The state of the art compounding technology of intermeshing intermixers ensures more homogeneous mixing compound as comparison to conventional kneader technology and open mills most Indian Rubber Companies have in house.
The production is totally computerized and automated including chemical weighing ensuring the consistency in compound properties in and between batches. Material flow is automated to a high degree too. The major part of the raw materials is transferred to hoppers at delivery. The material is weighed and transported directly to the kneader computer-controlled. Other raw materials, e.g. rubber, are weighed at the mixer. Mixing Mills are having stock Blenders as standard for heterogeneous compounding and Batch Off to ensure the online cooling and maturation.
Significance of Master Batch & Final Batch in Rubber Compounding
Rubber compound consists of a Polymer (selected for the specific properties), Activator, Process Aid, Anti Oxidants, Anti Ozonants, Flow Promoters, Reinforcing Fillers, Extenders, Plasticizers, Resins, Accelerators & curatives.
A good rubber compound is one in which all the ingredients are very well dispersed. All the above mentioned ingredients are dispersed well with low shear stress and in a short time except Reinforcing fillers like Carbon Black and Precipitated silica which require a higher energy in terms of higher shear stress for a longer time. This is due to the small particle size and large surface area and high Structure.
In order to effect High Shear Stress, low shear strain and shorter Mixing Cycles, Internal Mixers are used to produce large volumes of well dispersed Master batches in short time.
Master batches are made in order to get good dispersion of Fillers in the rubber compound.
Since the heat generated during the internal mixing is very high, the dumping temperature is also very high, close to125*C to 150*C. Since this dump temperature is above the threshold temperature of "Activation" of the accelerators, the Master batch is always mixed with out Accelerators and curatives. The master batches are sheeted out and cooled to room temperature and allowed to mature for 24 Hours.
The Final Batch is prepared by mixing the Accelerators and the Curatives with The Master batch on a KNEADER along with TWO ROLL MIXING Mill (provided with a stock blender) and good cooling arrangement for the Rolls. After the initial band formation on the rolls, The Compound stock is passed over the blender rolls and reversed and rolled until thorough distribution is achieved. The purpose of mixing the Accelerators & Curative on a Mill is to get even DISTRIBUTION of the chemicals which is possible only in a mixing mill which gives a low shear Stress and high Shear rate.
Summary: A good Rubber compound is made in two stages: 1. Master batch 2. Final Batch.