NBR rubber shows the steady curve on moving die rheometer (MDR) S curve with torque increasing endlessly even after 1 hr. With an increase in max torque value, T90 also increases. How do I know when to stop vulcanization to see optimum T90 value?Thanks
Dear Lwin Moe Thu,
Would you please display the rheometer curve?
Dear Lwin Moe Thu,
According to the slope of the curing curve, I suggest the best range of curing temperature is 40-42 min at 160C.
Hi Mina Karimi-Avargani,
Thank you for your reply. I used 165c 17 min last time and tensile strength was bad with a sign of over-curing (stiffness). I doubt 160c 40min will do the same to rubber. The manufacturer used 150c 15min and get the best tensile result, which doesn't make sense to me because, at that condition, the vulcanization curve hasn't been stabled yet and 20 min MDR duration is too short.
Do you think Mh-Ml value is so high? I appreciate it.
Dear Lwin Moe Thu,
According to the obtained results, I guess the hardness of the compound is more than 70 Sh.A. Moreover, the scorch time is low which indicates the curing system is efficient which the ratio of sulfur to the accelerator is less than one. In this situation, it is better to prepare enough time to be vulcanized completely to obtain excellent mechanical properties. In this situation, it is suggested to keep the temperature lower than 170 C and increase the cure time. Sometimes, post curing is necessary to achieve proper physical and mechanical properties.
If you know the hardness of the compound, try to perform rheometer test at different time and temperature (for example, at 150, 160, 170˚C for 50, 40, 30 min). Then measure the hardness of the specimen. In this way, you can be sure about the time and temperature that vulcanization process has been completely done.
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