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Rubber Processing Technology Q&A

2016.06.02

1. Why rubber need plastication

Rubber plastication aim to make rubber chopped macromolecular chains under mechanical, thermal, chemical and other effects. So rubber loses its elasticity temporary then increase in plasticity .To meet the technical requirements in the manufacturing process. For example: make easier when mix complexion agents, Facilitate rolling extrusion, Molded pattern clear, stable shape, Increased pressure pattern.

Increased pressure type and injection adhesive material liquidity. So easy to penetrate the rubber fibers, And can improve the rubber solvent resistance and adhesion mediated. Of course, sometimes some low viscosity, and constant viscosity rubber also cannot plastication. We suggest you domestic standard plastic particles and standard Malaysian rubber.  

2. Some factors affect the rubber plastication in internal mixer 

The rubber mixing machine plastication raw rubber belong to high temperature mastication, the minimum temperature above 120 ℃, generally between 155 ℃ -165 ℃ . When raw rubber in the mixer chamber influenced by the high temperature and strong mechanical action, resulting in severe oxidation, plasticity can be obtained over a relatively short period of time.

Thus the factors affect the rubber plastication are as follows:

(1)The technical performance of equipments, like rotating speed

(2)Crafts conditions, like time, temperature, wind pressure and capacity.

3. Why different rubber have different plastication character

Rubber plastication are closely linked with its chemical composition, molecular structure, molecular weight and molecular weight distribution. Natural rubber and synthetic rubber due to the different characteristics of the structure and performance, in general, natural rubber is easier to plastication. synthetic rubber more difficult. In terms of synthetic rubber, isoamyl rubber,Neoprene closed to natural rubber,Styrene-butadiene rubber, butyl rubber followed by,NBR most difficult.

4. Why raw rubber plasticity as the main quality standards of Plastic compounds

Raw rubber's plasticity is  important properties to the whole  manufacturing process .directly affects of the vulcanized rubber physical and mechanical properties and performance of products. If the plasticity of raw rubber is too high, the physical and mechanical properties of vulcanized rubber will decrease. Raw rubber plastic too low, it will cause difficulties in processing technology,Is not easy to make rubber mixing evenly,Calendaring, extruding semi-finished products 's surface not smooth,large Shrinkage , which is difficult to grasp the size of semi-finished products,When calendaring rubber is difficult to rubbed into the fabric, resulting in hanging plastic cord peel phenomenon, greatly reduce the adhesion between the fabric layers. Plasticity will result in uneven process performance and mechanical properties of rubber inconsistent, and even affect the product performance inconsistent. Therefore, proper understanding of the plasticity of raw rubber is an unavoidable problem.

5. What is the purpose of mixing  

Mixing is in accordance with the proportion of compound formula prescribed, put raw rubber and various complexion agents mixed together by a rubber device, And various complexion agents evenly dispersed in raw rubber . The purpose of kneading rubber is to obtain uniform between physical and mechanical performance,Performance indicators in line with rubber of the formula prescribed in order to facilitate the next process operation and assurance requirements to products quality.  

6. Why complexion agents agglomerate

Reasons causing complexion agents clumping:Raw rubber plastication inadequate,roller space too large,roller temperature too high, loading oversized,The flour complexion agents contained coarse particles or agglomerates, gels, etc. 

Improved approach is taken for specific situations:fully plastication,smaller the roller distance,reduce the roller temperature,adjust feeding methods, Powder drying and filtering;cutting with due.

7. Why it will create “dilution effect” if using too much carbon black in sizing material?

“Dilution effect” means that due to in the rubber formula,using too much carbon black,rubber quantity will reduce relatively. It leads to close contact between black particles,but not very good dispersion in the rubber. This is “dilution effect”. In this way,because there’s many big carbon black particles,rubber molecules couldn’t penetrate into carbon black particles. Interaction between rubber and carbon black reducing,strength decline but couldn’t reach expectant reinforcing effect.

8. What effects does the structure of carbon black to performance of the rubber?

Carbon black is made up of hydrocarbons generated by thermal decomposition. When the raw material is natural gas(Its composition is given priority to with fatty hydrocarbon),it will create carbon six-membered ring. When the raw material is heavy oil(Aromatic hydrocarbon content is higher),because there has been carbon six-membered ring,it will be further dehydrogenation condensation formation of polycyclic aromatic compounds. Then it will create hexagonal mesh structure aspects of carbon atoms. This structure 3-5 overlapping becomes crystallon. The spherical particles of carbon is amorphism crystallon,which made up of several groups of crystallon without certain standard orientation. There’s unsaturated free radicals around crystallon. This free radicals makes carbon black together and create  varying amounts of branch chain. This is called carbon black structure.

