Mechanical Adjustable Speed Drive

There are four basic types of mechanical adjustable speed (MAS) drives belt, chain, wooden block, and traction type. The latter two are not used on extruders because they are limited to low input speeds and easily damaged by shock loads [1, 2], 

Belt drives use adjustable sheaves. The axial distance between the sheaves can be varied this changes the effective pitch at which the belt contacts the sheave. This, in turn, changes the transmission ratio. The speed is usually varied by a vernier screw mechanism, which is hand cranked or activated electrically. Belt drives are used up to 100 hp. The largest speed ratio is about 10 1, and a maximum speed is typically 4000 rpm. Belt drives have a reasonable efficiency, tolerate shock leads, and provide optimum smoothness in a mechanical drive. Disadvantages are heat generation, possibility of slippage, and relatively poor speed control. In addition, belt drives are subject to wear and, thus, are maintenance-intensive belts generally have to be replaced every 2000 hours. 

Mechanical adjustable speed drives, nowadays, are rarely used in extruders because they are maintenance intensive, have limited speed control and speed ratio, and their power efficiency is not very good. 

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The two AC drive systems used on extruders are the adjustable transmission ratio drive and the adjustable frequency drive. The adjustable transmission ratio drive can be either a mechanical adjustable speed drive or an electric friction clutch drive. 

Motor Torque, 651 Power Factor for Alternating Current, 652 Motor Selection, 653 Speed Changes, 654 Adjustable Speed Drives, 659, Mechanical Drive Steam Tmbines, 659 Standard Size Turbines, 661 Applications, 662 Mtyor Variables Affecting Turbine Selection and Operation,... 

Throttling of the suction of centrifugal and axial compressors wastes less power than throttling the discharge. Even less power is wasted by adjustment of built-in inlet guide vanes with a servomechanism which is a feedback control system in which the controlled variable is mechanical position. Speed control is a particularly effective control mode, applicable to large units that can utilize turbine or internal combustion drives control is by throttling of the supply of motive fluids, steam or fuel. 

Feed tank and metering pump the flow rate through such a pump can be controlled by a stroke adjusting mechanism or a variable speed drive acting on the stoke frequency. Control can be achieved by a fixed adjustment or through a flow meter. 

The basic principles of the tape casting process are included in most of these machines whether they are laboratory casters or production-scale models. The major components needed for tape casting include a solid, level casting surface, a drying chamber with a built-in means for controlling the airflow over the drying tape, an adjustable speed carrier drive control with a constant speed regulation mechanism, an air heater to control the temperature of the filtered feed air to the... 

Most induction ac motors are fixed-speed. However, a large number of motor applications would benefit if the motor speed could be adjusted to match process requirements. Motor speed controls are the devices which, when properly applied, can tap most of the potential energy savings in motor systems. Motor speed controls are particularly attractive in applications where there is variable fluid flow. In many centrifugal pump, fan, and compressor applications mechanical power grows roughly with the cube of the fluid flow. To move 80 percent of the nominal flow only half of the power is required. Centrifugal loads are therefore excellent candidates for motor speed control. Other loads that may benefit from the use of motor speed controls include conveyers, traction drives, winders, machine tools and robotics. 

Figure 192 represents eccentric or crank-type drives that convert rotary motion to linear, reciprocating movement. The mechanisms feature a small final rate of pressing speed (approaching bottom dead center) and high loading with low torque at maximum compression (at bottom dead center). The stroke can be adjusted on the eccentric cam or Pitman link. Normally, this method is used when force is applied from only one side and, typically, it drives the top punch. 

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