Required data MUST for belt selection MUST for determination and calculation MUST for special applications Total load Chemical influences Max. / min. temperature Type of goods Belt width AccelerationAccumulation Diverting Adhesive or non-adhesive conveying side Special requirements: FDA; USDA; EU Flame-retardant Low noise, etc. Conveying length Material of slider bed Slider bed or carrying rollers ? ProfilesPerforation etc. Height of inclination Spec. operation conditions Arc of contact on driving pulley Smallest pulley diameter Antistatic requirements Driving pulley steel or with friction cover Special requirements ? Curved application Knife edge (edge radius) Reverse operation Head / tail / center drive
Procedure by stages 1. Selection of the optimal belt type: material properties structure 2. Determination of the required belt tensile class 3. Exact calculation of peripheral force, belt tensile force, initial tension, shaft load, required motor power etc.
Conveying sidematerial PVC, TPU, PUR, NBR, EPDM, SI, etc. “properties Hard, non-adhesive, adhesive, soft “structure Smooth, mat (rough), impregnated Textile, waffle, grooves Non-woven (fleece) Running side Fabric, impregnated, covered, low noise Special characteristics Non-antistatic / antistatic / conductive Suitable for smallest pulley diameter / knife edge FDA / USDA / EU conformable Temperature or chemical resistance Suitable for power turns, metal detectors Flame-retardant 1. Selection of the optimal belt type
2a. Determination of the belt tensile class With the given data Total load (mass of carried goods on total conveying length) m [kg] Belt width b0 [mm] Coeff. of slider friction mG [-] (for slider bed) Conveying length lT [mm] (for carrying rollers) Ratio of inclination hT/lT [-] Arc of contact b [°] Driving pulley steel or lagged the required belt tensile class can be determined
In most cases 3 values are sufficient for a conveyor belt determination 1. Belt type (Material, surface structure, tensile class) 2. Belt width bo (given through application) 3. Belt length lg (given by installation design) Conveyor belts are normally tensioned according to the actual application (load, operation conditions etc. ) The recommended minimal initial tension has to be observed: PES-fabric belts emin = 0.3 % PA-fabric belts emin = 0.5 %
3. Exact calculation In cases where data like the following are required an exact calculation has to be done: Exact initial tension eo Shaft load FW on driving pulley and rollers Required motor power Pulley deflection Minimal diameter and wall thickness of pulleys First of all the peripheral force FU has to be determined.
Peripheral force Peripheral force FU with slider bed m Total mass of carried goods [kg]mB Mass of the belt carried over the slider bed m = lT · bo · m"B [kg]G Dynamic coefficient of friction between belt and slider bed [-]
Slider bed material Stainless steel Pickled steel Duroplastic Hard wood Approx. value G * 0.15 0.20 0.25 0.30 Coefficient of friction G* * For belt running side of fabric and fabric impregnated
Equation of Eytelwein FU = F1 - F2 Forces on the driving pulley F1 Tensile force in the tight side [N] F2 Tensile force in the slack side [N]A Coefficient of static friction between belt and pulley [-]b Arc of contact on driving pulley [rad]e 2.718; Euler's constant, basis of natural logarithms [-]
Place of the driving pulley Depending on the place of the driving pulley, the initial tension eoand the shaft load FWare different: Head drive Tail drive Centre drive
Initial tension Shaft load on driving pulley FWA = F1 + F2 [N] Shaft load on tail roller FWU = 2 · F2 [N] Head drive Note: With reverse operation, the formulas are different
Initial tension Shaft load on driving pulley FWA = F1 + F2 [N] Shaft load on head roller FWU = 2 · F1 [N] Highest possible shaft load! Tail drive
Initial tension Shaft load on head roller FWH = 2 · F1 [N] on driving pulley FWA = F1 + F2 [N] on tail roller FWU = 2 · F2 [N] Highest possible shaft load! Center drive