CHAPTER VII.CARD CLOTHING, GRINDING, AND STRIPPING.

(154) As was shown in the preceding chapter, the cylinder, doffer rollers, &c., of carding engines are covered with a wire clothing, the proper construction of which is of high importance. It forms a sort of wire brush, in which the points are fixed in a special matrix, or “foundation,” as it is called. Formerly it was the universal practice to make the foundation of leather, but various considerations have led to its abandonment, except in the case of woollen cards where an oily or greasy material requires dealing with. In lieu of leather three specially prepared materials are now employed, one being what is called a cotton-wool-cotton, another cotton, and the third a natural rubber foundation. The first of these consists of two thicknesses of cotton cloth specially woven with a wool fabric cemented between them. The rubber foundation consists of a thin sheet of natural india-rubber imposed upon and securely cemented to a back of cotton and wool. Great care is taken that the india-rubber shall be pure, and in some cases the manufacturers of card clothing also produce their rubber sheets. The object aimed at in each case is to obtain a foundation which shall be strong enough to hold the wires securely, and at the same time be possessed of some elasticity, so as to aid the wires to recover their position when bent during work.

(155) It was at one time the practice to make the cards in sheets four inches wide, and long enough to cover the width of the machine, but this has been abandoned in favour of a plan by which they are made in long strips or “fillets.” These are long enough to completely cover the cylinder, on which they are wound in a way which will be hereafter described. Having obtained the fillet for the foundation, the next step is to introduce the wires. These are produced from a reel of specially drawn steel wire, which is frequently hardened and tempered by a continuous process. It is essential in conducting the latter that the wire should be free from scale, and, in the great majority of cases, this is attained. In fixing the wires into the foundation the preliminary step is to cut off from the wire carried on a reel a sufficient length, and bend it up into the form of a right angled staple, having two parallel arms joined by the third side. The extremities of these arms constitute two of the points to be fixed in the foundation, so that it will be seen these are always introduced in pairs, and not singly. In order to facilitate their passage through the foundation, two holes, pitched to correspond with the distance of the two points apart, are pierced in it, and immediately on the withdrawal of the piercer the staple is pushed in, and forced up to its place. Almost simultaneously with this operation it is set—that is, is bent to an angle as shown in Fig.85. After one pair of wire points are fixed the fillet is traversed, so as to introduce another pair at the required distance from the last one. When the width of the fillet has been filled with teeth it is moved a little lengthways, far enough to begin the nextline, and the direction of the carriage is reversed. It is highly important that the wire points should be set equidistant over the whole of the surface, so that when the cylinder is clothed, the regularity of the carding points will be unvarying. The whole of the operations of feeding, cutting, and bending the wire, piercing the fillet, forcing in the teeth, traversing and reversing the carriage, and traversing the fillet longitudinally, are automatically performed by a machine of great ingenuity, originally invented by Mr. J. C. Dyer. It is one of the best examples in the whole range of mechanics of the power of the cam, and works with great rapidity, being capable of fixing over 300 pairs of wire points per minute.

Fig. 76.

(156) The teeth can be set in the foundation in three ways—either plain, twilled, or ribbed, these settings being shown in Fig.76, the dots representing the wire points, the back of the teeth being shown by the dotted lines. In the first case the teeth are in straight lines; in the second they are, as the name implies, set diagonally; while in the third they are in straight lines, but set so that they are in sets of three, each of which overlaps its predecessor. Generally, plain setting is very little used, fillets being commonly made ribbed, except in the case of the flat covering, which, when mild steel wire is employed, is usually twilled. In manufacturing cards for covering the flats it is common to commence with a large sheet equal in width to the length of the flat. The teeth are then set for a space equal to the width of the flat, when the sheet is rapidly traversed longitudinally until the point for starting a new flat strip is reached. These strips are cut out of the sheet, and thus leave the necessary margins for fastening to the flat. In America twilled setting is preferred, but, in this country, it is objected that spaces are left between each lap when fixed on the cylinder, which is very objectionable. This fault does not occur where ribbed fillets are used, and it is now almost the universal practice to use this setting for cylinder and doffing coverings. However the teeth are set in this respect, they vary also in their distance from each other, and this variation depends on the “counts” of the wire. This phrase is used to indicate the fineness of the pitch of the wire teeth, and the method of counting is based on the number of teeth in the width of the sheets formerly made. Thus, if there were 100 teeth in a sheet four inches wide, the counts were said to be 100’s, the same rule being applied to-day. Longitudinally, the pitch of the teeth was ten “crowns,” or points, to the inch, this being also retained as a standard of measurement. In this way it is possible, by knowing the counts of wire, to calculate easilythe number of teeth per square inch. Thus, in the instance named, there would be 100 × 10 = 1,000 teeth in the four inches of width by one inch in length, which is equal to 250 teeth in every square inch.

