Re: Repeated Splice Failures
Re: Repeated Splice Failures
Is there a difference in rampup speed between the two drives at the conveyor's head?
Antonio Reis
Vitrom Mfg Consultants
Your Process and Manufacturing Solutions
Phone: 209.834.1900
Fax: 209.834.1039
www.vitrom.com ■
Re: Repeated Splice Failures
Dear Shri Raja,
You have mentioned 45 degree trough carrying idlers spaced at 1.2 m, and also return idlers of 45 degree trough spaced at 1.2 m. This information together with conveyor profile implies that possibly you have a special conveyor which is conveying the material on carrying side and also on return side.
Your data mentions only one material (hot clinker) which you may be conveying on carrying side. What about the details of the material being conveyed on return side and its capacity i.e.
- Conveying rate for return run.
- Material average lump size, maximum lump size, material name, material bulk density, material temperature etc. applicable to return run.
The joint failure can arise only with the reason that it is not adequate in strength compared to actual force occurring in your installation. This could be due to varied reasons such as
1) Joint weakening due to temperature. Check whether your belt materials and vulcanising materials are suitable to the actual temp conditions.
2) Joint weakening due to overstress leading to stress beyond yield limit. This can be due to more force by drive system, transition length strain, less radius of curvature, inadequate pulley diameter – which does not seem to be applicable for you, impact strain by lumps if these are big on return run, or belt is not of adequate strength. The sum effect of various forces arising simultaneously from these, should be within yield limit, as defined by various safety margins.
Your frequent failure signifies failure due to overstress rather than failure due to fatigue. Indication of reason / solution would require detailed investigation on all the concerned points. These would be an elaborate design exercise. As a first short cut, you need to get opinion / confirmation from belt manufacturer that the belt and vulcanising solutions are suitable to temperature conditions. Also check the actual temp of the clinker you are feeding, and also the actual conveying rate continuous record.
Regards,
Ishwar G Mulani, Pune, India.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
Advisor / Consultant for Bulk Material Handling System & Issues.
Email : parimul@pn2.vsnl.net.in
Tel.: 0091 (0)20 25882916 ■
Re: Repeated Splice Failures
Dear Shri Raja,
I suggest that you have a represntative of the belt manufacturer investigate your system. Although repeated failures suggest an underrated belt, there may be something in your system that is "picking" at the splice. In addition, by having angled return idlers, you are placing extra stress on the belt edges. If you are overtensioning the belt, the splices will suffer.
If you do not have confidence in the belt manufacturer's representation, try contracting the services of a reputable consultant or engineering frim that specializes in overland systems.
Good luck in resolving the problem.
Regards, ■
Re: Repeated Splice Failures
The first thing I would try is to carry out a “Bare Wire Splice”, this means removing all traces of the existing rubber from around the steel cords prior to the splice layup.
If the rubber compound is breaking down, redoing the splice without removing the rubber around the cord will continue to fail and probably, more frequently.
If you would like further information on “Bare Wire Splicing” please contact me. ■
Repeated Splice Failures
Originally, this conveyor carried material on the carrying and return runs. Then the idler spacing was 1.05 meters on both spans and ST 3150 belt was used.
Even after discontinuing material carry on the return run, the same belt continued but the problem of belt sway increased. A consultant increased the idler spacing and introduced belt turnover devices after which the ST 3150 belt worked very well.
When time came to replace the belt, the same consultant opined that a ST 2000 belt would suffice and hence the change.
The problem with splices have started with this belt and in the past 2 years we have had at least 10/12 splice failures. The belt manufacturer has provided prompt, efficient and competent service all the while but we do not perceive the belt or splice quality alone to be the source of the problem. The quality of their product and services in this part of the world is excellent and no organisation of their calibre could possibly continue to make errors in splicing over two years.
What is troubling me is that with my - admittedly low - knowledge of belt selection, I find that ST 2000 may have been underrated.
To answer the individual queries -
1. The head end drives are well synchronised and hence there is no abnormal start-up jerk
2. "Bare wire splice" techniques are being employed
3. Conveyor appears clean : we dont find anything "picking" on the joints
I am still hoping this forum will yield the answer we have not found till now.
