Texas FFA Nursery Landscape Practice Exam

What does the presence of blue spots on a rotary mower blade after sharpening indicate?

1. The blade was overheated during sharpening

2. There are dull spots remaining on the blade

3. The metal was distorted while sharpening

4. The blade was made of inferior metal

The correct answer is: The blade was overheated during sharpening

The presence of blue spots on a rotary mower blade after sharpening indicates that the blade was overheated during the sharpening process. When metal is subjected to excessive heat, such as from grinding or sharpening, it can undergo a change in color, often showing shades of blue or straw. This overheating can significantly affect the blade's hardness and temper, potentially leading to a reduction in its effectiveness and lifespan. It's crucial to maintain appropriate sharpening techniques to avoid such overheating, which can also lead to warping of the blade or deterioration of its cutting edge. Recognizing the signs of overheating, such as blue spots, helps in understanding the importance of temperature control during sharpening.