Rubber Database

Rubber is in this database for the jobs the rigid materials cannot do: sealing a joint, damping vibration, and taking up the movement between two parts that a metal fastener must not be asked to absorb. A flange that weeps or a bracket that cracks from vibration is usually solved by adding rubber, not by making the metal thicker.

The figures behave differently from every other family here, and that difference is worth reading before the numbers. Rubber is a compound, not an alloy. The polymer is the starting point, but the filler, the cure system and the processing set the finished properties — one family covers roughly 40 to 90 Shore A, and its temperature limit moves by tens of degrees between compounds sold under the same ASTM designation.

So the service temperature on each entry is a family screening range: the figure that tells you whether to keep reading, not a limit the finished part is guaranteed to hold. Every seal supplier ends its data sheet with the same sentence — the compound sheet governs — and this database repeats it because it is the correct way to use the number.

Hardness is the other figure that surprises people, and it is included as much to make one point as to give a value. Shore A is set by the gland and the seal geometry rather than by the polymer; most O-rings are 70 Shore A whatever they are moulded from. Changing the rubber rarely changes the hardness — one place this family behaves quite unlike metals, where a change of grade changes every number.

Density is quoted for the unfilled base polymer so the entries stay comparable with each other and with the rest of the database. Filled production compounds run higher, above 1.3 g/cm³ for several of these, so read it as a way to rank materials rather than to weigh a part.

Densest entry: Fluoroelastomer (FKM) at 1.85 g/cm³. Lightest: EPDM Rubber at 0.86 g/cm³. Temperature ranges are family screening figures, not limits guaranteed for any compound.