CDI can offer to apply our expertise in Finite Element Analysis (FEA) on belt splices which does include methods of cable insertions as patches. We have built splices to St-10,000 N/mm. CDI have developed many patch replacements for belts described by your thread.

I am confused on the notation of splice strength. Making a patch does not equate to splicing. Many installations in China are designed with excessive strength and low splice efficiencies. Therefore, it may be possible to insert the patch to handle impact forces without high regard for full 7 cable temporal integrity. The FEA will give an indication of the patch tensile carrying capacity or improvement.

It is significant that the damage is in the central cords and not the outer cords.

Details of how this patch can be done will be discussed outside of the forum.

Visit our website and ask for further details you may require. ■

By chance did CDI have involvement in the original design or design audit? What is the name of the mine? ■

Dear ZXM99,

Steel cord belts are typically rated by their breaking strength. Each cord has an individual rating and is so tested to pull it to failure. Multiply the individual cord strength rating by the number of cords and you then have the belt's total temporal capacity. Divide the total strength by the width in mm and you have the belts ST-XXXX N/mm strength rating.

However, the splice cannot achieve this breaking strength rating in service. The individual cords must transfer their tensile loads to adjacent cords in the splice through the rubber between cords. When the belt is rotated from low to high tension, such as across a drive pulley (T1 to T2), the repeated elastic strain flux, applied over many cycles, tends to break down the rubber at the molecular level starting at the point of maximum strain flux. This peak strain point is usually located at the passing butt end of the cables adjacent to cables under high load and which are pulling in opposite direction. In splice patterns, with more than one step sequence, there is a local maximum in one of the step patterns that exceeds all others. The local peak becomes more exaggerated with higher step configurations such as 3, 4 or 5 step patterns.

Hannover University, in Germany quantified this phenomenon in the 1960's by building a splice dynamic endurance test machine to determine the loss of tensile strength as measured against its breaking strength. The results were published and became the DIN and ISO standards which are used today.

The splice dynamic efficiency is a value less than 100%, often about 36%, which is why a typical belt has a Safety Factor multiple of 6.7:1. This derivation and more details of an explanation can be found in a number of papers I have published over the years. You can find many references beyond these publications, such as DIN 22101, 22129, 22131, and ISO equivalences.

They do not close the information loop on how to apply this information to: variations of splice patterns, cable construction and rubber or no rubber penetration into the cords, cable size, core rubber behaviors and differences between manufacturers, shock loadings during starting and stopping, pulleys and material build-up, stresses in the belt due to idler transitions, proximity of pulleys, errors in splice construction, degradation of splice kits, differences in drive pulley load sharing, and so on.

The DIN standard is a catch all number to account for these conditions.

The subject is much more complex than this short dissertation. First read the literature. If you wish, I can provide a few in electronic format that you can print out. You can search BSH and find a number of references. I have published some in BSH and some in other venues such as ASME here in the USA.

CDI has design or audited many of the world's highest strength belts in operation today. We also built the world's largest splice dynamic test machine capable of testing to ST-10,000 N/mm now owned and used by Goodyear Tire & Rubber Co (Vayence Technology). ■

I cannot say if the patch is the wiser move without knowing a lot more about the installation. Some facts that come to mind are:

1. age of installation

2. number of cables in the belt

3. configuration of cables

4. where the belt was constructed and to what standards

5. overall belt construction

6. where the breaks occurred and under what conditions

7. number of years of service left

8. loading utilization which tends to break down the rubber

9. how close the breaks are to a splice

10. design efficacy of conveyor and belt - evaluation by an expert ■

A 20m patch is normally no an acceptable practice. The patch is to short. It may affect the overall belt performance. With splices in very close proximity, the loading pattern of one can affect the other. This is especially true when designers are pulley happy and apply them willy nilly.

Interaction of splice rubber and cables between pulleys, pulleys with dirty side contact, pulley geometry irregularities, load sharing between drives, et al may require a greater replacement length. ■

In respect to your problem as to whether to patch or replace it depends on the width of the belt and the number of cables in it. As a rule of thumb if the the number of broken cables on such a critical belt exceeds 20% of the number in the belt then safety first says you put a 20 metre insert in.

If you are going to patch then there is a procedure that requires you to overlay alongside the broken cables a length of new cable. The cable length depends on the belt strength. Such a procedure and patch design is the only acceptable and permanent way to repair such a belt. Just putting a vulcanised or repair band there is only cosmetic and does nothing to assist the belt or stop further damage. If you want detailed advice on a repair methodology email me at colin.benjamin@gcsm.com.au giving details of the belt width, strength, cable diameter and cable spacing.

Given this is a critical belt CBMI have just released a complete new suite of belt monitoring technologies. Such damage could be permanentl monitored on line and any further damage could be alarmed back to your operators while the belt is operating.

