Influence of rubber fabric reinforced belt operational wear on change of belt’s percussive modulus of elasticity

Aleksander Lutyński, Stefan Gąsior

Belt conveyor is basic carrying device for underground coal mines. Flexible rubber belt is the most important and very expensive element of this device. Percussive modulus of elasticity belongs to the group of the most important features of the belt. This parameter defines the maximal dynamic tension at start up. It is used to define a dynamic occurrences, particularly to determine parameters of tension waves moving along the conveyor at starting.
Industrial investigations were conducted in the largest European under- ground coal mine „Piast” located the city Bieruń, Poland. Tests have been performed since 2002 to 2005. Percussive modulus of elasticity was calculated according to technical references taking into account speed of the tension wave, belt acceleration at start-up, geometric and mass parameters of belt conveyor. Operational wear of belt was determined by three parameters: number of the belt rotation around the conveyor, mass of transported material, and ratio of this two parameters.
Results of the calculations were statistically analyzed and the importance of the abovementioned parameters is significant. Dependences between the parameters were approximated using parabolic trend lines which were the most suitable according to the results. High coefficients of determination suggest reliability of results. It is claimed that the effects of belt operation are: significant increase in speed of tension wave as well as significant increase of percussive modulus of elasticity. Increase of 24,22% in percussive modulus of elasticity has been observed in four layer rubber-fabric belt as compared to a factory new belt. Its maximal value was at the ¾ of projected operational life-time of a belt.
Knowledge of dynamic effects at conveyor start-up lets to determine: tensions amplitude, belt speed straining, proper selection of drive start-up units, particularly time of increasing rotate modulus and sequence of turning on the driving motors in several drives. Percussive modulus of elasticy usually is not given by manufacturers. Published value is typical for a new belt and it evolves during operation. The results of this industrial investigations show this changes, and let the belt conveyor designers to forecast a dynamic conveyor behaviours.