to look at the transfers but the maintenance issues related to these potential sources as well.
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Fatigue in Steel Cord Conveyor Belts
Causes of elastomer fatigue in steel cord conveyor belts
Hi all,
Sorry if I am posting in the wrong area of this forum. this is my first post.
I have reviewing quite a bit of material regarding the causes for fatigue and longitudinal/transverse cracks in steel cord conveyor belts.
This does of course occur as a result of foreign objects piercing the surface as well as impact damage from mined material. But these are external factors
Two of the key causes that from my literature search that can be classified as being 'internal causes' are
1) belt edge vibration. this being the idler excitation reaching a frequency close or equal to the natural freq. of the belt in tension
2) cord twisting as a result of drive drum build up.
I also understand that tests have come to show an increase in force/torque as the belt moves over the drum from a state of compression to a state of tension.
I have a two part question then.
1) What causes this spike in torque. Does this occur when the splice goes around the drive drum?
2) Has there been or is there any technology in the market that specifically focuses on measuring what occurs in terms of torque when a splice travels over the drive drum of the conveyor system?
I understand there are online monitoring systems for steel cord condition and rip detection but has anything been done to try and understand how to regulate this tension differential to reduce the risk of rip without compromising drive ratio?
I hope I am making sense.
Thank you once again.
Regards,
Sidd ■