Fig. 77.J.N.

(157) In clothing the various parts of the machine experience has shown that there can be wise variations made in the kind used. Every spinner has ideas of his own, and as there is a wide difference in the class of material treated no rule can be laid down. In clothing the licker-in, a tooth which is known as the “Garnett” is universally used. An illustration of this is given, in full size, in Fig.77, the finer tooth shown being used when no undercasings are fitted, and the coarser when they are. It will be noticed that the former is a little more hooked than the latter, which enables it to carry round the cotton without flinging it below the licker-in. The presence of an undercasing obviates much of the necessity for this carrying power, and the tooth is only required to beat off the cotton from the lap and thus throw down the motes, etc. In covering the cylinders of roller carding engines, where medium counts of yarn are being spun, clothing with 90’s to 100’s wire is used, the rollers being covered with the same counts, the clearers with a finer wire, and the doffers from 100’s to 120’s. These, of course, are sizes which are commonly employed, and indicate the usual limits, but, as has been observed, practice varies considerably in this respect. In revolving flat carding engines the cylinders are covered with 110’s, and doffers and flats with 120’s for medium counts of yarn. It may be generally stated that the finer the counts of yarn spun, all other things being equal, the finer the wire clothing employed; but it can only be settled by practice what are the best counts to use in any individual case.

(158) As has been observed, the wires are, in the process of setting, bent to an angle, or, rather, a double angle, after leaving the foundation. A reference to Fig.85will show that they leave the foundation at an angle in one direction, and afterwards bend sharply in the opposite direction. The diagram given in Fig.78illustrates this construction. The foundation is shown by the letterD, to which the lineA Bis perpendicular, leaving the upper surface ofDatE. The tooth is indicated by the lineA C E B1, and it will be noticed that the point of the tooth atAis perpendicular to the pointEwhere it leaves the foundation. This is the correct setting, or nearly so, for the following reason. Some makers, it may be stated, prefer to let the pointAbe a little behind the perpendicular lineA E. In working, the wire point is pressed by the material and is sprung backward, in which case it—when set as shown—will radiate roundEand move in the circle shown by the lettersF A G. Thus, if another set of wire points are imposed upon the lower ones, the flexure of thelatter, in either direction, is followed by their recession from the former, and no danger exists of any interlocking, which, if it occurs, is injurious to both sets of teeth. As the relative positions of the upper and lower teeth are of the character described in the previous chapter, the adoption of the method of setting the teeth indicated is of considerable importance. It is, of course, possible to vary the angularity or “keen” as desired, and the more acute the angleE C Athe more fibre caught and retained. Thus the proportion of waste made in a machine during work is largely dependent on the angular setting of the wires, and this is a point specially worth noting. The essential element is the approximate perpendicularity of the pointAof the wire to that (E) where it leaves the foundation.

(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 bedetrimental. 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.80is 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.81a 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.81was 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.

Fig. 79.

Fig. 80.

Fig. 81.

Fig. 82.

