SHORE HARDNESS 1

[dazmac]

Help !

I'm an electrical engineer and have a large desk - this enables things outside of my field to land on it !!

I'm using vulcalon inserts on tablet press tooling, I just don't understand the Shore scale of hardness. Any explanation ?

Thanks in advance

 

[TheAnswerGuy]

The link below should help

http://www.machinist-materials.com/hardness.htm

 

[1399]

Hardness may be defined as the resistance to indentation under conditions that do not puncture the rubber.Different instruments designed to measure hardness do not usually agree well with each other.

The spring -loaded pocket durometer is the most common instrument to measure hardness (ASTM-2240). In this istrument the scale runs from form zero hardness (a liquid) to 100 for a hard plane surface such a glass. The type "A" durometer is used for soft stocks(generally rubbers)up to reading of 90. Above 90, the type "D" durometer , having a different indentor shape and different stiffness spring is used.

Hardness is a property of rubber that is expressed in terms of instrument parameters rather than basic units

 

[koshy]

Shore-Hardness
A very simple and inexpensive test device, which does not have to be installed stationary but can be carried around very easily, can be used to measure the Shore hardness. The hardness on soft rubber is mostly measured with the Shore A instrument, harder ones with Shore D instrument.

 

[koshy]

Further – (continued on Shore Hardness)
The penetrator is in the form of a truncated cone. By deflecting a leaf spring with calibrated stiffness characteristics, the resistance against penetration of the cone can be measured. At a theoretical shore A hardness of 100, an extremely hard material,the spring is compressed to its maximum position without any penetration of the truncated cone.The spring loading is then 822 g. At a theoretical shore A hardness of 0, an extremely soft material, the loading of the spring is 56 g. Intermediate values ate obtained by linear interpolation. The hardness is related to Young’s modulus. In order to obtain reproducible hardness values, the following device constants have been defined:1) Characteristic of the spring. 2) The cone angle of the penetrator and the diameters on both planes of the truncated cone. 3) The free length of the protruding pin.
(From Rubber Technology HandBook –Werner Hofmann)
Koshy