1st February 2003, 7:38
Equal Tension In Steel Cords
We all know that two essential pre-requisites of manufacturing steel cord belts are -
1. The cords should be in the same horizontal plane (with an allowance as permitted by DIN 22131 etc.), and
2. Equal tension must be applied while positioning the cords during the belt manufacturing procedure.
In case the above are not properly implemented, one obvious manifestation would be improper belt tracking.
What other manifestations can be expected ? Is it even likely that the resultant stress vector could be so skewed (with reference to the conveyor system & pulleys) that the corresponding torque would even create cracks in the pulley hubs ? Or perhaps bend / weaken the mechanical structures ?
Has any such incidence been observed anywhere in the world ?
I would appreciate some feedback here.
Thanks in anticipation.
4th February 2003, 17:46
Steel Cord Alignment
The following are affected:
1. Pulley lagging: irregular wear occurs due to vertical misplacement and the added shears stresses
2. Splice loads become irregular reducing the slice dynamic efficiency
3. Belt flap or excessive edge vibration
4. Drive load sharing due to the changing of the spin radius
Dont forget that horizontal misplacement has negative effects on belt performance as well.
I see yor many questions. Are you writing a book?
Conveyor Dynamics, Inc.
20th February 2003, 14:13
Technical Advisor Consultant
Anomalies in steel cord belts.
Referring to the topic of anomalies in steel cord belt, and consequent problems, I would like to inform as below :
Firstly, the belt should be manufactured strictly in accordance with the international reputed standard. All precautions should be taken to ensure that the belt has been really confirming to the said standard.
Belt conveyor operational behaviour would be the final indicator of the anomalies in manufacture of steel cord belt. If all other items are checked and aligned (i.e. pulleys, idlers, structures, take-up etc) and after that see for following situations :
- If belt has marginal misalignment at some spots and if these are travelling; but belt can be operated for commercial need. Then the anomalies may be said as minor and may be tolerated or rejected.
- The kind of problems you are referring i.e. failure of pulley, supporting frame etc if are happening due to serious anomalies in belt, then I think the belt would be running in unacceptable manner i.e. conveyor becomes unoperational. If it is so, then belt has serious faults.
- The pulley failure and structure failure but belt / conveyor runs properly, will imply that the belt is proper but other items need check.
- If you can narrate specific information / problem, then answer would be more useful because certain application data are often subjective within frame of observation data / conditions.
Ishwar G Mulani
Author of Book : Engineering Science and Application Design for Belt Conveyors.
Email : firstname.lastname@example.org
20th February 2003, 21:46
The standards you speak of regarding belt tracking are quite antiquated. Two examples:
1. CEMA, ISO, DIN issue belt edge clearance to allow for tracking errors at the loading point to be: edge clear = .055*W + 23 mm
where W = belt width in mm.
Thus, an 1800mm belt edge clearance is recommended = 122 mm.
This is a lot of belt to give up and it says nothing about what the contributors are such as:
a) belt manufacturer's construction tensile member align. errors
b) installation alignment errors - idlers, structure, settlement, etc.
c) off- center material loading
d) lump size containment against spillage
e) slippage containment up or down steep slopes vs angle
f) blocky vs round material and moisture content
g) horizontal curve rilling, and centripedal action - spillage control
h) windage, moisture, pulley buildup, ............
g) splice construction errors, .........................
2. What is a reasonable tracking error based on construction tolerances? We specify to the belt manufacturers that the belt center shall track within 25-40 mm measured from a selected low tension position for the complete belt loop, respective of narrow to wide belts. The words are a little different, in the spec., but the meaning is clear. This requires a valid field measurement is conducted where both belt edges are simutaneously measured. Manufacturers can meet this specification. Proper steel cord placement is manditory. Most manufacturers do not control the intercable tension, vertical and horizontal position to a sufficient accuracy to obtain this performance. The tolerances setforth in DIN et al guidelines do not control the position or tension variances to insure such tracking as witnessed by the above allowance. The equipment is capable of far better as has been proven.
I am sure others can add to this list.
Conveyor Dynamics, Inc.
21st February 2003, 4:00
Equal Cord Tension
Dear Mr. Nordell,
You have mentioned that most manufacturers do NOT provide equal cord tension or (if I understood you correctly) even uniplanar location for the cords.
Is this observation of yours based on experience of abnormalities in belt performance or actual knowledge of manufacturing hardware available with various manufacturers ?
21st February 2003, 4:18
Both. We evaluate postion of cords, post manufacturing and have first hand knowledge of the position control and tension monitoring.
We work on belts at the limit of steel cord technology - +ST-7000, long overlands +15 km, highest power +10,000 kw/ flight, and beyond.
The high price spreads and their owners are interested in risk control. We have built the strongest splice dynamic test machine, and continue research into the next generation conveyor systems.
Conveyor Dynamics, Inc.
21st February 2003, 14:34
Clarification to the above
All steel cord manufacturers do have hydraulic tension control and cord position combs. DIN and other standards specifiy the tolerances for horizontal and vertical cord placement. Our assessment and belt specifications require better tolerances for higher valued conveyors that some manufacturers can meet.
Press cord tension control, for most steel cord belt suppliers, is not of sufficient accuracy for these belts. We require specific tolerances to assure straight running belts, high dynamic splice strength, low belt edge vibration, and proper conformance to high tension pulleys.
Measured errors in belt tracking show obvious defects in shop labor and press tolerance limitations. In addition to tracking errors, field observation of belt edge vibration behavior and pulley lagging wear hint at defects in belt construction or poor tolerances.
Edge vibration is also a product of idler spacing, idler roll shape and dimensions, belt natural frequency modal properties, variations in belt tension, idler frame compliance and vibration coupling between belt, roll spin frequency and frame vibration modal frequency.
Proper mapping of vibration zones and timing can be very revealing.
Conveyor Dynamics, Inc.
21st February 2003, 14:45
Another note on the above:
Observe the position of the cables from a quality control cross sectional cut of belt roll ends. Look at the outer cable placements verses the interior cables. Often you can find significant anomolies that exceed even DIN tolerances. It is also a matter of Standards interpretation. These outer cables, for some manufacturers, are notoriously out of proper position. What does this mean to belt performance? What premium should you pay for proper position? What does this say about the press design, quality control and/or manufacturing techniques?
Cable manufacturing errors can also be significant.
Some manufacturers do invest in providing a superior product. Who are they?
21st February 2003, 15:05
Sorry for not gathering all thought into one note:
Clients are interested in performance for dollars spent. Designers endeavor to lower the belt safety factor (SF or FOS) to gain economy or to make a project viable. As we design for the limits of our knowledge, we encounter risks. Some of these risks can be controlled such as the proper or "best practice" in belt construction.
How does the industry/industrial standards determine fit for purpose at the leading edge? It is not clear. Request an audience from the leading belt suppliers and learn what is not in the Standards and why a higher standard is applied.
The Standards barely address dynamic stength properties and resort to static pull-out tests. This test has some quality control usefulness. It does not signify the benefits of superior dynamic properties and its influence meeting lower safety factors.
What about low rolling resistance rubber compounds and their benefits to the environment? Where are the voices of the world standards?
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