Spiral mandrel die

Tq eliminate spiders in the die and the inherent film weakness, the spiral mandrel die is used (Figure 17.11). This design usually is computer calculated since the flows and pressure drops are complicated. 

Processing can use spider dies, spiral mandrel dies, or basket-type dies that support the inner mandrel with a perforated sleeve through which the melt flows. Figure 17.12 provides examples of different die designs. 

Several types of blown film dies are available, varying in cost, complexity, and purpose. Side fed, bottom fed, and spiral mandrel dies are used for producing monolayer films. 

Figure 3.5 Spiral mandrel die produces excellent melt quality...

On the other hand, a spiral mandrel manifold creates flow in the helical direction, resulting in some degree in circumferential orientation. This combined with the near absence of weld lines make spiral mandrel dies capable of producing a tube or pipe with better mechanical properties simply by modifying the flow inside the die. 

The most common die used in blown film extrusion is the spiral mandrel die. In this die, the polymer is divided into a number of spiraling channels with the depth of the channels reducing in the direction of flow. The popularity of the spiral mandrel die is due to its relatively low pressure requirement and its excellent melt distribution characteristics. Spiral mandrel dies can be used with a wide range of materials over a wide range of operating conditions. 

The distribution characteristics of conventional crosshead dies may not be good enough for application in blown film extrusion, where wall thicknesses are generally quite small (the typical range is 0.005 mm to 0.25 mm). Spiral mandrel dies can achieve good flow distribution and largely eliminate weld lines. As a result, spiral mandrel dies are widely used in blown film extrusion. 

Rauwendaal [41] used the following assumptions to analyze the flow in the spiral mandrel die ... 

The residence time in the die can be increased by reducing the flow rate (extruder throughput) or by changing the die geometry. The flow splitter has to be located as far away from the die exit as possible. Some die geometries reduce weld line problems. For instance, spiral mandrel dies for pipe, tubing, and blown film spread out... 

In the blown sheet extrusion process, after leaving the extmder, gear pump and screen pack, the resin moves to a circular spiral mandrel die in which a tube of molten material is formed and inflated with air from the inside. The tube is then lifted in a haul-off tower up to 40 m high where it is cooled by an internal and external flow of cool air. It then proceeds to... 

Even though spiral mandrel dies are primarily used in blown film, they have obvious advantages in tubing and pipe extrusion. Both tube and pipe are often... 

Spiral-Mandrel Die n The most popular die design for extrusion of blown film, in which the melt, fed into a manifold at the bottom of the die, flows up to the die lip via multiple spiral grooves. The design is capable of handling a range of resins, provides even distribution to the lip, thus helping to minimize circumferential variations in film thickness, and has relatively low pressure drop. 

Spiral mandrel die - Central feed -Star-shaped melt distribution - Radial boreholes - Spiral channels... 

FIGURE 7.37 Two spiral mandrel die designs. (Reprinted with permission of the publisher from Michaeli, 1984.)... 

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