Trust all this helps

Colin Benjamin

Gulf Conveyor Systems P/L ■

Colin,

I am encouraged that you at least agree with the need to evaluate the break in terms its impact on the total belt construction. I also agree with the need to scan the cables for a base line assessment to determine if the fix will last for the belts life. THis should be done before and after the fix, if the belt is sufficiently operable to take the required readings.

However, I DO NOT agree with your approach and find your advice very risky. Allowing a "rule-of-thumb" 20 cables in a 100 cable belt to be locally removed even at its center area with symmetry. This would likely cause a zipper effect failure unless you can quantify and control the stress distribution in a prudent manner with a special means to reinforce the belt. We note the 7 cables will not likely make up the 20%. Just adding adjoining cables would likely not be sufficient. This depends on the present and future Safety Factor being utilized during steady-state and during dynamic action as well as many design factors which reduce splice integrity. In addition:

1. Cable damage must be assessed for longitudinal breaks beyond the obvious break point and removed or overlapped an appropruiate amount. The condition of the broken ends - bird nesting or other irregular breaks must be considered when correcting the patch

2. Outer cables near the broken cables may also be partially damaged and should have a cable-by-cable assessment as to their contribution to the field or remaining competent cables and how to treat they contribution in the fix

3. There are special reinforcement techniques that should be applied which enhance the tensile carrying capacity of all cables iusing special rubber and fabrics

4. Cable reinforcement diameters and construction elatic compatibility is critical if it is to be considered in adding to the remaining unbroken or partially broken cables and their strength

5. Unbroken cables near the broken field will carry a greater load as the field of broken cables shed their tensile loads before they enter the break zone and after they leave the break zone.

6. Any arm waving method is folly and risks life and limb. The procedure of finding a long term solution with such a break should only be done by experts with rubber property and steel cord property determination and their knowledge of proper application to a non-linear model in a code such as ANSYS or ABAQUS. Short of this is just guessing.

7. Elastic modulus and strain compatibility theory must be understood.

8. The safe and simple long term fix is to put in a new belt section.

9. The method of scanning should be able to identify individual wire breaks within the individual spun cords within each cable. Short of this is guess work. ■

All good comments Larry, but we have few details of the belt and as I said this was a rule of thumb approach. I have however seen repairs done where there has been 10 - 15 broken cables and done successfully. When there is no spare belt you have no choice.

In respect to repairing steel cord belts with broken cables I have seen the good and the bad for over 30 years and while there are always refinements the methods developed many years ago, if followed correctly they will work and have worked. Unfortunately there are few belts splicers who know or apply the correct techniques correctly and this is why repairing damaged steel cord belts has been such a hazardous business. It starts from where you get and how you prepare the replacement cables right through the the repair length. One thing that is worth adding is that a good quality repair will take as long to do as a replacement splice so one option is always (providing there is sufficient belt in the take up) is to cut and shut the belt at the damage location. The proviso is that the damage is not within 15 metres of an existing splice.

Col Benjamin

Gulf Conveyor Systems P/L ■

Colin,

We too have repaired steel cord belts with interlacing cords. Usually, the damage has been signinficant with numberous broken cables from stones on pulleys, skirtboards, and head end transition entrapments.

In the course of recommending repairs we conducted Finite Element Analysis (FEA). Analysis shows sensitivity to various design alternatives as already noted. Alternatives include manufacturers' recommendations. Most manufacturers have developed techniques based on necessary repairs as a stop-gap. They do not reflect best options for long life, only trial and error acceptables. As you know, just because something works, it is not a testimonial for best practice.

CDI claims there are best-suit-for-purpose options that may preclude mfgrs. recommendation. This is the sole reason for my response. ■

Hi,

The biggest issue is that there is a 1.5 metre gap between the 2 areas where the broken cables are. A 3 stage splice in this belt is reasonably long but my preferred option if you have enough belt in your take up to do this is to;

- Cut the belt at about the mid point between both lots of damage

- Do a conventional 3 stage splice. With only 7 cables broken, any interference to the lay up of the splice from broken cables should not be serious enough to impair the overall splice strength much. If it is an issue and you have enough belt just ask the belt splices to cut out a bit more belt.

This is the most practical solution and the most reliable solution. If you do not have enough spare belt in the take up then you have a very long repair to effect to do this correctly and well. I will email you details of what to do if the above option is not viable.

In respect to assessing belt life and other service factors CBMI now have a number of on-line monitoring systems that can measure the wear profile of the belt over its entire length giving max/min 2 dimensional wear profiles, look in detail at any section that is more worn than others. Such a system can be set up permanently on the belt if you see this belt as a critical system or it can used as something you do every 3-6 months, its up to you. You could couple this with their new visual monitoring system and this can monitor on-line the damage that has just occurred and advise you automatically if it is getting worse. I can once again give you further details by email if you are interested.

