Preform-drawing process

Figure 14. Schematic rod drawing process from quartz preforms. A large diameter siiica preform rod (1) is heated in a circumferentiai heater, i.e., a gas burner, an eiectncal furnace or laser source. (2) the molten jet solidifies and the resulting quartz filament (3) is passed over a sizing device (4) and collected on a winding dmm (5). Redrawn from M. S. Aslanova, Glass fibers, page 34, Khimia Publisher (in Russian), Moscow (1979).

A battery spool has been produced by fiber drawing technique [11], where copper and aluminum wires (electrodes) were inserted in fiber preform made from polyethylene that is shaped inside to contain electrolyte and the electrodes. These were assembled in continuous process and heat set, like in the fiber drawing process to form the battery. 

Prior to extrusion the fused silica preform is usually treated with dilute hydrofluoric acid to remove any imperfections and deformations present on the inner and outer surfaces and then rinsed with distilled water and followed by annealing (55). In a cleanroom atmosphere, the preform is vertically drawn through a furnace maintained at approximately 2000°C. Guidance and careful control of the drawing process is achieved by focusing an infrared laser beam down the middle of the capillary in conjunction with feedback control electronic circuitry in order to maintain nniformity in the specifications of the inner and outer diameters in the final prodnct. 

The preform-drawing method is a batch process where a polymeric preform is fabricated first, which is then followed by thermal drawing of the preform into the fiber. A schematic diagram of the process is shown in Figure 5.1. In this method, a cylindrical polymer rod consisting of a core and cladding layers, usually prepared by radical polymerization in bulk under a clean environment, is positioned vertically in the middle of the furnace where its lower portion is heated locally to the drawing temperature. The furnace temperature appropriate for the preform is... 

There are many methods to measure the RIP of the preform and the fiber. However, the RIP might be changed by the heat-drawing process, but some fabrication methods, such as coextrusion, can produce optical fibers directly from raw materials, not via preforms (see Chapter 5). In addition, we are interested in the final RIP of the fiber and not in the RIP of the preform during fabrication. Thus, this section focuses on measurements of the RIP of the fiber. 

Special optical fibres can also be produced by a modified jacketing method [270]. A tapered glass preform is produced by suction casting of the core material into a tube made of the cladding material. This initial preform is then drawn off and loosely joined to circular positioned outer tube glasses to form a secondary preform, which is used for the fibre drawing process. This method allows the production of multi-layer fibres with large refractive index steps. 

Gospodinov and Yarin [178] used an one-dimensional model to describe the drawing of microcapillaries based on hollow cylindrical preforms. Fitt et al. [149] used a model based on an asymptotic analysis of the Navier-Stokes equations to model the drawing process of hollow fibres. 

Channel plates have been manufactured from a preform consisting of a bundle of tubes [547]. Channel plates with various geometries were produced using a multi-step drawing process combined with various confectioning steps. 

Fig. 11. OVD process (a) soot deposition, (b) soot perform cross section, (c) preform sintering, and (d) fiber drawing.

From the wealth of observations on catalyst preformation and catalyst aging reported in the literature it is extremely difficult to draw definitive conclusions about the nature of the reactions which occur during this process step. Nevertheless, it is rather evident that contrary to metallocene catalysts, the majority of Nd-based catalyst systems do not exhibit the features of single site catalysts (SSC). As bimodal and multimodal MMDs are observed for Nd-based catalyst systems various active species (or active sites) are present... 

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