Thermoforming, part processing equipment

SB copolymers are produced via anionic polymerization by sequential addition of styrene and 1,3-butadiene monomers. These clear, tough plastics are easily processed with conditions and equipment similar to those used for HIPS. Various amounts of GPPS are usually mixed with the SB copolymers during sheet extrusion to maximize rigidity and economics in the thermoformed parts. Typical applications include drinkware, medical packaging, lids, containers, and blister packages. 

Steady state n. A condition of processes or parts of processes in which the state variables describing the process, e.g., temperature, pressure, compositions and velocities of streams, and amounts of materials residing in various process equipment, do not change with time. Most extrusion operations closely approximate the steady state except during startup and shutdown, whereas injection molding and sheet thermoforming are unsteady, intermittent processes. 

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). 

The cost of manufacturing thermoformed, polystyrene foam sheet parts is less dependent on raw material cost than other extrusion processes. This is largely due to the combined effects of additional energy costs required to operate two extruders, heat removal requirements in the secondary extruder, cost of pelletizing (densifying) regrind and the relatively low output of the process for the equipment scale and cost. Typical cost factors for the manufacture of thermoformed polystyrene foam sheet products include raw materials 35%, labor 27%, sales and administration 16%, depreciation 8%, utilities 7% and other 7%. 

As the final mold equipment for BM consists of female molds only, it is possible simply by changing machine parts or melt conditions to vary the wall thickness and the weight of the finished part. If the exact thickness required in the finished product cannot be accurately calculated in advance, this flexibility is a great advantage from the standpoint of both time and cost. With BM, it is possible to produce walls that are almost paper-thin. Such thicknesses cannot be achieved by conventional IM, but, with certain limitations, can be produced by thermoforming. Both BM and IM can be succesfully used for very thick walls. The final choice of process for a specific wall section is strongly influenced by such factors as tolerances, reentrant curved shapes, and costs. 

When not being used in conjunction with another process, like thermoforming or blow molding, profile extrusions are the variety most often used by product designers. They can be either solid or hollow and, for the most part, are made of thermoplastic materials (although thermoset materials can be extruded with special equipment). Therefore, the effect of nonuniform cooling is precisely the same for extrusion as it is for the molding processes sink and distortion. 

In the thermoforming process, the sheet is extruded either in-line or off-line and formed, either in melt phase or solid phase, into a part of desired shape. Sheet uniformity is important. Historically, iPP has not been used in conventional melt-phase thermoforming equipment because of its narrow forming temperature range and the tendency of the melt to sag. Controlling the sag is particularly important... 

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