(165) Having prepared the fillets for wrapping on, the operation is completed. Formerly they were wound on manually, but this is now almost invariably done automatically by a machine made by Messrs. J. Whiteley and Sons, which is illustrated in Fig.82. One end of the fillet is securely fixed, and the cylinder is then started. The cross slideKis fixed on the frame of the machine, or on a special frame if preferred, when the doffers are being clothed, and the apparatus is then ready for work. On the slideKa carriage is fitted which is traversed by a screw, on the end of which is a chain wheelL, by means of which the necessary movement can be given from the chain-pulleyOautomatically, or it can be manually given by the handleR. The carriage bears a drum mounted on a cradle hinged to the carriage. The angular position of the drum is regulated by the tension screw, and the tension put upon the fillet, in pounds, is registered by a finger moving over a graduated scale. The card fillet is taken from the basket through the troughD, thence over the drum, from which it is taken to the cylinder. The cylinder is revolved by means of the handleR, and the card clothing is slowly wrapped on, the traverse of the carriage being arranged to be at the required speed. In lieu of the drum Messrs. Dronsfield Brothers use a stepped cone, which gives a similar result. Thus, cylinder fillets, when made of hardened and tempered wire, can be wound under a tension of 270lbs., while doffer fillets of the same quality only require one of 175lbs., andfor roller fillets, which are only 1 inch wide, 120lbs. is sufficient. What is required is to so wrap the fillets that, without straining them, they adhere closely to the surface of the cylinder or doffer; and do not, after working, rise in places or “blister,” as it is called. After the cylinder is covered the fillet is fastened at its free end, and is then allowed to rest for a few hours, so that it adjusts itself throughout its length. It is necessary to shape the fillet at each end so that, when wound, no break in the carding surface occurs; and, for this purpose, it is usually cut to a shape which permits the first and second coils and the last two to lie close together. It is then tacked on in the way previously described, a special tool being used to drive the tack and avoid damaging the wire.

Fig. 83.J.N.

(166) In fastening the clothing upon the flats several methods are pursued. A reference to Fig.83shows two of these. InA, which is 2 inches wide, andB, which is 13⁄8inches wide, the edges of the flats are drilled with small holes, and the strip of clothing is similarly punched. One side of the strip is then fastened to the flat by means of lead rivets, and it is then drawn tight along its whole length by a special clip. The other edge is, while the strip is held in tension, riveted firmly in a similar manner. A machine for this purpose, made by Messrs. Dronsfield Brothers, is shown in Fig.84. Another method is one originated by Messrs. Ashworth Brothers, and is shown inCandD. In this case the strip is attached by means of wirestitching, the flat being sawn at its edge at regular intervals, as is very clearly shown. A third plan is illustrated in Figs.85and86in partial perspective and transverse section, this being made by Messrs. John Whiteley and Sons. A clip is passed through the clothing and flat, and is then clenched, as shown separately in Fig.87. The strip of clothing is then drawn tight, and the second clip fixed in the same way. This method is rapid and effective, and possesses one important advantage. By it the margins of the flat strip are protected from being frayed by the revolving brush used to clean them.

(167) In dealing with the construction of the flats it has been shown that there is a movement towards the use of shorter ones, for the reason that it is felt to be desirable to prevent any deflection by having a stiff flat. Upon this point the consideration of the advantages of various systems of fastening the clothing largely turns. It is quite clear that any removal of metal, either by drilling or sawing, is likely to weaken the flat. It is, however, not so readily seen which is the most weakening, but actual experiments show that wire sewing is so. Mr. B. A. Dobson, of Bolton, has made a series of tests of flats, both drilled and sewn, to ascertain the deflection during working and grinding positions, and the side deflection. These establish very clearly the superior strength of the riveted flat, which is very considerable. For instance, a flat 455⁄8inches long by 13⁄8inches wide, with the same thickness in flat and web, gave the following deflections when loaded with a 1lb. and 2lbs. weight respectively. Unclothed, sawn for wire sewing: 1st, when face up,1⁄380th and1⁄200th inch; 2nd, when on its side,1⁄330th and1⁄166th inch; and, 3rd, when face downwards,1⁄660th and1⁄400th inch. Unclothed, drilled for rivets, the deflections in the three positions named were as follows: 1st,1⁄1000th and1⁄500th inch; 2nd,1⁄400th and1⁄275th inch; and, 3rd,1⁄875th and1⁄400th inch. The reason for this is not far to seek. The riveted flat has throughout its length an unbroken metallic surface along its edge, while the sewn flat is broken at intervals to permit the passage of the wire. For the reasons given in paragraph 118, the difference between1⁄660th and1⁄875th inch is material, especially when the settings of the flats are supposed to be regulated to the1⁄1000th inch.

