Rubber Isolator Failure Mode

[Ninja202]

Hey, I am new to rubber engineering, was wondering if anyone has seen this type of failure of rubber before. The part is not mechanically overloaded and is made from natural rubber. I was thinking it possibly could be ozone cracking but not sure. I noticed between the cracks were small dots of white. Any help would be much appreciated.

 

[tom1953]

Is the part very old? It looks like some rubber parts >100 years old that I've seen in museums.
Is there stress on the parts, across the picture (perpendicular to the cracks)? That's how ozone cracks would show up.
tom

 

[Ninja202]

Cheers tom1953,
the part is not that old 2 or 3 years and is placed in a sealed electrical cabinet. Yes there is stress perpendicular to the cracks (compressive). Is there any way telling from the picture whether it could be caused by compressive stress and temperature or compressive stress and ozone?
Regards, Michael

 

[GrahamBennett]

Looking at the photograph I would say that the part failed due to severe ozone cracking. NR is unsuitable for longterm use in applications where ozone is generated. An EPDM-based compound would be much, much better here.

 

[Ninja202]

Cheers Graham

 

[kakani]

hey,
if epdm cost is high for you then you can blend epdm with natural and add some ozone protector. it will work.

 

[GrahamBennett]

I'm not that keen on blending EPDM and NR because of the differences in rate of cure with accelerator/sulfur cure systems (NR is much faster curing compared to even the fastest curing grade of EPDM). If you go down the blend route, I suggest you use either a peroxide cure for EPDM/NR or, if you want to use a conventional accelerator/sulfur system, then use an EPDM/SBR blend (SBR is slower curing compared to NR).

 

[Metten]

ozone and/or electrical corrosion. is the part normally conductive and not in this case?

what white product is used in the formulation, can you test if the white dots are that material?