Extmsion blow molding

Blends of PET and HDPE have been suggested to exploit the availability of these clean recycled polymers. The blends could combine the inherent chemical resistance of HDPE with the processing characteristics of PET. Since the two polymers are mutually immiscible, about 5% compatibilizer must be added to the molten mixture (41). The properties of polymer blends containing 80—90% PET/20—10% HDPE have been reported (42). Use of 5—15% compatbilizer produces polymers more suitable for extmsion blow molding than pure PET. 

Grivory. [EMS-Am. Grilon] Amorphous nylon used for extmsion, blow molding, inj. molding, blending with other resins. 

There are four different blow molding processes extmsion blow molding, injection blow molding, stretch blow molding and the less frequent dip blow molding. 

Extmsion blow molding can be semi-continu-ous, with a continuously rotating screw, extmd-... 

The blow-up ratio of 4 1 for extmsion blow-molded bottles or parts is considered a maximum. This applies overall and to separate sections as well. For example, bottle handles that are deeper than they are wide across the mold-parting face are difficult to mold and are often thin and weak. 

Figure 7-52. This diesel tmck surge fuel tank (left), next to a stainless-steel tank, was extmsion blow molded of glass-fiber-reinforced Du Pont Zytel nylon. The stainless-steel tank cost more and required welding and assembly. The weight went from 10 to 4 lbs. with the RP nylon. A new comigated wall design also minimizes deflection, resists harsh under-the-hood temperatures and solvents, and has other advantages.

Starch-based polymers can be produced from potato, com, wheat, cassava, or tapioca. In the United States and Europe, com starch is the predominate source for starch-based polymers. Corn starch is mostly used for animal feed. Starch-based polymers can be processed on traditional thermoplastic forming operations of injection molding, extmsion, blow molding, compression molding, rotational molding, etc. Starch can be made from corn or vegetable oils and other renewable sources. The most common plasticizers for starch are water and glycerol. 

Extmsion blow molding Hollow bodies (i.e., bottle)... 

Variation of wall thickness has a direct impact on the way in which rotationally molded parts are dimensioned. Since the wall section may vary and in many cases cannot accurately be predicted before a part is made, the part must be dimensioned to an external feature. If an internal dimension is required, then allowances for the upper tolerance of wall thickness variation must be made. Designers used to specifying injection molded parts with controlled surfaces both inside and outside of the part can find this difficult to deal with. However, extmsion blow-molding and twin sheet thermoforming share the same limitations and rotational molding actually maintains more uniform wall thicknesses than either one of these competitive processes. 

Figure 12 Principal steps of extmsion blow molding, (a) Parison extrusion (b) encapsulation of parison (c) insertion of blowing needle (d) inflation and eooling (e) ejection.

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