The CTC Process : The triple process of Curling Tearing and Crushing is done by the “teeth” on the two rollers, moving against each other at different speeds. Therefore, the Shape, Siize and the Differential Speed of these teeth, should be of vital importance in the process. How are three process functions achieved by these “teeth”? Experiments were conducted and the results obtained leads one to believe that following takes place. From diagram 1 it is noted that when 8” dia rollers are meshed and set with a gap of only 0.002” between rollers, 2.24 teeth of slow speed roller always remain within the “Arch of engagement” A-D. And, if the speed ratio is taken at 10:1 then 10 teeth of high speed roller will pass each slow speed tooth within the Arch of engagement. Diagram 2 is a vertical view of the part of the slow speed roller which is within the Arc of Engagement and the path of the particle of leaf as it is processed is traced on it. As mentioned, 10 teeth of high speed roller passes each tooth of slow speed roller while it traverses the Arc of Engagement A-D but since the leaf particle is also moving downwards at a faster rate than the slow speed tooth in actual fact probably only 5 to 6 High Speed teeth pass the leaf particle, depending on the characteristic of the leaf. Diagram 2a shows that high speed roller teeth that are involved in the process. So if one imagines these teeth sliding over diagram 2 the process the leaf undergoes may be described as follows Between A and B High speed tooth no 1 tears off a fraction of leaf. The initial tearing is done by the scissor action of the two helical grooves and the torn particle is transferred to the right side of the high speed tooth acroos the inclined head as shown in figure 2a. This piece is then trapped between the two sides of the teeth and rolled along the left side of the 1st slow speed tooth. After the 1st High speed tooth passes the particle is taken up by the 2nd High speed tooth, torn again and rolled or curled further along the same slow speed tooth it is discharged across its slope (milling cut of the 1st slow speed tooth onto the right side of the 2nd slow speed tooth. This discharge takes place due to sudden release of pressure on the particle. The particle is then picked up by the 3rd High Speed tooth, torn again and rolled along the right side of the 2nd slow speed tooth till the 4th High speed tooth picks up the particle. This tooth tears the particle again and by the scissor action transfers a part of the particle across the groove to the left side of the 3rd Slow Speed tooth on the same row. Here it is again curled twice and torn once by the High speed teeth no 4 and 5 being finally discharged out, across the milling cut of the slow speed tooth. The first half of the process of curling and tearing is being done under rapidly increasing pressure as the gap between the rollers narrows along the arc. This simultaneously crushes the curling particle. Considering 8”rollers that meshes and set close enough to leave only a .002” gap between them. At a much ‘looser adjustment’ leaving a gap of .020” between rollers the “Arc of Engagement” A-D and the area of process is much reduced. The number of slow speed teeth that remains within the arc of engagement is reduced to 1.83 from the original 2.24 and therefore, the action of process remaining the same, this will mean less Tearing, Curling and lower Crushing pressures. The particle will therefore be larger, more open and flabby - a fact known to tea maker. 1. Tearing action is related to – i) The closeness of setting or the Gap between the two rollers because the total number of teeth passes reduce as the arc of engagement reduce (e.g. 1.83 x 10 compared to 2.24 x 10). ii) On the Speed Ratio : as this determines the number of tooth passes which in turn determines the number of tears. Therefore closer setting or higher speed ratio will both increase smaller grades. 2. The Curling and Crushing actions are simultaneous process both dependant on- a. The surface area available on the teeths sides (as seen by figure 2). b. The closeness of setting. c. The linear speed differential between High Speed and Slow Speed Teeth. Therefore, closer the setting, harder the crushing action and since the two processes are simultaneous, closer the setting, harder the curl, i.e., more grainy particles. Since the SIDES of the Teeth are doing all the work, if the surface area of teeth is not adequate sufficient curl will not be obtained. Conversely, if the surface area of the teeth is increased (e.g. by decreasing the milling angle) a better curl or grain will be obtained. Therefore. The minimum surface area which will give sufficient curl and optimum linear differential speed could determine requirement. 3. Discharge capacity and output- Since the leaf particle is discharged across the slope (milling cut) of the slow speed tooth as described in fig 2. a reduction in discharge area will reduce the discharge capacity of a roller. As the discharge is related to the milling angle. This means the output of the pair of roller will drop as the milling angle is decreased though a more grainy tea will be obtained through increase in surface area. Therefore, the processing capacity of rollers with different milling angles could be determined as that maximum efficiency obtained.
Posted on: Sun, 26 Jan 2014 09:12:51 +0000
Trending Topics
Recently Viewed Topics
© 2015