Parison tooling

This technique is also called nonaxisym-metric blow molding. In conventional EBM the parison enters the mold rather in a straight tube. In 3-D BM the parison is laid or oriented in the mold prior to closing. It is manipulated in the tool cavity providing complex geometric products that can have... 

Blow-molding processes consists of five main operations plastication of the resin, formation of the parison, inflation of the parison, solidification of the part, and removal of the part from the tooling. The best process economics will occur with a part optimized for weight and a minimum cycle time. In order to have a minimum cycle time, the cooling operation must be the rate-limiting step. For the case study... 

The location of the nozzle should also be carefully planed because the different flow velocity in various areas within the cavity can appear as flow lines. The extrusion blow molding process with the accumulator unit can also be the reason for flow lines. Usually the incoming melt is separated by the ram, which causes a flow line in the back. This can sometimes be moved to the parting line of the tool, where it becomes almost invisible. In cases where this is not feasible, it may be possible to create a spiral action (turbulence) when filling the accumulator system. The resulting flow patterns are then mixed as they exit, creating the parison. 

Rough parison orange peel Melt fracture melt temperature too low Polish all tooling Raise melt temperature... 

Holes in parison and/or bottles Contaiminated or degraded resin Trapped air Moisture in resin Purge and clean tooling and screw Let extruder run for a few minutes Dry the resin... 

Handle missing Insufficient die swell Position parison closer to handle Use larger tooling... 

The pressure is reduced further to P3 to maintain intimate contact between the glass and the tooling as the parison stabilizes (plnnger contact)... 

Extrusion blow molding uses a section of hot extruded tubular material called a parison. This is extruded into an open mold, and compressed air or steam forces the walls of the parison to the sides of a cold mold. The process is commonly used to make bottles, industrial containers, medical items, technical parts, and toys. Blow molding has a low tool and die cost, and parts can be made very rapidly and in one piece. It also can be used to produce relatively complex shapes, although limited to hollow or tubular parts. The wall thickness is difQcult to control. Continuous tubing and film can be made in a manner similar to blow molding. 

Aluminum, steel, or beryllium-copper is used for the bottle cavity and neck ring. For polyolefin resins, aluminum No. 7075, as well as QC-7, is used. The surface is usually finished with No. 120-grit sandblast, which increases the venting of trapped air. For rigid resins, A-2 tool steel air-hardened to 52-54 HRC is used. The surface finish is highly polished with chromium plating. Cast beryllium-copper is often used for minute detail. As with the parison cavity, water lines are drilled as closely together as possible, perpendicular to the cavity axis. 

A growing trend in extrusion blow molding is to coextrude parisons that contain up to seven layers of different materials. However, as of this time, coextrusion is limited to machines that only use one (1) parison as on a wheel and the continuous-type machine. Since the different materials combine in the head tooling (see Fig. 35), the use of manifolds for multiple cavity is not feasible, nor are accumulator machines (see Coextrusion). 

The parison will continue to extrude until it reaches the base of the mould. At this point the mould will close and the parison will be cut above the mould with a hot knife. The mould is now moved away from the parison, taking the cut off slice of parison closed in the mould with it. The next parison continues to extrude. The inflation of the parison can now commence. A blow pin comes down into the top of the mould and blows air in to inflate the hot parison against the sides of the mould (Figure 6.13). The mould is cooled with water this aids heat removal to help solidify the newly formed article. The blow pin is removed and the tool opens to eject the part. The mould can then return to collect the next parison and start a new moulding cycle. 

In extrusion blow moulding of bottles, for the bottle to be sealed the parison must weld at the seam. The parison is pressed together by the blow moulding tool, creating a weld line as shown in Figure 6.16. 

Tooling for injection blow molding consists of injection molding die set, injection molding manifold, parison injection molds, blow mold die set, blow molds, neck rings, core rods, face bars, end plates for the parison injection molds, secondary nozzles for the injection manifold, stripper bar, and retractable bottom plugs for the blow molds if the bottle push up exceeds 0.045 in. in depth. 

The tooling costs are obviously greater than for extrusion blow moulding since two moulds are required for each article produced. Cycle times, too, tend to be higher because of the transfer time for moving the parison from one mould to another. 

Numerical simulations on the parison formation can minimize machine setup times and tooling costs. Several research teams modeled the parison formation stage to predict the parison dimensions [1-6]. The results showed that the finite-element-based numerical simulation method can predict the parison dimensions with certain precision. Huang et al. [7, 8] utilized the artifieial neural networks (ANN) method to predict the diameter and thickness swell of the parison and showed that the ANN method can predict the parison dimensions with a high degree of precision. However, the parison formation simulations and... 

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