Dump temperature

[mageshbabu12124]

I have a bunch of doubts, it will be helpful if anyone can help me with this.
1.On which basis we are fixing the kneader's dump temperature for vairous rubbers in kneader mixing?
2.What are all the important parameters in setting the dump temperature?
3.Are there any different rheo attributes for kneader mixing and open mixing?
4.Will TS2 and TC90 be affected when the ML value of the compound changes?

 

[Metten]

1. A higher temperature will melt more ingredients, making the dispersion much easier. Too high temperatures will break down your elastomers or cause side reactions.
The type of rubber (and formulation) will determine your dump temperatures. CR rubbers have low dump temperatures, very soft EPDM just don't cause enough friction to go high.
2. I assume you should mix as economically as possible. Shortest time, high energy input to have a good dispersion.
If your dispersion is not good enough, you need to change your mixing procedure.
3. viscosity might differ a bit, open mixing takes far longer.
4. yes, but the question too vague or broad to give a usefull answer.

 

[mageshbabu12124]

Thank you metten. When I mix NR compound of 80 hardness in the open mill , the resulting ML is 13 to 15. But when I tried mixing in kneader , the resulting ML is 20 to 22. I have tried various mastication time in kneader (about 3 to 12 mins). And my tried various dump temperature 105°C to 130°C . When I mix in kneader ,the ML is high and TS2 ,TC90,hardness is low.
I don't know how to decrease the ML in kneader mixing.

 

[Metten]

Have you tried two stage mixing? First stage up to 150°C fe and second stage with accelerators up to 100°C one day later?

 

[GrahamBennett]

mageshbabu - you mention you use a kneader to mix your compounds. Who is the manufacturer of your machine? If you are using a Chinese, Taiwanese, Korean, or Japanese type mixer with a tilt-chamber you will have extraordinary problems with ingredient dispersion and general quality levels of the final compound properties.

For compounds containing NR, SBR and BR, you can mix masterbatches (i.e. no curatives) up to 170°C in an internal mixer (Banbury, Intermix). Once mixed, dump and batch off in sheets or pellets and cool down. Leave for 24-48hrs before mixing the final stage when you add the curatives. Final stage mix temperature must never exceed 100-105°C and you must cool the batch down very quickly once it has been dumped in order to prevent any pre-curing.

As Metten said, polymers containing chlorine (Neoprene, Chlorobutyl, etc) or bromine (Bromobutyl) must be mixed to lower dump temperatures (around 130-135°C for masterbatch stage).

forumtowers.com

 

[mageshbabu12124]

Hello metten.yes, I have already tried this

 

[mageshbabu12124]

Thank you graham!! We are using Chinese machine only. You said that dump temperature for NR,SBR,BR master batches is up to 170°C and for Neoprene and halo butyl is 135°C. On which basis you are telling this. I want to know the science or reason behind this. Thanks in advance.

 

[GrahamBennett]

Neoprene and halobutyls are very reactive at high temperatures and will exhibit premature curing in the mixer at temperatures above 135°C even without any curatives being added to the mix.

NR and SBR have much higher molecular weights than most other elastomers so mixing to high temperatures helps break down the polymer chains to make downstream processing that much easier.

forumtowers.com

 

[mageshbabu12124]

Thank you graham