Buna N vs. NBR 1

[pollack]

In regards to using NBR as a replacenent for Buna N in small motors, are there any significant differences that could affect performance. My company uses Buna N, but our new plant in China does not have it available. The research I have done seems to suggest the two are interchangable and that Buna N is just the old name for NBR. However, if that is the case, why are they having a problem? If the percent of acrylonitrile is the same, is this essentially the same material? Any help would be appreciated, thanks.

 

[BCAREY]

BUNA-N, NITRILE, NBR, HYCAR, PARACRIL are all the same material. a co polymer of Butadiene ( which provides the resilience properties of rubber) and acrylonitrile ( which provides the oil resistance property). The ratios may vary, but if your ratios are the same then it is the same compound and your source in China is simply not correct

 

[pollack]

Thanks. I was pretty sure this was the case, but I wanted some confirmation.

 

[aholloway]

To elaborate further on BCAREY's response, Buna-N, NBR and Nitrile are the same base co-polymer as he described. Hycar (now Nipol), Paracril, Krynac, and numerous others are brand names of the manufacturer of the base co-polymer. However, there are other differences than their ACN (acylonitrile) content, such as their polymerization method (hot or cold), inherent cure rate, mooney viscosity and incorporated stabilizer some of which only matter to the processor of the finished mix used for molding, extruding, etc but others will influence part performance.

The biggest influence will in the formulation the base is used in. We have dozens of NBR formulas that we use for select applications. Most formulations have 10-20 other ingredients in them that very much influence part performance. In very broad terms, in addition to the base co-polymer (may be one or more of the more than 200 commercial grades available) they will have the filler system (re-inforcement, low/high temp plasticizers, etc), protectants (antioxidants, antiozonants), process aids and the very influential cure system (sulfur based, sulfur donor based, accellerators, peroxide based/co-agent).

In short no two 35% ACN NBR formulas are the same and they will range from exactly what the application calls for to complete failures. I suggest that you get down to specifics of formulation as well as material properties specifications with your suppliers.