(168) In Fig 88 is illustrated a plan by which the necessity for piercing the flat either with holes or nicks is entirely obviated. This is patented by Mr. Tweedale, manager for Messrs. Howard and Bullough, and consists in the employment of a metallic clip, which grips the clothing at one side, and is bent round and under a small rib on the underside of the flat. The clip is closed by means of a special machine, which runs rapidly along the flat, the two sides being gripped simultaneously, and the fillet stretched by the same machine and at the same time. With this construction the maximum strength of the flat is preserved throughout all its positions and under all working pressures. A similar arrangement is used by Messrs. Ashworth Brothers, but the shape and construction of the clip and the method of fixing slightly varies from that described. It is to be noted, however, that the width of the flat strip must be rather less in each case than that of the flat, and that the strip must in consequence be stretched so as to cover the surface. It is essential that the clips shall be fixed so as to be in contact with the planed edge of the flat throughout its entire length. The edges of the flats ought to be quite straight, especially if they are closely pitched, as otherwise they would come into contact in places. If, therefore, the clips referred to are not pressed closely against the sides of the flats throughout their entire length the danger of touching is increased.

Fig. 84.

Fig. 85.

Fig. 86.

Fig. 87.

Fig. 88.

(169) Messrs. Platt Brothers and Company have recently devised a fastening of tinned wire, which is bent up by special machinery so as to form a continuous series of staples, the pitch of the points of which is about1⁄2inch. The staples are connected at the points, so that a length can be produced sufficient for fastening any flat. Holes are drilled in the flat through which the staples are pushed, and are pressed downwards and held. While in that position the points are clenched similarly to Messrs. Whiteley’s clip, and the clothing thus secured. This arrangement is practically a system of sewing without the disadvantage arising from the sawing of the edge of the flat. A strength equal to a riveted flat is obtained, with the advantage of a continuous grip along the flat strip. All these arrangements, however, imply the use of special machines to fix them, which is a condition not always attainable in a mill. For these reasons, where it is difficult to return the flats to a machinist for re-clothing, the use of rivets is most desirable.

(170) No less important than the proper fixing of the clothing in position is the operation of grinding it before starting work and after the points have worn. The licker-in is not ground, as the teeth do not require it, and their shape is such that grinding is impracticable. The cylinder is ground in position, and the question as to which is the correct method is one about which there is a good deal of controversy. In theory it is quite true that the periphery of a cylinder revolving, say, 180 times per minute, will tend to follow a path which is not an absolutely true circle. Further, the vibration set up in working, and the constant tendency from centrifugal action for the cylinder to roll forward, have a certain bearing on the subject. For these reasons there are some persons who contend that during the grinding of the cylinder teeth the cylinder should be run at its normal velocity, and the emery grinding roller be driven at a surface speed approximating to that of the cylinder. While this contention is theoretically correct, the disturbance caused by the high velocity of the cylinder is not of practical moment, and it is found to give the best results to run the cylinder slowly and the emery roller quickly. In all operations in which a true surface has to be established these conditions are found to be the best, and the grinding of a carding engine cylinder forms no exception to the rule. The danger of damage to the wire joints is much less likely, and the high speed of the grinder aids materially in light grinding, which it will be shown is of great moment. It is, therefore, the universal practice to reduce the normal speed of the cylinder to one varying from 7 to 11⁄2revolutions per minute, and several special devices are in the market for the purpose. Before passing on to describe these, it may be said that the cylinder is ground by an emery roller, sustained in special brackets fitted to the machine framing, the position of which is shown in Fig.44atR. A similar method of procedure is adopted with the doffer, the brackets being placed atS.

(171) The most common appliance to obtain a slow motion of the cylinder is that known as Sykes’, which is shown in Fig.89, as made by Messrs. Dronsfield Brothers, of Oldham. This consists of fast and loose pulleys, which are driven by a strap from a pulley on the line shaft. The pulleys are sustained in a frame which also carries a short strap, on which is fastened at one end a bevel and at the other end a worm. The frame is supported by the two legs shown, which can be adjusted to any length. The worm wheel is fixed on the cylinder shaft in place of the ordinary pulley, and is driven by the worm andgearing as described. A slow motion is thus given to the cylinder, and at the same time the grinding rollers are driven by bands or cords from grooves formed in a flange on the fast pulley.

Fig. 89.

Figs. 90-92.

