Säkring av samtliga kritiska skruvförband i mellanstora asynkronmotorer
The purpose with this thesis is to get a compilation of all the critical bolted joints of all enginesproduced at LV Motors. ABB LV Motors produces induction engines with seven shaft heights. Eachengine size exists several variants of components ex. standard shield and flange shield. Depending onwhich components the engine is equipped with arises various types of strains in the engine's parts,certain assembly ways are more favourable than other.The most critical parts in the engine from a mechanical point of view are the screw units betweenshield/stator, feet/stator and bearing cover/shield. In order to get a overview of the engine's restrictionsa summary of all engines has been done and a calculation software been produced. The screw programhandles data from the engines and makes mechanical calculations on the screw units. The screwprogram is used to analyze the existing design and to evaluate new proposals on designs. The screwprogram has among other things shown that cost saving redesigns is possible above all in the screwunit feet/stator.There is always an uncertainty around which prestress that in reality arise in the screws whenassembly with a certain tightening moment with certain lubricate condition.Experiments of the prestressing force in the screws have shown that this becomes smaller thanexpected at tightening without lubricate. On the other hand, screws with lubrication risk to get to highprestress when operating because that more forces are added to the prestressing force.Because of locally high pressures around the screw units, a risk exists for subsidence in the colour onthe engine's components, shield, stator and feet. Subsidence can lead to loss of prestressing force.Analyzes of the colour on shields and feet?s have shown that the highest surface pressure is achievedin the surface under the screw scale, it?s also there the biggest subsidence in the colour occur. Surveyshave shown that a toothed plate connector placed between screw and feet detains the prestressrelatively well during heating of the unit.An evaluation has shown on that the painting procedure of the feet should be seen over, at present acolour thickness that is four to five times thicker than expected. A reduction of the colour thicknesswould mean smaller subsidence of the colour and possible to put right the problem with aftertightening of the foot screws.