Finally the new CBMI on-line carcass monitoring system has such high resolution that the number and location of these cable breaks could have been identified while the belt is still running and could have avoided the production disruption that occurs with x-rays as the belt does not have to be stopped. The other advantage of the CBMI system of carcass scanning is that it scans the whole belt so if there are any other areas where there is cable damage or cable movement, this could also be picked up. For such a critical belt the new CBMI monitoring systes have a lot to offer. Be aware also I am a Director of CBMI and very much involved in the evolution of these monitoring systems.

Trust all this helps. Once again I have given you a best option. Separately I will send by email a lot more detail on CBMI monitoring systems for you to look at.

Col Benjamin

Gulf Conveyor Systems P/L ■

Dear Mr. zxm99,

It is advisable to remove that three meter belt patch between two holes and make a new joint if no other joints are avaialble in the vicinity of the said spot.

The reason behind this is, even if you repair such spot the strength of the same will never be the same as original belt and after repairing if even a single cord came out bottom cover, there is a danger of belt getting damaged.

Consider the facts before taking decision as I had sufferred a lot because of this. ■

Urwithdilip:

Yes, all splices degrade the belt tensile rating or breaking strength. While this is true, it is taken into account in the design of the belt. That is why we have the Safety Factor (SF) x Operating Strength = Tensile Strength (ST).

Adding a splice by itself does not significantly degrade the expected usable operating strength. It does pose a problem in anticipating the belt's reliablility by increasing the likelyhood of local man made defects and by.

Having splices too close together may cause local man made defects. Then the man made defects will degrade the expected strength by overstressing certain portions of one or both splices. ■

Larry,

With broken cables in the belt it is still very advisable to repair the damage and a new splice is far more likely to result in a successful repair than any other type of repair, even if done well. The issue of an additional splice in such circumstances is of a far lesser consequence to the life expectancy of the belt than the possibility of broken cables being the source of far greater damage prpogation through snagging or other means

All the best

Col Benjamin

Gulf Conveyor Systems P/L ■

Colin,

I agree the damaged sections of this belt should be removed for long term viability.

Sometimes I try to inform on tangents to the thread. Maybe a bad idea. Somehow we all become lost. ■

Dear Mr. Urwithdilip,

We have been belt service providers in INDIA since 1953. We were the first one to introduce the concept of cold vulcanizing in INDIA as partners of REMA TIP TOP, Germany.

We have come a long way since than offering Vulcanizing, High Quality belt reapirs, Pulley lagging, Highest quality vulcanizing adhesives etc.

As far as repairs are concerned the largest IRON ORE mining project in INDIA, NMDC Bailadila and for Nyveli Lignite Corp survive on our repairs and lagging for there belts.

With partical work ex i can say we have successfully repaired ST5000 belts with upto 15% per meter steel cords damaged and broken with our T2 repairing system. We can have a DEMO organized on your belts.

regards,

varun chaudhri ■

Hi Guys

Some good info on this, I have the following questions

-How do you determine what length the cables should be for an inlay repair?

- Should they be of exact same diameter or perhaps a little smaller?

- How criticial is it that there is rubber between the cables when you inlay them, what is the consequences of cables touching wach other

- Is pulley diameter a consideration for cable length

- Should cables be taken out of an existing section of spare belt, or can they be obtained from manufacturer

- Should 7 broken cables from the edge be considered worse than 7 in the middle of the belt

- If a splice is to be done on a belt 13 years old should it be done as a bare wire splice?

Regards

Shane ■

Dear Shane

Response to your questions:

1. Length of repair overlap L > 75 (min.) and 125 (recommended) x cable diameter for each overlap end if you are anticipating to achieve near full strength transfer from cable to cable through rubber gap. This is a CDI criteria determined from many laboratory coupon tests and finite element analysis (FEA).

2. The diameter of "patch cable" often cannot be equal to original cable due to available space and therefore needs to be smaller. As a rule-of-thumb, you need to transfer the tensile load from one cable to the adjacent cable through the rubber in shear. The patch rubber gap should be > 1.5 mm and preferrably >= 2 mm. This is only if you wish to gain back some of the lost tensile strength. After applying this criteria, you now have an approximation of the patch cable diameter. Often the patch is to stop product spillage, safety, and removal of potential damage to pulley surfaces et al. In this later case the patch should include a fabric layer as well.

3. The pulley diameter is no influential in determining the patch step length.

4. New bare cable will be superior to a old belt. However, if this is all you have, it should do well enough. We have tested both encased and bare cable pullout and fatigue performance. The only reason we measure such test is to quantify the effect of build a splice with typical rubber stripping procedures.

5. Broken cables near the edge reduce the belt's strength rating to a far greater degree than broken cables from the center.

