Thermoform drape

Thermoformability is a property required by the many sheet materials used in the thermoforming industry. These properties are unique for the specific forming methods used, and are best determined by actual thermoforming tests on smaU-scale equipment. The softening or drape temperature of the material, residual stress in the sheet from its manufacture, and its melt strength and viscosity are important parameters relating to this use. 

There are many methods for molding the sheet of plastic, once it has been softened by heat. The simplest are drape forming, vacuum forming, and pressure forming. Other thermoforming techniques are modifications or combinations of these basic methods. 

Drape drap [prob. back-form. fr. drapery] (1847) V. (1) With reference to plastics films and coated fabrics, their abfiity to hang without creases and to form graceful folds when used as draperies, shower curtains, and the like. (2) In sheet thermoforming, the ability of the preheated sheet to conform to the mold under the influence of gravity. 

Thermoforming Heat-softened thermoplastic sheet is placed over male or female mold. Air is evacuated from between sheet and mold, causing sheet to conform to contour of mold. There are many variations, including vacuum snapback, plug assist, drape forming, etc. 

Fig, 19 43. Thermoforming with draping. The heated sheet is drawn over the mold, creating a seal. Vacuum then is appfied, forcing the sheet against the mold, Courtesy Modern Plastics Encyclopedia. 1989 )... 

Fig. 19.44. Thermoforming with matched molds. Heated sheet may be clamped over the female mold or draped over the male mold. The mold is closed, forming the sheet between the male and female parts. Mold vents allow trapped air to escape. Courtesy Modern Plastics Encyclopedia, 1989.)...

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