You might remember back in the school days there were a wide range of pencils that students used for drafting or arts classes. The pencils were rated on a scale containing letters and numbers such as HB, 2H, 2B, F and others. The scale was meant to rate the softness or hardness of the lead of the pencil. Well, similarly in the rubber materials world, there is a scale that is used to measure the level of hardness and durability of silicon rubber for the manufacturing of keypads. This measure is the Durometer.
There are different scales of measure for durometer, but the most common scales are assigned with a letter “A” for softer materials, and a letter “D” for harder materials. The scales follow the American Society for Testing and Materials (ASTM), in the use of a 0-100 range to define the softness or hardness of a given material. We owe the name of the scales to an instrument maker Albert F. Shore, who developed the first instrumentation to measure material softness, that’s why both scales “A” and “D” are best known as Shore A and Shore D after its inventor.
Here is a list of various items and their given durometer ratings:
Rubber Band – Shore A 20
Pencil Eraser – Shore A 40
Tire Tread – Shore A 70 or Shore D 15
Shoe Heel – Shore A 80 or Shore D 30
Shopping Cart Wheel – Shore A 95 or Shore D 50
Hard Hat – Shore D 80
But, why is durometer so important to our industry and our daily lives? Well, the durometer of a material defines factors as: the functionality of a rubber keypad, the use, the cycles of the keys and the durability. The suggested measure for a silicone rubber keypad is Shore A from 40 to 60, and this will depend on the requirement of the cycles, actuation force and tactile response. If you are thinking of an application where you need a high actuation force and snap ratio, a high hardness rubber keypad is advised, but the life of the keypad will be reduced. If your application calls out for a low actuation force and snap ratio, a lower hardness rubber keypad is advised, and the life of the keypad will be longer.
It is important to know the durometer number of the silicone rubber you will be using for your specific application. If you are not sure what durometer to use or if you want to discuss your application, please feel free to leave a comment or a question and we will be more than happy to help you in your decision making.