Sometimes the most useful ideas are those that are taken for granted. Frequently, those ideas – like the mousetrap – are hard to improve on. Such is the case for the sun visor. Introduced in the 1930s, the visor became an automotive fixture that remains much as it was introduced over 90 years ago.
Prior to the introduction of the visor as we know it, cars such as the Model A utilized external “visors” similar to the bill of a baseball cap. These external visors continued as an accessory (mod) long after the internal visors were incorporated.
Sure, the visor has morphed a bit over the years. It has grown in size to help shield a greater area from sun glare. Part of the reason it has grown in size is because it has become a convenient storage area. Soon after being introduced, it became a repository for maps, written directions and fountain pens. Although the advent of GPS has reduced the need for these things, the visor is still a convenient storage place for sunglasses, tissues, notepads and CDs. With today’s handy, lighted flip-up mirrors, it often serves as a cosmetic-application aid or even a mirror by which to shave. Neither of which should be done with the car in motion, of course!
All of this stuff has only added to the need for a part that is well designed for its application. This part is the metal rod on which the visor moves. Made from 1008-1010 carbon steel, this rod can be hollow or solid, and the same basic rod is used for vehicles from Hondas to Hummers.
Thermal processing consists of a carbonitriding treatment to a total case depth of 0.005-0.010 inch. This is followed by a cleaning treatment in a vibratory mill. Mechanically testing a part of this configuration is difficult, so the established test is a “file hard” requirement. A metal file of RC 60 is used to see if it can mark the part, which indicates that the surface hardness of the part meets RC 60. Parts are then placed in an injection-mold process to be coated in plastic prior to assembly.
In a single U.S.-based heat-treatment facility, approximately 50,000 pieces were processed per week. Regrettably, the majority of this business has been lost to competitors in China. The unfortunate reality in our global economy is that even if you buy a car made in the U.S., many of its components are manufactured overseas.
Although mechanical testing of this part is limited, the testing requirements are nonetheless challenging. The visor is required to be moved up and down 45,000 times without squeaking. Squeaking could likely have several causes, one of which would be the wear of the rod through the hardened case. If you consider this test requirement, however, it’s easy to see that it is a worst-case scenario. If you own your car 10 years, you would need to move your visor up and down 12 times every day, 365 days a year, for all 10 years to reach the 45,000-cycle threshold.
Although a well-established vehicle component, the visor might soon go the way of the buggy whip. Several dozen patents exist for automatic sun visors, which may soon replace the old standby. The benefit of some of these new systems – the better mousetrap – is that unlike our current sun visors, they shade the light without blocking it. And if the light can get through, you will also be able to see out, which will make certain driving conditions much safer.