Special Dies

Some special dies are shown in Fig. 3-20 they produce interesting flow patterns and products such as tubular to flat netting dies. For a circular output, a counter-rotating mandrel and orifice have semicircular-shaped slits through which the melt flow emerges. If one part is held stationary, then a rhomboid or elongated pattern is formed if both parts rotate, then a true rhombic mesh is formed. When the slits overlap, a crossing point is formed 

Dt = Diameter of Guider Tip Dd = Diameter of Die Opening dbw Diameter of Bare Wire cW = Diameter of Coated Wire 

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In the manufacture of meltblown fabrics, a special die is used in which heated, pressurized air attenuates the molten polymer filament as it exits the orifice of the dye or nozzle (Fig. 9). Air temperatures range from 260—480°C with sonic velocity flow rates (43). 

Special dies and tools, die sets, jigs and fixtures, and Industrial molds... 

Another major type of coating process is wire covering. The tremendous demand for insulated cables in the electrical industry means that large tonnages of plastic are used in this application. Basically a bare wire, which may be heated or have its surface primed, is drawn through a special die attached... 

To achieve a compound that meets these feeding requirements, compounders form their product into small pellets. To obtain these small pellets, they use specialized dies consisting of a metal plate with many small holes through which the molten compound is forced. This part of the process is very similar to how spaghetti is formed from pasta dough. To generate small pellets, the extruded strands are chopped into small pieces by rotating blades. 

A wire crosshead die is used to manufacture wire coatings, which is illustrated in Fig. 11.10. This specialized die turns the melt flow 90° before it leaves the die. At this turn, the wire to be coated enters the melt stream and exits the die co-axially with the polymer. This process yields a seamless polymer coating around the wire. 

A strainer equipped with a special die which extrudes the strained rubber as a tube, which is then slit at the head to produce a continuous sheet, which may then be cut into slabs of convenient length. 

One approach to the study of solubility is to evaluate the time dependence of the solubilization process, such as is conducted in the dissolution testing of dosage forms [70], In this work, the amount of drug substance that becomes dissolved per unit time under standard conditions is followed. Within the accepted model for pharmaceutical dissolution, the rate-limiting step is the transport of solute away from the interfacial layer at the dissolving solid into the bulk solution. To measure the intrinsic dissolution rate of a drug, the compound is normally compressed into a special die to a condition of zero porosity. The system is immersed into the solvent reservoir, and the concentration monitored as a function of time. Use of this procedure yields a dissolution rate parameter that is intrinsic to the compound under study and that is considered an important parameter in the preformulation process. A critical evaluation of the intrinsic dissolution methodology and interpretation is available [71]. 

Zinc is used with copper and other metals to produce alloys of brass, bronze, and special die-casting alloys (e.g., copper, aluminum, nickel, and titanium). 

Freeze-Dried Samples. Solid Materials and Tissues. These are first cut into approximately 1-inch cubes, frozen on a Teflon cookie sheet in a freezer, and placed in 1200-ml. freeze-dry flasks to capacity. The flasks are attached to the freeze-dried (lyophilizer) manifold, the valves are opened to vacuum, and the flasks are evacuated. The water from the tissues is trapped on a condenser. The dry tissues (drying time about 2-3 days) are removed from the lyophilizer and compressed into thin-walled aluminum cans with a Carver Laboratory press fitted with a special die, at about 24,000 lb. pressure (total). From 150-250 grams of the dry material, representing 500-1000 grams of fresh tissue, can be packed into a single can. The cans are sealed with a hand sealer and set aside for counting. Samples can be removed from the cans at a later date for chemical analysis or beta-emitter analyses. 

In the pressed disc technique a known weight of sample is intimately ground with pure, dry potassium bromide and the mixture inserted into a special die and subjected to pressure under vacuum. The concentration of sample in the disc is usually in the region of 1.0 per cent. The disc so produced may be mounted directly in the sample beam path of the spectrophotometer and the spectrum recorded. This method has the advantage that the spectrum so produced is entirely due to the sample since pure dry potassium bromide is infrared transparent in the 2-25 /xm region. To eliminate the possibility of impurities in the potassium bromide, however, a blank disc (no sample) can be made and mounted in the reference beam path of the spectrophotometer. Care should be taken to ensure that both discs are of equal thickness otherwise inverse peaks may occur if the potassium bromide is damp or impure, and this will be particularly noticeable if the reference disc is thicker than the sample disc. 

The pellet (pressed-disk) technique depends on the fact that dry, powdered potassium bromide (or other alkali metal halides) can be compacted under pressure to form transparent disks. The sample (0.5-1.0 mg) is intimately mixed with approximately 100 mg of dry, powdered KBr. Mixing can be effected by thorough grinding in a smooth agate mortar or, more efficiently, with a small vibrating ball mill, or by lyophilization. The mixture is pressed with special dies under a pressure of 10,000-15,000 psi into a transparent disk. The quality of the spectrum depends on the intimacy of mixing and the reduction of the suspended particles to 2 gm or less. Microdisks, 0.5-1.5 mm in diameter, can be used with a beam condenser. The microdisk technique permits examination of samples as small as 1 fxg. Bands near 3448 and 1639 cm-1, resulting from moisture, frequently appear in spectra obtained by the pressed-disk technique. 

Solids. Resonance Raman spectra of solid samples can be measured using pellets such as those described previously and rotating them using the technique depicted in Fig. 2-22a. This rotating device is available commercially from Raman instrument manufacturers. A special die with... 

Extrusion granules generally occur as cylinders 0 5 10 0 mm in diameter Hollow cylinders can also be obtained with special dies... 

Monolith is now one of the most widespread form of catalysts. Monoliths are formed by extrusion through special dies creating multiple channels. (A variant in monolith manufacture uses corrugated foils of the support which are joined together to create channels). 

It is also possible to make other shapes than just cylindrical ones. By using special dies one can make cylindrical pellets with a hole in the centre, corrugated cylinders, and even spheres. 

The results are reported of a study of plate-out in PVC extrusion carried out using several analytical techniques, including DSC, SEM-EDX, FTIR spectroscopy and laser ionisation mass spectrometry. A special die and calibrator unit developed to investigate plate-out are illustrated and the reproducibility of the method evaluated. The effects of water content and anti-plate-out additives, such as alumina and silica, on plate-out are discussed and mechanisms explaining the formation of plate-out are proposed. 11 refs. 

Formerly the Chinese Rung Food, Vegetarian Zone (2949 Fifth Ave., o 619-298-7302) has taken on a more international flair. Additions such as the spinach mushroom lasagna and the mushrooms Aphrodite - fresh mushrooms stuffed with spinach, onions, walnuts and sunflower seeds - have transformed the aging eatery into something special. Die-hard Rung Food fans needn t worry entrees such as the sesame mock chicken are still on the menu. The popularity of Cafe India (3760 Sports Arena Blvd., s 619-224-7500) stems from its all-you-can-eat vegetarian lunch buffet. The buffet is served daily at this little gem near the sports arena. 

Electric resistivity. The electric resistance measurement is the same as discussed below under volume resistivity, to which this measurement is temporary adapted. For flexible materials, special electrode systems are developed to clamp sample and electric wires. The measuring equipment is based on a Wheatstone bridge circuit. The conductivity of metal powder-containing epoxy was measured in special dies equipped with built-in brass electrodes inserted to the die. The material was cured in the die to assure good contact with electrodes. Special sample holders and clamping devices are used for precise determination of rubber compounds containing carbon black. ... 

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