Quality Control for Rubber Mixing and/or link to related forum

[Miner]

In Reply to Parent Post by humtum1977

1) As we are manufacturing epdm rubber gaskets for architectural sealing application such as windows, doors, curtain wall etc,which property of rubber should we focus to satisfy customer, i thinkg tensile and ozone perofrmance is ok? ur comments plz.

Are these closed/open cell sponges or solid rubber gaskets? Compression set, UV resistance, tear and abrasion resistance come to mind. Temperature resistance, flexibility at low temperature are others. Another might be not staining the mating surface if it is painted, not freezing to the mating surface in winter, or the ability to retain an adhesive tape for mounting.

In Reply to Parent Post by humtum1977

2) can you give me any material regarding rubber mixing, that you think a beginner must have.

See my earlier post as well as other posters.

In Reply to Parent Post by humtum1977

3) Please give me brief notes on following chemical, their properties, and purpose of use in rubber mixing, as i have googled a lot but did not get satisfied answer.

a) FEF N550, SRF N550.
b) Stearic Acid, Poly Plastol.
c) TMTD, ZDBC, MBT,ZNO, CBS.
d) Tetrone A
e) IPPD, KHS 68, MMBI.
f) Paraffinic oil, Aromatic oil, Wax.

a) FEF and SRF are carbon blacks that give rubber its strength and hardness.
b) Stearic acid is used as used as an activator, dispersing agent, plasticizer and lubricant. Plastol is a plasticizer that improves the rubbers ability to flow. This helps during extrusion, injection/transfer molding
c) TMTD is an inhibitor that delays scorch time (or the onset of cure). ZDBC, MBT and CBS are accelerators that increases the cure rate (slope) of the rubber. ZNO (zinc oxide) is used for a quicker and more controllable cure as well as a reinforcing agent.
d) Tetrone A is a plasticizer.
e) IPPD is an antioxidant, which increase rubber aging resistance. KHS 68 is an SBR latex/styrene mix with good abrasion, flex and tear resistance. MMBI is an antidegradant that improves heat stability.
f) oils are typically used to improve processability, while waxes migrate to the surface and form a thin film covering the surface protecting the rubber from the attack of ozone.

[humtum1977]

Dear Craig

Yes we are planning to use kaolin clay, but i dont have any idea about the quality, if you can give me notes on that, i will be thankful to you.

Regards.

[humtum1977]

Dear Miner

You have cleared my doubts and have given me the satisfied answer, you have very good experience on rubber, cheers to you, i will be back with some more questions.

Regards.

[qualityforlife]

Or just open this:

[humtum1977]

Well we have started our epdm rubber mixing and tested the mixed product in the lab, every thing was correct, when we extruded the rubber in extruder there we air bubbles on the surface of the extruded gaskets, what went wrong can any one calrify it, is it pure machine problem or is due to any chemical

chemicals we used (EPDM 965,FEF N550,PARAFINIC OIL,ZNO,STEARIC ACID
TMTD,MBT,ZDBC,TETRONE A )


Is there any way to test these air bubbles in testing lab before extrusion.


thks and regards.

[Miner]

Blistering on the surface is typically caused by moisture. This may be caused by a leak in the water jacket of the extruder barrel, or may be moisture on the uncured strip rubber. If you are spraying/dipping a release agent onto the rubber to prevent sticking, make sure that you dry it before putting it into the basket.

Porosity throughout the cross-section may be caused by moisture, trapped air, over/under mixing, wrong plasticizer, or incorrect cure rate/time. Trapped air is typically caused by starving the extruder screw. There should be a rolling ball of rubber in the mouth of the extruder. If this ball is not present, the extruder screw is not full and is mixing air into the rubber. Some formulation may form porosity if the cure rate/time is incorrect. Some plasticizers with low boiling point constituents may also cause porosity.

[humtum1977]

Before mixing we need to weigh the ingredients, is there any tolerance to weigh these materials or the exact quantity is must to weigh

1) Suppose we weigh 250 grms of chemical to mix is it necessary that it
should weigh 250 grms exactly or threse is any tolerance (250 ± ......) so
that it will not effect the out put.
Is there any special weigh scale required, can u give me any example of
good weigh scale with good accuracy.

2) How much time is standard to mix rubber in mixing mill to mix 25 kg batch3
so that all chemicals are mixed properly.

3) Why is sulphur most widely used as vulcanizing agents any specific
reason to use it, what are another vulcanizing agents.

4) can u give me the in detail the diagramatic representation of mixing
process.

5) Is there any requirement of Std. temperature setting for the mixing room.
is there any standard condition for mixing raw material storage.
does raw material gets damaged if kept for long time.

[Miner]

1) A rubber chemist would be better able to answer this. My experience has been an exact weight. When we upgraded our mixing area, we invested in higher precision scales to improve the control.

2) When I left, there were two schools of thought on this. One was to drop the batch at a specific time. The other was to drop when it reached a specific temperature. We dropped on temperature. But both methods were unique to the rubber formulation being mixed.

3) There are only three methods for curing rubber. Sulfer is the most widely used. The other two are peroxide, which is the next used. This is more expensive and is used when sulfur is not desireable. The last, more rare for obvious reasons, is a radiation cure.

4) I do not have time to do this now and do not have an existing one. We had a two-floor setup. The chemicals were stored and added to a Banbury mixer on the second floor, mixed and dropped directly onto a mill on the first floor. The rubber was stripped off and dipped through a release slurry. The strip was then festooned through a series of blowers to dry the slurry, then wig-wagged into baskets. The sponge rubbers were then stored in a temperature controlled room at 68 degrees F.

5) Until the rubber is mixed, the ingredients are not particularly sensitive to temperature. After mixing, rubber will immediately start the curing process, albeit at a very slow rate. The rate of this cure will depend on the ambient temperature and on the specific formulation of the rubber. We used a 3-day shelf life on closed cell rubber formulae and 5 days on dense rubber formulae. However, we had one specialty compound that had a 12-hour shelf life.