KNEADING

As the kneading energy moves away from the optimum, the dough becomes wetter, it starts to stick to trough walls and its gasholding ability drops (cf. 15.4.2.5 and Fig. 15.44, 14 and 5(5). Dough development of wheat flours requires close to double the kneading time of rye flours. 

Dough mixer/ kneader Speed (rpm) Kneading time (min) Dough heat AT(°C) 

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Kneaders Kneading Kneading mixers Knecht compound Knecht method Knife mills Knight and Allen Knives Knize Ten Knockdown Knockdown resistance... 

In the calendering method, a PVC compound which contains plasticizers (qv) (60—120 phr), pigments (qv) (0—10 phr), fillers (qv) (20—60 phr), stabilizers (10—30 phr), and other additives, is kneaded with calender roUs at 150—200°C, followed by extmsion between clearance-adjusted roUs for bonding onto the substrate. This method is employed for products with thick PVC layers, ie, of 0.05—0.75 mm thickness. The main plasticizer used is di-2-ethylhexyl phthalate (DOP). For filler to reduce cost, calcium carbonate is mainly used. A woven or knit fabric made of cotton, rayon, nylon, polyester, and their blend fiber is used as substrate. For foamed vinyl-coated fabrics, the bonded materials are heated in an oven to decompose the foam-blowing... 

Another method is extmsion the PVC compound is kneaded in an extmder, and then extmded through a T-die for bonding onto a substrate. 

Fig. 2. Internieshing co-iotating twin-sciew extrudei A, motoi B, geai box C, feed poit D, clam shell baiiel E, vent poit F, sciew shafts G, conveying screws H, kneading paddles 1, baiiel valve and J, bhstei rings. Courtesy of APV Chemical Machinery Inc.

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Cera.mic, The ceramic substrate is made from a mixture of siUcon dioxide, talc, and kaolin to make the compound cordierite [12182-53-5]. Cordierite possesses a very low coefficient of thermal expansion and is thermal-shock resistant. The manufacturing process involves extmding the starting mixture (which is mixed with water and kneaded into a sort of dough) through a complex die to form the honeycomb stmcture. The extmded piece is dried and fired in a kiln to form the cordierite. The outside or circumferential dimension is formed by the die, and the length is cut later with a ceramic saw. 

Kneading Devices These are closely related to the agitated pan but differ as being primarily mixing devices with heat transfer a secondary consideration. Heat transfer is provided by jacketed construction of the main body and is effected by a coolant, hot water, or steam. These devices are applicable for the compounding of divided solids by mechanical rather than chemical action. Apphcation is largely in the pharmaceutical and food-processing industries. For a more complete description, illustrations, performance, and power requirements, refer to Sec. 19. 

FIG. 18-50 Intermeshing corotating twin screw extruder (a) drive motor, (h) gearbox, (c) feed port, (d) barrel, (e) assembled rotors, (f) vent, (g) barrel valve, (h) kneading paddles, ( ) conveying screws, (/) splined shafts, (k) blister rings, (APV Chemical Machinery, Inc.)... 

The wet pan is used for developing plasticity or molding qualities in ceramic reed materials. The abrasive and kneading actions of the mullers blend finer particles with the coarser particles as they are crushed (Greaves-Walker, Am. Refract. Jnst. Tech. Bull. 64, 1937), and this is necessary so that a high packing density can be achieved to result in strength. 

The filtered dough is then returned to a mixer and the alcohol content reduced to 25% by kneading under vacuum. Further reduction in the alcohol content is brought about by rolling the compound on a hooded two-roll mill. The milled product is then consolidated on a two-bowl calender and sheeted off in hides about j in thick. At this stage the solvent content is between 12 and 16%. 

IHtralblech, n. duralumin sheet, durch, prep, thru by, owing to, — adv. thru, durch-. thru, thru and thru, thoroly. durcharbeiten, v.t. work, work thru, finish knead (dough) elaborate (Dyeing) pole. 

Knet-gummi, n. a soft cleaning composition, art gum. -holz, Ti. plastic wood, -legienmg, /. wrought alloy, -maschine, -mUhle,/. kneading machine, malaxator masticator (Ceram.) pug mill. 

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