Four classification characteristics of hollow blow molding

Author: MULAN - Plastic Molding Manufacturer

Hollow blow molding is to place the semi-molten plastic parison obtained by extrusion or injection molding into various shapes of molding molds, close the mold, and blow it into the parison with compressed air so that it is in contact with the mold wall. Bonding, demoulding after cooling and shaping to obtain hollow products. It can be used to produce plastic bottles for edible oil, wine, beverages, condiments, milk and other food packaging, and various hollow products such as round, square, special-shaped and handle barrels and cans. Hollow blow molding is to put the plastic parison in the plastic state into the mold, inject compressed air into the parison, blow it up, make it close to the wall of the cavity, and obtain a hollow plastic part of a certain shape after cooling and shaping processing method. According to different molding methods, it can be divided into four forms. 1. Extrusion blow molding 1—Extruder head 2—blow mold 3—Tubular parison 4—Compressed air blowpipe 5—Plastic parts First, the extruder extrudes the tubular parison; cut off a section of the tube blank and put it into the mold while it is hot, and clamp the upper and lower ends of the parison while closing the split mold; Then pass compressed air into the mold cavity to inflate the parison and attach it to the surface wall of the mold cavity; Finally, after maintaining the pressure, cooling and shaping, the compressed air can be removed and the mold can be opened to take out the plastic parts. The extrusion blow molding mold has simple structure, low investment and easy operation, and is suitable for hollow blow molding of various plastics. The disadvantage of extrusion blow molding is that the wall thickness is not easy to be uniform, and the plastic parts need to be post-processed to remove flash. 2. Injection blow molding 1—Injection machine nozzle 2—Injection parison 3—Hollow punch (core) 4—heater 5—Blow mold 6—Plastic parts Firstly, use an injection mold to make a hollow bottomed parison on the injection machine; Then move the core together with the parison into the blow mold, the core is hollow and has micro holes on the wall; Then close the mold and pass compressed air from the pipe of the mandrel to inflate the parison and attach it to the surface wall of the cavity of the mold; Finally, after maintaining the pressure, cooling and shaping, the compressed air can be removed and the mold can be opened to take out the plastic parts. The advantage of injection blow molding is that the wall thickness of the plastic part is uniform without flash, and no post-processing is required. Since the injection parison has a bottom, there is no stitching seam at the bottom of the plastic part, which has high strength and high production efficiency, but the investment in equipment and molds is relatively large, and it is mostly used for mass production of small plastic parts. 3. Injection stretch blow molding 1—Injection machine nozzle 2—Injection mold 3—Drawing Mandrel (Blowpipe) 4—blow mold 5—Plastic parts Injection stretch blow molding is a processing method in which the injection-molded bottomed parison is heated to an appropriate temperature below the melting point and then placed in the mold, first stretched axially with a stretch rod and then blown into compressed air. . The transparency, impact strength, surface hardness, stiffness and gas barrier properties of the stretch-blow molded parts are greatly improved. The most typical product of injection stretch blow molding is a linear polyester beverage bottle. Injection stretch blow molding can be divided into two molding methods: hot billet method and cold billet method. First, the hollow parison with bottom is injection molded; the parison is moved to the stretching and blowing station for stretching and blow molding; after pressure maintaining and cooling, the mold is opened and the plastic part is taken out. This molding method saves energy by eliminating the reheating of the cold parison. At the same time, the preparation of the parison and the stretch blow molding are carried out on the same equipment, which occupies a small area, and the production is easy to carry out continuously and has a high degree of automation. Cold billet injection stretch blow molding is a molding method in which the injected parison is heated to a suitable temperature and then placed in a blow mold for stretch blow molding. When the cold billet molding method is used, the injection of the parison and the stretch blow molding of the plastic part are carried out on different equipment. Before stretch blow molding, in order to compensate for the heat dissipated by the cooling of the parison, secondary heating is required to ensure the stretch blow molding of the parison. 4. Sheet blow moldingSheet blow molding reheats the calendered or extruded sheet to soften it, put it into the cavity, and inject compressed air between the sheets after mold closing to form a hollow plastic part.