Patent ID: 6851943

Claim:
A pressure box for thermoforming a heated sheet of thermoforming material against a mold, the pressure box comprising: a top plate, side and end plates extending downwardly below the top plate, the top plate and the side and end plates defining a pressure chamber open at the bottom of the pressure box, and a resilient circumferential seal on the bottom of the pressure box, the seal extending around the pressure chamber to form a seal when the pressure box is pressed against a heated sheet for thermoforming the sheet; at least one of the said side and end plates comprising a pair of walls defining an essentially uniform width slot open at the lower end of such plate, the slot extending along the length of such plate; a resilient sealing member in the slot, the sealing member extending downwardly below the lower end of such plate to an end surface below the lower end of such plate, the end surface forming a portion of the seal, the sealing member comprising a plurality of holes; and a first connection retaining the sealing member in the slot, the first connection comprising retaining members extending from one or both of the walls into the slot, the retaining members extending through the holes in the sealing member to engage the sealing member and resist movement of the sealing member out of the slot.