Rubber Shore Hardness

Depends entirely on the application.
for peristaltic pump tube, harder may give higher pressure, but may overload the motor, it may give longer or shorter life. It's about matching the material to the application.

When in doubt run some tests.

Del

Can you give us some more information on the application. It is dificult to give advice without knowing the application. Generally the Shore "A" specification allows for a tolerance of +-1 point, so you need to keep that in mind as well.

It is for sealing arrangement. (Seal wiper)

In the broadest of terms, squeeze out of the tube silicones are around 40 durometer while your windshield wiper would be in the 50-55 range. Please, no expert opinions telling me I'm off by 5 points.

You can go with it and expect some loss of conformance to the "wiped" surface and some increase in abrasion to same. How much, only testing can tell you that.

Lower the Hardness(40ShoreA) will give Better result,In order to get better result of wiping from Wiper Seal on uneven shape or curve Shape like wipers used on wind Glass of Cars which is curve shape & when it rotate to lower position it become Stright due to softer Rubber it takes shape of Glass & Hence you get Better Result, it is upto Rubber processer to maitain the Hardness by using composition of Rubber & curing it on Specified Tempreture

The right Shore "A" depends on the application. You want to make sure that when the rubber is squeezed it fully fills the groove in which it is located. In some cases to soft a rubber causes creep. Creep is when the rubber tends to bounce when squeezed. I have used 40 Shore A rubber in applications where the pressure was 100 psig with no problems. The biggest thing to remember is the groove where the rubber is placed has to be correct. There is a difference between 40 and 50-55 Shore A and depending on the application that difference could make the difference between your application working correctly or you will have leaks everywhere.

For the same pressure, a softer seal material requires a smaller seal gap in order to prevent the material from extruding through the gap it is intended to seal.

You have described a 10 to 15 point increase in the hardness of your rubber product. The hardness is determined by the ratio of different ingredients in the compound mix. There are tradeoff's. To increase hardness typically the compounder would add a larger percentage of "Filler" materials, in this instance possibly Carbon Black or Clay. Tradeoff's; the carbon black is a reinforcing material which may make the material have a higher tensile strength, but, may also reduce elasticity. Think of it as a cake mix, adding different ingredients to make a different kind of cake. Rubber is the same, you add different ingredients at different proportions to get different types, hardnesses and other physical properties. If your current supplier can't make 40 shore, then it's time to find another vendor.

Chris Muir, Seal Science, Inc.

Chris , I like the cake correlation!

Another one I like to use is the Human Muscle.

The locked in power.

Our muscle is nicely lined up were as rubber is like an SOS pad.

Depending on how the bonds are created during vulcanization you have long and short chains linked together in your compound.

So you can have two 40 duro compounds feel very different.

One feeling stiffer than the other or when you stretch your part one can pull longer or easier than the other.

So when you design a part its best to follow the ASTM D2000 call out to insure you get the right properties you want from which ever vendor you select.