Thanks ■
Re: Repeated Splice Failures
Dear Mr. Raja & Mr. Kayem,
It sounds as if there is a tensioning problem, although I have not run the numbers.
How much weight is the being used in the gravity take-up system, including the pulley and take-up carriage?
What is the sag percentage between idlers?
Regards, ■
Re: Repeated Splice Failures
Anything beyond 12.5 MT is risky although we have found that the optimum weight should be around 16 MT.
As for the sag, it is definitely nothing abnormal - although I dont believe it has been measured in recent times. ■
Re: Repeated Splice Failures
Dear Raja:
As other have stated, there are too many factors you have left out and need addressing to render an informed opinion. Without being too pedantic, here are a few:
1. edge faliure signifies local overloading - where is it overloaded?
a. 5 convex vertical curves of unknown radii
b. turnovers of unknown design
c. pulley happy -- counting equiv. +16 unknown arrangement
d. takeup mass 16000kg? ~ 80 kN? multipart reeving, etc. ?
e. center cords carry less load than edge due to thermal exp.
2. edge cords can be overloaded from thermally expanding center cords via higher center cord heating. Center expands lowering center cord tension with respect to edge. Assuming nominal tension stays the same, ergo the edge must carry more. Most engineers overlook this critical factor on HR belt designs.
3. Heat resistant belt usually requires greater power in the high heat spectrum. Your 140-180 C temp will normally further increase the power demand and reduce rubber shear and fatigue strength. However, your amps indicated a sedentary power draw. All HR belts we have rheologically tested show much higher power draw than you note. Either your mfgr has found something quite unusual wrt to the norm, or your measurements are incorrect. Here at CDI we nor
mally dont test viscoelastic properties beyond 65C. HR rubber will draw about 50% more power than CEMA numbers in this range. Higher heat (140-180C) will, I believe, pull more.
4. amp measurements indicate around 450kW power draw. Theory says over 750 kW for below 65C HR. Need better power vs tonnage data to point study in proper direction
5. CDI has studied HR belt splice capacity using the Instron hydraulic fatigue tester and heating system that synthesizes your case. Thermal couples give feed back on front and back side of belt to ascertain core temperature. We find elevated temperatures can seriously diminish the shear strength and fatigue dynamic capacity. We have tested belts to 120C. Results show a 30-80% drop in dynamic capacity, depending on mfgr.
The condition is exacerbated by the thermal differential between center and edge as I have previously stated.
6. comments above need to be integrated together into a more meaningful analysis. As I said ,you do not have sufficient information to allow an informed opinion. If you need, help we can oblige.
Regards,
Lawrence Nordell
Conveyor Dynamics, Inc.
www.conveyor-dynamics.com
email: nordell@conveyor-dynamics.com ■
Splice Failure
I have looked at the figures that you posted and find that the design is generally OK I would have suggested a higher counterweight at 122Kn not 80Kn but this depends as Mr Nordell states could also be achieved by reeving.
As the belt is a Hi Temp I would ask in the components in the splice are compatible with the splice material being introduced.
You have said it is but the splice should handle the workload. You need to provide more information on the system. The RS-1 view that you posted is hard to read so figures may be incorrect.
Information like
Counterweight reeving
Counterweight movement during start and stop.
Drive type. Fluid coupling, VVVF what ever.
Spacing at turnover and pulley sizes.
As Mr Nordell sates you do need to have someone review this system and I would suggest either Mr Nordell from USA or The Gulf Group in Australia. Both companies are providing solid information on problems such as this. ■
Splice Failures
Sorry forgot to mention that the belt would appear OK. What are you transitions like with 45 deg troughs this could cause high edge tension at that point which would see splice failure from edge as mentioned.
Don’t get distracted form the basics it is what gets us all. ■
Re: Repeated Splice Failures
As BKD and others noted, idler transition stress must be considered.
In addition, I have seen belt mistracking, at the high tension head pulley, cause excessive edge stress. Mistracking with the addition of idler transition stress, caused edge cable pullout in the splice. The condition was so bad the operator used a side guide roll, mounted at a 45 degrees directly in front of the head pulley, attempting to guide the belt around the pulley without properly adjusting structure, pulley, et al.
