Molding Dry Ligno-Cellulosic Materials Above 325 Degrees C.

It was found that dry, that is, water free, sheets of various types hardboard softened to such an extent at elevated temperatures that they were easily bent and molded at temperatures exceeding 325C. Dry board samples, 2.2 millimeters thick, were heated for 5 to 30 seconds between iron platens Preheated to temperatures between 200 and 4300C. The modulus of rupture and Youngs’ modulus in bending decreased with increasing platen temperature, most abruptly in the range of 2500 to 325C. Values as low as 10 percent of those at room temperature were obtained in 15 seconds of heating at platen temperatures greater than 325C. The deflection at rupture was fairly constant below 200C. The softening of the material was found to be almost entirely reversible on cooling, providing the heating, time did not exceed 5 seconds. The addition of a low percentage of water caused a marked decrease in the temperature needed to form and bend the hardboard.

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