Rubber,mixing-hardnes?

[orion1]

Hello,
We have problem with rubber hardness it is sometimes higher and sometimes lower with same raw materials, so could somebody tell me how can we encrease hardness during mixing step in our production. Does the odrder of adding raw matterials has some infulance of the hardness or temperature of mixer or something else. Of course I know that hardness is function of filler properties and quantity.
Thank you.

 

[JIM317]

It may be that your filler and oil scales are inaccurate--Pigments and oils/softners will effect durometer the most. If you are mixing a masterbatch + final the accuracy of curative weighings can have an effect. Is the sp. grav of your compound varying too? I would have to know details of formula for a more detailed answer.

 

[orion1]

JIM317 (Chemical), can you please describe the"If you are mixing a masterbatch + final the accuracy of curative weighings can have an effect".
We have good hardnes when we mix the whole batch in the open mill , but we have 2 shores lower hardnes when we mix it in the internall mixer? And we also have problems with some types of formulations with lower hardness on the internall mixer?
Regards,

 

[JIM317]

Orion1
What I meant to tell you was that a 2 pass mix in an internal mixer (banbury) is more liable to weighing errors than a one pass open mill mix. With a mill mix it is easy to see the iunincorporated materials in the pan, sweep them up and add them to the batch--you should not "loose" anything.
If you are getting 2 points lower durometer on this compound mixed in a banbury then you are probably losing pigments due to 1)a worn out mixer, 2)incorrect material addition, or 3) mix cycle (time) or a combination of all three--carbon black or other pigment will be visible when the batch is discharged. Are you getting a lower sp. grav. on the mixer batch vs. the mill batch?? If you run rheometers is their a difference in the curves from mill mix and banbury??
You haven't provided enough info to make a thorough analysis. If you are running both high and low durometer on different compounds I am sure I can heelp you correct this but I would need the formula and mix spec details for each problem compound.
KEL2149@yahoo.com cell.. 513.312.0457

 

[orion1]

Helo JIM317,
Thank you for the answer.
I'm on the holliday now, but after I'll check reo curves and spec gravity .
What does it mean "worn out mixer"?
Thank you for the lot off information and of course for your time.
Regards,

 

[JIM317]

Worn out--means the clearances between the mix chanber sides and the rotors are too great. The dimensions (cleaances can be corrected. If the wear is too great the materials don't disperse as well as they should.
What part of the world are you located in? Hope ur holdiay is enjoyable