Vacuum forming, thermoplastic sheet

Equipment differs with sheet thickness. There are generally three groups of machines—the general-purpose for drape and vacuum forming the sheet-fed machine which is usually a shuttle or rotary type, and the roll-fed machine for thin sheet (0.07 in.). It is doubtful if the roll-type machine would be used with reinforced thermoplastics. 

Noryl. Noryl engineering thermoplastics are polymer blends formed by melt-blending DMPPO and HIPS or other polymers such as nylon with proprietary stabilizers, flame retardants, impact modifiers, and other additives (69). Because the mbber characteristics that are required for optimum performance in DMPPO—polystyrene blends are not the same as for polystyrene alone, most of the HIPS that is used in DMPPO blends is designed specifically for this use (70). Noryl is produced as sheet and for vacuum forming, but by far the greatest use is in pellets for injection mol ding. 

The rigidi d thermoplastic sheet - Tiocess combines thermoplastic sheet vacuum forming with a spray-up or cold press molding process to add a thermoset composite stmctural backing to a decorative thermoplastic skin. Large parts such as bathtubs, hot tubs, recreation vehicle components, and camper tops have been produced by this process. 

Table 2.17 analyses some examples of the relative processing cost versus the annual production in units. The various technologies listed are not suitable for all materials or parts machining is used with numerous materials rotational moulding uses liquid resins vacuum forming uses thermoplastic sheets blow moulding uses special grades of thermoplastics... 

In drape forming, the thermoplastic sheet is clamped and heated and the assembly then sealed over a male mold. The mold may be forced into the sheet or the sheet may be pulled into the mold by introduction of a vacuum between the sealed sheet and mold. By draping the sheet over the mold, the part of the sheet touching the mold remains close to the original thickness. Foamed PS and polyolefins are generally used in this procedure. 

Thermoforming has close similarities with vacuum forming, except that greater use is made of air pressure and plug assisted forming of the softened sheet. The process is invariably automated and faster cycle times are achieved than in the vacuum forming process. Only thermoplastic sheet can be processed by this method. 

In vacuum forming, the thermoplastic sheet can be clamped or simply held against the RIM of a mold and then heated until it becomes soft. The soft sheet is then sealed at the RIM, and the air from the mold cavity is removed by a suction pump so that the sheet is forced to take the contours of the mold by the atmospheric pressure above the sheet (Figure 2.39a). The vacuum in the mold cavity is maintained until the part cools and becomes rigid. 

In the thermoforming process, heat and pressure are applied to thermoplastic sheets which are placed over moulds to adopt their shapes (Figure 3.35). Pressure can be applied using air, compression or vacuum (vacuum forming). Compression is a low cost process because the moulds used are inexpensive and automation allows a production cycle of less than 2 seconds. Details are... 

Vacuum forming A manufacturing technique for thermoplastic polymer in which a sheet is heated and formed over a mold while a vacuum is present under the sheet. 

Polyethersulphone is a true thermoplastic and can be processed by all the traditional techniques we associate with thermoplastics. These include Injection moulding, blow moulding, extrusion of rod and sheet, and vacuum forming sheet into con lex shapes. PES requires slightly higher processing temperatures than those needed for most other thermoplastics but these temperatures are well within the capabilities of most modern screw... 

Vacuum forming (straight vacuum forming) n. Process in which heated thermoplastic sheets are converted to other configurations by causing them to flow into molds with apphcation of a vacuum. The simplest, original technique of sheet thermoforming. 

Mold release agents are used in a variety of applications, including fiber-reinforced plastics, castings, polyurethane foams and elastomers, injection-molded thermoplastics, vacuum-formed sheets, and extruded profiles. Because each application has its own plastic, mold material, cycle time, temperature, and final product use, there is no universal... 

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. 

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