Taper centre tube

Conventional feeder screws have full-face flights welded to a centre shaft or tube. Uniform pitch screws are sometimes used in simple feeding applications. In order to secure differential intake of product along the axis of a screw, a range of techniques can be adopted, either individually or in combination where appropriate. Typical constructional features are (see Fig. 4.5) stepped pitch variable pitch stepped or taper centre tube or shaft variable screw diameter part ribbon or shaftless construction. (Occasionally the construction is stepped on the outside diameter.)... 

Tubes are typically 20-30 mm long and 5-10 mm in diameter after the design of Massman. In the past, the tube may have been turned down at the centre to increase the temperature at that point, or the whole tube may have tapered towards the centre ( profiling ) to shape the tube to the optical beam and increase the free atom density at the centre. Modem tubes tend not to have either of these modifications made to them. The graphite tube is held in place between two electrodes, axially in line with the light source, as shown in Fig. 3.4. 

Split liners are typically narrow and straight tubes, while splitless Uners are wider and typically show a tapered end, see Figure 2.55. These bottom tapers keep the sample cloud in the centre of the hner for an optimized transfer into the column. Tapers prevent a possible exposure of sample components to the metal (gold) seal... 

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