Process for continuously producing shaped articles of polystyrene foam

In the known process for the continuous production of a foam product wherein preliminarily expanded beads of polystyrene are formed into a confined moving mass, moving the confined mass of the beads through a heating zone wherein the mass is directly heated with steam so as to cause said mass of beads to reexpand and adhere together, the improvement which comprises:

• a. enveloping the moving mass of the preliminarily expanded beads of polystyrene so as to cover the top, bottom and lateral side surfaces thereof with at least one steam permeable cloth belt having a sufficient width to form overlapping parts of the cloth belt around the exterior surface of the mass of beads,
• b. causing said mass of beads enveloped in steam permeable cloth belt to move through a pressurized steam heating zone which is provided with a pressure sealing zone on both the inlet and the outlet openings thereof,
• c. applying mechanical pressure to said enveloped mass of beads at a point adjacent to the inlet of said pressurized steam heating zone so as to prevent the mass of beads in said envelope from flowing backwards through the enveloping cloth belt,
• d. retaining the enveloped mass of beads in said pressurized steam heating zone for a long enough time to cause reexpansion of the mass of beads,
• e. reducing the reexpanded volume of the mass of beads prior to leaving the pressurized steam heating zone so as to secure the mutual firm adhesion of the beads and to achieve a definite shape for the foamed mass leaving the pressurized steam heating zone,
• f. applying mechanical pressure to the enveloped foamed mass at a point adjacent to the outlet of the pressure sealing zone so as to minimize the leakage of steam from said pressurized steam heating zone,
• g. cooling the enveloped foamed mass, and
• h. separating the enveloping cloth belt from the foamed mass and recovering as a final product a foamed mass of polystyrene.