Vertical extrusion

Discs use large conical-type deflectors usually mounted in the vertical downward position so that powder is deflected in a horizontal position in a 360°radius. An omega (Q) loop conveyor system normally surrounds the powder disc that is usually mounted on an oscillator or reciprocator for vertical up-and-down motion. The powder can be charged by a corona edge or by tribocharging guns. Typical applications for the powder disc are vertical extrusions or wire goods. 

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. 

Figure 14.1 illustrates the general principles of extrusion blow molding. A molten tube of polymer, known as a parison, is extruded vertically downwards from an extrusion die, as shown in Fig. 14.1 a). The two halves of the blow mold surround and then close on the... 

In the extrusion of rubber tubing, a central core determines the inside diameter. This core is supported by the spider or core-bridge which is itself fitted in the head of the extruder and may be adjusted laterally and vertically to produce a concentric tube. 

Extrusion direction vertical cutting direction vertical. Y - "Y shaped junction between microfibrils. 

A parison of variable thickness can be generated by moving the mandrel vertically during extrusion as shown in Fig. 3.58. A thinner wall not only results in material savings but also reduces the cycle time due to the shorter required cooling times. 

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. 

Extrusion is mainly by a single screw horizontal machine which changes to vertical flow via a swan neck arrangement. Air is fed to the centre of the parison. 

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