(172) A motion patented by Messrs. John Hetherington and Sons is illustrated in Figs.90and91. In Fig.92a side view of a carding engine is shown, with the motion applied to it. On the studG, which usually carries the intermediate band pulleys, shown by the dotted lineI, the bossFof the supporting frameAis fitted. The apparatus is shown in Fig.90in section, and consists of the supporting frame named, the bossA1of which forms a bearing for the shaftB, with the eccentricB1formed on it. On one end of the shaft the double grooved pulleyCis fixed, by means of which it is revolved. An internal rackA2is formed on the fixed frameA, and adjoining the latter is the compounded pulleyD.Dis also formed with aninternal rack and a single grooved pulley, and revolves on the outer end of the shaftB, being kept in position by the nut and washer shown. There are thus two racks, each containing the same number of teeth, one fixed and the other free to revolve. Mounted on the eccentricB1are two wheelsEE1, the latter being smaller in diameter than the other, this arrangement being shown clearly in front view in Fig.91

(173) The action of this mechanism is as follows: The pulleyCis driven by a bandKpassing over the pulleyJon the main cylinder shaftH. In this wayCis revolved, and the eccentric movement of the shaftBcauses the wheelE1to fall into gear with the rackA2. This gives a rotary motion to the wheelsEE1, and the larger diameter ofEcauses it to revolve at a greater rate thanE1. The revolution ofB, in addition to setting up this rotary motion in the compound wheelEE1, also puts E into gear with the rackD1, and causes the latter to revolve. The motion of the pulleyCis thus communicated toD, but the latter is revolved at a much slower velocity in the direction of the shaft. By proportioning the pulleys and wheels the necessary reduction in speed can be obtained. The revolution ofDis communicated to the cylinder by the bandLpassing over the grooved pulleyM.

Fig. 93.J.N.

Fig. 94.

(174) In the machine as made by Mr. Samuel Brooks, the motion is compounded with the barrow wheel detaching motion, as illustrated in Figs.93and94. On the same stud as the barrow wheel is a helical wheelC, which is driven from the former by a clutch, and which engages with a wheelDfastened on the lower end of a shaft placed at an angle of 97°. On the other end of the shaft a wormFis fixed, and gearing with the wheelG. During grinding the barrow wheel is disengaged by means of the lever in which the stud carrying the former is fixed, and the worm is thrown into gear. The speed of the cylinder is thusreduced to about one revolution, the necessary rotation of the wheelCbeing obtained from the pulley on the cylinder shaft. When it is desired to grind the cylinder the strap is thrown on to the pulley, and the necessary rotation given to the barrow wheelBand helical wheelC. The arrangement thus described is always in position, and does not require separately attaching to the machine, as is the case with most of the motions in use.

Figs. 95 and 96.J.N.

(175) Another form of apparatus recently introduced by Mr. Thomas Knowles is the one shown in Figs.95and96. In this case the boss of the loose pulleyLcarries a pinionJinside the pulley which gears withI, fixed on a short shaft borne by a central plate. Through the train of wheelsH G F E CandBthe central pinionA, fastened on the inner boss of the fast pulleyM, is revolved. Over the central plate, in which the spindles on which the wheelsE F G HandIare fixed, are fitted, a bandKis passed. By tightening the latter the plate can be prevented from revolving. In grinding, the strap is moved on to the loose pulley, the bandKis tightened, and the revolution of the pulley gives motion to the whole of the wheels, thus reducing the ultimate velocity to the required extent. During work the bandKis slipped off the plate, and the whole nest of wheels is carried round with the pulleys as they revolve.

Fig. 97.

(176) The rollers used for grinding the cylinder and doffer are made in two forms. One of these is shown in Fig.97. It consists of a light roller made with a thin wrought iron shell secured upon a shaft, running in brackets fixed to the frame side. The driving pulley is fastened at one end, and at the other is a traverse arrangement, consisting of an eccentric rotated by a worm on the shaft. By means of a short rodthe revolution of the eccentric gives a small lateral movement—about an inch—to the roller during the whole time it is in motion. The surface of the roller can be covered with emery in the ordinary manner, and is either made plain or grooved. Another method adopted by Messrs. Dronsfield Brothers, is to wrap round the roller a narrow fillet of emery cloth, either plain or grooved as desired. In covering, one end of the fillet is passed into the slit Fig.98, and is then secured by the clamp shown. About half of the width of the fillet is left projecting, and after it is secured, it is wound on by revolving the roller. As soon as the fillet is wound its loose end is passed into one of the three slits Fig.99, formed at the other end of the roller, and is secured by the clamps. The ends are then trimmed off, and the roller is ready for its work. The grooved covering is preferred by many carders, as it is found to grind the wire teeth better, and to meet the various requirements of the trade it is made in various degrees of fineness. Three of these are shown in Figs.100,101, and102, the coarser of the three being used for mild steel or iron wire, and the finer variety for hardened and tempered wire. All the rollers are carefully made, so as to be evenly and truly balanced, and great care is taken to ensure them having a perfectly true surface on which to wrap the filleting. This method of covering rollers has a good many advantages, the chief of which is the ease with which the operation can be conducted as compared with the older method of covering.

