Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Dear Mr. Barry Chung,
It is advisable to use belt splicing and joining method as suggested by the belt manufacturers, because the same have been arrived after appropriate testing and long time experience by belt manufacturers and users. This has also bearing on contractual matter. The use of unsubstantiated method in running system is risky.
For conventional multi-ply belts, if you try to join all the plies by overlapping the faces, you will be creating uneven surface of belt which is harmful to belt and also to idlers, cleaners and pulleys. Therefore, to keep reasonable even surface of belt, the step joints are less by one number compared to number of plies.
In case of special two ply belt with thick inter-ply rubber, the condition is different, and its splicing method is also different. Please refer to the belt manufacturers or their literature / catalogue for specific information in such matter.
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 ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Originally posted by I G Mulani
[B]Dear Mr. Barry Chung,
It is advisable to use belt splicing and joining method as suggested by the belt manufacturers, because the same have been arrived after appropriate testing and long time experience by belt manufacturers and users. This has also bearing on contractual matter. The use of unsubstantiated method in running system is risky.
I agree.
From past experiences, the recommended Splicing Type and Specs from the Belt Manufacturerare the best to stick with.
Depending on the Manufacturing Brand of the belt you are using, it should be spliced to that.
The DIN (International) standard for EP500/3 is 200mm Step lengths with 1/3 Bias.
Generally Manufacturers Splicing Standards are the same as this, increasiong the Splice Step length or adding steps should not give any extended life to a splice as these variables have been assessed when manufacturing the belt and testing.
corey.... ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Dear Gentlemen,
Thank you for your replies.
But wouldn't it be, by conventional wisdom, that an extra ply of fabric would add strength to the joint? Or, as the resulting joint is thicker, is this benefit negated by higher shear stresses and displacement between the plies as the joint moves through the pulleys leading to higher fatigue and perhaps premature delaminating of the joint? Would appreciate if you can confirm this.
Also, can anyone comment on the flow and curing of the tie and stock rubbers during vulcanization when attempting to do a thicker joint as mentioned?
Best regards.
Barry Chung ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Not sure about what problems you would create by splicing with extra steps/plies, but it would most asured lead to a higher abrasion to the splice area as it passes belt cleaners, being thicker than than the aparent belt.
As with Curing the splice, say for example 'M' Grade (NATURAL)Fabric/Rubber belting we cure it at 145 Degrees Celcius for a Time of 3Minutes for every Millimeter of Belt Thickness.
So it would be timed by the thickness of the thicker spliced area.
As previously mentioned though, i would NOT recommend any variation to the Manufacturers Splicing Specs, unless you contact them directly to get any answers.
Why is it necessary to want a Stronger/Thicker splice, are you having Failures?
What application are you looking at?
corey.... ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Dear Corey,
Yes, that is also my understanding of how a hot splice is normally done.
My questions are in response to a couple of recent joint failures experienced by one of our clients. When I examined the original failed joint (prior to ones above), I discovered the following.
1. Torn carcass just outside the joint area up to 180mm deep measured from the belt edge. I was told the damage was about a year old was probably caused by mechanical contact. No reinforcement fabric was visible and the edge was repaired by simply closing up using a cover strip.
2. Half of the joint (on side transversely across from 1 above) had delaminated while the remaining half suffered catastrophic fabric failure.
3. The conveyor is possibly loaded up to 40% above its design capacity based on the observed discharge rate of the wagon cars.
4. Examination of the subsequent failed joints showed the fabric at about the same transverse location as the latter half of (2) had sheared.
5. I concluded that the subsequent failures were due to a longitudinal stretch of carcass that had become weakened or damaged just prior to the catastrophic failure of the original joint. I imagined, at the time of failure, that the belt would quite probably have cupped both upstream and downstream of the joint due to the uneven distribution of stresses brought about by the delaminating of half the joint area described in (2).
While such analysis is possible posthumous, it would understandably be difficult to call simply by visually inspecting the remaining belt at site. Therefore, short of making a recommendation for a belt change and so that one remains on the safe side, would a 3-stepped joint be justified under these dodgy circumstances?
Best regards.
Barry ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Hello Mr. Barry Chung,
As informed earlier the thicker joint will create problem with respect to idlers, cleaners and also at pulleys. Every time the joint passes over the idler it will create jerky forces on belt and also on idlers. This will be occurring at very high frequency. For example, belt running at 3 mps and having idler spacing at 1 m, will result in to jerky forces three times in a second!
