Downhill - How Much, And Where To
Dear Mr. mikesch,
the choice of the tension member of a conveyor belt is not dependand on purely a verbal parameter like "downhill" or "uphill". The more, as "downhill" is not a straight technical term and could mean anything between 0,1 % and 10° or more. Even from your own description / story of the failed belt it seems not conclusive, as that belt was off the limits, and imo in no way the procedure could be named "engineered", if that calculation was based on the BELIEF to have a nominal strength of 1000 N/mm. And not having a proof / analysis / certificate of the actual nominal strength. I for my part could not conclude from the failure story to that current project / calculation problem.
Perhaps you could seek in-depth professional guidance with design calculation + safe project procedures.
But as there're some very eminent professional members in this forum, perhaps someone else could still offer some short way guidance or help on the numbers.
Regards
R. ■
Re: Downhill Conveyors With Steel Cord Belts?
You need to consider and calculate the belt tensions under all conditions of Start-up, Running and Braking.
If there is a ply belt that will withstand the tensions that will be applied to it then there is no reason not to use it. They are less expensive and easier to maintain.
If you do end up using steel cord be absolutely sure there are no pulleys in the system with a center crown or you will soon be seeing faiures of the steel cords.
You may also want to take a close look to see how fast the brake is being applied. Braking a system too quickly will have the same affect on the sytem as starting a conveyor across the line with no hydraulic coupling. Both of which can be very damaging to the system. ■
Gary Blenkhorn
President - Bulk Handlng Technology Inc.
Email: garyblenkhorn@gmail.com
Linkedin Profile: http://www.linkedin.com/in/gary-blenkhorn-6286954b
Offering Conveyor Design Services, Conveyor Transfer Design Services and SolidWorks Design Services for equipment layouts.
Rock And Reel.
Alas. It sounds like you were conveying down from the old Parker plant and for that you would need a concave curve (?) to provide headroom to the Turkish/Welsh set up.
As Roland intimates, your belt appears suspect and you have also mentioned that the customer is not happy when it comes to vulcanising and maybe splicing.
By the way Roland Heilmann is a very eminent professional in his own right. ■
Thanks For Support
Dear All,
thanks for your support.
Regards
Mikesch ■
Downhill Belts And Brakes
Calculating the brake torque from rigid-body dynamics, will result in a poor estimate of the brake torque and belt tension. Usually, caliper disk brakes will generate their greatest brake torque on initiation of the stopping cycle.
You can get a glimmer of the potential braking torque by recording the stopping cycle to see the rate of stopping and convert that into a belt line force. This may get you with 25% if you are lucking and the downhill slope is small, like your 11% slope.
The degree of braking also depends if the brake design has a constant torque type (fail-safe to a fixed spring) without benefit of a proportional control.
There are many variants of brake designs and brake controllers and brake logic.
It seems like you have already made the greatest discovery in discarding a bad belt supplier. ■
Stocking(S)
On re-reading, it would however be interesting to request a more detailed information about that damaged belt, Mr. Mikesch. Could you pls. check whether in your storage control system there's a reliable document as to the belts quality? A delivery note, perhaps a certificate? What was the storing condition, and then for how long? Did you apply new splice kits, or did you use the stored ones? What was their condition, their best-before date in relation to their application?
Imo questions of interest, so it would be very kind to take on the labour and give back some in-depth info.
Thank you in advance!
R. ■
Stocking(S)
Dear Roland,
Unfortunately I don't know from where our customer get this poor quality belt.
And I don't know also how long this belt was stored.
The damaging of the belt was by the way not happens in the splicing area.
Belt rating was specified as EP 1000/5.
Observed was in laboratory test a rating of 350/5 only.
Regards
Mikesch ■
Downhill And Steel Cord Belting
We have designed hundreds of downhill conveyors. Very few use fabric belt. When the fabric strength is greater than ST-1000 N/mm I would strongly suggest not to use fabric. ST-2000 N/mm fabric, even at SF=10:1, is a bad selection, except in a few cases.
First, the number of plies will likely preclude using an overlap splice that can be claimed by knowledgable folks, to be less that reliable verses a steel cord of SF=6:1 or 5:1. While the steel cord maximum rubber stress between cables is near the belt tensions neutral axis, the fabric is at the splices bending extreme surfaces. This coupled with any build-up exacerbates the reliability problem and does the pulley geometric defects and tolerances. I would give a steel cord probability of success vs. a fabric where the tension levels are at their relative limits ( 5 vs. 10 :1 steel vs. fabric), to be much higher maybe close to double the safe operating conditions with all the "what if" factors.
Fabrics are used where steel cord spark that may ignite a gaseous environment or where finger splicing can be applied with mechanical fasteners. Clackity, clackity, ...
Fabric belts are useful when heavy impact shock must be tolerated, or unusual build-up on pulleys is a norm. For these cases, fabric is the choice, but, not for high tensile strength.
The user must have knowledge of good splice contractors for either construction. All large downhill conveyors, where thousands of kilowatts are required use steel cord belt. No exceptions.
No fabric will come close to the reliable strength of a well designed steel cord belt. ■
Downhill Conveyors with Steel Cord Belts?
Downhill Conveyors with steel cord belts only?
Dear All,
We had a problem with a belt failure on a downhill conveyor.
Not a long one. 290 meters in length with a height difference of -32.5 meters.
The customer said if it's possible to use a stock belt EP 1000/5 - 12 + 5 it would be great.
I did calculate a safety factor of 18.73 during steady run and 11.79 when the disc brake is active on power cut.
The belt was broken when the disc brake stops the conveyor.
Then somebody told me, that in downhill applications is a general use of steel cord belts required.
After we made a test of the belt we found out, that the quality of it was less than EP 400.
It was even not possible for the testing labor to specify the ecaxt belt description.
Now I'm on the design of some other downhill conveyors and I have it in my mind what somebody told me about the general use of steel cord conveyors in this kind of application.
But our customer is not familiar with vulcanizing steel cord belts and he prefer EP belts only.
On my actual conveyor I calculate an EP 2000/5 with a safety factor of 10.94 during steady run and 8.43 when disc brake will stop the conveyor.
It's an 730m conveyor with a height difference of -59.8 meters.
Do somebody knows about this general use of steel cord belts in downhill applications?
It would be very helpful.
Regards
Mikesch ■