Thermoplastics thermoforming

TPEs permit thermoplastic fabrication methods not feasible for thermoset rubbers. These methods include blow molding, coextrusion with rigid thermoplastics, thermoforming, heat welding, and film blowing. 

DR Fitchmun. Thermoplastic Thermoformable Composite Material and Method of Forming Such Material. U.S. Patent 5604020, February 18, 1997. 

Precharge preheating If the precharge is preheated to a temperature just below the resin gel point before it is placed into the mold, the process cycle time can be reduced. Also, this method is generally employed for the thermoplastic thermoforming process. 

Nylon. Nylon is the designation for a family of thermoplastic polyamide materials which in film form are moderate-oxygen barriers. The gas-barrier properties are equal to odor and flavor barrier properties important in food appHcations. Nylon films are usually tough and thermoform able, but are only fain moisture barriers (see Polyamides). 

Thermoforming and Extrusion. Improved equipment and polymers have increased the capabiUty to extmde and thermoform polypropylene however, consumption of polypropylene in these areas has not grown dramatically. Drinking straws are commonly extmded from polypropylene, however most larger diameter tubes, such as pipes and conduits, are predominantly extmded from other thermoplastics. Extmded sheet is thermoformed into food containers and trays polypropylene is used when microwavabiUty is desired. 

Polysulfones are easily processible by other thermoplastic fabrication techniques, including extmsion, thermoforming, and blow mol ding. Extmsion... 

AH forms and compositions of reinforcements, ie, mats, woven roving, glass, carbon, and aramid, are commonly used with these processes. Special continuous glass strand mats with a thermoplastic binder aHow preforms to be made using thermoforming techniques. These processes are used for tmck and autobody components, medical equipment cabinets, transportation seating, and other parts needed in the intermediate volume range (1,000—10,000 parts/yr). 

This material is a tme amorphous thermoplastic with a T of 185°C and can be made into thermoforming composite with 20—40 wt % glass fiber (see... 

Engineering thermoplastics have also been used ia preimpregaated coastmctioas. The thermoplastic is thoroughly dispersed as a coatiauous phase ia glass, other resias, carboa fibers (qv), or other reinforcement. Articles can be produced from these constmctions usiag thermoforming techaiques. For example, the aerospace iadustry uses polyetheretherketoae (PEEK) ia wovea carboa-fiber tapes (26). Experimental uses of other composite coastmctioas have beea reported (27) (see also Composite materials, polymer-matrix). 

Provided due care is taken with respect to predrying and to crazing tendencies, polycarbonates may also be thermoformed, used for fluidised bed coating and machined and cemented. Like metals, but unlike most thermoplastics, polycarbonates may be cold formed by punching and cold rolling. Cold rolling can in fact improve the impact resistance of the resin. 

If a thermoplastic sheet is softened by heat and then pressure is applied to one of the sides so as to generate a freely blown surface, it will be found that the shape so formed has a uniform thickness. If this was the case during thermoforming, then a simple volume balance between the original sheet and the final shape could provide the wall thickness of the end product. 

Replacing PVC with PP allows compliance with environmental standards in some pharmaceutical markets. These materials are cold formed instead of being thermoformed. Such packages require more packaging materials than thermoplastic plastic films for the packaging of the same number and same size of tablets or capsules. 

Processing and Application. Polystyrene and the other thermoplastics would not have been able to enter on their triumphal march if the manufacturers of processing equipment had not been able to provide efficient fabrication methods. A decisive factor was that between 1950 and 1960 the injection molding machine with a screw preplasticizer was developed and extrusion through slit dies to give sheeting or film followed by thermoforming was evolved. 

The shaping of the core thermoset and metal cores are generally machinable only. The linear thermoplastic foams are thermoformable. 

Thermoforming consists of applying a thermoplastic sheet softened by heat onto the walls of a mould to shape it (see Figure 5.29). 

The following rules are some of the basic ones and are not sufficient to optimize the design, which must be discussed with the producer of the chosen thermoplastic and the thermoformer. These rules can be modified according to the actual problems. 

Development of a glossy, aesthetic and unpainted roof module on the Smart Roadster by DaimlerChrysler AG s Smart. The two-piece, removable roof, built by ArvinMeritor, is surfaced with a thermoformable three-layer film (Lexan by GE Plastics) that can be co-moulded with either thermoplastic or thermoset substrates. The film exhibits 95% gloss retention after the equivalent of 10 years of Florida sun exposure. Weight saving is 50% versus a painted steel roof system. 

Another non-paint approach is being developed by Mayco and DaimlerChrysler Corp, consisting of the extrusion of a glossy, coloured film. After thermoforming to the part shape, it is placed in an injection mould, and thermoplastic is injected behind it. Cost savings are estimated to be 5 to 12 per fascia. 

Although some molding techniques are adaptable to the production of thermoset materials, thermoforming is carried out using thermoplastic materials. 

Molding employs a mobile prepolymer that may be thermoset or using a thermoplastic polymer. The polymer can be injection-molded (often for solid objects), blow-molded (for hollow objects such as bottles), rotation-molded, compression-molded, transfer-molded, or thermoformed. Casting is closely related to molding, except that the pressure is typically not used. 

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