Vad är ”rätt” gjutkvalitet? Hur uppnås det?

Sammanfattning

Ever since ABB has begun diecasting their rotors instead of permanent mold casting it,

variation in the quality of the cast has arisen. Diecasting is performed in three different

machines, M1, M2, M3 with 400, 660 respectively 800 tons of die locking pressures.

The aim of this thesis is to answer the following questions:

What is the ”right” cast quality? How is the right quality achieved?

For sizes 160-180 solutions will be proposed that consider eccentricity between the

laminate and the short circuit ring as well as elimination of the thin Al film that appears

on the outer periphery of the rotors.

Through considering the statistic material the most often diverging rotor type has been

identified and one of the actual rotors has been sent to a laboratory to be analyzed in

order to establish the current defects. The result of the analysis shows that there are

plenty of gas- and oxide-porosity.

It has been proved that every time the dies temperature decreased below 120

°C the

content of gas porosity increased. It is due to rapid solidification of metal that flows

through the ”cold” laminate.

It has confirmed that enhanced porosity in squirrel cage causes high impedance in the

rotors. In order to solve these defects keeping the die temperature above 120

°C has

been suggested. Through better production practices such as arming operators with

thermometer or pre warming the laminates has been proposed.

Analysis of the eccentricity has shown that it mostly is caused by wear, insufficient

maintenance of machines and dies and inexperienced operators. By doing some

reparation the eccentricity has been reduced to an acceptable level but keeping this level

of quality requires a lot more.

Aluminum film on outer periphery is caused by a too large die chamber; wear on the

dies guiding taps and insufficient adjustment of first injection phase. In order to solve

these defects it has been suggested to reduce the diameter of die chambers after more

studying of other subsystems that could have influence combined with more frequent

control of guide taps and better adjustment of the first injection phase.