Rotary Screw Compressor Analysis

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5. ROTARY SCREW COMPRESSOR The compressors used in APCW, Ultra Tech Cements Limited are single stage, oil-flooded, water cooled rotary screw compressors. 5.1. Screw compression Process The rotary screw compressor draws air in between the lobes and then inter lobular space is sealed and volume is reduced and then sent to outlet. Position 1: As the lobe-flute pair unmeshes, the air inlet is uncovered and air at atmospheric pressure is drawn into the space between lobe-flute pair. Position 2: As the rotation continues, the inter-lobular space is sealed off from air inlet and compression continues. Position 3: The compression continues as lobe-flute pair moves from one end to another end by reducing the volume of air. Position 4: As the lobe-flute…show more content…
Housing to mount bearings to seal rotors off from atmosphere 4. A driving mechanism to obtain rotor speed 5.2.1. Rotor set The rotor set has a male rotor and a female rotor. The male rotor has four helical lobes which are 90 degrees apart and female rotor has six helical flutes 60 degrees apart. The male rotor is driven by the motor and female is meshed with male. For meshing the male has to rotate 1.5 times faster than female. The asymmetrical rotor profile is used for rotors. In symmetric profile, the lobe of male rotor perfectly fits flute freely but shallowly. Asymmetric profile fits male lobe more deeply into female flute than symmetric profiles. The advantages of asymmetric profile are 1. Smaller blow-hole between rotors leads to lower internal losses resulting in higher efficiency. 2. Higher capacity for same size rotors and same rpm as profile is cut more deeply. 3. Ability of rotors to withstand rotor contact without problems for oil injected screws, due to small relative motion between the rotors where contact occurs. This means we do not need timing gears. 5.2.2. Rotor…show more content…
Bearings The bearings used to carry the rotors are anti-friction bearings. Anti-friction bearings have many advantages over slide bearings. These bearings have small mechanical losses, high reliability etc. These bearings are necessary to absorb axial forces pushing rotors away from each other because of pressure difference between inlet and outlet ends and radial forces are caused by compressed air trying to force the rotors apart from each other. Also in case if gear, the radial forces on rotor on which the gear is installed is to be considered. There are two types of bearings used in compressors. They are 1. Angular contact ball bearings 2. Roller bearings 5.2.4. Housings Rotor Housing: The rotor housing is where compression actually takes place. Air enters the housing via an axial inlet, to prevent oil to splash in the system. The intake valve is mounted on the top of rotor housing. Compressed air is discharged through a discharge port at the bottom of the

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