Greetings,

It is the maximum stress that the belt can withstand. ■

Lyle's right but more specifically it is pretty fundamental to modern conveyor system design. For instance a low modulus belt will stretch a lot more. This means longer take ups, during the start the belt will dynamically stretch and in longer conveyors this complicates your start up procedures but conversely the lower the modulus usually means that the belt will withstand impact loading better. Low modulus belts are invariably of fabric construction. Low modulus belts also allow you to design tighter curves and use smaller pulleys. How you make a selection then becomes a matter of balance for the designer. Most design software will take this into consideration and by doing a number of iterations you can work through the design impact if the belt modulus changes.

Cheers

Colin Benjamin

Gulf Conveyor Systems P/L ■

Dear Shri Ganesh,

Belt modulus is the modulus of elasticity for belt, and its purpose is the same as modulus of elasticity for other materials.

For materials, it is E = (Stress) / (Strain). This mathematically translates into required stress to create extension of length equal to original length i.e. strain = 1 which is called unit strain. In actual testing, only readings in relation to load conditions are used and nobody creates length extension equal to original length.

In case of belt, it is convenient to define belt modulus of elasticity Eb in slightly different form, for the same purpose.

For belt, Eb = (F x L) / (B x dL)

This mathematically translates in to required force (tension) for unit width of belt, to create belt extension equal to original length.

In above formula, F is force, L is test piece belt length, B is test piece belt width and dL is extension in belt length attributed to force F. When dL = L, then Eb is equal to applied force (tension) per unit width of belt.

In actual testing, the test results are in context of operating loads and nobody creates extension equal to original length (the belt will break before reaching that situation).

Eb numerical value is same in kN/m = N/mm = practically kgf/cm.

Belt modulus of elasticity is required for sophisticated designs of belt conveyors. The specific values are to be obtained from manufacturers, in accordance with the specific construction for each rating. However for widely used regular NN, EP and St belts; Eb preliminary values are as below :

For NN belts Eb = 6 x (belt breaking strength), fairly approximate.

For EP belts Eb = 15 x (belt breaking strength), approximate.

For St belts Eb = 40 x (belt breaking strength), tentative.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: parimul@pn2.vsnl.net.in ■

This is an old thread that was only now brought to my attention.

Vertical radius of curvature constraints, which are governed by the troughed geometry and the belt (elastic) modulus value, are at the heart of our DSI Sandwich Belt high angle conveyor technology. The curves are deliberate in our case not incidental as with conventional conveyors. I have found that belt modulus is generally not well understood even with many belting experts. As a result our customers have to often gotten bad advice (from their belt suppliers) on replacement belts.

Colin, you are correct that the modulus effects curves, transitions and pulley diameters but the first two are effected directly by the longitudinal modulus while the last also is effected by the distance between plies, and it is empirical actually tolerating some carcass crimping.

Dr. Mulani, thank you for your summary that generally relates the modulus to the breaking strength for the different carcass types. Unfortunately in North America it tends to be expressed as a function of the tension rating (which is the case in the CEMA book) which is an ambiguous number depending on the chosen safety factor. I do note that we are able to get Bm values of about 78% of your tabulated for nylon warp belts.

Joe Dos Santos ■