6. Often 13 year old belt cables should have all core rubber removed. After the core rubber is removed, a primer should be applied that acts to bind the new core gum to a cable which has lost much of the zinc coating. Many belt manufacturers can recommend or supply such primer. ■

I have a second thought on the effect of the pulley diameter:

I would first assume the pulley diameters are selected to be compatible with the belt cable size. There may be an effect when one considers the torsional action of the cable to bending around the pulley. The torsional response reaches its greatest level at about 70 degrees of pulley wrap. Beyond 70 degrees, there is little additional cable torsional strain. Thus, I would recommend the overlap to meet or exceed the 70 degree of the pulley wrap rule associated with its diameter.

On a 1000mm diameter pulley, this would be about 600mm. Assuming the pulley diameter is selected for the cable diameter or about cable diameter = pulley diameter/ 150 (CDI criteria) = 6.7 mm then the 75-125 x cable diameter = 500- 800 mm or in the same range as 600mm. ■

I have a second thought on the effect of the pulley diameter:

I would first assume the pulley diameters are selected to be compatible with the belt cable size. There may be an effect when one considers the torsional action of the cable to bending around the pulley. The torsional response reaches its greatest level at about 70 degrees of pulley wrap. Beyond 70 degrees, there is little additional cable torsional strain. Thus, I would recommend the overlap to meet or exceed the 70 degree of the pulley wrap rule associated with its diameter.

On a 1000mm diameter pulley, this would be about 600mm. Assuming the pulley diameter is selected for the cable diameter or about cable diameter = pulley diameter/ 150 (CDI criteria) = 6.7 mm then the 75-125 x cable diameter = 500- 800 mm or in the same range as 600mm. ■

Thanks Larry

So the idea of a bare wire splice is to remove that core rubber because the properties have deteriated after time is that correct? If so what is it that happens to this core rubber and why?

Are you aware of any papers I could read on the the deteriation of rubber adhesions due to multiple vulcanising or just age?

Cheers

Shane ■

Thanks Larry

So the idea of a bare wire splice is to remove that core rubber because the properties have deteriated after time is that correct? If so what is it that happens to this core rubber and why?

Are you aware of any papers I could read on the the deteriation of rubber adhesions due to multiple vulcanising or just age?

Cheers

Shane ■

Shane,

With all due respects to Larry there are procedures as to determining the length that have have been developed by belt manufacturer's and that have proven to be reliable. Most belt manufacturer's have recommendations in their splice manuals. Generally the overlay length is twice the length of the gap between the broken ends of the cable but there is a minimum length that I don't recall at the moment. The overlaid cable is laid either side of each broken cables and therefore you need one extras piece of cable for the number of cables broken.

In respect to selection of the cables to use, in order its is almost impossible to create adequate adhesion if the zinc coating has been abraded or lost through oxidation so bare old cables are best not used even if you clean them up as all the cleaning may do is remove the zinc. New fresh cables are OK but their prep must be very carefully done as bare wire splicing is far less efficient than splicing with cables that are already coated with rubber. The best selection is to get a piece of conveyor belt and extract the cables from this (make sure the belt is of the same rubber specification eg M, FRAS etc.). It is far easier and you get higher adhesions when you are bonding rubber to rubber. The overall procedure to achieve a satisfactory result requires care and good preparation and should only done by experienced belt splicers. Curing is usually with a spot press of sufficient size for the repair area. You must do the repair as one cook otherwise the uncured area will see cables move.

Regards

Col Benjamin

Gulf Conveyor Systems Pty Ltd ■

Shane,

With all due respects to Larry there are procedures as to determining the length that have have been developed by belt manufacturer's and that have proven to be reliable. Most belt manufacturer's have recommendations in their splice manuals. Generally the overlay length is twice the length of the gap between the broken ends of the cable but there is a minimum length that I don't recall at the moment. The overlaid cable is laid either side of each broken cables and therefore you need one extras piece of cable for the number of cables broken.

In respect to selection of the cables to use, in order its is almost impossible to create adequate adhesion if the zinc coating has been abraded or lost through oxidation so bare old cables are best not used even if you clean them up as all the cleaning may do is remove the zinc. New fresh cables are OK but their prep must be very carefully done as bare wire splicing is far less efficient than splicing with cables that are already coated with rubber. The best selection is to get a piece of conveyor belt and extract the cables from this (make sure the belt is of the same rubber specification eg M, FRAS etc.). It is far easier and you get higher adhesions when you are bonding rubber to rubber. The overall procedure to achieve a satisfactory result requires care and good preparation and should only done by experienced belt splicers. Curing is usually with a spot press of sufficient size for the repair area. You must do the repair as one cook otherwise the uncured area will see cables move.

Regards

Col Benjamin

Gulf Conveyor Systems Pty Ltd ■