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Finite element analysis of the bullgear in an integral gear compressor
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Many industrial processes uses so-called integral gear compressors (also called integrally geared compressors or multi-shaft centrifugal compressors) to compress different gases. As the name implies, the central component of the integral gear compressor is a large gear wheel called bullgear. This bullgear carries one till four pinion shafts with overhung mounted compressor stages. The torque needed to accelerate the rotating parts of the compressor during start-up depends on the mass moment of inertia of the rotating parts and on the work done in the compressor stages. The mass moment of the bullgear contributes considerably to the total mass moment of inertia. This means that the motor size could be reduced if the mass moment of the bullgear is reduced, since a smaller torque is needed during start-up. This master thesis investigates the loading of the bullgear and how the influence of the different types of loading changes if the bullgear is made thinner. There are four types of loads: • Centrifugal load due to the rotational speed of the bullgear • Contraction stresses due to the shrink fit • Gear forces due to the driving torque • Axial thrust due to the pressure differences in the compressor stages These loads were investigated analytically and restrictions concerning stresses and displacements were stipulated. In order to investigate how thin the bullgear can be made, three cross-sections were created, each with a different thickness between rim and hub. The finite element software ANSYS was used to calculate the stresses and displacements of a unity load of all types of loads in all cross-sections. These calculations show that the axial thrust is the only critical load. If the bullgear is to thin it behaves like a rim on a soft membrane with very large axial deformations. In order to avoid this behaviour the bullgear thickness must be more than 4% of the bullgear diameter. However, this does not ensure uncritical displacements. Therefore, the displacements must be calculated for each case. It was also investigated how the eigenfrequencies change when the bullgear is made thinner and if the stresses in the bullgear influence the eigenfrequencies. In general the eigenfrequencies decrease when the bullgear thickness is decreased, but they remain clearly over the main exciting frequencies. The influence on the eigenfrequencies from the stresses must be considered to be small.

Place, publisher, year, edition, pages
2001.
Keyword [en]
Technology, bullgear, compressor, FEM, mass moment of inertia
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-55601ISRN: LTU-EX--01/315--SELocal ID: c72d07d0-f0d7-49dc-b69d-1e5ba9914798OAI: oai:DiVA.org:ltu-55601DiVA: diva2:1028985
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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