Spinning at High Speeds

As the spinning speed is increased, the effect of air drag and inertial forces on the total stress value of the spinline increases substantially. Many studies have modeled the highspeed spinning process of various polymers to explain the spinline dynamics [14-19]. 

TABLE 203 Effect of Spinning Parameters on the Structure of the As-Spun Fibers at Low Spinning Speeds 

Parameter Effect on Spinning Stress Effect on Filament Temperature Time Spent in Spinning Line Fiber Orientation Fiber Crystallinity Remarks 

At higher spinning speeds, the initial drop in the apparent viscosity is higher and faster, followed by even faster rise after the stress-induced crystallization takes place. The freeze point is achieved soon after this strain-hardening phenomenon takes place. In contrast, no such changes in apparent viscosity are seen at low spinning speeds. 

As the filaments are spun above the critical speeds, that is, above the stresses that induce crystallization, their temperature profile is also likely to change significantly. At the region of the neck where stress-induced crystallization takes place, the temperature of the filament rises due to the heat liberated by the crystallization process. This may reduce the apparent viscosity by a small amount. However, since the stress-induced crystallization locks the structure of the spun material, further deformation does not take place and the orientation of the crystalline region is not lost even at this higher temperature. However, the orientation in the amorphous region may be lost to some extent. 

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The other is the Eclipse reusable capsule-based device marketed to date by Sanofi-aventis (France) in Japan and Scandinavia. It contains up to four capsules at a time, loaded body first into the four chambers of the device. Eclipse uses a single blade to cut off the dome of the capsule body when the patient twists the device. Above the capsule, there is a vortex chamber in which a ball starts rotating as the patient inhales. The ball spins at high speed during inhalation, helping to disperse the powder into inhalable particles. 

This is the basic concept of Magic Angle Spinning NMR the sample is placed in a rotor, spinning at high speed around an axis at 54,7° to the axis of the applied magnetic field. 

The size and shape of macromolecules in solution can be studied using two techniques termed equilibrium and velocity ultracentrifugation. These techniques use an ultracentrifuge to rotate solutions of macromolecules and place them under a centrifugal force to study their physical properties. The size and shape of the macromolecules can then be determined from the solution physical properties. The ultracentrifuge is equipped for direct measurement of the solution as it spins at high speed. 

For mixing operations which require the continuous production of finely dispersed solids, emulsions, stable foams, etc., the in-line dynamic mixer in one of its several forms could be used. These usually consist of a rotor which spins at high speed inside a casing and the feed materials are pumped continuously to the unit. Inside the casing the fluid is subjected to extremely high shear forces which are required for the dispersing operation, see Figure 7.10. 

The electrons surround the nucleus like clouds, spinning at high speeds on then-paths called orbitals. They have the same electrical charge as protons, but have the opposite sign, namely negative. 

Domestic equipment should not be overlooked for examples of active enhancement. The domestic washing machine spins at high speed to enhance water ranoval, while the novel Dyson machine also agitates the load, to enhance contact between the clothes and cleaning medium. 

Spin Welding. Spin welding is an efficient technique for joining circular surfaces of similar materials. The matching surfaces are rotated at high speed relative to each other and then brought into contact. Frictional heat melts the interface and, when motion is stopped, the weld is allowed to soHdify under pressure. 

Ziabicki and Jericki reported the crystallization characteristics of PET as well as a theory of molecular orientation and oriented crystallization [5a], Besides these theoretical considerations, the rate of recrystallization understandably seems to play an important role, particularly in high-speed spinning. Little is known about the crystallinity gradient caused during melt spinning at high take-up speeds. 

A cyclone collector is another type of dry collector and is in the form of an inverted cone, but with no box. The incoming air containing contaminants is passed into the cone where it is spun at high speed. The spinning causes the solids to settle out to the periphery and fall into the apex of the cone for removal. Because of the relative densities, it is most effective with larger coarse particles, and not useful for fine particles. 

Figure 28-7 Shatterbox laboratory mill spins a puck and ring inside a container at high speed to grind up to 100 mL of sample to a fine powder. [Courtesy Spex Industries, Edison, NJJ...

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