Internal mixer, efficiency

Table 2 Melt Stabilizing Efficiency of Antioxidants in PP (processed in an internal mixer at 190°C). Melt flow index (MFI) Measured at 230 C and 2.16 Kg...

With unidirectional shear, the efficiency of mixing, as expressed by instantaneous stretching starts with zero when the interfacial area element is perpendicular to the direction of shear, it reaches a maximum value at 45°, and from that point on it begins to diminish, making the mixing less and less efficient. Frequent reorientation is therefore desirable, as is the case with random chaotic mixing, which occurs in typical internal mixers and some continuous mixers. 

Before introduction of the intensive internal mixers, the mixing was accomplished on open mills — a slow, dirty process requiring skilled operators. An efficient, counter rotating twin shaft internal mixer with elhptical rotating discs was... 

Compounds may also be mixed on open mills, but this takes considerably more time, batch weights are lower, and it is thus less efficient than use of internal mixers. 

Mechanical mixing of polymers carried out on either an open mill or in a Banbury internal mixer has advantages in efficiency, productivity, and lower cost. However, natural rubber in many instances must first undergo an initial breakdown. 

The undiluted silane is added directly to the polymer before or together with the filler. It is essential that the resin does not prematurely react with the silane as otherwise the coupling efficiency will be reduced. Typical compounding equipment consists of internal mixers, kneaders, Banbury mixers, two-roll mills, or extruders. The integral blend technique is widely used in resin/filler systems because of its great simplicity and possible cost advantages. This is mainly due to the one-step process and the lower raw material costs (untreated mineral plus silane compared to pretreated mineral) despite the fact that more silane is needed to achieve comparable performance in the finished composite. 

Blending and mixing are important unit operations in the polymer blend industry. Hancock patented the first internal mixer in 1923. Freyburger in 1876 improved the device to a more efficient counter-rotating twin-shaft machine. The Banbury mixer is a modification of this patent. The Parrel Co. introduced two-roll mills, then the Ram extruder surfaced in 1797. Screw machines that were capable of manufacturing... 

By far the most common technique for mixing NR with polar synthetic elastomers is melt blending. Equipment such as open mills, internal mixers and extruders supports dispersive mixing. Also, the relatively high viscosity that appears after mixing prevents phase separation and promotes efficient... 

Mixing. The oldest processing operation is mixing. The first patent on an internal mixer, an annular container with a spiked rotor, was granted to T. Hancock in 1823. A more efficient, coimter rotating twin shaft internal mixer was patented by Freyburger in 1876, and its modified versions by P. Pfleiderer [1882] and B. F. Banbvuy [1916]. The two-roll mill was invented by E. M. Chaffe [1836], and manufactured by Farrel Foundry and Machine Co. 

Against all expectations considering compatibility difficulties, simple dry mixing of azo polystyrene in an internal mixer at 100-120 C gave almost quantitative grafting (based on functionality) as assessed by gel permeation analysis. This was for polyisoprene or purified NR commercial grades of NR gave a few percent lower efficiency due to the reaction of the azo function with non-rubbers. 

As a tangential rotor type mixer, a Werner and Pfleiderer GK-2 internal mixer was used with a chamber volume of 3150 cm. The mixer was operated at a fill factor of 76%, the optimum with regard to mixing efficiency for such a type mixer. Rotor speeds of 46 and 50 rpm were used, running at a friction factor of 1.1. A ram pressure of 5 bars (maximum oil pressure on the plunger of the ram) and a wall temperature of 40°C held constant throughout the mixing cycle. 

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