Mixer, pin

Flight width and flight clearance were 13.5 and 0.12 mm, respectively, in all sections of the screw. The extruder had a smooth-bore feed section. Three rings of pin mixers were evenly positioned in the middle portion of the metering section of the screw. All pins in a single ring had the same axial position as the type shown by Fig. 8.25. The specific rotational flow rate for the metering section was calculated at 5.0 kg/(h rpm). The compression ratio was 2.7. 

Although the full history of this screw is unknown, the mixing pins appeared to have been added to the screw after the screw failed to mix and homogenize the extrudate. Pin mixers have been retrofitted to screws for many years as a way to improve the distributive mixing for an extruder. Here the pin mixers would distribute the solid polymer fragments evenly in the extrudate, hut the mixers lacked the ability to trap and disperse them. Pin mixers were clearly the wrong type of mixer to use for this application. Instead, a dispersive mixer such as a Maddock-style mixer would be preferred see Section 8.5.1. 

Fig. 23. Screw sections for enhancing distributive mixing in single-screw extruders (a) Dul-madge mixer, (b) Saxton mixer, (c) pin mixer, (d) pineapple mixer, (e) cavity transfer mixer, (f) slotted screw flight, (g) Kenics and Ross ISG static mixers [148]...

Low-Pressure Technique — Mixing of the components is achieved by a mechanical mixer in the mixhead. More often than not, the mixing is done by rotating pins within a metal housing. Usually referred to as pin mixers, these devices spin at 2000 or more revolutions per minute. 

Figure 12.13. Pin mixers which operate at high speed for granulation of fine and aerated powders, (a) Pinmixer for the granulation of wetted fine powders, (b) Performance of a pinmixer, dimensions 0.67 m dia by 2.54 m, for pelleting a furnace oil carbon black Capes, 1980).

In the PhoSAI process of Scottish Agricultural Industries (Figure 12.1), ammonia reacts with phosphoric acid (minimum concentration 42 % P2O5) in a stirred-tank reactor to produce a slurry with an N/P ratio of 1.4 (the point of maximum solubility) under atmospheric pressure. The slurry flows to a pin mixer in which the N/P ratio is brought back to 1.0 by the addition of more concentrated phosphoric acid. During this step the solubility decreases and more water vaporizes due to the heats of reaction and crystallization. A solid product is formed that typically contains 6% to 8 % moisture. The product is screened, the oversize particles are ground and the product is sent to storage296. 

Pin mixer, see High speed shaft mixers Piston extrusion presses capacity, 115 description, 113, 114 operating characteristics, 114, 115 power requirements, 115 Piston presses... 

FIG. 21-159 Examples of horizontal high-shear mixers, (a) CB 75 horizontal pin mixer Courtesy Lodige GmbH), h) Peg granulator [Capes, Size Enlargement, 1985). 

FIG. 21-165 Two-stage continuous granulation process, consisting of high-shear nucleation (pin mixer) and moderate shear growth and consolidation (plough shear). [Mart et al.. Powder Technoh, 117,173 (2003).]... 

B.3 Turbulent mixers (Lddige- and Eirich-type mixers, pin mixers)... 

Fig. 7.39 (a) Pin mixer wirn open cover showing the built-in screw... 

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