Screw drive

The distinguishing feature of this dryer is the bottom-screw drive, as opposed to a top-drive unit, thus ehminating any mechanical drive components inside the vessel. The bottom-driven screw rotates about its own axis (speeds up to 100 rpm) and around the interior of the vessel (speeds up to 0.4 rpm). The screw is cantilevered in the vessel and requires no additional support (even in vessel sizes up to 20 m operating volume). The dryer is available in a variety of materials of construction, including SS 304 and 316, as well as Hastelloy. 

Product discharge Mixer screw drive unit... 

To increase shot size upsizing the plasticator can be made. A number of items have to be considered for the upsizing process, such as barrel wall thickness, resultant screw L/D, injection speed reduction, screw drive torque, and injection pressure drop. Before considering the upsizing process, one has to determine whether the output can be met properly using the decreased pressure and speeds that occur. The pressure and speeds will decrease directly proportional to the difference in the barrel ID projected areas. If this poses no problems, the L/D and structural integrity of the barrel have to be considered before proceeding. 

Design of experiments methodology was used to determine the maximum variability in viscosity which a poly(vinyl chloride)/wood fibre profile extrusion process was able to tolerate. Fourteen critical dimensions, profile bow, shrinkage, Young s modulus, and stress and strain under maximum load were measured. Quadratic models were created from the dimensional measurements, bow, maximum tensile stress, pressure in the die adaptor and the current drawn by the screw drive, and used to establish the tolerances within which the dimensional and physical specifications were simultaneously achieved. 

Extrusion (dry heat) cookers have been ideal for stabihzation because excess moisture is not added, eliminating the need for drying. The heating of the bran occurs through conversion of mechanical energy of the screw drive to heat the bran. Temperatures used for stabilization vary from 100° to 140°C. The bran is kept hot for 3-5 minutes after extrusion to ensure lipase inactivation. The hot bran is then cooled using ambient air. 

The sweep device rests on the edges of the trough and is used to clean the surface before the experiment and to compress the film once it is formed. For accurate work, it is preferable that the sweep is attached to support rods (as shown in Fig. 46) which can be moved along the trough by means of a screw drive. It is usually necessary to place the film balance inside an air thermostat, with provision for operation from the outside. 

Other developments have not been as dramatic, but they have nevertheless contributed significantly to the process efficiency. The electric screw drives were replaced by hydraulic motors with a gear box on the reciprocating screw unit. In the future the hydraulic motor may in turn be replaced by a direct hydraulic drive (19). The Introduction of stack molds has also increased productivity. In a stack mold, two cavity plates are placed on top of each other so that the projected area is the same and twice as many parts can be formed with the same clamping tonnage. This technique works best with thin wall, flat parts with short cycle times. 

Available screw drive seal designs include posurve lip seals, single acting mechanical, or double acting mechanical. All seals dry running. 

Extruders are also used in the production of sintered industrial parts. Of special importance is their application for the manufacture of catalyst carriers (Section 6.3.2, Figs. 6.3-20 and 6.3-21). The use of wear-resistant alloys for all parts that come in contact with the material to be extruded make the extruders suitable for the processing of highly abrasive catalysts, other chemicals, and minerals, such as molecular sieves, high-purity aluminas, and kaolin carriers. Interchangeable die plates allow the extrusion of an almost unlimited variety of sizes and shapes on the same basic machine that is then equipped with a variable-speed screw-drive to adjust retention time, pressure, and production rate. 

After the sample capillary tube is in position, the furnace platform, C is raised so that the tube is positioned into the aluminum heat transfer sleeve, located on the sample thermojunction. Movement of the furnace platform is controlled by a reversible electric motor connected to the platform by a screw drive. Upper and lower limits of travel are controlled by two microswitches. The furnace is insulated from the platform by a 0.25-in. layer of transite and, while in the heating position, by a Marinite sleeve, E. The rotation interval for sample changing is 15 sec, while it takes 50 sec to raise the furnace platform to the full upper limit. 

The following table shows some thermal properties of three thermoplastic polymers. Compute the screw output for each polymer material if the screw drive power input is 60 hp and the mechanical efficiency is 75%. Assume that the heat requirement for molding the materials is satisfied by the viscous dissipation... 

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