(159) With regard to the shape of the tooth a good deal can be said. Ideal carding would be obtained by the use of fine needle points closely set, as will be seen in dealing with the combing machine, but it is manifestly impossible to employ teeth of this description in a carding engine. Although they might be inserted and used in new clothing, as soon as they became blunt it would be impossible to restore their points owing to their position in the clothing. But the principle remains; and, failing the employment of needle points, the attention of makers has been directed to the production of a wire which will present to the cotton what is practically a needle—or more accurately—a knife edge, which can easily be renewed after wear. To Messrs. Ashworth Brothers belongs undoubtedly the credit of this important step, which brought in its train many changes in the general construction of the machine. They use a wire which is round in section, but which they grind at the side so that above the foundation it becomes oblong, thus presenting a sharp edge to the fibres while preserving all the necessary strength in the portion fixed in the foundation. Various other sections have been employed, such as double convex, triangular, and oblong, and by a special system of grinding the same kind of edge is produced. The teeth when fixed in the fillets are ground on their edges by thin emery disc wheels formed with bevelled edges, which pass between the teeth and grind them to a sharp edge. A pair of teeth of this character, magnified 13 times, are shown in Fig. [79], which is from a photograph lent by Messrs. J. Whiteley and Sons. It will be noticed that the line of the tooth is gradually tapered until the point, which assumes very nearly the character of a needle point, is reached.
(160) The question as to how far this “plough” grinding is a good thing is one which it is worth while dealing with at length. It is undoubtedly true that steel wire carefully hardened and tempered will, under equal conditions, wear longer than a softer variety, but it is sometimes argued that the advantage thus derived is counterbalanced by the grave faults often existing after a surface of this kind has been side ground. The idea of a needle point is the right one, but it is worse than useless unless the wire remains smooth. There are two evils to be guarded against—the barbing or hooking of the wire points and the striation of the sides of the teeth. Both of these faults are often produced in side grinding, this fact having been fully established by a number of investigations made by various observers.
(161) It is apparent that the abrasion of a wire surface by means of an emery wheel is sure to produce a certain degree of roughness. If any student of the subject will take the trouble to examine newly-ground clothing by the aid of a glass magnifying from 10 to 20 times, the scratches caused by the rotation of the emery wheel are easily seen. It requires very little reflection to show that this is sure to be detrimental. Mr. B. A. Dobson, of Bolton, who has gone very extensively into the subject, published with an address delivered by him in America an interesting series of photographic representations of side ground teeth. These were enlarged a number of times, and were then reproduced. Striated sides and barbed points are common in this series. Now the inevitable effect of such a tooth is to break or destroy the fibre, or remove from its surface a portion of the waxy covering. This leads to an increased waste in the subsequent processes, although that produced in the carding machine may be less. It is hardly worth while discussing the point further, but there is one fact which speaks volumes as to the general opinion on the subject. It is agreed that the treatment of the teeth by those of a wire burnishing brush has a very beneficial effect upon them, and the carding afterwards carried out is much cleaner and better. This is one reason why the brush used to strip the flats is occasionally made of wire. As the action of a burnisher is to remove scratches previously made, its use is a confession of their existence.
Fig. 78.J.N.
(162) The roughening of the wire teeth is not, however, inevitable. In Fig. [80] is shown a side view of a plough ground tooth magnified 32 diameters. In this the striations are most marked, and there needs no comment to demonstrate their existence. In Fig. [81] a similar tooth ground in a special manner, and similarly enlarged, is shown. The surface of this is so much smoother than the other, that practically it is perfect. At any rate it is so much better than the one shown in Fig. [80], which is ground in the usual way, as to be an entirely different article. Both of these photographs are supplied by Messrs. John Whiteley and Sons, and the system of grinding by which the tooth shown in Fig. [81] was obtained, is now in regular use by them. The objection is not to needle or chisel shaped teeth side ground, but to these plus striation, and if the addition can be removed, many of the objections rightly entertained will be obviated.
(163) When the clothing has worn it is desirable to grind it frequently but lightly. The practice of allowing the tooth to become very blunt prior to grinding is very objectionable, as it leads to heavy grinding and there is a danger of hooked teeth. It is impossible to state a general rule on the subject, as the periods of grinding depend so largely on the class of cotton treated, but it is better to give a light grinding to the wire every few weeks.
(164) In the last chapter, in paragraph 107, it is pointed out that the cylinder is drilled with a number of holes arranged in straight lines across its periphery, in which wooden plugs are tightly driven. These are intended to aid in fastening on the fillets, and before clothing the cylinder or doffer, it is desirable to mark the centre of each line of holes on each edge, and to set out the position of each hole in one line on a staff. In this way, when the surface is covered, the exact position of each plug can be ascertained, and the tack inserted without damaging the wire. As the cylinder surface is quite level, the fillets are in some cases wrapped on the bare face, but there is some danger of the clothing slipping, especially if made with a rubber foundation. To obviate this serious defect, the surface of the cylinder is covered with a specially woven cotton cloth, or with brown paper, the former being preferable. This covering is put on without any puckers or creases—a very essential thing—and is attached to the cylinder by a special kind of cement or paste. On a surface prepared in this manner rubber foundations will not slip in working. With fillets in which the foundation is a woollen one, these precautions are not necessary. If it is intended to employ rubber foundations, great care must be taken before proceeding to clothe the cylinder. The fillets must be kept in a room heated to the same, or a little higher, temperature than the card room in which they have to work. This treatment causes the fillet to expand to a certain extent, and should be continued for some hours prior to their being used. Thus when the fillets are fixed in their position they do not expand as they would do if kept in a cold room before being used. Woollen foundations do not expand by heat, and can, therefore, be used and fixed without the preparation named. For this reason they are suitable for employment in places where the direct sunlight can fall on them. Oil being detrimental to india-rubber, fillets with that foundation should never be used where oil is likely to fall on them. A certain disintegration of rubber foundations occurs in some cases in hot climates, but they are largely used in England.
