Serrated plates

For low-viscosity, low-elasticity melts, a cup-and-cone arrangements is needed in order to contain the material. In cases of highly filled materials, there is a significant concern of slip between the plates and the material. Serrated plates are often used to overcome this problem. 

With the serrated plates, the compound leaked out even at 90 kPa when the top plate was rotated. This indicates that the transmission of force and breaking of structure were more effective with the serrated plates. Only with a 0.9 kg load (18 kPa pressure) could the leakage be avoided. In Figure 3.21 curves 1 and 2 were obtained with the flat plates and curve 3 with the serrated plates. Curve 1 is without the top plate rotating and curves 2 and 3 with the rotation. The trend shown by curves 1 and 2 is the same as the case with 90 kPa pressure, that with the application of shear, the compaction occurs faster in the beginning. 

Figure 3.21 Time dependent compression curves at 100 °C under 18 kPa. Curves 1 and 2 with flat plates curve 3 with serrated plates curve 1 without shear curves 2 and 3...

Curve 3 shows that with the serrated plates, the effect of shear is even more dramatic. Almost immediately after the application of the load, the volume reached the ultimate value, which is in agreement with the apparent specific volume of RH line. Figure 3.19. In addition, the thickness of the compound fluctuated as shown in Figure 3.22. This behaviour is very different from the smooth curves obtained with the flat plates. 

Subsequently, a number of differences in material behaviour were found between the cases with the flat plates and those with the serrated plates. After the compaction experiment was over and the top flat plate was lifted, the compound surface was shiny, indicating that the plate was slipping at the surface. With the serrated plates, there was no slipping at the plate-compound interface. With the flat plates, the compacted material was still friable. With the serrated plates, the rubber particles were fused together and no longer friable. 

When the top plate was lifted, the flat plate cleanly separated at the plate-compound interface. This also implies that there was slipping. When the serrated plate was lifted, the sample broke in the middle. The fractured surface showed that the rubber particles were stretched and torn. The behaviour observed with the serrate plates is very significant, and it will be discussed in section 3.3.7. 

The significant points deduced from the observation with the serrated plates are as follows ... 

Typically the plate is half-moon in shape and is sloped slightly in the direction of liquid flow. Gas contacts the liquid as it showers from the plate, and a serrated lip or weir at the edge of the plate can be used to improve the distribution of liquid in the shower. 

In which the vapour passes up through short pipes, called risers, covered by a cap with a serrated edge, or slots. The bubble-cap plate is the traditional, oldest, type of cross-flow plate, and many different designs have been developed. Standard cap designs would now be specified for most applications. 

Similar charges having much the same effect may be made by using coiled chain (automobile tire chain size), short lengths of barbed wire, or serrated or grooved metal plates which break into fragments when the charge is exploded. 

Wood chips are passed through a narrow gap of a double-disc steel refiner consisting of stationary and rotating plates having serrated surfaces. This process results in the mechanical separation of fibers that are subsequently frayed for bonding. The strength of the refiner pulp is better than that of ground-wood pulps. 

Figure 8.6. Examples of extended surfaces on one or both sides, (a) Radial fins, (b) Serrated radial fins, (c) Studded surface, (d) Joint between tubesheet and low fin tube with three times bare surface, (e) External axial fins, (f) Internal axial fins, (g) Finned surface with internal spiral to promote turbulence, (h) Plate fins on both sides, (i) Tubes and plate fins.

The efficient operation of the distillation, or fractionating, tower requires the rising vapors to mix with the liquid on each tray. This is usually achieved by installing a short chimney on each hole in the plate and a cap with a serrated... 

Botanically, Cannabis sativa can be identified on the basis of its gross morphological features and, more importantly, by the presence of microscopic structures on the surface of the plant, namely the trichomes. At the macro-morphological level, it has a square stem, with four comers, and has palmate leaves with serrated edges. These are the characteristics with which most people are familiar. Microscopically, three types of trichome are observed, namely the glandular trichomes (Plate 4.1), unicellular trichomes (Plate 4.2) and cystolithic trichomes (Plate 4.3). 

This apparatus consists, essentially, of a graduated rod furnished at one end with a plate and at the other with a ball 20 mm. in diameter. This ball rests on a circle 90 mm. in diameter taken from the sheet to be tested and gripped between two serrated annular rings of 50 mm. internal diameter. 

The dynamic shear storage modulus (G1) and loss modulus (G") were measured from -150° to 50°C using the forced torsion fixture on a Rheometric Mechanical Spectrometer (RMS). When the storage modulus dropped below 10 Pa. this fixture became insensitive. For moduli less than 10 Pa, the parallel plate fixture with serrated disks was used. The parallel plate fixture was used to extend the dynamic mechanical measurements to high temperatures. Degradation above about 250°C dictated this temperature as an upper limit for RMS measurements. Further discussion of equations and use of these fixtures are given elsewhere (2,8). 

Bubble caps round or rectangular cups with serrated edges inverted over nozzles spaced uniformly over the plate area require downcomers on each tray. 

The specimen grip system was 100 mesh stainless steel screen wrapped around 2.5 cm of each end before clamping between two stainless steel plates (0.6 cm thick) cross-serrated with 10 lines/cm. After assembly in an alignment jig, three pairs of 10-32 screws, torqued to 2.3 to 4.5 N-m (20 to 40 in-lbs), were used to clamp the grip onto the specimen. Holes in the steel plates allowed a load pin attachment to clevises on each pull-rod. The test frame design made it possible to immerse the entire system in a dewar of liquid helium. 

The fin plates are shaped from 0.15 to 0.6 mm thick aluminium sheets by periodical distortion. The fin height, i.e. the clearance between the neighbouring partition plates, ranges between 3.8 and 12 mm. The distortions form channels with diameters ranging between 1.2 and 4.5 mm. The Reynolds number calculated on the basis of this diameter lies between about 500-10 000, i.e. the flow is in the transition range between laminar and turbulent In order to improve the turbulence and thus the heat transfer, additional obstacles are installed. To this end, fins are either perforated or are serrated and periodically displaced against each other with a certain clearance. 

The parallel-disk viscometer used for measuring the shear stress and normal stress difference of molten thermoplastics is similar in principle to the cone-n-plate viscometer except that the lower cone is replaced by a smooth circular disk. This type of viscometer was initially developed for measuring the rheological properties of rubber [29-33] and therefore made use of serrated disks placed in a pressurized cavity to prevent rubber slippage. When it was adapted for thermoplastic melts [1534,35], measurements were performed using smooth disks and without pressure. 

An attrition mill uses a stationary and a rotating disk with a series of radially serrated teeth machined into them within a mill housing. The disks are positioned opposite each other with a narrow gap that tapers down from the center of the plates to the outer edge. Fig. 15.2 shows the layout of a two-stage grinding mill and its... 

A first experimental campaign has been carried out to verify the efficiency trend versus the plate spacing and at same time to set up the equipment and the test procedures. During the preliminary tests conventional power supplies and serrated strip emitting electrodes have been itsed. 

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