Figs. 98, 99.

Figs. 100-102.

(177) Another form of roller is shown in Fig.103, this being a modification of the Horsfall type. It differs from the one previously described, which covers the whole width of the surface to be ground, whereas the Horsfall roller is a narrow roll to which a rapid reciprocal movement is given across the surface of the wire. It consists of a light shaft, in which is formed a straight groove for the greater part of its length. In the bottom of this a zig-zag groove is formed, into which a fork enters. The fork in the roller shown in the illustration is mounted in a plug fitted into the boss of the grinding roller, and can be removed andreplaced without difficulty. Oil pads are fitted at each end of the grinding pulley, and are covered with brass caps, so as to keep them in position. In this way the parts are always efficiently lubricated, while at the same time grit and dirt are excluded. The emery roll or pulley is traversed as described by the engagement of the fork and the spiral groove, and as soon as it reaches either end of the longitudinal groove, it is automatically reversed. This action takes place throughout the whole period of grinding. On the whole, the employment of the Horsfall type of roller is not so great as that of the continuous roller shown in Fig.97. When the latter is used all the teeth are ground in a straight line across the cylinder, while the use of the Horsfall implies the grinding of the teeth in a spiral line over the whole surface. It is quite true that the whole of the teeth are ground in either case, but there is an obvious advantage in treating all those in the same line at one time.

Fig. 103.

(178) In grinding the cylinder the cover above the doffer is removed, and the wire surface bared. The cylinder is then stripped in a way which will be afterwards described, and the roller is fixed in bracketsR, Fig.44, placed to receive it. The construction of these brackets is a matter of importance. They are accurately planed, and fitted so as to move to and from the cylinder centre in radial lines. They must be so fixed to the bend or framing that they are quite level and parallel with the surface of the cylinder or doffer, as otherwise they would grind more off the wire at one side than the other. This is an essential feature, and it is also required that they should be set so as to grind lightly, otherwise there is a danger of producing hooked teeth, which are very detrimental to good work. Generally, the remarks just made apply also to the grinding of the doffer, which is effected by means of the bracketsS, the doffer cover being removed, and the doffer stripped.

(179) The grinding of the flats in revolving flat engines is usually performed by a roller sustained by the bracketsT, which are fitted on the side nearest the cylinder, with a surface against which the flat end is pressed by the weighted levers shown. The accurate grinding of the flats involves a nice problem which is worth a special explanation. As was stated in the last chapter, paragraph 117, the flats are formed with a heel which throws up the edge nearest the licker-in, and thus prevents any rolling up of the fibre. In Fig.104a diagrammatic representation of the relative position of the flat end and wire surface is given. The flat end is shown by the lettersA B C D, and the wire byC D E F. It will be noticed that the lineE Fis not parallel withA B, which represents the surfaces on the top of the flat ends, but is parallel withC D, which represents the surface on which the flat travels. It is obvious that if during grinding the flat is held against a prepared surface, by means of its faceA B, and traversedthereon, there will be a corresponding formation of the faceE Fof the wire, which would become parallel withA B. If this happened, the whole object of reducing one of the faces on the surfaceC Dwould be destroyed, as while the heel would be in that surface it would be removed from the wire face. But if, on the other hand, the flat is sustained on the faceC Dduring its passage under the grinding roller, the parallel relation ofC DandE Fis not altered, and therefore the flat is as fit for its work as before grinding. How to sustain the flat when being ground so as to maintain this parallel position is the problem, which is, however, in a fair way towards solution. The steady, forward movement of the flats during grinding somewhat increases the difficulty, but as it is one of the necessary elements of the case it must be duly taken into account.

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