Experimental expression of the resistance of belt conveyor’s plough

The article deals with a theoretical expression of resistances that occur in pushing loose material off the conveyor belt surface with a single-sided plough. The working branch of a belt conveyor is designed in a flat, single-idler arrangement. Theoretical prerequisites and derivations are practically tested on a belt conveyor model in the laboratory of the Department of Research and Testing of the Institute of Transport at the Engineering Faculty of VSB-TU in Ostrava.


Introduction
Discharging of conveyed materials out of a belt conveyor may be performed using three basic methods: the conveyed material is most often discharged through the end drum of the belt conveyor ( Fig. 1,a) [4]; if discharging the material at a certain point of the conveyor track is required that may have any distance along the length of the track, ploughs (singlesided and double-sided) are used ( Fig. 1,b). For a continuous discharge of conveyed material along the entire length of the belt conveyor, tripper cars are used (Fig. 1,c). designed as removable. They are moved to their working positions manually, or by pneumatic or hydraulic linear motors.

Single-sided plough
We assume that on a conveyor belt an isolated grain is conveyed with its weight m [kg], of a nonspherical shape (the grain cannot rotate around its centre) and speed v [m.s -1 ], which is equal to the conveyor belt speed vp [m/s]. The peripheral force F [N] on the driving drum of the belt conveyor is given by the sum of partial resistances that may be defined, according to [5][6][7][8] (3).
After putting down the expressions from relations (4) and (5), we obtain: By adjusting the relation (7), we obtain: From the edge Lagrange's conditions the following results: for The gravity centre of the grain will run path l [m] for time t1 [s] assumption in time t = 0 [s]: 1 [kg] 3, 6 3,6 (v + v )

Description of the belt conveyor plough model
In the laboratory of the Department of Research and Testing of the Institute of Transport, a structural design and realization of a model of a single-sided plough of belt conveyor was made, see Fig. 7 according to the drawings necessary for the delivery of individual components of contacted companies. Acc. to [2], an EP 250/2 conveyor belt is chosen, width B = 500 mm, thickness of the upper cover layer s1 = 2 mm, thickness of the lower cover layer s2 = 1 mm, overall thickness of conveyor belt s = 5 mm, thickness of frame 3  Acc. to [1, page 16, Table 12] the smallest diameter of driving drum d = 200 mm is chosen (for the insert material it is polyester and a combination of E, EP, Evs, EvsPvs; for the thickness of frame s3 = 2 mm and for the use of permitted tension load ft = from 60% to 100%). Acc. to [1, page 16, Table 12] the smallest diameter of reversing drum d = 160 mm is selected (for the insert material it is polyester and combination of E, EP, Evs, EvsPvs; for thickness of frame s3 = 2 mm and for the use of permitted tension load ft = from 60% to 100%). The reversing drum and the driving electric drum, type EB 220 -510 x 0,4 -1,5 were purchased from Privat STS Pacov. The drums 220 mm in diameter are made of steel, they rotate in bearings pressed on shafts 40 mm in diameter. Based on drawings the carrying idlers of the conveyor belt (Fig. 8,a) were made by Tranza a.s. based in Břeclav; the dimensions comply with CSN 261102 in accordance with ISO 1537. The idlers of the manufacturer's type designation "smooth idler 63 x 500/6204, 3-20024-00030" are in diameter D = 63 mm, length L = 508 mm, length L2 = 576 mm. The idler jacket is made of a steel tube with the wall thickness of 2.5 mm, the idler is fitted with a two-level labyrinth seal with grease pre-chamber. The ends of idler axes were adjusted based on drawings to the shape acc. to Fig. 8,b.

Conclusion
On the belt conveyor model (Fig. 10), which is equipped with a single-sided plough, resistance was determined that occurs at pushing the loose material off the conveyor belt surface with a single-sided plough. These resistances were expressed for different tilt angles of plough  [deg], a different speed of the belt conveyor movement v [m.s -1 ] and for different conveyed materials. First, resistance against the movement K0 [N] of the conveyor belt was expressed, without the presence of conveyed loose material, then resistance against the movement K [N] of the conveyor belt filled with loose material, and finally resistance against the movement Ks [N] of the conveyor belt filled with loose material at discharging the material using the plough (as the function of the plough's tilt angle against the conveyor belt's longitudinal axis  [deg]).