Blow molding needle-blowing

In principle, the gas-assisted injection molding process is similar to co-injection molding. Here, the second or core component is nitrogen, which is injected through a needle into the polymer melt, blowing the melt out of the way and depositing it against the mold surfaces. 

The type of molding machine available has an important influence upon the blow opening system used. Some machines, for instance, use needle blowing exclusively. Hollow needle insertion at the mold parting line is considered when a very small opening is required that may even need closing or if the hollow object must be blown up on the side, e.g., on carousels with a series of molds. 

Beilstein Handbook Reference) AI3-02247 BRN 1912251 Dimethyl 1,3-benzenedi-carboxylate Dimethyl isophthalate Dimethyl m-phthalate Dimethylester kyseliny isoftalove EINECS 215-951-9 HSDB 6138 Isophthalic acid dimethyl ester Methyl 3-(carbomethoxy)benzoate Methyl isophthalate Morflex 1129 NSC 15313 Uniplex 270. Chemical intermediate in the synthesis of polyesters. Used as a plasticizer, modifies clarity and melting point of PET resins used in films, blow-molded bottles, and similar products. Needles mp = 67.5° bp = 282° d = 1.194 Xm = 280, 288 nm (MeOH) slightly soluble in H2O, Morfiex Unitex. 

In extrusion blow molding, homogeneous melted thermoplastic resin is extruded as a tube into the air. This tube, called a parison, is captured between two mold halves that are of the female type. Gas usually air, enters as the female molds are closed, either through a blow pin or needle, and expands the homogeneous melted thermoplastic into the female mold halves, taking design of whatever is cut into the two female mold halves, alllowed to cool, then the gas is exhausted, the molds... 

Blow needles are usually used when the article does not have a large opening such as in toys or flat products (e.g., blown cardboard boxes with a needle diameter of 5 mm) and when the blowing area is not allowed to be in the mold parting plane (Figure 1.145 and Figure 1.146). 

FIGURE 1.146 Blow mold twister board with blow needle... 

The blowing air can be introduced in a variety of ways. In the simplest case, the parison is extruded downwards so that the open end slips over a blow pin. Alternatively, the blow pin can be introduced from above the mold after the parison is severed, or blow needles can be built into the mold, where they pierce the parison as the mold closes. 

Many blow molded articles do not have an integral aperture that can accept a blow pin. In such cases, blowing air can be supplied through a blow needle that punctures the parison wall after the mold closes (Fig. 10.45). The needle can be advanced and retracted by means of an air or hydraulic cylinder and is located at a point close to a pinch-off edge. The parison is gripped... 

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.

Figure 17 Wheel type of blow molding process, (a) Eneapsulation of parison (b) insertion of blowing needle (e) inflation and cooling (d) ejection.

In extrusion blow molding, molten resin is extruded into a cylindrical shape called a parison. This parison hangs downward, and then two mold halves close around it. At the top and the bottom of the mold, the cylindrical shape is pinched together, leaving a hollow tube in the middle. A needle is inserted into this tube, and pressurized air is injected into tube, forcing the walls of the tube to stretch and expand outward, until they conform to the mold. Once the material cools and solidifies, the mold is opened and the part is removed. 

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