Types of Blow Molding Machines

There are three basic types of blow molding machines which are shown in Table 6.11. 

The details of each type of machine are very clearly described in Lees text [28] and the reader is directed to this book for additional information. 

Injection blow molding Smaller bottles, injection molded neck, no scrap 

Extrusion blow molding Most common method bottles from 0.2 liter 300 gallon Can fabricate bottles with handles 

Stretch blow molding Intermediate size bottles 0.5-2 liter 

---

Probably, each of you has your preference for a specific brand of an extrusion blow molding machine. This may be due to having exposure to specific manufacturer s brand, or based on your broad exposure to many different manufacturers equipment for your type of blow molding. 

This type of extrusion blow molding machine uses something called a shuttle machine to get all the parts in place. Alternatively, a rotary machine, illustrated in Figure 14-61, can be used. Rotary extrusion blow molders are used in high volume applications, as in the production of laundry detergent bottles. 

The above list of typical faults and their remedies show the interdependence between the parameters setup on processing machine and the selection of plasticizeifs) type(s) and concentration(s). Examples known from literature show further details of influence of plasticizers on properties of blow molded materials and on processing conditions during blow molding. 

Preference for a specific type and manufacturer of a blow-molding machine is based on experience, exposure to specific extrusion blow-molding methods, and different manufacturer equipment. 

The ram pushes the accumulated material through the die head to form the parison as a shot. This type of machine is obsolete however, there are machines of this type out in the industry still in use. The extruder or plasticizer is stationary and can continuously feed heated plastic into the accumulator. The extruder may be programmed to stop when the die is filled to a predetermined volume and then start again after the parison is extruded. The extruder speed is adjusted to fill the accumulator at the proper rate so the parison is extruded almost immediately after the blow mold has opened and the product ejected. Fig. 13.8 is a photo of an original product blow molding machine of this style of equipment. 

Blow molding accumulators take one of two forms. The separate accumulator is a heated chamber which is an integral part of the blow molding machine. The capacity of such a chamber can be very large and can, if necessary, be served by several extruders. The other type of accumulator is built into the parison head (Fig. 10.36). This takes the form of an armular ram that surrounds the mandrel and torpedo. The construction of the parison head becomes quite complicated and there is the potential for melt leakage and degradation... 

Shuttle-type blow molding machines translate their molds linearly between the pinch-off point and the blowing station. Alternatively, it is possible to mount a series of blow molds on the circumference of a wheel (either vertical or... 

FIGURE 14.30 Vertical wheel type of continuous extrusion blow molding machine molds are carried to the die head by rotation of the wheel. In a horizontal table type, all steps of the process are carried out simultaneously also. (Data from Morgan, B. T. et al.. Mod. Plast., 45, 797, September 1967.)... 

Plasticator A very important component in a melting process is the plasticator with its usual specialty designed screw and barrel used that is used in different machines (extruders, injection molding, blow molding, etc.). If the proper screw design is not used products may not meet or maximize their performance and meet their cost requirements. The hard steel shaft screws have helical flights, which rotates within a barrel to mechanically process and advance (pump) the plastic. There are general purposes and dedicated screws used. The type of screw used is dependent on the plastic material to be processed. 

In USA machinery sales yearly demand normally is about 1.5 billion (not taking into account the depressed years that occur at least every 10 to 20 years. IMM is the largest category that accounts for at least 50% of all the machinery sales. Blow molding (extrusion and injection types) machines are now at about 505 million, extrusion reaches 440 million, and thermoforming reaches 455 million. There are now over 350 USA machinery builders with about five having over 50% of sales.136 139... 

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. 

A set of bottles made on a customer s wheel-type machine showed negligible disorientation of the mica platelets. Barrier results on these samples gave the expected three-fold improvement (Table VI). Summarizing these results on platelet orientation in blow molded bottles versus related barrier enhancement (J /J ) (Table VII) shows that the same level of improvement is achieve ) as in other container processes when the platelets are aligned parallel to the container walls. 

The low melt index grades of PPE blends with PS or HIPS Noryl , Luranyl ) are most suitable for blow molding. The optimal processing conditions depend on the article type and machine and thus should be experimentally optimized. The typical temperature range for parison extrusion is 250-260°C whereas it is 230-255°C for the adapter and accumulator. HOPE should be used for purging. 

---