The structure of carbon is different because of different making ways. Generally the structure of furnace carbon black above the slot method of carbon black. The structure of the acetylene carbon black is highest. In addition,the raw material will also effect carbon black structure. The high aromatic hydrocarbon content of raw material, the structure of the carbon black is high, the yield is high. On the other hand, the structure is low, the yield is low. The smaller the carbon black particle diameter, structure will be higher. Particle size in the same area, the structure will be higher,pressure out more easily, and product surface is smooth, closed reduction. The structure of carbon black will be measured by the size of oil absorption value. Under the same size,big oil absorption value,structure will be high,the opposite said structure is low. High structure carbon black is difficult to disperse in the synthetic rubber. But soft synthetic rubber needs high modulus carbon black to improve its strength. Fine particles of high structure carbon black can improve the abrasion resistance of tread rubber. The advantage of low structure carbon black is high break strength,high elongation,low tensile modulus,small  hardness,sizing material soft,themogenesis also small. But wear resistance is worst  than same size with high structure carbon black.

9. Why carbon black will effect scorch safety of sizing material?

(1)The structure of carbon black will effect the scorch time of sizing material. Higher structure,shorter scorch time;smaller diameter of carbon black,shorter scorch time.

(2)Surface properties of carbon black will also effect scorch. Mainly means oxygen content of the carbon black surface. Higher oxygen content,lower PH,acidic,such as channel black,the scorch time is longer.

(3) Using quantity of carbon black will effect scorch time. Using more quantity,it will obviously shorten scorch time. It is because carbon black increases,generate combined rubber,which have a tendency to promote scorch. Carbon black has different effect for mooney scorch time of sizing material in different vulcanization system.

10. What’s one section mixing? What’s two section mixing?

One section mixing is putting plastic rubber mixing and all kinds of compounding agent(For some compounding agent which is difficult to disperse or use less,it could  be made into masterbatch in advance) one by one according to requirements of process. Making masterbatch mixing in banbury mixer. Then add sulphur or other vulcanizing agent and some super promoter which couldn’t add in banbury mixer on the pressing sheet machine. In short,one section mixing is not stop in the middle but finishing mixing one time.

Two section mixing is uniform mixing all kinds of compounding agent and raw rubber except vulcanizing agent and super promoter. Making masterbatch,batch-off cooling,stop for a certain time. Then adding vulcanizing agent to supplementary processing in the banbury or open mixing mill.

11.  Why the rubber sheet should be cooled before storing ?

The press slice machine cut off the rubber sheet temperature is very high,If not immediately cooled, It is prone to premature vulcanization, and viscose ,cause trouble for the next process.

The rubber mixing mill pass rubber sheet cooling installation Isolate the leaching、blow-dry、slice up, It is for this purpose.

General cooling is required to cool the rubber sheet temperature below 45 degrees Celsius, sizing material parking time should not be too long, otherwise it will cause plastic spray.

12. Why do you want to control the temperature below 100℃ ?

Because the material in the mix when adding sulfur and accelerators, if the temperature exceeds 100 ℃, can easily lead to premature vulcanization of rubber (ie scorch). In addition, at a high temperature for dissolving sulfur in the rubber, after cooling sulfur agglutination rubber surface, resulting in bloom, and can cause uneven dispersion of sulfur.

13. Why  mix rubber sheet to be want to parked some time before use?

After cooling the rubber sheet by mixing object store has four: 

(1) make the rubber fatigue, mechanical stress suffered when kneading relaxation; 

(2) reducing compound shrinkage; 

(3) complexing agent in park the process continues to spread and promote uniform dispersion; 

(4) make further generate combined rubber to improve the reinforcing effect between the rubber and carbon black.

14. Why should strictly implement the subsection add medicine and pressurized time?

Adding medication order and time pressure is an important factor affecting the quality of mixing. Piecewise chemical dosing can be to improve the mixing efficiency, increase the uniformity, and some spices dosing sequence and its special provisions, such as: liquid softeners shall not with carbon black and adding to avoid. So we must strictly enforce the dosing section. Pressure time short rubber and spices to full friction kneading, caused by mixing uneven; such as pressurization time is too long and the mixing chamber temperature is too high, affecting the quality, will reduce efficiency. Therefore, the pressure time must be strictly enforced.

15. What is the impact on the capacity of the rubber and plastic rubber mixing quality ?

Loaded adhesive capacity refers to the mixer actual mixing capacity, it often accounts for only mixer 50-60% of the total capacity of the mixing chamber mixer if the capacity is too large, the mixing has no sufficient space cannot be mixed fully, resulting in mixed uneven mixing; temperature is high, easy to cause the compound sulfur; can also cause motor overload. Capacity is too small, the rotor without enough frictional resistance, spin, also caused mixing, the mixing of rubber quality affected, while also reducing the equipment utilization rate

16. Sizing material mixing , why last add liquid softener?

Compound during mixing, if adding liquid softener, can make the rubber excessive expansion effect of mechanical friction effect between molecular glue and filler, rubber mixing speed is decreased, and will cause the uneven dispersion of powder, and agglomerate. So when mixing liquid softener is usually added at the end.

17. Why the mix is placed for a long time "from sulfur"  

Rubber mixture during the placement "sulfur" reason mainly: 

(1) for use in vulcanizing agent, accelerator too much; 

(2) adhesive capacity big, rubber mixing machine temperature is too high, the film does not cool enough; 

(3) or premature and sulfur, spices dispersion caused by uneven promoter and sulfur local set in; 

(4) improperly parked, parking places high temperature and air circulation.


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