Shore hardness
#1 What is Shore hardness?
Shore hardness is the hardness of an O-ring.
In the field of elastomers (NBR, EPDM, FKM, etc.), the Shore hardness can be between 5 and 100 Shore. However, only the 40 to 90 Shore range is of interest for the manufacture of O-rings.
Note: The tolerance specification for Shore hardness is ± 5 Shore.
Each O-ring material has a standard hardness. We have put together a short table to give you a quick overview of all the important O-ring materials:
Material | Friction |
|---|---|
NBR | 70 Shore A |
HNBR | 70 Shore A |
EPDM | 70 Shore A |
VMQ (silicone) | 70 Shore A |
FVMQ | 70 Shore A |
FEPM (Aflas) | 70 Shore A |
CR (Neoprene) | 70 Shore A |
ACM | 70 Shore A |
FKM (Viton) | 75 Shore A |
FFKM (ECOLAST) | 75 Shore A |
FEP coated | 90 Shore A |
PTFE | 60 Shore D |
The Shore hardness is specified on every data sheet and is definitely an important key figure. However, it must be noted that the tolerance is ± 5 Shore. It can be deduced from this that the Shore hardness should only be used as a guide value in the design.
Do I have a high pressure in my system (>50 bar)?
-> Then I prefer to use an O-ring with a hardness of 80 or even 90 Shore.
Are my sealing surfaces uneven and I want to even them out?
-> Then I prefer to use 50 or 60 Shore O-rings.
Important: The Shore hardness is divided into Shore A and Shore D.
#2 What is the difference between Shore A and Shore D?
The measurement of Shore A and Shore D differ and are also intended for different materials.
Shore A = elastomers (e.g. FKM 75 Shore A)
Shore D = thermosets (e.g. PTFE 60 Shore D)
Note: There is no official conversion table from Shore A to Shore D. It is only important to know that 60 Shore D is approximately 100 Shore A. Accordingly, a PTFE O-ring with 60 Shore D is significantly harder than an FKM O-ring with 75 Shore A.
