Drives And Motors

Drives system is an important part of the extrusion machine. It is very important to have the right kind of motor and drive combination that will help in saving energy and enable in improving the efficiency of the extrusion machine. Nearly 40% of the fuel consumption goes for generating electricity so as to convert the the energy into mechanical energy. 

Types of Drives 
The main types of drives that are commonly available are:

AC drive system: AC drive refers to the device used to control the speed of an AC motor. The AC drive system consist of a converter, a regulator and an inverter. In an AC driver the electrons alternates in direction as the voltage force alternates between pushing and pulling of electrons.

DC drive system: A basic DC drive controller consist of a drive controller and DC motor. In DC systems, electrons flow continually in one direction. The drive controller converts AC power to DC power. DC drive is the speed control system of the DC motors. 

Hydraulic drive system: It consist of a constant speed AC motor driving a hydraulic pump which in turn drives a hydraulic motor and the associated controls. The entire package is often referred as the hydrostatic drive.


Qualities of Drive
In the drive system alternating current or the direct current is converted into the required energy form. The main work of a drive is to maintain a constant speed of the screw throughout because the fluctuation of the screw will cause changes in the dimension of the extrudate. Thus, constancy of speed is a very important requirement of an extruder drive. The drive must supply the required amount of torque and must be able to continuously adjust from zero to maximum screw speed.

Today's motor design and construction are highly refined. A wide range of machines are available in the market that allows the operator to start, stop, and change direction and speed of the motor. Industrial drives are available in a variety of configurations and combinations. When one selects a motor one mus t ensure that the drive suits the requirement in terms of the the motor type, horse power, input voltage , etc.

Hydraulic Power Drives and Motors

A drive system that is different from the AC and DC drive, this drive does not require a transmission system. It consist of a constant speed AC motor driving a hydraulic pump which in turn drives a hydraulic motor and the associated controls. The entire package is often referred as the hydrostatic drive.

The hydraulic drive are preferred because the drive can be controlled quite well. Advanced version of hydraulic drives is being increasingly used in new and varied applications. Compared to other derives, the advantage of hydrostatic drives for extruders is the elimination of the need for a transmission between the hydraulic motor and extruder screw. The hydraulic drive in ideally suited for operations where there is are a constant requirement for stop and go motion.

Types of hydraulic drives
Hydrostatic drives are presently used in many demanding applications. At least three types of output performance are commonly available.

Variable Power, Variable torque transmissions: are based on a variable displacement pump supplying a variable displacement motor. These transmissions provide a combination of constant torque and constant power. These units are the most adjustable, most flexible and most expensive.

Constant Power, Constant variable torque transmissions: are based on a variable displacement pump supplying fluid to a fixed displacement motor under constant load. Speed is controlled by varying pump delivery. This is considered the best general-purpose drive, with wide speed range and simple controls.

Constant Power Variable Torque: transmission are based on a variable displacement pump with a power limited , driving a fixed displacement motor. Th main strength of this transmission is the efficiency.

Advantages

• Step-less adjustment of speed, torque and power,
• Smooth and controllable acceleration,
• Ability to be stalled without damage
• Easy controllability.

Drives And Motors - DC drives

DC drive system has been in use for nearly a century now, with the first drive ever to be developed being claimed to be operated on direct current. DC drive is the speed control system of the DC motors. The basic DC drive control system helps in starting, stopping, changing the direction and speed of the motor. The DC drive system which has only two main component, a converter and a regulator, is simpler is operation to the AC drive and is ideal in many operations. Another advantage is that the DC drive can be retrofitted with existing DC motors. Speed of a DC motor is directly propotionae depends on the armature voltage and field current, the DC drives helps in controlling both the two currents. Motor Speed is primarily determined by Applied Armature Voltage.Motor Torque is controlled by Armature Current (amperes). Understanding these two concepts of DC motors provides the key to understanding total drive performance. Types of DC drives: There are several types of DC drives available with various speed controls. Some of them being: Nonregenerative DC Drives - It is the most conventional type and basic type of drive that is commonly used. In the most simple form the control motor speed and the torque are in one direction. Certain additional components like the electromechanical (magnetic) armature reversing contator are provided to enhance the capability of the drive.Regenerative DC Drives - A regenerative DC drive basically consit of two coordinated DC drives integrated within a common package. Regenerative adjustable speed drives are capable of controlling not only the speed and direction of motor rotation, but also the direction of motor torque. Brushless DC Drives: A drive that is frequently being used, a brushless drive does not contain a brush. The motor contains permanent magnets, the size of the magnets determine the horse power capabilities of the motor.

Drives And Motors - AC Drives

One of the most sought after device when stable speed is required, AC drive refers to the device used to control the speed of an AC motor. AC drives converts the AC power into an adjustable frequency, adjustable voltage output for controlling motor operation. Changing the frequency is the primary function of an AC drive. The AC motor consist of two part - a stationary part called the stator and a rotational part called the rotor. The shaft part of the rotor extends outside the motor and connects the equipment to be rotated. AC drives and motors and drives are getting increasingly used with the use of the modern PMW technology solution. The two AC drive systems used on extruders are the adjustable transmission ratio drive and the adjustable frequency drive. Mechanical Adjustable Speed Drive: They are of belt, chain, wooden block and traction type. These drives are rarely used nowadays because it is maintenance intensive and provides only limited speed control. Mechanical adjustable speed drives are rarely used nowadays because they are maintenance intensive, have limited speed control, etc. The adjustable transmission ratio drive: can have either mechanical adjustable speed drive or an electric friction clutch drive. Adjustable Frequency Drive: An AC squirrel caste induction motor is connected to a solid-state power supply for providing an adjustable frequency to the AC Motor. The AC squirrel cage induction motor has several advantages in terms of low price, simplicity, low maintenance, compact construction,etc. The cost of the adjustable frequency drive is mostly determined by the solid-state power supply. Eddy Current Drive: In the extrusion industry the eddy current drive has been widely applied in the past. The continuing popularity of the drive is due to the simplicity of the drive. An eddy current drive consist of a fixed speed AC motor driving a steel drum. Inside the drum the wire is wound round a rotor. By controlling the speed of the rotor, the rotor speed can be varied. Due to the simplicity of the operation eddy currents are widely used. Advantages Dynamic response with vector operation Low maintenance and are suitable to harsh environments Dynamic response with vector operation Motor designs for extruder duty units feature high overload capabilities and very wide constant torque speed ranges. AC motors continue to be the most moving equipment for fixed speed requirements of industry. Their basic simplicity, dependability and ruggedness make AC motors the natural choice for the vast majority of industrial drive applications.