Department of Mining, Dressing and Transporting Machines AGH

Transkrypt

1 Conveyors Department of ining, Dressing and Transporting achines AGH Belt Conveyor Theory Piotr Kulinowski, Ph. D. Eng. Piotr Kasza, Ph. D. Eng. - piotr.kulinowski@agh.edu.pl ( B- ground-floor room 6 consultations: ondays Belt drives - history 1

2 Euler-Eytelwein formula n P n z P n max n z R max b a e P z Euler-Eytelwein e R a b z z (e a z 1) a P z,n R b R b a angle of wrap [rad] friction coefficient driving force[n] belt tension [N] driving torque [Nm] radius of pulley [m] P Ways to increase the maximum driving force P max z (e a 1) a ncreasing the angle of wrap z ncreasing and stabilizing tension force - take-up devices ncreasing and stabilizing the friction coefficient

3 Tandem drive n n a a P z P a P z,n R b angle of wrap [rad] friction coefficient driving force[n] belt tension [N] driving torque [Nm] radius of pulley [m] z n z necessary condition! Zasada sprzężenia ciernego napędu wielobębnowego a n n a P z P n z e a a z e z n n z e a e = e a z e n z e a a n a a 3

4 Zasada sprzężenia ciernego napędu wielobębnowego a n n a P z P n z e a a P P P P max z n z e z n a a 1 z n z tatic Characteristics of the Tensioning Device Belt sag min g mt mu 8 f u l g Drive - driving - braking N R b N e a a a e 1 H Rb 1H e 1 Rb H a e 1 N 1 1N H 1 1H α R b N H 4

5 tatic Characteristics of the Tensioning Device a A H Braking a e a R e 1 b H N R e b tarting N a 1 Z b tationary work top c mt mu 8 f u l g B C D` set of prohibited values of force Driving torque 0 Nmax inimum force value in the belt coming off the drive pulley Types of take-up devices used in belt conveyors Those with a fixed position of the tensioning pulley during conveyor operation so called fixed take-up device; Fixed take-up Those with a changing position of the tensioning pulley during conveyor operation oveable take-up: Gravity weight Hydraulic, pneumatic Regulated take-up winch Follow-up 5

6 Fixed Take-up Device with a constant position of the tensioning pulley during conveyor operation. With a tensioning pulley periodically moved during conveyor stoppage. Elastic elongations of a belt loaded with a longitudinal force cause a reduction of forces in the zone where the belt comes off the drive pulley. This necessitates causing much greater forces of preliminary belt tensioning. Permanent deformations of the belt are periodically compensated by moving the tensioning pulley during conveyor stoppages. required tensioning force force caused by the action of the tensioner 0 ust Nmax Fixed Take-up Device Rozruch Hamowanie N [kn] Nmax P [kn] 6

7 Gravity Weight n conditions of a variable load of output on the belt, weight (gravity) devices stabilise the belt tension forces within limits conditional on the efficiency of the tackle and rope system. n non-steady-state operation of the conveyor, tensioning force changes are observed due to inertia forces and longitudinal vibrations of the belt. 0 Nmax Gravity Weight [kn] 400 Rozruch Praca ustalona Hamowanie N t [s] [kn] Nmax P [kn] 7

8 Tensioning force [kn] easured tatic Characteristics of the Gravity Weight =0.3 = Driving force [kn] 15 Hydraulic or pneumatic take-up devices with a limited tensioning path Tensioning cart motion blocking Tensioners with linear cylinders may employ various solutions: the so-called constant tension ones are connected to a trunk line with a pressurised liquid or ones with their own drive and a controlled pressure range. The characteristic feature of this type of devices is that the length of the tensioning path is limited by the length of stroke of the cylinder piston; the speed of tensioning is also limited. 0 Nmax 8

9 Automatic take-up devices with a periodic operation Tensioners in which the tensioning cart is pulled by the rope from a winch driven by an electric motor. They are controlled by three-position controllers, sometimes with the ability to change the force adjustment range for the duration of the conveyor startup. 0 Nmax odel of follow-up, mechanical take-up devices 9

10 Follow-up, mechanical take-up devices i zl A B echanical tensioners receiving their power from the main drive of the conveyor. Two tried and tested solutions are worth mentioning here. The first has a tilting drive system suspended from the pulley shaft hanging from a system of ropes and tackle connecting it to the tensioning cart. The tensioning force of this device is the sum of a part of the weight of the driving system and the reaction to the driving torque. The second type of tensioners with a similar solution are those with two tensioning carts installed before and after the drive pulley in the main drive zone and connected with a rope system of a constant ratio ensuring that the friction contact between the drive pulley and the belt is correct. Tensioning cart A motion blocking 0 Nmax Follow-up Device i zl 0 Nmax 10

11 Follow-up Device Centering belt run - Causes of belt mistracking 11

12 Centering belt run v t Vt Belt speed Vk Circumferential idler speed Vp lip speed Belt v t v k F c v p F t F o Ft Friction force Fo Resistance of centering Fc Centering force Axis Bibliography Kulinowski, wykłady Transport przenośnikowy, 1