Patent ID: 7707778

Claim:
A frame assembly, the frame assembly comprising: a) an integrally moulded unitary one piece master frame including upper and lower horizontal master frame members, and opposed first and second vertical jamb members extending between the upper and lower horizontal master frame members; and b) an integrally moulded unitary one piece sash frame slidably mounted within the master frame, the sash frame including upper and lower horizontal sash frame members, and a pair of opposed side members extending vertically between the upper and lower horizontal sash frame members, wherein the master frame further comprises a center mullion defined by a vertical member extending contiguously from, and vertically between, the upper and lower horizontal master frame members, the mullion being integrally moulded and one piece with the master frame, the mullion having a vent side directed towards the first vertical jamb member and a fixed side directed towards the second vertical jamb member, and wherein the integrally moulded mullion, as viewed in horizontal cross-section, has a profile comprising a first U-shaped groove with an opening which faces in a direction toward a front of the master frame and a second U-shaped groove with an opening which faces in a direction opposite to the direction the opening of the first U-shaped groove faces, and the mullion being free of internal enclosed cavities to facilitate injection moulding of the master frame.