Helical spindle

FIGURE 1.22 Unscrewing motion, driven by the mold movement a Helical spindle b pinion c transport nut [15]... 

The Alfa-Laval contactor shown in Figure 13.41, has a vertical spindle and the rotor is fitted with concentric cylindrical inserts with helical wings forming a series of spiral... 

One of the major features in the sequence of cell division is the formation of the mitotic spindle and the subsequent separation of chromosomes into their respective daughter cells. An important element of the spindle is the highly conserved, helical molecule tubulin. In addition to spindle formation and the segregation of chromosomes in cell division, alternating helices of a- and -tubulin form the microtubules that form part of the cytoskeleton and have active roles in cell organelle organisation. 

Two Brookfield viscometers were used to collect the data necessary for rheologic property studies of wet grains a Brookfield RVDV III viscometer with a cone-and-plate spindle and a Brookfield HBDV III viscometer with a double helical ribbon impeller attachment. The Brookfield RVDV III had a full-scale torque of 7187 dyn-cm, and the HBDV III had a full-scale torque of 57,496 dyn-cm. Each viscometer had a maximum rotational speed of 250 rpm. Both viscometers had accuracy limits of 5% full-scale torque. 

Microtubule filaments are hollow cylinders made of the protein tubulin. The wall of the microtubule is made up of a helical array of alternating a- and 13-tubulin subunits. The mitotic spindle involved in separating the chromosomes during cell division is made of microtubules. Colchicine inhibits microtubule formation, whereas the anticancer agent, taxol, stabilizes microtubules and interferes with mitosis. 

Figure 13.15. Inhibition of mitosis by vincristine, a The mitotic spindle consists of tubulin fibers, which are helical polymers of a,P tubulin dimers, b Structure of vincristine, an inhibitor of tubulin polymerization, c Mode of action of vincristine. The drug binds to an a,P dimer. These dimers retain the ability to associate with growing filaments however, the further attachment of dimers is inhibited. At high concentrations, vincristin-associated tubulin is also sequestrated within mis-assembled polymers.

A class of motile systems completely different from and unrelated to the actin-myosin contractile systems is used in cellular structures as diverse as the mitotic spindle, protozoan and sperm flagella, and nerve axons. These systems are constructed from microtubules, very long, tubular structures built from a helical wrapping of the protein tubulin (Figure 8.19). There are two kinds of tubulin subunits, oi and each of molecular weight 55,000. They are present in equimolar quantities in the microtubule, which can be considered a helical array of ot-/i dimers. Alternatively, we can view the microtubule as consisting of 13 rows, or protofilaments, of alternating ot and subunits. Because the oi and b units are asymmetrical proteins, with a defined and reproducible orientation in the fiber, the microtubule has a definite sense of direction. 

Microtubules are systems of very long tubular structures built from a helical wrapping of tubulin (Figure 8.19). Tubulin is involved in motility within cells, such as in the mitotic spindle, flagella, and nerve axons. Tubulin is composed of two subunits, ot and each of molecular weight 55,000. They are present in equimolar amounts in tubulin as dimers. 

The primary classes of FW are hoop, polar, and helical. The simplest is hoop or circumferential winding, in which fibers are wound approximately normal to the mandrel axis of rotation with the fiber payout head advancing one band width for each revolution of the spindle. Hoop winding is usually combined with helical winding in more complex parts. Polar or tumble machines are used for parts wound using a planar winding path (such as for a short closed-end pressure vessel). These machines normally have the mandrel mounted vertically, over which a rotating arm wraps fiber onto the mandrel. 

The majority part of the interior of the fiber mass is the cortex, which, from the point of view of mechanical properties, is also the most important component. The cortex consists of elongated, spindle-shaped cells aligned in the direction of the fiber axis. Within these cells resides the major part of the keratinized protein in the form of macrofibrils, which in turn are formed by lower levels of organization, i.e., microfibrils and finally protofibrils. The latter two are low-sulfur proteins and more or less crystalline in nature with their a-helical parts as crystalline lattice components. They are embedded in a noncrystalline, nonfibrillar matrix of disulfide cross-linked, globular proteins. 

Planetary roller extruders (PRE) have been used for many years in the compounding of temperature sensitive polymers and rubber compounding [57-64]. PREs are comprised of long helically geared components comprising a driven central shaft, freely rotating planetary spindles and a stationary, temperature-controlled outer cylinder, all of which must closely intermesh. The planetary spindles are located between the central shaft and the outer cylinder. To illustrate this relationship. Fig. 12.43 shows... 

Figure 12.43 Cross-sectional view of a planetary roller extruder from US Pat. 4,192,617 showing reiationship of the helically geared rotating central spindle, planetary spindles, and the outer cylinder.

Figure 12.46 Pictures of three planetary spindle types, fully flighted, spindles with open sections and helically back cut spindles. Fig. 12.20 Rubber the tailor made material, on the occasion of the extrusion seminar held at the DIK in Hannover on 24.03.2003 by Dipl.-Ing. Harald Rust, ENTEX Rust Mitschke GmbH, Bochum. http //www.entex.de/fileadmin/user upload/2003 Elasto-meraufbereitung engl.pdf...

Two main types of viscosity tests are performed on solder paste. The first method utilizes a T shaped spindle that is spun inside a container of paste in a helical path. The T spindle viscometer is also known as a Brookfield viscometer. The bar is rotated at 5 20 revolutions per minute (RPM) in 5 RPM increments. The viscosity is recorded at each speed for several minutes. The bar moves up and down in the Z axis (perpendicular to the surface of the paste sample jar) as the bar rotates. The helical path ensures the paste is shear thinned excessively by the bar during the viscosity test. 

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