Fabrication processes blow molding

F. N. Cogswell, The Scientific Design of Fabrication Processes Blow Molding, Plast. Polym., October, (1971). 

Blow molding is a versatile conversion process used to produce a wide variety of objects by inflating a molten tube of polymer inside a hollow mold. Two major variations of the method exist extrusion blow molding and injection blow molding. The former is predominant in polyethylene molding. Common items fabricated by blow molding include bottles, drums, chemical storage tanks, and toys. 

Blow Molding. Blow mol ding is a multistep fabrication process for manufacturing hoUow symmetrical objects. The granules are melted and a parison is obtained by extmsion or by injection mol ding. The parison is then enclosed by the mold, and pressure or vacuum is appHed to force the material to assume the contour of the mold. After sufficient cooling, the object is ejected. 

The functions and property characteristics of a product will be largely determined by the performance requirements and material selected for fabrication. The basic requirement of the process is its capability of handling a suitable material. For example, if a major function requirement is for resistance to creep under high loads, it is probable that a long-fiber RP will be necessary. Thus it would immediately eliminate such processes as blow molding and conventional injection molding. 

Important are behaviors associated and interrelated with plastic materials (thermoplastics, thermosets, elastomers, reinforced plastics, etc.) and fabricating processes (extrusion, injection molding, blow molding, forming, foaming, reaction injection molding, etc.). They are presented so that the technical or non-technical reader can readily understand the interrelationships. 

Polymer scientists and engineers have developed a wide variety of processes by which to convert polypropylene into useable articles. These processes include fiber-spinning, production of melt blown and spun bond non-woven fabrics, film production, blow molding, and injection molding. The following sections describe these processes and the resulting properties of the product as a function of the process. 

Polysulfones are easily processible by other thermoplastic fabrication techniques, including extmsion, thermoforming, and blow molding. Extrusion... 

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

Polyethylene is readily fabricated by all methods of thermoplastic processing. The principal methods used are film and sheet extrusion, extrusion coating, injection molding, blow molding, pipe extrusion, wire and cable extrusion coating, rotomolding, and hot melt and powder coatings. 

Blow molding—A process used in the fabrication of plastic bottles and other hollow shapes a heated tube of plastic (a preform or parison) is forced against the sides of a mold by air pressure. 

EVOH have superior gas barrier properties.80 89 They are often used as the internal layer in multilayer food packaging films, blow molded rigid containers, gasoline tanks for automobiles for a variety of purposes, etc. EVOH can be fabricated by the usual melt processing methods. The barrier properties of films decrease in the presence of moisture, so multilayer with protective polypropylene (especially biaxially oriented material), low-density polyethylene, nylons, or other moisture barrier films provides films or products that are useful even with liquids. The... 

As explained in the previous sections of this chapter, elastomers are used to fabricate many different products to meet many different requirements (Tables 2.7 and 2.8). Practical all fabricating processes are used (such as extrusion, injection molding, blow molding, compression molding, casting, and encapsulation) are used. 

The major processing methods that process well over 80wt% of all plastics are extrusion, injection molding, and blow molding. These processes as well as a few others use a plasticator to melt plastics. It is a very important component in a melting process with its usual barrel and screw. If factors such as the proper screw design and/or barrel heat profile are not used correctly fabricated products may not meet or maximize their performance and very important not provide for low cost process. 

The injection molding with rotation (MWR) is an example of processing at lower temperatures, pressure, etc. It is also called injection spin molding or injection stretched molding. This BM process combines injection molding and IBM, as performed in IBM reviewed, except it has the additional step of with melt orientation (Dow patent). The equipment used is what is commercially available for IM except the mold is modified so that either the core pin or outside cavity rotates. The rotated melt on its preform pin is transferred to a blow mold. The end product can come directly from the I MM mold or be a result of two-stage fabrication malting a parison and BM the parison.164... 

Figure 8. I 3 Example of a suction extrusion blow molding process fabricating 3-D products (courtesy of SIG Plastics International)...

The final product may take any one of a vast multitude of final forms. These include, but are not limited to, construction materials, toys, automotive parts, kitchen aids, industrial parts, sports and recreational equipment, containers of all sizes and description, and an unlimited variety of packaging products for foods, drugs, cosmetics, and other consumer products. The processes that are used to produce or mold or fabricate the final products are also varied and depend on the design and purpose of the product. Some of these processes include extrusion, compression molding, roto-molding, blow molding, sheeting, and films. 

The term dispersion refers to how well the pigments are wetted out in the plastic matrix (see below), whereas distribution refers to the uniformity of color in the part. Finally, in referring to the parts fabrication process, the term molder is used below to represent any the following pieces of equipment injection molding machine, injection or extrusion blow molding machine, or rotational molding machine. 

Processing. SAN copolymers may be processed using die conventional fabrication mediods of extrusion, blow molding, injection molding, diennofomiing, and casting. Small amounts of additives, such as antioxidants, lubricants, and colorants, may also be used. Typical temperature profiles for injection molding and extrusion of predried SAN resins are as follows (101). 

Polyethylene is the least costly of the major synthetic polymers. It has excellent chemical resistance and can be processed in a variety of ways (blown film, pipe extrusion, blow molding, injection molding, etc.) into myriad shapes and devices. Fabrication methods will be briefly discussed in Chapter 8. 

The most suitable properties for polyethylene used in each fabrication method vary. For example, for blow molding applications, it is preferred to use FFDPE having broad or bimodal molecular weight distribution. Figures 8.4-8.6 show how the major types of polyethylene are processed. 

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