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Plasticizing N21 and N41 have high Mooney viscosity and must be plasticized. Generally, plasticization takes 3-5 minutes.

N32 does not need plasticization and can be directly mixed.

(2) Mixing NBR on a mixing mill

When mixing, the roller temperature should be controlled at around 40°C, and the roller speed ratio should be 1:1.4. The mixing capacity depends on the size of the mixing mill. Because sulfur has a low solubility in NBR, it should be added first. The mixing time is about 25 minutes. The mixing procedure is as follows:

1. Open the roller gap to 1.4mm, and mix for 2 minutes;
2. Add ZnO, SA, S, and mix for 2 minutes;
3. Make 3/4 cuts three times on each side, and mix for 2 minutes;
4. Add half of the carbon black or other fillers evenly along the rubber at a constant speed, and mix for 5 minutes;
5. Make 3/4 cuts three times on each side, and mix for 2 minutes;
6. Add the remaining carbon black or other fillers evenly along the rubber at a constant speed, and mix for 5 minutes;
7. Add plasticizer, and mix for 1 minute;
8. Add accelerator, and mix for 1 minute;
9. Make 3/4 cuts three times on each side, and mix for 2 minutes;
10. Roller gap 0.8mm, and thin pass 6 times to unload the sheet.

The total time is 23 minutes, and the maximum is 25 minutes.

(3) Mixing in an internal mixer

The mixing temperature of the internal mixer is controlled at 100-115°C, and the mixing time is 8-15 minutes. The operation procedure is as follows:

Internal mixer: 0 min. Add materials and start mixing; 2 min. Add ZnO, SA, S, 1/2 carbon black; 6 min. Add other additives; 10 min. Open mixer: Use open mixer to beat into the required thickness and package.

(4) Extrusion of NBR

During the extrusion process, scorching must be prevented. Strict control of extrusion and careful selection of formula should be used. The formula should choose a vulcanization system with a long scorching time. The sulfur/accelerator DM system has a better effect. Adding an appropriate amount of lubricant is also helpful to prevent scorching.

When using a hot feed extruder, the rubber compound should be heat-refined on an open mixer before extrusion. The heat-refining conditions are 40°C for the front roller and 50°C for the rear roller for 4-5 min. During heat refining, the proportion of extruded return rubber should be controlled to prevent fluctuations in the plastic value of the rubber compound. The heat-refined rubber compound must be supplied to the extruder in a timely manner.

The extrusion conditions of NBR rubber are generally: barrel and screw temperature 40-60 ℃, die temperature 80-90 ℃, and die head temperature 90-100 ℃. To prevent scorching, the barrel and screw temperatures should be kept low, and the temperature should be raised at the die temperature. For this purpose, the screw is preferably cooled with cooling water. To make the surface smooth, lubricants can be used. Common lubricants are paraffin, lanolin, operating oil, etc.

(5) Calendering

NBR must be heat-refined before calendering. The process conditions are: roller temperature 40-50 ℃, speed ratio 1:1.4, and after heat-refining to the plasticity value required for calendering, it can be provided to the calender for calendering. If the requirements for the rubber are higher, it can also be filtered after heat refining and then provided to the calender for calendering.

(6) Vulcanization

From the perspective of vulcanization technology, it has two major advantages: thermoplasticity and good thermal stability. The vulcanization curve of NBR is flat and the vulcanization temperature range is wide. NBR shows good thermoplasticity as the temperature rises. Therefore, NBR is often manufactured by molding and injection molding. Molding is the most commonly used method. The flat plate vulcanization conditions are 140℃～200℃, 2.4～10MPa, and the vulcanization time varies with the size, shape and rubber formula (especially the vulcanization system) of the product. Small products are vulcanized at about 180~200℃ for 0.5～ For thick products, in order to avoid uneven vulcanization degree inside and on the surface, low temperature (140～150℃) and long-term vulcanization are generally used.