Dear Mr.Kayem:

I am a senior engineer for the design of various conveyor belt,accoding to my experience (sure i have plenty of data for the splicing test),I think the material compatibility is very important indeed. Sure you need not to use the same compound formula for the spelicing material,but must be compatibility.

You are warmly welcome to contact me to discuss some problem for belt spelicing .

You could send me email to :info@mt87.com

Thanks

Thomas SU ■

Dear Shri Kayem,

Your question pertains to chemistry / rubber-chemistry / rubber technology; and so only they will be the right people to give you point blank answers.

The general understanding is that for any type of joint (whether welding, brazing, belt joint, etc) the joining solution (medium) should merge with the items to be joined, for strong joint. If the merger happens to be at molecular level and the physical characteristics of the medium is similar to the items to be joined, the joint will be very strong and it will become a uniform body with minimum discontinuities. There is also joining by adhesion force, but it may not be so strong (like paper joined by natural gum). However, if the papers are joined by special adhesive (like cellulose based), possibly joining surface dissolves in medium and it is very strong, as strong as the paper itself.

Well, as I said before, this is not my subject and concerned people can correct this reply.

For rubber joint also, aforesaid consideration may apply. So, which solution will merge with what quality of rubber can only be told by rubber chemist who knows the chemistry of the particular rubber and the particular solution. Mere brand name may not be sufficient.

Regards,

Ishwar G Mulani.

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 ■

Kayem,

There are many aspects to your query about splice kit compatability and acceptable splice strength:

1. steel cord - what is the bonding process - sulfur, cobalt, ....

2. fabric plies - what type of bonding, how fabric is prepared, ....

3. core gum compatability - aside from bonding agent

4. fire retardant core gum life factors

5. acid resistant

6. splice reinforcing techniques

7. environmental treatment of splice rubber incl. hygiene

8. others you mention

9. points below

We have and you can test these factors with a cyclic destructive test procedure. A special molded block, of selected cables from the belt in question, is used to hold the cables when they are placed in a defined pattern to test the interaction of rubbers and their fatigue life vs shear load. This has been called the H-block test.

The cables are taken from the parent belt with rubber left surrounding the cables. The cables are placed the the mold in a pattern to produce the desired shear stress, when cables are pulled from opposing ends, with a 100-200 mm rubber shear zone between opposing cable arrangements.

The mold is filled with the selected splice rubber compound and cured in the standard manner. A shear stress level vs life cycle curve is produced from 3-6 testings altering shear stress magnitudes. This replicates the shear stress fatigue cycle of low to highbelt tensions and stress of a belt's splice for one revolution over the drive.

This can replicate belt ageing by selecting the cable with attached rubber from parent belt specimen that has been in service for a prolonged time.

We have designed the mold system and test procedure to identify compound compatability. We use an Instron hydraulic cyclic load control machine. There is a special procedure for grabbing the cables.

This fatigue test is more effective than any theory.

There are substantial differences in splice rubber compound fatigue strength defined by the test life cycle expectation just as there is in the differences with core rubber fatigue strength, independent from splice kit compatability with core gums.

Splice compound environmental storage can have a major efffect. The splice kits need to be stored in a < 8 C temperature environment to minimize premature curing.

Depending on how you intend to operate the conveyor (ie lower safety factor), should be a guide to the study of splice fatigue efficiency and cyclic loading.

There are many more important aspects to splice efficiency that should be covered outside this discussion.

Others, I/m sure will have more to offer.

Lawrence Nordell

www.conveyor-dynamics.com ■

Pipe Conveyor vs Conventional Belt Spices:

There usually is no difference in the core gums. There is a difference due to the fabric forming reiforcement used in pipe conveyors. This is often ignored in splice construction.

LKN ■

Hello Kayem,

Belt manufacturers are correct in stating that compatibility of splice materials is very important for strong splices. However, As Mr. Nordell has pointed out, compatibility of materials is only part of the issue. You must ensure that the splice materials will bond properly with the substrate and will provide the shear strength required for the belt in question. Another important factor to consider is the shelf life of the materials being used and any special storage requirements.

