Fig. 24.
(74) Messrs. Howard and Bullough use, in addition to the fixed bars shown, the additional bars D, which are pivoted at their lower end, as shown, in a movable plate. This plate is attached to a lever E, which can be operated from the outside. The purpose of these bars is to admit of the admission of more or less air as desired. The space below the fixed bars and that below the air bars are separated by a thin division plate F. It is claimed for this arrangement that the fall of the dirt through the bars C is considerably facilitated.
(75) After passing the dirt grids, the cotton falls on to a second grid, or plate, as preferred, and then between a short “dead” plate and “beater sheet” to the cage J on to which it is drawn. The cage J consists of a skeleton cylinder revolving on a shaft, and having its periphery formed of finely-perforated sheet metal. Each end of the cage terminates in an air passage or trunk extending upward as shown. At the foot of the trunk the fan I is placed, which exhausts the air through the cages, and sucks the cotton on to them so as to form a continuous sheet or fleece. From the cages the fleece is taken to the lap attachment, which has been previously described.
(76) Messrs. Crighton and Sons, a perspective view of whose machine is given in Fig. [25], make their cages in a somewhat different manner to that just described. The ends of the cages are fitted into the framing, which is recessed at each side to receive them. Their peripheries are formed of woven wire webbing, instead of the perforated zinc sheets mostly used. At the end of the cage the webbing is protected by a brass ring, which keeps it firmly in position. The effect of this arrangement is two-fold. A greater space is left for the passage of the air than is possible with a perforated metal covering, and as a result, the intensity of the current is reduced. In addition to this, the fleece of cotton is laid on the whole of the face of the cages, because the manner in which they are fitted into the framing practically causes the latter to act as a guide, beyond which the cotton cannot spread. In this way the edge, or “selvedge,” of the lap is rendered very even, a subject the importance of which is further dealt with in paragraph 99.
Fig. 25.
(77) Another point of special construction, adopted by the same firm, is the position of the “dead plate.” This is the name given to a plate below which the scutched cotton travels, extending across the machine immediately behind the beater. As the cotton leaves the range of the beater, it falls upon a plate or sheet called the “beater sheet,” immediately below the “dead plate.” Now, for reasons to be given, the position of this plate is important, and in the machine as made by Messrs. Crighton, its distance from the beater sheet is 21⁄2 inches. Immediately beyond this point the same firm use an appliance known as a “leaf extractor,” of which an illustration is given in Fig. [26]. It consists of an endless brattice or canvas band D, as wide as the space between the frames, and having fastened to it transverse bars of wood B. These are shaped as shown, with an edge meeting the cotton as it moves forward, thus scraping off the leaf, and the space contained between each pair of these practically forms an air-tight box for the reception of the leaf. The brattice moves in the direction of the arrow, and thus meets the cotton as it passes from the beater. It is kept in tension by means of the rollers E F and G, and as the bars pass over E, which is unattached, its weight causes them to open, and so drop the leaf into the chamber below. Having thus described the mechanism of this special arrangement, it is necessary to say something of the draught regulation and the effect it has upon the work.
