Variable Rotor Speed

During mixing this has become commonplace for achieving the best possible quality in a single mixing pass. Control of batch temperature and batch discharge conditions are two areas where this technique is very powerful. 

This will alw s give a better dispersion of the finer particle size blacks and is used for compounding tougher 

---

Most turbines are designed to rotate at a constant speed over a specific range of wind speed conditions. The generators in these turbines produce electricity compatible with the established grid system into which electricity is fed. Operating the turbine at variable rotor speeds increases the range of wind speeds over which the turbine operates. The amount of energy produced annually is increased as well. However, sophisticated power electronics is required to convert the electricity to the gi id standard frequency. 

Rotor speed control is an integral part of the process of rate of temperature rise. The modem mixer is generally supplied with variable speed, constant torque electric motors driving via gear reducers or by a hydraulic drive system which has a motor shaft mounted tachometer to control rotor speed. Systems that can monitor, adjust and record the mixer rotor speed provide improvement in resultant compound uniformity. Changes in rotor speed within a cycle can be programmed. 

Two-stage rotors are also available for continuous mixers (Fig. 22), which incorporate a second screw section to enable down-stream feeding of additives such as heat or shear sensitive fillers, or extraction of volatiles from the mixture [147]. For a fixed rotor geometry, rotor speed, fiow rate, barrel temperature and orifice opening are the principal operational variables which control mixing intensity. 

Options for connecting the motor drive to the shaft depend on the shaft orientation. A vertical-shaft cantilever design would prefer a belt drive to reduce the cost of manufacture of the support structure and to facilitate maintenance. A horizontal shaft has the additional option of direct coupling. Variable speed can be accomplished through a gearbox or preferably through variable frequency control on the motor. In addition to the power requirements discussed previously, the startup power to overcome the torque of the rotor must be considered. This startup power is related to the time required to reach the desired rotor speed. 

The whipping process directly affects the amount of air incorporated into the matrix and therefore, variable process parameters should be selected in order to optimize foam quality and to avoid deterioration of the foam. A study by Hanselmann and Windhab (1999) showed that an increase in the rotor speed from 600 to 2000 rpm led to a decrease in bubble size and thus improved drainage stability. Lees (1991) demonstrated that at the upper limits of the beating temperature, aeration was faster and the volume of the foam increased as the temperature increased. This effect was attributed to the fact that higher temperatures lower the viscosity of the mixture and when the mixture is less viscous, more aeration is likely to occur. 

In the present study we utilized Plasticorder torque values (polymer viscosity) on a relative basis, principally to follow the course of thermoplastic polyurethane elastomer polymerization, and the effect of several relevant variables on this polymerization. These torque data, expressed in meter-grams, served our purposes well, and we have not attempted to translate them to absolute rheological units. Such translation, which is a rather complex problem, has been addressed by others using a different rotor type and other polymers in the Plasticorder.14 That study concluded that the shear rate, y, of the Brabender Plasticorder with a somewhat different rotor configuration (roller blade) is in the range of 23 - 228 sec 1 over the rotor speed range of 30 - 200 rpm. 

Variable-Speed Wind Turbines - Turbines in which the rotor speed increases and decreases with changing wind speed, producing electricity with a variable frequency. 

During the 1980 s attention turned to AC machines technology with both synchronous and induction being successfully applied. Variable speed and torque control was made possible by variable rotor resistance in the form of Wound Rotor Induction Motors and then the Cyclo Convertor which applied thyristor technology to produce low frequency ac output suitable for the driving large AC machines. 

Key features are extra mixing length and residence time, with a greatly expanded processing window. There is a variable operating LD ratio from 5 1 to 10 1, and the counter-rotating mixer has rotor speeds of up to 1000 rpm. As well as using rotor speed, fill factor and temperature as control variables, the machine also introduces the possibility of variation in clearances of the chamber wall... 

Type of hammers, rotor speed, screen type, thickness, and opening size are important variables relative to the machine. 

The TMS rheometer from Negretti is effectively a modification of the Mooney viscometer principle for use with elastomeric materials. The elastomer is introduced into a cavity containing a shearing disc by injection, and measurements of torque under fixed or variable conditions of temperature and rotor speed can be made. Effective simulation of a variety of process conditions can be made. The instrument has found particular use in the investigation of rubber-to-metal adhesion behaviour, a problem of importance to mould fouling and extrusion processing. 

Most rotor-stator devices are equipped with variable speed drives to allow operations at different rotor speeds. There is sufficient know-how about variable speed drives. However, one must pay careful attention to ... 

---