Laboratory studies of the cutting of grass stems

Abstract

Studies were undertaken of the principle of employing static elements to support stems during cutting, using a relatively large clearance (about 5 mm) with a moving blade or blades. The objective of the work was to examine whether cutting speeds could be significantly reduced below the 80 to 90 m/s used in practice. Equipment was constructed which employed a piezoelectric force transducer to measure the specific force and energy for a single stem during a cutting cycle at speeds up to 45 m/s; high speed cine photography was used to study stem kinetics. Work was done on the effect of cutting speed, blade arrangement, clearance between static and moving elements, blade rake angle and blade sharpness. In addition, studies were made of restraint at the tops of stems, cutting of groups of stems and stem inclination. The results showed a critical cutting speed of 15 to 30 m/s, below which cutting became progressively more inefficient in terms of specific cutting energy. Relatively low energies were recorded at 5 to 10 m/s when stems remained uncut. The double shear blade arrangement was the most effective. The clearance between blades had no significant effect in the range 2 to 5 mm. Sharp blades required about 1 3 of the specific energy and peak force at speeds below the blunt blades. Increasing rake angle reduced specific energy and peak force at speeds below the critical value. For stems rigidly clamped at the top, the specific cutting energy was markedly reduced. A group of stems required significantly greater specific energy and peak force than a single stem. Highly inclined stems (at 70° to the vertical) required critical speeds greater than 40 m/s.