When I was involved with belt splicing and repair work with a belt service company, we made it company policy to use belt manufacturer?s splice materials or belt manufacturer approved materials (Rema, Blair, etc.) ? unless directed otherwise in writing by our customers. Not because those materials were the best for the job, but because it eliminated one point of contention in the event of problems. If you are an independent service company that violates the splicing recommendations of the belt manufacturer, you leave yourself open to full liability. If you follow the belt manufacturer?s recommendations and use their approved materials, you are in a much better position to receive assistance from them. The savings from using substitute materials is not worth it in the long run.

If you are splicing belts for your own use, you can be more adventuresome and try alternate materials. However if you take this approach, start with non-critical belts (i.e. ones that you can afford to have down in case of splice failure) or with belts where the recommended splice methods and materials do not work.

One caution is with the specialty nature of the various rubber compounds. Tie gum must be compounded for its shear strength and peel strength (bonding); and be compatible with the substrate or substrate?s bonding material. Cover material must be designed for the conditions it be exposed to (chemical resistance, abrasion resistance, heat resistance, etc.).

Finally, low cost materials generally provide poor service. That is, although you may not get what you pay for ? you definitely get what you don?t pay for!

Hope this helps. ■

One caution is with the specialty nature of the various rubber compounds. Tie gum must be compounded for its shear strength and peel strength (bonding); and be compatible with the substrate or substrate’s bonding material. Cover material must be designed for the conditions it be exposed to (chemical resistance, abrasion resistance, heat resistance, etc.).

I am new here to this forum but I do like what I see so far! I would ask when you refer to bonding are you referring to cross linking? Or are you referring to mechanical adhesion or both? I would also like to hear your thoughts on fillers, extenders, plasticizers ect as they pertain not only to splice materials but to cured skim stocks found in textile belting. I would also like to hear your thoughts on solvents. Sorry for pulling off the original question but excitement got the best of me.

Regards

D W Davis ■

Dear D W Davis,

With splicing, bonding includes both cross-linking and mechanical adhesion (locking?) with the fabric carcass. Typically, RF dips are used with the fabric and this does provide some double bonds that standard sulphur cure rubber compounds can cross-link to - depending on the cure state of the resorcinal formaldehyde. The fabric offers good mechanical link points. Although it will vary with rubber compound and carcass mixes, I would place the ratio at approximately 60% mechanical and 40% chemical (cross-linking).

With tie gum to fill rubber, the primary (sole?) bonding is with cross-linking (Ratio approximately 90% to 10%). With fresh rubber (tie gum & fill strip) to old rubber (cover contact points), the bonding is again a mix of mechanical and chemical, with a ratio of approximately 60% chemical to 40% mechanical.

These numbers are extremely arbritrary.

As far as fillers, cure packages, plasticizers, et cetera are concerned in the rubber compounds are concerned - they are necessary to achieve the desired ASTM D2000 specification for a given purpose. The judicious use of these chemicals allow the compounder to achieve his/her goal. Unfortunately, pricing pressures often lead to unsuitable rubber compounds (see forum comments on poor bonding of ceramic squares to rubber lagging backing compounds -- good compounds, such as those used by Rema, give a good product. Bad compounds make users look for alternatives.)

As far as solvents are concerned, care must be taken to use solvents that are both compatible with the materials and that will not leave a coating, which could interfere with bonding. That is, rubber solvent (white gas) is generally safe, while xylene tends to create problems. Toluene is generally good, while acetone is too aggressive.

Obviously, I'm getting off the original topic - so I'll stop.

Regards, ■

I can relate to your questions and through field experience I can offer some experiences I have had over the past 17 years on a couple of types of the belt compounds you have mentioned. Heat belts are not easy to work with and small errors are magnified when high temperatures are thrown into the mix. I did use one specific splice material for EPDM and BUTYL belts in the past and the results were stunning to say the least. On two occasions the adhesion values were 40% higher than factory splice materials. Unfortunately these materials are no longer on the market (at least from one supplier I have used in the past) don’t quote me on this I believe the compound was Bromulated (spelling?) Well Bromine is not ozone friendly so that clears up the reason for discontinuation in my mind.

