Diverter cutters

The diverter cutters divert the stream increment clear of the main stream and, providing they are properly designed, they do not allow accumulation or sticking up of the powder anywhere inside they require considerable head-room, however, and can only deposit the increment below the point of sampling and not very far from it laterally. 

Conventional design of most mechanical sampling systems for large tonnages of coal use some form of cross-stream primary cutter to divert the primary increments from the main stream of coal (Figure 2.2). A major advantage of these systems is that they sample coal from a moving stream, and most of them satisfy the principle that every particle in the entire mass has an equal opportunity to be included in the primary increments. 

The cutters in use in mechanical sampling are divided into diverter types and bucket types. Both types are used to cut a stream falling due to gravity off the end of a conveyor belt or from the discharge end of a pneumatic conveying pipe or a chute. 

The bucket-type cutters have the advantage of being able to collect and transport the sample laterally, without the loss of headroom they collect and hold the sample, however, and thus allow material build-up within the bucket if the powder is a little sticky. Another disadvantage is that, whilst the mass of the diverter-type cutter remains the same during its traverse across the falling stream, the mass of the bucket cutter increases rapidly and the drive systems must be powerful enough to maintain its speed. 

This same type of slitter is also used to cut a wider piece of tape into narrower sections at the exit end of the machine. For example, a 200-mm-wide tape may be slit into four 50-mm strips. Each of the 50-mm strips would then be rolled as a separate entity onto the take-up roller(s). Another type of slitter used to cut a wide tape into sections is based upon the scissors principle—that is, it has two cutter wheels or block knives that overlap each other and shear the tape like a pair of scissors. The block knives on each of these systems are driven and are synchronized with the movement of the tape-cast product. When a wide tape is slit into two or more narrower widths, there are usually two take-up axles. As the slit tape moves from the slitter, alternating strips are diverted to different take-up axles, thus eliminating the possibility of overlap or interference between adjacent rolls. 

Fig. 29. TWin-screw extrusion compounding line for the preparation of mineral-filled thermoplastics showing pre-mixing, compounding and pelletizing stages [155] (a) Filler/poly-mer/additive feedstock, (b) high-speed pre-mixer, (e) dosing screw, (d) twin-screw compounder, (e) vacuum devolatilization, (f) water-cooled die-face cutter, (g) start-up diverter, (h) de-watering chute, (i) pellet dryer, (k) bagging...

The droplet velocity is delimited to 2-3 m/s because of the mechanical coti-structiOTi of the droplet generator. At a too low velocity the pulsed liquid column is easily diverted sideways by the rotational movement of the cutter disc. On the other hand, with a too high droplet velocity, the resulting droplet frequency is so high that the friction between the cutter disc and the nozzle plate heats up the liquid considerably. 

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