Unicom Corp. expanded its subsidiaries with the purchase of mechanical contractor Midwest Mechanical, according to sources. The sale price was not disclosed.

The purchase of the Willowbrook, Ill.-based Midwest Mechanical "provides a foundation" to help Unicom grow in the mechanical business. Unicom, at present, does not handle the design, installation or service aspect of heating or mechanical systems.

Midwest Mechanical has an annual revenue of $45 million, and provides service to more than 1,600 customers in the Chicagoland area. Kenneth Beard, president and founder of Midwest Mechanical, will become CEO of Unicom Mechanical Services, which will be the parent company of Midwest Mechanical.

Unicom has an annual revenue of $7 billion, and owns the large electric utility Commonwealth Edison, which services 3.4 million customers in northern Illinois, according to Unicom. The company has not commented on the possibility of any further acquisitions.