Method for making stator frame for dynamoelectric machine

A method for making an integral single piece stator frame for use in a dynamoelectric machine, wherein the stator frame comprises a housing having a generally annular wall defining an axial bore and having a plurality of external longitudinally extending cooling fins integral with the annular wall, said method comprising the steps of;

• a. forming an integral single piece vaporizable pattern having a configuration substantially identical to the stator frame and being capable of vaporization when contacted by a molten metal;
• b. forming a coating on the full surface of the pattern which is gas permeable but will not vaporize when contacted by said molten metal,
• c. burying the coated pattern in sand in a manner enabling molten metal to be poured into contacting relation with the pattern,
• d. pouring a sufficient quantity of molten metal into contacting relation with the pattern so as to vaporize the pattern and fully fill the resulting void,
• e. allowing the molten metal to solidify and cool to thereby form a stator frame casting, and
• f. removing the casting from the sand, said pattern being configured to form said annular wall and said external longitudinal cooling fins so that said fins establish a ratio of effective cooling fin height over annular wall outer diameter of at least approximately 4.0, and have an effective cooling fin height over annular wall thickness ratio of at least about 200.