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 ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
I am not sure the Width of the belt in question BUT, a 180mm fracture in the belt Across from the Edge is a SIGNIFICANT damage, and in my opinion requires MORE than a mere Converstrip Solution.
As a yard stick we use the '>1/3 BELT WIDTH' rule where damages are to be Spliced out, classed as beyond a satisfactory repair condition.
If there was a 180mm rip in close proximity to a splice, and there is a noticeable opening of the rip due to tensions lost, then there would would be increased tensions placed onto the opposite edge, therefore if on a splice, increasing the shear tensions on that side of the belt/splice area, ultimately causing a splice failure.
Without literally seeing the conveyor system, and if the splices are simply pulling apart due to longitudinal tensions placed on them by the increase in production tonnage, then although stepping outside of the Manufacturers recommendations (which has obviously been done to the conveyor system design capacity), i would rather increase the step lengths than try to add strength to the splice by adding a ply to it.
Conveyor Design Capacities are there for a simple reason, and most industries simply increase the loads on their conveyor systems to increase production, BUT for the GAIN in production there is a LOSS in the belt Integrity, with the ONLY longterm solution being to upgrade the Conveyor Belt Specs to suit.
Sometimes the Expensive (belt change-out) solution is ultimately the ONLY solution due to these increases in tonnages, and a mere band-aid approach may seem to be cost saving, but it generally just prolongs the inevitable.
corey.... ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Dear Gentlemen,
Thanks for concurring with my findings on the failures. The belt width is actually 900mm. My calculations showed that the maximum running tension under the overloaded condition was at exactly 100% rating of belt and used exactly 100% of the trough area. Coincidence? Maybe not. I suspect the designers had known in advance that the belt was going to be operated at those levels but maybe underbelted to save on cost. To make matters worse, the designers actually reduced the takeup weight by 40% to keep the running tension within the rating of the belt. Smart huh! As a result, the inclined conveyor suffers frequent spillage and mistracking especially at the tail end as evidenced by the severe ply separation and edge damage observed along the entire length of one side of the belt.
I doubt increasing the splice length on the 2-stepped pattern would have help because of the dodgy integrity of that suspect longitudinal section I mentioned. Also, as Mr. Mulani has advised against doing the 3-step pattern in view of the attendant problems on the idlers, pulleys and cleaners, I think I would be compelled to advise this client to use fasteners as a temporary measure until they can decide on the change-out.
I would still welcome more opinions, apart from the ones already expressed, especially on the differences in the dynamic stresses between the 2-step and the overlapping pattern (despite the 3-step being a non-starter.)
Best regards.
Barry Chung ■
Re: 2 Step Vs 3 Step Splice For 3-Ply Belt
Dear Mr. Barry Chung,
You have made sincere efforts to know the reasons and solve the problem. If you intend to use fasteners instead of vulcanized joint, please check whether a fastener joint will have a matching strength. Also, if your observation indicates that the belt (and thereby joint) are not of adequate strength, you can consider changing the belt with higher strength. For example, if you maintain the same number of ply and adopt for higher rating (say 630 / 3) then, mostly there may not be change in pulley diameter and consequent changes at many places.
Also, nylon-nylon belt of the same rating compared to EP belt, needs smaller size pulley. That is, higher strength nylon-nylon belt may not need bigger pulleys. Of course this will entail advantages / disadvantages of nylon-nylon belt compares to EP belt. Higher strength belt will also have more capability to withstand impact. So, if you are problem is being created by inadequate impact strength, the proposed change could reduce the difficulty.
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 ■
2 Step vs 3 Step Splice for 3-Ply Belt
Gentlemen,
I have some questions concerning the hot splicing of an EP500/3-ply x 900mm BW x 3+1.5mm (NR covers) belt.
Can anyone enlighten as to whether a 3-stepped (overlapping)splice is stronger and more reliable than a 2-stepped one, assuming the bias and the total splice length remained the same. If not, would increasing the length of the 3-stepped splice improve its strength and reliability? And would the same conditions apply to cold splicing?
While I noticed most manufacturers usually recommend the n-1 pattern for their belts having 3 plies or more, what circumstances would compel one to perform a n-stepped splice instead?
Also, as the overlapped splice is thicker, would the joint be affected in any way by the cleaners?
Best regards.
Barry Chung ■