Traction thickeners

The traction thickener includes a traction mechanism where the movement of the rake is suppHed by a single long arm pivoted around the center column and driven by a troUey that moves on a peripheral rail around the basin. Such units have diameters of 60—130 m. 

Traction Thickeners These thickeners are most adaptable to tanks larger than 60 m (200 ft) in diameter. Maintenance generally is less difficult than with other types of thickeners, which is an advantage... 

Tracheobronchitis effect on heart, 5 107 Trachoma, 74 338 Tracking resistance testing, 79 587 Traction, 3 726-727 Traction thickener, 22 65 Trade... 

Design Features There are three classes of thickeners, each differentiated by its drive mechanism (1) bridge-supported, (2) center-column supported, and (3) traction drives. The diameter of the tank will range from 2 to 150 m (6.5 to 492 ft), and the support structure often is related to the size required. These classes are described in detail in the subsection Components and Accessories for Sedimentation Units. ... 

Circular Clarifiers Circular units are available in the same three basic types as single-compartment thickeners bridge, center-column, and peripheral-traction. Because of economic considerations, the bridge-supported type is limited generally to tanks less than 20 m in diameter. 

Figure 10.11. Types of thickener and clarifier (a) Bridge supported (up to <40 m dia.) (b) Centre column supported (<30 m dia.) (c) Traction driven (<60 m dia.)...

Figure 17.3 Airway obstruction, (a) Normal, patent airway with radial traction offered to it by surrounding airways. Resistance in this airway is low and air flows through it freely, (b) The airway is obstructed by the presence of excess mucus and airway resistance is increased. Airflow is reduced, (c) Thickening of the airway wall due to inflammation or edema narrows the lumen of the airway. The decrease in airway radius increases airway resistance and decreases airflow, (d) Destruction of surrounding airways results in the loss of interdependence, or radial traction. Without the structural support offered by surrounding airways, the central airway collapses and airflow through it is reduced.

Thickeners may vary from a few metres to several hundred metres in diameter. Small ones are made of wood or metal and the rakes rotate at about 0.02 Hz (1 rpm). Very large thickeners generally consist of large concrete tanks, and the stirrers and rakes are driven by means of traction motors which drive on a rail running round the whole circumference the speed of rotation may be as low as 0.002 Hz (0.1 rpm). 

Under the action of the craze traction cr, the craze thickens a bit further by the elastic stretch of the craze fibrils. If E is the effective averaged craze lentil modulus in the fibril direction, the final shape h(x) of the craze lentil under full traction becomes... 

Motivated by the Kramer and Berger [3] description of the crazing process, Tijssens et al. [9] proposed a viscoplastic crazing model within the fiamework of a cohesive zone methodology. The traction-separation law proposed in [9] comprises three parts corresponding to initiation, thickening and breakdown of the craze. 

Drive-Support Structures There are three basic drive mechanisms. These are (1) the bridge-supported mechanism, (2) the center-column-supported mechanism, and (3) the traction-drive thickener containing a center-column-supported mechanism with the driving arm attached to a motorized carriage at the tank periphery. 

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