Calculated Forces during Cross-Cutting of Rafting Bundles in Coastal Warehouse Conditions

Abstract

For long distances of round timber delivery, transport in rafts is often the only economically viable option. The bank bundling of logs predominates. To increase their strength and solid-volume ratio, which implies a reduction in towing costs, cross-cutting of the bundles is provided. The formulas obtained earlier for determining the cutting force do not include the bundle shape coefficient – the main criterion by which the resistance to the longitudinal movement of timber is evaluated during timber rafting. The additional pressure in the bundle due to the presence of strapping has not been taken into account, or has had no direct relationship with the shape factor. The aim of this research has been to derive formulas for calculating the force of cross-cutting of bundles at coastal warehouses, taking into account the presence of strapping and the shape factor, as well as to establish the nature and degree of influence of the factors determining it. The research method has been theoretical, based on the principles of theories of flexible threads and granular media. A formula for calculating the force in question has been obtained analytically. Its use in practical calculations is problematic due to the need for multiple calculations of integrals. The formula components that require the calculation of integrals have been replaced by the K parameter – the parameter of resistance to cross-cutting. Its value, corresponding to the cross-sectional area of the bundle equal to one, has been designated k – the specific parameter of resistance to cross-cutting. It has been established that this indicator depends on the shape factor of the bundle and the ratio of its height to the average diameter of the log. By varying these factors in the ranges of 1.5–2.5 and 4–20, respectively, k calculations have been performed using the specified integrals. Approximating dependencies have been obtained for determining the k parameter based on the ratio of the bundle height to the average diameter of the log, and graphs have been constructed that make it possible to determine the cutting force in practical calculations without resorting to integration. It has been found that changing the ratio of the bundle height to the average diameter of the log from 4 to 20 causes an approximately 5-fold increase in the cutting force, the relationship is linear. A decrease in the shape factor from 2.5 to 1.5 leads to an increase in this force by almost 2 times. Its dependence on the density of timber, the solidvolume ratio, the size of the bundle and the coefficient of sliding friction is direct and linear. Of these factors, the most significant is the friction coefficient, the variation of which can lead to a change in the output value by more than 2 times. Its dependence on the angle of internal friction is inverse and insignificant.

Keywords

• timber rafting
• raft
• coastal warehouse
• cross-cutting of bundles
• cutting force