| 摘要 |
This rotary filament vegetation trimmer improves the life expectancy of plastic filaments by improved and simplified control of a refrigerated air flow path about the filament of sufficient magnitude to prevent overheating resulting in catastrophic failure from the stresses of twisting as the rotary trimmer head whirls the filament at high rotation speeds. Thus, the head and its filament passageway therethrough are shaped to constitute a centrifugal air pump that draws both air and the filament through the head to position the filament for trimming. The passageway diverges from the shaft into a chamber of significantly increased volume to produce expanding and refrigerated air in the critical region at which the filament curves and induces twisting as the head rotates to tend to heat and cause failure of the plastic filament. The head can thus be made simply in one or two pieces constituting an uppermost rotary shaft with an axial filament feed passageway downwardly through it and flanging outwardly to curve the filament as it passes through the refrigerating chamber normally to the shaft axis to extend outwardly for trimming vegetation. The uppermost member thus may comprise a bell shaped flanged lower mouth of a hollow driveshaft into which an apex of a conically shaped bottom member is directed to form therebetween a conically directed lamination of air dimensioned so that centrifugal force draws air into the hollow drive shaft past the filament to cool it and keep it from melting and failing.
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