Improvement of the working equipment design of single-bucket excavators for the excavation of dense and frozen soils

Abstract

Excavation of dense and seasonally frozen soils remains the operation in which a single-bucket excavator loses a multiple share of its rated output, while the usual ways of raising efficiency run into dimensional and cost boundaries: growth of operating mass and of hydraulic pressure is limited by transport requirements. The choice among a passive bucket, an active-action bucket and preliminary ripping is made from the contractor's experience, and no quantitative transition criterion is fixed in industry practice. The aim is to compare four working equipment layouts of a hydraulic excavator of the second size group by force, energy and productivity indicators at a uniaxial compressive strength of the massif from 1,15 to 11,80 MPa. An author's calculation model has been developed linking the reduced specific digging resistance, the limiting chip thickness, the cycle duration and the specific energy intensity; normative and climatic values are taken from the codes and standards in force, and the parameters of the model object are set as a calculation example. A stepped tooth arrangement with a reduced sharpening angle lowers the specific energy intensity by 12,0-17,8% and keeps its advantage over the whole strength range. A hydraulic impact drive of the teeth adds 25.4% of operational productivity at minus 8° C and 37,8% at minus 14° C, yet on thawed dense loam it loses 9,5% in energy intensity to the basic bucket. The effect changes sign at 3.0-3.6 MPa. The boundary obtained shows that active action on the face is reasonably implemented as a switchable function of a replaceable working member tied to the measured strength of the massif, and that the potential of the passive cutting edge geometry is not exhausted.