(55) When the cotton enters the beater chamber it is at once struck by the blades of the beater, which revolve at a speed of about 1,000 turns per minute. The peripheral velocity of the blades is thus at the bottom 4,712 feet per minute, and at the top 8,639 feet. The blow thus given disentangles the cotton and flings it against the inner surface of the grid, thus momentarily arresting its motion. As the beater revolves, the cotton continues to find its way upwards, and in its course is repeatedly struck by the blades, which, as has been seen, have a continually increasing peripheral velocity as they near the top. In this way, as the cotton nears the exit orifice, which is placed at the upper part of the machine frame, on the opposite side to the tube C, it is thoroughly beaten into a fleecy condition, with its fibres well disentangled.
(56) The shape of the grids surrounding the cylinder is an important matter. In the form illustrated in Fig. [16], the projections on the grid are triangular in shape, and have slots between each pair through which the dirt can freely pass. It will be easily seen that the shape of these grids is one which will only exercise a little clinging effect upon the cotton, which, as it is impelled by the stroke of the beating blade, will very readily roll pass the projections. As the rapid rotation of the cylinder tends to slightly compress the air, the latter finds an outlet if possible. This is the object of the slots in the grid casing, and they fulfil it very well. But there is always a liability that along with the air and dirt—which also passes the grids—a little fibre may escape. It is desirable to avoid “fat droppings” as they are called, and the grid shown in Figs. [17] to [19] has been designed for this purpose. Each of the pockets C Fig. [18] shown becomes a resting place for the opened fibre, and as its lower end C2 is open, the dirt can fall freely. In order that the air can easily get away, between each pair of pockets a small slot is formed, and in this way there is no downward impulse given to the cotton while held in the pocket. Thus each blow given to the material opens it, drives it into the pockets where it dwells for a short time, and from which after the passage of the beater blade A, it is drawn by the suction of the air. By this system there are given short periods of rest, which very materially facilitate the fall of the dirt.
(57) Instead of feeding the opener manually as shown in Fig. [15], a lattice feed can be adopted. Among the many important points in connection with the Crighton, or, as it is sometimes called, the “exhaust” opener, none is more so than the construction and lubrication of the footstep. This is arranged so that the foot of the beater shaft revolves in a constant bath, either of oil or water, and great care is taken to cover it so as to prevent the entrance of sediment or dust.
(58) In Fig. [20], a longitudinal section of the machine as made by Messrs. Lord Bros., is given, and is accompanied by a plan of the same machine as combined with a porcupine feed. Referring first to the plan, the lattice feed A delivers the cotton to the porcupine roller C, by which it is passed in a partially opened condition to the air trunks D. By these it is conducted to the opening chamber F, being admitted to it by flap valves G. The cotton enters the chamber F by the tube H, terminating in the dish I. The exit orifice is placed at the top of the chamber F, the course of the cotton being shown by the arrows. The cylinder is similar to the Crighton, but the blades E are fixed in malleable iron arms L fastened to the shaft, and can, after wear, be reversed. Below the foot of the shaft, and within the bearing O, is a loose washer P, which can rotate with the pressure of the shaft, this arrangement considerably lessening the wear. At each side of the exit of the delivery tube, fans N are fixed, which, like those in the Platt machine, can be adjusted sideways for the same object. The cotton then passes over grids R on to the cages T, from whence it passes through the scutching beater W to another pair of cages S, as indicated by the arrows, and is finally formed into a lap as shown. The special construction of the beaters enables the cotton to pass freely upwards, and prevents any stringing occurring. The speed of the beater in this machine is 520 revolutions per minute for American cotton, and 720 for Indian. The slower velocities used necessarily imply the use of less power.
(59) There are one or two points to be noticed in concluding the consideration of the Crighton type of machine. The distance from the face of the grids to the ends of the beater blades should be carefully arranged to suit the class of cotton treated, as, if it is too great, the opening is not properly effected, and, if too little, the cotton is liable to be damaged. The rate at which the feed is conducted should always be carefully watched, because, if the material is passed in too quickly, its bulk becomes so great in the lower part that the dirt cannot fall freely, but is received by the entering cotton. Cleaning is not, therefore, so effectually carried out. In addition to this, it is desirable that the cotton should be allowed to assume a perfectly open condition, which it would do with difficulty if the space were overfilled. Cotton has been passed through, for a short time, at the rate of 110,000lbs. per week of 60 hours, but for the reasons stated, 30,000lbs. is ample.
(60) It might be thought that the pitch of the projections on the inner surface of the grid should be as small as possible, but this is a mistake. It is essential that the cotton should strike not merely the top or apex, but one face or side of the projection, if the full cleaning effect is to be obtained. It is obvious that if the pitch is too fine no such face blow would be given, and very inefficient purification would occur. The considerations thus stated are founded on actual experience in working the machines, and should be borne in mind in constructing or controlling an opener of this type.
(61) It is considered by some makers to be advisable when using this style of machine to employ one with two beaters revolving in separate chambers, connected to each other by an air pipe. This is more especially the case when Indian or short stapled cotton is used. When the double machine is used, the conducting tube between the two leaves the first chamber at the top, and enters the second at the bottom. The driving of the opening machine is usually obtained from a counter shaft, by which means the speed of the driving pulley becomes a moderate one.
(62) A machine, of which large numbers have been made by Messrs. Lord Brothers and Howard and Bullough, has a conical beater placed in a horizontal position, and the opener proper is usually combined with a scutching and lap machine. As this type of machine is very similar in its general principles to that previously described, and is not now so largely made as formerly, it is not necessary to give a detailed description of its mechanism.
(63) It has been repeatedly stated that the various machines are united by means of tubes, so that the cotton can readily be taken from one machine to another. It does not matter whether the machines are in the same room or not, or what distances separate the rooms in which they are placed. This has been shown in Figs. [6], [7], and [8], referred to in the preceding chapter, and the further arrangement is illustrated in Fig. [13]. In this case the cotton, after being delivered into the dust trunk, or tube D, on its way to the opening cylinder, may be carried two or three hundred yards, if desired, before it reaches the latter. There is, of course, a limit to the distance it may be conveyed, but it is a very wide one. There are many conveniences arising from this procedure. It is becoming a very common practice to build the mixing and scutching rooms away from the main body of the mill in order to minimise the risk of fire. But even where this practice does not obtain, the employment of air tubes is a good one, as it enables the material to be transferred from one point to another without handling. In this way the cost of labour is much reduced, and in addition the cotton is less liable to damage.
(64) At one portion K of the conducting tube D an arrangement is fitted by which a partial cleansing of the cotton occurs before it reaches the opener. Below the level of the tube a chamber nearly square in section is formed, as shown in section at the left-hand corner in Fig. [20], forming the tube into a D shape. This chamber is made of a length which is determined by the character of the material used and considerations of its position, etc. At intervals of a few inches plates are arranged so as to divide the chamber into a number of compartments, as shown by the sectional view. Over the top of these plates the material rolls in its forward movement, and a large quantity of dust, sand, and heavy impurities are deposited in the trunk. Doors are fitted to the underside of the chamber, by which the droppings can be removed at intervals as desired. The use of these grids has been attended with unmistakeable benefit, and leads to a much more effective cleaning of the cotton.