In fire retardant belting you have two factors that I consider critical. Does the belt achieve fire-resistance through the use of earth type fillers?(compounded into the base elastomer) or is the fire-resistance achieved through organic or inorganic chemical additives? On one end of the spectrum you have a belt that is easy to bond with a range of splice materials. On the opposite side you have a belt that is compound specific so factory kits are a must. Fire-resistance specs vary greatly at the four corners of the world and with an emerging global economy the belt in question could be made in a different country in a different hemisphere. In retrospect the belt should have passed testing criteria to be allowed to be supplied in a different country but you will never know what the belt is made of ( trade secrets) I have had good luck with standard grade one and grade two materials and disastrous results with factory supplied materials.

I sure am glad you never mentioned PVC belting (gross sticky messy toxic finger splicing yuck.) It may not burn but then again the off gasses will get you quick enough. I have only been involved in 250-300 steel cable splices so I will leave that one to the more experienced here on the forum. Oil resistant belts (with heat or not) are a pain in the butt and I have never been satisfied with one I have ever done (application was probably more the issue on these) still not my favorite to work with for sure.

D W Davis ■

Hi Kayem

I totally agree with all the above that the manufacturers splice kits should be used especially with the types of belts you mentioned.

* Steel Cord belts

* Pipe conveyor belts

* Oil resistant grade belts

* High heat resistant grade belts

* Fire resistant grade belts

However this is not always practical due to supply and demand, for instance.

A mine or plant breaks a belt and needs to have it running as soon as possible, the splice kit [ HR, OR, Steelcord etc ] is 2 to 3 days away.

They won’t want the plant down any longer than necessary, so a generic kit is used with every ones blessing.

It’s not practicable for a Belt Splicing Service company who’s looking after 20 or 30 plants to hold stocks for all types and variations of all manufactures belts, on the chance that they may or may not be required.

The range is too large and expensive, shelf life is an issue, so they generally use one or two brands of a particular supplier as a generic type splice kit.

There is also the issue of knowing the belt type before the service company goes to site, often if it is in a smaller plant, quarry or similar type facility the belt could have been purchased from one of several manufacturers and installed anytime over the last 10 years.

In this type scenario it’s very difficult to ascertain the brand, make and or type.

From experience these generic type kits will usually do the job, however the client and installer need to consider compatibility, warrantee issues and life expectancy of the join.

Some of the larger mines will stock the necessary kits for emergency situations, but once again shelf like comes into the mix and many are reluctant to throw away many thousands of dollars worth of splice kits, [ Steelcord kits ] when they are a couple of days, weeks or months out of date.

I’d hesitate to guess, but I’d say that the ratio of generic versus manufacturer’s kit being used would be many, many times higher.

Once again, I’d like to reiterate that the manufacturers splice kits should be used when ever possible. ■

I would agree with Mr. Baker generic splice kits are very common in the industry. I have also seen generic splice kits out perform factory kits in some instances(Rema Tip Top) Any testing that was done prior to field splicing was done in shop in a controlled environment, so would not be a perfect representation of field conditions. None the less I think it would be reasonable to assume the field results for kits that tested better (in shop conditions) would be at least on par with factory materials. I currently stock generic splice materials for my standard belting (mining and aggregate use) any specialty belting I have to splice that is supplied by the customer is spliced using proper splice materials supplied by the manufacturer.

Here is an excellent representation of generic versus manufacturer in splice materials. We installed and spliced a belt for a customer this past Saturday. The belt replaced was installed and spliced by us 3 months before. The previous belt was supplied by the customer and was purchased based on price only. A generic splice kit was used and was supplied by us and held together while the belting itself delaminated and lost cover rubber at an alarming rate. The new belt supplied by the customer for the change out came with a factory splice kit. The salesman recommended to the customer to use factory materials to ensure a long lasting durable splice. This time the customer made the right decision bought a quality belt with factory produced splice materials. In this situation even if the splice materials were not supplied by the customer we would have purchased them from the belt supplier to insure that the splice in this belt was the best it could be. I don't know what kind of liability others have around the world but, I do know that here in my area if a splice fails prematurely we are on the hook for the associated down time and loss of productivity incurred by the customer. Workmanship is also always a factor in any splice. Factory kits will never make up for poor workmanship or for those who cut corners by reducing splice lengths or shortening cure times by increasing cure temperature.

Best Regards

DW Davis ■