The Physics of Chip Arch Formation and Breaking-Down

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UDС

676.012.1-50

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Abstract

Pulp chip is considered in the article as a coherent mobile unit of macroparticles. To analyze the properties of pulp chips we used a model of effective continuum. We show that the main equation defining the behaviour of chips is the rheological one. Using this equation, we demonstrate that along the perimeter of the bunker case towards its vertical axis, there concentrically are formed elastic, limit state, creep, abnormal friction and Coulomb friction areas. Long term storage of chips in the bunker makes the wall areas (elasticity and creep) increase and the central areas (abnormal friction and Coulomb friction) reduce. In the bunker's conic part at discharge, the chip flow becomes narrower and the radial pressure increases significantly, leading to formation of dynamically unstable arches. We studied the changing density of chips in a prototypical bunker depending on the storage time, height of the chip column and moisture content. Based on the data obtained, we modified Janssen's equation to calculate the pressure on the bottom and walls of the bunker. Jansen's equation gives too low pressures as it does not take into account the influence of time on chip density. The axial and radial pressures on the walls and bottom of the bunker calculated by the modified equation are confirmed by experimental measurements. Bunkers must be designed with a smaller tilt angle between the bunker's conic bottom and the vertical or the devices preventing the formation of arches. Prediction of formation and development of the various regions of chip dynamical states in the bunker makes it possible to design a device preventing the chip arches from forming. Using 15 m high bunkers will not result in more frequent formation of arches, but will increase the accumulating capacity of the enterprise.

Authors

V.P. Sivakov – Professor, Doctor of Engineering; М.Yu. Golynsky – Candidate of Engineering

Affiliation

The Ural State Forest Engineering University

Keywords

bunker, chips, arching.

References

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