Cost-efficient and Application-oriented Design of Steel Cord Conveyor Belts for the Mining Industry
Conveyor belts in the mining industry are facing ever higher demands as regards conveying capacity, conveyor length, service life and energy efficiency. In addition to designs according to various general standards manufacturers further develop their products for better economy.
Dr. Andrey Minkin
(ed. WoMaMarcel - 23/4/2015)
DIN 22101 version 2011
According to DIN 22101 version 2011 (DIN 22101: 2011-12), the minimum nominal breaking strength kN,min of a belt is calculated according to Eq. (5):
cK is a coefficient for determining the minimum dynamic splice efficiency of a conveyor belt corresponding to the belt tension in the belt edge relative to the belt width. For steel cord conveyor belts, cK = 1.25 is for trough transition zones and cK = 1 for transition curves.
kK,max is the maximum belt tension in the belt edge relative to the width of the belt, which is generally 1 to 1.2 times the mean belt tension.
The safety factor S0 is a function of the features of splice manufacturing (competence of the splicers, quality of the splicing material, ambient temperature and conditions, etc.) whereas the safety factor S1 is a function of the features of operating conditions (chemical/physical stress, rotational frequency, expected service life, starting/stopping cycles, etc.)
The safety factors are selected within the range of S0 = 1 ... 1.2 and S1 = 1.5 ... 1.9.
kt,rel designates dynamic splice efficiency of the belt splice, which according to DIN for steel cord conveyor belts should be at least 45%. For all Contitech “Stahlcord” steel cord conveyor belts, the relative reference fatigue strength of the belt splice is at least 50%!
Therefore, according to Eq. (5) for our numerical example (steel cord conveyor belt with B = 2100 mm belt width and maximum belt tension in normal operation Tmax = 1000 kN resulting in the belt tension in the edge kK,max ≈ 1.1 ∙ 476 N/mm = 524 N/mm), the following minimum nominal breaking strength kN,min of a steel cord conveyor belt results
For this numerical example, a standard steel cord conveyor belt St2500 is selected.
In this example, according to a new standard a significantly lower required belt nominal breaking strength results. This results in enormous cost savings for a belt which, depending on the cover ratio, can be around a third. Moreover, an St3500 requires a three-step splice, which is more complicated and takes more time to produce than a two-step splice of an St2500.
Transverse Reinforcement on the Impact Strength of a “Stahlcord Barrier” type Belt
A transverse reinforcement (of whatever kind) is generally incorporated in the top (carry side) cover of a steel cord conveyor belt in order to prevent impact breaks and the associated belt rips in the longitudinal direction and to protect the belt carcass (steel cord). Often these are belts used in heavy mining machinery or in short- and middle-distance belt conveyors in surface mining areas close to heavy mining machinery that are very heavily stressed by coarse and sharp-edged bulk material (Fig. 6).