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(Patent #4,752,136)
The Pulsar® screw is a low shear distributive mixing device that is machined near the discharge end of a plasticating screw. The feeding and pumping mechanism of the Pulsar is the same as a single flighted screw; however, the melting and mixing effects are superior to a single flighted design without a mixer.
The Pulsar assists in the melting phase by having a portion of the mixer at a shallower root depth, thus delivering a degree of increased shear and melting capability. Even though there is an increase in the localized shear rate with this design, the deep channel controls shear stress, cools the polymer and delivers a more homogenous melt.
The homogenizing effect is accomplished by the wavy root action of the design that delivers a change in velocity, a sliding movement and tumbling when it goes from the deep section to shallow sections. This distribution delivers a more uniform, homogenized melt with minimal temperature differential. The more uniform the polymer, the more consistent the viscosity and hence the potential for consistent repeatable flow through the die or into the mold. The more repeatable the flow, the greater the molecular orientation which determines the physical properties of the molded component.
Application
The Pulsar® design is Spirex’s answer to the processing of all thermoplastic materials when designed with a medium compression ratio. For processing crystalline materials such as PA, PE, LCP, PP etc., a high compression design should be used. For processing amorphous materials such as ABS, PC, PMMA, Rigid PVC and sensitive blends, a low compression design is best.
Advantages
- Low melt temperature
- Low fiber breakage
- No marbling
- Strong weld lines
- Less back pressure required
- Quick color and material changes
Rating
When compared to a single stage, general purpose screw with similar root geometry, the Pulsar® screw delivers a mixing quality of 3-4 times better. | |
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