Blow molding stripping

Parison cooling significantly impacts the cycle time only when the final parison thickness is large. In thin blown articles the mold is opened when the pinched-off parts have solidified so that they can be easily stripped off thus they are the rate-controlling element in the cooling process. For fast blow molding of even very thin articles, the crystallization rate must be fast. For this reason, HDPF, which crystallizes rapidly, is ideally suited for blow molding, as are amorphous polymers that do not crystallize at all. 

First station usually has multiple preform injection molds where preforms are formed over core pins. The preforms have hemispherical closed ends (resembles a laboratory test tube). The other ends have an open bore, formed by the core pin. External details, such as the thread and neck flange for a screw-top container, are directly produced by injection molding. While the preform is still hot, the injection split mold is opened and the preforms, still on the core pins, are rotated to the blowing station two. Here the preforms are enclosed within the blow mold, and introducing blowing air through the core pins followed with cooling produces the BM. Blow molds opened and the finished products, still on the core pins, are rotated to an ejection station where they are stripped off mechanically and/or air. 

Injection and blow molded products based on inhibited PE and PP produced by the Northern Instruments Corp. (USA) have become world standard for anticorrosion plastic containers. Similar plastic products modified by VCI are manufactured by the German companies Rose Plastic and Brangs and Meinrich [20]. Another original sort of inner packages for small diameter metal tubes is a tube strip. Tube strips are extruded PE tubings inserted into metal tubes to protect their interior surfaces from corrosion [21]. 

Geometry or shape also has a major impact on process selection. Unless a part has a continuous cross-section, it would not be extruded unless it were relatively thin waUed and bottle shaped, it would not be blow molded. Again, calendering is restricted to flat sheet or strip designs, and the use of inserts is restricted to the molding processes. 

In injection blow molding, the parison is injected into a preform cavity and around a core pin in the exact quantity required to form a container. The preform mold is kept at a precisely controlled temperature, which is just a little cooler than the melt temperature. After injection, the mold opens, and the core pin and the still warm preform are rotated 120°. A blow mold then closes over the preform, and air is injected through the core pin. After the container is blown, it is rapidly cooled by contact with the walls of the blow mold, which are kept at around 102-122°C by cold air or fluid circulating through the mold passageway. The mold then opens, a second 120° rotation occurs, and the part is stripped from the core pin. Then a third 120° rotation of the transfer head returns the core pin to the preform injection mold, and the cycle is repeated. 

It should be noted that the properties of oriented films show considerable dependence on the processing conditions (e.g., biaxially oriented films are obtained by blow molding, while extrusion produces uniaxially oriented films). This is important because the mechanical properties of oriented specimens are considerably different in the flow and transverse directions of the films as shown hi Fig. 4.22 (measurements were done by a traditional tensile tester). When the film samples in the form of strips are prepared for TMA measurements, the strips should always be cut from the same orientation (Menczel et al. 1997). When preparing such samples, film widths of >2 mm are recommended in order to minimize edge effects. 

P Dow Chemical Specimen Notched thin strips, blow molding grade... 

Different foundry casting techniques are used. Included are plastic-based binders mixed with sand. Various types of molds and cores are produced that include no-bake or cold-box, hot-box, shell, and oven-cured. Usual binders are phenolic, furan, and thermoset polyester. There is the foundry shell casting, also called dry-mix casting. It is a type of process used in the foundry industry, in which a mixture of sand and plastic (phenolic, thermoset polyester, etc.) is placed on to a preheated metal pattern (producing half a mold) causing the plastic to flow and build a thin shell over the pattern. Liquid plastic pre-coated sand is also used. After a short cure time at high temperature, the mold is stripped from its pattern and combined with a similar half produced by the same technique. Finished mold is then ready to receive the molten metal. Blowing a liquid plastic/sand mix in a core-box also produces shell molds. 

Polymer materials in the form of powder or pellets are fed to screw extruder in which they are heated into a homogeneous melt. The melt is forced through a die. The die forms the polymeric melt into a pari-son shaped as a cylindrical tube. Compressed air is introduced into the parison by a blow pin at the top. The air pressure forces the parison to conform to the inner shape of the mold. Indirect cooling water that passes inside the mold halves solidifies the blown melt into its final product shape. When the part has sufficiently cooled to hold the desired shape, the mold halves open and the part is stripped from the mold. 

Methylene chloride is used in many paint and varnish stripping formulations, as a solvent for cold cleaning of metal parts, as an extraction solvent for heat sensitive substances, as an extraction media for pharmaceutical products, as a solvent to clean polyurethane molding equipment, as an auxiliary blowing agent for flexible polyurethane foam, and as a solvent in the manufacture of... 

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