I still believe the belt thermal differential between center and edge has some bearing on the problem. However, the solutiion must consider all additive stresses on the splice and differential cable forces in the splice.
You did not say if all failures are on the same side. There was also a hint that you were not sure if all failures were at the edge.
The fact that the cables are pulling out from the pulley side (bottom) cover is usually a result of the thinner bottom cover thickness. As cables pullout under high tension, they tear directional wedges in the form of conical arrows. THis does not allow the cable to reinsert itself in the failed zone when the tension drops, such as after the head drive. The cable then is buckled, and forces the bottom cover to displace.
You ask, "Is the belt under-rated?" Based on modern cable design supplied in the last 5 years, you appear to have a ST-2800+ N/mm belt strength. The manufacturer may have rated the HR belt lower due to its poor HR rubber strength in the splice.
What is the spice step length? Normally, the belt splice length is increased with HR belts not adding more cables. You have 40% more cable strength than its rating implies, if my cable strength calculation is correct. You don't say which DIN pattern is used. I assume it to be a two step.
Further, using 81 cables shows the mfgr. is not informed of modern splice methods and strengths. An odd number of cable is inferior to an even number. I won't dwell on this detail here since it is not significant.
Lawrence Nordell
Conveyor Dynamics, Inc.
www.conveyor-dynamics.com ■
Re: Repeated Splice Failures
Clarification:
The directional wedges or conical arrows are the shape of the core rubber remaining on the cable as it tears away from the main body of the belt. When you examine the failed cable, after it is removed from the splice, the rubber appears to be serrated and directional. Conical might be a slight stretch - no pun intended.
LKN ■
Re: Repeated Splice Failures
Please excuse me. I errored in the ST value. The belt rating is closer to ST-2300 N/mm than 2800 N/mm. Too much red wine.
This depends whether the cable is an open weave and impregnated with core rubber or not.
Sorry.
LKN ■
Repeated Splice Failures
Raja,
One of my clients has recently has a splice failure and several splice ruptures on ST1250 x 1800mm belt. The finger was initially pointed to the quality control of the splice (materials, compatibility, workmanship etc etc.). However, lot was revealed when they undertook a CBM scan of the belt and discovered hundreds of cords broken in small groups, well away from the splices - indicating overstressing of the steel cords away from the splices beyond their safety factor of about 7. If the cords are breaking away from splices, you can't blame the splice for failing as well. The cause of the overtensioning of the belt seems to have been combination of excessive starting ramp tensions, poor transitions, excessive pulley wear and some splice quality control. Maybe you should look at the rest of the belt to see if you have the same issue - it might help to direct you more closely to some of the other things those before me have suggested - transitions, starting ramps, drive sharing etc. ■
Splice Failures
Contact details of Conveyor Belt Monitoring (CBM) is ++61 94821866 ask for Mike Lay or email michaell@gulfch.com.au ■
Re: Repeated Splice Failures
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Re: Repeated Splice Failures
After reading all of the replys, there may be one more thing to check that could cause splice failure. Using a crown face pulley in a high tension area of the belt may cause undue stress on the splices. ■
Repeated Splice Failures
On a long distance overland conveyor, we are facing repeated instances of failure of the splice joints. The joints are done as per DIN recommendations for a type 2 splice. The compounds are fresh, there is nothing wrong with the splicing machine, the workmen are skilled and yet the splices keep failing. The same crews use the same hardware and same source of splicing compounds at various other conveyors and experience not a single splice failure.
The relevant data pertaining to the conveyor as well as a profile sketch are attached.
We are looking for some pointers here.
* Is the belt under-rated ?
* Is a DIN splice not adequate because of the turn-over arrangements ?
* Is it necessary to take greater factors of safety for the splice or belt if hot material is being carried ?
The belt used is 1000 x ST 2000 x 10/6 Heat Res. Grade. This belt has a rip-check breaker on top; there are 81 cords of 5.4 mm diameter and 12 mm pitch.
Almost EVERY splice failure has been from the edge, starting on the non-carrying side.
Could someone please help us in identifying the probable reasons for this repeated failure ? We are seriously wondering if the belt rating is appropriate. Can someone comment on that ?
Thanks in anticipation
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