Apparatus for forming modular building structures

An expandable form for hollow core castings comprising:

• a pair of spaced substantially parallelly arranged vertically positioned side members forming platens one on each side of a longitudinal axis,
• a second frame member coaxially aligned with said platens and comprising at least one pair of spaced vertically positioned legs one on each side of said longitudinal axis and a top laterally positioned on the top of said legs,
• each of said legs being attached to and supported by the juxtapositioned platen in one position and pivotally movable relative to the platen to another position,
• actuating means mounted to extend between said platens and said legs of the associated juxtapositioned frame member,
• the side edges of said top cooperating with the top edges of said platens to form corner openings,
• a plurality of inside corner forming members pivotally mounted on and extending along the top edges of said platens, and
• means connected to said corner forming members for pivoting said corner forming members into said corner openings to close said corner openings and to pivot said corner forming members away from said corner openings previous to actuation of said actuating means,
• said actuating means when energized moving said platens inwardly toward each other and said top downwardly to collapse the expandable form,
• said inside corner forming members each comprising a flexible filler piece having plane surfaces which extend laterally to each other to form the corners between the juxtapositioned edges of said top and the top edges of the associated platens,
• said flexible filler piece comprising a mass split into two pieces along its center line to a point adjacent the intersection of said planar surfaces, and
• said split being increased in size when said corner forming member is extended and positioned in said corner opening to completely close said opening.