DIE HEAD

In the tubular process a thin tube is extruded (usually in a vertically upward direction) and by blowing air through the die head the tube is inflated into a thin bubble. This is cooled, flattened out and wound up. The ratio of bubble diameter to die diameter is known as the blow-up ratio, the ratio of the haul-off rate to the natural extrusion rate is referred to as the draw-down ratio and the distance between the die and the frost line (when the extrudate becomes solidified and which can often be seen by the appearance of haziness), the freeze-line distance. 

Using a head-end unloader on each cylinder, die head-end horsepower should he reduced ... 

The pumping pressure required on the melts entering the different designed die heads differs to meet their melt flow patterns within the die cavities. The pressure usually varies as follows (1) blown and lay-flat films at 13.8-41.3 MPa (2000-6000 psi) (2) cast film, sheet, and pipe at 3.5-27.6 MPa (500-4000 psi) (3) wire coating at 10.3-55.1 MPa (1500-8000 psi), and (4) monofilament at 6.9-20.7 MPa (1000-3000 psi). 

Viscous forces within the fluid will always prevent a completely unhindered discharge, but in extrusion practice an additional die head resistance is used to generate backflow and mixing, so that a more uniform product is obtained. The flow profile along the channel is then of some intermediate form, such as that shown in Figure 8.18c. 

The machines are generally short, with an enclosed barrel with an L/D ratio of around 6 1. This barrel length is normally sufficient to create enough pressure for the non-restrictive die heads that... 

Compression of the rubber compound as it travels up the barrel is developed in the extruder by either decreasing the thread pitch but maintaining a constant root diameter, or alternatively by increasing root diameter whilst maintaining constant thread pitch. Each of these situations increases the pressure as the rubber compound travels up the barrel. The last portion of the screw prior to the die entry, however, is maintained at a constant pitch or root diameter to enable stock to stabilise in characteristics just prior to entering the die head, to ensure uniformity for extrusion through the die. Conventional extruder screws achieve a compression ratio of 2.5 1. 

A variety of extruder die heads are used to produce the different tread profiles required for the different tyre types. 

Fig. 8 Blown film line for PE-LD. 1 Extruders, 2 die head with air cooling ring, 3 sizing unit, 4 thickness measuring unit, 5 haul-off unit and collapsing boards, 6 reversing unit, 7 winder. (Reproduced with permission from Reifenhauser)...

Fig. 14.23 Typical blow molding die A, choke adjusting nut B, mandrel adjustment C, feed throat D, choke screw E, die head F, plastic melt G, die barrel H, heater band /, choke ring J, centering screw K, clamp ring L, die heater M, die N, mandrel. [Reprinted by permission from J. D. Frankland, A High Speed Blow Molding Process, Trans. Soc. Rheol., 19, 371 (1975).]...

The parison head, sometimes called the die head or simply the die, is a specialized form of tube extrusion die (Chapter 17). Its function is to deliver a straight parison in the correct diameter, length, wall thickness, and at the correct temperature for BM. Prior to being clamped in the mold, the parison is suspended unsupported in free air. To avoid undue deformation, it is necessary to extrude the parison vertically downwards. 

Figure 6.4 Simplified view of a heart shaped parison die head (left) and grooved core parison die...

Figure S.7 Introduction to a continuous extruded blow molding system with its accumulator die head...

Sequential EBM is a special multi-material technique used for the production of special designed products. The different plastics are chosen typically to contribute complementary mechanical properties and are present in distinct sequential zones in the finished part. Normally two materials are used but three or more are also used. Separate external ram accumulators for each material serve the die head. These are operated sequentially, typically in A-B-A sequence, to produce a parison with three distinct material zones in axial succession. The parison is subsequently BM by normal techniques. 

The devolatilizer (7) is held under a very high vacuum to remove unreacted monomer and solvent from the polymer melt. The monomer is distilled in the styrene recovery unit (8) and recycled back to the prepolymizer. The polymer melt is then pumped through a die head (9) to form strands, a waterbath (10) to cool the strands, a pelletizer (11) to form pellets and is screened to remove large pellets and fines. The resultant product is air-conveyed to bulk storage and packaging facilities. 

Technical data are given for the PVC foam line from the Bausano Group. Illustrations are included of the die and calibrators, door panel die heads, turbomixer, and extruder. 

FIGURE 14-9 Schematic diagram of the die head and mandrel for a single screw extruder. 

At die head of each monograph an indication is given of the classification of the compound according to its dierapeutic or commercial use or its pharmacological action. The substance may, of course, have odier uses or actions in addition to that stated. 

Names under die heading Synonyms include alternative names, common titles, and abbreviations. 

If online extraction techniques are used, calculation of die different types of recovery could be particularly challeiigiiig. Different approaches has been used in literature to overcome diis problem, such as using an external injection valve for adding die neat solntion to die extracted blank from die online extraction column just on die head of die analytical column [9,10]. Aldiotigh liquid matrix can be extracted direcdy, a solid matrix such as tissue needs to be disrupted in... 

The plastic is heated to a melted or viscous state and a section of molten polymer tubing (parison) is extruded usually downward from the die head into an open mold. The mold is closed around the parison, sealing it at one end. Compressed air is blown into the open end of the tube, expanding the viscous plastic to the walls of the cavity, thus forming the desired shape of the container. The material cools in the cavity and solidifies. The mold is opened and the molding is removed. This technique is used for the manufacture of bottles, toys, and large containers. 

MB (2007). Updated principles for risk analysis M-07-24 Memorandum for die heads of executive departments and agenices (September 19, 2007), http //www.whitehouse.gov/omb/memoranda/fy2007/ m07-24.pdf, pp. 1-13. 

---