One of the great mysteries of the world is why exactly razor blades cost so much. They never seem to last long as after a few shaves there so dull they basically rip the hair out instead of cutting it. MIT has performed a new study to figure out why, despite that human hair is 50 times softer than steel, razor blades dull quickly.
Razors, scalpels, and knives are typically made from stainless steel honed to a razor-sharp edge encoded with harder materials such as carbon. Knives require regular sharpening, and razor heads have to be replaced despite cutting materials much softer than they are. Engineers at MIT have studied the act of shaving up close and observed how the razor blade can be damaged as it cuts human hair.
The team found that shaving deforms the blade in a way that is more complex than simply wearing down the edge over time. The study found that a single strand of hair can cause the edge of the blade chip under certain conditions. Once the initial crack forms, the blade is then vulnerable to further chipping leading to the edge of the blade quickly dulling.
The researchers say the blade’s microscopic structure plays a key role, and the blade is more prone to chipping if the microstructure of the steel is not uniform. The angle at which the blade approaches a strand of hair and the presence of defects in the steel’s microscopic structure plays a role in initiating cracks. The team believes that the research may offer clues on how to preserve the sharpness of a blade.
The main goal of the study was to determine why blades become useless when they interact with a much softer material. In the study, the team used disposable razors to shave facial hair, and after every shave they took images of the edge of the razor blade with a scanning electron microscope to see how the blade wore. The team used blades from various commercial razors at various angles for shaving.
The blades chipped in certain spots, and when the hair was free to bend, chips were less likely to occur. Chips in the blade most commonly occurred at places where the blade edge met the hair strands’ sides. The result of the study is a patent filed on a process to manipulate steel into a more homogeneous form to make it longer-lasting.