Extrusion Blow Molds

Designers and processors to produce products at the lowest cost have unconsciously used the basic concept of the FALLO approach. This approach makes one aware that many steps are involved to be successful, all of which must be coordinated and interrelated. It starts with the design that involves specifying the plastic, and specifying the manufacturing process. The specific process (injection, extrusion, blow molding, thermoforming, and so forth) is an important part of the overall scheme and should not be problematic. 

Fig. 3-37 Example of an extrusion blow molded container with a living hinge.

Injection Molding Extrusion Blow Molding Thermoforming Reaction Injection Molding Rotational Molding Compression and Transfer Molding Matched Mold Spray-up... 

Standard Extrusion Blow-molding 2-Parison Head 4-Fold Stretch Blow Molding PVC (2) Single-parison Heads 4-Fold Stretch Blow Molding PET... 

An unwritten rule says that a mold or die should cost almost half the cost of the basic machine (injection, extrusion, blow molding, etc.). If it does not then something is wrong such as you probably have an oversized machine for the job for the lower cost mold or die. 

Figure 14.1 illustrates the general principles of extrusion blow molding. A molten tube of polymer, known as a parison, is extruded vertically downwards from an extrusion die, as shown in Fig. 14.1 a). The two halves of the blow mold surround and then close on the... 

Figure 14.1 Schematic diagram of extrusion blow molding ...

The extrusion blow molding cycle is illustrated in Fig. 14.2. The extrusion component of the cycle is normally continuous. As soon as one length of parison has been captured by the mold, another length starts to form. To allow room for a new length of parison to emerge from the die, the mold moves aside as soon it has captured a parison and the knife has severed it. The mold is rapidly translated to a remote blowing station where inflation takes place. After the product is ejected, the open mold moves back under the die where it surrounds and captures another length of parison. 

Figure 14.2 Simplified extrusion blow molding cyde...

Describe both the extrusion blow molding and injection blow molding processes. Why would one method be chosen over the other ... 

Figure 18.11 contains a sketch of an extrusion blow-molding scheme. Here a heat-softened hollow plastic tube, or parison, is forced against the walls of the mold by air pressure. The sequence of material introduction into the mold and subsequent rejection of the material from the mold is generally rapid and automated. Approximately 1 million tons of thermoplastics are produced by this technique annually. 

Extrusion blow molding that uses an extruded tube preform or parison... 

Stretch blow molding that employs an injection molded, extrusion blow-molded preform, or extruded tube preform... 

The major difference between injection and extrusion blow molding is the way the soft hollow tube (called a preform or parison) is made. In injection blow molding, two different molds are used. One mold forms the preform and the other mold is used in the actual blow-molding operation to give the final shaped article. In the molding process, the softened material preform, from the preform mold, is introduced into the blowing mold and blow-molded to... 

FIGURE 18.11 Steps employed in simple extrusion blow molding of a test tube. From left to right mold closed softened material introduced air or other gas injected forcing the softened thermoplastic against the walls of the mold and, after suitable cooling, the mold is opened giving the molded plastic test tube. 

In continuous extrusion blow molding, the preform is continuously produced at the same rate as the article is molded, cooled, and released. To avoid interference with the preform formation, the mold-clamping step must be rapid to capture the preform and move it to the blow mold station. There are various modifications of this that allow essentially continuous operation. 

Belcher, S. 1999. Practical Extrusion Blow Molding. Dekker, New York. 

Figure 7.81 Schematic diagram of rotating mold system used in continuous extrusion blow molding. Reprinted, by permission, from A. B. Strong, Plastics Materials and Processing, 2nd ed., p. 489. Copyright 2000 by Prentice Hall, Inc.

The multilayer film is formed by injection molding, co-injection blow molding, co-injection stretch-blow molding or co-extrusion blow molding techniques. 

Processing. SAN copolymers may be processed using the conventional fabrication methods of extrusion, blow molding, injection molding, thermo forming, and casting. 

The organic cellulose ester plastics are versatile materials and can be processed by almost any hot-processing technique used for thermoplastics. The principal techniques for all three plastics are injection molding and extrusion. Blow molding is also possible. Butyrate and propionate powder are used in tluidized-bed and electrostatic coating processes, as well as in the rotational molding process. 

Practical Extrusion Blow Molding, edited by Samuel L. Belcher... 

Secondary shaping operations such as extrusion blow molding, film blowing, and fiber spinning occur immediately after the extrusion profile emerges from the die. The thermo-... 

Figure 3.56 Schematic of the extrusion blow molding process.

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